JP2008139558A - LIGHT EMITTING ELEMENT DRIVE DEVICE, EXPOSURE DEVICE, AND IMAGE FORMING DEVICE - Google Patents

Abstract

A light-emitting element driving apparatus that performs accurate light-emission driving control of a light-emitting element, an exposure apparatus using the same, and an image forming apparatus are provided.
A capacitor element Cs of a pixel circuit 113 accumulates charges for light emission of an organic electroluminescence element 110 and sets a driving condition of the organic electroluminescence element 110. A charge mode is stored in the capacitive element Cs by the switching action of the transistor Tr2, and a program mode in which driving conditions are set based on the stored charge by the switching action of the transistor Tr3, and the organic electroluminescence element 110 is set according to the set driving conditions. Switches the element emission mode for emitting light. On / off of the two transistors is controlled independently.
[Selection] Figure 12

Description

  The present invention relates to a light emitting element driving apparatus that drives a plurality of light emitting elements, an exposure apparatus using such a light emitting element driving apparatus, and an image forming apparatus including the exposure apparatus.

  A photosensitive body charged in advance at a predetermined potential is exposed according to image information to form an electrostatic latent image, the electrostatic latent image is developed with toner, and the visualized toner image is transferred to a recording paper. As an exposure device used in an image forming apparatus applying the so-called electrophotographic process to obtain an image by heating and fixing, a light beam using a laser diode as a light source passes through a rotating polygonal mirror called a polygon mirror on the photoreceptor. Each light emitting unit is formed using a method of forming an electrostatic latent image by scanning, and a light emitting element array in which light emitting elements (hereinafter referred to as LEDs) and organic electroluminescent materials are arranged in a line. There is known a system in which an electrostatic latent image is formed on a photoreceptor by individually controlling lighting (ON / OFF).

  In general, an exposure apparatus including a light-emitting element array using LEDs or organic electroluminescent materials as a constituent element selectively illuminates each light-emitting element in the very vicinity of the photoconductor to irradiate the photoconductor with exposure light. The image forming apparatus equipped with a laser diode has no moving parts like a rotating polygon mirror in an image forming apparatus using a laser diode, and has high reliability and quietness. A large optical space serving as a path for the image forming apparatus is unnecessary, and the image forming apparatus can be downsized.

  In particular, an exposure apparatus equipped with an organic electroluminescence element as a light emitting element integrates a drive circuit composed of a thin film transistor (hereinafter referred to as TFT) switching element and an organic electroluminescence element on a substrate such as glass. Therefore, the structure and manufacturing process are simple, and there is a possibility that further downsizing and cost reduction can be realized as compared with an exposure apparatus in which an LED is mounted as a light emitting element.

However, on the other hand, it is known that the organic electroluminescence element undergoes so-called light quantity deterioration in which the light emission luminance gradually decreases with the driving thereof. An organic electroluminescence element applied to a general display device or the like has a light emission luminance of about 1000 [cd / m ² ] at most, but is applied to an exposure device mounted on an image forming apparatus such as an electrophotographic apparatus. For example, assuming that the specifications of the image forming apparatus are 600 dpi (dot / inch) and 20 ppm (pages / minute), the organic electroluminescence element is required to have an emission luminance of 10,000 [cd / m ² ] or more. The driving conditions are very severe with high voltage and large current. For this reason, the organic electroluminescence elements applied to the exposure apparatus are more susceptible to the deterioration of the amount of light than those applied to the display device, and the amount of light emitted from each organic electroluminescence element is equal to the initial state. In order to maintain the light intensity, some light amount correction is required.

  It is also known that the light emission luminance of an organic electroluminescence element has temperature dependence. This temperature dependency is determined by the organic material constituting the organic electroluminescence element, and can have both positive characteristics and negative characteristics. The above-described image forming process of the electrophotographic apparatus includes a step of fixing the toner image on the recording paper by heat and pressure. Since the apparatus has a heat source capable of generating a large amount of heat, the temperature change inside the apparatus is prevented. Along with this, the emission luminance of the organic electroluminescence element changes. Also in this case, it is necessary to correct the amount of light emitted from each organic electroluminescence element.

  In addition, since it is difficult to prevent variations in emission luminance between individual organic electroluminescence elements, it is also necessary to perform light amount correction to prevent variations in the amount of light between elements.

  With respect to light amount correction, for example, a configuration disclosed in Patent Document 1 is known for an image forming apparatus equipped with an exposure apparatus to which a conventional organic electroluminescence element is applied. The exposure apparatus in Patent Document 1 has a configuration in which a light detection element is disposed on a glass substrate on which an organic electroluminescence element is formed, and the light emission amount of each organic electroluminescence element is detected by the light detection element.

  Further, there is a light emitting element driving circuit applied to such an image forming apparatus as disclosed in Patent Document 2. This document discloses a technique for setting the gradation of a light emitting element by an active matrix driving method.

  FIG. 28 shows a current programming circuit 340 for driving the organic EL element 320 in Patent Document 2. In this circuit, the light emission gradation of the organic EL element 320 is set in a predetermined programming period Tpr. The gate signal V2 is set to L level and the transistors 311 and 312 are turned on while flowing the current value Im corresponding to the light emission gradation on the sub data line U. At this time, the current generation circuit 412 functions as a constant current source that supplies a constant current value Im corresponding to the light emission gradation. The current value Im is set to a value corresponding to the light emission gradation of the organic EL element 320 within a predetermined current value range RI.

As a result of programming with this current value Im, the holding capacitor 330 is in a state of holding the gate potential of the transistor 314 corresponding to the current value Im flowing through the fourth transistor 314. At the time of light emission at a predetermined timing when the gate signal V3 becomes L level, the current IEL almost the same as the programming current value Im flows through the transistor 313 and the organic EL element 320, and light is emitted at a gradation corresponding to the current value.
Japanese Patent Laid-Open No. 2004-082330 Japanese Patent Laid-Open No. 2003-177709

  As described above, the transistors 311 and 312 are driven by the gate signal V2 which is a common signal. However, it has not been verified whether or not two transistors can be driven at exactly the same timing with only a single signal. If such driving is not performed properly, there is a possibility that the programming and thus the light emission of the organic EL element 320 is not performed properly.

  An object of the present invention is to provide a light emitting element driving apparatus capable of appropriately driving a light emitting element, an exposure apparatus using the light emitting element driving apparatus, and an image forming apparatus.

  The present invention includes, firstly, a capacitive element, a first switching element that charges the capacitive element, a first mode that charges the capacitive element, and a light emitting element that drives the light emitting element based on the charged potential. There is provided a light emitting element driving apparatus including a second switching element that switches between two modes, and a control unit that controls the first switching element and the second switching element independently.

  With this configuration, the two switching elements can be appropriately controlled, the driving of the light emitting elements can be made appropriate, and appropriate light emission can be obtained.

  Secondly, the present invention provides a capacitive element, a first switching element for charging the capacitive element, a first mode for charging the capacitive element, and a first mode for driving the light emitting element based on the charged potential. A second switching element that switches between the two modes, a third switching element that is connected in parallel to the capacitive element, and to which a gate potential is applied based on a potential charged in the capacitive element, and the first switching element There is provided a light emitting element driving device including an element and a control unit that independently controls the second switching element.

  With this configuration, the three switching elements can be appropriately controlled, the light emitting elements can be driven appropriately, and appropriate light emission can be obtained.

  Thirdly, the light-emitting element driving apparatus according to the first or second aspect, wherein the control unit sets a current value for driving the light-emitting element by a potential charged in the capacitor element. A light emitting element driving apparatus is provided.

  With this configuration, appropriate light emission can be easily obtained.

  Fourthly, the present invention relates to a light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission, a capacitor element that holds a potential by charge and discharge, and holding of the capacitor element A first switching element for determining a capacitance; a program mode for setting a holding potential of the capacitive element; a second switching element for switching an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element; There is provided a light emitting element driving device including a first switching element and a control unit that independently controls on / off of the second switching element.

  With this configuration, the two switching elements can be appropriately controlled, the driving of the light emitting elements can be made appropriate, and appropriate light emission can be obtained.

  Fifthly, the present invention provides a light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission, a capacitive element that holds a potential by charge and discharge, and holding of the capacitive element A first switching element for determining a potential; a program mode for setting a holding potential of the capacitive element; a second switching element for switching an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element; A third switching element that is connected in parallel with the capacitive element and to which a gate potential is applied based on the potential of the capacitive element; and the first switching element and the second switching element are independently turned on / off There is provided a light emitting element driving device including a control unit for controlling.

  With this configuration, the three switching elements can be appropriately controlled, the driving of the light emitting elements can be made appropriate, and appropriate light emission can be obtained.

  Sixthly, the present invention is the light emitting element driving device according to the fourth or fifth aspect, wherein the driving condition is a current value for driving the light emitting element, and the control unit drives the light emitting element. A light-emitting element driving apparatus is provided that sets a current value to be set according to the potential of the capacitor element.

  With this configuration, appropriate light emission can be easily obtained.

  Seventhly, the present invention provides the light-emitting element driving device according to any one of the first, second, fourth, and fifth, wherein the capacitive element, the first switching element, and the second switching element are used to provide one light-emitting element driving device. One pixel circuit for driving a light emitting element is defined, and the light emitting element driving device includes a plurality of the pixel circuits, and further includes a current supply unit that supplies a current set to each pixel circuit, and a current supply unit And a light-emitting element driving device in which one terminal of the second switching element is connected to the amplifier.

  With this configuration, a current having an appropriate magnitude can be obtained in the pixel circuit.

  Eighth, the present invention is the light emitting element driving device according to the seventh, wherein the amplifying unit is configured to emit light configured along the light emitting element array in the arrangement direction of the light emitting element array formed by the light emitting element. An element driving apparatus is provided.

  With this configuration, an amplification unit can be easily created.

  Ninthly, the present invention provides the light emitting element driving apparatus according to the seventh aspect, wherein the amplifying section is configured by a current mirror circuit.

  With this configuration, an amplification unit can be easily created.

  10thly this invention is a light emitting element drive device as described in 7th, Comprising: The light emitting element drive device which comprises the said amplifier part by amplifier with a gain of 1 is provided.

  With this configuration, an amplification unit can be easily created.

  11thly, this invention is the light emitting element drive device of 7th, Comprising: The said current supply part is comprised from a current discharge type | mold circuit, and the said amplifier converts the discharge current by the said current supply part into drawing current A light emitting element driving apparatus is provided.

  With this configuration, the light emitting element driving device can be used even when a current discharge type current supply unit is employed.

  The twelfth aspect of the present invention is the light emitting element driving apparatus according to the seventh aspect, wherein the amplifying section is constituted by a TFT circuit.

  With this configuration, an amplification unit can be easily created.

  A thirteenth aspect of the present invention is the light emitting element driving apparatus according to any one of the first, second, fourth, and fifth aspects, further comprising a third switching element that controls on / off of the light emitting element. It is provided.

  With this configuration, driving of the light emitting element can be simplified.

  The fourteenth aspect of the present invention is the light emitting element driving device according to any one of the first, second, fourth, and fifth aspects, further comprising a fifth switching element that controls to open or short-circuit both terminals of the light emitting element. An element driving apparatus is provided.

  With this configuration, driving of the light emitting element can be simplified.

  According to a fifteenth aspect of the present invention, there is provided the light emitting element driving apparatus according to any one of the first to fourteenth aspects, wherein at least one of the first to fifth switching elements is constituted by a TFT circuit. Is provided.

  With this configuration, the switching element can be easily created.

  Sixteenth, the present invention provides the light emitting element driving apparatus according to any one of the first to fifteenth aspects, wherein the light emitting element includes an organic electroluminescence element. .

  With this configuration, a light emitting element can be easily created.

  According to the seventeenth aspect of the present invention, there is provided an exposure apparatus including the light emitting element driving apparatus according to any one of the first to sixteenth aspects.

  With this configuration, an appropriate light emission exposure apparatus can be obtained.

  In the eighteenth aspect of the present invention, there is provided an image forming apparatus including the exposure apparatus according to the seventeenth aspect.

  With this configuration, an image forming apparatus capable of forming an appropriate image can be obtained.

  According to the nineteenth aspect of the present invention, there is provided a light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission, a capacitive element that holds a potential by charge / discharge of charges, At least one of a function of switching between a first switching element for determining the potential, a program mode for setting a holding potential of the capacitor, and an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitor. And when switching from the program mode to the element emission mode, the timing for turning off the first switching element is earlier than the timing for turning off the second switching element. There is provided a light emitting element driving device including a control unit that controls the light emitting element.

  With this configuration, the two switching elements can be appropriately controlled, the driving of the light emitting elements can be made appropriate, and appropriate light emission can be obtained.

  20thly, the present invention provides a light emitting element driving apparatus for controlling driving conditions and light emission on / off of a light emitting element, a capacitive element that holds a potential by charge / discharge of charges, and the holding of the capacitive element A part of a function of switching a first switching element for determining a potential, a program mode for setting a holding potential of the capacitor, and an element emission mode for causing the light-emitting element to emit light according to the holding potential of the capacitor A second switching element, a third switching element connected in parallel with the capacitive element, to which a gate potential is applied based on the potential of the capacitive element, and switching from the program mode to the element emission mode. The timing for turning off the first switching element is earlier than the timing for turning off the second switching element. Light emitting element driving apparatus is intended to be provided and a control unit for controlling so.

  With this configuration, the three switching elements can be appropriately controlled, the light emitting elements can be driven appropriately, and appropriate light emission can be obtained.

  The light emitting element driving device according to the twenty-first, the nineteenth or twentieth aspect of the present invention is the light emitting element driving device according to the nineteenth or twentieth aspect, wherein the fourth switching element for controlling on / off of the light emitting element and both terminals of the light emitting element are opened or short-circuited. There is provided a light-emitting element driving device further including a fifth switching element that is controlled to be controlled.

  With this configuration, the driving of the light emitting element can be simplified and appropriate.

  According to a twenty-second aspect of the present invention, in the light-emitting element driving device according to the twenty-first aspect, in the program mode, the first switching element, the second switching element, and the fifth switching element are turned on. And the fourth switching element is turned off, and the first switching element, the second switching element, and the fifth switching element are turned off in the element emission mode, and the fourth switching element is turned off. Is turned on, and when switching from the program mode to the element emission mode, after the first switching element is turned off, the period between the second switching element is switched from on to off, A light emitting device driving apparatus in which a transition period mode is defined is provided.

  With this configuration, the light emission of the light emitting element can be reliably ensured.

  According to a twenty-third aspect of the present invention, there is provided the light-emitting element driving device according to the twenty-second aspect, wherein the first switching element and the second switching element in a predetermined period between the transition period mode and the element light-emitting mode. An element and a light emitting element driving apparatus in which the third switching element is turned off and the fourth switching element is turned on are provided.

  With this configuration, the light emission of the light emitting element can be reliably ensured.

  According to a twenty-fourth aspect of the present invention, there is provided a light-emitting element driving apparatus for controlling a drive current value of a light-emitting element and on / off of light emission. When connected and turned on, the capacitive element forms a closed loop circuit and is connected to the first switching element that charges and discharges the capacitive element, and is connected to the first switching element at a position outside the closed loop circuit, A programming mode for setting a holding potential of the capacitive element; a second switching element for switching an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element; A third switching element to which a gate potential is applied based on the potential of the element, and in the program mode, The closed loop circuit is formed by the first switching element, the third switching element, and the capacitive element, and at the end of the program mode, the first switching element is turned off and the closed loop circuit is eliminated. Thereafter, a light emitting element driving device is provided in which the second switching element is maintained in an on state for a predetermined period.

  With this configuration, the two switching elements can be appropriately controlled, the driving of the light emitting elements can be made appropriate, and appropriate light emission can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, the light emitting element drive device which drives a light emitting element appropriately and light-emits, the exposure apparatus containing the said drive device, and an image forming apparatus can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Basic configuration)
FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, an image forming apparatus 1 includes a photoconductor (image carrier), a charger 9, a transfer roller 16, a developing station (developing device) 50, an exposure device 60, and a controller in a housing 2 made of resin or the like. 70, an engine control unit 80, a power supply unit 43, and the like.

  The developing station 50 includes units for four colors of a yellow developing station 50Y, a magenta developing station 50M, a cyan developing station 50C, and a black developing station 50K, and these developing stations are arranged in a stepwise manner in the vertical direction. Further, a paper feed tray 4 for storing a recording paper R as a recording medium is disposed above the recording paper, and recording paper supplied from the paper feed tray 4 is provided at locations corresponding to the developing stations 50Y to 50K. A recording paper conveyance path P, which is an R conveyance path, is configured in the vertical direction from the top to the bottom.

  The developing stations 50Y to 50K form yellow, magenta, cyan, and black toner images in order from the upstream side of the recording paper conveyance path P. The yellow developing station 50Y has a photosensitive member 8Y, the magenta developing station 50M has a photosensitive member 8M, the cyan developing station 50C has a photosensitive member 8C, and the black developing station 50K has a photosensitive member 8K.

  The developing stations 50Y to 50K are different in the color of the filled developer, but the configuration is the same regardless of the development color. Therefore, the development is performed except when it is particularly necessary to clarify the following explanation. A description will be given without specifying a specific color such as the station 50, the photoconductor 8, and the exposure device 60.

  FIG. 2 is a configuration diagram showing the periphery of the developing station 50 in the image forming apparatus 1 of the present invention. In FIG. 2, the developing station 50 is filled with a developer DL which is a mixture of a carrier and a toner. The developing station 50 includes a stirring paddle 51 (51a, 51b), a developing sleeve 53, and a thinning blade 52.

  The agitation paddles 51a and 51 are sufficiently agitated and mixed by charging the toner in the developer DL to a predetermined potential by friction with the carrier by rotating, and circulating the toner and the carrier inside the developing station 2. The charger 9 charges the surface of the photoreceptor 8 rotating in the direction D3 to a predetermined potential by a driving source (not shown). The developing sleeve 53 has a magnet roll 54 in which a plurality of magnetic poles are formed. The layer thickness of the developer DL supplied to the surface of the developing sleeve 53 is regulated by the thinning blade 52, and the developing sleeve 53 is rotated in the direction D4 by a driving source (not shown). As a result, the developer DL is supplied to the surface of the developing sleeve 53, and an electrostatic latent image formed on the photoconductor 8 is developed by an exposure device 60 described later, and the developer DL not transferred to the photoconductor 8 is developed. Collected in the developing station 50.

  Under the developing stations 2Y to 2K, exposure devices 60Y to 60K for exposing the surfaces of the photoreceptors 8Y to 8K to form electrostatic latent images are arranged. The exposure device 60 has a light emitting element array in which organic electroluminescence elements as exposure light sources are arranged in a line at a resolution of 600 dpi (dot / inch), and the photosensitive member 8 charged to a predetermined potential by the charger 9 is provided. On the other hand, an electrostatic latent image of maximum A4 size is formed by selectively turning on / off the organic electroluminescence element according to the image data. When a predetermined potential (developing bias) is applied to the developing sleeve 53 of the developing station 50, a potential gradient is generated between the electrostatic latent image portion and the developing sleeve 53. Then, the Coulomb force acts on the toner in the developer DL that is supplied to the surface of the developing sleeve 53 and is charged to a predetermined potential, and only the toner out of the developer DL adheres to the photoreceptor 8, and electrostatic The latent image is visualized.

  The exposure device 60 is provided with a light amount measuring unit (light amount measuring means) that measures the light emission amount of the organic electroluminescence element. The configuration of the exposure apparatus 60 will be described in detail later.

  As shown in FIG. 2, the transfer roller 16 is provided at a position facing the recording paper conveyance path P with respect to the photoreceptor 8, and is rotated in the direction D5 by a driving source (not shown). A predetermined transfer bias is applied to the transfer roller 16, and the toner image formed on the photoconductor 8 is transferred to the recording paper R conveyed through the recording paper conveyance path P.

  As shown in FIG. 1, a toner bottle 17 that stores yellow, magenta, cyan, and black toner is attached to the top of the housing 2. A toner transport pipe (not shown) is provided from the toner bottle 17 to each of the development stations 50Y to 50K, and supplies toner to each of the development stations 50Y to 50K. Further, adjacent to the toner bottle 17, a paper feed tray 4 that holds the recording paper R is attached to the upper portion of the housing 2.

  A paper feed roller 18 is provided below the toner bottle 17, and rotates in a direction D <b> 1 by controlling an electromagnetic clutch (not shown), so that the recording paper R loaded in the paper feed tray 4 is sent out to the recording paper conveyance path P.

  In the recording paper transport path P located between the paper feed roller 18 and the transfer portion of the most upstream yellow developing station 50Y, a pair of registration rollers 19 and a pinch roller 20 serve as a nip transport section (nip transport means) on the entrance side. Is provided. The registration roller 19 and the pinch roller 20 pair temporarily stop the recording paper R conveyed by the paper supply roller 18 and convey it in the direction of the yellow developing station 50Y at a predetermined timing. This temporary stop restricts the leading edge of the recording paper R in parallel with the axial direction of the registration roller 19 and pinch roller 20 pair, thereby preventing the recording paper R from being skewed.

  A recording paper passage detection sensor 21 is provided adjacent to the registration roller 19. The recording paper passage detection sensor 21 is constituted by a reflective sensor (photo reflector), and detects the leading edge and the trailing edge of the recording paper R based on the presence or absence of reflected light.

  When the power transmission is controlled by an electromagnetic clutch (not shown) and the rotation of the registration roller 19 is started, the recording paper R is conveyed along the recording paper conveyance path P in the direction of the yellow developing station 50Y, but the rotation of the registration roller 19 is started. The timing of writing the electrostatic latent image by the exposure devices 60Y to 60K arranged in the vicinity of the developing stations 50Y to 50K, ON / OFF of the developing bias, ON / OFF of the transfer bias, etc. are independent from each other. Controlled.

  Since the distance from the exposure device 60 shown in FIG. 2 to the development area (near the portion where the distance between the photoconductor 8 and the development sleeve 10 is the narrowest) is a design matter, for example, exposure by the exposure device 60 is started and the photoconductor 8 is started. The time for the latent image formed above to reach the development area is also a design matter.

  In the present embodiment, starting from the rotation start timing of the registration roller 19, as described later, when printing a plurality of pages continuously, between the recording paper and the recording paper conveyed through the recording paper conveyance path P (that is, In between the sheets), the light quantity of the organic electroluminescence elements constituting the exposure device 60 is set and turned on, and control is performed to turn off the developing bias with respect to the latent image position formed on the photosensitive member 8. Yes.

  Furthermore, the internal structure of the housing | casing 2 is demonstrated based on FIG. A fixing device 23 is provided as a nip conveyance section (nip conveyance means) on the outlet side in the recording paper conveyance path P located further downstream of the most downstream black developing station 2K. The fixing device 23 includes a heating roller 24 and a pressure roller 25.

  Further, a temperature sensor 27 is provided above the heating roller 24 and detects the temperature of the heating roller 24. The temperature sensor 27 is a ceramic semiconductor obtained by sintering at a high temperature using a metal oxide as a main raw material, and can measure the temperature of a contacted object by applying a change in load resistance depending on the temperature. it can. The output of the temperature sensor 27 is input to an engine control unit 80, which will be described later, and the engine control unit 80 controls the power supplied to a heat source (not shown) built in the heating roller 24 based on the output of the temperature sensor 27, The surface temperature of the heating roller 24 is controlled to be about 170 ° C.

  When the recording paper R on which the toner image is formed is passed through the nip formed by the heating roller 24 and the pressure roller 25 that are controlled in temperature, the toner image on the recording paper R is added to the heating roller 24. The toner image is fixed on the recording paper R by being heated and pressurized by the pressure roller 25.

  Further, a recording paper trailing edge detection sensor 28 for monitoring the discharge state of the recording paper 3 is provided at the bottom of the housing 2, and a toner image detection sensor 32 is provided in the vicinity thereof. The toner image detection sensor 32 is a reflective sensor unit that uses a plurality of light emitting elements (both visible light) having different emission spectra and a single light receiving element, and changes the image color between the background of the recording paper R and the image forming portion. Accordingly, the image density is detected by utilizing the fact that the absorption spectrum is different. Further, since the toner image detection sensor 32 can detect not only the image density but also the image forming position, in the image forming apparatus 1 in the embodiment, two toner image detection sensors 32 are provided in the width direction of the image forming apparatus 1 and the recording paper R is provided. The image formation timing is controlled based on the detection position of the image positional deviation amount detection pattern formed in the above.

  A recording paper transport drum 33 is provided below the fixing device 23. The recording paper transport drum 33 is a metal roller whose surface is covered with rubber having a thickness of about 200 μm, and the recording paper R after fixing is transported along the recording paper transport drum 33 in the direction D2. At this time, the recording sheet R is cooled by the recording sheet conveying drum 33 and is bent and conveyed in the direction opposite to the image forming surface. As a result, curling that occurs when a high density image is formed on the entire surface of the recording paper can be greatly reduced. Thereafter, the recording paper R is conveyed in the direction D6 by the kicking roller 35 and discharged to the paper discharge tray 39.

  Further, the face-down paper discharge unit 34 is configured to be rotatable around a support member 36 attached to the housing 2. When the face-down paper discharge unit 34 is opened, the recording paper R is discharged in the direction D7. In the closed state of the face-down paper discharge unit 34, ribs 37 are formed on the back surface along the transport path so as to guide the transport of the recording paper R together with the recording paper transport drum 33.

  In the present embodiment, the drive source 38 is constituted by a stepping motor. Peripheral portions of the developing stations 50Y to 50K including a paper feed roller 18, a registration roller 19, a pinch roller 20, photoconductors 8Y to 8K, and a transfer roller 16 (see FIG. 2), a fixing device 23, and recording paper. The conveying drum 33 and the kicking roller 35 are driven.

  The controller 70 receives image data from a computer (not shown) via an external network, and develops and generates printable image data. As will be described in detail later, a controller CPU (not shown) mounted on the controller 70 receives light amount measurement data of the organic electroluminescence elements as light emitting elements from the exposure devices 60Y to 60K and generates light amount correction data. In addition to the light amount correction unit (light amount correction unit), it is also a light amount setting unit (light amount setting unit) that sets the light amount of the organic electroluminescence element based on the light amount correction data.

  The engine control unit 80 controls the hardware and mechanism of the image forming apparatus 1, forms a color image on the recording paper R based on the image data and the light amount correction data (lighting data) transferred from the controller 70, and has been described above. The entire control of the image forming apparatus 1 including the temperature control of the heating roller 24 of the fixing device 23 is performed.

  The power supply unit 43 supplies power of a predetermined voltage to the exposure apparatuses 60Y to 60K, the drive source 38, the controller 70, and the engine control unit 80, and supplies power to the heating roller 24 of the fixing device 23. The power supply unit also includes a so-called high-voltage power supply system such as a charging potential for charging the surface of the photoconductor 8, a developing bias applied to the developing sleeve (see FIG. 2), and a transfer bias applied to the transfer roller 16. . The engine control unit 80 controls the power supply unit 43 to adjust not only the ON / OFF of the high-voltage power supply but also the output voltage value and the output current value.

  The power supply unit 43 includes a power supply monitoring unit 44 so that at least the power supply voltage supplied to the engine control unit 80 and the output voltage of the power supply unit 43 can be monitored. This monitor signal is detected by the engine control unit 80 to detect a decrease in power supply voltage that occurs when the power switch is turned off or a power failure occurs, and particularly an output abnormality of the high-voltage power supply.

  The operation of the image forming apparatus 1 configured as described above will be described with reference to FIGS.

  In the following description, FIG. 1 is mainly used for the description relating to the overall configuration and operation of the image forming apparatus 1, and colors such as the developing stations 50Y to 50K, the photoconductors 8Y to 8K, and the exposure apparatuses 60Y to 60K are used. For the sake of simplicity, explanations relating to single colors such as exposure and development processes will be given without distinguishing colors such as the developing station 50, the photoconductor 8, and the exposure device 60. .

(Initialization operation)
First, an initialization operation when the image forming apparatus 1 is turned on will be described.

  When the power is turned on, an engine control CPU (not shown) mounted in the engine control unit 80 performs an error check on electrical resources constituting the image forming apparatus 1, that is, a register / memory capable of writing / reading. Execute. When this error check is completed, the engine control CPU (not shown) starts to rotate the drive source 38. As described above, the peripheral portion of each developing station 50Y-50K including the paper feed roller 18, registration roller 19, pinch roller 20, photoconductors 8Y-8K, and transfer roller 16 by the driving source 38, the fixing device 23, and the recording paper conveyance The drum 33 and the kicking roller 35 are driven. However, immediately after the power is turned on, the feeding roller 18 and the registration roller 19 involved in the conveyance of the recording paper R are immediately set to OFF so that the electromagnetic clutch (not shown) for transmitting the driving force to them is set to OFF. There is no control.

  As shown in FIG. 2, as the drive source 38 (see FIG. 1) rotates, the stirring paddles 51a and 51b and the developing sleeve 53 of the developing station 50 also start to rotate, thereby the toner and carrier filled in the developing station 50. The developer DL made of circulates in the developing station 50, and the toner is given a negative charge by friction between the toner and the carrier.

  The engine control CPU (not shown) starts the rotation of the drive source 38 (see FIG. 1) and controls the power supply unit 43 (see FIG. 1) to turn on the charger 9 after a predetermined time has elapsed. The surface of the photoconductor 8 is charged to a potential of, for example, −650 V by the charger 9. The photosensitive member 8 is rotated in the direction D3, and the engine control CPU (not shown) determines the power supply unit 43 (FIG. 1) after the charged region reaches the developing region, that is, the closest position between the photosensitive member 8 and the developing sleeve 53. For example, a developing bias of −250 V is applied to the developing sleeve 53. At this time, the surface potential of the photosensitive member 8 is −650 V, and the developing bias applied to the developing sleeve 53 is −250 V. Therefore, the electric lines of force are directed from the developing sleeve 53 toward the photosensitive member 8 and have a negative charge. The Coulomb force acting on the toner is in the direction from the photoconductor 8 to the developing sleeve 53. Therefore, the toner does not adhere to the photoreceptor 8.

  As described above, the power supply unit 43 (see FIG. 1) has a function of monitoring an output abnormality (for example, leakage) of the high-voltage power supply, and an engine control CPU (not shown) is connected to the charger 9 and the developing sleeve 53. It is possible to check for abnormalities when a voltage is applied.

  The engine control CPU 82 (see FIG. 7) executes light amount correction of the exposure device 13 at the end of the series of initialization operations or at another predetermined timing as described later. The engine control CPU 82 mounted on the engine control unit 80 (see FIG. 1) outputs a request for creating dummy image information for light amount correction to the controller 70 (see FIG. 1). Based on this creation request, the controller 70 (see FIG. 1) generates dummy image information for light amount correction, and based on this, the organic electroluminescence elements constituting the exposure apparatus 60 are actually controlled to be turned on at the time of initialization. .

  Further, the image forming apparatus 1 according to the present invention includes an exposure apparatus 60 provided with a light emitting element array in which a plurality of light emitting elements (organic electroluminescence elements) are formed in a line, and a photoconductor on which a latent image is formed by the exposure apparatus 60. 8 and a developing means (developing sleeve 53 constituting the developing station 50) for developing and developing the latent image formed on the photoconductor 8, as will be described in detail later. A light amount setting unit (controller CPU mounted on the controller 41) for setting the light amount of the light emitting element (organic electroluminescence element) and a light amount measuring unit for measuring the light amount of the light emitting element (organic electroluminescence element) are provided.

  At a predetermined timing as will be described later, the organic electroluminescence element as an exposure light source constituting the exposure apparatus 60 emits light, and this light quantity is measured. Therefore, the toner does not adhere and the toner is not wasted. Further, toner adheres to the transfer roller 16 that rotates in contact with the photosensitive member 8, and in image formation performed following the initialization operation, the toner attached to the transfer roller 16 adheres to the back surface of the recording paper R and the recording paper R No pollution.

  In this light amount correction, the region where the photoconductor 8 is exposed by turning on the organic electroluminescent element is close to the developing sleeve 53 and passes through a so-called developing region, that is, in a measurement period for measuring the light amount of the organic electroluminescent element. It is desirable to turn off the developing bias applied to the developing sleeve 53 for the exposed region of the photosensitive member 8. This makes it possible to more effectively prevent the toner from adhering to the photoreceptor 8.

(Image forming operation)
Next, the operation of the image forming apparatus 1 during image formation will be described with reference to FIG. 1 and FIG.

  When the image information is transferred from the outside to the controller 70, the controller 70 develops the image information in an image memory (not shown) as binary image data that can be printed. When the development of the image information is completed, a controller CPU (not shown) mounted on the controller 70 issues an activation request to the engine control unit 80. This activation request is received by an engine control CPU (not shown) mounted on the engine control unit 80, and the engine control CPU (not shown) receiving the activation request immediately rotates the drive source 38 to prepare for image formation. To start.

  When the preparation for image formation is completed through the above-described process, an engine control CPU (not shown) installed in the engine control unit 80 controls the electromagnetic clutch (not shown) to rotate the paper feed roller 18 and perform recording. The conveyance of the paper R is started. The paper supply roller 18 is, for example, a half-moon roller that lacks a part of the entire circumference. The paper supply roller 18 conveys the recording paper R in the direction of the registration roller 19 and stops its rotation when it rotates once. When the leading edge of the conveyed recording paper R is detected by the recording paper passing sensor 21, an engine control CPU (not shown) controls an electromagnetic clutch (not shown) after providing a predetermined delay period to register rollers. 19 is rotated. The recording paper R is supplied to the recording paper conveyance path P along with the rotation of the registration roller.

  An engine control CPU (not shown) controls the electrostatic latent image writing timing by each of the exposure devices 60Y to 60K independently from the timing of starting the rotation of the registration roller 19 as a starting point. Since the electrostatic latent image writing timing directly affects color misregistration and the like in the image forming apparatus 1, the writing timing is not directly generated by an engine control CPU (not shown). Specifically, the engine control CPU (not shown) presets the electrostatic latent image writing timing by each exposure device 60 in a timer, which is hardware (not shown), and rotates the registration roller 19 described above. As a starting point, timer operations corresponding to the exposure apparatuses 60Y to 60K are started simultaneously. Each timer outputs an image data transfer request to the controller 70 when a preset time has elapsed.

  The controller CPU (not shown) of the controller 70 that has received the image data transfer request is synchronized with the timing signal (clock signal, line synchronization signal, etc.) generated by the timing generation unit (not shown) of the controller 70. The value image data is independently transferred to each of the exposure devices 60Y to 60K. In this way, binary image data is sent to the exposure devices 60Y to 60K, and on / off of the organic electroluminescence elements constituting the exposure devices 60Y to 60K is controlled based on the binary image data, and a photoconductor corresponding to each color. 8Y to 8K are exposed.

  The latent image formed by the exposure is visualized by the toner contained in the developer DL supplied onto the developing sleeve 53 as shown in FIG. The visualized toner images of the respective colors are sequentially transferred onto the recording paper R conveyed through the recording paper conveyance path P. The recording paper R on which the transfer of the four color toner images has been completed is conveyed to the fixing device 23, and is nipped and conveyed by the overheating roller 24 and the pressure roller 25 constituting the fixing device 23. The toner image is recorded on the recording paper by this heat and pressure. Fixed to R.

  When the image to be formed is a plurality of pages, the engine control CPU (not shown) detects the trailing edge of the recording paper R of the first page by the recording paper passage detection sensor 21 and then temporarily rotates the registration roller 19. After the predetermined time has elapsed, the paper feeding roller 18 is rotated to start the conveyance of the next recording paper 3, and after the predetermined time has elapsed, the registration roller 19 is again rotated to start the recording paper R for the next page. Is supplied to the recording paper conveyance path P. Thus, by controlling the rotation ON / OFF timing of the registration roller 19, it is possible to set the sheet interval between the recording sheets R when an image is formed over a plurality of pages. The time between the sheets (hereinafter referred to as the sheet interval) varies depending on the specifications of the image forming apparatus 1, but is generally set to about 500 ms. Of course, a normal image forming operation (that is, an exposure operation for the photosensitive member 8 by the exposure device 60) is not performed during the period between the sheets.

  FIG. 3 is a block diagram of the exposure device 60 in the image forming apparatus 1 according to the embodiment of the present invention. The exposure apparatus 60 includes a housing A (lower housing) 61a, a housing B (upper housing) 61b, a lens array 62, a relay substrate 63, a connector A (first connector) 64a, and a connector B (second connector). ) 64b, cable 65, FPC (Flexible Printed Circuit) 66, and optical head 100 (glass substrate 101).

  The glass substrate 101 that occupies most of the optical head 100 in volume is composed of a colorless and transparent glass substrate. In this embodiment, borosilicate glass, which is advantageous in terms of cost, is used as the glass substrate 101. However, heat generation from a light emitting element or a control circuit or a drive circuit formed by a thin film transistor on the glass substrate 101 is more efficiently radiated. If necessary, glass containing a thermal conductivity additive factor such as MgO, Al2O3, CaO, ZnO, or quartz may be used.

  On the surface A of the glass substrate 101, an organic electroluminescence element as a light emitting element is formed with a resolution of 600 dpi (dot / inch) in a direction perpendicular to the drawing (main scanning direction). A lens array 62 in which rod lenses (not shown) made of plastic or glass are arranged in a row is arranged on the surface opposite to the surface A of the glass substrate 101. The lens array 62 guides the emitted light of the organic electroluminescence element formed on the surface A of the glass substrate 101 to the surface of the photoconductor 8 as an erecting equal-magnification image. The positional relationship among the glass substrate 101, the lens array 62, and the photoconductor 8 is adjusted so that one focus of the lens array 62 is the surface A of the glass substrate 101 and the other focus is the surface of the photoconductor 8. . That is, when the distance L1 from the surface A to the surface closer to the lens array 62 and the distance L2 from the other surface of the lens array 62 to the surface of the photoconductor 8 are set, L1 = L2.

  The relay board 63 is formed, for example, by forming an electronic circuit on a glass epoxy board, and at least a connector A 64a and a connector B 64b are mounted thereon. The relay substrate 63 temporarily relays image data, light amount correction data, and other control signals supplied from the outside to the exposure apparatus 60 through a cable 65 such as a flexible flat cable, etc., via the connector B 64b, and these signals are transmitted to the optical head. Pass to 100.

  Since it is difficult to directly mount a connector on the surface of the glass substrate 101 of the optical head 100 in view of bonding strength and reliability in various environments, in this embodiment, the connector A 64a of the relay substrate 63 and the glass substrate 101 are not connected. FPC 66 is employed as a connection means, and the glass substrate 101 and FPC are joined using, for example, ACF (Anisotropic Conductive Film), for example, ITO (Indium Tin Oxide) formed on the glass substrate 101 in advance. It is configured to be directly connected to the (doped indium oxide) electrode.

  On the other hand, the connector B64b is a connector for connecting the exposure apparatus 13 to the outside. In general, connection by ACF or the like often has a problem of bonding strength. However, by providing the connector B 64b for connecting the exposure apparatus 13 on the relay substrate 52 in this way, the interface directly accessed by the user is provided. Sufficient strength can be ensured.

  The casing A61a is formed by bending a metal plate, for example. An L-shaped portion L is formed on the side of the housing A 61 a facing the photoconductor 8, and the optical head 100 and the lens array 62 are disposed along the L-shaped portion L. By aligning the end surface of the housing A61a on the photoconductor 8 side with the end surface of the lens array 62 and further supporting one end of the glass substrate 101 by the housing A61a, the molding accuracy of the L-shaped portion L is improved. Is ensured, the positional relationship between the optical head 100 and the lens array 62 can be accurately adjusted. As described above, since the casing A61a is required to have dimensional accuracy, it is preferable that the casing A61a be made of metal. In addition, by making the casing A61a metal, it is possible to suppress the influence of noise on electronic components such as a control circuit formed on the glass substrate 101 and an IC chip surface-mounted on the glass substrate 101. is there.

  The casing B61b is obtained by molding a resin. A notch (not shown) is provided in the vicinity of the connector B64b of the housing B61b, and the user can access the connector B64b from this notch. From the controller 70 (see FIG. 1) already described via the cable 65 connected to the connector B 64b to the exposure device 60, image data, light amount correction data, control signals such as clock signals and line synchronization signals, drive power for the control circuit, A driving power source for the organic electroluminescence element which is a light emitting element is supplied.

  FIG. 4 is a top view of the optical head 100 in the exposure apparatus 60 as viewed from the surface A side in FIG. The optical head 100 is configured by patterning various elements and circuits on the upper surface of a glass substrate 101 or arranging them in the form of a chip. The optical head 100 is a unit that generates light for exposing the photoconductor 8 and also has a function of detecting light to correct the amount of light.

  The glass substrate 101 in the optical head 100 is a rectangular substrate having at least a long side and a short side with a thickness of about 0.7 mm. In the long side direction (main scanning direction), a plurality of organic light-emitting elements are used. The electroluminescence elements 110 are formed in a row to form a light emitting element row 110A. In the embodiment, an organic electroluminescence element 110 necessary for at least A4 size (210 mm) exposure is arranged in the long side direction of the glass substrate 101. In the embodiment, the glass substrate 101 is described as a rectangle for the sake of simplicity. However, a notch is provided in a part of the glass substrate 101 for positioning when the glass substrate 101 is attached to the housing A61a. It may be accompanied by deformation.

  The FPC 66 is an interface for connecting the connector 64 a of the relay substrate 63 and the optical head 100, and is directly connected to a circuit pattern provided on the glass substrate 101. As already described, binary image data, light amount correction data and control signals such as clock signals and line synchronization signals supplied from the outside to the exposure apparatus 60, a driving power source for the control circuit, and the organic electroluminescence element 110 which is a light emitting element. 3 is supplied to the optical head 100 through the FPC 66 after passing through the relay substrate 63 shown in FIG. In the present embodiment, three sets (66a, 66b, 66c) of FPCs 66 are arranged along the longitudinal direction of the glass substrate 101. As will be described later, the FPCs 66a and 66c at both ends supply a signal for driving the organic electroluminescence element 110, and the central FPC 66b supplies a signal for detecting and processing the light amount of the organic electroluminescence element 110.

  The organic electroluminescence elements 110 are exposure light sources in the exposure apparatus 60. In the embodiment, 5120 organic electroluminescence elements 110 are formed in a row at a resolution of 600 dpi in the main scanning direction to form a light emitting element row 110A. Yes. Each organic electroluminescence element 110 is independently controlled to be turned on / off by a TFT circuit described later.

  On the glass substrate 101, a source driver 180 (180a, 180b) (as a light emitting element) supplied as an IC chip for controlling the driving of the organic electroluminescence element 110 is flip-chip mounted. In consideration of performing surface mounting on the glass surface, the source driver 180 employs a bare chip product. The source driver 180 is supplied with lighting data (see FIG. 8) based on 8-bit light amount correction data from the outside of the exposure apparatus 60 via the FPC 66.

  The source driver 180 is a drive current setting unit for the organic electroluminescence element 110. More specifically, it is also a light amount setting unit of the organic electroluminescence element 110, and based on light amount correction data generated by a controller CPU (not shown) mounted on the controller 70 (see FIG. 1), the source driver 180. Sets a driving current for driving each organic electroluminescence element 110. The operation of the source driver 180 based on the light amount correction data will be described in detail later.

  In the glass substrate 101, the joint portion of the FPC 66 and the source driver 180 are connected via, for example, an ITO circuit pattern (not shown) in which metal is formed on the surface.

  A portion indicated by hatching corresponds to a light emitting element driving circuit (light emitting element driving unit) 181 formed on the glass substrate 101. The light emitting element driving circuit 181 supplies a driving current to a gate controller 114 that controls the timing of turning on / off the organic electroluminescent element 110, such as a shift register and a data latch unit, and individual organic electroluminescent elements 110, as will be described later. The pixel circuit 113 and the like are included (see FIG. 8). The light emitting element driving circuit 181 is configured by a TFT (Thin Film Transistor) circuit 190 (see FIG. 8) patterned on the glass substrate 101. The light quantity sensor 220 (see FIG. 10), which will be described later, is a light quantity detection target. A selection signal generation circuit (switching circuit) 240 that activates the light quantity sensor 220 corresponding to a desired organic electroluminescence element 110 and a pixel circuit 113 (see FIG. 8) that drives the organic electroluminescence element 110 are also formed by TFTs. Is formed. One pixel circuit 113 is provided for each organic electroluminescent element 110, and is provided in parallel with a light emitting element array 110 </ b> A formed by the organic electroluminescent element 110. A drive current value for driving each organic electroluminescence element 110 is set in the pixel circuit 113 by the source driver 180 which is a drive parameter setting unit.

  A gate controller 114 (see FIG. 8) constituting the TFT circuit 190 is supplied with a control signal such as a power supply, a clock signal, and a line synchronization signal and binary image data from the outside of the exposure apparatus 60 via the FPC 66. Controls the on / off timing of each light emitting element based on these power sources and signals. Operations of the gate controller 114 and the pixel circuit 113 (see FIG. 8) will be described in detail later with reference to the drawings. The configuration of the TFT circuit 190 on the light amount sensor 220 (see FIG. 10) side will be described in detail later.

  A sealing glass is formed in the region SL indicated by the alternate long and short dash line. When the organic electroluminescent element 110 is affected by moisture, the light emitting characteristics are extremely deteriorated due to shrinkage of the light emitting region over time (shrinking) and non-light emitting sites (dark spots) in the light emitting region. Sealing is necessary to block moisture. In the embodiment, a solid sealing method in which sealing glass is attached to the glass substrate 101 via an adhesive is employed, but the sealing region is generally from the light emitting element array 110A formed by the organic electroluminescence element 110 in the sub-scanning direction. About 2000 μm is required, and in the embodiment, 2000 μm is secured as a sealing margin.

  A light amount sensor as a light detection element for measuring the light amount of each organic electroluminescence element 110 is provided on the back side (the depth direction in FIG. 4) of the organic electroluminescence element 110, that is, on the side closer to the glass substrate 101. 220 overlaps with the organic electroluminescence element 110. An insulating layer and a protective layer (both not shown) such as silicon oxide and silicon nitride are disposed between the two, and the light quantity sensor 220 and the organic electroluminescence element 110 are separated by these insulating layer and protective layer. It is illustrated.

  In principle, when measuring the amount of emitted light, it is necessary to measure the amount of light by individually lighting the organic electroluminescence elements 110 one by one, but it is sufficiently separated from the organic electroluminescence element 110 to be measured. The light quantity sensor 220 is hardly affected by the light emission. The light emitted from the organic electroluminescence element 110 propagates while reflecting the inside of the glass substrate 101. However, since the above-described TFT and the metal layer for wiring are formed on the surface of the glass substrate 101, basically, It becomes specular reflection. The light is attenuated by repeating the specular reflection many times. Accordingly, in the embodiment, the light amount sensor 220 is configured by a plurality of light amount sensors, whereby the light amounts of the plurality of organic electroluminescence elements 110 can be simultaneously measured. In this embodiment, a light amount sensor 220 is formed for each of the organic electroluminescence elements 110, and the light emitting unit 105 is configured by a combination of the light emitting element array 110A and all the light amount sensors 220. However, one light quantity sensor 220 may be associated with a plurality of organic electroluminescence elements 110 (that is, organic electroluminescence element 110: light quantity sensor 220 = multiple: 1).

  As described above, in the present embodiment, the organic electroluminescence element 110, the light amount sensor 220, the selection signal generation circuit 240, and the light emitting element driving circuit 190 (see FIG. 8) are included in the TFT circuit 190 as a monolithic device of polysilicon. It is formed by integration. Since the light transmittance of the low-temperature polysilicon constituting the TFT circuit 190 is relatively high, a light amount sensor corresponding to each organic electroluminescence element 110 even in a so-called bottom emission configuration in which exposure light is extracted through the glass substrate 101. 220 can be formed substantially integrally with the TFT circuit 190.

  The light amount sensor 220 is formed on the entire surface immediately below the light emitting surface of each organic electroluminescence element 110, but may be formed corresponding to a part thereof.

  Outputs of the plurality of light quantity sensors 220 are input to a light quantity sensor output processing unit 210 (210a, 210b, 210c, 210d) including a chip part. The output of the light quantity sensor (light quantity sensor output), which will be described later, is subjected to voltage conversion by the charge accumulation method in the light quantity sensor output processing unit 210, further amplified by a predetermined amplification factor, and then converted from analog to digital. Digital data (hereinafter referred to as light quantity measurement data) is output to the outside of the exposure apparatus 60 via the FPC 66b, the relay board 63, and the cable 65 (both see FIG. 3). As will be described in detail later, the light quantity measurement data is received and processed by a controller CPU (not shown) mounted on the controller 70 (see FIG. 1) to generate, for example, 8-bit light quantity correction data.

  As will be described in detail later with reference to FIG. 22, in the optical head 100 of the present embodiment, positions separated in the sub-scanning (+) direction as viewed from the light emitting element array 110A and the light amount sensor 220, that is, substantially other components. A selection signal generation circuit 240 (see FIG. 10) and a selection transistor 232 (see FIG. 13) are arranged and formed on the side where no signal exists. On the other hand, the source driver 180, the light emitting element drive circuit 181, and the light quantity sensor output processing unit are positioned apart from each other in the sub-scanning (−) direction as viewed from the light emitting element array 110 </ b> A and the light quantity sensor 220, i. 210 is arranged. Specifically, a selection signal generation circuit 240 and a light emitting element driving circuit 181 are arranged adjacent to both sides of the light emitting unit 105 (sub-scanning (±) direction in FIG. 4), and further, viewed from the light emitting element driving circuit 220, A light amount sensor output processing unit 210 (210a, 210b, 210c, 210d) is disposed at a position in the sub-scanning (−) direction. Each light quantity sensor output processing unit 210 includes a charge amplifier 250 and an analog / digital converter (ADC) 260, which will be described in detail later.

  That is, in the present embodiment, a light emitting element array composed of a plurality of light emitting elements (organic electroluminescence element 110) arranged on the substrate 101, and a plurality of lights for detecting light output from each of the light emitting elements. A detection element (light quantity sensor 220), a first processing section (selection signal generation circuit 240, selection transistor 232) that processes the output of the light detection element, a second processing section, and (light quantity sensor output processing section 210) are provided. The light emitting element array and the light detecting element are arranged between the first processing unit and the second processing unit.

  With such an arrangement, the formation area of the selection signal generation circuit 240 shown in FIG. 4 can be used also as the area SL where the sealing glass is arranged, and the size of the optical head 100 in the sub-scanning direction is reduced. It becomes possible.

  In addition, since the arrangement area of the light quantity sensor output processing unit 210 (210a, 210b, 210c, 210d) including the chip parts is in the vicinity of the FPC 66 that also supplies power to the optical head 100, the power lines of these IC chips are provided. It has the effect of stabilizing.

  Furthermore, although the output current from each light quantity sensor 220 (exactly sensor pixel circuit 230) selected by the selection signal generation circuit 240 is very small, the transmission paths RoA to RoP (all refer to FIG. 10) Since both are provided on the side where the selection signal generating circuit 240 is arranged, that is, on the opposite side of the light emitting element driving circuit 181 with the light emitting element row in between, the influence of noise when driving the organic electroluminescent element 110 is reduced. It becomes difficult to receive.

  As shown in FIG. 4, the width A in the sub-scanning direction of the entire optical head 100 is set to 28 mm, for example, and the width B on the side where the selection signal generation circuit 240 is arranged is set to 4 mm. The selection signal generation circuit 240 is arranged in a region having a width B (= A / 7) which is considerably smaller than the entire width A. Further, the width C of the area where the light quantity sensor output processing unit 210 is arranged is larger than the width B.

  FIG. 5 is a block diagram showing the configuration of the controller 70 in the image forming apparatus 1 according to the embodiment of the present invention. Hereinafter, the operation of the controller 70 will be described with reference to FIG. The controller 70 includes an image memory 71a, a light amount correction data memory 71b, a buffer memory 71c, a network interface 72, a ROM (Read Only Memory) 73, a RAM (Random Access Memory) 74, a CPU (Central Processing Unit) 75, and an image processing unit 76. A timing generation unit 77 and a printer interface 78.

  As shown in FIG. 5, an external computer 300 is connected to a network N, and print job information such as image information, the number of prints, and a print mode (for example, color / monochrome) is transferred to the controller 70 via the network N. The controller 70 receives image information and print job information transferred from the computer 300 via the network interface 72, develops the image information into binary image data that can be printed, and conversely, is detected on the image forming apparatus side. Error information or the like is transmitted as so-called status information to the computer 300 via the network N.

  The controller CPU 75 controls the operation of the controller 70 based on a program stored in the ROM 84. The RAM 85 is used as a work area for the controller CPU 75, and temporarily stores image information, print job information, and the like received via the network interface 72.

  Based on the image information and print job information transferred from the computer 300, the image processing unit 76 can perform printing by performing image processing (for example, image development processing based on printer language, color correction, edge correction, screen generation, etc.) on a page basis. Binary image data is generated and stored in the image memory 71a in units of pages.

  FIG. 6 is an explanatory diagram showing the contents of the light quantity correction data memory 71b constituted by a rewritable nonvolatile memory such as an EEPROM. The data structure and data contents in the light quantity correction data memory will be described with reference to FIG.

  As shown in FIG. 6, the light quantity correction data memory 71b has three areas from a first area to a third area. Each area includes 5120 8-bit data equal to the number of organic electroluminescence elements 110 (see FIG. 4) constituting the exposure apparatus 60 (see FIG. 3), and occupies a total of 15360 bytes.

  First, data DD [0] to DD [5119] stored in the first area will be described with reference to FIGS. 3 and 4 in FIG.

  The exposure apparatus 60 (see FIG. 3) already described includes a step of adjusting the amount of light of each organic electroluminescence element 110 (see FIG. 4) constituting the exposure apparatus 60 in the manufacturing process. In this step, the exposure apparatus 60 is attached to a predetermined jig (not shown), and the organic electroluminescence element 110 is individually controlled to be turned on based on a control signal supplied from the outside of the exposure apparatus 60.

  Further, a CCD camera provided on a jig (not shown) measures the two-dimensional exposure amount distribution of each organic electroluminescence element 110 at the image plane position of the photoreceptor 8 (see FIG. 3). A jig (not shown) calculates the potential distribution of the latent image formed on the photoconductor 8 based on the exposure amount distribution, and further correlates with the toner adhesion amount based on the actual development condition (development bias value). Calculate the latent image cross section. In a jig (not shown), the drive current value for driving the organic electroluminescence element 110 is changed {as described above, the TFT circuit 190 (see FIG. 4) is connected via the source driver 180 (see FIG. 4). A current value for driving the organic electroluminescence element 110 can be set by programming an analog value in the pixel circuit 113 (see FIG. 8). } A drive current value at which all of the latent image cross-sectional areas formed by the individual organic electroluminescence elements 110 are substantially equal, that is, a set value for the pixel circuit 113 (from the viewpoint of control, set data for the source driver 180) ).

  When the light emission area of the organic electroluminescence element 110 and the light emission amount distribution in the light emission surface are equal and the normal development conditions are assumed, the above-described latent image cross-sectional area is substantially proportional to the exposure amount. Furthermore, “(light emission) light amount when the exposure time is constant” and “exposure amount” are synonymous, and generally, the light emission light amount and drive current value of the organic electroluminescence element 110 (that is, the pixel circuit 113 (see FIG. 8). ) Is proportional, the drive current settings for all the pixel circuits 113 are made the same, and the amount of light emitted from each organic electroluminescence element 110 is measured once, whereby each organic electroluminescence element 110 is measured. It is also possible to obtain a setting value (setting data to the source driver 180 as described above) for the pixel circuit 113 that makes the latent image cross-sectional area by the calculation constant.

  The first area of the light quantity correction data memory 71b stores setting data for the source driver 180 obtained in this way. The number is 5120 equal to the number of organic electroluminescence elements 110 constituting the exposure apparatus 60 as described above (that is, equal to the number of pixel circuits). As described above, the first area of the light quantity correction data memory 71b stores “the set value of the source driver 180 for equalizing the cross-sectional areas of the latent images formed by the individual organic electroluminescence elements 110 in the initial state”. .

  Next, data ID [0] to ID [5119] stored in the second area will be described with reference to FIGS.

  At the same time that the jig acquires data stored in the first area, the jig measures 8-bit light quantity based on the output of the light quantity sensor 220 (see FIGS. 4 and 10) via the source driver 180 (see FIG. 4) of the exposure apparatus 60. Get the data. As a result, “light quantity measurement data when the cross-sectional areas of the latent images formed by the individual organic electroluminescence elements 110 in the initial state are equal” can be acquired. The 8-bit light quantity measurement data ID [n] is stored in the second area.

  Now, the driving condition of the organic electroluminescence element 110 when acquiring ID [n] by the jig needs to be the same as that at the time of measuring the light amount. In the embodiment, as will be described later, one line period of the image forming apparatus 1 is used. A 350 μs (raster period) is applied a plurality of times to give a lighting period of about 30 ms in total.

  In this way, data stored in the first area and the second area is acquired in the manufacturing process of the exposure apparatus 60, and these data are written from the jig into the light amount correction data memory 71b by an electric communication means (not shown). .

  Next, data ND [0] to ND [5119] stored in the third area will be described with reference to FIG. 6, FIG. 4, and FIG.

  The image forming apparatus 1 according to the embodiment of the present invention includes a light amount correction unit (light amount correction unit) that corrects each light amount of the organic electroluminescence element 110 approximately equally based on a measurement result by the light amount sensor 220 serving as a light amount measurement unit. Controller CPU 75 (see FIG. 5)}, and based on the output of the light amount correction unit, the light amount setting unit (also controller CPU 75) sets the light amount of each organic electroluminescence element 110 when performing image formation. In the third area, a light amount setting value of each organic electroluminescence element 110 when image formation is performed by the controller CPU 75 as light amount correction means, that is, light amount correction data is written.

  In the image forming apparatus 1 according to the embodiment, the exposure apparatus 60 is configured at predetermined timings, which will be described later, such as the initialization operation of the image forming apparatus 1, the start of the image forming operation, the interval between sheets, and the completion of the image forming operation. As described above, the light quantity of the organic electroluminescence element 110 to be measured is measured. The controller CPU 75 equalizes the light quantity measurement data measured at these points in time and the “latent image sectional areas formed by the individual organic electroluminescence elements 110 in the initial state” stored in the first area in the manufacturing process of the exposure apparatus 60. The setting value of the source driver 180 for performing the process is the same as the “cross-sectional area of the latent image formed by each organic electroluminescence element 110 in the initial state” stored in the second area in the manufacturing process of the exposure apparatus 60. Light quantity correction data is generated based on the "light quantity measurement data". That is, the controller CPU 75 functions as a light amount correction unit that refers to the light amount of the organic electroluminescence element 110 detected by the light amount sensor 220 and corrects the light amount of the element.

  Hereinafter, the calculation contents of the light amount correction data by the controller CPU 75 will be described. First, the description will be made assuming that the light amount at the time of measuring the light amount is equal to that at the time of image formation.

  DD [n] (where n is a value in the main scanning direction) stored in the first area is “the set value of the source driver 180 for equalizing the cross-sectional areas of the latent images formed by the individual organic electroluminescence elements 110 in the initial state”. Individual organic electroluminescence element numbers (hereinafter the same), “light quantity measurement data when the latent image cross-sectional areas formed by the individual organic electroluminescence elements 110 in the initial state are equal” stored in the second area is ID [ n], when the light quantity measurement data newly measured in the initialization operation or the like is PD [n], the new light quantity correction data ND [n] written in the third area is based on (Equation 1) based on the controller CPU75. Generated by. The light quantity measurement data ID [n] corresponds to the measured light quantity of the organic electroluminescence element, but the light quantity correction data ND [n] is a current value that flows to each element set in the source driver 180. Applicable.

  The light quantity correction data ND [n] generated in this way is once written in the third area of the light quantity correction data memory 71b (see FIG. 5). Thereafter, prior to image formation, the light amount correction data ND [n] is copied from the light amount correction data memory 71b to a predetermined area of the image memory 71a (see FIG. 5). The light amount correction data ND [n] copied to the image memory 71a when forming an image is temporarily stored together with binary image data in a buffer memory 71c (see FIG. 5), which will be described later, and a printer interface 78 (see FIG. 5). ) To the engine control unit 80 (see FIG. 5).

  In the present embodiment, the light amount correction data ND [n] is obtained using the proportional calculation as described above. However, after the light amount correction data ND [n] is determined, the organic electroluminescent element is again used. 110 may be turned on to obtain light quantity measurement data, and if the difference between this and the initial light quantity measurement data ID is larger than a predetermined value, the light quantity measurement operation may be repeated again.

  It is also possible to repeat the light amount measurement until the measured light amount measurement data substantially matches the initial light amount measurement data ID [n], thereby obtaining the light amount correction data ND [n].

  The light quantity measurement data is subjected to voltage conversion by the charge accumulation method in the light quantity sensor output processing unit 210. The charge accumulation method is effective for improving the S / N ratio, but the output (current value) of the light quantity sensor 220 (see FIGS. 4 and 10) is very small, so that charge accumulation requires a certain accumulation time. . This will be described later.

  As described above, the binary image data and the light amount correction data stored in the image memory 71a are temporarily stored in the buffer memory 71c when transferred to the engine control unit 80. The buffer memory 71c is constituted by a so-called dual port RAM in order to absorb the difference between the transfer speed from the image memory 71a to the buffer memory 71c and the data transfer speed from the buffer memory 71c to the engine control unit 80.

  The binary image data and light amount correction data in page units stored in the image memory 71a are transferred to the engine control unit 80 via the printer interface 78 in synchronization with the clock signal and line synchronization signal generated by the timing generation unit 77. The

  In the present embodiment, the main body that performs the light amount correction has been described as the controller 70. However, this light amount correction function may be executed by a component other than the controller 70, for example, the light amount correction data ND [n] described above. You may comprise so that all the calculation functions may be given to the exposure apparatus 60. FIG. In this case, an arithmetic unit such as a CPU, a memory, or the like may be configured in the exposure apparatus 60.

  FIG. 7 is a block diagram showing the configuration of the engine control unit 80 in the image forming apparatus 1 according to the embodiment of the present invention. The engine control unit 80 includes a controller interface 81, an engine control CPU 82, a ROM 83, a RAM 84, a nonvolatile memory 85, a serial interface 86, and a bus 87.

  The controller interface 81 receives light amount correction data transferred from the controller 70, binary image data in units of pages, and the like.

  The engine control CPU 82 controls an image forming operation in the image forming apparatus 1 based on a program stored in the ROM 83. The RAM 84 is used as a work area when the engine control CPU 82 operates. The non-volatile memory 85 is constituted by a so-called rewritable non-volatile memory such as an EEPROM, and relates to the lifetime of components such as the rotation time of the photoconductor 8 of the image forming apparatus 1 and the operation time of the fixing device 23 (see FIG. 1). Information is stored.

  Information from sensor groups such as the recording paper passage detection sensor 21 (see FIG. 1) and the recording paper trailing edge detection sensor 28 (see FIG. 1) and the output of the power supply monitoring unit 44 (see FIG. 1) are not shown. Is converted into a serial signal having a predetermined cycle and received by the serial interface 86. The serial signal received by the serial interface 86 is converted into a parallel signal and then read by the engine control CPU 82 via the bus 87.

  On the other hand, the actuator group 45 such as an electromagnetic clutch (not shown) for controlling the start / stop of the sheet feeding roller 18 and the driving source 38 (both see FIG. 1) and the driving force transmission to the sheet feeding roller 18 (see FIG. 1) is controlled. Signals and control signals for the high voltage power supply control unit 46 that manages potential settings such as development bias, transfer bias, and charging potential are sent to the serial interface 86 as parallel signals. The serial interface 86 converts the parallel signal into a serial signal and outputs it to the actuator group 45 and the high voltage power supply control unit 46. As described above, in the embodiment, sensor inputs and actuator control signals that do not need to be detected at high speed are all output via the serial interface 86. On the other hand, for example, a control signal for driving / stopping the registration roller 19 that requires a certain high speed is directly connected to the output terminal of the engine control unit 80.

  In addition, an operation panel 47 installed in a predetermined portion of the housing 2 is connected to the serial interface 86. The instruction given to the operation panel 47 by the user is recognized by the engine control CPU 82 via the serial interface 86. In the embodiment, an operation panel is provided as an instruction input unit for inputting a user instruction, and based on the input to the operation panel, the light quantity of the organic electroluminescence element 110 constituting the exposure apparatus 60 is measured, and the light quantity May be corrected. This instruction can of course be given from an external computer or the like via the controller 70. As a specific usage mode, for example, when the user discovers density unevenness on the printing surface when performing a large amount of printing, the user forcibly corrects the amount of light to ensure image quality. Is assumed. If the image forming apparatus 1 is on standby, the user can instruct the execution of forced light amount correction at any time, and even during image formation, the image forming apparatus 1 is shifted to offline to temporarily form an image. Thus, the user can instruct execution of light amount correction.

  In any case, when a light quantity correction request is input from the operation panel 47 or the like as an instruction unit, the engine control CPU 82 starts driving the components of the image forming apparatus 1 as described in (Initialization operation). , A request for creating dummy image information for light amount correction is output to the controller 70. Based on this request, the controller CPU 75 mounted on the controller 70 generates dummy image information for light amount correction, and based on this, the organic electroluminescence element 110 constituting the exposure apparatus 13 is controlled to be lit. At this time, the light quantity sensor 220 provided in the exposure apparatus 60 described above detects the light quantity of each organic electroluminescence element 110, and the light quantity of each organic electroluminescence element 110 is substantially equal based on the detection result of this light quantity. The amount of light is corrected so that

  Next, the operation when measuring the amount of light of the organic electroluminescence element 110 will be described in detail with reference to FIGS. 1, 5 and 6 in FIG.

  As will be described later, the correction of the amount of light is performed at the timing specified by the user using the operation panel 47 or the like after the initialization operation immediately after the start of the image forming apparatus 1, before the start of printing, between sheets, after the start of printing. Next, a case where the light amount measurement is executed at the time of initialization operation of the image forming apparatus 1 will be described. The image forming apparatus 1 according to the embodiment is configured to be capable of forming a full-color image, and has exposure apparatuses 60Y to 60K (see FIG. 1) corresponding to four colors as described above. For the sake of simplicity, only the operation for one color will be described and described as an exposure apparatus 60. In the situation shown below, for example, it is assumed that the drive source 38 (see FIG. 1), the development station 50 (see FIG. 2), etc. are already activated as described in detail in (Initialization operation).

  Since the image forming operation is managed by the engine control unit 80 in the image forming apparatus 1, the light quantity correction sequence is started by the engine control CPU 82 of the engine control unit 80. First, the engine control CPU 82 outputs to the controller 70 a request for creating dummy image information that is different from the regular binary image data related to image formation.

  The engine control unit 80 and the controller 70 are connected by a bidirectional serial interface (not shown), and can exchange a request command (request) and an acknowledgment (response information) with respect to the request command. The dummy image information creation request issued by the engine control CPU 82 is output from the controller interface 81 to the controller 70 via the bus 87 using this bidirectional serial interface (not shown).

  Based on this request, the controller CPU 75 mounted on the controller 70 directly creates dummy image information, that is, binary image data used for light quantity measurement, in the image memory 71a. Further, the controller CPU 75 stores “the source driver 180 for equalizing the cross-sectional areas of the latent images formed by the individual organic electroluminescence elements 110 in the initial state” stored in the first area (see FIG. 6) of the light amount correction data memory 71b. “Setting value” DD [n] (n: 0 to 5119) is read, and this value is written in a predetermined area of the image memory 71a. When these processes are completed, the controller CPU 75 outputs response information to the engine control unit 80 via the printer interface 78.

  The engine control CPU 82 of the engine control unit 80 that has received the response information immediately sets a writing timing for the exposure apparatus 60. In other words, the engine control CPU 82 sets the timing for writing the electrostatic latent image by the exposure device 60 in a timer, which is not shown, and starts the operation of the timer as soon as response information is received (this function is originally provided with a plurality of exposure devices). This is for determining the start timing for each color of 60. In the measurement of the light amount, such a strict timing setting is unnecessary, and for example, the timer may be set to 0). Each timer outputs an image data transfer request to the controller 70 when a preset time has elapsed. Upon receiving the image data transfer request, the controller 70 transfers the binary image data to the exposure device 60 in synchronization with the timing signal (clock signal, line synchronization signal, etc.) generated by the timing generator 77 via the controller interface 81. . At the same time, the light intensity setting value already written in the image memory 71a is also transferred to the exposure device 60 in synchronization with the timing signal.

  The binary image data transferred in synchronization with the timing signal in this manner is input to the TFT circuit 190 of the exposure apparatus 60, and at the same time, the light amount setting value is input to the source driver 180 of the exposure apparatus 60. In the exposure apparatus 60, lighting and extinguishing of the corresponding organic electroluminescence element 110 are controlled based on the input binary image data, that is, ON / OFF information. At this time, the light quantity of each organic electroluminescence element 110 is measured by the light quantity sensor 220.

  As described above, the lighting of the organic electroluminescence element 110 is controlled, and the light amount is measured by the light amount sensor 220. The output (analog current value) of the light quantity sensor 220 is converted into a voltage by the charge accumulation method in the sensor pixel circuit 230 as will be described in detail later with reference to FIG. After being amplified in step, analog-to-digital conversion is performed and the light amount sensor output processing unit 210 outputs 8-bit light amount measurement data (digital data).

  The light amount measurement data output from the light amount sensor output processing unit 210 is transferred from the engine control unit 80 to the controller 70 via the controller interface 81 and received by the controller CPU 75 of the controller 70.

  FIG. 8 is a circuit diagram of the exposure device 60 in the image forming apparatus 1 according to the embodiment of the present invention. Hereinafter, the lighting control by the TFT circuit 190 and the source driver 180 will be described in more detail with reference to FIG. Here, the illustration of the configuration relating to the light quantity measurement including the light quantity sensor 220, the selection signal generation circuit 240 (see FIG. 4) and the like is omitted. Also, the description of the engine control unit 80 in FIG. 7 is omitted.

  The TFT circuit 190 here is roughly divided into a pixel circuit 113 and a gate controller 114. One pixel circuit 190 is provided for each organic electroluminescent element 110, and N groups are provided on the glass substrate 101 with the M pixels of the organic electroluminescent element 110 as one group. Further, the light emitting element driving circuit 181 in FIG. 4 corresponds to the portion of the TFT circuit 190 in FIG.

  In the embodiment, one group is 8 pixels (that is, M = 8), and this group is 640. Therefore, the total number of pixels is 8 × 640 = 5120 pixels. Each pixel circuit 113 supplies a current to the organic electroluminescent element 110 to drive the driver unit 111, and a current value supplied by the driver to control the lighting of the organic electroluminescent element 110 (that is, a driving current value of the organic electroluminescent element 110). ) Is stored, and the organic electroluminescence element 110 can be driven at a constant current according to a drive current value programmed in advance at a predetermined timing.

  The gate controller 114 sequentially shifts the input binary image data, a latch unit that is provided in parallel with the shift register and holds them collectively after a predetermined number of pixels have been input to the shift register, It consists of a control part which controls these operation timings (both not shown). The gate controller 114 receives binary image data (image information converted by the controller 70 at the time of image formation and dummy image information converted by the controller 70 at the time of light quantity measurement) from the controller 70, and this binary image data, that is, ON. The SCAN_A and SCAN_B signals are output based on the / OFF information, and thereby the timing of turning on / off the organic electroluminescence element 110 connected to the pixel circuit 113 and the timing of the current program period for setting the drive current are controlled. .

  On the other hand, the source driver 180 has a number (640 in the embodiment) of D / A converters 182 corresponding to the number N of groups of the organic electroluminescence elements 110 inside. The source driver 180 sets a driving current for each organic electroluminescence element 110 according to lighting data based on 8-bit light amount correction data supplied via the FPC 66. On the other hand, a control signal is directly input to the gate controller of the TFT circuit 190 via the FPC 66. The control signal is a signal for giving an operation timing to the TFT circuit 190, and includes a synchronization signal for synchronizing one line in the image forming apparatus and a clock signal. The source driver 180 in FIG. 8 corresponds to the source drivers 180a and 180b in FIG. 4, but illustrates an arrangement different from that in FIG. 4, and only one source driver is shown in FIG. Thus, in the present embodiment, the number of source drivers, the arrangement method, and the like are not particularly limited.

(Light emitting element drive control configuration)
Next, details of the light emitting element drive control which is the subject of the present invention will be described. In the present invention, by controlling the light emission control of the organic electroluminescence element 110 which is a light emitting element, it is possible to achieve the control for causing the organic electroluminescence element 110 to emit light appropriately. In addition, this invention is applicable not only to an organic electroluminescent element but other light emitting elements.

  FIG. 9 shows the TFT circuit 190 (excluding the gate controller 114) and the source driver 180 in FIG. 8 in more detail. The TFT circuit 190 shown in FIG. 9 does not include a light amount measurement part, is substantially equal to the light emitting element driving circuit 181, and may be referred to as a “driver circuit”. In addition, the pixel circuit 113 that is a minimum unit circuit for driving each of the organic electroluminescence elements 110 may also be referred to as a “driver circuit”. In this embodiment, a unit of a pixel circuit that includes one organic electroluminescence element 110 that is a light emitting element and drives and controls the one light emitting element is referred to as a “pixel”. Further, from the viewpoint of the function of driving the light emitting element, the driver circuit plays a role as the light emitting element driving device, but the whole of FIG. 9 including the source driver 180 can be grasped as the light emitting element driving device.

  One output of the source driver 180 is responsible for a program of 8 pixels (8 pixel circuits). That is, all the pixels are divided into one group in units of 8 pixels, and a program operation command is issued from the source driver 180 to each element belonging to the group in units of groups. That is, the number of groups is 640, 640 D / A converters 72 are mounted on the source driver 180, and a total of 640 source driver signal lines (SD *) are connected to the TFT circuit 190.

  Here, the pixel circuit 113 will be described with reference to FIG. FIG. 10 shows an enlarged view of the pixel circuit 113 shown in FIGS. This example is a pixel circuit driven by a so-called “current programming method”. In the description of this figure, SCNA1 _ ** and SCNA2 _ ** may be simply referred to as “SCNA signal (or SCNA1 signal, SCNA2 signal)”, and SCNB _ ** may be simply referred to as “SCNB signal” (see FIG. 8). ).

  The pixel circuit 113 shown in FIG. 10 includes transistors Tr1 to Tr5 as five switching elements, a capacitor element Cs, and an organic electroluminescence element 110. The transistors Tr1 to Tr5 are composed of MOS (Metal Oxide Semiconductor) transistors.

  Tr1 (third switching element) and Cs connected in parallel to each other are connected to a power source Vs. The source of Tr2 (first switching element) is connected to the gate of Tr1 and Cs. The source of Tr3 (second switching element) is connected in series via the intermediate connection point P to the drain of Tr1 and the drain of Tr2. The SCNA1 signal and SCNA2 signal output from the gate controller 114 (FIG. 8) are input to the gates of Tr2 and Tr3, respectively. The source of Tr4 (fourth switching element) is connected to the connection intermediate point P, and the drain of Tr4 is connected to Tr5 and the organic electroluminescence element 110 connected in parallel to each other. The SCNB signal is input to the gates of Tr4 and Tr5. The drain of Tr5 (fifth switching element) and the organic electroluminescence element 110 are grounded on the opposite side of Tr4 (GND). Furthermore, a current having the same magnitude as Ip (program current) output from the D / A converter 182 of the source driver 180 is output from the drain of Tr3. The driver unit 111 also shown in FIG. 8 is composed of Tr4 and Tr5, and the program unit 112 is composed of Cs, Tr1, Tr2, and Tr3.

  The current for driving the organic electroluminescence element 110 depends on the characteristics of Tr1. FIG. 27 shows an example of output current (Id) characteristics with respect to the gate potential (Vgs) of Tr1. The output current of Tr1 is basically determined by the potential of Vgs. When Vgs is near 0 potential, Tr1 is off and Id is 0. However, since Tr1 is a P-channel transistor, Tr1 is turned on from a certain gate potential level when the gate potential is lowered with respect to the source. Id starts to flow. When the gate potential is further lowered, Tr1 reaches the saturation region, and even if the gate potential is changed, Id keeps a constant level and does not flow any more. By utilizing such characteristics, the output current (Id) is set by the gate potential (Vgs) of Tr1, and a predetermined current is supplied to the organic electroluminescence element 110.

  More specifically, during the current programming period, Tr2 and Tr3 are turned on, and control is performed so that the source driver 180 (see FIG. 9) outputs a predetermined program current (Ip) (current is drawn into the source driver 180 side). Thus, the pixel circuit 113 operates so that the output current (Id) of Tr1 is equal to Ip. At this time, according to the characteristics of Tr1 as shown in FIG. 27, the potential of Cs (the gate potential of Tr1) settles to the potential (Vgs1) for outputting Ip via the power supply (Vs), Tr1, and Tr2. When Tr2 and Tr3 are turned off in this state, the gate potential of Tr1 is held at Vgs1 by Cs. Thereafter, when Tr4 is turned on, a path is formed to pass current to the organic electroluminescent element 110 via the power source (Vs), Tr1, and Tr4. At that time, the gate potential of Tr1 is held at Vgs1, so that the organic electro A current equal to Ip flows through the luminescence element 110. By repeating such an operation, a current value for driving the organic electroluminescence element 110 can be programmed in the pixel circuit 113 in advance, and light emission can be controlled.

  A gate signal V2, which is a common signal, is input to the transistors 311 and 312 in the conventional current programming circuit 340 shown in FIG. Unlike this configuration, in this embodiment, different independent signal lines SCNA1 _ ** and SCNA2 _ ** are connected to the transistors Tr2 and Tr3 corresponding to the transistors 311 and 312. SCNA1 _ ** connected to the transistor Tr1 constitutes a so-called program control signal line, outputs either a High / Low program control signal, and switches the transistor Tr2 on and off. The program control signal here is a signal for controlling the gate potential of Tr1 for controlling the value of the current supplied to the organic electroluminescence element 110 by turning on / off the transistor Tr2. Specifically, the transistor Tr2 charges the capacitor Cs by a program control signal from the signal line SCNA1 _ **. In other words, due to the switching action of the transistor Tr2, the capacitive element Cs plays a role of applying and holding the gate potential of the transistor Tr1 for determining the current value supplied to the organic electroluminescence element 110.

  The SCNA2 _ ** connected to the transistor Tr3 also functions similarly to the SCNA1 _ ** and can be said to be a program control signal line. However, the SCNA1 _ ** signal and the SCNA2 _ ** signal are independent from each other. This will be described later.

  SCNB _ ** in FIG. 10 is a light emission control signal line, and is a signal for turning on and off the current supplied to the organic electroluminescence element 110. In the present embodiment, Tr4 is turned on when SCNB _ ** is at a low level, while Tr5 is turned off. Therefore, when SCNB _ ** is on, a current flows from the power source (Vs) to the organic electroluminescence element 110 via Tr1 and Tr4, and the organic electroluminescence element 110 emits light. That is, Tr4 and Tr5 constitute a push-pull circuit and have current characteristics opposite to each other. On the other hand, when SCNB_P * is at a high level, Tr4 is turned off, so that the current path to the organic electroluminescent element 110 is cut off, and no current flows through the organic electroluminescent element 110, and no light is emitted. That is, Tr5 opens or shorts both terminals of the organic electroluminescence element 110 depending on the on / off control of the current flowing through the organic electroluminescence element 110 by Tr4.

  Further, the light emission control signal lines (SCNB _ **) output from the gate controller 114 in FIG. 8 are a total of 5120 signals, which are input to the pixel circuit of each pixel, and at a predetermined timing according to the image data of each pixel. , High / Low (on / off) emission control signal is output. As a result, the light emission control signal is a signal indicating light emission or non-light emission of each organic electroluminescence element 110.

  That is, the light emission control signal (SCNB _ **) is independent for each pixel, and is turned ON / OFF according to image data of each pixel (data for forming an image formed by light from the light emitting element). Is set. In other words, the light emission control signal is switched to ON / OFF depending on the image data of each pixel independently of each pixel.

  On the other hand, the program control signals SCNA1 _ ** and SCNA2 _ ** are not independent for each pixel but are supplied to each of the 640 groups constituting all the pixels. Further, as will be described later, the program unit 112 functions as a drive condition setting unit that sets the drive conditions (drive current, drive voltage, etc.) of the organic electroluminescence element 110, and the driver unit 112 performs organic electroluminescence at a predetermined cycle. It functions as a drive control unit that controls light emission and non-light emission of the luminescence element 110.

  FIG. 11 is a diagram for explaining the operation in the pixel circuit similar to the circuit described in FIG. That is, as shown in FIG. 11A, a common SCNA signal is input to the transistors Tr2 and Tr3 corresponding to the transistors 311 and 312 in FIG. The SCNB signal is input to the transistors Tr4 and Tr5. As shown in FIG. 11B, for one pixel circuit, a program period corresponding to a program mode (first mode) for setting a driving condition based on the gate potential of Tr1 (= Cs holding potential), The light emission periods corresponding to the element light emission mode (second mode) in which the organic electroluminescence element 110 emits light according to the set driving conditions are alternately provided at predetermined intervals.

  First, during the program period, the SCNA signal becomes Low, and Tr2 and Tr3 are turned on. In this case, as shown in FIG. 11C, the gate potential of Tr1 (= the holding potential of Cs) is determined by the program current. At the end of the program, the SCNA signal becomes High, so it is considered that both Tr2 and Tr3 are simultaneously turned off.

  However, as shown in FIG. 11 (d), it has been found that Tr3 may be turned off before Tr2 due to signal delay due to the influence of wiring and other factors in the program end transition period. In this case, since the closed loop circuit is constituted by Tr1, Tr2, and Cs, the Cs potential may change so as to balance the circuit. In this case, as shown in FIG. 11E, Tr2 is turned off at the end of the program period, and at that time, the previous closed loop circuit is canceled and the Cs potential is determined for the first time. Therefore, the Cs potential is different between the states of FIG. 11C and FIG. 11E, and as a result, the organic electroluminescence element 110 is driven with a current value different from the program current, resulting in variations in light emission. It can be a cause.

  FIG. 12 is a diagram for explaining the operation of the pixel circuit 113 according to the embodiment of the present invention shown in FIG. In the present invention, in order to solve the above-described problem, at the end of the program, Tr2 is turned off first to determine the Cs potential, and control is performed to turn off Tr3 after a delay.

  That is, in the program mode state of FIG. 12A similar to FIG. 11C, a closed loop circuit is formed by Tr1, Tr2, and Cs (t1 to t2 of FIG. 12D). Next, at the end of the program mode, as shown in FIG. 12B, the SCNA1 signal is set to High before the SCNA2 signal, and Tr2 is turned off (t2 in FIG. 12D). At this point, the SCNA2 signal is still low and Tr3 is on. That is, as shown in FIG. 12A, while the closed loop circuit formed by Tr1, Tr2, and Cs is configured in the program mode, Tr3 positioned outside the closed loop circuit via the intermediate connection point P is always turned on. As shown in FIG. 11 (d), the closed loop is not isolated from the outside at the end of the program mode. Therefore, once the potential of Cs is determined, the potential does not fluctuate due to equilibration.

  Thereafter, the SCNA2 signal is set to High, and Tr3 is turned off (t3 in FIG. 12D). Accordingly, when switching from the program mode to the element emission mode, a period between when Tr3 is turned off and when Tr3 is switched from on to off, that is, a period from t2 to t3 is inevitably set. This period is defined as the transition mode. In other words, at the end of the program mode, after Tr3 is turned off and the closed loop circuit is eliminated, Tr3 is kept on for a predetermined period (t2 to t3).

  Thereafter, after a predetermined period as usual, the SCNB signal becomes Low, Tr4 is turned on, and Tr5 is turned off (t4 in FIG. 12D). Then, a current flows from the power source (Vs) to the organic electroluminescent element 110 via Tr1 and Tr4, and the organic electroluminescent element 110 emits light. That is, a predetermined time (t3 to t4) is provided in a predetermined period between the transition period mode and the element light emission mode, and the organic electroluminescence element 110 can emit light reliably.

  As described above, in the present invention, the transistor Tr2 for controlling the gate potential of Tr1 (= the holding potential of Cs), the program mode (first mode) corresponding to the program period, and the element corresponding to the light emission period The transistor Tr3 for switching the light emission mode (second mode) is controlled by the independent SCNA1 signal and SCNA2 signal. In particular, by turning off the transistor Tr2 earlier than Tr3, a closed loop that fluctuates the potential of Cs after the potential is determined is prevented from being formed in the pixel circuit. Therefore, a current based on the Cs holding potential as programmed can be supplied to the organic electroluminescence element 110, and the amount of light emitted from the organic electroluminescence element 110 can be made accurate. The independent control of the transistor Tr2 and the transistor Tr3 by the SCNA1 signal and the SCNA2 signal can be performed by, for example, the control unit of the gate controller 114 described above.

  FIG. 13 shows an example of an embodiment of a TFT circuit 190 including the source driver 180 (180a, 180b) and the light emitting element driving circuit (light emitting element driving unit) 181 in the optical head 100 shown in FIG. This corresponds to a modification. The source driver is composed of source drivers 180a and 180b divided into two chips, and 320 D / A converters 182 are mounted on each of the two source drivers. The source driver 180 functions as a current supply unit that supplies current to the light emitting element driving circuit 181 and the pixel circuit 113.

  Further, the light emitting element driving circuit 181 also corresponds to the two source drivers 180a and 180b, the light emitting element driving circuit 181a in charge of the left half block (the left half of the light emitting element driving circuit 181 in FIG. 4), and the right half. Are divided into a light emitting element driving circuit 181b in charge of the block (right half of the light emitting element driving circuit 181 in FIG. 4). Further, in the present embodiment, the SCNA signal controller 114a and the SCNB signal controller 114b are shown in the gate controller 114, but this is the same in the case of FIG.

  Further, in the present embodiment, the current mirror circuit 183 (183a, 183b) is inserted between the source driver 180 and the light emitting element driving circuit 181. The current mirror circuit 183 includes a plurality of sub-circuits 184 corresponding to the respective lines, and the sub-circuit 184 includes two transistors 184a and 184b connected to face each other. The source of the transistor 184a is connected to the output of the D / A converter 182, and the source of the transistor 184b is connected to the drain of the transistor Tr3.

  Although not shown in FIG. 13, the sub-circuit 184 is formed in the TFT circuit 190 of the optical head 100 so as to correspond structurally to the corresponding eight pixel circuits. Therefore, as shown in FIG. 4, the current mirror circuits 183 are arranged in parallel along the light emitting element array 110 </ b> A and the light emitting element driving circuit 181.

  The current mirror circuit 183 functions as an amplifying unit that amplifies the current of the source driver 183 with a predetermined amplification factor and flows the amplified current to the light emitting element driving circuit 181. There are several means for setting the amplification factor. For example, if the design parameters of the transistor 184a and the transistor 184b are the same (the channel length, channel width, etc., which are transistor design parameters are the same), If the characteristics variation factor is excluded, the transistor 184a and the transistor 184b have substantially the same characteristics, so the amplification factor is almost 1. In addition, since the transistor output current characteristics with respect to the gate potential can be changed by the channel width which is a design parameter of the transistor, the amplification factor can be increased to 1 or more by increasing or decreasing the channel width of the transistor 184b with respect to the transistor 184a. If possible, it can be 1 or less. Alternatively, even if the transistor 184a and the transistor 184b have the same parameters, if a plurality of (n) output side transistors 184b are arranged in parallel with the transistor 184a on the input side of the current mirror circuit 183, The amplification factor can be increased by a factor of n.

  On the other hand, in the present embodiment, the number of the input side transistors 184a and the output side transistors 184b of the current mirror circuit 183 is 1: 1, and the transistors 184a and 184b are the same (channel length and channel which are transistor design parameters). Therefore, the current of the source driver 183 is equal to the current of the light emitting element driving circuit 181. That is, the amplification factor = 1, and the substantial amplification function is not performed.

  However, many current source discharge types of source drivers 183 can be seen. This is because the commercialization using organic electroluminescence elements is still in the dawn of products mainly using displays, and the drive system itself is mainly passive matrix driving. In passive matrix driving, it is generally composed of a source (column) driver and a row driver for driving, and it seems that one of the reasons is that the source (column) driver is generally a current discharge type. .

  Further, as shown in FIG. 12 and the like, the pixel circuit 113 of the light emitting element driving circuit 181 is also a current discharge type circuit in which the program current flows out of the Tr3 starting from the power source Vs. Therefore, it is difficult to connect the two directly. In the present embodiment, the current mirror circuit 183 performs an action of converting the current discharged from the D / A converter 182 into a drawn current through the action of the transistors 184a and 184b, and is a light emitting element driving circuit which is a current discharge type circuit. The current characteristic consistency with the pixel circuit 113 of 181 is ensured.

  FIG. 14 is an explanatory diagram showing a current program period and a lighting period of the organic electroluminescence element 110 according to the exposure apparatus 60 in the image forming apparatus 1 of the embodiment of the present invention. Hereinafter, the lighting control of the embodiment will be described in more detail with reference to FIG. 14 together with FIG. Hereinafter, for the sake of simplicity, one pixel group composed of 8 pixels (for example, “pixel number in the main scanning direction” = 1 to 8 in FIG. 14) will be described.

  In the embodiment, one line period (raster period) of the exposure apparatus 60 is set to 350 μs, and 1/8 (43.75 μs) of the one line period is driven to the capacitor formed in the current program unit 112. It is used as the program period for setting the value.

  First, the gate controller 114 (see FIG. 8) sets the program period by turning on the SCAN_A signal and turning off the SCAN_B signal for the pixel of pixel number = 1. Lighting data based on the 8-bit light quantity correction data is supplied to the D / A converter 182 built in the source driver 180 (see FIG. 8) during the program period, and the analog data obtained by D / A converting the supplied digital data. The capacitor of the current program unit 112 (see FIG. 8) is charged by the level signal. This program period is executed regardless of ON / OFF of the binary image data input to the gate controller 114. As a result, an analog value based on 8-bit lighting data is written to the capacitor formed in the current program unit 112 every time one line period. That is, the holding potential of the capacitor formed in the current program unit 112 is always refreshed, and the driving current of the organic electroluminescence element 110 determined based on this is always kept constant.

  When the program period is completed, the gate controller 114 (see FIG. 8) immediately sets the lighting period by switching the SCAN_A signal to OFF and the SCAN_B signal to ON. As described above, binary image data is supplied to the gate controller 114 (see FIG. 8) according to the time of image formation and the measurement of the amount of light. When the image data is OFF even during the lighting period, organic electroluminescence is provided. The element 110 is not lit. On the other hand, when the image data is ON, the organic electroluminescence element 110 continues to be lit for the remaining 306.25 μs (350 μs−43.75 μs) (actually, the light emission time is slightly shortened because there is a control signal switching time). ). As already described, in the embodiment, when measuring the light amount of the organic electroluminescence element 110, a measurement period of 30 ms is assumed, so that the number of times of lighting at the time of light amount measurement is, for example, 100 times (that is, 100 lines). The dummy image information is generated by the controller 70.

  On the other hand, when the program period for the pixel circuit 113 (see FIG. 8) with the pixel number = 1 shown in FIG. 14 ends, the gate controller 114 (see FIG. 8) immediately applies to the pixel circuit 113 with the pixel number = 8 (see FIG. 8). Sets the current program period. Thereafter, as in the procedure for the pixel circuit having the pixel number 1, as soon as the program period for the pixel circuit having the pixel number 8 is completed, the process proceeds to the lighting period of the organic electroluminescence element 110 having the pixel number (see FIG. 8).

  In this way, the gate controller 114 (see FIG. 8) sets the pixel number in the main scanning direction = “1 → 8 → 2 → 7 → 3 → 6 → 4 → 5 → 1. Will be set. By adopting such a lighting order, the lighting timing of the nearest pixel is adjacent in time between adjacent pixel groups, so that the image step at the time of forming one line can be made inconspicuous.

(Light intensity measurement operation)
Next, the light quantity measurement unit 200 that is a part related to light quantity measurement in the image forming apparatus according to the embodiment of the present invention will be described. The light amount measuring unit 200 measures the amount of light emitted from the organic electroluminescence element 110.

  FIG. 15 is an explanatory diagram showing a main configuration of the light quantity measuring unit 200 according to the embodiment of the present invention. As shown in FIG. 15, the light quantity measurement unit 200 includes a plurality of light quantity sensors 220 provided corresponding to each of the plurality of organic electroluminescence elements 110 and a sensor pixel circuit provided corresponding to each light quantity sensor 220. 230, a selection signal generation circuit 240 that outputs a sensor selection signal to each of the sensor pixel circuits 230, and 16 detection processing circuits 270A to 270P. The detection processing circuits 270A to 270P constitute the light quantity sensor output processing unit 210 already described. The light quantity measurement unit 200 is an example of a light quantity measurement device, and the sensor pixel circuit 230 is an example of a light quantity detection circuit.

  The detection processing circuits 270A to 270P have the same configuration, and when it is not necessary to distinguish them, the detection processing circuits 270 will be described. Further, the number of detection processing circuits 270 is not limited to 16, and m (m is a positive integer of 1 or more) may be provided.

  As described above, the light amount sensor 220, the sensor pixel circuit 230, and the selection signal generation circuit 240 are integrated with the organic electroluminescence element 110 as a monolithic device of polysilicon of the TFT circuit 190. Therefore, in the sensor pixel circuit 230, the TFT circuit 190, and the like, when the same type of element such as a transistor is formed, it can be formed in the same process, so that the manufacturing process can be simplified.

  In FIG. 15, the TFT circuit 190 constituted by the light quantity sensor 220, the sensor pixel circuit 230, and the selection signal generation circuit 240, and the light quantity sensor output processing unit 210 are drawn so as to be arranged very close to each other. In the present embodiment, as will be described in detail later, these are disposed separately on both sides of the light emitting element array formed by the organic electroluminescence element 110.

  The selection signal generation circuit 240 is connected to the engine control unit 80 via the FPC 66 and is connected to each sensor pixel circuit 230 via the selection signal lines SEL1 to SEL5120. Note that “X” of the symbol “SELX” of the selection signal lines SEL1 to SEL5120 is the sensor pixel number SPNO assigned to the sensor pixel circuit 230 that is the connection destination, and is selected when it is not necessary to distinguish them. This will be described as the signal line SEL.

  The selection signal generation circuit 240 generates a sensor selection signal for controlling the operation of the sensor pixel circuit 230 based on the sensor control input SC input from the engine control unit 80 via the FPC 66 via the selection signal line SEL. Output to the sensor pixel circuit 230. Thereby, the light quantity detection timing can be controlled for each of the sensor pixel circuits 230. That is, the selection signal generation circuit 240 functions as a selection circuit that selects any one of the plurality of light quantity sensors 220 at a predetermined timing, and processes the output of the selected light quantity sensor 220, thereby corresponding organic electroluminescence. The amount of light emitted from the element 110 can be measured.

  The sensor pixel circuit 230 is connected to the selection signal generation circuit 240 via the selection signal line SEL, and is connected to the detection processing circuits 270A to 270P via any of the driver lines RoA to RoP. Then, the light amount is detected based on the sensor selection signal input from the selection signal generation circuit 240, and the sensor pixel circuit output signal is output to the detection processing circuit 270. Note that “X” of the code “RoX” of the driver lines RoA to RoP is an output ID (A to P) given to the detection processing circuit 270 that is a connection destination, and it is not necessary to distinguish these This will be described as a driver line Ro.

  The detection processing circuits 270A to 270P are provided in the light amount sensor output processing unit 210, and are connected to the sensor pixel circuits 230 via the driver lines RoA to RoP, respectively, and from the sensor output signal lines DoA to DoP via the FPC 66. The engine control unit 80 is connected. Then, the sensor pixel circuit output signal from the sensor pixel circuit 230 is acquired, and the light quantity measurement data is output to the FPC 66. Note that “X” of the symbol “DoX” of the sensor output signal lines DoA to DoP is an output ID (A to P) of the detection processing circuit 270 to be connected. The output signal line Do will be described.

  The sensor pixel circuit 230 is divided into a plurality of groups, and is connected to any one of the driver lines RoA to RoP according to the division. These sections of the sensor pixel circuit 230 will be described with reference to FIG.

  FIG. 16 is an explanatory diagram showing a group of sensor pixel circuits in the light quantity measurement unit 200 according to the embodiment of the present invention. As shown in FIG. 16, the organic electroluminescence elements 110 are formed in a row at a resolution of 5120 and 600 dpi in the main scanning direction. Each of the organic electroluminescent elements 110 is assigned an identification number (hereinafter referred to as ELNO). This ELNO is a sequential number starting from 1, and is assigned sequentially from the organic electroluminescence element 110 formed at the end in the main scanning direction.

  5120 sensor pixel circuits 230 are formed in a one-to-one correspondence with the organic electroluminescence elements 110, and each detects the light quantity of the corresponding organic electroluminescence element 110. And the identification number (henceforth SPNO) of the sensor pixel circuit 230 is attached | subjected with the same number as ELNO of the corresponding organic electroluminescent element 110. FIG. For example, the SPNO of the sensor pixel circuit 230 provided corresponding to the organic electroluminescence element 110 having an ELNO of 3000 is 3000.

  Then, 320 (5120 ÷ 16 = 320) sensor groups are configured with n sensor pixel circuits 230 (hereinafter, n = 16 in the description of the present embodiment) having consecutive SPNOs as one unit. Yes. Each sensor group is assigned a group number of 1 to 320 in order from the smallest SPNO included in the sensor group. In each sensor group, line IDs a, b,..., P are assigned in order from the sensor pixel circuit 230 having the smallest SPNO. That is, the sensor pixel circuit 230 is given the same line ID every n (16).

  Furthermore, 20 sensor groups (320 ÷ 16 = 20) with m sensor groups having consecutive group numbers (as described above, m is the number of detection processing circuits 270 and m = 16 in the present embodiment) as one unit. ) Block is configured. Each block is assigned block numbers 1 to 20 in order from the smallest group number included in the sensor group.

  In each block, output IDs A, B,..., P are assigned in order from the sensor group with the smallest group number. The sensor pixel circuits 230 included in the sensor groups with output IDs A, B,..., P are detected by the detection processing circuits 270A, 270B, 270B, respectively via the driver lines DoA, DoB,. ..., connected to 270P. In other words, the same output ID is assigned to every m (16) sensor groups.

  In the following description, a group ID represented by a combination of a block NO and an output ID is also used as identification information for each sensor group for convenience. For example, a sensor group with a group number of 17 has a block number of 2 and an output ID of A, so the group ID is 2A.

  FIG. 17 is a circuit diagram showing a partial internal configuration of the light quantity measurement unit 200 of the present embodiment. As shown in FIG. 17, the sensor pixel circuits 230 belonging to the same sensor group are connected to the same driver line Ro. Each sensor group is connected to a driver line Ro with the same output ID (A to P). For example, the groups 1A, 2A... 20A (20 groups in total) are connected to the driver line RoA, and the groups 1P, 2P,... 20P are connected to the driver line RoP.

  The driver lines RoA to RoP are connected to detection processing circuits 270A to 270P provided in the light amount sensor output processing unit 210, respectively. That is, a total of 16 detection processing circuits 270 </ b> A to 270 </ b> P are provided in the light quantity sensor output processing unit 210 corresponding to all the driver lines RoA to RoP. On the other hand, the selection signal generation circuit 240 is formed in the TFT circuit 190, like the gate controller 68 shown in FIG. The selection signal generation circuit 240 (and the selection transistor 232: FIG. 18) is a switching circuit that inputs a sensor drive signal for driving the light amount sensor at a predetermined timing, which will be described later, to the sensor pixel circuit 230 via the selection line SelX. Function as.

  FIG. 18 is a circuit diagram showing an internal configuration of the sensor pixel circuit 230 and the detection processing circuit 270 according to the embodiment of the present invention.

  As shown in FIG. 18, the sensor pixel circuit 230 is connected in parallel to the light amount sensor 220, the light amount sensor 220, the capacitor 231 constituting the capacitive element, and the light amount sensor 220 and the capacitor 231 in series. A switching select transistor 232 for switching electrical connection with the charge amplifier 250 via the line Ro. A potential on one end side, which is a side to which the light quantity sensor 220 and the selection transistor 232 of the capacitor 231 are connected, is represented as Vs. Note that the other ends of the light quantity sensor 220 and the capacitor 231 are fixed to a predetermined potential Vp. The light quantity sensor 220 is an example of a light quantity detection element.

  The selection transistor 232 constitutes a switching circuit of the light quantity sensor together with the selection signal generation circuit 240. The selection line Sel is connected to the gate of the selection transistor 232, and a sensor selection signal including an ON / OFF signal output from the selection signal generation circuit 240 is input to the selection transistor 232, and the selection transistor 232 is set according to the sensor selection signal. Performs ON / OFF operation.

  Then, a total of 20 groups (block numbers 1 to 20) of sensor groups to which the same output ID (A to P) is attached, in other words, a total of 320 sensor pixel circuits (16 × 20) 230 have the same output ID. Is connected to one driver line Ro marked with. Each driver line Ro is connected to the detection processing circuit 270.

  The detection processing circuit 270 includes a charge amplifier 250 and an analog / digital converter (hereinafter referred to as ADC) 260. The charge amplifier 250 is connected between an inverting input terminal and an output terminal of the operational amplifier 251 having two input signal terminals, a non-inverting input terminal and an inverting input terminal, and an output signal terminal. The capacitor 252, which is an example of an amplifier capacitance element, and a charge / discharge selection transistor 253 connected in parallel with the capacitor 252 are configured.

  The non-inverting input terminal of the operational amplifier 251 is fixed to a predetermined reference voltage Vref, and the sensor pixel circuit 230 is connected to the inverting input terminal via a driver line Ro. Note that the output voltage of the operational amplifier 251 is Vro.

  A signal line CHG is connected to the gate of the charge / discharge selection transistor 253, and the charge / discharge selection transistor 253 performs an ON / OFF operation according to a charge reset signal composed of an ON / OFF signal. Note that the charge reset signal input through the signal line CHG is one of the sensor control inputs SC shown in FIG.

  The charge amplifier 250 described above cooperates with the capacitor 231 of the sensor pixel circuit 230 to constitute a sensor driving unit.

  The ADC 260 is connected to the output terminal of the operational amplifier 251 of the charge amplifier 250. Based on the AD conversion start trigger signal SMPL, which is one of the sensor control inputs SC, the output voltage Vro of the charge amplifier 250 is taken and subjected to analog / digital conversion, and light quantity measurement data is output.

  FIG. 19 is a timing chart showing a light amount detection operation regarding each light amount sensor according to the embodiment of the present invention. In other words, this corresponds to a timing chart of the light amount measurement data read operation performed for each light amount sensor 220. As described above, the output of the light quantity sensor 220 that is the basis of the light quantity measurement data is subjected to voltage conversion by the charge accumulation method in the light quantity sensor output processing unit 210, and further amplified by a predetermined amplification factor, and then converted from analog to digital. The following timing chart corresponds to this process.

  As shown in the timing charts of FIGS. 19A to 19G, the light amount measurement data based on the light amount sensor output of the light amount sensor 220 is obtained by using the switching of the selection transistor 232 as an opportunity to store the charge accumulated in the capacitor 231 in advance. Extraction is performed by irradiating light to the light amount sensor 220 of the organic electroluminescence element 110, and measurement is performed based on the charge of the capacitor 252 used to compensate for the lost charge. Therefore, in this embodiment, it corresponds to the light quantity sensor output based on the electric charge lost by the light irradiation of the organic electroluminescence element 110.

  Here, FIG. 19A is a diagram showing the charge state (charge state) of the capacitor 252 in the charge amplifier 250, FIG. 19B is a diagram showing the operation of the selection transistor 232, and FIG. FIG. 19D is a diagram illustrating the lighting timing of the organic electroluminescence element 110, FIG. 19D is a diagram illustrating a potential (Vs) on one end side to which the selection transistor 232 of the capacitor 231 is connected, and FIG. 19E is an output of the operational amplifier 251. FIG. 19 (f) is a diagram showing an AD conversion start trigger signal (SMPL) given to an analog / digital converter (ADC) 260, and FIG. It is a figure which shows the state from which data was obtained.

  First, the selection transistor 232 is turned on by receiving an ON signal from the selection signal generation circuit 240 at a timing from time t1 to time t2 via the selection line Sel (see FIG. 19B), and FIG. As shown in d), the capacitor 231 is charged, and the potential Vs on one end side of the capacitor 231 becomes the reference voltage Vref (S1: reset step). This reset step is an example of the first period.

  When the selection transistor 232 is turned off at time t2 (see FIG. 19B), the charge charged in the capacitor 231 is discharged and reduced by the photocurrent Is flowing through the light amount sensor 220, and FIG. As shown in FIG. 4, the potential Vs on one end side of the capacitor 231 gradually decreases from the reference voltage Vref (S2: light irradiation discharge step).

  Then, after elapse of a predetermined time in this state, at time t3, the charge / discharge selection transistor 253 of the charge amplifier 250 is turned off (see FIG. 19A), the charge of the capacitor 252 becomes movable, and the charge amplifier 250 is moved. Is in a state in which the amount of light of the organic electroluminescence element 110 can be measured (S3: measurement start step).

  Further, when the charge / discharge selection transistor 253 is turned off, the selection transistor 232 is turned on at the same time as the time t3 or at a time t4 after a predetermined time from the time t3 (see FIG. 19B). Charge is supplied from the capacitor 252 of the charge amplifier 250 to the capacitor 231 from which charge has been lost between t2 and time t4. As a result, the potential at one end of the capacitor 231 returns to Vref (see FIG. 19D), and the output voltage Vro of the operational amplifier 251 of the charge amplifier 250 increases as shown in FIG. 19E (S4: Charge transfer step). In addition, since the photocurrent Is of the light quantity sensor 220 flows also during the period of the charge transfer step S4, Vro rises though it is a very small value. Note that the period from time t2 to t4 is an example of a second period, and the period from time t4 to t5 (charge transfer step) is an example of a third period.

  Thereafter, at time t5, the selection transistor 232 is turned off again, and Vro is determined. The analog / digital converter (ADC) 260 reads the determined voltage in conjunction with the AD conversion start trigger signal SMPL (see FIG. 19F) at the same time as the time t5 or a predetermined time after the time t5. Thus, as shown in FIG. 19 (g), the effective light quantity measurement data is output from the light quantity measuring unit 200 via the sensor output signal line Do, whereby the light quantity measurement data reading operation is completed at time t8 (S5: Lead step).

  At time t6 after the AD conversion start trigger signal SMPL is input, the charge / discharge selection transistor 253 of the charge amplifier 250 is turned on (see FIG. 19A), and the capacitance of the capacitor 252 is reset.

  In addition, after the selection transistor 232 is turned off at the accumulation period of the above-described steps S2 to S4, that is, at time t2, the charge / discharge selection transistor 253 of the charge amplifier 250 is turned off, and the selection transistor 232 is turned on at time t5. The timing setting is preferably as short as possible from the viewpoint of shortening the waiting time of the image printing apparatus. However, from the viewpoint of ensuring a predetermined SN and voltage detection resolution, it is desirable that the potential difference Vout between the output voltage Vro and the reference voltage Vref determined at time t5 be as large as possible as shown in FIG. In this case, it is required to secure an accumulation period as long as possible. Therefore, the accumulation time is set from both viewpoints.

  As shown in FIG. 19C, in the light quantity measuring unit 200 of the present embodiment, the light emitting operation of the organic electroluminescence element 110 is one raster period of the image forming apparatus 1 including the lighting Telon that is turned on and the program period Tpro that is turned off. Has Tras. The raster period Tras is a short period of about 350 μs as described above. Further, when the light amount sensor 220 is made of a material having a high light transmittance such as polysilicon, the photocurrent Is flowing based on the irradiated light becomes a very small amount.

  Therefore, in the present embodiment, the organic electroluminescence element 110 that is the target of light quantity detection is driven in a plurality of raster periods Tras from time t0 to time t7, and the accumulation period from step S2 to step S4 is Set over multiple raster periods. One raster period Tras is one line period of the exposure apparatus 60 described above, that is, one unit of the light emission period (exposure period) of the organic electroluminescence element 110 in the image forming apparatus 1. Therefore, predetermined SN and voltage detection resolution can be ensured by performing light amount detection for one raster period Tras or more, that is, for one light emission period or more of the light emitting element.

  In this way, the electrical connection between the charge amplifier 250 and the light quantity sensor 220 / capacitor 231 is switched by the selection transistor 232 provided in the sensor pixel circuit 230, so that a desired accumulation period is accurately switched. be able to.

  In addition, the light quantity sensor 220, the capacitor 231 and the driver line Ro are cut off by the selection transistor 232 during a period from time t2 to time t4. Accordingly, since the influence of noise from the charge amplifier 250 and the driver line Ro on the light quantity sensor 220 and the capacitor 231 is eliminated, the light quantity can be detected with high accuracy.

  Next, the selection signal generation circuit 240 that outputs a sensor selection signal will be described. FIG. 20 is a circuit diagram showing an internal configuration of the selection signal generation circuit 240 according to the embodiment of the present invention. As shown in FIG. 20, the selection signal generation circuit 240 includes 5120 AND circuits 241, a group selection signal output circuit 242, and a line selection signal output circuit 243.

  As shown in FIG. 20, the AND circuit 241 is a circuit that outputs a logical product of three inputs. Signals input to the AND circuit 241 are output from the selection timing signal ROEN that is one of the sensor control inputs SC, the group selection signal gs output from the group selection signal output circuit 242, and the line selection signal output circuit 243. The line selection signal ls. Each output of the AND circuit 241 is input to the gate of the selection transistor 232 of the sensor pixel circuit 230 via the selection lines SEL1 to SEL5120.

  The block selection signal GSelDAT and the block switching clock signal GSelCLK are input to the group selection signal output circuit 242 as the sensor control input SC. The group selection signal output circuit 242 outputs group selection signals gs1 to gs20 based on the input block switching signal GSelDAT and block switching clock signal GSelCLK. These group selection signals gs1 to gs20 are generated corresponding to the respective block IDs shown in FIG. 16, and are AND circuits connected to the sensor pixel circuits 230 of the sensor groups to which the blocks NO1 to 20 are attached, respectively. It is output to 241.

  FIG. 21 is a circuit diagram showing an internal configuration of the group selection signal output circuit 242 according to the embodiment of the present invention. As shown in FIG. 21, the group selection signal output circuit 242 is a shift register having 20 D flip-flops DFFg1, DFFg2,... DFFg20 connected in series. The D flip-flops DFFg1 to DFFg20 output group selection signals gs1 to gs20, respectively.

  The line selection signal output circuit 243 receives the line switching signal LSelDAT and the line switching clock signal LSelCLK as the sensor control input SC. The line selection signal output circuit 243 outputs line selection signals lsa to lsp based on the input line switching signal LSelDAT and line switching clock signal LSelCLK. The line selection signals lsa to lsp are generated corresponding to the line IDs shown in FIG. 16, and are AND circuits connected to the sensor pixel circuits 230 of the sensor groups to which the lines IDa to p are attached, respectively. It is output to 241. For example, the line selection signal lsa is output to the AND circuit 241 connected to the sensor pixel circuit 230 whose line ID is a, that is, the sensor pixel circuit 230 whose SPNO is 1, 17,.

  FIG. 22 is a circuit diagram showing an internal configuration of the line selection signal output circuit 243 according to the embodiment of the present invention. As shown in FIG. 22, the line selection signal output circuit 243 is a shift register including 16 D flip-flops DFFla, DFFlb,... DFFlp connected in series. The D flip-flops DFFla to DFFlp respectively output line selection signals lsa to lsp.

  Next, the operation of the selection signal generation circuit 240 will be described with reference to FIGS. FIG. 23 is a diagram illustrating a partial configuration of the selection signal generation circuit 240 according to the embodiment of the present invention, and FIG. 24 is a timing chart for explaining the operation of the selection signal generation circuit 240 according to the embodiment of the present invention. . 23 and 24, an operation for generating a selection signal to be output to the selection signal line SEL259 will be described.

  As shown in FIG. 23, the sensor pixel circuit 230 with SPNO of 259 connected to the selection signal line SEL259 has a block NO of 2 and a line ID of c, and therefore the sensor selection timing signal is input to the AND circuit 241. In addition to ROEN, a group selection signal gs2 and a line selection signal lsc are input. That is, the input of the AND circuit 241 is connected to the output of the second stage D flip-flop DFFg2 in the group selection signal generation circuit 242 and the output of the third stage D flip-flop DFFlc in the line selection signal generation circuit 243. The

  As shown in FIG. 24, first, the line selection signal lsc is turned on at the rise of the line switching clock signal LSelCLK inputted for the third time after the line switching signal LSelDAT is turned on to the line selection signal generation circuit 243. It becomes. In this way, the sensor pixel circuit 230 whose line ID is c is selected.

  Next, the group selection signal gs2 is turned ON at the rise of the group switching clock signal GSelCLK input for the second time after the group switching signal GSelDAT is turned ON to the group selection signal generation circuit 242. In this way, the sensor pixel circuit 230 with the block ID 2 is selected.

  When the sensor selection timing signal ROEN for selecting any of the sensor pixel circuits 230 is input to the selection signal generation circuit 240, all the signals input to the AND circuit 241 are turned on. A sensor selection signal output via the signal line SEL259 is turned ON.

  Thereafter, when ROEN is turned off, the sensor selection signal is also turned off. When the group switching clock signal GSelCLK input for the third time rises, the group selection signal gs2 is turned OFF, and when the line switching clock signal LSelCLK input for the fourth time rises, the line selection signal lsc is turned OFF.

  In the above description, the case where the sensor selection signal output via the selection signal line SEL259 is ON has been described. However, at the timing when the sensor selection signal of the selection signal line SEL259 is ON, the block NO is 2 and the line ID is c. All the selection transistors 232 of the sensor pixel circuit 230 are turned on, that is, the sensor selection signals of the selection signal lines SEL259, SEL275, SEL291,... SEL483, SEL499 are turned on. This means that the light quantity detection operation is simultaneously switched by simultaneously switching the selection transistors 232 of the sensor pixel circuits 230 of the same block NO and the same line ID.

  Next, a light amount detection sequence of the entire light amount measuring unit 200 will be described. In the present embodiment, the light amount detection operation of one sensor pixel circuit 230 to which a predetermined line ID is assigned in each sensor group is performed in parallel for all sensor groups. Hereinafter, the light amount detection operation of the entire sensor group per line ID is referred to as group read. In this embodiment, since there are 16 sensor pixel circuits 230 with line IDs a to p for each sensor group, the light quantity detection for all the organic electroluminescence elements 110 is performed by performing group reading 16 times. Is called.

  First, the group read operation described above will be described. FIG. 25 is a timing chart for explaining the group read operation according to the embodiment of the present invention, and shows the group read with the line ID “a”.

  As shown in FIG. 25, first, when the group switching signal GSelDAT is input at the start of the group read for the line IDa, the sensor selection circuit receives the group switching clock signal GSelCLK. , SEL241 are simultaneously output to the selection signal lines SEL1, SEL17,. In the sensor pixel circuit 230 (block ID is 1 and line ID is a) to which the sensor selection signal is input, the reset step S1 and the light irradiation discharge step S2 are started simultaneously.

  Then, each time the group switching clock signal GSelCLK is input, the block NO is sequentially switched from 1. That is, the reset step S1 and the light irradiation discharge step S2 regarding the sensor pixel circuit 230 of different blocks NO are sequentially started.

  Next, when the group switching signal GSelDAT is input before the start of the charge transfer step, the sensor selection signal is connected to the sensor pixel circuit 230 whose block NO is 1 by the input of the group switching clock signal GSelCLK. Are simultaneously output to the lines SEL1, SEL17,. In the sensor pixel circuit 230 (block ID is 1 and line ID is a) to which the sensor selection signal is input, the charge transfer step S4 and the read step S5 are started simultaneously. That is, charge transfer is simultaneously performed between the 16 sensor pixel circuits 230 whose line IDs of the sensor groups 1A to 1P are a and the detection processing circuits 270A to 270P.

  Then, each time the group switching clock signal GSelCLK is input, the block NO is sequentially switched from 1. That is, a sensor selection signal is sequentially output to the sensor pixel circuits 230 of different blocks NO, and the charge transfer step S4 and the read step S5 are started.

  In this way, the light amount detection operation (group read for the line IDa) is performed for all the sensor pixel circuits 230 with the line ID a.

  Here, the plurality of sensor pixel circuits 230 with the same output ID are connected to the same driver line Ro. In such a configuration, a single charge amplifier 250 can simultaneously perform a plurality of sensor pixel circuits 230 via the same driver line Ro. Therefore, the reset step S1 is connected to the same driver line Ro. It may be performed simultaneously in a plurality of sensor pixel circuits 230. In the light irradiation discharge step S2, the sensor pixel circuit 230 is electrically disconnected from the driver line Ro. Therefore, the reset step S2 is also simultaneously performed in the plurality of sensor pixel circuits 230 connected to the same driver line Ro. May be.

  However, since charge transfer is performed from each sensor pixel 230 to the detection processing circuit 270 via the driver line Ro at least in the charge transfer step S4 (see FIG. 19: from time t4 to t5), the charge transfer step S4 is the same. It cannot be performed simultaneously in the plurality of sensor pixel circuits 230 connected to the driver line Ro.

  Therefore, in the light quantity measurement unit 200 of this embodiment, as shown in the timing chart of FIG. 25, in the group read for the same line ID, the charge transfer step is performed for each of the sensor pixel circuits 230 to which the same output ID is assigned. Since the timing is controlled so that S4 does not overlap, the light quantity detection of the plurality of light quantity sensors 220 can be efficiently performed by one detection processing circuit 270. That is, since the light amount detection of the plurality of light amount sensors 220 can be performed by one detection processing circuit 270, it is not necessary to provide the detection processing circuit 270 with the sensor pixel circuit 230 as a pair, thereby reducing the circuit scale and reducing the manufacturing cost. Can be suppressed.

  Furthermore, since the light irradiation / discharge step S2 that can be performed simultaneously is performed at a timing at which some of the sensor pixel circuits 230 having the same output ID are partially overlapped with each other, the time required for light amount detection is shortened. can do.

  As described above, the timing of the light amount detection operation can be switched for each of the plurality of sensor pixel circuits 230 by using the selection transistor 232 provided in each sensor pixel circuit 230. Reduced and efficient light quantity detection can be performed.

  FIG. 26 is a timing chart for explaining the overall operation of the light quantity measuring unit 200 according to the embodiment of the present invention. As shown in FIG. 26, the light amount detection operation of the entire light amount measurement unit 200 is started in response to the line switching signal LSelDAT input to the selection signal generation circuit 240. Each time the line switching clock signal LSelCLK is input, the group ID of the group lead is switched. Note that a period Tbl is given between the group reads for each line ID.

  In this embodiment, since there are 16 line IDs from a to p, it is possible to read out the light amount detection results in all the light amount sensors 220 in the period Tall by performing group read 16 times.

  As described above, since the sensor pixel circuits 230 having the same line ID are sequentially detected one by one, at the time of light amount detection, the organic electroluminescence elements for each number of line IDs (16 in the present embodiment) in the main scanning direction. 110 may emit light. As a result, the influence of light other than the organic electroluminescent element 110 that is the target of light quantity detection, for example, the influence of light from the adjacent organic electroluminescent element 110, so-called crosstalk, is suppressed, and high-precision light quantity detection is possible.

  In addition, when performing light amount correction, each of the bright current and the dark current is detected, and each light amount detection result is reflected on the light emission amount of the organic electroluminescence element 110 to detect the light amount. By performing the light amount measurement operation performed a plurality of times, it is possible to perform light amount correction with higher accuracy.

  Now, in the embodiment, the description has been made on the assumption that the light amount of the organic electroluminescence element 110 is controlled by changing the current value while keeping the lighting time of the organic electroluminescence element 110 constituting the exposure apparatus 60 constant. The present invention can be easily applied to a so-called PWM method in which the driving current value of a light emitting element such as the organic electroluminescence element 110 is fixedly set, and the light amount of the light emitting element is controlled by changing the lighting time. In this case, the contents of the first area described with reference to FIG. 6 may be replaced with “setting value of driving time for equalizing latent image cross-sectional areas”.

  Also, depending on the exposure apparatus, there are a plurality of light emitting element arrays composed of organic electroluminescence elements, etc., and a latent image is formed by performing multiple exposures at substantially the same position with respect to the rotation direction of the photoreceptor. Is also known. Even in such an exposure apparatus, it is possible to apply the technical idea of the present invention by setting the light amount and the PWM time so that a latent image formed by a plurality of exposures does not contribute to development. . In such an exposure apparatus, a single light emitting element array does not form a latent image that contributes to development. Therefore, for example, a sequence in which the amount of light is measured in units of columns between sheets can be considered.

  In the embodiment, the light amount of the organic electroluminescence element 110 is measured using a light amount sensor configured as a monolithic device of polysilicon same as the TFT circuit and the organic electroluminescence element. However, the technical idea of the present invention is as follows. It is not limited to. For example, the present invention can also be applied to a configuration in which a plurality of film-like light quantity sensors are formed of amorphous silicon and arranged along the end surface of the glass substrate 101 (see FIG. 4).

  As described above, the image forming apparatus to which the electrophotographic method is applied has been described in the embodiment, but the present invention is not limited to the electrophotographic method. Since an RGB light source can be easily realized by an organic electroluminescence element, for example, a plurality of exposure apparatuses each having an R light source, a G light source, and a B light source are arranged as exposure light sources, and photographic paper is directly applied based on image data of each RGB color. Needless to say, the present invention can also be easily applied to an image forming apparatus that exposes the light.

  Although various embodiments of the present invention have been described, the present invention is not limited to the matters shown in the above-described embodiments, and those skilled in the art may modify or apply the description based on the description of the specification and well-known techniques. The present invention is intended to be included in the scope for which protection is sought.

  According to the light emitting element driving apparatus of the present invention, the light emitting element can emit light with an accurate light emission amount, and an exposure apparatus and an image forming apparatus using the light emitting element can be provided.

1 is a configuration diagram of an image forming apparatus according to a basic embodiment of the present invention. The block diagram which shows the periphery of the developing station in the image forming apparatus of the embodiment Configuration diagram of an exposure apparatus in the image forming apparatus of the embodiment The upper surface enlarged view of the optical head which concerns on the exposure apparatus in the image forming apparatus of the embodiment 2 is a block configuration diagram showing a configuration of a controller in the image forming apparatus of the embodiment. Explanatory drawing which shows the content of the light quantity correction data memory in the image forming apparatus of the embodiment Block configuration diagram showing a configuration of an engine control unit in the image forming apparatus of the embodiment Circuit diagram of exposure apparatus in image forming apparatus of same embodiment The figure which shows the relationship between a light emitting element drive circuit and a source driver The figure which shows the detailed structure of a pixel circuit (pixel) The figure explaining the effect | action of the pixel circuit of the similar structure of a prior art The figure explaining the effect | action of the pixel circuit of embodiment of this invention. The figure which shows other embodiment of a light emitting element drive circuit. Explanatory drawing which shows the electric current program period and lighting period of an organic electroluminescent element which concern on the exposure apparatus in the image forming apparatus of the embodiment Explanatory drawing which shows the main structures of the light quantity measurement part which concerns on embodiment of this invention. Explanatory drawing which shows the group of the sensor pixel circuit in the light quantity measurement part which concerns on embodiment of this invention. Circuit diagram showing a part of the internal configuration of the light quantity measurement unit of the present embodiment 1 is a circuit diagram showing an internal configuration of a sensor pixel circuit and an output processing circuit according to an embodiment of the present invention. It is a timing chart which shows the light quantity detection operation regarding each light quantity sensor which concerns on embodiment of this invention. 1 is a circuit diagram showing an internal configuration of a selection signal generation circuit according to an embodiment of the present invention. The circuit diagram which shows the internal structure of the group selection signal output circuit which concerns on embodiment of this invention 1 is a circuit diagram showing an internal configuration of a line selection signal output circuit according to an embodiment of the present invention. The figure which shows the structure of a part of selection signal generation circuit which concerns on embodiment of this invention Timing chart for explaining the operation of the selection signal generation circuit according to the embodiment of the present invention Timing chart explaining operation of group read according to the embodiment of the present invention Timing chart for explaining the overall operation of the light quantity measuring unit according to the embodiment of the present invention The figure which shows the characteristic of the output current with respect to the gate potential in the transistor in the pixel circuit Diagram of prior art current programming circuit

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Case 4 Paper feed tray 8,8Y, 8M, 8C, 8K Photoconductor 17 Toner bottle 19 Registration roller 20 Pinch roller 21 Recording paper passage detection sensor 23 Fixing device 24 Heating roller 25 Pressure roller 27 Temperature sensor 28 Recording paper trailing edge detection sensor 32 Toner image detection sensor 33 Recording paper transport drum 34 Face down paper discharge unit 35 Kicking roller 36 Support member 37 Rib 38 Drive source 39 Paper discharge tray 43 Power supply unit 44 Power supply monitoring unit 45 Actuator group 46 High Voltage Power Supply Control Unit 47 Operation Panel 50, 50Y, 50M, 50C, 50K Development Station 51, 51a, 51b Stir Paddle 52 Thinning Blade 53 Development Sleeve 54 Magnet Roll 60, 60Y, 60M, 60C, 60K Exposure Device 61a Case A (lower housing)
61b Housing B (upper housing)
62 Lens array 63 Relay board 63
64a Connector A
64b Connector B
65 Cable 66 FPC
70 Controller 71a Image memory 71b Light quantity correction data memory 71c Buffer memory 72 D / A converter 73 ROM
74 RAM
75 Controller CPU
76 Image processing unit 77 Timing generation unit 78 Printer interface 80 Engine control unit 81 Controller interface 82 Engine control CPU
83 ROM
84 RAM
85 Nonvolatile memory 86 Serial interface 87 Bus 100 Optical head 101 Glass substrate 105 Light emitting unit 110 Organic electroluminescence element 110A Light emitting element array 111 Driver part 112 Current program part 113 Pixel circuit 114 Gate controller 180, 180a, 180b Source driver 181 Light emitting element Drive circuit 183 Current mirror circuit 184 Sub circuit 190 TFT circuit 200 Light quantity measurement unit 210, 210a, 210b, 210c, 210d Light quantity sensor output processing unit 220 Light quantity sensor 230 Sensor pixel circuit 231 Capacitor 232 Selection transistor 240 Selection signal generation circuit 241 AND circuit 242 Group selection signal output circuit 243 Line selection signal output circuit 250 Charge amplifier 251 Operational Amplifier 252 Capacitor 253 Charge / Discharge Select Transistor 260 Analog / Digital Converter (ADC)
270, 270A to 270P Detection processing circuit 300 Computer DFFg1 to DFFg20, DFFla to Dfflp D flip-flop DL Developer N Network R Recording paper P Recording paper transport path SL Sealing glass

Claims (24)

A capacitive element;
A first switching element that charges the capacitive element;
A first mode for charging the capacitor element, a second switching element for switching a second mode for driving the light emitting element based on the charged potential,
A controller that independently controls the first switching element and the second switching element;
A light emitting element driving device comprising: A capacitive element;
A first switching element that charges the capacitive element;
A first mode for charging the capacitor element, a second switching element for switching a second mode for driving the light emitting element based on the charged potential,
A third switching element connected in parallel with the capacitive element and to which a gate potential is applied based on a potential charged in the capacitive element;
A controller that independently controls the first switching element and the second switching element;
A light emitting element driving device comprising: The light-emitting element driving device according to claim 1 or 2,
The control unit is a light-emitting element driving device that sets a current value for driving the light-emitting element according to a potential charged in the capacitor element. A light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission,
A capacitive element that holds a potential by charging and discharging electric charge;
A first switching element for determining a holding capacity of the capacitive element;
A second switching element that switches between a program mode for setting a holding potential of the capacitive element and an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element;
A controller for independently controlling on / off of the first switching element and the second switching element;
A light emitting element driving device comprising: A light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission,
A capacitive element that holds a potential by charging and discharging electric charge;
A first switching element for determining a holding capacity of the capacitive element;
A second switching element that switches between a program mode for setting a holding potential of the capacitive element and an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element;
A third switching element connected in parallel with the capacitive element and applied with a gate potential based on the potential of the capacitive element;
A controller for independently controlling on / off of the first switching element and the second switching element;
A light emitting element driving device comprising: The light-emitting element driving device according to claim 4 or 5,
The driving condition is a current value for driving the light emitting element,
The control unit is a light-emitting element driving device that sets a current value for driving the light-emitting element according to a potential of the capacitive element. The light-emitting element driving device according to any one of claims 1, 2, 4, and 5,
One pixel circuit for driving one light emitting element is defined by the capacitive element, the first switching element, and the second switching element, and the light emitting element driving device includes a plurality of the pixel circuits, Furthermore,
A current supply for supplying a current set for each pixel circuit;
An amplification unit that amplifies each output current of the current supply unit,
A light emitting element driving apparatus in which one terminal of the second switching element is connected to the amplifying unit. The light-emitting element driving device according to claim 7,
A light emitting element driving apparatus in which the amplifying unit is configured along a light emitting element array in an arrangement direction of the light emitting element arrays formed by the light emitting elements. The light-emitting element driving device according to claim 7,
A light-emitting element driving device in which the amplification unit is configured by a current mirror circuit. The light-emitting element driving device according to claim 7,
A light emitting element driving apparatus in which the amplifying unit is configured by an amplifier having an amplification factor of 1. The light-emitting element driving device according to claim 1,
The light-emitting element driving device, wherein the current supply unit includes a current discharge type circuit, and the amplification unit converts the discharge current from the current supply unit into a drawing current. The light-emitting element driving device according to claim 1,
A light emitting element driving device in which the amplifying unit is constituted by a TFT circuit. The light-emitting element driving device according to claim 1,
The light emitting element drive device further provided with the 4th switching element which controls ON / OFF of the said light emitting element. The light-emitting element driving device according to claim 1,
The light emitting element drive device further provided with the 5th switching element controlled to open or short-circuit both the terminals of the said light emitting element. The light-emitting element driving device according to any one of claims 1 to 14,
A light-emitting element driving device in which at least one of the first to fifth switching elements is constituted by a TFT circuit. The light-emitting element driving device according to any one of claims 1 to 15,
The light emitting element drive device by which the said light emitting element was comprised by the organic electroluminescent element.   An exposure apparatus including the light emitting element driving apparatus according to claim 1.   An image forming apparatus comprising the exposure apparatus according to claim 17. A light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission,
A capacitive element that holds a potential by charging and discharging electric charge;
A first switching element for determining a holding potential of the capacitive element;
A second switching element that performs at least a part of a function of switching between a program mode for setting a holding potential of the capacitive element and an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element;
A controller for controlling the timing for turning off the first switching element to be earlier than the timing for turning off the second switching element when switching from the program mode to the element emission mode;
A light emitting element driving device comprising: A light emitting element driving apparatus for controlling driving conditions of light emitting elements and on / off of light emission,
A capacitive element that holds a potential by charging and discharging electric charge;
A first switching element for determining a holding potential of the capacitive element;
A second switching element that is a part of a function of switching between a program mode for setting a holding potential of the capacitive element and an element emission mode for causing the light emitting element to emit light according to the holding potential of the capacitive element;
A third switching element connected in parallel with the capacitive element and applied with a gate potential based on the potential of the capacitive element;
A controller for controlling the timing for turning off the first switching element to be earlier than the timing for turning off the second switching element when switching from the program mode to the element emission mode;
A light emitting element driving device comprising: The light-emitting element driving device according to claim 19 or 20,
A fourth switching element for controlling on / off of the light emitting element;
The light emitting element drive device further provided with the 5th switching element controlled to open or short-circuit both the terminals of the said light emitting element. The light-emitting element driving device according to claim 21,
In the program mode, the first switching element, the second switching element, and the fifth switching element are turned on, the fourth switching element is turned off,
In the element light emission mode, the first switching element, the second switching element, and the fifth switching element are turned off, the fourth switching element is turned on,
When switching from the program mode to the element emission mode, a transitional mode is determined depending on a period of time from when the first switching element is turned off to when the second switching element is switched from on to off. A light emitting element driving device defined. The light-emitting element driving device according to claim 22,
In a predetermined period between the transient mode and the element light emission mode, the first switching element, the second switching element, and the third switching element are turned off, and the fourth switching element is turned on. A light emitting element driving device. A light-emitting element driving device for controlling a drive current value of a light-emitting element and on / off of light emission,
A capacitive element that holds a potential by charging and discharging electric charge;
A first switching element that is connected to the capacitive element and forms a closed loop circuit together with the capacitive element when turned on, and charges and discharges the capacitive element;
A program mode that is connected to the first switching element at a position outside the closed loop circuit and sets the holding potential of the capacitor element, and an element emission mode that causes the light emitting element to emit light according to the holding potential of the capacitor element. Two switching elements;
A third switching element connected in parallel with the capacitive element and to which a gate potential is applied based on the potential of the capacitive element,
In the program mode, the closed loop circuit is formed by the first switching element, the third switching element, and the capacitor element in an on state.
The light-emitting element driving device in which the second switching element is maintained in an on state for a predetermined period after the first switching element is turned off and the closed loop circuit is eliminated at the end of the program mode.

Images