JP2009160915A - Exposure head, exposure head control method, and image forming apparatus - Google Patents

Abstract

A technique for improving the degree of freedom of wiring connected to a light emitting element is provided.
An imaging optical system LS, first light emitting elements Ea1 to Ea4 and Eb1 to Eb4 that emit light that is imaged by the imaging optical system LS, and light that is imaged by the imaging optical system LS Light emitting elements Ec5 to Ec8, Ed5 to Ed8, and first TFT circuits TCa1 to TCa4, TCb1 to TCb4 connected to the first light emitting elements Ea1 to Ea4 and Eb1 to Eb4 via the wiring WL And second TFT circuits TCc5 to TCc8 and TCd5 to TCd8 connected to the second light emitting elements Ec5 to Ec8 and Ed5 to Ed8 via the wiring WL, and the first TFT circuits TCa1 to TCa4, TCb1 to Between the TCb4 and the second TFT circuits TCc5 to TCc8, TCd5 to TCd8, the first light emitting elements Ea1 to Ea4, Eb1 to Eb4 and the second light emitting elements Ec5 to Ec8, Ed5 to Ed8 are arranged.
[Selection] Figure 17

Description

  The present invention relates to an exposure head that forms an image of light emitted from a light emitting element by an imaging optical system, a method for controlling the exposure head, and an image forming apparatus using the exposure head.

  As such an exposure head, a line head in which a plurality of light emitting elements such as LEDs (Light Emitting Diodes) are arranged on a substrate is known, as described in Patent Document 1, for example. The driving of these light emitting elements can be controlled by a circuit composed of a thin film transistor called a so-called TFT (Thin Film Transistor). That is, the light emitting element is driven by the TFT circuit and emits a light beam. The light beam thus emitted from the light emitting element is imaged by the lens, and the surface of the latent image carrier such as a photoconductor is exposed.

Hei 2-4546

  By the way, in the above line head, in order to give a signal from the TFT circuit to the light emitting element, the light emitting element and the TFT circuit are connected by wiring. However, due to the inadequate arrangement of the TFT circuit, it may be necessary to draw all of the wiring connected to each light emitting element to the same side, resulting in a reduction in the degree of freedom of wiring. There was a case.

  The present invention has been made in view of the above problems, and an object thereof is to provide a technique for improving the degree of freedom of wiring connected to a light emitting element.

  In order to achieve the above object, an exposure head according to the present invention forms an image by an imaging optical system, a first light emitting element that emits light imaged by the imaging optical system, and an imaging optical system. Second light emitting element that emits light, a first TFT circuit connected to the first light emitting element via a wiring, and a second TFT circuit connected to the second light emitting element via a wiring The first light emitting element and the second light emitting element are disposed between the first TFT circuit and the second TFT circuit.

  In order to achieve the above object, the exposure head control method according to the present invention includes an imaging optical system, a first light emitting element that emits light imaged on an exposed surface by the imaging optical system, A second light emitting element that emits light imaged on an exposed surface by the image optical system, a first TFT circuit connected to the first light emitting element via a wiring, and a wiring to the second light emitting element And a second TFT circuit connected via the first TFT circuit, and the first light emitting element and the second light emitting element are disposed between the first TFT circuit and the second TFT circuit. An exposure step of exposing a surface to be exposed by a head is provided.

  In order to achieve the above object, the image forming apparatus according to the present invention emits a latent image carrier, an imaging optical system, and light that is imaged on the latent image carrier by the imaging optical system. A light emitting element, a second light emitting element that emits light imaged on the latent image carrier by the imaging optical system, a first TFT circuit connected to the first light emitting element via a wiring, and A second TFT circuit connected to the two light emitting elements via a wiring, and the first light emitting element and the second light emitting element are disposed between the first TFT circuit and the second TFT circuit. The exposure head is provided.

  In the invention thus configured (exposure head, exposure head control method, image forming apparatus), the first TFT circuit connected to the first light emitting element via the wiring and the wiring to the second light emitting element And a second TFT circuit connected through the first TFT circuit. A first light emitting element and a second light emitting element are disposed between the first TFT circuit and the second TFT circuit. Therefore, the wiring can be drawn out to both sides of the first light emitting element and the second light emitting element, and the degree of freedom of wiring is improved.

  Note that the first light-emitting element, the second light-emitting element, the first TFT circuit, and the second TFT circuit can be provided on the first surface of the substrate. Further, the light from the first light-emitting element and the second light-emitting element is configured to pass through the substrate from the first surface to a second surface different from the first surface and enter the imaging optical system. be able to.

  By the way, an exposure head can be comprised so that the detection part which detects the light from a 1st light emitting element and a 2nd light emitting element may be provided. In this case, the following effects can be achieved by arranging the detection unit on the substrate. That is, it is possible to detect the light reflected from the inside of the substrate out of the light emitted from the light emitting element. In addition, in the present invention, a TFT circuit is provided on the substrate, and since this TFT circuit reflects light from the light emitting element, a larger amount of light can be detected by the detection unit, and the accuracy of the detection result is improved. be able to.

  A plurality of detection units may be arranged. This makes it possible to detect a large amount of light and improve the accuracy of the detection result.

  Moreover, the optical sensor which detects light with a light-receiving surface can be used as a detection part. At this time, the light receiving surface may be bonded to the substrate with an optical adhesive. In such a configuration, since the interface between the substrate and the light receiving surface is removed by the optical adhesive, unnecessary light reflection between the substrate and the light receiving surface can be suppressed. As a result, the light incident on the light receiving surface increases, and the accuracy of the detection result can be improved.

  Further, the first TFT circuit is configured to drive the first light emitting element based on the detection result of the detection unit, and the second TFT circuit is configured to drive the second light emitting element based on the detection result of the detection unit. You may do it. With this configuration, the light emitting element can be driven with an appropriate amount of light, and a favorable exposure operation can be performed.

  The first light emitting element and the second light emitting element are particularly preferably configured to drive the light emitting element based on the detection result of the detection unit for the exposure head which is an organic EL element. That is, since the organic EL element has a relatively short life, if the light emission frequency varies among the organic EL elements, the light amount of each organic EL element may also vary. Therefore, for a configuration using an organic EL element, it is preferable to drive the light emitting element with an appropriate amount of light by applying the present invention including the detection unit.

  Moreover, you may comprise so that the light-shielding member which provided the light guide hole toward the imaging optical system from the 1st light emitting element and the 2nd light emitting element may be provided. As will be described later, in such a configuration, incidence of ghost light to the imaging optical system is suppressed by the light shielding member, and good exposure is possible.

  Further, the above-described exposure head control method includes a detection step of detecting the light amounts of the first light-emitting element and the second light-emitting element, and the exposure step includes the first light-emitting element and the first light-emitting element based on the detection result of the detection step. You may comprise so that a 2nd light emitting element may be driven. With this configuration, the light emitting element can be driven with an appropriate amount of light, and a favorable exposure operation can be performed.

  In the line head according to the present invention, in order to achieve the above object, a plurality of light emitting element groups in which a plurality of light emitting elements are grouped are arranged on one side, and light emitted from the light emitting elements is transferred from one side to the other side. A TFT circuit for controlling the driving of the light emitting element on one surface of the head substrate. The TFT circuit is provided with a head substrate that can be transmitted toward the head substrate and a detecting unit that is disposed on the head substrate and detects light emitted from the light emitting element. And a wiring for connecting the light emitting element and the TFT circuit, and in the light emitting element group, a light emitting element row in which a plurality of light emitting elements are arranged in the first direction is provided, and is orthogonal or substantially orthogonal to the first direction. The TFT circuit is arranged on both sides of the light emitting element group in the second direction.

  In order to achieve the above object, the image forming apparatus according to the present invention has a plurality of light emitting element groups each having a plurality of light emitting elements grouped on one surface, and light emitted from the light emitting elements is emitted from the one surface. A head substrate that is transmissive to the other surface; a line head that is disposed on the head substrate and that has a detection means that detects light emitted from the light emitting element; and a latent image carrier that is exposed by the line head; And a wiring for connecting the light emitting element and the TFT circuit is arranged on one surface of the head substrate, and in the light emitting element group, the plurality of light emitting elements are arranged in the first direction. Are arranged, and TFT circuits are arranged on both sides of the light emitting element group in the second direction orthogonal or substantially orthogonal to the first direction. .

  In the invention thus configured (line head, image forming apparatus), TFT circuits are arranged on both sides of the light emitting element group in the second direction. Therefore, the wiring connected to each light emitting element of the light emitting element group can be drawn out to both sides in the second direction, and improvement in the degree of freedom of the wiring is realized.

  In the present invention, the detecting means for detecting the light emitted from the light emitting element is arranged on the head substrate. Such detection means is provided mainly for the purpose of controlling the light quantity of each light emitting element. That is, for example, the TFT circuit performs drive control of the light emitting element based on the detection result of the detection means, thereby enabling light emission drive control with high accuracy. By the way, from the viewpoint of performing such light emission drive control with high accuracy, it is desirable that the amount of light incident on the detection means is as large as possible. On the other hand, in the present invention, a TFT circuit is arranged on one surface of the head substrate. Therefore, as will be described later, since this TFT circuit functions as a reflective film that reflects light, the amount of light incident on the detection means can be increased. Therefore, the present invention is preferable because the light emission drive control can be executed with high accuracy.

  Further, the TFT circuit may be configured to control the driving of the light emitting elements based on the detection result of the detecting means so that the amount of light emitted from each light emitting element is uniform. When configured in this manner, the amount of light emitted from each light emitting element is uniform, and good exposure is possible.

  Further, a plurality of detection means may be arranged on the head substrate. With this configuration, it is possible to detect the light amount of the light emitting element with high accuracy.

  Moreover, you may comprise a light emitting element so that it may be an organic EL element. That is, since such an organic EL element has a relatively short lifetime, if the emission frequency varies among a plurality of organic EL elements, the amount of light of each organic EL element may also vary. Therefore, it is preferable to apply high-precision light emission drive control to the configuration using the organic EL element by applying the present invention having the detection means.

  The detecting means is an optical sensor that detects light on the light receiving surface, and the light receiving surface may be attached to the head substrate by an optical adhesive. With this configuration, it is possible to remove the interface between the head substrate and the light receiving surface and suppress unnecessary reflection on the head substrate and the light receiving surface. As a result, the light incident on the light receiving surface is increased, and more accurate light emission drive control is possible.

  In addition, a lens array provided with a lens facing the light emitting element group from the other surface side of the head substrate for each light emitting element group, and a light shielding member provided between the head substrate and the lens array, A light guide hole from the light emitting element group to the lens may be provided for each light emitting element group. That is, in the configuration including such a lens array, the light beam emitted from the light emitting element group is imaged by the lens provided corresponding to the light emitting element group, so that the exposure operation is executed. Therefore, from the viewpoint of performing a good exposure operation, it is desirable that only the light beam emitted from the light emitting element group corresponding to the lens is incident on each lens. The incidence of light) is preferably suppressed as much as possible. On the other hand, in the said structure, the light shielding member which has the light guide hole which goes to a lens from a light emitting element group for every light emitting element group is provided. Therefore, such ghost light can be shielded by the light shielding member. As a result, the ghost light is prevented from entering the lens, and a good exposure operation is possible.

A. Explanation of Terms Before explaining embodiments of the present invention, terms used in this specification will be explained.

  1 and 2 are explanatory diagrams of terms used in this specification. Here, the terms used in this specification will be organized using these drawings. In this specification, the transport direction of the surface (image surface IP) of the photosensitive drum 21 is defined as a sub-scanning direction SD, and a direction orthogonal or substantially orthogonal to the sub-scanning direction SD is defined as a main scanning direction MD. . The line head 29 is arranged with respect to the surface (image surface IP) of the photosensitive drum 21 so that the longitudinal direction LGD corresponds to the main scanning direction MD and the width direction LTD corresponds to the sub-scanning direction SD. Has been.

  A set of a plurality of (eight in FIG. 1 and FIG. 2) light emitting elements 2951 arranged on the head substrate 293 in a one-to-one correspondence with the plurality of lenses LS included in the lens array 299 is defined as a light emitting element group 295. To do. That is, in the head substrate 293, the light emitting element group 295 including the plurality of light emitting elements 2951 is disposed for each of the plurality of lenses LS. Further, the light beam from the light emitting element group 295 is imaged toward the image plane IP by the lens LS corresponding to the light emitting element group 295, whereby a set of a plurality of spots SP formed on the image plane IP is obtained. It is defined as group SG. That is, the plurality of spot groups SG can be formed in one-to-one correspondence with the plurality of light emitting element groups 295. In each spot group SG, the most upstream spot in the main scanning direction MD and the sub-scanning direction SD is particularly defined as the first spot. The light emitting element 2951 corresponding to the first spot is particularly defined as the first light emitting element.

  Further, as shown in the column “on image plane” in FIG. 2, a spot group row SGR and a spot group column SGC are defined. That is, a plurality of spot groups SG arranged in the main scanning direction MD are defined as spot group rows SGR. The plurality of spot group rows SGR are arranged side by side in the sub-scanning direction SD at a predetermined spot group row pitch Psgr. A plurality (three in the figure) of spot groups SG arranged at the spot group row pitch Psgr in the sub-scanning direction SD and at the spot group pitch Psg in the main scanning direction MD are defined as a spot group column SGC. The spot group row pitch Psgr is a distance in the sub-scanning direction SD between the geometric centroids of two spot group rows SGR adjacent to each other in the sub-scanning direction SD. The spot group pitch Psg is the distance in the main scanning direction MD of the geometric centroids of two spot groups SG adjacent to each other in the main scanning direction MD.

  Lens rows LSR and lens columns LSC are defined as shown in the “lens array” column of FIG. That is, a plurality of lenses LS arranged in the longitudinal direction LGD are defined as a lens row LSR. The plurality of lens rows LSR are arranged side by side in the width direction LTD at a predetermined lens row pitch Plsr. A plurality (three in the figure) of lenses LS arranged at the lens row pitch Plsr in the width direction LTD and at the lens pitch Pls in the longitudinal direction LGD are defined as a lens row LSC. The lens row pitch Plsr is a distance in the width direction LTD of the geometric centroids of two lens rows LSR adjacent to each other in the width direction LTD. The lens pitch Pls is a distance in the longitudinal direction LGD between the geometric centroids of the two lenses LS adjacent to each other in the longitudinal direction LGD.

  As shown in the column “Head Substrate” in the drawing, a light emitting element group row 295R and a light emitting element group column 295C are defined. That is, a plurality of light emitting element groups 295 arranged in the longitudinal direction LGD is defined as a light emitting element group row 295R. The plurality of light emitting element group rows 295R are arranged side by side in the width direction LTD at a predetermined light emitting element group row pitch Pegr. In addition, a plurality of (three in the figure) light emitting element groups 295 arranged at the light emitting element group row pitch Pegr in the width direction LTD and at the light emitting element group pitch Peg in the longitudinal direction LGD are defined as a light emitting element group column 295C. The light emitting element group row pitch Pegr is a distance in the width direction LTD between the geometric centroids of two light emitting element group rows 295R adjacent to each other in the width direction LTD. The light emitting element group pitch Peg is the distance in the longitudinal direction LGD between the geometric centers of gravity of two light emitting element groups 295 adjacent to each other in the longitudinal direction LGD.

  As shown in the “light emitting element group” column of FIG. 2, a light emitting element row 2951R and a light emitting element column 2951C are defined. That is, in each light emitting element group 295, a plurality of light emitting elements 2951 arranged in the longitudinal direction LGD is defined as a light emitting element row 2951R. The plurality of light emitting element rows 2951R are arranged side by side in the width direction LTD at a predetermined light emitting element row pitch Pelr. A plurality of (two in the figure) light emitting elements 2951 arranged in the width direction LTD at the light emitting element row pitch Pelr and at the longitudinal direction LGD in the longitudinal direction LGD are defined as a light emitting element row 2951C. The light emitting element row pitch Pelr is a distance in the width direction LTD of the geometric centroids of two light emitting element rows 2951R adjacent to each other in the width direction LTD. The light emitting element pitch Pel is a distance in the longitudinal direction LGD between the geometric centroids of two light emitting elements 2951 adjacent to each other in the longitudinal direction LGD.

  As shown in the column “Spot Group” in the figure, a spot row SPR and a spot column SPC are defined. That is, in each spot group SG, a plurality of spots SP arranged in the longitudinal direction LGD are defined as spot rows SPR. The plurality of spot rows SPR are arranged side by side in the width direction LTD at a predetermined spot row pitch Pspr. Further, a plurality of (two in the figure) spots arranged at the spot pitch Pspr in the width direction LTD and at the spot pitch Psp in the longitudinal direction LGD are defined as a spot row SPC. The spot row pitch Pspr is a distance in the sub-scanning direction SD between the geometric centroids of two spot rows SPR adjacent to each other in the sub-scanning direction SD. The spot pitch Psp is a distance in the longitudinal direction LGD between the geometric centroids of two spots SP adjacent to each other in the main scanning direction MD.

B. First Embodiment FIG. 3 is a diagram showing an example of an image forming apparatus according to the present invention. FIG. 4 is a diagram showing an electrical configuration of the image forming apparatus of FIG. This apparatus uses a color mode in which four color toners of black (K), cyan (C), magenta (M), and yellow (Y) are superimposed to form a color image, and only black (K) toner. Thus, the image forming apparatus can selectively execute a monochrome mode for forming a monochrome image. FIG. 3 is a diagram corresponding to the execution of the color mode. In this image forming apparatus, when an image forming command is given from an external device such as a host computer to a main controller MC having a CPU, a memory, etc., the main controller MC gives a control signal to the engine controller EC and also outputs an image forming command. Corresponding video data VD is supplied to the head controller HC. The head controller HC controls the line head 29 for each color based on the video data VD from the main controller MC, the vertical synchronization signal Vsync from the engine controller EC, and parameter values. As a result, the engine unit EG executes a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  An electrical component box 5 containing a power circuit board, a main controller MC, an engine controller EC, and a head controller HC is provided in the housing main body 3 of the image forming apparatus. An image forming unit 7, a transfer belt unit 8, and a paper feed unit 11 are also disposed in the housing body 3. In FIG. 3, a secondary transfer unit 12, a fixing unit 13, and a sheet guide member 15 are disposed on the right side in the housing body 3. The paper feeding unit 11 is configured to be detachable from the apparatus main body 1. The paper feed unit 11 and the transfer belt unit 8 can be removed and repaired or exchanged.

  The image forming unit 7 includes four image forming stations Y (for yellow), M (for magenta), C (for cyan), and K (for black) that form a plurality of images of different colors. Each of the image forming stations Y, M, C, and K is provided with a cylindrical photosensitive drum 21 having a surface with a predetermined length in the main scanning direction MD. Each of the image forming stations Y, M, C, and K forms a corresponding color toner image on the surface of the photosensitive drum 21. The photosensitive drum is arranged so that the axial direction is substantially parallel to the main scanning direction MD. Each photosensitive drum 21 is connected to a dedicated drive motor and is driven to rotate at a predetermined speed in the direction of arrow D21 in the figure. As a result, the surface of the photosensitive drum 21 is conveyed in the sub-scanning direction SD that is orthogonal or substantially orthogonal to the main scanning direction MD. A charging unit 23, a line head 29, a developing unit 25, and a photoconductor cleaner 27 are disposed around the photoconductive drum 21 along the rotation direction. Then, a charging operation, a latent image forming operation, and a toner developing operation are executed by these functional units. Therefore, when the color mode is executed, the toner images formed at all the image forming stations Y, M, C, and K are superimposed on the transfer belt 81 of the transfer belt unit 8 to form a color image, and the monochrome mode is executed. In some cases, a monochrome image is formed using only the toner image formed at the image forming station K. In FIG. 3, the image forming stations of the image forming unit 7 have the same configuration, and therefore, for convenience of illustration, only some image forming stations are denoted by reference numerals, and the other image forming stations are omitted. .

  The charging unit 23 includes a charging roller whose surface is made of elastic rubber. The charging roller is configured to rotate in contact with the surface of the photosensitive drum 21 at the charging position, and at a peripheral speed in the driven direction with respect to the photosensitive drum 21 as the photosensitive drum 21 rotates. Followed rotation. The charging roller is connected to a charging bias generator (not shown). The charging roller is supplied with the charging bias from the charging bias generator and is charged at the charging position where the charging unit 23 and the photosensitive drum 21 come into contact with each other. The surface of 21 is charged.

  The line head 29 is disposed with respect to the photosensitive drum 21 such that the longitudinal direction thereof corresponds to the main scanning direction MD and the width direction thereof corresponds to the sub-scanning direction SD. Is substantially parallel to the main scanning direction MD. The line head 29 includes a plurality of light emitting elements arranged side by side in the longitudinal direction, and is spaced apart from the photosensitive drum 21. Then, light is emitted from these light emitting elements to the surface of the photosensitive drum 21 charged by the charging unit 23, and an electrostatic latent image is formed on the surface.

  The developing unit 25 has a developing roller 251 on which toner is carried. The charged toner is developed at a developing position where the developing roller 251 and the photosensitive drum 21 come into contact with each other by a developing bias applied to the developing roller 251 from a developing bias generator (not shown) electrically connected to the developing roller 251. Is moved from the developing roller 251 to the photosensitive drum 21, and the electrostatic latent image formed by the line head 29 becomes obvious.

  The toner image that has been made visible at the developing position in this way is conveyed in the rotational direction D21 of the photosensitive drum 21, and then a primary transfer position TR1 at which each of the photosensitive drums 21 comes into contact with the transfer belt 81, which will be described in detail later. 1 is primarily transferred to the transfer belt 81.

  In this embodiment, the photosensitive drum cleaner 27 is provided in contact with the surface of the photosensitive drum 21 on the downstream side of the primary transfer position TR1 in the rotational direction D21 of the photosensitive drum 21 and on the upstream side of the charging unit 23. It has been. The photoconductor cleaner 27 abuts on the surface of the photoconductor drum to clean and remove toner remaining on the surface of the photoconductor drum 21 after the primary transfer.

  The transfer belt unit 8 includes a driving roller 82, a driven roller 83 (blade facing roller) disposed on the left side of the driving roller 82 in FIG. 3, and a stretched direction of these rollers in the direction of the arrow D81 (conveying direction). And a transfer belt 81 that is driven to circulate. Further, the transfer belt unit 8 is disposed on the inner side of the transfer belt 81 so as to be opposed to each of the photosensitive drums 21 included in the image forming stations Y, M, C, and K when the photosensitive cartridge is mounted. Four primary transfer rollers 85Y, 85M, 85C, and 85K are provided. Each of these primary transfer rollers 85 is electrically connected to a primary transfer bias generator (not shown). As will be described in detail later, when the color mode is executed, as shown in FIG. 3, all the primary transfer rollers 85Y, 85M, 85C, 85K are positioned on the image forming stations Y, M, C, K side. Then, the transfer belt 81 is pushed and brought into contact with the photosensitive drums 21 included in the image forming stations Y, M, C, and K, so that the primary transfer position TR1 is set between each photosensitive drum 21 and the transfer belt 81. Form. Then, by applying a primary transfer bias from the primary transfer bias generator to the primary transfer roller 85 at an appropriate timing, the toner images formed on the surfaces of the photosensitive drums 21 correspond respectively. A color image is formed by transferring to the surface of the transfer belt 81 at the primary transfer position TR1.

  On the other hand, when the monochrome mode is executed, among the four primary transfer rollers 85, the color primary transfer rollers 85Y, 85M, and 85C are separated from the image forming stations Y, M, and C facing each other, and the monochrome primary transfer is performed. By bringing only the roller 85K into contact with the image forming station K, only the monochrome image forming station K is brought into contact with the transfer belt 81. As a result, the primary transfer position TR1 is formed only between the monochrome primary transfer roller 85K and the image forming station K. Then, by applying a primary transfer bias from the primary transfer bias generator to the monochrome primary transfer roller 85K at an appropriate timing, the toner image formed on the surface of each photosensitive drum 21 is subjected to primary transfer. A monochrome image is formed by transferring to the surface of the transfer belt 81 at a position TR1.

  Further, the transfer belt unit 8 includes a downstream guide roller 86 disposed on the downstream side of the monochrome primary transfer roller 85K and on the upstream side of the driving roller 82. Further, the downstream guide roller 86 is formed between the primary transfer roller 85K and the photosensitive drum 21 at the primary transfer position TR1 formed by the monochrome primary transfer roller 85K contacting the photosensitive drum 21 of the image forming station K. It is configured to contact the transfer belt 81 on a common inscribed line.

  The driving roller 82 circulates and drives the transfer belt 81 in the direction of the arrow D81 in the figure, and also serves as a backup roller for the secondary transfer roller 121. A rubber layer having a thickness of about 3 mm and a volume resistivity of 1000 kΩ · cm or less is formed on the peripheral surface of the driving roller 82, and secondary transfer is omitted by grounding through a metal shaft. The conductive path of the secondary transfer bias supplied from the bias generation unit via the secondary transfer roller 121 is used. When the rubber layer having high friction and shock absorption is provided on the driving roller 82 in this way, the sheet enters the contact portion (secondary transfer position TR2) between the driving roller 82 and the secondary transfer roller 121. Is difficult to be transmitted to the transfer belt 81, and image quality deterioration can be prevented.

  The sheet feeding unit 11 includes a sheet feeding unit having a sheet feeding cassette 77 capable of stacking and holding sheets and a pickup roller 79 that feeds sheets one by one from the sheet feeding cassette 77. The sheet fed from the sheet feeding unit by the pickup roller 79 is fed to the secondary transfer position TR2 along the sheet guide member 15 after the sheet feeding timing is adjusted by the registration roller pair 80.

  The secondary transfer roller 121 is provided so as to be able to come into contact with and separate from the transfer belt 81 and is driven to come into contact with and separate from a secondary transfer roller drive mechanism (not shown). The fixing unit 13 includes a heating roller 131 that includes a heating element such as a halogen heater and is rotatable, and a pressure unit 132 that presses and biases the heating roller 131. Then, the sheet on which the image is secondarily transferred is guided to a nip portion formed by the heating roller 131 and the pressure belt 1323 of the pressure portion 132 by the sheet guide member 15, and in the nip portion, a predetermined value is provided. The image is heat-fixed at temperature. The pressure unit 132 includes two rollers 1321 and 1322 and a pressure belt 1323 stretched between them. A nip portion formed by the heating roller 131 and the pressure belt 1323 by pressing the belt tension surface stretched by the two rollers 1321 and 1322 against the peripheral surface of the heating roller 131 among the surfaces of the pressure belt 1323. Is configured to be widely taken. Further, the sheet thus subjected to the fixing process is conveyed to a paper discharge tray 4 provided on the upper surface of the housing body 3.

  Further, in this apparatus, a cleaner portion 71 is disposed to face the blade facing roller 83. The cleaner unit 71 includes a cleaner blade 711 and a waste toner box 713. The cleaner blade 711 removes foreign matters such as toner and paper dust remaining on the transfer belt after the secondary transfer by bringing the tip of the cleaner blade 711 into contact with the blade facing roller 83 via the transfer belt 81. The foreign matter removed in this way is collected in a waste toner box 713. Further, the cleaner blade 711 and the waste toner box 713 are integrally formed with the blade facing roller 83. Therefore, when the blade facing roller 83 moves as will be described below, the cleaner blade 711 and the waste toner box 713 also move together with the blade facing roller 83.

  FIG. 5 is a perspective view showing an outline of the line head according to the present invention. FIG. 6 is a cross-sectional view in the width direction of the line head shown in FIG. As described above, the line head 29 is arranged with respect to the photosensitive drum 21 such that the longitudinal direction LGD corresponds to the main scanning direction MD and the width direction LTD corresponds to the sub-scanning direction SD. The longitudinal direction LGD and the width direction LTD are substantially orthogonal to each other. The line head 29 includes a case 291, and positioning pins 2911 and screw insertion holes 2912 are provided at both ends of the case 291 in the longitudinal direction LGD. Then, the positioning pin 2911 covers the photosensitive drum 21 and is fitted into a positioning hole (not shown) formed in a photosensitive cover (not shown) positioned with respect to the photosensitive drum 21, thereby The head 29 is positioned with respect to the photosensitive drum 21. Further, the line head 29 is positioned and fixed with respect to the photosensitive drum 21 by screwing and fixing a fixing screw into a screw hole (not shown) of the photosensitive member cover through the screw insertion hole 2912.

  The case 291 holds the lens array 299 at a position facing the surface of the photosensitive drum 21, and includes a light shielding member 297 and a head substrate 293 in the order close to the lens array 299. The head substrate 293 is formed of a material (for example, glass) that can transmit a light beam. In addition, a plurality of light emitting element groups 295 in which a plurality of light emitting elements are grouped are arranged side by side on the back surface of the head substrate 293 (the surface opposite to the lens array 299 of the two surfaces of the head substrate 293). The light emitting elements constituting each light emitting element group 295 are so-called bottom emission type organic EL (Electro-Luminescence) elements. As will be described in detail later, a TFT circuit TC that controls driving of the light emitting elements of the light emitting element group 295 is provided on the back surface of the head substrate 293. The light beams emitted from the respective light emitting element groups 295 are transmitted from the back surface to the front surface of the head substrate 293 and directed to the light shielding member 297.

  A plurality of light guide holes 2971 are formed in the light shielding member 297 on a one-to-one basis with respect to the plurality of light emitting element groups 295. Further, as will be described later, in the lens array 299, a lens LS is provided for each light emitting element group 295, and each light guide hole 2971 is drilled from the light emitting element group 295 toward the lens LS. Is formed. As described above, since the light shielding member 297 is provided between the head substrate 293 and the lens array 299, the light guide hole 2971 corresponding to the light emitting element group 295 out of the light beams emitted from the light emitting element group 295. The light beam toward the other side is blocked by the light blocking member 297. Thus, all the light emitted from one light emitting element group 295 is directed to the lens array 299 through the same light guide hole 2971, and interference between light beams emitted from different light emitting element groups 295 is prevented by the light shielding member 297. The Then, the light beam that has passed through the light guide hole 2971 formed in the light shielding member 297 is imaged as a spot on the surface of the photosensitive drum 21 by the lens array 299.

  As shown in FIG. 6, the back cover 2913 is pressed against the case 291 via the head substrate 293 by the fixing device 2914. That is, the fixing device 2914 has an elastic force that presses the back cover 2913 toward the case 291, and presses the back cover with the elastic force, thereby making the inside of the case 291 light-tight (that is, from the inside of the case 291. It is sealed so that light does not leak and so that light does not enter from the outside of the case 291. Note that a plurality of fixing devices 2914 are provided in the longitudinal direction of the case 291. The light emitting element group 295 is covered with a sealing member 294.

  FIG. 7 is a plan view schematically showing the lens array, and corresponds to the case where the lens array is viewed from the image plane side (that is, the surface side of the photosensitive drum 21). As shown in the figure, in this lens array 299, a plurality of lenses LS are arranged along the longitudinal direction LGD to form a lens row LSR, and three lens rows LSR are arranged in the width direction LTD. These three lens rows LSR are shifted from each other in the longitudinal direction LGD so that the positions of the lenses LS are different from each other in the longitudinal direction LGD. As a result, the positions of the lenses LS in the longitudinal direction LGD are different from each other.

  FIG. 8 is a cross-sectional view of the lens array in the longitudinal direction, and corresponds to a case where the lens array is viewed in a cross section including the optical axis OA of each lens. In the figure, the upper side is the image plane side, and the lower side is the light emitting element group side. In the lens array 299, one lens substrate LB formed of glass is provided, and the lens LS is configured by two lens surfaces LSF1 and LSF2 arranged in the direction of the optical axis OA so as to sandwich the lens substrate LB. . These lens surfaces LSF1, LSF2 can be formed of, for example, a photocurable resin. Of the two lens surfaces, the lens surface LSF1 is formed on the back surface LBF1 of the lens substrate LB, and the lens surface LSF2 is formed on the surface LBF2 of the lens substrate LB. The lens row LSR is configured by arranging the lenses LS in the longitudinal direction LGD.

  FIG. 9 is a diagram showing the configuration of the back surface of the head substrate, which corresponds to the case where the back surface is viewed from the front surface of the head substrate. In FIG. 9, the lens LS is indicated by a two-dot chain line. This is for indicating that the light emitting element groups 295 are provided in one-to-one relationship with the lens LS. It does not indicate that it is arranged on the back surface of the head substrate. As shown in FIG. 9, a light emitting element group 295 in which a plurality of light emitting elements 2951 are grouped is provided on the back surface of the head substrate 293. More specifically, light emitting element group rows 295R in which a plurality of light emitting element groups 295 are arranged along the longitudinal direction LGD are arranged in three rows (295R_A, 295R_B, 295R_C) in the width direction LTD. In each light emitting element group row 295R_A to 295R_C, a plurality of light emitting element groups 295 are arranged. The light emitting element group rows 295R are shifted from each other in the longitudinal direction LGD, and the positions of the light emitting element groups 295 are different from each other in the longitudinal direction LGD. More specifically, the positions LCA, LCB, and LCC in the longitudinal direction LGD of the light emitting element groups 295A1, 295B1, and 295C1 are different from each other. In the figure, positions LCA, LCB, and LCC are representatively represented by perpendicular legs drawn from the center of gravity of each light emitting element group 295A1, 295B1, and 295C1 to the longitudinal LGD axis.

  In each light emitting element group 295, light emitting element rows 2951R in which four light emitting elements 2951 are arranged in the longitudinal direction LGD are arranged side by side in the width direction LTD. The light emitting element rows 2951R are arranged so as to be shifted by the light emitting element pitch Pel in the longitudinal direction LGD, and the positions of the respective light emitting elements 2951 are different from each other in the longitudinal direction LGD. Thus, in the light emitting element group 295, two columns of light emitting element rows 2951R are arranged in a staggered manner.

  FIG. 10 is a diagram showing the positional relationship between the light emitting element group and the TFT circuit in the first embodiment, and shows the back surface of the head substrate 293. Also in this figure, the lens LS is indicated by a two-dot chain line, but this is for showing that the light emitting element groups 295 are provided one-to-one with respect to the lens LS. Does not indicate that it is arranged on the back surface of the head substrate. As shown in the figure, on the back surface of the head substrate 293, a TFT circuit and a wiring WL are formed in addition to the light emitting element group 295. That is, TFT circuits TC are formed on both sides of each light emitting element group 295 in the width direction LTD. In other words, the two TFT circuits TC are arranged so as to sandwich the light emitting element group 295 from the width direction LTD, and these two TFT circuits are provided adjacent to the light emitting element group 295.

  The light emitting element group 295 and the TFT circuit TC provided for the light emitting element group 295 are connected by a wiring WL. The light emitting element group 295A1 will be described in detail as a representative. Among the light emitting element rows 2951R constituting the light emitting element group 295A1, the wiring WL_a connected to the light emitting element row 2951R_a on one side in the width direction LTD is connected to the light emitting element row It is pulled out to one side of 2951R_a. The wiring WL_a drawn in this way is connected to a TFT circuit TC_a provided on one side of the light emitting element group 295A1. In addition, among the light emitting element rows 2951R configuring the light emitting element group 295A1, the wiring WL_b connected to the light emitting element row 2951R_b on the other side in the width direction LTD is led out to one side of the light emitting element row 2951R_b. The wiring WL_b drawn in this way is connected to the TFT circuit TC_b provided on one side of the light emitting element group 295A1.

  The TFT circuit TC is configured to be able to control light emission driving of the light emitting element 2951. That is, each TFT circuit TC gives a drive signal corresponding to the video data VD to each light emitting element 2951 of the corresponding light emitting element group 295. Each light emitting element 2951 to which the drive signal is given emits light beams having the same wavelength. The light emitting surface of the light emitting element 2951 is a so-called perfect diffusion surface light source, and the light beam emitted from the light emitting surface follows Lambert's cosine law. Then, the light beam is formed as a spot by the lens LS, and a latent image is formed on the surface of the photosensitive drum 21.

  FIG. 11 is a diagram showing a spot forming operation by the above-described line head. The spot forming operation by the line head in this embodiment will be described below with reference to FIGS. In order to facilitate understanding of the invention, a case where a line latent image is formed by arranging a plurality of spots in a straight line extending in the main scanning direction MD will be described here. In general, in such a latent image forming operation, a plurality of light emitting elements are set in a predetermined manner according to video data VD output from the head controller HC while conveying the surface of the photosensitive drum 21 in the sub-scanning direction SD (width direction LTD). By emitting light at this timing, a plurality of spots are formed side by side in a straight line extending in the main scanning direction MD (longitudinal direction LGD). Details will be described below.

  First, among the light emitting element rows 2951R belonging to the most upstream light emitting element group 295A1, 295A2,... In the width direction LTD, the light emitting element row 2951R on the downstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. In the present embodiment, the lens LS has an inverted characteristic, and the light beam from the light emitting element 2951 is imaged while being inverted. Thus, a spot is formed at the position of the “first” hatching pattern in FIG. In the figure, white circles represent spots that have not yet been formed and are to be formed in the future. In the same figure, the spots labeled with reference numerals 295C1, 295B1, 295A1, and 295C2 are spots formed by the light emitting element groups 295 corresponding to the reference numerals.

  Next, among the light emitting element rows 2951R belonging to the light emitting element groups 295A1, 295A2,..., The light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. In this way, a spot is formed at the position of the “second” hatching pattern in FIG. Here, the reason why light is emitted in order from the light emitting element row 2951R on the downstream side in the width direction LTD is to correspond to the fact that the lens LS has an inverted characteristic.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295B1,... From the upstream side in the width direction, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “third” hatching pattern in FIG.

  Next, among the light emitting element rows 2951R belonging to the second light emitting element group 295B1,... From the upstream side in the width direction, the light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “fourth” hatching pattern in FIG.

  Next, among the light emitting element rows 2951R belonging to the third light emitting element group 295C1,... From the upstream side in the width direction, the light emitting element rows 2951R on the downstream side in the width direction LTD are caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “fifth” hatching pattern in FIG.

  Finally, among the light emitting element rows 2951R belonging to the third light emitting element group 295C1,... From the width direction upstream side, the light emitting element row 2951R on the upstream side in the width direction LTD is caused to emit light. The plurality of light beams emitted by the light emitting operation are imaged on the surface of the photosensitive drum by the lens LS. Thus, a spot is formed at the position of the “sixth” hatching pattern in FIG. In this way, by performing the first to sixth light emission operations, a plurality of spots are formed side by side in a straight line extending in the longitudinal direction LGD (main scanning direction MD).

  Incidentally, in the line head 29 as described above, there may be a problem that the amount of light varies between the plurality of light emitting elements 2951. As a cause of the light quantity variation, for example, a variation in the light emission frequency among the plurality of light emitting elements 2951 can be cited. That is, if there is a variation in the light emission frequency among the plurality of light emitting elements 2951, some of the light emitting elements 2951 reach their lifetime relatively quickly, and the amount of light may decrease compared to other light emitting elements 2951. is there. In particular, since the organic EL element has a short lifetime as compared with the LED element or the like, such a problem becomes remarkable when the organic EL is used as the light emitting element 2951 as in the above embodiment. On the other hand, the line head 29 of the present embodiment includes an optical sensor that detects the amount of light beam emitted from the light emitting element 2951.

  12 and 13 are diagrams showing the arrangement of the photosensors in the first embodiment. 12 is a view of the line head 29 viewed from the longitudinal direction LGD, and FIG. 13 is a perspective view of the head substrate 293. As shown in FIG. 13, the head substrate 293 has a longitudinal direction LGD corresponding to the main scanning direction MD as a major axis direction and a width direction LTD corresponding to the sub-scanning direction SD as a minor axis direction. As described above, the back surface 293B of the head substrate 293 is provided with the plurality of light emitting element groups 295 and the TFT circuit TC that controls the light emission driving of each light emitting element group 295. In FIG. 13, the description of the TFT circuit TC is omitted.

  Further, as shown in the figure, a plurality of photosensors SC are provided on the surface 293A of the head substrate 293 so as to be arranged at an equal pitch in the longitudinal direction LGD. Each optical sensor SC is provided on the downstream side of the light shielding member 297 in the width direction LTD. The light receiving surface SCF of the optical sensor SC faces the surface 293A of the head substrate 293 and is bonded to the head substrate surface 293A with a transparent optical adhesive. And the light beam inject | emitted from each light emitting element 2951 is detectable with the optical sensor SC provided in this way. That is, not all of the light beam emitted from the light emitting element 2951 is emitted from the front surface 293A of the head substrate 293, and a part of the light beam is reflected toward the back surface 293B by the front surface 293A. Furthermore, a part of the reflected light beam is reflected again toward the front surface 293A by the back surface 293B. In particular, in the first embodiment, since the TFT circuit TC is provided on the back surface 293B of the head substrate, the TFT circuit TC functions as a reflective film. Therefore, the head substrate back surface 293B can reflect the light beam with high reflectivity.

  In this way, a part of the light beam emitted from the light emitting element 2951 proceeds inside the head substrate 293 and enters the optical sensor SC while repeating reflection between the front surface 293A and the back surface 293B of the head substrate 293. (A light beam LB indicated by a broken line in FIG. 12). The light beam incident on the light receiving surface SCF is detected by the optical sensor SC, and the detected value is output from the optical sensor SC to the engine controller EC.

  In the first embodiment, based on the detection result of the optical sensor SC, the driving of each light emitting element 2951 is controlled so that the light amount of each light emitting element 2951 becomes uniform. The specific contents of this drive control operation will be described below. The drive control operation is executed based on a correction coefficient obtained in advance. The correction coefficient is obtained in advance, for example, at the timing when the line head 29 is assembled or shipped. Therefore, in the following description, first, after describing how to obtain the correction coefficient, the drive control operation will be described.

  In order to obtain the correction coefficient, for example, when the line head 29 is assembled or shipped, a light beam is emitted from the light emitting element 2951, and the light amount of a spot formed at a position corresponding to the surface of the photosensitive drum 21. Is measured. This light quantity measurement is executed for each light emitting element 2951. Specifically, the line head 29 is attached to the inspection jig. The inspection jig is equipped with a light amount detector that detects the light amount of the light beam emitted from each light emitting element 2951 of the line head 29 at an image plane position corresponding to the surface of the photosensitive drum 21. This light amount detector may detect the light amount of the light beam from each light emitting element 2951 while moving one detector, or may be one in which a detector is arranged for each light emitting element 2951. Then, while each light emitting element 2951 emits light sequentially, the detection value Pgn of the light quantity detector of the inspection jig and the detection value Phn of the optical sensor SC of the line head 29 (n represents the nth light emitting element) are obtained. . In this way, the correction coefficient Pgn / Phn can be calculated for each light emitting element 2951. The correction coefficient Pgn / Phn obtained in this way is stored, for example, in the engine controller EC shown in FIG. Then, as will be described next, the drive control operation is executed based on the correction coefficient Pgn / Phn.

  In the drive control operation, first, the light amount variation of the light emitting element 2951 is detected. Such light amount variation detection is performed when the image forming apparatus is turned on, before the image forming operation is started, or while a normal image forming operation is not performed, such as between sheets. Specifically, the detection value of the optical sensor SC is measured while each light emitting element 2951 emits light in order. Then, by multiplying the measurement value at this time by the correction coefficient Pgn / Phn, the light amount of the spot formed on the surface of the photosensitive drum 21 by each light emitting element 2951 is calculated.

  Then, when the calculated light amount varies and the desired light amount is not realized, the driving of the light emitting element 2951 is controlled so that the desired light amount is obtained. That is, the desired light amount is compared with the calculated light amount, and the drive current flowing through the light emitting element 2951 is adjusted so that the calculated light amount becomes the desired light amount. The TFT circuit TC supplies the drive current adjusted in this way to each light emitting element 2951. Thus, the TFT circuit TC drives the light emitting elements 2951 so that the light amount of the light beam emitted from each light emitting element 2951 becomes uniform. Note that information regarding a desired light quantity, a program for executing a drive control operation, and the like may be stored in advance in the engine controller EC, for example.

  As described with reference to FIG. 10, in the first embodiment, the TFT circuits TC are arranged on both sides of the light emitting element group 295 in the width direction LTD. Therefore, the wiring WL connected to each light emitting element 2951 of the light emitting element group 295 can be drawn out on both sides in the width direction LTD, and the degree of freedom of the wiring WL is improved.

  In the first embodiment, the TFT circuit is provided adjacent to the light emitting element group 295 (FIG. 10). Therefore, the length of the wiring WL that connects the TFT circuit to the light emitting element group 295 can be shortened, and a driving signal with less dullness due to stray capacitance or the like can be supplied to the light emitting element 2951. .

  In the first embodiment, the TFT circuit TC is disposed on one surface of the head substrate 293. Therefore, since the TFT circuit TC functions as a reflective film that reflects light, the amount of light incident on the optical sensor SC can be increased. Therefore, in the first embodiment, it is possible to execute the light emission drive control with high accuracy.

  In the first embodiment, a light shielding member 297 having a light guide hole 2971 directed from the light emitting element group 295 to the lens is provided for each light emitting element group 295 (FIGS. 5 and 6), and a good exposure operation is realized. Has been. That is, in the first embodiment, the light beam emitted from the light emitting element group 295 is imaged by the lens LS provided corresponding to the light emitting element group 295, whereby the exposure operation is executed. Therefore, from the viewpoint of executing a good exposure operation, it is desirable that only the light beam emitted from the light emitting element group 295 corresponding to the lens LS is incident on each lens LS. It is desirable that the incidence of the beam (ghost light) is suppressed as much as possible. On the other hand, in the first embodiment, such ghost light can be blocked by the light blocking member 297. As a result, the ghost light is prevented from entering the lens LS, and a good exposure operation can be performed.

  In the first embodiment, the light receiving surface SCF of the optical sensor SC faces the head substrate surface 293A and is bonded to the head substrate surface 293A with a transparent optical adhesive. Therefore, the light beam emitted from the head substrate surface 293A toward the light receiving surface SCF can enter the light receiving surface SCF via the optical adhesive. By bonding with the optical adhesive in this way, the interface between the head substrate surface 293A and the optical sensor SC is removed, and reflection of an unnecessary light beam between the head substrate surface 293A and the optical sensor SC is suppressed. As a result, light incident on the light receiving surface SCF is increased, and more accurate light emission drive control is possible.

  In the first embodiment, a plurality of optical sensors SC are arranged on the head substrate 293. Therefore, it is possible to detect the light amount of the light emitting element with high accuracy.

C. Second Embodiment FIG. 14 is a diagram illustrating a configuration of a line head in a second embodiment. FIG. 15 is a partial side view corresponding to the line head viewed from the right side in FIG. In the following description, differences from the first embodiment will be mainly described, and the same parts as those in the first embodiment will be denoted by the same reference numerals and description thereof will be omitted. As shown in the figure, also in the second embodiment, the light emitting element groups 295 are formed on the back surface of the head substrate 293, and the TFT circuits TC are arranged on both sides of each light emitting element group 295 in the width direction. Has been. Therefore, as in the first embodiment, the wiring connected to each light emitting element 2951 of the light emitting element group 295 can be drawn out on both sides in the width direction LTD, and the degree of freedom of the wiring WL is improved. Has been.

  What should be noted in the second embodiment is the arrangement of the optical sensors SC. As shown in FIGS. 14 and 15, in the second embodiment, a through hole 2979 is formed on one end side in the width direction LTD of the light shielding member 297. The through hole 2979 is formed to penetrate from the outside of the light shielding member 297 toward the light guide hole 2971, and the optical sensor SC is disposed inside the through hole 2979. Moreover, the optical sensor SC is arranged so that a part thereof is located inside the light guide hole 2971 (FIG. 14). Therefore, the optical sensor SC can directly detect the light beam passing through the light guide hole 2971. As a result, in the second embodiment, the light beam detection accuracy is improved, and the light amount detection with higher accuracy is possible.

D. Third Embodiment FIG. 16 is a partial plan view showing the configuration of the back surface of the head substrate in the third embodiment, and FIG. 17 is a partial plan view showing an enlarged configuration in the vicinity of the light emitting element group in FIG. In these drawings, the lens LS is indicated by a one-dot chain line, which indicates that the light emitting element group 295 and the lens LS are provided in a one-to-one correspondence, and the lens is provided on the back surface of the head substrate. It does not indicate that LS is arranged.

  As shown in FIG. 17, one light emitting element group 295 is composed of 16 light emitting elements Ea1 to Ea4, Eb1 to Eb4, Ec5 to Ec8, Ed5 to Ed8. And these 16 light emitting elements are arranged as follows. That is, four light emitting elements (for example, light emitting elements Ea1 to Ea4) are arranged linearly in the longitudinal direction LGD to form one light emitting element row (for example, light emitting element row 2951R_a). The four light emitting element rows 2951R_a to 2951R_d are arranged in this order in the width direction LTD. Moreover, the light emitting element rows 2951R_a to 2951R_d are shifted from each other in the longitudinal direction LGD, and the positions of the respective light emitting elements are different from each other in the longitudinal direction LGD.

  In the third embodiment, one TFT circuit (for example, a TFT circuit TCa1 for the light emitting element Ea1) is provided for one light emitting element. Although not shown, a power supply line is connected to the TFT circuit. In addition, TFT circuits (for example, TFT circuits TCa1 to TCa2) provided for the same light emitting element row (for example, light emitting element row 2951R_a) are arranged linearly in the longitudinal direction LGD. The TFT circuits TCa1 to TCa4 and TCb1 to TCb4 provided for the light emitting elements in the light emitting element rows 2951R_a and 2951R_b are provided on one side in the width direction LTD with respect to the light emitting element group 295. The TFT circuits TCc5 to TCa8 and TCd5 to TCd8 provided for the light emitting elements in the light emitting element rows 2951R_c and 2951R_d are provided on the other side in the width direction LTD with respect to the light emitting element group 295. As described above, the light emitting element group 295 is arranged between the TFT circuits TCa1 to TCa4 and TCb1 to TCb4 and the TFT circuits TCc5 to TCa8 and TCd5 to TCd8.

  The light emitting element and the TFT circuit (for example, the light emitting element Ea1 and the TFT circuit TCa1) corresponding to each other are connected by the wiring WL. That is, the wiring WL led out from each light emitting element of the light emitting element rows 2951R_a and 2951R_b to one side in the width direction LTD is connected to the TFT circuits TCa1 to TCa4 and TCb1 to TCb4. Further, the wiring WL drawn from the light emitting elements of the light emitting element rows 2951R_c and 2951R_d to the other side in the width direction LTD is connected to the TFT circuits TCa5 to TCa8 and TCb5 to TCb8.

  As described above, in the present embodiment, the light emitting element group 295 is disposed between the TFT circuits TCa1 to TCa4 and TCb1 to TCb4 and the TFT circuits TCc5 to TCa8 and TCd5 to TCd8. Therefore, the wiring WL can be drawn out to both sides (one side and the other side) of the width direction LTD, and the degree of freedom of wiring is improved.

  A data line and a select line are connected to the TFT circuit. That is, eight data lines Ld1 to Ld8 that are parallel or substantially parallel to the longitudinal direction LGD are provided on both sides in the width direction LTD of the light emitting element and TFT circuit formation region (FIG. 16). Two TFT circuits share one data line. For example, both the TFT circuit TCa1 and the TFT circuit TCb1 are connected to the data Ld1 by wiring. Further, four select lines Lsa to Lsd are provided for the light emitting element group 295. These select lines Lsa to Lsd are provided corresponding to the light emitting element rows 2951R_a to 2951R_d. For example, the select line Lsa is connected to each of the TFT circuits TCa1 to TCa4 corresponding to the issuing element row 2951Ra.

  The drive control of the light emitting element using the data lines Ld1 to Ld8 and the select lines Lsa to Lsb will be described by exemplifying a case where the light emitting element Ea1 is driven. First, data information corresponding to the video data VD is input to the data line Ld1. Then, data information is written in the TFT circuit TCa1 by activating the select line Lsa. The TFT circuit TCa1 holds the written information, and drives the light emitting element Ea1 based on this information.

E. Fourth Embodiment FIG. 18 is a partial cross-sectional view in the width direction showing the relationship between a light emitting element and an optical sensor in a fourth embodiment. FIG. 19 is a plan view showing the relationship between the light emitting element and the optical sensor in the fourth embodiment, and shows the configuration of the back surface of the head substrate. In FIG. 19, the lens LS is indicated by a one-dot chain line, which indicates that the light emitting element group 295 and the lens LS are provided in a one-to-one correspondence relationship on the back surface of the head substrate. It does not indicate that the lens LS is arranged.

On the back surface 293-t of the head substrate 293, ITO (Indium
An anode AD made of Tin Oxide) and a TFT are formed adjacent to each other in the width direction LTD. A switching electrode SW is laminated on the TFT. Further, the insulating layer IL is formed by being laminated on the TFT, the switching electrode SW, and the anode AN. An opening AP is formed in the insulating layer IL so as to face the anode AN. In the opening AP, a hole transport layer HIL is formed by laminating on the anode AN, and further, a light emitting layer EM made of an organic EL material is formed on the anode AN. Then, the cathode CA is formed by being laminated on substantially the entire surface of the light emitting layer EM and the insulating layer IL. The organic EL element thus formed emits light as follows. That is, when an on voltage is applied to the switching electrode SW, the TFT is turned on and holes are injected from the hole transport layer AN into the light emitting layer EM. At the same time, electrons are injected from the cathode CA into the light emitting layer EM. The light emitting layer EM emits light by combining holes and electrons in the light emitting layer EM. The light LB from the light emitting layer EM enters the head substrate back surface 293-t through the opening AP of the insulating layer IL, and then passes through the head substrate 293 that is a light transmissive member, so that the head substrate surface 293-h. Ejected from. Thus, the light emitting layer EM made of an organic EL material functions as a light emitting element.

  A plurality of photosensors SC are arranged in the longitudinal direction LGD on both sides in the width direction LTD of the formation area of the cathode CA. The optical sensor detects light incident on the light receiving surface SCF. The light receiving surface SCF is fixed to the head substrate back surface 293-t with an optical adhesive. As shown in FIG. 19, two photosensors SC are provided for one light emitting element group column 295C so as to sandwich the light emitting element group column 295C from the width direction LTD. The optical sensor SC is connected to a sensor wiring Wsc, and a detection signal of the optical sensor SC is output to the head controller HC via the sensor wiring Wsc. These optical sensors SC are used for light quantity correction of the light emitting elements, but since this is the same as described above, the description thereof is omitted.

  Thus, in this embodiment, the optical sensor SC is provided on the head substrate 293. Therefore, light LBr (FIG. 18) reflected from the inside of the head substrate 293 out of the light from the light emitting layer EM can be detected by the optical sensor SC. In addition, in this embodiment, a TFT is provided on the head substrate 293, and since this TFT reflects light from the light emitting layer EM, a larger amount of light can be detected by the optical sensor SC, and the detection result Accuracy can be improved.

  In this embodiment, a plurality of photosensors SC are provided. Therefore, it is possible to detect a large amount of light and improve the accuracy of the detection result.

  In this embodiment, the light receiving surface SCF of the optical sensor SC is bonded to the head substrate 293 with an optical adhesive. Therefore, the interface between the head substrate 293 and the light receiving surface SCF is removed by the optical adhesive, and unnecessary light reflection at the boundary between the head substrate 293 and the light receiving surface SCF can be suppressed. As a result, the amount of light incident on the light receiving surface SCF is increased, and the accuracy of the detection result can be improved.

F. Others As described above, in the first and second embodiments, the back surface 293B of the head substrate 293 corresponds to “one surface” of the present invention, and the front surface 293A of the head substrate 293 corresponds to “other surface” of the present invention. Further, the optical sensor SC corresponds to a “detection unit” or “detection unit” of the present invention. The longitudinal direction LGD corresponds to the “first direction” of the present invention, the width direction LTD corresponds to the “second direction” of the present invention, and the photosensitive drum 21 corresponds to the “latent image carrier” of the present invention. Yes.

  In the third and fourth embodiments, the line head 29 corresponds to the “exposure head” of the present invention. The light emitting element rows 2951R_a and 2951R_b correspond to “first light emitting elements” of the present invention, and the light emitting element rows 2951R_c and 2951R_d correspond to “second light emitting elements” of the present invention. The TFT circuits TCa1 to TCa4 and TCb1 to TCb4 correspond to the “first TFT circuit” of the present invention, and the TFT circuits TCc5 to TCc8 and TCd5 to TCd8 correspond to the “second TFT circuit” of the present invention. Yes. The lens LS corresponds to the “imaging optical system” of the present invention. The head substrate 293 corresponds to the “substrate” of the present invention, the head substrate back surface 293-t corresponds to the “first surface of the substrate” of the present invention, and the head substrate 293 surface 293-h corresponds to the “substrate” of the present invention. This corresponds to the “second surface of the substrate”. The optical sensor SC corresponds to the “detecting means” of the present invention.

  The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the first and second embodiments, the optical sensor SC is arranged on the surface 293A of the head substrate 293. However, the arrangement position of the optical sensor SC is not limited to this, and the optical sensor SC is arranged as follows. You can also Note that, in the following description, parts that are common to the above-described embodiment are denoted by corresponding reference numerals and description thereof is omitted. FIG. 20 is a view showing another arrangement mode of the optical sensor. In the example illustrated in FIG. 20, the optical sensor SC is disposed on the back surface 293 </ b> B of the head substrate 293. FIG. 21 is a view showing still another arrangement mode of the optical sensor. In the example illustrated in FIG. 21, the head substrate 293 is disposed on the end surface 293 </ b> C in the width direction LTD.

  In the first and second embodiments, the optical sensor SC is provided only on one side in the width direction LTD. However, for example, as shown in FIG. 22, photosensors SC may be provided on both sides in the width direction LTD. Here, FIG. 22 is a diagram illustrating a case where the optical sensors are arranged on both sides in the width direction.

  In the first and second embodiments, the four light emitting elements 2951 arranged in the longitudinal direction LGD constitute the light emitting element row 2951R (FIG. 10). However, the light emitting elements 2951 constituting the light emitting element row 2951R The number is not limited to four. The light emitting element group 295 includes two light emitting element rows 2951R (FIG. 10), but the number of light emitting element rows 2951R constituting the light emitting element group 295 is not limited to this. That is, the light emitting element row 2951R and the light emitting element group 295 can be configured as follows.

  FIG. 23 is a diagram showing another configuration of the light emitting element group. As shown in the figure, the light emitting element row 2951R is composed of 16 light emitting elements 2951 arranged in the longitudinal direction LGD. The light emitting element group 295 is composed of four light emitting element rows 2951R arranged in the width direction. In the light emitting element group 295, the light emitting element rows 2951R are shifted from each other so that the positions of the light emitting elements 2951 are different in the longitudinal direction LGD. Also in the example shown in the figure, TFT circuits TC are arranged on both sides of the light emitting element group 295 in the width direction LTD. Therefore, the wiring WL connected to each light emitting element 2951 of the light emitting element group 295 can be drawn out on both sides in the width direction LTD, and the degree of freedom of the wiring WL is improved.

  In the above embodiment, three light emitting element group rows 295R are arranged in the width direction LTD, but the number of light emitting element group rows 295R is not limited to three.

  In the above embodiment, the case where an organic EL element is used as the light emitting element 2951 has been described. However, the configuration of the light emitting element 2951 is not limited thereto, and for example, an LED (Light Emitting Diode) may be used.

Explanatory drawing of the term used by this specification. Explanatory drawing of the term used by this specification. 1 is a diagram illustrating an example of an image forming apparatus according to the present invention. FIG. 4 is a diagram illustrating an electrical configuration of the image forming apparatus in FIG. 3. The perspective view which shows the outline of the line head concerning this invention. FIG. 6 is a cross-sectional view in the width direction of the line head shown in FIG. 5. The top view which shows the outline of a lens array. Sectional drawing of the longitudinal direction of a lens array. The figure which shows the structure of the back surface of a head board | substrate. The figure which shows arrangement | positioning of the light emitting element group and TFT circuit in 1st Embodiment. The figure which shows the spot formation operation | movement by the above-mentioned line head. The figure which shows arrangement | positioning of the optical sensor in 1st Embodiment. The figure which shows arrangement | positioning of the optical sensor in 1st Embodiment. The figure which shows the structure of the line head in 2nd Embodiment. FIG. 15 is a partial side view corresponding to the case where the line head is viewed from the right side in FIG. The partial top view which shows the structure of the head substrate back surface in 3rd Embodiment. The fragmentary top view which shows the structure which expanded the structure of the light emitting element group vicinity of FIG. The width direction fragmentary sectional view which shows the relationship between the light emitting element and optical sensor in 4th Embodiment. The top view which shows the relationship between the light emitting element and optical sensor in 4th Embodiment. The figure which shows another arrangement | positioning aspect of an optical sensor. The figure which shows another arrangement | positioning aspect of an optical sensor. The figure which shows the case where the optical sensor is arrange | positioned on the both sides of the width direction. The figure which shows another structure of a light emitting element group.

Explanation of symbols

  21Y, 21K ... photosensitive drum (latent image carrier), 29 ... line head, 293 ... head substrate, 295 ... light emitting element group, 295R ... light emitting element group row, 2951 ... light emitting element, 2951R ... light emitting element row, 299 ... Lens array, LS ... lens, MD ... main scanning direction, SD ... sub-scanning direction, LGD: longitudinal direction (first direction), LTD ... width direction (second direction), WL ... wiring, TC ... TFT circuit, SC ... Light sensor (detection means), Ea1 to Ea4, Eb1 to Eb4 ... Light emitting element (first light emitting element), Ec5 to Ec8, Ed5 to Ed8 ... Light emitting element (second light emitting element), TCa1 to TCa4, TCb1 to TCb4 ... TFT circuit (first TFT circuit), TCc5 to TCc8, TCd5 to TCd8 ... TFT circuit (second TFT circuit)

Claims (14)

An imaging optical system;
A first light emitting element that emits light imaged by the imaging optical system;
A second light emitting element that emits light imaged by the imaging optical system;
A first TFT circuit connected to the first light emitting element via a wiring;
A second TFT circuit connected to the second light emitting element via a wiring,
An exposure head, wherein the first light emitting element and the second light emitting element are disposed between the first TFT circuit and the second TFT circuit.   The exposure head according to claim 1, further comprising: a substrate on which the first light emitting element, the second light emitting element, the first TFT circuit, and the second TFT circuit are disposed on a first surface. The substrate is a light transmissive member;
Light from the first light emitting element and the second light emitting element passes through the substrate from the first surface to a second surface different from the first surface and enters the imaging optical system. The exposure head according to claim 2.   4. The exposure head according to claim 2, further comprising a detection unit configured to detect light from the first light emitting element and the second light emitting element.   The exposure head according to claim 4, wherein the detection unit is disposed on the substrate.   The exposure head according to claim 4, wherein a plurality of the detection units are arranged.   The exposure head according to claim 4, wherein the detection unit is an optical sensor having a light receiving surface that receives light from the light emitting element.   The exposure head according to claim 7, wherein the light receiving surface is bonded to the substrate with an optical adhesive.   The first TFT circuit drives the first light emitting element based on the detection result of the detection unit, and the second TFT circuit drives the second light emitting element based on the detection result of the detection unit. The exposure head according to any one of claims 4 to 8.   The exposure head according to claim 9, wherein the first light emitting element and the second light emitting element are organic EL elements.   The exposure according to any one of claims 4 to 10, further comprising a light shielding member provided with a light guide hole for allowing light from the first light emitting element and the second light emitting element to pass through the imaging optical system. head. An imaging optical system, a first light emitting element that emits light imaged on the exposed surface by the imaging optical system, and a second light source that emits light imaged on the exposed surface by the imaging optical system A light emitting element, a first TFT circuit connected to the first light emitting element via a wiring, and a second TFT circuit connected to the second light emitting element via a wiring ,
An exposure step of exposing the surface to be exposed by an exposure head in which the first light emitting element and the second light emitting element are arranged between the first TFT circuit and the second TFT circuit; A method of controlling an exposure head provided.   A detection step of detecting the amount of light emitted from the first light emitting element and the second light emitting element, and the exposure step includes: 13. The exposure head control method according to claim 12, wherein the exposure head is driven. A latent image carrier;
An imaging optical system, a first light emitting element for emitting light imaged on the latent image carrier by the imaging optical system, and a light imaged on the latent image carrier by the imaging optical system A second light emitting element, a first TFT circuit connected to the first light emitting element via a wiring, and a second TFT circuit connected to the second light emitting element via a wiring An image forming apparatus comprising: an exposure head in which the first light emitting element and the second light emitting element are disposed between the first TFT circuit and the second TFT circuit. .

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