JP2010197271A - Density measurement apparatus and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a response speed, and to stabilize the quantity of a light emitted from a light-emitting section by an APC, in matching with the response speed data of a phototransistor and the drive voltage of a photodiode. <P>SOLUTION: A density measurement apparatus 1 includes an APC light-receiving circuit 91 with the phototransistor 9; an APC circuit 93 for determining a current supplied to the light-emitting section 81, based on the difference between an output from the APC light-receiving circuit 91 and a reference voltage; a control section 7 for inputting the reference voltage to the APC circuit 93; a drive voltage changing section for changing the drive voltage of the phototransistor 9; and a storage section 72 for storing the response speed data and a drive voltage determining data of the phototransistor 9. The drive voltage determining data is defined so as to set the phototransistor 9 with the lower response speed to be higher in response speed than the lower drive voltage of the phototransistor 9; and the control section 7 determines the drive voltage and the reference voltage, based on the response speed data and the drive voltage determining data. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a density measuring apparatus that irradiates light on a measurement target on which a toner image is formed and receives the reflected light with a light receiving element to measure density. The present invention also relates to an image forming apparatus such as a multifunction machine, a copier, or a printer provided with the density measuring device.

  Conventionally, the density of the toner image formed on the photosensitive drum or the intermediate transfer belt is measured using an optical sensor including a light emitting unit that irradiates light on the surface of the measurement target and a light receiving unit having a light receiving element. There is a concentration measuring device that performs the measurement. For example, the density measuring device is provided in the image forming apparatus, and reflects the reflectance of light from a background portion (for example, a photosensitive drum or an intermediate transfer belt) to be measured and an adherent (for example, toner) to the background. The concentration is measured by using the fact that the output of the light receiving element is different depending on the degree of distribution (concentration) of the deposit on the background from the difference in the absorption rate and the like.

An example of an image recording apparatus provided with such a density measuring apparatus is described in Patent Document 1. Specifically, Patent Document 1 discloses an image carrier, an exposure unit, an image forming unit that develops an electrostatic latent image on the image carrier, an intermediate transfer belt to which the formed image is transferred, and a toner. A light emitting unit for irradiating light on the image and the intermediate transfer belt; an image information detecting unit having a light receiving unit for receiving the toner image and reflected light from the intermediate transfer belt; and a unit for adjusting the output of the image detecting unit; It has a reference voltage switching means for binarizing the output of the image detection means, performs image density correction and color shift correction using the image information detection means, and responds to the amount of reflected light from the surface of the intermediate transfer belt An image forming apparatus is described in which the output of the image information detecting means is adjusted and the reference voltage is switched in accordance with the result of image density correction. Specifically, a plurality of resistors 64 and resistors 67 are arranged in parallel, and the value of the combined resistance is changed by switching between each resistor and GND with a transistor to change the sensitivity of the light receiving unit and the light receiving. The threshold value related to the output of the unit is adjusted. (See Patent Document 1: Claim 1, paragraphs [0063], [0067], etc.).
JP2007-121414A

  Here, in the concentration measuring apparatus, the light emission amount of the light emitting unit may change due to a temperature rise or the like. Therefore, in order to stabilize the light emission amount of the light emitting unit so that accurate concentration measurement can be performed, APC (Auto Power Control) is used. ) May be equipped with a circuit. This circuit has a light receiving element for monitoring the light emission amount of the light emitting unit, and grasps from the output of this light receiving element that the current light emission amount of the light emitting unit is less than or exceeds the desired light amount, and feedback Thus, the current supplied to the light emitting unit is adjusted to stabilize the light emission amount.

  A phototransistor may be used as the light receiving element for monitoring the light emission amount. The phototransistor can eliminate the need for an amplifier circuit compared to the case of using another light receiving element such as a photodiode, can reduce the number of components, and has advantages such as cost and space saving. However, phototransistors, for example, have a slower response speed than light receiving elements such as photodiodes (generally, photodiodes are on the order of a few nanoseconds, whereas phototransistors are on the order of several to several tens of microseconds). There is a problem in that the stability of the APC may be impaired due to failure to follow the change in the amount of light in the part. In other words, the amount of light can be unstable.

  The invention described in Patent Document 1 focuses on not mounting an APC circuit (see Patent Document 1: Paragraph [0012], etc.), and the stability of APC is impaired due to the slow response speed of the phototransistor. Can not cope with the problem of being. In addition, although it is understood that a phototransistor is used for concentration measurement even in the invention described in Patent Document 1 (the use is not specified in Patent Document 1; see Patent Document 1: FIG. 8), There is no description about the problem of the response speed of the phototransistor.

  In view of the above problems, the present invention stores response speed data of a phototransistor mounted in a concentration measuring device, and changes the response speed by changing the drive voltage of the photodiode in accordance with the response speed data. It is an object to improve and stabilize the light emission amount of the light emitting part by APC.

  In order to solve the above-described problem, the concentration measuring apparatus according to claim 1 includes a light emitting element that emits light toward a measurement target on which a toner image is formed, and reflected light from the measurement target. In a concentration measuring apparatus for measuring the density of a toner image in accordance with the amount of light received by the light receiving unit, the light emitting element of the light emitting element is provided. An APC light receiving circuit having a phototransistor for monitoring the amount of light emission, an APC circuit that receives an output of the APC light receiving circuit and determines a current to be supplied to the light emitting unit according to a difference from a reference voltage, and the APC circuit A control unit for inputting the reference voltage; a drive voltage changing unit for changing the drive voltage of the phototransistor; response speed data indicating a response speed of the phototransistor; and the response speed data. According to the driving voltage determination data for determining the driving voltage of the phototransistor and the reference voltage according to the determined driving voltage of the phototransistor so that the light emission amount of the light emitting unit is constant. A storage unit that stores reference voltage determination data for determination, and the drive voltage determination data is driven by the phototransistor that is slower in the phototransistor than in the phototransistor that has a fast response speed. The control unit determines a driving voltage of the phototransistor based on the driving voltage determination data, and applies the determined driving voltage to the phototransistor to the driving voltage change unit. And determining the reference voltage based on the reference voltage determination data, and the determined reference voltage It was entering the APC circuit.

  According to this configuration, the phototransistor uses the characteristic that the response speed improves when the drive voltage is lowered. The slower the response speed of the mounted phototransistor, the more the reference voltage is applied to cope with the output change of the phototransistor. Since the drive voltage is lowered while changing, the response speed of the phototransistor in the APC light receiving circuit can be increased. Therefore, it becomes easy to follow the light quantity change of the light emitting element, and the stability of the light emission amount from the light emitting part is improved. Since the light quantity is constant and stable, accurate concentration measurement can be performed.

  Here, the response speed data is determined based on the result of measuring the response speed of the phototransistor in advance by irradiating the phototransistor mounted on the concentration measuring device with a predetermined amount of light. Any data may be used. The drive voltage determination data can be determined based on, for example, a result of measuring in advance a drive voltage that can ensure a response speed of a certain level or more, regardless of variations (individual differences) in response speed of mounted phototransistors. The reference voltage determination data can be determined based on the result of measuring in advance a reference voltage that corresponds to the change in the output of the phototransistor depending on the drive voltage and at which the light emission amount of the light emitting unit is constant at each drive voltage. The drive voltage determination data and the reference voltage determination data are stored in the storage unit, for example, in the form of a data table.

  According to a second aspect of the present invention, in the first aspect of the invention, there is provided a plurality of load resistors for converting the output current of the phototransistor into a voltage, and a load resistance selection section for switching the load resistance to be used. The storage unit is configured to determine the load resistance for determining the load resistance to be used according to the response speed data, and the load resistance determined so that the light emission amount of the light emitting unit is constant. And reference voltage determination data for determining the reference voltage according to the driving voltage of the phototransistor, and the load resistance determination data is slower than the phototransistor with a fast response speed. The load resistance to be used is determined to be smaller, and the control unit determines the load resistance to be used based on the load resistance determination data. The load resistance selected by the load resistance selection unit is connected to the phototransistor, the reference voltage is determined based on the reference voltage determination data, and the determined reference voltage is input to the APC circuit. It was decided.

  According to this configuration, the response speed of the mounted phototransistor is reduced as the response speed of the mounted phototransistor is improved by using the characteristic that the response speed is improved by lowering the resistance value of the load resistor that converts the current output from the phototransistor into voltage by light reception. Since the resistance value of the load resistor is lowered while changing the reference voltage, the response speed of the phototransistor in the APC light receiving circuit can be increased. Therefore, it becomes easy to follow the light quantity change of the light emitting element, and the stability of the light emission amount from the light emitting part is improved.

  Here, the load resistance determination data can be determined based on, for example, a result of measuring in advance a load resistance that can ensure a response speed of a certain level or more, regardless of variations in response speed of the mounted phototransistors. The reference voltage determination data can be determined based on a result of measuring in advance a reference voltage at which the amount of light emitted from the light emitting unit is constant at each drive voltage according to changes in the drive voltage or load resistance. The load resistance determination data is stored in the storage unit in the form of a data table, for example.

  According to a third aspect of the present invention, in the first or second aspect of the present invention, the drive voltage changing unit is a DC / DC converter. According to this configuration, the drive voltage of the phototransistor can be arbitrarily changed by the DC / DC converter, and the response speed of the phototransistor can be improved.

  According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the drive voltage changing unit includes a plurality of power supplies that output different voltages. According to this configuration, the driving voltage of the phototransistor can be arbitrarily changed by a plurality of power supplies, and the response speed of the phototransistor can be improved.

  According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the APC circuit is a differential amplifier, and amplifies a difference between an output voltage of the APC light receiving circuit and the reference voltage. . According to this configuration, since the current supplied to the light emitting unit is changed using the output voltage of the APC light receiving circuit that follows the change in the light emitting amount from the light emitting unit, the current is supplied if the light emitting amount of the light emitting unit decreases. If the current is increased and the light emission amount of the light emitting portion is increased, the current supplied can be reduced, and the light emission amount from the light emitting portion can be maintained constant.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus according to any one of the first to fifth aspects and the density of the formed image based on the measurement result of the density measuring apparatus. In the case where there is a deviation and an ideal density of the image, an image forming unit that adjusts the deviation to form an image is provided. According to this configuration, it is possible to adjust the density of the toner image using an accurate density measurement result of the density measuring device. Accordingly, it is possible to provide an image forming apparatus in which the density of the formed toner image is not shifted and the image quality is maintained.

  As described above, the concentration measuring device of the present invention can improve the response speed without being influenced by variations in the response speed of the mounted phototransistor, so that the amount of light emitted from the light emitting unit does not become unstable. The amount of light emitted from the light emitting unit can be kept constant.

It is a front model sectional view showing an example of composition of a printer concerning an embodiment. 2 is an enlarged schematic cross-sectional view illustrating an example of a configuration of an image forming unit according to an embodiment. FIG. It is a block diagram showing an example of a hardware configuration of a printer including a density measuring device according to an embodiment. (A) is explanatory drawing which shows an example of the density | concentration measuring apparatus which concerns on embodiment, (b) is an example of the pattern image formed on the photoreceptor drum or the intermediate transfer belt. FIG. 5 is an equivalent circuit diagram around the phototransistor for explaining the response speed of the phototransistor according to the embodiment and measures for improving the response speed. It is a circuit diagram of an example of an APC circuit, an APC light receiving circuit, and a light emitting unit according to the embodiment. It is explanatory drawing which shows an example of the differential amplification of the APC circuit which concerns on embodiment. It is explanatory drawing which shows an example of the data table as reference voltage determination data, drive voltage determination data, and load resistance determination data corresponding to the response speed data according to the embodiment. It is a flowchart which shows an example of the control flow in the density | concentration measurement of the density | concentration measuring apparatus which concerns on embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. However, each element such as the configuration described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

(Schematic configuration of image forming apparatus)
First, the structure and operation of a printer 2 (corresponding to an image forming apparatus) including the density measuring apparatus 1 according to the present embodiment will be described with reference to FIGS. FIG. 1 is a front model cross-sectional view showing an example of the configuration of a printer 2 according to an embodiment of the present invention. FIG. 2 is an enlarged schematic cross-sectional view showing an example of the configuration of the image forming unit 50 according to the embodiment of the present invention.

  As shown in FIG. 1, the printer 2 of the present embodiment has an operation panel 3 in front of the front, inside of which a paper feed unit 4 a, a conveyance path 4 b, an image forming unit 5 a, a fixing unit 5 b, and an intermediate transfer unit 6. As a main component.

  First, the operation panel 3 (illustrated by a broken line) displays a menu screen, and is provided with a liquid crystal display unit 31 on which a function setting input can be performed by a touch panel, and various setting keys. Therefore, the user can input setting of operation of the printer 2 through the operation panel 3.

  The paper feed unit 4a (in this embodiment, two of 4a1 and 4a2) is arranged at the lowermost part in the main body, and accommodates various sizes of paper such as copy paper. Each paper feed unit 4a feeds paper one by one to the transport path 4b during printing. The transport path 4b is a path for transporting paper from the paper feed unit 4a to the discharge tray 41 (the transport direction is indicated by broken line arrows in FIG. 1). The conveyance path 4b is provided with a pair of conveyance rollers 43 and 44 that are connected to a guide plate 42 for guiding the paper and a drive mechanism (not shown) such as a motor and are driven to rotate. A registration roller pair 45 is provided below the secondary transfer roller 67 to allow the sheet to enter the nip between the secondary transfer roller 67 and the intermediate transfer belt 65 in a timely manner.

  Next, the image forming unit 5a will be described with reference to FIGS. As shown in FIG. 1, the image forming unit 5 a is provided above the paper feeding unit 4 a and below the intermediate transfer unit 6. The image forming section 5a is arranged in parallel from the left side of FIG. 1 in the order of a black image forming unit 50K, a yellow image forming unit 50Y, a magenta image forming unit 50M, and a cyan image forming unit 50C. The plurality of image forming units 50 and an exposure unit 51 that scans and exposes the plurality of photosensitive drums 52 with laser light below the plurality of image forming units 50. The image forming units 50 </ b> K to 50 </ b> C are arranged in parallel near the intermediate transfer belt 65. Here, although the color of the toner to be used is different, the image forming units 50K to 50C have the same structure, and unless otherwise described below, “K”, “Y”, “M”, and “C”. Symbols are omitted, and the same symbols are used for common members.

  As shown in FIG. 2, each image forming unit 50 includes a photosensitive drum 52 that carries a toner image on its peripheral surface, a charging unit 53, a developing unit 54, a cleaning unit 55, and the like. Then, based on image data received from the user terminal 100 or the like, the exposure unit 51 forms an electrostatic latent image on each photosensitive drum 52, and each developing unit 54 generates a visible image (toner image). ) To develop.

  The photosensitive drum 52 is a cylindrical member in which a photosensitive layer is provided on the outer peripheral surface of a conductive substrate such as aluminum, and carries a toner image on the surface thereof. The charging unit 53 charges the surface of the photosensitive drum 52 to a predetermined potential. The charging unit 53 of the present embodiment is a corona discharger that discharges and charges by applying a high voltage (large absolute value) by a high voltage applying unit 53a (see FIG. 3) using the discharge wire W as an electrode. The charging may be performed with a roller, a brush, or the like. The exposure unit 51 turns on / off a semiconductor laser device (not shown) according to the image data, irradiates a laser beam according to the image data to be formed, and scans and exposes the charged photosensitive drum 52. For example, an LED unit on the array may be employed as the exposure unit 51.

  The developing unit 54 stores toner and charges the toner to a predetermined potential. Further, the developing unit 54 is provided with a developing roller 54a for carrying toner. During development, a predetermined voltage is applied to the developing roller 54a to cause the toner to fly and supply the toner to the electrostatic latent image. As a result, the electrostatic latent image is developed as a toner image. The cleaning unit 55 includes a blade 55 a and a rubbing roller 55 b that are in contact with each other along the axial direction of the photoconductive drum 52. The cleaning unit 55 rubs and polishes the photoconductive drum 52 and adheres to residual toner and the photoconductive drum 52. Moisture, charged products, etc. are collected and removed.

  Next, returning to FIG. 1, the intermediate transfer portion 6 will be described. The intermediate transfer portion 6 is a portion that primarily transfers the toner image from each photosensitive drum 52 and performs secondary transfer onto the paper. The intermediate transfer unit 6 includes a driving roller 61, two driven rollers 62 and 63, four primary transfer rollers 64, an endless intermediate transfer belt 65 stretched around these plural rollers, and belt cleaning. The apparatus 66, the secondary transfer roller 67, and the like. The drive roller 61 is disposed opposite to the secondary transfer roller 67 and is rotationally driven by connection of a drive mechanism (not shown) composed of a motor, a gear, and the like.

  The intermediate transfer belt 65 rotates in the clockwise direction in FIG. Each primary transfer roller 64 is disposed to face each photosensitive drum 52 so as to sandwich the intermediate transfer belt 65 therebetween. The belt cleaning device 66 is provided at the right end in FIG. 1 and removes and collects toner remaining on the surface of the intermediate transfer belt 65 after the secondary transfer. The secondary transfer roller 67 faces the drive roller 61 and presses against the intermediate transfer belt 65 in the direction of the drive roller 61.

  Here, in the toner image transfer process, each primary transfer roller 64 is applied with a predetermined voltage, and the respective color toner images carried by the respective photosensitive drums 52 are superimposed on the surface of the intermediate transfer belt 65 in time. And primary transfer is performed. Then, the registration roller pair 45 conveys the sheet at the same timing, and the toner image and the sheet on the intermediate transfer belt 65 enter the nip between the intermediate transfer belt 65 and the secondary transfer roller 67 at the same time. At this time, a predetermined voltage is applied to the secondary transfer roller 67, and the toner image is secondarily transferred from the intermediate transfer belt 65 to the sheet.

  The fixing unit 5b includes a heating roller 56 containing a heating element and a pressure roller 57 that is in pressure contact with the heating roller 56. The fixing unit 5b is disposed above the secondary transfer roller 67, and fixes the second-transferred toner image on the sheet. Let The sheet after the secondary transfer enters the nip between both rollers, and the toner image is fixed on the sheet by heating and pressing. Then, the sheet after fixing is discharged to the discharge tray 41, and the image formation is completed.

(Hardware configuration of printer 2)
Next, an example of a basic hardware configuration of the printer 2 including the density measuring apparatus 1 according to the embodiment of the present invention will be described based on FIG. FIG. 3 is a block diagram illustrating an example of a hardware configuration of the printer 2 including the density measuring apparatus 1 according to the embodiment of the present invention.

  As shown in FIG. 3, a control unit 7 is provided in the apparatus for controlling the operation of each unit and each member of the printer 2 according to the present embodiment. The control unit 7 is connected to each unit such as the image forming unit 5a and the intermediate transfer unit 6 of the printer 2, and performs various controls such as rotation, charging, and development of the photosensitive drum 52, for example. The control unit 7 controls the operation of the apparatus, and detects the density of the toner image on the measurement target based on the output values of the amplification units 74A and 74B.

  For example, the control unit 7 is provided with a CPU 71, a storage unit 72, and the like. The CPU 71 is a central processing unit that issues a control signal to each unit of the printer 2 based on a control program and data, receives signals from each unit, and performs various calculations. The storage unit 72 is configured by combining volatile and nonvolatile storage devices such as ROM, RAM, HDD, and flash ROM. The storage unit 72 stores data such as control programs, control data, image data, and setting data.

  In particular, the present invention relates to the present invention. Although details will be described later, the storage unit 72 determines the response speed data indicating the response speed of the APC phototransistor 9 and the drive voltage of the phototransistor 9 according to the response speed data. Drive voltage determination data and reference voltage determination data for determining a reference voltage according to the determined drive voltage of the phototransistor 9 so that the light emission amount of the light emitting unit 81 is constant are stored.

  Next, a basic configuration of the concentration measuring apparatus 1 according to the present embodiment (enclosed line with a two-dot chain line in FIG. 3) will be described. A plurality of density measuring apparatuses 1 can be provided to face the respective photosensitive drums 52 and the intermediate transfer belt 65. The density measuring apparatus 1 is connected to the control unit 7, has a light emitting element, and is directed toward a measurement target on which a toner image is formed. The sensor unit 8 (sensor head) includes a light emitting unit 81 that emits light and a light receiving unit 83 (83A, 83B) that receives reflected light from a measurement target and changes an output current or voltage according to the amount of received light. 4 (a)). Further, the concentration measuring apparatus 1 includes a control unit 7 (CPU 71, storage unit 72), a temperature sensor S1 connected to the control unit 7 and used for detecting the ambient temperature of the sensor unit 8, and the like. With these configurations, the density measuring apparatus 1 measures the density of the toner image according to the amount of light received by each light receiving unit 83.

  The control unit 7 also functions as the control unit 7 and the storage unit 72 of the density measuring device 1 built in the printer 2. The amplified output of each light receiving unit 83 is input, and the output value of each light receiving unit 83 is input. From this, the density of the toner image on the measurement object (photosensitive drum 52 and intermediate transfer belt 65) is detected. A control circuit and a memory dedicated to the concentration measuring device 1 may be provided.

  The temperature sensor S1 provided in the apparatus is used to correct the density measured according to the temperature change, and usually changes the image forming conditions (density adjustment, etc.) according to the environmental temperature change. Includes one or a plurality of temperature sensors S1, and the temperature sensor S1 of this embodiment is shared with the one for controlling the printer 2. And the control part 7 is connected with temperature sensor S1, and recognizes the ambient temperature of each sensor part 8 with the output voltage value of temperature sensor S1. In this embodiment, an example is shown in which one temperature sensor S1 is provided in the vicinity of the drive roller 61 (see FIG. 1). For example, a plurality of temperature sensors S1 may be provided adjacent to each sensor unit 8. good.

  In FIG. 3, only one printer is shown for convenience, but the printer 2 is connected to one or a plurality of user terminals 100 (for example, personal computers) via a network or the like. Accordingly, the printer 2 can perform printing (printer 2 function) upon receiving transmission of image data and the like from the user terminal 100.

  The printer 2 of this embodiment forms a pattern image P1 for density adjustment (details will be described later with reference to FIG. 4B), and the density measuring device 1 reads the pattern image P1 as a toner image, and density Measure. When there is a deviation from the ideal density, the control unit 7 instructs the image forming unit 5a to perform density adjustment.

  Specifically, the control unit 7 actually adjusts the transfer bias applied to the development bias application unit 54b for adjusting and controlling the development bias applied to each development roller 54a, the primary transfer roller 64, and the secondary transfer roller 67. Then, a bias increase / decrease instruction is issued to the transfer bias applying unit 64a to be controlled. By this instruction, the toner flying amount, transfer efficiency, and the like are adjusted, and the density is adjusted. That is, the printer 2 adjusts the deviation when there is a deviation between the density of the formed image and the ideal density of the image to be formed based on the measurement result of the density measuring apparatus 1 and the density measuring apparatus 1. An image forming unit 5a for forming an image is provided.

(Reading with concentration measuring device 1)
Next, the configuration of the density measuring apparatus 1 and the reading of the toner image (pattern image P1) according to the embodiment of the present invention will be described with reference to FIGS. FIG. 4A is an explanatory diagram showing an example of the density measuring apparatus 1 according to the embodiment of the present invention, and FIG. 4B shows a pattern image P1 formed on the photosensitive drum 52 or the intermediate transfer belt 65. It is an example. The image data of the pattern image P1 is stored in the storage unit 72, and is read out and used as necessary.

  The density measuring device 1 reads the toner image (here, the pattern image P1) formed on the photosensitive drum 52 and the intermediate transfer belt 65, and detects the density of the toner image. For this detection, a sensor unit 8 (sensor head) is provided to face each photosensitive drum 52 and the intermediate transfer belt 65 (see FIG. 1). The density measuring apparatus 1 reads the pattern image P1 and measures the toner density in the image.

  Therefore, a configuration for reading the sensor unit 8 and the like of the concentration measuring apparatus 1 will be described with reference to FIG. The sensor unit 8 of the concentration measuring apparatus 1 according to the present embodiment (the enclosed portion in the two-dot chain line in FIG. 4A) includes a light emitting unit 81, two light receiving units 83 (83A and 83B), and 2 made of glass, for example. The polarizing plate 86 (86A, 86B) is provided.

  The light emitting unit 81 emits light toward the surface of the photosensitive drum 52 or the intermediate transfer belt 65 as a measurement target on which the toner image (pattern image P1) is formed, and for example, a light emitting element such as an LED and a light emitting circuit 82. Can be configured. In this embodiment, in order to avoid the influence of ambient light, the light emitting element includes an LED 81a for infrared light emission. The light emitting circuit 82 is a circuit for driving the LED 81a.

  On the other hand, each light receiving unit 83 includes a light receiving element that receives reflected light from a measurement target and changes an output current or voltage according to the amount of received light such as a photodiode, and light receiving circuits 85A and 85B. In the present embodiment, photodiodes 84A and 84B for receiving infrared light are used as the light receiving elements corresponding to the LEDs 81a. The light receiving circuit 85 is configured by a circuit or the like that applies a bias to the photodiodes 84A and 84B, and converts a light output current due to light reception into a voltage by a resistor or the like.

  Each of the two polarizing plates 86 of the sensor unit 8 transmits the P wave, reflects the S wave, and emits the light irradiated from the light emitting unit 81 to the measurement object and the light received by each light receiving unit 83. The light emitted from the light emitting unit 81 is polarized by being separated into P wave and S wave.

  And as shown to Fig.4 (a), the amplification part 74 (74A, 74B) which amplifies the output of each light receiving part 83 is connected to each light receiving part 83, respectively. Each amplifying unit 74 is a circuit that amplifies the output voltage of each light receiving unit 83 and outputs it to the analog-digital conversion ports PT1 and PT2 of the CPU 71 so that it can be used by the CPU 71 (control unit 7). Thereby, the CPU 71 recognizes the voltage value output from each amplification unit 74.

  Next, concentration detection of the concentration measuring apparatus 1 will be described. The light emitted from the light emitting unit 81 is converted into a P wave (light parallel to the incident surface) and an S wave (perpendicular to the incident surface) by the polarizing plate 86A provided on the optical path between the light emitting unit 81 and the measurement target. Only the P wave reaches the photosensitive drum 52 and the intermediate transfer belt 65. The light applied to the toner image on the photosensitive drum 52 and the like is reflected again while having P wave and S wave components, and a polarizing plate 86B is provided on the optical path of the reflected light, and the reflected light is converted into P wave and S wave. The components are separated again, and the respective components are received by the light receiving portions 83A (for S-wave reflected light) and 83B (for P-wave reflected light).

  Here, taking the density measurement of the toner image on the photosensitive drum 52 as an example, since the surface of the photosensitive drum 52 has a photosensitive layer such as silicon having a high glossiness, the reflected light is parallel to the object surface. It tends to be biased in the direction. Accordingly, the P wave reflected from the surface of the photosensitive drum 52 is not disturbed in polarization, passes through the polarizing plate 86B, and is received by the light receiving unit 83B. The intermediate transfer belt 65 is also provided with a release layer or the like, and the ratio of the P wave and the S wave in the reflected light is different from that of the toner. On the other hand, the P wave applied to the dielectric toner is disturbed in polarization, becomes reflected light including P wave and S wave, is separated by the polarizing plate 86B, and is received by each light receiving unit 83.

  Therefore, when the toner image is irradiated with light, the ratio of the area where the toner adheres to the area of the surface of the photosensitive drum 52 where the light emitting unit 81 irradiates the light, and the P wave received by each light receiving unit 83. The ratio of the received light amount and the received light amount of the S wave received by the light receiving unit 83A changes. Therefore, when the toner image is read, the output of each light receiving unit 83 is different in the ratio depending on the density of the toner image. For example, the higher the density of the toner image (the higher the toner distribution ratio), the smaller the P wave component from the photosensitive drum 52 and the smaller the output of the light receiving unit 83B.

  As described above, there is a corresponding relationship between the density of the toner image and the output ratio of each light receiving unit 83, and the relationship is acquired in advance through experiments or the like. For example, the density of the toner image for each color is stored in the storage unit 72. The correspondence with the output ratio is stored as data in a table. During density measurement (detection), the CPU 71 (see FIGS. 3 and 4) disposed in the control unit 7 refers to the table and detects and measures the density of the toner image from the amplified output of each light receiving unit 83. To do.

  Here, as an example of a toner image read by the density measuring apparatus 1, as shown in FIG. 4B, a plurality of patches having different densities and different colors are formed on the photosensitive drums 52 and the intermediate transfer belt 65. A pattern image P1 for density adjustment (image quality confirmation) for confirming whether there is a density deviation is read from the density of each configured patch to be formed. The storage unit 72 stores image data of the pattern image P1.

  The pattern image P1 shown in FIG. 4B is formed, for example, at a substantially central position in the main scanning direction of the photosensitive drum 52 or the intermediate transfer belt 65 and extending in the rotation direction (sub-scanning direction). And the sensor part 8 is arranged in the position which reads this image. The formation position of the pattern image P1 and the installation position of the sensor unit 8 are not limited to the center position and can be set as appropriate in the main scanning direction.

  For example, as shown in FIGS. 1 and 2, the sensor unit 8 of the density measuring apparatus 1 can be provided between each developing unit 54 and the intermediate transfer belt 65. Further, when the intermediate transfer unit 6 is provided as in the printer 2 of the present embodiment, the density of the toner image can be confirmed by reading the pattern image P1 transferred to the intermediate transfer belt 65, as shown in FIG. The cost may be reduced by providing one sensor unit 8 between the drive roller 61 and the image forming unit 50K (in FIG. 1, the case where both are provided is shown).

(Configuration of automatic light output control)
Next, a configuration for automatic light output control (hereinafter referred to as “APC”) of the concentration measuring apparatus 1 according to the embodiment of the present invention will be described with reference to FIG. The configuration for APC (Auto Power Control) of the concentration measuring apparatus 1 of the present embodiment is for maintaining the light emission amount of the LED 81a constant. The APC light receiving circuit 91, the APC circuit 93, the DC / DC converter 94 (drive) Equivalent to a voltage changing unit). Then, the CPU 71 controls these operations. In place of the CPU 71, an APC controller may be provided.

  First, the APC light receiving circuit 91 includes a phototransistor 9 that receives a part of the emitted light of the LED 81a, monitors the light emission amount of the LED 81a, and outputs a photocurrent according to the light reception amount. The phototransistor 9 receives S-wave component light reflected by the polarizing plate 86A, light not irradiated on the photosensitive drum 52 or the intermediate transfer belt 65, and the like, and outputs a photocurrent. The photocurrent is converted into a voltage by the load resistor RL. Although details will be described later, the APC light receiving circuit 91 of the present embodiment includes a plurality of load resistors RL (see FIG. 6), and a load resistor selection unit based on an instruction (load signal selection signal) from the port PT3 of the CPU 71. The load resistance RL used by 92 is selected.

  The APC circuit 93 receives the output of the APC light receiving circuit 91, compares this input voltage with the reference voltage from the digital-analog conversion port PT4 of the CPU 71, and the current supplied to the light emitting unit 81 by the difference. Determine and supply the quantity. As described above, the APC circuit 93 receives the output of the APC light receiving circuit 91 and performs feedback control so that the light emission amount of the light emitting unit 81 is always equal to or close to the set value.

  The DC / DC converter 94 can be constituted by, for example, a chopper type switching power supply, and applies a driving voltage to the phototransistor 9. The DC / DC converter 94 can change the drive voltage of the phototransistor 9 in order to improve the response speed of the phototransistor 9, and the CPU 71 inputs a signal from the port PT5 to the DC / DC converter 94. The level of the supply voltage of the DC / DC converter 94 is controlled.

(Response speed of phototransistor 9)
Next, when the response speed of the phototransistor 9 is slow, the APC reaction may be delayed and the amount of light emitted from the light emitting portion 81 may become unstable. However, the response speed of the phototransistor 9 is higher than that of a photodiode or the like. An example of a slow factor and a response speed improvement measure will be described with reference to FIG. FIG. 5 is an equivalent circuit diagram around the phototransistor 9 for explaining the response speed of the phototransistor 9 according to the embodiment of the present invention and measures for improving the response speed. FIG. 5 illustrates a case where an output voltage is obtained by connecting one load resistor RL to the emitter of the phototransistor 9.

  First, basically, the time required for rising when the phototransistor 9 is turned on and the time required for falling when the phototransistor 9 is turned off become longer as the collector voltage becomes higher. Therefore, the higher the drive voltage of the phototransistor 9, the slower the response speed. That is, the response speed of the phototransistor 9 increases as the driving voltage is lowered.

  Next, FIG. 5 describes the relationship between the response speed and the load resistance RL. In general, it has been empirically obtained that the smaller the resistance value of the load resistor RL, the faster the response speed of the phototransistor 9. An example of the factor will be described with reference to FIG.

  First, FIG. 5A is an equivalent circuit around the phototransistor 9 when the LED is turned off. In general, the phototransistor 9 has a base-emitter capacitance Cbe. Even when the LED is turned off, a current flows into the base due to discharge from the base-emitter capacitance Cbe, and the current gradually decreases. The smaller the load current during conduction, the easier it is for the phototransistor 9 to continue conducting even if the base current is small, and the time required for discharge becomes longer. Therefore, it takes a long time to enter the OFF state.

  Next, FIG. 5B will be described. FIG. 5B is an equivalent circuit around the phototransistor 9 at the time of falling. In general, the phototransistor 9 also has a capacitor Ccb between the collector and the base, and when the collector potential starts to rise, charging between the collector and the base starts. The current at the time of charging flows into the base, negative feedback is applied from the collector to the base, and the time required for falling becomes longer. The smaller the load current during conduction, the longer the time required for charging the collector-base capacitor Ccb. From these factors, it can be seen that the delay in response speed due to the capacitance between the base and the emitter or between the collector and the base can be reduced by increasing the current flowing through the load resistance RL, that is, by reducing the load resistance RL. .

(APC control)
Next, APC control of the concentration measuring apparatus 1 according to the embodiment of the present invention will be described based on FIGS. 6 and 7. FIG. 6 is a circuit diagram showing an example of the APC circuit 93, the APC light receiving circuit 91, and the light emitting unit 81 according to the embodiment of the present invention. FIG. 7 is an explanatory diagram showing an example of differential amplification of the APC circuit 93 according to the embodiment of the present invention.

  First, control for making the light amount of the LED 81a of the light emitting unit 81 of the present embodiment constant will be described. As shown in FIG. 6, the APC circuit 93 is provided with a differential amplifier 95 using an operational amplifier OP (IC chip). Further, a resistor R1 and a feedback resistor R2 as an output of the operational amplifier OP are connected between the negative terminal and the input voltage V1 to the negative terminal of the operational amplifier OP. Further, a resistor R3 is connected between the + terminal and the input voltage V2, and a resistor R4 is connected between the + terminal of the operational amplifier OP and the ground.

  The output Vo of the operational amplifier OP is connected to the light emitting unit 81. For example, the light emitting unit 81 is provided with an npn transistor Tr as a part of the light emitting circuit 82, and the output Vo of the operational amplifier OP is input to the base of the npn transistor Tr. The collector of the npn transistor Tr is connected to the resistor R5 and the power source Vcc, and the emitter is connected to the ground via the LED 81a.

  Further, as the APC light receiving circuit 91, a phototransistor 9, a plurality of load resistors RL (for example, five of RL1 to RL5, which may be two or four, or six or more), and a load resistor selection unit 92 are provided. An output voltage from the DC / DC converter 94 is applied between the collector of the phototransistor 9 and the ground. That is, the concentration measuring apparatus 1 includes a plurality of load resistors RL for converting the output current of the phototransistor 9 into a voltage, and a load resistor selection unit 92 that switches the load resistor RL to be used. The photocurrent output of the phototransistor 9 is converted into a voltage by the load resistor RL, and becomes the input voltage V1 of the operational amplifier OP.

  In the present embodiment, the load resistance RL can be changed to improve the response speed of the phototransistor 9. Then, the load resistance selection unit 92 performs switching so as to use the selected load resistance RL. For example, the load resistance selection unit 92 can be configured by a multiplexer that receives the emitter of the phototransistor 9 as an input, selects each load resistance RL (RL1 to RL5) according to an instruction from the CPU 71, and outputs it as an output destination. Further, a switching element (for example, a transistor, not shown) may be connected to each load resistor RL, and the CPU 71 may control conduction by each switching element.

Further, a reference voltage is input from the CPU 71 as the input voltage V2 to the + terminal of the operational amplifier OP. And, if the differential amplifier 95 using the operational amplifier OP has resistance values R1 = R3 and R2 = R4, the output voltage Vo is
Vo = R2 / R1 (V2-V1)
It is known that As described above, the APC circuit 93 is the differential amplifier 95 and amplifies the difference between the output voltage of the APC light receiving circuit 91 and the reference voltage. In the present embodiment, the amplification factor can be adjusted by adjusting the resistance values of the resistors R1 to R4 as shown in the equation.

  Therefore, the differential amplifier 95 amplifies the difference between the reference voltage and the output voltage of the phototransistor 9 with an amplification factor determined by R2 and R1, and inputs the amplified voltage to the base of the npn transistor Tr. Therefore, an example of a concept when the light amount is made constant by the differential amplifier 95 will be described with reference to FIG.

  For example, as shown in FIG. 7, the reference voltage for reference is output from the CPU 71 to the + terminal of the operational amplifier OP at a constant value. For example, the reference voltage is basically set larger than the output voltage of the phototransistor 9. FIG. 7 shows the difference between the output voltage of the phototransistor 9 and the reference voltage when the amount of light is appropriate as Δ1.

  If the light emission amount of the LED 81a increases due to a decrease in temperature or the like, or the light emission amount increases due to APC control, the light reception amount of the phototransistor 9 also increases, and the output voltage of the phototransistor 9 also increases. Then, as shown by Δ2 in FIG. 7, the difference between the reference voltage and the output voltage of the phototransistor 9 is reduced, and the output voltage Vo of the differential amplifier 95 is also reduced. As a result, the amount of current supplied to the LED 81a is reduced. The light emission amount of the LED 81a is suppressed.

  On the other hand, if the light emission amount of the LED 81a decreases due to a rise in temperature or the light emission amount too much due to APC control, the light reception amount of the phototransistor 9 also decreases, and the output voltage of the phototransistor 9 also decreases. Then, as indicated by Δ3 in FIG. 7, the difference between the reference voltage and the output voltage of the phototransistor 9 increases, and the output voltage Vo of the differential amplifier 95 also increases, and as a result, the amount of current supplied to the LED 81a increases. The amount of light emitted from the LED 81a increases. Thus, the light emission amount of the LED 81a is controlled to be constant based on the reference voltage.

(Response speed improvement control of phototransistor 9)
Next, the response speed improvement control of the phototransistor 9 mounted on the concentration measuring apparatus 1 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 8 is an explanatory diagram showing an example of a data table DT as reference voltage determination data, drive voltage determination data, and load resistance determination data corresponding to the response speed data according to the embodiment of the present invention.

  First, in the APC control, the light emission amount is kept constant while increasing or decreasing the amount of current flowing to the LED 81a (while increasing or decreasing the voltage applied to the LED 81a). If the response speed of the phototransistor 9 is slow, the light emission amount by the APC function There are cases where the light emission of the LED 81a becomes unstable, for example, the phototransistor 9 cannot follow the increase / decrease. Therefore, in the concentration measuring apparatus 1 of the present embodiment, even if there is a variation (individual difference) in the response speed of the phototransistor 9, by changing the power supply voltage applied to the phototransistor 9 or the load resistance RL, at least Ensure a certain response speed.

  Therefore, response speed data indicating the response speed of the phototransistor 9 mounted in the concentration measuring apparatus 1 is stored in the storage unit 72 shown in FIG. This is because the response speed of the phototransistor 9 varies among products of the same type, and control is performed to improve the response speed while responding to this variation.

  The response speed data is determined based on the result of individually measuring the response speed of the phototransistor 9 in advance. For example, a certain voltage is applied to the phototransistor 9, a predetermined amount of light is irradiated for a certain period of time, and thereafter, from a certain starting point (for example, at the start of irradiation or at the end of irradiation), the phototransistor 9 is irradiated. It may be determined based on the length of time until is turned off. In addition, for example, the response speed obtained by statistically quantifying the response speed according to the length of the response time may be used as the response speed data, or the inverse of the actually measured response time may be used as the response speed data. That is, any data indicating the response speed may be used based on a certain standard.

  In the APC control, based on the response speed data stored in the storage unit 72, based on the data table DT similarly stored in the storage unit 72 as shown in FIG. The voltage and load resistance RL are determined.

  First, X1 to X9 in the response speed data column in the data table DT indicate threshold values in the response speed data. Based on this threshold, the drive voltage of the phototransistor 9 is determined. Although there are various ways of defining the data table DT, in this description, a case will be described in which the response speed increases as X9 approaches X1. And the value of x in the response speed data column indicates the numerical value of the response speed data stored in the storage unit 72. In the data table DT of this example shown in FIG. Indicates that it is fast.

  Then, the drive voltage of the phototransistor 9 is determined according to the response speed data and the threshold value. Here, the drive voltage column shown in FIG. 8 is the drive voltage determination data, and the magnitude relationship is Va> Vb> Vc> Vd> Ve> Vf> Vg> Vh> Vi> Vj. Therefore, as the phototransistor 9 has a slower response speed, the drive voltage of the phototransistor 9 is set lower and the response speed is increased. That is, the drive voltage determination data is determined such that the drive voltage of the phototransistor 9 is lower in the phototransistor 9 that is slower than the phototransistor 9 that has a fast response speed. The drive voltages Va to Vj are actually measured so that, for example, when the phototransistor 9 is actually driven at each voltage value, for example, at least exceeds a predetermined response speed or the threshold value X1 with the fastest response speed. Can be determined.

  Specifically, the CPU 71 refers to the data table DT, determines the drive voltage of the phototransistor 9, and gives an instruction to the DC / DC converter 94 to output the determined drive voltage. As a result, the determined drive voltage is applied to the phototransistor 9.

  When the drive voltage of the phototransistor 9 changes, the reference voltage for making the light emission amount of the LED 81a constant also changes. Therefore, the drive voltage of the phototransistor 9 and the magnitude of the load resistance RL (details will be described later). In addition, the reference voltage is also changed. This reference voltage is also determined with reference to the data table DT. Here, the reference voltage column shown in FIG. 7 is reference voltage determination data, and the magnitude relationship is Vk> Vl> Vm> Vn> Vp> Vq> Vr> Vs> Vt> Vu. Accordingly, the phototransistor 9 with a slower response speed has a lower drive voltage and the output voltage of the phototransistor 9 tends to decrease, so the reference voltage also decreases. Thereby, even if a drive voltage changes, the light emission amount of the light emission part 81 is maintained constant. Further, for example, the reference voltages Vk to Vu are applied with various drive voltages, irradiate the phototransistor 9 with a light amount when the light emission amount is appropriate, and the difference between the output voltage of the phototransistor 9 and the reference voltage at that time is a constant value. The result measured in advance can be determined as the reference voltage.

  As described above, the control unit 7 determines the drive voltage of the phototransistor 9 based on the drive voltage determination data, causes the DC / DC converter 94 to apply the determined drive voltage to the phototransistor 9, and determines the reference voltage. The reference voltage is determined based on the data for use, and the determined reference voltage is input to the APC circuit 93.

  In the following, the case of changing the load resistance RL will be described. However, if the response speed of the phototransistor 9 can be ensured so that the amount of light emission does not become unstable only by changing the power supply voltage, the load resistance RL is changed. It is not necessary to provide a plurality of load resistance selection units 92.

  As described above, since the response speed is improved even if the load resistance RL is lowered, the load resistance RL is increased as the response speed is slower based on the load resistance determination data shown in the load resistance RL column in the data table DT of FIG. Reduce the resistance value. In this example, the magnitude relationship between the resistance values is RL1> RL2> RL3> RL4> RL5. Specifically, the CPU 71 refers to the data table DT and gives an instruction to change the load resistance RL according to the response speed data to the load resistance selection unit 92. As a result, the response speed can be further increased. Further, when the resistance value of the load resistor RL is lowered, the output voltage from the phototransistor 9 is lowered. Therefore, the reference voltage is measured in advance in the state of each driving voltage of the phototransistor 9 and the load resistor RL to be used. It is determined from.

  Therefore, when the response speed of the phototransistor 9 is also improved using the load resistance RL, the storage unit 72 uses the load resistance determination data for determining the load resistance RL to be used according to the response speed data. And the reference voltage determination data for determining the reference voltage according to the determined load resistance RL and the driving voltage of the phototransistor 9 so that the light emission amount of the light emitting unit 81 is constant, and the load resistance determination The data for use is determined such that the phototransistor 9 having a slower response speed is smaller than the phototransistor 9 having a faster response speed, and the control unit 7 uses the load resistor RL based on the data for determining the load resistance. The load resistance RL is determined, and the load resistance RL determined by the load resistance selection unit 92 is connected to the phototransistor 9 and based on the reference voltage determination data. Determining a reference voltage, and inputs the determined reference voltage to the APC circuit 93.

  Next, an example of control in concentration measurement of the concentration measurement apparatus 1 according to the embodiment of the present invention will be described based on FIG. FIG. 9 is a flowchart showing an example of a control flow in the concentration measurement of the concentration measurement apparatus 1 according to the embodiment of the present invention.

  The start shown in FIG. 9 is a predetermined execution timing of concentration measurement. For example, the predetermined timing is determined when the printer 2 is turned on, when the operation panel 3 instructs density measurement and adjustment using the pattern image P1, or after the previous density measurement, for example, a certain number of sheets (for example, several hundred to several thousand). Sheet), it can be set as appropriate, for example, in the case of automatic density adjustment executed when printing, or when a certain time has passed since the printer 2 was not used.

  Thereafter, the control unit 7 reads response speed data from the storage unit 72 (step # 1). Next, the control unit 7 refers to the data table DT in the storage unit 72 (step # 2). Then, the control unit 7 determines the drive voltage, reference voltage, and load resistance RL to be used for the phototransistor 9 (step # 3). Thereafter, the CPU 71 of the control unit 7 controls the DC / DC converter 94 and the load resistance selection unit 92 based on the determined drive voltage, reference voltage, and load resistance RL at the ports PT3 to PT5, and causes the APC circuit 93 to A reference voltage is input (step # 4).

  Next, the control unit 7 detects the density of the toner image on the measurement target while maintaining the light emission amount of the light emitting unit 81 by APC (step # 5). Next, the control unit 7 confirms whether all the density detections are completed (step # 6). For example, it is confirmed whether the density detection of all the patches of the pattern image P1 is completed. If all the density detections are not completed (No in Step # 6), for example, the process returns to Step # 1 (or may be Step # 5). If completed (Yes in Step # 6), the density measurement is performed. Control is complete (end).

  Then, if there is a deviation from the ideal density from the acquired density measurement result, the control unit 7 adjusts the density by adjusting various biases of the image forming unit 5a, etc., and the density of the image to be formed Maintain a state where is appropriate.

  As described above, according to the configuration of the present invention, the phototransistor 9 uses the characteristic that the response speed is improved when the drive voltage is lowered. Since the drive voltage is lowered while changing the reference voltage to cope with the output change, the response speed of the phototransistor 9 in the APC light receiving circuit 91 can be increased. Therefore, it becomes easy to follow the light amount change of the light emitting element (LED 81a), and the stability of the light emission amount from the light emitting unit 81 is improved. Since the light quantity is constant and stable, accurate concentration measurement can be performed.

  Further, the response speed is improved by lowering the resistance value of the load resistor RL that converts the current output from the phototransistor 9 into a voltage by light reception. The lower the response speed of the mounted phototransistor 9 is, the lower the reference speed is. Since the resistance value of the load resistor RL is lowered while changing the voltage, the response speed of the phototransistor 9 can be increased. Therefore, it becomes easy to follow the light quantity change of the light emitting element, and the stability of the light emission amount from the light emitting unit 81 is improved.

  Further, since the supply current to the light emitting unit 81 is changed using the output voltage of the APC light receiving circuit 91 that follows the change in the light emission amount from the light emitting unit 81, the supply current is reduced if the light emission amount of the light emitting unit 81 decreases. If the light emission amount of the light emitting unit 81 is increased, the supply current can be reduced, and the light emission amount of the light emitting unit 81 can be kept constant. Further, the density adjustment of the toner image can be performed using the accurate density measurement result of the density measuring apparatus 1. Therefore, it is possible to provide an image forming apparatus (for example, the printer 2) in which the density of the toner image is not shifted and the image quality is maintained.

  Next, another embodiment will be described. In the above embodiment, the differential amplifier 95 is exemplified as the differential amplifier 95 using one IC of the operational amplifier OP. However, for example, it may be configured by an instrumentation amplifier using a plurality of operational amplifiers OP. . Further, instead of the operational amplifier OP of the IC, for example, a differential amplifier using a transistor such as an FET may be used.

  In the above embodiment, the response speed data is shown as individual data numerical values for each phototransistor 9, but the distribution of the response speed data of the phototransistor 9 is shown as rank information divided into rank ranges. Also good.

  In the above embodiment, the DC / DC converter 94 is shown as a drive voltage changing unit to be applied to the phototransistor 9. However, for example, a power supply and a switch having different output voltages are prepared by a regulator or the like, and this is driven. The drive voltage may be changed by selecting the power source used by the CPU 71 while using the voltage changing unit. That is, the drive voltage changing unit may be composed of a plurality of power supplies that output different voltages. According to this configuration, the driving voltage of the phototransistor 9 can be arbitrarily changed by a plurality of power supplies, and the response speed of the phototransistor 9 can be improved.

  In addition to the control of the above embodiment, the temperature sensor provided in the printer 2 in response to the fact that the output voltage characteristic of the phototransistor 9 changes with temperature (generally, the output current increases as the temperature rises). For example, the data table DT shown in FIG. 8 is prepared for each detected temperature range by using S1, and the drive voltage, the reference voltage, and the load resistance RL to be used are determined according to the ambient temperature of the sensor unit 8. May be.

  In the above embodiment, the drive voltage and the reference voltage are determined as voltage values in the data table DT, but the coefficient for multiplying the drive voltage determination data and the reference voltage determination data by, for example, response speed data. The coefficient may be included in the data table DT, and the drive voltage and the reference voltage may be obtained by calculation by the CPU 71.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention can be used for a density measuring apparatus including an APC circuit and an image forming apparatus including the density measuring apparatus.

1 Density measuring device 2 Printer (image forming device)
5a Image forming unit 52 Photosensitive drum (measurement target)
65 Intermediate transfer belt (measurement object) 7 Control unit 72 Storage unit 81 Light emitting unit 81a LED (light emitting element) 83 (83A, 83B) Light receiving unit 9 Phototransistor 91 APC light receiving circuit 92 Load resistance selecting unit 93 APC circuit 94 DC / DC Converter (drive voltage changing unit) 95 Differential amplifier RL Load resistance (RL1, RL2, RL3, RL4, RL5)

Claims (6)

A light emitting unit having a light emitting element that emits light toward a measurement target on which a toner image is formed, and a light reception unit that receives reflected light from the measurement target and changes an output current or voltage according to the amount of received light A density measuring device that measures the density of a toner image according to the amount of light received by the light receiving unit.
An APC light receiving circuit having a phototransistor for monitoring the light emission amount of the light emitting element;
An APC circuit that receives an output of the APC light receiving circuit and determines a current to be supplied to the light emitting unit according to a difference from a reference voltage;
A control unit for inputting the reference voltage to the APC circuit;
A drive voltage changing unit for changing the drive voltage of the phototransistor;
Response speed data indicating the response speed of the phototransistor, drive voltage determination data for determining a drive voltage of the phototransistor according to the response speed data, and a light emission amount of the light emitting unit are constant. A storage unit for storing reference voltage determination data for determining the reference voltage according to the determined drive voltage of the phototransistor,
The drive voltage determination data is determined such that the drive voltage of the phototransistor is lower in the phototransistor that is slower than the phototransistor that has a fast response speed.
The control unit determines a drive voltage of the phototransistor based on the drive voltage determination data, causes the drive voltage change unit to apply the determined drive voltage to the phototransistor, and also supplies the reference voltage determination data. And determining the reference voltage and inputting the determined reference voltage to the APC circuit. A plurality of load resistors for converting the output current of the phototransistor into a voltage;
A load resistance selection section for switching the load resistance to be used;
The storage unit includes load resistance determination data for determining the load resistance to be used according to the response speed data, and the load resistance determined so that the light emission amount of the light emitting unit is constant. Storing reference voltage determining data for determining the reference voltage according to the driving voltage of the phototransistor;
The load resistance determination data is determined so that the phototransistor having a low response speed is smaller than the phototransistor having a fast response speed,
The control unit determines the load resistance to be used based on the load resistance determination data, connects the load resistance determined by the load resistance selection unit to the phototransistor, and uses the reference voltage determination data as the reference voltage determination data. 2. The concentration measuring apparatus according to claim 1, wherein the reference voltage is determined based on the determined reference voltage, and the determined reference voltage is input to the APC circuit.   The concentration measuring apparatus according to claim 1, wherein the drive voltage changing unit is a DC / DC converter.   The concentration measuring apparatus according to claim 1, wherein the drive voltage changing unit includes a plurality of power supplies that output different voltages.   The concentration measuring apparatus according to claim 1, wherein the APC circuit includes a differential amplifier, and amplifies a difference between an output voltage of the APC light receiving circuit and the reference voltage. The concentration measuring apparatus according to any one of claims 1 to 5,
Based on the measurement result of the density measuring device, when there is a deviation from the density of the formed image and the ideal density of the image to be formed, an image forming unit that adjusts the deviation to form an image;
An image forming apparatus comprising:

Images