Image forming apparatus

Abstract

To provide an image forming apparatus that can determine an adjustment value more quickly than in conventional light quantity adjustment processing.SOLUTION: A sensor substrate 7 of a printer 10 receives, with a phototransistor PTr, light emitted from a light-emitting diode LED to an endless belt 63 and reflected on the endless belt 63. A light quantity changing circuit 81 changes the quantity of light emitted from the light-emitting diode LED according to a control signal LED_PWM. A comparison circuit 82 outputs, to an ASIC 71, a comparison result signal SG indicating that a light signal level according to the quantity of light received by the phototransistor PTr exceeds a threshold level. The ASIC 71 sequentially outputs, to the light quantity changing circuit 81, the control signals LED_PWM each updated from an initial value IV by a search width W and determines an adjustment value on the basis of the comparison result signal SG (S2, S3, S4). The ASIC 71 executes S2 and the like, using the initial value IV and the search width W according to a deterioration state of the endless belt 63.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present application relates to an image forming apparatus equipped with a sensor having a light emitting portion that emits light toward a belt and a light receiving portion that receives light reflected from the belt. [Background technology]

[0002] Some image forming devices have multiple photosensitive drums arranged along a paper transport belt, and toner images are transferred sequentially from each photosensitive drum to the paper transported on the belt. In these image forming devices, techniques called registration and density correction are implemented to prevent misalignment of the transfer positions (color misalignment) between the photosensitive drums.

[0003] In image forming devices that employ technologies such as registration and density correction, a light emitting unit emits light onto a belt, while a light receiving unit receives the light reflected from the belt, and the light receiving unit outputs a light receiving signal according to the amount of light received. When performing registration or density correction, the image forming device forms a mark on the belt and corrects the transfer position misalignment and density by reading the difference in reflectance between the belt surface and the mark surface based on the light receiving signal from the light receiving unit.

[0004] The image forming apparatus disclosed in Patent Document 1 controls a light projecting unit (corresponding to a light emitting unit) with a light projecting control signal and outputs a PWM (Pulse Width Modulation) signal as the light projecting control signal. The image forming apparatus executes a light intensity adjustment process to determine the PWM value of the light projecting control signal used when performing registration and density correction. In the light intensity adjustment process, the image forming apparatus sequentially increases the PWM value by a predetermined amount starting from a predetermined value corresponding to a PWM value with a low light receiving signal level. The image forming apparatus then determines the PWM value at the stage when the light receiving signal level reaches a threshold level. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-256715 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional image forming devices perform a light intensity adjustment process to determine the PWM value at the stage when the light receiving signal level reaches the threshold level by sequentially increasing the PWM value, which is an adjustment value, by a predetermined amount. However, when the PWM value is increased by a predetermined amount, there is a problem in that it takes a long time to determine the PWM value.

[0007] The present invention has been proposed in view of the above-mentioned problems, and has an object to provide an image forming apparatus that can determine an adjustment value more quickly than in conventional light amount adjustment processes. [Means for solving the problem]

[0008] In order to achieve the above object, the image forming apparatus of the present application comprises a plurality of photosensitive drums, an endless belt positioned opposite the plurality of photosensitive drums, a sensor including an light-emitting unit positioned opposite the endless belt and emitting light toward the endless belt, and a light-receiving unit receiving light reflected by the endless belt, a light emission amount change circuit that changes the amount of light emitted by the light-emitting unit in response to input of a control signal indicating an adjustment value, a comparison circuit that compares a light reception signal level corresponding to the amount of light received by the light-receiving unit with a threshold level and outputs a comparison result signal indicating that the light reception signal level exceeds the threshold level, and a control unit, wherein the control unit sequentially outputs control signals updated by a search width from an initial value, and performs a light intensity adjustment process that determines an adjustment value at which the light reception signal level exceeds the threshold level based on the comparison result signal, and when performing the light intensity adjustment process, at least the initial value or the search width is set to a value corresponding to the deterioration state of the endless belt.

[0009] According to this, the control unit sequentially outputs control signals updated by the search width from a predetermined initial value to the light emission amount change circuit, and determines an adjustment value at which the light reception signal level exceeds the threshold level based on the comparison result signal output from the comparison circuit. When performing this light amount adjustment process, the control unit sets at least the initial value or the search width to a value corresponding to the deterioration state of the endless belt. This makes it possible to make adjustments such as increasing the initial value or the search width when the deterioration of the endless belt progresses and the glossiness of the endless belt surface decreases. As a result, when searching for an adjustment value at which the light reception signal level exceeds the threshold level, the processing time from the start of the search to determining the adjustment value can be shortened. The adjustment value can be determined more quickly.

[0010] The control unit may also be configured to set a plurality of different judgment values, output control signals corresponding to the judgment values ​​to the light emission amount change circuit in order from the smallest judgment value, receive the comparison result signal from the comparison circuit, and perform an initial value determination process that determines the initial value and the search width based on the judgment value that corresponds when the comparison result signal is received.

[0011] According to this, before searching for the adjustment value, an initial value determination process is performed to determine an initial value and a search width. The control unit uses a plurality of different judgment values, using the smallest judgment value first, and when a comparison result signal is received, that is, when the light reception signal level exceeds the threshold level, determines the initial value and the search width based on the judgment value. This makes it possible to determine the initial value and the search width using the judgment value that matches the deterioration state of the endless belt from among the plurality of judgment values.

[0012] The control unit may also be configured such that a search width corresponding to each of the plurality of judgment values ​​is determined in proportion to the magnitude of the judgment value, and in the initial value determination process, the initial value is determined to be the judgment value that is closest to and smaller than the corresponding judgment value, and the search width is determined to be the search width corresponding to the corresponding judgment value.

[0013] According to this, the control unit executes a search to use the determination value in order from the smallest to the largest, and determines as the initial value the determination value that is the smallest immediately before the determination value when the light-receiving signal level exceeds the threshold level. This allows the search to be started from a light-receiving signal level that is lower than the threshold level, and makes it possible to more reliably prevent the light-receiving signal level from exceeding the threshold level at the time the search is started. In addition, the search width is proportional to the magnitude of the judgment value, and by increasing the search width as the judgment value increases, the processing time from the start of the search to determining the adjustment value can be reduced.

[0014] The control unit may also be configured such that a search width corresponding to each of the plurality of judgment values ​​is determined in proportion to the magnitude of the judgment value, and in the initial value determination process, a common value is determined as the initial value for each of the plurality of judgment values, and the search width is determined to be the search width corresponding to the corresponding judgment value.

[0015] According to this method, the initial value used in the search is not changed, but the search width is changed. By using a search width that is proportional to the magnitude of the judgment value as the search width, the search width can be increased in accordance with the progression of deterioration of the endless belt, and the processing time from the start of the search to determining the adjustment value can be shortened.

[0016] In addition, the control unit may be configured to, in the initial value determination process, determine a common value as the search width for each of the multiple judgment values, and determine the initial value to be a value equal to or greater than the judgment value that is closest to and smaller than the corresponding judgment value.

[0017] According to this, the search width used in the search is not changed, but the initial value is changed. By determining the initial value to be the judgment value immediately smaller than the judgment value when the received light signal level exceeds the threshold level, it is possible to more reliably prevent the received light signal level from exceeding the threshold level at the time the search is started.

[0018] Furthermore, after executing the initial value determination process, the control unit may sequentially output control signals updated from the initial value by the search width to the light emission amount change circuit, and perform a light intensity adjustment process to determine an adjustment value at which the light reception signal level exceeds the threshold level based on the comparison result signal, and a color shift correction process to determine the adjustment value determined in the light intensity adjustment process as a correction adjustment value, output a control signal according to the correction adjustment value to the light emission amount change circuit, and correct color shift of the marks formed on the endless belt.

[0019] According to this, the control unit can shorten the time required to search for an adjustment value in the light intensity adjustment process by using at least one of an initial value and a search width that corresponds to the deterioration state of the endless belt.The control unit then uses the adjustment value determined in the light intensity adjustment process as a correction adjustment value and outputs a control signal corresponding to the correction adjustment value to the light emission amount change circuit to execute the color misregistration correction process.This allows the light emitting unit to emit light at an amount of light that corresponds to the deterioration state of the endless belt, allowing the marks formed on the endless belt to be detected and color misregistration correction to be executed more accurately.As a result, it is possible to prevent misalignment of the transfer position between multiple photosensitive drums in the image formation process after correction.

[0020] The control unit is also capable of changing the threshold level, and a first threshold level, a second threshold level, and a third threshold level are respectively set, and in the initial value determination process, the control unit outputs a threshold signal indicating the first threshold level to the comparison circuit and determines an initial value and a search width based on the first threshold level, and after executing the initial value determination process, with the threshold signal indicating the first threshold level output to the comparison circuit, sequentially outputs control signals updated from the initial value by the search width to the light emission amount change circuit, and determines a first adjustment value at which the light reception signal level exceeds the first threshold level based on the comparison result signal; and after the first light amount adjustment process, with the threshold signal indicating the second threshold level output to the comparison circuit, sequentially outputs control signals updated by the search width with the first adjustment value as an initial value to the light emission amount change circuit, and determines a second adjustment value at which the light reception signal level exceeds the second threshold level based on the comparison result signal. a third light amount adjustment process in which, after the second light amount adjustment process, a threshold signal indicating the third threshold level is output to the comparison circuit, and a control signal corresponding to the second adjustment value is repeatedly output to the light emission amount change circuit a predetermined number of times; if the number of times the comparison result signals are received exceeds a predetermined percentage or more of the predetermined number of times, the second adjustment value is determined to be the third adjustment value; and if the number of times the comparison result signals are received does not exceed a number equal to or greater than the predetermined percentage, the third adjustment value is determined by correcting the second adjustment value so that the light reception signal levels of the number equal to or greater than the predetermined percentage exceed the third threshold level. Also, a color shift correction process in which a correction adjustment value is determined based on the first threshold level, the third threshold level, the first adjustment value, and the third adjustment value, and a control signal corresponding to the correction adjustment value is output to the light emission amount change circuit to correct color shift of the marks formed on the endless belt may be executed.

[0021] According to this, in the initial value determination process, the first threshold level is used to determine an initial value and a search width corresponding to the deterioration state of the endless belt. The control unit determines the first adjustment value using the determined initial value and search width and the first threshold level, thereby shortening the time required to search for the first adjustment value. The control unit sets the first adjustment value as the initial value and uses the search width determined in the initial value determination process to determine a second adjustment value at which the received light signal level exceeds the second threshold level. The control unit uses the second adjustment value and the third threshold level to determine a third adjustment value at which the number of received comparison result signals is a predetermined percentage. The control unit then outputs a control signal corresponding to the correction adjustment value determined based on the first threshold level, the third threshold level, the first adjustment value, and the third adjustment value to the light emission amount change circuit to perform the color misregistration correction process. This allows the light emission amount of the light-emitting unit to be accurately adjusted to a light emission amount corresponding to the deterioration state of the endless belt. As a result, it is possible to prevent misalignment of the transfer position between multiple photosensitive drums during the image formation process after correction. [Effects of the Invention]

[0022] According to the image forming apparatus of the present application, the adjustment value can be determined more quickly than in the conventional light amount adjustment process. [Brief explanation of the drawings]

[0023] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of a color laser printer according to a first embodiment of the present invention. [Figure 2] 1 is a block diagram showing a control configuration of a color laser printer according to a first embodiment. [Figure 3] FIG. 2 is a circuit diagram of a main board and a sensor board according to the first embodiment. [Figure 4] 10 is a flowchart showing a color misregistration correction control process according to the first embodiment. [Figure 5] 10 is a flowchart showing an initial value determination process according to the first embodiment. [Figure 6] 10A and 10B are diagrams illustrating a state of a search process for a first adjustment value in the first light amount adjustment process according to the first embodiment. [Figure 7] 10 is a flowchart showing a third light amount adjustment process according to the first embodiment. [Figure 8] 5 is a flowchart showing a sampling process according to the first embodiment. [Figure 9] 10 is a flowchart showing an initial value determination process according to the second embodiment. [Figure 10] 11 is a flowchart showing an initial value determination process according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0024] (First embodiment) A color laser printer according to a first embodiment, which is an embodiment of the image forming apparatus of the present application, will be described below with reference to FIGS. 1 and 2. FIG. 1 is a cross-sectional view showing the schematic configuration of a color laser printer 10 according to the first embodiment. FIG. 2 is a block diagram showing the control configuration of the color laser printer 10. The color laser printer 10 is an example of the image forming apparatus of the present application. Hereinafter, the color laser printer 10 will be abbreviated as printer 10. As shown in FIGS. 1 and 2, the printer 10 includes a main body housing 2, a conveying unit 3, a processing unit 4, a fixing device 5, a main board 6, and a sensor board 7. For ease of explanation, the up-down direction and the front-rear direction of the printer 10 will be defined as indicated by the arrows in FIG. 1. The front side of the paper is defined as the right, and the far side of the paper is defined as the left.

[0025] The main body housing 2 has an openable front cover 11 and a rear cover 12, a supply tray 13, a discharge tray 15, and a transport path 17. The supply tray 13 is detachably attached to the bottom of the main body housing 2. Sheets S are placed on the supply tray 13. The sheets S are standard-sized paper such as A4 size. The sheets S are not limited to paper media such as plain paper or cardboard, and may be other recording media such as overhead projector film. The discharge tray 15 is located at the top of the main body housing 2, and sheets S on which images have been formed are placed on the discharge tray 15.

[0026] The conveying unit 3 includes a pickup roller 21, a separation roller 22, a registration roller 24, and a plurality of conveying rollers 23. The pickup roller 21 picks up the sheets S in the supply tray 13 and conveys them toward the conveying path 17. The separation roller 22 separates the sheets S picked up by the pickup roller 21 one by one and sends them to the registration roller 24. The registration roller 24 corrects skew of the sheet S, and then conveys the sheet S to the process unit 4 (on an endless belt 63 described later). The plurality of conveying rollers 23 convey the sheet S that has passed through the fixing device 5 along the conveying path 17 and discharges it onto the discharge tray 15. The conveying unit 3 rotates each roller based on the drive of a main motor (not shown) arranged in the main body housing 2.

[0027] The conveying unit 3 also includes a plurality of switchback rollers 25 that reverse the sheet S printed on one side, and a reverse conveying path 27. The printer 10 can switch the conveying destination of the sheet S between the discharge tray 15 and the reverse conveying path 27 indicated by the dashed line by swinging a flapper 28 located downstream of the fixing device 5 on the conveying path 17. The conveying unit 3 swings the flapper 28 to the position indicated by the two-dot chain line based on the drive of the main motor, and rotates the plurality of switchback rollers 25, thereby conveying the sheet S upward along the reverse conveying path 27. The conveying unit 3 reversely rotates the switchback rollers 25 to convey the sheet S conveyed upward along the reverse conveying path 27, passing below the supply tray 13 and conveying it to the front side. As a result, the sheet S is reversed and conveyed to the base end of the conveying path 17. The printer 10 performs double-sided printing by printing on the top side of the reversed sheet S (the side opposite to the side printed the first time). Furthermore, the printer 10 is capable of printing even with the rear cover 12 open, and the printed sheet S can be discharged onto the open rear cover 12.

[0028] The process unit 4 has a function of forming an image on the sheet S, and transfers a toner image onto the sheet S. The process unit 4 includes a laser unit 30, an image forming unit 31, and a transfer unit 34. The image forming unit 31 includes a drum unit 32 and four developing cartridges 33Y, 33M, 33C, and 33K.

[0029] The laser unit 30 is located at the top of the main body housing 2 and is equipped with a semiconductor laser, an LD driver that drives the semiconductor laser, a polygon mirror, etc., and exposes the surface of the photosensitive drum 41 of the drum unit 32 by emitting laser light shown by the dotted line onto the surface of the photosensitive drum 41.

[0030] Drum unit 32 is disposed between supply tray 13 and laser unit 30 inside main body housing 2, and includes four photosensitive drums 41, four chargers 43, and a support frame 45 that supports photosensitive drums 41 and the like. Drum unit 32 is detachable from main body housing 2 when front cover 11 is open.

[0031] The developer cartridges 33Y, 33M, 33C, and 33K correspond to four colors: yellow (Y), magenta (M), cyan (C), and black (K), respectively, and are detachably mounted in the drum unit 32 in that order from the front to the rear of the printer 10. Each of the developer cartridges 33Y, 33M, 33C, and 33K includes a developer roller 51, a supply roller 52, and a toner storage section 53. Note that the four developer cartridges 33Y, 33M, 33C, and 33K differ in toner color but are otherwise identical in configuration. For this reason, in the following description, the four developer cartridges 33Y, 33M, 33C, and 33K corresponding to each color will be collectively referred to as developer cartridges 33.

[0032] The transfer unit 34 is disposed between the supply tray 13 and the drum unit 32 within the main body casing 2 and includes a drive roller 61, a driven roller 62, an endless belt 63, and four transfer rollers 64. The endless belt 63 is stretched between the drive roller 61, which is disposed below the rear end of the drum unit 32, and the driven roller 62, which is disposed below the front end of the drum unit 32. The endless belt 63 is made of a resin material such as polycarbonate, and its surface is mirror-finished. The upper surface of the endless belt 63 extends substantially horizontally directly below the image forming unit 31, contacts the photosensitive drum 41, and serves as a sheet conveying surface 63A that abuts against the back surface of the sheet S to convey the sheet S. The four transfer rollers 64 are disposed inside the endless belt 63 so as to sandwich the endless belt 63 between themselves and the corresponding photosensitive drum 41. Each of the transfer rollers 64 is installed in a state where it contacts the endless belt 63 from the rear side of the sheet conveying surface 63A. The endless belt 63 is negatively charged by applying a negative transfer bias to each of the transfer rollers 64, and conveys the sheet S along the conveying path 17 while attracting it to the sheet conveying surface 63A by the electrostatic force.

[0033] The charger 43 is disposed above the photosensitive drum 41 and is, for example, a scorotron charger having a charging wire or grid. The image forming unit 31 generates a corona discharge using the charger 43 based on power supplied from a high-voltage power supply board 47 (see FIG. 2), thereby uniformly and positively charging the surface of the photosensitive drum 41. The laser unit 30 irradiates the surface of the photosensitive drum 41 with laser light to expose it, thereby forming an electrostatic latent image based on image data on the surface of the photosensitive drum 41. The device that charges the photosensitive drum 41 is not limited to a scorotron charger, and may be another device such as a roller-type charging roller. The polarity with which the photosensitive drum 41 is charged is not limited to a positive charge, and may be a negative charge.

[0034] The process unit 4 also supplies toner from a toner storage unit 53 to a supply roller 52, which then supplies the toner to the developing roller 51. The toner supplied to the developing roller 51 is carried on the developing roller 51 as the developing roller 51 rotates. The developing roller 51 is rotated by the rotational driving force of the main motor, supplies toner to the photosensitive drum 41, and develops the electrostatic latent image formed on the surface of the photosensitive drum 41, thereby carrying a toner image. The toner carried on the developing roller 51 moves to the electrostatic latent image on the photosensitive drum 41 due to the potential difference between the developing roller 51 and the electrostatic latent image formed on the photosensitive drum 41, forming a toner image. This toner image is transferred to the sheet S by applying a negative transfer bias to the transfer roller 64 while the photosensitive drum 41 is in contact with the sheet S on the endless belt 63. The sheet S is then transferred by the four photosensitive drums 41 so that multiple color toner images are sequentially superimposed on top of each other, and is transported to the fixing device 5.

[0035] The fixing device 5 is disposed behind the process unit 4 within the main body casing 2. The fixing device 5 includes a heating roller 67 that heats the sheet S and a pressure unit 68 that sandwiches the sheet S between the heating roller 67 and the sheet S. The heating roller 67 includes a heater 69 that heats the heating roller 67. The pressure unit 68 includes an endless belt, a pressure pad that sandwiches the endless belt between the heating roller 67 and the pressure pad, a holder that supports the pressure pad, and a belt guide. The pressure unit 68 is rotated by the rotational driving force of the main motor and presses the sheet S against the heating roller 67, thereby applying pressure to the sheet S. In this way, the fixing device 5 fixes the toner image on the sheet S. A cleaning device 8 is disposed below the endless belt 63 to collect toner (marks, described later), paper dust, and the like adhering to the surface of the endless belt 63.

[0036] The main board 6 is a control board that controls the printer 10 overall, and as shown in FIG. 2, has an ASIC 71, a ROM 72, a RAM 73, and an NVRAM 74. The ASIC 71 is an Application Specific Integrated Circuit and has a CPU and the like. The ASIC 71 is an example of the control unit of the present application. Note that the control unit of the present application is not limited to an ASIC, and may be another device such as an SoC (System on a Chip).

[0037] The ROM 72 stores various control programs and various setting information for controlling the printer 10. These control programs include a program for executing the color misregistration correction control process shown in FIG. 4, which will be described later. The RAM 73 is, for example, a DRAM, and is used as a work area for reading out the various control programs and as a storage area for temporarily storing image data based on a print job. The NVRAM 74 is used to store setting values ​​(such as flag values) used in various processes. For example, the NVRAM 74 stores a first threshold level TH1, a second threshold level TH2, a third threshold level TH3, a judgment value, a search width W, and the like, which will be described later. The ASIC 71 executes processes in accordance with the control programs read from the ROM 72 and signals input from various sensors (such as the phototransistor PTr on the sensor board 7, which will be described later), stores the processing results in the RAM 73 and the NVRAM 74, and controls each part of the printer 10 to perform image formation and color misregistration correction processes.

[0038] 2 is an example. For example, the main board 6 may have a non-volatile storage device such as an HDD or SSD. The control program for executing the color misregistration correction control process may be stored in the NVRAM 74. The first threshold level TH1, the judgment value, etc. may be stored in the ROM 72. The main board 6 does not need to include the NVRAM 74. The storage medium for storing the control program, the first threshold level TH1, etc. may be an external storage medium such as a USB memory, or may be a storage medium such as a CD-ROM or DVD-ROM.

[0039] Next, a mechanism for detecting marks (toner images) formed on the surface (sheet conveying surface 63A) of endless belt 63 will be described. As shown in FIG. 1, sensor board 7 is disposed behind and below endless belt 63 (drive roller 61). Sensor board 7 is attached to main body housing 2. FIG. 3 is a circuit diagram of main board 6 and sensor board 7. As shown in FIG. 3, main board 6 has a light emitting amount change circuit 81 and a comparison circuit 82. Sensor board 7 also has a light emitting diode LED, a phototransistor PTr, a second smoothing circuit 87, and a non-inverting amplifier circuit 88. Main board 6 and sensor board 7 are connected to each other via harness 91 including a plurality of wires (wires 89, 90, etc.).

[0040] The light emission amount change circuit 81 is a circuit that changes the light emission amount of the light emitting diode LED in response to an input of a control signal LED_PWM. The light emission amount change circuit 81 has a first smoothing circuit 93, a transistor TR, and a resistor element R1. The transistor TR is, for example, an NPN transistor. The control signal LED_PWM is a pulse width modulated signal that is repeatedly turned on and off at a predetermined frequency. When the control signal LED_PWM is on, the ASIC 71 applies a predetermined voltage to the first smoothing circuit 93, and when the control signal LED_PWM is off, the ASIC 71 does not apply a voltage to the first smoothing circuit 93. Terminal 76 of ASIC 71 is connected to the base of transistor TR via first smoothing circuit 93. First smoothing circuit 93 includes a resistor element and a capacitor, smooths the voltage of control signal LED_PWM input from terminal 76, and outputs the smoothed voltage to the base of transistor TR. Therefore, by changing the value of control signal LED_PWM (hereinafter referred to as PWM value), ASIC 71 can change the output voltage of first smoothing circuit 93 and change the value of current flowing from the collector to the emitter of transistor TR.

[0041] The PWM value is a value that indicates the duty ratio of a pulse width modulation signal, and the duty ratio is the ratio of the time that the pulse width modulation signal is on in one cycle.

[0042] The ASIC 71 can adjust the duty ratio of the control signal LED_PWM in stages, for example, using a 10-bit PWM value. Specifically, a PWM value of 0, which is the minimum value of 10 bits, indicates that the duty ratio is 0%. Also, a PWM value of 2, which is the maximum value of 10 bits, indicates that the duty ratio is 0%. 10 A PWM value of -1 (=1023) indicates a duty ratio of 100%. The ASIC 71 changes the duty ratio of the control signal LED_PWM in stages according to the bit value (0 to 1023) of the PWM value.

[0043] The emitter of the transistor TR is connected to ground via a resistor R1. The collector of the transistor TR is connected to a light-emitting diode LED via a wire 89 included in a harness 91. The anode of the light-emitting diode LED is connected to a power supply Vcc, and the cathode is connected to the collector of the transistor TR. The light-emitting diode LED is an example of a light-emitting unit of the present application. Note that the light-emitting unit of the present application is not limited to the light-emitting diode LED, and may be a laser diode, a halogen lamp, an organic EL, or the like.

[0044] A voltage is output from the first smoothing circuit 93 to the base of the transistor TR, causing a current to flow between the base and emitter, resulting in a current flow between the collector and emitter. A current Iled flows from the power supply Vcc through the light-emitting diode LED, the transistor TR, and the resistor R1 to ground, causing the light-emitting diode LED to emit light. The ASIC 71 adjusts the PWM value of the control signal LED_PWM, thereby changing the value of the current Iled and adjusting the light-emitting diode LED's light output. The ASIC 71 increases the PWM value of the control signal LED_PWM to increase the value of the current Iled and increase the light-emitting diode LED's light output. The ASIC 71 also decreases the PWM value of the control signal LED_PWM to decrease the value of the current Iled and decrease the light-emitting diode LED's light output. The above-described configuration of the light-emission amount change circuit 81 is merely an example. For example, the transistor TR may be a PNP transistor.

[0045] The light emitting diode LED is disposed facing the endless belt 63, and emits light toward the outer peripheral surface of the endless belt 63. The phototransistor PTr is disposed in a position where it receives the light emitted from the light emitting diode LED and reflected by the endless belt 63. Therefore, the amount of light received by the phototransistor PTr is adjusted by changing the PWM value of the control signal LED_PWM and changing the amount of light emitted by the light emitting diode LED.

[0046] The collector of the phototransistor PTr is connected to the power supply Vcc, and the emitter is connected to ground via a resistor R2. When the phototransistor PTr receives light reflected from the endless belt 63, a photocurrent Ipt is generated between the collector and emitter, the magnitude of which corresponds to the amount of light received. The photocurrent Ipt flows from the power supply Vcc through the phototransistor PTr and resistor R2 to ground. The phototransistor PTr is an example of a light receiving unit of the present application. Note that the light receiving unit of the present application is not limited to the phototransistor PTr, and may be any other light receiving element capable of converting light into an electrical signal, such as a photodiode or a CMOS image sensor.

[0047] The input terminal of the second smoothing circuit 87 is connected to a connection 95 between the phototransistor PTr and the resistor R2, and receives a voltage corresponding to the photocurrent Ipt, i.e., the amount of received light. The output terminal of the second smoothing circuit 87 is connected to the non-inverting input terminal of the non-inverting amplifier circuit 88. The second smoothing circuit 87 smoothes the voltage input from the connection 95 and outputs the smoothed voltage as an input voltage Vin to the non-inverting input terminal of the non-inverting amplifier circuit 88. The output terminal of the non-inverting amplifier circuit 88 is connected to the inverting input terminal via the resistor R3. The output terminal of the non-inverting amplifier circuit 88 is connected to ground via the resistors R3 and R4. The non-inverting amplifier circuit 88 amplifies the input voltage Vin by an amplification factor corresponding to the resistance values ​​of the resistors R3 and R4 and outputs the amplified signal as a light-receiving signal Vout from its output terminal. The sensor substrate 7 outputs a light-receiving signal Vout with a higher voltage value as the amount of light received by the phototransistor PTr increases.

[0048] The comparison circuit 82 includes a comparator 97, a third smoothing circuit 98, and a pull-up resistor Rup. The output terminal of the non-inverting amplifier circuit 88 is connected to the inverting input terminal of the comparator 97 via a wiring 90 included in a harness 91. The comparator 97 is a hysteresis comparator, and its output terminal is connected to the non-inverting input terminal via a resistor R5. The comparator 97 reduces the effects of noise by changing its threshold depending on the output state. The output terminal of the comparator 97 is connected to the power supply Vcc via a pull-up resistor Rup and to a terminal 78 of the ASIC 71. The output terminal is also connected to ground via resistors R5 and R6. The resistor R5 is a feedback resistor for the comparator 97, which is a hysteresis comparator.

[0049] The input terminal of the third smoothing circuit 98 is connected to the terminal 77 of the ASIC 71, and the threshold signal TH_PWM, which is a pulse-width modulated signal, is input from the terminal 77. The output terminal of the third smoothing circuit 98 is connected to the non-inverting input terminal of the comparator 97 via a resistor R7. The third smoothing circuit 98 smoothes the voltage generated by the threshold signal TH_PWM. The voltage smoothed by the third smoothing circuit 98 is divided by resistors R6 and R7 at a connection 99. The voltage divided by the resistors R6 and R7 is input to the non-inverting input terminal of the comparator 97 as the threshold voltage TH. The comparator 97 compares the light-receiving signal Vout input from the inverting input terminal with the threshold voltage TH input from the non-inverting input terminal, and outputs the comparison result as a comparison result signal SG to the terminal 78 of the ASIC 71.

[0050] The comparison circuit 82 compares the voltage value of the light reception signal Vout (hereinafter sometimes referred to as the light reception signal level) corresponding to the amount of light received by the phototransistor PTr with the voltage value of the threshold voltage TH (hereinafter sometimes referred to as the threshold level), and if the light reception signal level exceeds the threshold level, outputs a low-level comparison result signal SG. In this case, the ASIC 71 receives the low-level comparison result signal SG from the terminal 78. Furthermore, if the light reception signal level does not exceed the threshold level, the comparison circuit 82 outputs a high-impedance signal. In this case, the ASIC 71 receives the high-level comparison result signal SG from the terminal 78 via the pull-up resistor Rup.

[0051] The threshold level can be changed under the control of the ASIC 71. Specifically, the ASIC 71 outputs a pulse width modulated signal as the threshold signal TH_PWM, and the voltage of the output threshold signal TH_PWM is smoothed by the third smoothing circuit 98. The ASIC 71 can change the threshold level to a first threshold level TH1, a second threshold level TH2, or a third threshold level TH3, which will be described later, by changing the PWM value of the threshold signal TH_PWM, for example.

[0052] (Regarding color misregistration correction control processing) Next, the color misregistration correction control process executed by the ASIC 71 will be described. FIG. 4 shows a flowchart of the color misregistration correction control process. By executing the process of FIG. 4, the ASIC 71 corrects the misregistration (color misregistration) of the transfer position where the photosensitive drum 41 of each color transfers the toner image onto the sheet S. The ASIC 71 starts the process shown in FIG. 4, for example, when the printer 10 is turned on. Note that the condition for starting the process shown in FIG. 4 is not limited to the condition that the printer 10 is turned on, and other conditions may also be used. For example, the ASIC 71 may execute the process of FIG. 4 when a condition is met, such as that the drum unit 32 is replaced, that a predetermined number of sheets S have been printed since the previous execution of the color misregistration correction control process, or that the temperature of the environment in which the printer 10 is used has changed by more than a threshold value.

[0053] The ASIC 71 determines a judgment PWM value DT in S5 based on the threshold determined by the light intensity adjustment process of steps (hereinafter referred to as S) 2, S3, and S4 in Figure 4, outputs a control signal LED_PWM of the determined judgment PWM value DT to the light emission intensity change circuit 81, and performs color shift correction in S8 while causing the light emitting diode LED to emit light. In conventional image forming apparatuses, the light intensity adjustment process determines the PWM value DT for determination by sequentially increasing the PWM value by a predetermined search width starting from an initial value corresponding to a PWM value with a low light-receiving signal level, and determining the PWM value at the stage where the light-receiving signal level reaches a threshold level as the threshold. However, in this light intensity adjustment process, if the difference between the initial value and the determined threshold increases, such as when the endless belt 63 deteriorates and its glossiness decreases, the processing time from the initial value to the threshold value becomes long. Therefore, in this embodiment, the ASIC 71 adjusts the initial value IV and the search width W to values ​​corresponding to the deterioration state of the endless belt 63 in S1, and then executes the light intensity adjustment process from S2 onward, thereby shortening the processing time until the threshold value (such as the first adjustment value AV1 described below) is determined.

[0054] More specifically, in S1, the ASIC 71 executes the initial value determination process shown in Fig. 5. As shown in Fig. 5, in S11, the ASIC 71 sets the PWM value of the threshold signal TH_PWM to a first threshold level TH1. The first threshold level TH1 is, for example, 0.47 V. The ASIC 71 sets the PWM value of the threshold signal TH_PWM to a magnitude that causes the threshold voltage TH to become the first threshold level TH1.

[0055] Next, the ASIC 71 drives the sensor board 7 to cause the light-emitting diode LED to emit light (S12). The ASIC 71 also sets a second judgment value JV2 as the PWM value of the control signal LED_PWM. The NVRAM 74 stores a plurality of different judgment values ​​for determining the initial value IV and the search width W. For example, in this embodiment, four judgment values ​​are stored: a first judgment value JV1, a second judgment value JV2, a third judgment value JV3, and a fourth judgment value JV4. The NVRAM 74 also stores a value for the search width W corresponding to the magnitude of each judgment value. The judgment values ​​and the search width W may be stored not only in the NVRAM 74 but also in the ROM 72, etc.

[0056] Each judgment value indicates a PWM value (adjustment value) of the control signal LED_PWM. For example, the first judgment value JV1, the second judgment value JV2, the third judgment value JV3, and the fourth judgment value JV4 are set to PWM values ​​of 150, 300, 500, and 700, respectively. Furthermore, the search width W values ​​corresponding to the first judgment value JV1, the second judgment value JV2, the third judgment value JV3, and the fourth judgment value JV4 are set to values ​​of 1, 2, 3, and 4, respectively. Therefore, the four search widths W are set to values ​​that increase by 1 in proportion to the magnitudes of the first to fourth judgment values ​​JV1 to JV4. Note that the values ​​and numbers of the judgment values ​​and search widths W described above are merely examples.

[0057] The ASIC 71 outputs the control signal LED_PWM corresponding to the judgment value to the light emission amount change circuit 81 in order from the smallest judgment value, and determines the initial value IV and the search width W based on the judgment value corresponding to when it receives a low-level comparison result signal SG from the comparison circuit 82. More specifically, in S12, the ASIC 71 outputs the control signal LED_PWM at the PWM value (300) indicated by the second determination value JV2. Next, the ASIC 71 determines whether the light reception signal level exceeds the first threshold level TH1 (0.47 V) (S13).

[0058] If the light reception signal level exceeds the threshold level, that is, if the light reception signal level when light is emitted by the control signal LED_PWM having the PWM value indicated by the second judgment value JV2 exceeds the first threshold level TH1, the comparison circuit 82 outputs a low-level comparison result signal SG. If a low-level comparison result signal SG is input from the terminal 78, the ASIC 71 makes an affirmative determination in S13 (S13: YES) and executes S14.

[0059] In S14, the ASIC 71 determines a first judgment value JV1 as the initial value IV. Accordingly, the ASIC 71 determines, as the initial value IV, a value smaller than the second judgment value JV2, which is the judgment value corresponding to the received light signal level (hereinafter, sometimes referred to as the corresponding judgment value) when the comparison result signal SG indicating that the received light signal level exceeds the threshold level, and a judgment value (in this case, the first judgment value JV1 (150)) that is closest to the corresponding judgment value among the four judgment values. Furthermore, the ASIC 71 determines, as the search width W, a value (=1) corresponding to the first judgment value JV1 (S14). The ASIC 71 stores information about the determined initial value IV and search width W, for example, in the RAM 73. After executing S14, the ASIC 71 ends the processing shown in FIG. 5.

[0060] On the other hand, in S13, if the light-receiving signal level when the light-emitting diode LED is caused to emit light by the control signal LED_PWM having the PWM value of the second determination value JV2 does not exceed the first threshold level TH1, the comparison circuit 82 outputs a high-level comparison result signal SG to the terminal 78. When a high-level comparison result signal SG is input, the ASIC 71 makes a negative determination in S13 (S13: NO) and executes S15.

[0061] The following processing from S15 onward is similar to the processing in S12, S13, and S14 described above, and therefore description thereof will be omitted where appropriate. In S15, the ASIC 71 sets the PWM value of the control signal LED_PWM to a third judgment value JV3 (=500) to cause the light-emitting diode LED to emit light. Next, if the light-receiving signal level when the light-emitting diode LED is caused to emit light by the control signal LED_PWM of the third judgment value JV3 exceeds the first threshold level TH1 (S17: YES), the ASIC 71 determines the second judgment value JV2 (=300), which is immediately smaller than the corresponding judgment value (in this case, the third judgment value JV3), as the initial value IV (S18). The ASIC 71 also determines the value corresponding to the second judgment value JV2 (=2) as the search width W (S18), and ends the processing of FIG. 5.

[0062] Furthermore, in S17, if the light-receiving signal level does not exceed the first threshold level TH1 and a high-level comparison result signal SG is input (S17: NO), the ASIC 71 sets the PWM value of the control signal LED_PWM to a fourth judgment value JV4 (=700) and causes the light-emitting diode LED to emit light (S19). Next, if the light-receiving signal level when the light-emitting diode LED is caused to emit light by the control signal LED_PWM of the fourth judgment value JV4 exceeds the first threshold level TH1 (S21: YES), the ASIC 71 determines the third judgment value JV3 (=500), which is immediately smaller than the corresponding judgment value (in this case, the fourth judgment value JV4), as the initial value IV (S22). Furthermore, the ASIC 71 determines the value corresponding to the third judgment value JV3 (=3) as the search width W (S22), and ends the processing of FIG. 5. Also, in S21, if the received light signal level does not exceed the first threshold level TH1 (S21: NO), ASIC71 determines the fourth judgment value JV4 (=700) as the initial value IV, determines the value corresponding to the fourth judgment value JV4 (=4) as the search width W (S23), and terminates the processing of Figure 5.

[0063] Returning to FIG. 4, after executing S1, the ASIC 71 executes a first light intensity adjustment process (S2). In the first light intensity adjustment process, the ASIC 71 determines a first adjustment value AV1 using the initial value IV and search width W determined in S1. In S2, the ASIC 71 sequentially outputs the control signal LED_PWM, whose PWM value is updated by the search width W from the initial value IV determined in S1, to the light emission intensity change circuit 81, and determines the PWM value of the control signal LED_PWM at which the light reception signal level exceeds the first threshold level TH1 as the first adjustment value AV1. More specifically, first, the ASIC 71 sets the PWM value of the threshold signal TH_PWM so that the threshold level is the first threshold level TH1 (=0.47 V), as in S11 of FIG. 5. Next, the ASIC 71 outputs the control signal LED_PWM with the PWM value of the initial value IV determined in S1, causing the light emitting diode LED to emit light.

[0064] Next, the ASIC 71 determines whether the received light signal level exceeds the first threshold level TH1. If the received light signal level does not exceed the first threshold level TH1, the ASIC 71 increases the PWM value of the control signal LED_PWM by the search width W determined in S1, and again determines whether the received light signal level exceeds the first threshold level TH1. The ASIC 71 increases the PWM value of the control signal LED_PWM by the search width W until the received light signal level exceeds the first threshold level TH1. Then, the ASIC 71 determines the PWM value of the control signal LED_PWM that was set at the time when it determined that the received light signal level exceeded the first threshold level TH1 as the first adjustment value AV1.

[0065] FIG. 6 shows the state of the search process for the first adjustment value AV1 in the first light intensity adjustment process. The vertical axis of FIG. 6 represents the voltage value (light reception signal level) of the light reception signal Vout, and the horizontal axis represents the PWM value of the control signal LED_PWM. (1) to (3) in FIG. 6 show different cases of deterioration of the endless belt 63, with the deterioration of the endless belt 63 progressing in the order of (1) to (3). As the deterioration progresses in the order of (1) to (3), the glossiness of the endless belt 63 decreases. Therefore, when the light-emitting diode LED is caused to emit light with the same PWM value, the amount of light received by the phototransistor PTr decreases in the order of (1) to (3). The first adjustment value AV1 increases as the deterioration of the endless belt 63 progresses. For example, in the deterioration state (3), if the first judgment value JV1 is set as the initial value IV and the search width W is set to 1, the processing time until the first adjustment value AV1 is determined will be long. Therefore, the ASIC 71 uses the first threshold level TH1 and four judgment values ​​in the initial value determination process to adjust the initial value IV and the search width W in advance, and then executes the first light intensity adjustment process.

[0066] In the initial value determination process, the ASIC 71 starts judging the comparison result signal SG from the second judgment value JV2 (S13 in FIG. 5) and increases or decreases the judgment value depending on whether the received light signal level exceeds the first threshold level TH1. For example, as shown at point P1 in FIG. 6, if the received light signal level exceeds the first threshold level TH1 at the second judgment value JV2 (=300) in S13, the ASIC 71 sets the judgment value at that time, i.e., the first judgment value JV1 (=150), which is one value smaller than the second judgment value JV2, as the initial value IV (S14). In this case, in the first light intensity adjustment process, the ASIC 71 searches for the first adjustment value AV1 by increasing the PWM value of the control signal LED_PWM by a search width W (=1) corresponding to the first judgment value JV1, from point P2 where the first judgment value JV1 was set as the initial value IV.

[0067] On the other hand, as shown at point P3 in FIG. 6 , if the received light signal level does not exceed the first threshold level TH1 in S13, the PWM value of the control signal LED_PWM is set to the third judgment value JV3, and the judgment of S17 is executed. Then, as shown at point P4, if the received light signal level exceeds the first threshold level TH1 at the second judgment value JV2 (=500) in S17 (S17: YES), the ASIC 71 searches for the first adjustment value AV1 by increasing the PWM value of the control signal LED_PWM by the search width W (=2) corresponding to the second judgment value JV2, starting from point P5 where the second judgment value JV2, which is one value smaller than the third judgment value JV3, is set as the initial value IV. Similarly, the initial value IV and the search width W are changed according to the judgment result of S21. This allows the initial value IV to be set to a value smaller than the first adjustment value AV1, which increases as the endless belt 63 deteriorates, but closer to the first adjustment value AV1. Furthermore, by increasing the search width W as the initial value IV increases, the processing time required to increase the PWM value of the control signal LED_PWM from the initial value IV to the first adjustment value AV1 can be shortened.

[0068] 4, after executing S2, the ASIC 71 executes a second light intensity adjustment process in S3. In the second light intensity adjustment process, the ASIC 71 determines a second adjustment value AV2 using the first adjustment value AV1 determined in S2 and the search width W determined in S1. In addition, in the second light intensity adjustment process, a second threshold level TH2 (e.g., 1.62 V) that is greater than the first threshold level TH1 is used.

[0069] In S3, the ASIC 71 sequentially outputs the control signal LED_PWM, whose PWM value is updated by the search width W from the first adjustment value AV1 determined in S2, to the light emission amount change circuit 81, and determines the PWM value of the control signal LED_PWM at which the received light signal level exceeds the second threshold level TH2 as the second adjustment value AV2. More specifically, first, similar to S11 in FIG. 5, the ASIC 71 sets the PWM value of the threshold signal TH_PWM so that the threshold level becomes the second threshold level TH2 (=1.62 V). Next, the ASIC 71 outputs the control signal LED_PWM with the PWM value of the first adjustment value AV1 determined in S2, causing the light emitting diode LED to emit light. Similarly to the first light amount adjustment process, if the received light signal level does not exceed the second threshold level TH2, the ASIC 71 increases the PWM value of the control signal LED_PWM by the search width W determined in S1. The ASIC 71 increases the PWM value of the control signal LED_PWM by the search width W until the light reception signal level exceeds the second threshold level TH2. Then, the ASIC 71 determines that the light reception signal level has exceeded the second threshold level TH2 as the second adjustment value AV2.

[0070] After executing the second light intensity adjustment process in S3, the ASIC 71 executes the third light intensity adjustment process in S4. In the third light intensity adjustment process, the ASIC 71 determines the third adjustment value AV3 using the second adjustment value AV2 determined in S3 and the search width W determined in S1. In the third light intensity adjustment process, the ASIC 71 determines as the third adjustment value AV3 the PWM value of the control signal LED_PWM at which the number of times the light reception signal level exceeds the third threshold level TH3 is a predetermined percentage (in this embodiment, 30% or more and 70% or less) of a predetermined number of sampling times (in this embodiment, 120 times). This makes it possible to accurately determine the PWM value of the control signal LED_PWM (third adjustment value AV3) that is closest to the target third threshold level TH3.

[0071] As shown in FIG. 7, when the ASIC 71 starts the third light intensity adjustment process, first, similar to S11 in FIG. 5, it sets the PWM value of the threshold signal TH_PWM so that the threshold level becomes the third threshold level TH3 (=1.65 V) (S31). Note that a value greater than the second threshold level TH2 is used as the third threshold level TH3, but the same value may also be used. Next, the ASIC 71 sets the set value X to the second adjustment value AV2 (S32). The set value X is a variable that ultimately becomes the third adjustment value AV3.

[0072] Next, the ASIC 71 executes the sampling process of S33. As shown in FIG. 8, when the ASIC 71 starts the sampling process, it first sets a set value (the second adjustment value AV2 at this stage) as the PWM value of the control signal LED_PWM and causes the light-emitting diode LED to emit light (S41). Next, the ASIC 71 sets both the number of samplings N and the L count to 0 (S43). The sampling count N is a variable that counts the number of times (the number of samplings) that the light-receiving signal level is compared with the third threshold level TH3 in the sampling process. In this embodiment, the number of samplings is, for example, 120. Note that the number of samplings is not limited to 120. The L count is a variable that indicates the number of times that the light-receiving signal level exceeds the third threshold level TH3 in S45, which will be described later.

[0073] Next, after waiting for a predetermined time (S44), the ASIC 71 determines whether the light reception signal level has exceeded the third threshold level TH3 based on the comparison result signal SG (S45), and if it has exceeded it (S45: YES), it increments the L count by 1 (S46) and increments the number of samplings N by 1 (S47).On the other hand, if the light reception signal level has not exceeded the third threshold level TH3 (S45: NO), the ASIC 71 increments only the number of samplings N by 1 (S47).

[0074] After executing S47, the ASIC 71 determines whether the number of samplings N has reached 120 (S48). The ASIC 71 makes a negative determination in S48 (S48: NO) until the number of samplings reaches 120, and repeatedly executes the process from S44. As a result, the ASIC 71 compares the light-receiving signal level with the third threshold level TH3 every predetermined waiting time, i.e., every predetermined sampling time, and counts the number of times the light-receiving signal level exceeds the third threshold level TH3 as the L count. The ASIC 71 executes this sampling 120 times.

[0075] When the number of samplings N reaches 120 (S48: YES), the ASIC 71 ends the process shown in FIG. 8. As shown in FIG. 7, after executing the sampling process of S33, the ASIC 71 calculates the L ratio by dividing the L count counted in S33 by 120 (the number of samplings) (S34). The ASIC 71 determines whether the calculated L ratio is equal to or less than an upper limit value (=0.7) (S35). If the L ratio is equal to or less than the upper limit value (S35: YES), the ASIC 71 executes S36. If the L ratio is greater than the upper limit value (S35: NO), the ASIC 71 subtracts the search width W from the set value X (S37). That is, the PWM value of the control signal LED_PWM is reduced by the search width W. The ASIC 71 executes the sampling process of S33 again.

[0076] Furthermore, in S36, the ASIC 71 determines whether the L ratio is equal to or greater than the lower limit (=0.3). If the L ratio is equal to or greater than the lower limit (S36: YES), the ASIC 71 sets the set value X at that time as the third adjustment value AV3 (S38) and ends the processing of FIG. 7. If the L ratio is smaller than the lower limit (S36: NO), the ASIC 71 adds the search width W to the set value X (S39). That is, the PWM value of the control signal LED_PWM is increased by the search width W. The ASIC 71 again executes the sampling processing of S33.

[0077] Therefore, the ASIC 71 searches for a set value X such that the L ratio of the number of times (L count) that the light reception signal level exceeds the third threshold level TH3 out of 120 sampling times is greater than or equal to the lower limit value (=0.3) and less than or equal to the upper limit value (=0.7), and sets the set value X that satisfies the condition as the third adjustment value AV3. As a result, the PWM value of the control signal LED_PWM that exceeds the target third threshold level TH3 at approximately half the rate can be set as the third adjustment value AV3. Note that the above-mentioned upper and lower limit values ​​are merely examples. Alternatively, the ASIC 71 may determine the third adjustment value AV3 using only either the upper limit value or the lower limit value.

[0078] 4, after executing S4, the ASIC 71 determines the judgment PWM value DT to be used in the color misregistration correction process of S8 (S5). The ASIC 71 determines the judgment PWM value DT using the first adjustment value AV1, third adjustment value AV3, first threshold level TH1, and third threshold level TH3 determined by the above-mentioned processes. For example, the determination PWM value DT can be determined by the following formula: DT=AV3+(VT-TH3)×{(AV3-AV1) / (TH3-TH1)} In the color shift correction process of S8, the ASIC 71 sets the received light signal level to a target level. VT is the target signal level of the received light signal Vout in this color shift correction process of S8, and is, for example, 2.1 V. Using the above formula, the determination PWM value DT is determined from the difference between the target level VT and the third threshold level TH3, the difference between the third adjustment value AV3 and the first adjustment value AV1, and the difference between the third threshold level TH3 and the first threshold level TH1.

[0079] After determining the determination PWM value DT in S5, the ASIC 71 executes S7 and S8 to perform color shift correction processing using the determined determination PWM value DT. The color shift correction processing can be realized using well-known technology such as that described in prior art document (JP 2010-256715 A), and therefore detailed description thereof will be omitted. The ASIC 71 uses, for example, black as a reference color and yellow, magenta, and cyan as adjustment colors, and adjusts the image formation position of each adjustment color based on the image formation position of the reference color. The ASIC 71 forms toner patches for determining color misregistration correction on the endless belt 63 (S7). These toner patches have, for example, elongated marks of each color in the main scanning direction, and multiple sets of marks are formed on the sheet conveying surface 63A of the endless belt 63 at intervals in the sub-scanning direction, with each set consisting of four marks arranged in the order of black, yellow, magenta, and cyan.

[0080] If the transfer position of the adjustment color is shifted in the sub-scanning direction relative to the transfer position of the reference color, the relative distance between the position of the adjustment color mark and the position of the reference color mark will change. Therefore, the ASIC 71 calculates the relative distance between the position of each adjustment color mark and the position of the reference color mark for each set, and calculates the average value of the relative distances for each adjustment color based on the calculation results for all sets (S8).

[0081] The ASIC 71 outputs a control signal LED_PWM representing the PWM value of the determination PWM value DT determined in S5 to the light emission amount change circuit 81, causing the light emitting diode LED to emit light. The ASIC 71 also sets the PWM value of the threshold signal TH_PWM to a value (e.g., 2.1 V) that causes the threshold voltage TH to become the target level VT. Depending on the presence or absence of a mark on the sheet conveying surface 63A of the endless belt 63, the magnitude relationship between the light reception signal level and the threshold level of the target level VT is reversed, and accordingly, the comparison result signal SG is reversed between high and low levels. The ASIC 71 detects the position of each mark based on the timing at which the signal level of the comparison result signal SG is reversed, and calculates the average value of the relative distance for each adjustment color.

[0082] Then, the ASIC 71 determines the difference between the calculated average value and a predetermined ideal value as the amount of misalignment in the sub-scanning direction of the transfer position relative to the reference color, and stores this amount of misalignment in the sub-scanning direction in the NVRAM 74 (S8). The ASIC 71 ends the color misalignment correction process of S8 and terminates the processing of FIG. 4. Thereafter, when performing image formation based on a print job or the like, the ASIC 71 adjusts the timing of exposing the photosensitive drums 41 corresponding to each adjustment color to offset the amount of misalignment in the sub-scanning direction stored in the NVRAM 74. This makes it possible to eliminate misalignment of the transfer position (color misalignment) between the photosensitive drums 41.

[0083] As described above, the first embodiment provides the following effects. (1) In this embodiment, the ASIC 71 sequentially outputs the control signal LED_PWM, which is updated from the initial value IV by the search width W, to the light emission amount change circuit 81, and determines an adjustment value at which the light reception signal level exceeds the threshold level based on the comparison result signal SG of the comparison circuit 82 (S2, S3, S4, an example of the light amount adjustment process of the present application). When performing each light amount adjustment process, the ASIC 71 sets the initial value IV and the search width W to values ​​that correspond to the deterioration state of the endless belt 63.

[0084] This makes it possible to adjust the initial value IV and the search width W by increasing them when the deterioration of the endless belt 63 progresses and the glossiness of the surface of the endless belt 63 decreases. As a result, when searching for an adjustment value that causes the light reception signal level to exceed the threshold level, the processing time from the start of the search to determining the adjustment value can be shortened. The adjustment value can be determined more quickly.

[0085] (2) In addition, the ASIC 71 outputs the control signal LED_PWM corresponding to the judgment value among the four judgment values ​​(first to fourth judgment values ​​JV1 to JV4) in order from the smallest value to the light emission amount change circuit 81, and determines the initial value IV and the search width W based on the judgment value corresponding to the reception of the comparison result signal SG in which the received light signal level exceeds the threshold level (see Figure 5).

[0086] According to this, before searching for an adjustment value, an initial value determination process (S1) is executed to determine an initial value IV and a search width W. The ASIC 71 uses a plurality of different judgment values, using the smallest judgment value first, and when a low-level comparison result signal SG is received, that is, when the light reception signal level exceeds the threshold level, determines the initial value IV and the search width W based on the judgment value. This makes it possible to determine the initial value IV and the search width W using a judgment value that matches the deterioration state of the endless belt 63 from among the plurality of judgment values.

[0087] (3) The NVRAM 74 also stores search width W values ​​(1 to 4) corresponding to each of the first to fourth judgment values ​​JV1 to JV4 in proportion to their magnitudes. In the initial value determination process, the ASIC 71 determines the initial value IV to be the judgment value that is closest to and smaller than the corresponding judgment value (S14, S18, S22, S23). The ASIC 71 also determines the search width W to be the search width W corresponding to the corresponding judgment value (S14, S18, S22, S23).

[0088] According to this, the ASIC 71 performs a search to use the determination value in ascending order, and determines as the initial value IV the determination value that is immediately smaller than the determination value when the light-receiving signal level exceeds the threshold level. The search can be started from a light-receiving signal level that is lower than the threshold level, and the light-receiving signal level can be more reliably prevented from exceeding the threshold level at the time the search is started. Furthermore, a search width W proportional to the magnitude of the judgment value is used as the search width W. By increasing the search width W as the judgment value increases, the processing time from the start of the search to determining the adjustment value can be shortened.

[0089] (4) After executing the initial value determination process in S2, the ASIC 71 sequentially outputs the control signal LED_PWM, which is updated from the initial value IV by the search width W, to the light emission amount change circuit 81, and determines an adjustment value at which the light reception signal level exceeds the threshold level based on the comparison result signal SG (S2, S3, S4). The ASIC 71 determines the adjustment values ​​(first adjustment value AV1, third adjustment value AV3) determined in the light intensity adjustment process as correction adjustment values, and outputs the control signal LED_PWM (determination PWM value DT) corresponding to the correction adjustment value to the light emission amount change circuit 81 to correct the color shift of the mark formed on the endless belt 63 (S5, S7, S8, an example of the color shift correction process of the present application).

[0090] According to this, the ASIC 71 can shorten the time required to search for an adjustment value in each light intensity adjustment process by using the initial value IV and search width W according to the deterioration state of the endless belt 63. Then, the ASIC 71 outputs a control signal LED_PWM according to the first adjustment value AV1 and the third adjustment value AV3 (determination PWM value DT) determined in the light intensity adjustment process to the light emission amount change circuit 81, and executes the color misregistration correction process. This allows the light emitting diodes LED to emit light at an emission amount according to the deterioration state of the endless belt 63, and allows the marks formed on the endless belt 63 to be detected and color misregistration correction to be executed with higher accuracy. As a result, it becomes possible to prevent misalignment of the transfer position between the multiple photosensitive drums 41 in the image formation process after the correction.

[0091] (5) Furthermore, in the initial value determination process of S2, the ASIC 71 outputs a threshold signal indicating a first threshold level TH1 to the comparison circuit 82, and determines an initial value IV and a search width W based on the first threshold level TH1 (FIG. 5). After executing the initial value determination process, the ASIC 71 outputs, to the comparison circuit 82, a threshold signal indicating the first threshold level TH1, and sequentially outputs control signals LED_PWM updated from the initial value IV by the search width W to the light emission amount change circuit 81, and determines a first adjustment value AV1 at which the light reception signal level exceeds the first threshold level TH1 based on the comparison result signal SG (first light intensity adjustment process of S2). After the first light intensity adjustment process, the ASIC 71 outputs a threshold signal indicating the second threshold level TH2 to the comparison circuit 82, and sequentially outputs to the light emission intensity change circuit 81 the control signal LED_PWM updated by the search width W using the first adjustment value AV1 as the initial value IV, and determines the second adjustment value AV2 at which the light reception signal level exceeds the second threshold level TH2 based on the comparison result signal SG (second light intensity adjustment process of S3). After the second light intensity adjustment process, the ASIC 71 outputs a threshold signal indicating the third threshold level TH3 to the comparison circuit 82, and repeatedly outputs the control signal LED_PWM according to the second adjustment value AV2 to the light emission intensity change circuit 81 120 times, and if the number of times it receives a Low-level comparison result signal SG is within a predetermined range (0.3≦L≦0.7) out of 120 times, it determines the second adjustment value AV2 as the third adjustment value AV3 (see FIG. 7). If the L ratio of the L count is not 0.3 or more (S36: NO), the ASIC 71 determines the third adjustment value AV3 by correcting the second adjustment value AV2 so that the L ratio is 0.3 or more (S39).The ASIC 71 then determines the determination PWM value DT based on the first threshold level TH1, the third threshold level TH3, the first adjustment value AV1, and the third adjustment value AV3 (see the above formula), and outputs the control signal LED_PWM according to the determination PWM value DT to the light emission amount change circuit 81 to correct the color shift.

[0092] According to this, the ASIC 71 determines the first adjustment value AV1 using the initial value IV and search width W determined in the initial value determination process, and the first threshold level TH1, thereby shortening the time required to search for the first adjustment value AV1. Using the first adjustment value AV1 as the initial value IV and the search width W determined in the initial value determination process, the ASIC 71 determines the second adjustment value AV2 at which the received light signal level exceeds the second threshold level TH2. Using the second adjustment value AV2 and the third threshold level TH3, the ASIC 71 determines the third adjustment value AV3 at which the L ratio becomes a predetermined ratio (0.3≦L≦0.7). The ASIC 71 then outputs the control signal LED_PWM corresponding to the determination PWM value DT determined based on the first threshold level TH1 and the like using the above formula to the light emission amount change circuit 81 to perform color shift correction processing. This allows the light emission amount of the light-emitting diode LED to be accurately adjusted to a light emission amount corresponding to the deterioration state of the endless belt 63. As a result, it is possible to prevent deviation of the transfer positions among the plurality of photosensitive drums 41 in the image forming process after the correction.

[0093] (Second embodiment) Next, a second embodiment of the present invention will be described. In the first embodiment described above, in the initial value determination process shown in Fig. 5, both the initial value IV and the search width W are determined in accordance with the deterioration state of the endless belt 63. In contrast, the initial value determination process of the second embodiment shown in Fig. 9 differs from the first embodiment in that only the search width W is determined in accordance with the deterioration state of the endless belt 63. In the following description, the same reference numerals are used to designate the same components as in the first embodiment, and their description will be omitted as appropriate.

[0094] 9, when the light reception signal level exceeds the first threshold level TH1 (S13: YES), the ASIC 71 determines the search width W to be 1. Similarly, the ASIC 71 gradually increases the search width W as the light reception signal level does not exceed the first threshold level TH1 and the judgment value increases (S52, S53, S54). The ASIC 71 increases the search width W as the judgment value increases, i.e., as the deterioration of the endless belt 63 progresses.

[0095] In the second embodiment, for example, in the initial value determination process, the ASIC 71 determines 150 as the initial value IV to be used in the subsequent first light intensity adjustment process. That is, in the first embodiment, the smallest value selected as the initial value IV is set as the initial value IV. As shown in FIG. 6 , when the initial value determination process of the first embodiment is executed, the search width W is increased each time the initial value IV is increased, thereby shortening the processing time until the first adjustment value AV1 is determined. On the other hand, when the initial value determination process of the second embodiment is executed, the initial value IV is set to 150 regardless of the deterioration state of the endless belt 63, and the search is performed from point P2. However, the ASIC 71 increases the search width W as the deterioration of the endless belt 63 progresses. As a result, even if the deterioration of the endless belt 63 progresses and the first adjustment value AV1 increases, the processing time until the first adjustment value AV1 is determined can be shortened by increasing the search width W.

[0096] As described above, the second embodiment provides the same effects as the first embodiment. Furthermore, the second embodiment provides the following effects. (1) In the initial value determination process, the ASIC 71 of the second embodiment determines a common value (=150) for each of a plurality of judgment values ​​as the initial value IV, and determines the search width W to be the search width W corresponding to the corresponding judgment value. According to this, the initial value IV used in the search is not changed, but the search width W is changed. By using a search width W that is proportional to the magnitude of the judgment value as the search width W, the search width W can be increased in accordance with the progress of deterioration of the endless belt 63, and the processing time from the start of the search to the determination of the first adjustment value AV1 can be shortened.

[0097] (Third embodiment) Next, a third embodiment of the present invention will be described. In the first embodiment described above, the first threshold level TH1 was used as the threshold level in the initial value determination process shown in FIG. 5 , but this is not limiting. When only the search width W is determined as in the second embodiment, the threshold level used in the initial value determination process can be changed to any threshold level. In this case, the second to fourth judgment values ​​JV2 to JV4 are changed according to the magnitude of the threshold level (the magnitude of the threshold voltage TH) used in the initial value determination process. The initial value determination process of the third embodiment shown in FIG. 10 differs from the second embodiment in that, for example, the third threshold level TH3 (1.65 V) is used as the threshold level and the magnitudes of the second to fourth judgment values ​​JV2 to JV4 correspond to the third threshold level TH3. In the following description, the same reference numerals are used to designate components similar to those in the second embodiment, and their description will be omitted as appropriate. In addition, in the third embodiment, the initial value determination process determines only the search width W without determining the initial value IV, and therefore the first judgment value JV1 is not used.

[0098] 10, when the ASIC 71 starts the initial value determination process, it first sets the PWM value of the threshold signal TH_PWM to a PWM value of a magnitude (1.65 V) that causes the threshold voltage TH to become the third threshold level TH3 (S61). Therefore, for example, the second to fourth determination values ​​JV2 to JV4 in the third embodiment are set to values ​​obtained by converting the second to fourth determination values ​​JV2 to JV4 (300, 500, 700) when the first threshold level TH1 (0.47 V) shown in FIG. 5 is used as the threshold level to a value when the third threshold level TH3 (1.65 V) is used as the threshold level. Specifically, values ​​of 400, 600, and 800 are set as the second to fourth determination values ​​JV2 to JV4. In this case, values ​​obtained by adding a PWM value of +100 to each of the second to fourth determination values ​​JV2 to JV4 in the first embodiment are respectively used. The values ​​of the second to fourth judgment values ​​JV2 to JV4 described above are merely examples, and the values ​​of the second to fourth judgment values ​​JV2 to JV4 may be changed as appropriate depending on the magnitude of the threshold level used in the initial value determination process and the type and value of the search width W to be determined.

[0099] After executing S61, the ASIC 71 sets the second determination value JV2 (400) as the PWM value of the control signal LED_PWM to cause the light emitting diode LED to emit light (S62), and determines whether the light reception signal level exceeds the third threshold level TH3 (S63). If the light reception signal level exceeds the third threshold level TH3 (S63: YES), the ASIC 71 sets the search width W to 1 (S51).

[0100] On the other hand, if the light-receiving signal level does not exceed the third threshold level TH3 (S63: NO), the ASIC 71 sets the PWM value of the control signal LED_PWM to the third judgment value JV3 (600) to cause the light-emitting diode LED to emit light (S64), and determines whether the light-receiving signal level has exceeded the third threshold level TH3 (S65).If the light-receiving signal level has exceeded the third threshold level TH3 (S65: YES), the ASIC 71 sets the search width W to 2 (S52).

[0101] Similarly, if the ASIC 71 makes a negative determination in S65 (S65: NO), it sets the PWM value to the fourth determination value JV4 (800) (S66), determines the light-receiving signal level (S67), and sets the search width W according to the determination result (S53 or S54). In this way, the search width W can be determined by using a value other than the first threshold level TH1 as the threshold level and setting the determination value to a value according to the changed threshold level.

[0102] (Fourth embodiment) Next, a fourth embodiment of the present invention will be described. In the first embodiment, in the initial value determination process, both the initial value IV and the search width W are determined in accordance with the deterioration state of the endless belt 63. In contrast, the initial value determination process of the fourth embodiment differs from the first embodiment in that only the initial value IV is changed in accordance with the deterioration state of the endless belt 63. That is, contrary to the second embodiment, of the initial value IV and the search width W, only the initial value IV is changed in accordance with the deterioration state.

[0103] Explaining this with reference to FIG. 5 of the first embodiment, the ASIC 71 determines the initial value IV as the first judgment value JV1 in S14, determines the initial value IV as the second judgment value JV2 in S18, determines the initial value IV as the third judgment value JV3 in S22, and determines the initial value IV as the fourth judgment value JV4 in S23. However, the search width W is not changed. In this case, the ASIC 71 determines, for example, 1 as the search width W to be used in the light intensity adjustment process from S3 onward in the initial value determination process. That is, in the first embodiment, the smallest value selected as the search width W is set. In this case, in the first light intensity adjustment process, etc., the search width W is set to 1 to search for the first adjustment value AV1 regardless of the magnitude of the initial value IV. Note that the search width W may be another value, and different search width W values ​​may be set for each light intensity adjustment process.

[0104] As described above, the fourth embodiment provides the same effects as the first embodiment. Furthermore, the fourth embodiment provides the following effects. (1) In the initial value determination process, the ASIC 71 of the fourth embodiment determines a common value (=1) for each of a plurality of judgment values ​​as the search width W. In addition, the ASIC 71 determines the initial value IV to be a value equal to or greater than the judgment value that is closest to and smaller than the corresponding judgment value. According to this, the search width W used in the search is not changed, but the initial value IV is changed. By determining the initial value IV to be the judgment value immediately smaller than the judgment value when the light reception signal level exceeds the first threshold level TH1, it is possible to more reliably prevent the light reception signal level from exceeding the threshold level at the time when the search is started. In addition, the initial value IV can be used according to the deterioration state of the endless belt 63.

[0105] The present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, in the above embodiments, the initial value IV and the search width W are changed when performing color misregistration correction (registration), but the initial value IV, etc. may also be changed when changing the light emitting amount of the light emitting diode LED in other processes. For example, when performing density correction by making the light emitting diode LED emit light, the ASIC 71 may determine the initial value IV, etc. in accordance with the deterioration state of the endless belt 63, determine the first adjustment value AV1, etc. using the determined initial value IV, etc., adjust the light emitting amount of the light emitting diode LED, and perform density correction by making the light emitting diode LED emit light at the adjusted light emitting amount. Although the ASIC 71 executes the three processes, the first light intensity adjustment process, the second light intensity adjustment process, and the third light intensity adjustment process, it may execute only one of the three light intensity adjustment processes. Therefore, the ASIC 71 may determine the determination PWM value DT using at least one adjustment value among the first adjustment value AV1, the second adjustment value AV2, and the third adjustment value AV3. In addition, similar to the third light intensity adjustment process, after executing the first light intensity adjustment process, ASIC71 may execute a process to determine the received light signal level using the first adjustment value AV1 a predetermined number of samplings, and execute a light intensity adjustment process to determine an adjustment value that will cause the received light signal level to exceed the threshold level at a predetermined rate. In addition, in the above-described embodiments, the deterioration state of the endless belt 63 is determined based on the light reception signal level, but this is not limited to this. For example, the ASIC 71 may determine that the deterioration of the endless belt 63 has progressed as the cumulative number of printed sheets in the printer 10 increases, and may increase the initial value IV and the search width W.

[0106] In addition, in each of the above embodiments, a so-called direct tandem type image forming apparatus is employed as the image forming apparatus of the present application, in which the developing cartridges 33 are arranged along the conveyance direction within a predetermined range on the conveyance path 17 of the sheet S. However, the image forming apparatus of the present application is not limited to this, and for example, an intermediate transfer type image forming apparatus in which a toner image is transferred to the sheet S via an intermediate conveyance belt or the like can also be employed. In this case, the intermediate conveyance belt is an example of the endless belt of the present application. In addition, although the above embodiments have employed a color laser printer as the image forming apparatus of the present application, the present application is not limited to this and may be a multifunction peripheral having multiple functions such as a printing function, a copying function, a fax function, and a scanning function. [Explanation of symbols]

[0107] 10 color laser printer (image forming apparatus), 7 sensor board (sensor), 31 image forming unit, 41 photosensitive drum, 63 endless belt, 71 ASIC (control unit), 81 light emission amount change circuit, 82 comparison circuit, AV1 first adjustment value (correction adjustment value), AV2 second adjustment value, AV3 third adjustment value (correction adjustment value), DT judgment PWM value (correction adjustment value), IV initial value, JV1 first judgment value (judgment value), JV2 second judgment value (judgment value), JV3 third judgment value (judgment value), JV4 fourth judgment value (judgment value), LED light emitting diode (light emitting unit), LED_PWM control signal, PTr phototransistor (light receiving unit), SG comparison result signal, TH threshold voltage (threshold level), TH1 first threshold level, TH2 second threshold level, TH3 third threshold level, Vout light receiving signal (light receiving signal level), W search width.

Claims

1. A plurality of photosensitive drums; an endless belt disposed in a position facing the plurality of photosensitive drums; a sensor disposed opposite the endless belt, the sensor including a light-emitting unit that emits light toward the endless belt and a light-receiving unit that receives light reflected by the endless belt; a light emission amount change circuit that changes the amount of light emitted by the light emitting unit in response to an input of a control signal indicating an adjustment value; a comparison circuit that compares a light receiving signal level corresponding to the amount of light received by the light receiving unit with a threshold level, and outputs a comparison result signal indicating that the light receiving signal level exceeds the threshold level; A control unit; Equipped with The control unit a light intensity adjustment process for sequentially outputting control signals updated by the search width from the initial value, and determining an adjustment value at which the light reception signal level exceeds the threshold level based on the comparison result signal; When the light amount adjustment process is executed, at least the initial value or the search width is set to a value corresponding to the deterioration state of the endless belt. Image forming device.

2. The control unit an initial value determination process in which a plurality of different judgment values ​​are set, control signals corresponding to the judgment values ​​are output to the light emission amount change circuit in order from the smallest judgment value, and the comparison result signal is received from the comparison circuit, and the initial value and the search width are determined based on the judgment value corresponding to the comparison result signal received; To execute The image forming apparatus according to claim 1 .

3. The control unit a search width corresponding to each of the plurality of judgment values ​​is determined so as to be proportional to the magnitude of the judgment value, In the initial value determination process, determining the initial value to be the closest smaller determination value than the corresponding determination value; determining the search width to be a search width corresponding to the relevant judgment value; The image forming apparatus according to claim 2 .

4. The control unit a search width corresponding to each of the plurality of judgment values ​​is determined so as to be proportional to the magnitude of the judgment value, In the initial value determination process, determining a common value for each of the plurality of determination values ​​as the initial value; determining the search width to be a search width corresponding to the relevant judgment value; The image forming apparatus according to claim 2 .

5. The control unit In the initial value determination process, determining a common value for each of the plurality of determination values ​​as the search width; determining the initial value to be equal to or greater than the judgment value that is closest to the corresponding judgment value and smaller than the corresponding judgment value; The image forming apparatus according to claim 2 .

6. The control unit a light intensity adjustment process in which, after the initial value determination process is executed, control signals updated from the initial value by the search width are sequentially output to the light emission amount change circuit, and an adjustment value at which the light reception signal level exceeds the threshold level is determined based on the comparison result signal; a color misregistration correction process in which the adjustment value determined in the light amount adjustment process is determined as a correction adjustment value, and a control signal corresponding to the correction adjustment value is output to the light emission amount change circuit to correct color misregistration of the marks formed on the endless belt; The image forming apparatus according to claim 2 , wherein the image forming apparatus executes the above.

7. The control unit The threshold level is changeable, and a first threshold level, a second threshold level, and a third threshold level are set, In the initial value determination process, a threshold signal indicating the first threshold level is output to the comparison circuit, and an initial value and a search width are determined based on the first threshold level; a first light amount adjustment process in which, after the execution of the initial value determination process, a threshold signal indicating the first threshold level is output to the comparison circuit, control signals updated from the initial value by the search width are sequentially output to the light emission amount change circuit, and a first adjustment value at which the light reception signal level exceeds the first threshold level is determined based on the comparison result signal; a second light amount adjustment process in which, after the first light amount adjustment process, a threshold signal indicating the second threshold level is output to the comparison circuit, control signals updated by the search width using the first adjustment value as an initial value are sequentially output to the light emission amount change circuit, and a second adjustment value at which the light reception signal level exceeds the second threshold level is determined based on the comparison result signal; After the second light amount adjustment process, a threshold signal indicating the third threshold level is output to the comparison circuit, and a control signal corresponding to the second adjustment value is repeatedly output to the light emission amount change circuit a predetermined number of times; If the number of times the comparison result signal has been received exceeds a predetermined percentage of the predetermined number of times, the second adjustment value is determined to be a third adjustment value; a third light amount adjustment process for determining a third adjustment value by correcting the second adjustment value when the number of received comparison result signals does not exceed the predetermined percentage or more, so that the light receiving signal levels of the number of received comparison result signals that is equal to or greater than the predetermined percentage exceed the third threshold level; a color misregistration correction process that determines a correction adjustment value based on the first threshold level, the third threshold level, the first adjustment value, and the third adjustment value, and outputs a control signal according to the correction adjustment value to the light emission amount change circuit to correct color misregistration of the mark formed on the endless belt; 3. The image forming apparatus according to claim 2, wherein the image forming apparatus executes the following.

Images