JP2016090927A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably and accurately perform color shift detection even when there is unevenness in intensity of the reflection light from an image carrier such as an intermediate transfer belt.SOLUTION: A laser printer 30 comprises: a plurality of image forming parts 5 that each form a toner image on a photoreceptor drum 1; an intermediate transfer belt 8 to which a toner image is transferred; a color shift detection sensor 41 that has a light emitting element 51 and a light receiving element 52 and detects color shift correction toner images 44L and 44R on the intermediate transfer belt 8; and a printer control part 101 that adjusts, when the color correction toner images 44L and 44R are detected, the emission intensity of the light emitted by the light emitting element 51 according to each of a plurality of positions of the intermediate transfer belt 8 on the basis of the intensity of the reflection light from the plurality of positions of the intermediate transfer belt 8, which is received by the light receiving element 52.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus, and more particularly, to a color image forming apparatus using an electrophotographic recording method such as a laser printer, a copying machine, a facsimile.

  2. Description of the Related Art Conventionally, an image forming apparatus using an electrophotographic recording method has been advanced in speed and functionality. In particular, various systems have been put to practical use in color image forming apparatuses that enable multicolor image formation. For example, in an in-line color image forming apparatus using an intermediate transfer belt, a laser beam is irradiated on a photosensitive drum, and an electrostatic latent image on the photosensitive drum is generated by an electrophotographic process by an image forming unit corresponding to each color. Developed. The electrostatic latent image on the photosensitive drum is developed by the developing device to become a toner image, and the color toner images are sequentially transferred onto the recording paper to obtain a color image.

  At this time, if the transfer position of the image of each color on the recording paper is relatively shifted, the color of the color image changes. As the degree of positional deviation on the recording paper of each color further progresses, an image with color misregistration is formed on the recording paper, and as a result, the quality of the image printed on the paper surface decreases. Therefore, in recent years, color image forming apparatuses perform control for correcting color misregistration (hereinafter referred to as color misregistration correction control) when the main body is turned on or at an arbitrary timing. In the color misregistration correction control, the image forming unit forms a detection pattern for color misregistration detection (hereinafter referred to as a color misregistration detection pattern) on an intermediate transfer belt (hereinafter referred to as a belt). Then, the color misregistration detection sensor optically reads the color misregistration detection pattern. The control unit calculates a deviation amount of the image writing position on the photosensitive drum corresponding to each color based on the color deviation amount detected as reflected light from the belt surface, and the image writing position with respect to the image signal. Control to apply electrical correction to correct the.

  The amount of light emitted by the light emitting part of the detection sensor when detecting the color misregistration detection pattern is adjusted in consideration of dirt on the intermediate transfer belt and the light receiving part of the color misregistration detection sensor, variation in the density of the color misregistration detection pattern, etc. (For example, refer to Patent Documents 1 and 2).

JP-A-6-127039 JP 2008-96744 A

  However, when the belt itself has unevenness of reflected light depending on the detection position on the belt surface, it may be difficult to detect color misregistration with high accuracy. The belt has a multilayer structure, and the reflected light on the belt surface is interference light of a plurality of reflected light such as light reflected on the surface of the belt and light reflected on a layer inside the belt. Depending on the belt material, the light reflected by the layers inside the belt may affect the reflected light on the belt surface. If the thickness of the surface layer of the belt varies, the intensity of the reflected light on the inner layer of the belt during the rotation of the belt (hereinafter referred to as the belt rotation) also varies. If the reflected light intensity on the belt surface varies within the belt rotation, the difference in intensity between the reflected light intensity on the belt surface and the reflected light intensity from the color misregistration detection pattern will fluctuate, and color misregistration detection accuracy will change. May be affected.

  The present invention has been made under such circumstances, and it is an object of the present invention to detect color misregistration stably and accurately even when the intensity of reflected light from an image carrier such as an intermediate transfer belt is uneven. And

  In order to solve the above problems, the present invention has the following configuration.

  (1) An image forming apparatus, each having a photosensitive drum, a plurality of image forming means for forming a toner image on each photosensitive drum, and an image onto which the toner image on the photosensitive drum is transferred A carrier, a light emitting unit that emits light toward the image carrier, and a light receiving unit that receives reflected light from the image carrier, and is used to correct color misregistration formed on the image carrier. Detecting means for detecting a toner image; and, when detecting the toner image for color misregistration correction, based on the intensity of reflected light from a plurality of positions of the image carrier received by the light receiving means. An image forming apparatus comprising: an adjusting unit that adjusts the light emission intensity of the light emitted by the light emitting unit according to a plurality of positions of the body.

  (2) An image forming apparatus, each having a photosensitive drum, a plurality of image forming means for forming a toner image on each photosensitive drum, and an image onto which the toner image on the photosensitive drum is transferred A carrier, a light emitting unit that emits light toward the image carrier, and a light receiving unit that receives reflected light from the image carrier, and is used to correct color misregistration formed on the image carrier. Detecting means for detecting a toner image; and, when detecting the toner image for color misregistration correction, based on the intensity of reflected light from a plurality of positions of the image carrier received by the light receiving means. An image forming apparatus comprising: an adjusting unit that adjusts the light receiving sensitivity of the light receiving unit according to each of a plurality of positions on the body.

  (3) An image forming apparatus, each having a photosensitive drum, a plurality of image forming means for forming a toner image on each photosensitive drum, and an image onto which the toner image on the photosensitive drum is transferred A carrier, a light emitting unit that emits light toward the image carrier, and a light receiving unit that receives reflected light from the image carrier, and is used to correct color misregistration formed on the image carrier. Detecting means for detecting a toner image; and, when detecting the toner image for color misregistration correction, based on the intensity of reflected light from a plurality of positions of the image carrier received by the light receiving means. An image forming apparatus, comprising: a correction unit that corrects a light detection result by the light receiving unit according to each of a plurality of positions of the body.

  According to the present invention, even when the intensity of reflected light from an image carrier such as an intermediate transfer belt is uneven, color misregistration can be detected stably and accurately.

Schematic configuration diagram and control block diagram of laser printers according to first and second embodiments Configuration explanatory diagram of the color misregistration detection sensor of Examples 1 and 2, a layout diagram explaining the arrangement state of the color misregistration detection sensor, a graph showing the output voltage value of the color misregistration detection sensor and its compare value The figure explaining the nonuniformity of the reflected light intensity from an intermediate transfer belt, The graph which shows the output voltage of the color shift detection sensor of Example 1. Flowchart of color misregistration correction control according to the first embodiment, flowchart of control for adjusting the amount of emitted light in color misregistration correction Waveform graph of specular reflection light intensity and light emission intensity in Example 1 and conventional color misregistration correction control Flowchart of color misregistration correction control of Example 2, flowchart of control for adjusting light emission quantity in color misregistration correction control Timing chart of color misregistration correction control of embodiment 2 Flow chart of color misregistration correction control in Embodiments 3 and 4

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail by way of examples with reference to the drawings.

<Overall configuration of image forming apparatus>
FIG. 1A is a schematic diagram of a laser printer 30 as an image forming apparatus. The laser printer 30 is a color electrophotographic image forming apparatus capable of multicolor printing using an electrophotographic image forming process. A laser printer 30 shown in FIG. 1A includes a plurality of (four in the first embodiment) cartridges 5Y, 5M, 5C, and 5K, an intermediate transfer belt unit U, and a feeding / conveying device that can be attached to and detached from the apparatus main body 30a. An apparatus (feed / conveying means) 12 and a fixing device 17 are provided. In the present invention, the cartridge is also referred to as an image forming unit (image forming unit). The four image forming units 5Y, 5M, 5C, and 5K have the same structure, but toners (developers) of different colors of yellow (Y), magenta (M), cyan (C), and black (K). ) Is different in that an image is formed. Hereinafter, the entire image forming unit will be described with reference numerals. When a member corresponding to a specific color is described, Y, M, C, and K are added to the reference numerals, such as Y for yellow and M for magenta.

  The image forming unit 5 includes a toner container 23, a photosensitive drum 1 as a photosensitive member, a charging roller 2, a developing roller 3, a cleaning blade (photosensitive member cleaning unit) 4, and a waste toner container 24. An exposure device 7 is disposed below the image forming unit 5 in FIG. 1, and exposure based on the image signal is performed on the photosensitive drum 1 by the exposure device 7. Here, as an example, the process cartridge is defined as having the toner container 23, the photosensitive drum 1, the charging roller 2, the developing roller 3, the cleaning blade 4, and the waste toner container 24, but is not limited thereto. For example, a cartridge in which the toner container 23, the photosensitive drum 1, and the developing roller 3 are integrated may be used.

  In this embodiment, the photosensitive drum 1 is an OPC (organic optical semiconductor) photosensitive drum having a negative charging characteristic of 25 mm in diameter. The photosensitive drum 1 is rotationally driven at a peripheral speed (process speed) of 180 mm / sec during image formation. The photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by the charging roller 2 in the process of rotation. When the photosensitive drum 1 is subjected to image exposure based on a predetermined image by the exposure device 7, an electrostatic latent image corresponding to the image is formed on the photosensitive drum 1. For example, an electrostatic latent image corresponding to a yellow image is formed on the photosensitive drum 1Y corresponding to yellow by the exposure device 7Y. The same applies to the other colors (magenta, cyan, black).

  The image forming unit 5Y corresponding to yellow corresponds to the first image forming unit, the image forming unit 5M corresponding to magenta corresponds to the second image forming unit, the image forming unit 5C corresponding to cyan corresponds to the third image forming unit, and black. The image forming unit 5K that performs this process is referred to as a fourth image forming unit. The photosensitive drums 1Y, 1M, 1C, and 1K are arranged so that their peripheral surfaces are in contact with an endless belt-like intermediate transfer belt (image carrier) 8 described later.

  The charging roller 2 is driven to rotate as the photosensitive drum 1 rotates. The exposure apparatus 7 used in the first embodiment has a polygon scanner using a laser diode, forms an image of a laser beam modulated according to image information on the photosensitive drum 1, and generates an electrostatic latent image. Form. The start timing of laser exposure is delayed by a predetermined time from the position signal (BD signal) in the polygon scanner for each scanning line in the main scanning direction (direction perpendicular to the transport direction in the surface of the transfer material). . Further, in the sub-scanning direction (transfer material transport direction), exposure is performed with a predetermined time interval between the image forming units 5. In other words, in order to synchronize the positions of the toner images when superimposing the toner images of the respective colors, the exposure start timing between the image forming units 5 is set according to the time during which the intermediate transfer belt 8 moves between the image forming units 5. It is shifted. As a result, the positions of the toner images of the respective colors in the first to fourth image forming units 5 can be synchronized, and color misregistration can be suppressed.

  The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing roller 3. Each color toner adheres to the electrostatic latent image on the photosensitive drum 1 through the developing roller 3 and is developed as a toner image. The toner in each toner container 23 is a non-magnetic one-component toner charged to a negative polarity, and development of the electrostatic latent image is performed by a non-magnetic one-component contact development method. The developing roller 3 has a diameter of 12 mm, for example, and rotates with respect to the photosensitive drum 1 in the forward direction at the same peripheral speed. A developing voltage is applied to the developing roller 3 by a developing voltage power source (not shown), and development is performed by this developing voltage.

  The intermediate transfer belt unit U includes an intermediate transfer belt 8, a driving roller 9, and a secondary transfer counter roller 10. A primary transfer roller 6 is disposed so as to sandwich the intermediate transfer belt 8 together with the photosensitive drum 1. A primary transfer voltage having a positive polarity is applied to the primary transfer roller 6 by a primary transfer voltage power source (not shown). The intermediate transfer belt 8 is rotated by a driving roller 9 that is driven to rotate by a motor (not shown). As the intermediate transfer belt 8 rotates, the secondary transfer counter roller 10 also rotates. In the first embodiment, the driving roller 9 has a diameter of 30 mm, and the rotation speed of the intermediate transfer belt 8 is 180 mm / sec. The photosensitive drum 1 rotates in the arrow direction (clockwise direction) in FIG. 1, and the intermediate transfer belt 8 rotates in the arrow A direction in FIG. A positive primary transfer voltage is applied to the primary transfer roller 6, and the toner images on the photosensitive drum 1 are primarily transferred onto the intermediate transfer belt 8 in the order of the photosensitive drums 1Y, 1M, 1C, and 1K. Thereafter, in a state where the four color toner images are superimposed on the intermediate transfer belt 8, the toner images are transferred to the secondary transfer roller (transfer means) 11 disposed so as to sandwich the intermediate transfer belt 8 together with the secondary transfer counter roller 10. Be transported. The cleaning blade 4 of the photosensitive drum 1 contacts the photosensitive drum 1 and removes toner remaining on the surface of the photosensitive drum 1 without being transferred to the intermediate transfer belt 8.

  The feeding / conveying device 12 includes a sheet feeding roller 14 that feeds the transfer material P from the sheet feeding cassette 13 that houses the transfer material P, and a conveyance roller that conveys the fed transfer material P toward the registration roller pair 16. Pair 15. A registration roller pair 16 is arranged in the middle of the conveyance path from the feeding / conveying device 12 to the secondary transfer roller 11. The transfer material P conveyed from the feeding / conveying device 12 is conveyed to the secondary transfer roller 11 by the registration roller pair 16. A positive voltage is applied to the secondary transfer roller 11, and the four color toner images on the intermediate transfer belt 8 are transferred to the transferred transfer material P. Hereinafter, the transfer of the toner image from the intermediate transfer belt 8 to the transfer material P is referred to as secondary transfer. After the toner image is transferred, the transfer material P is conveyed to the fixing device 17 and heated and pressed by the fixing roller 18 and the pressure roller 19 to fix the toner image on the surface. The transfer material P on which the toner image is fixed is discharged by the paper discharge roller pair 20.

  In the laser printer 30 having such an intermediate transfer belt 8, if toner remains on the surface of the intermediate transfer belt 8 and adheres to it, it may cause the backside of the transfer material P or image stains. Specifically, when the toner adheres to the surface of the intermediate transfer belt 8, the non-image portion is caused by the toner remaining on the intermediate transfer belt 8 after the secondary transfer to the transfer material P, the paper jam of the transfer material P, or the like. There is a so-called fog toner or the like in which the toner adheres. In addition, a color misregistration detection toner image (also referred to as a color misregistration correction toner image or a test pattern image) transferred from the photosensitive drum 1 for color misregistration detection remains on the surface of the intermediate transfer belt 8 and becomes attached toner. obtain. These toners remaining on and adhering to the intermediate transfer belt 8 are removed by the transfer belt cleaning blade 21 and accumulated in the collection container 22.

  The laser printer 30 according to the first embodiment includes a color misregistration detection sensor (detection unit) 41, a circumference detection mark 43, and a circumference detection sensor (perimeter detection unit) 42 for detecting a color misregistration (position misalignment). (See FIGS. 2A and 2B). The color misregistration detection sensor 41 is located on the upstream side of the secondary transfer roller 11 in the rotation direction of the intermediate transfer belt 8 and is located on the most downstream side of the four image forming units (image forming unit). Part 5K) on the downstream side. Further, the color misregistration detection sensor 41 is disposed at a position facing the secondary transfer counter roller 10. The color misregistration detection sensor 41 is for detecting a color misregistration detection toner image transferred onto the intermediate transfer belt 8 by the photosensitive drum 1. Generally, an optical sensor is used for the color misregistration detection sensor 41. It is done.

  The circumference detection mark 43 is a reference mark that is disposed on the intermediate transfer belt 8 and detects the rotational position of the intermediate transfer belt 8. By detecting the circumference detection mark 43 by the circumference detection sensor 42, it is possible to grasp the presence / absence of driving of the intermediate transfer belt 8, the circumference, and the reference position within the circumference. The circumference detection mark 43 has a color (eg, black, silver, etc.) that can be detected by the circumference detection sensor 42 and a shape (eg, line shape, dot shape, etc.). The circumference detection mark 43 is arranged near the side edge (non-image forming area) on the intermediate transfer belt 8 so as not to affect image transfer from the photosensitive drum 1.

  The circumference detection sensor 42 is a sensor for detecting the circumference detection mark 43, and generally an optical sensor is used as the circumference detection sensor 42. The circumferential length detection sensor 42 is disposed in the vicinity of the side edge of the intermediate transfer belt 8 and at a position facing the secondary transfer facing roller 10 in order to detect the circumferential length detection mark 43.

<Control block diagram>
FIG. 1B is a control block diagram of the laser printer 30 according to the first embodiment. The printer control unit 101 includes a memory having a ROM 201 a and a RAM 201 b and a CPU 201, and executes a program for controlling each device in the laser printer 30. The CPU 201 controls each device in the laser printer 30 while using the RAM 201b as a work area according to various programs stored in the ROM 201a. Furthermore, the CPU 201 has a timer function and can also measure time.

  The printer control unit 101 controls each unit of the laser printer 30 based on various control programs while using the memory as a work area. The host computer 104 transfers data for printing to the laser printer 30. The controller 103 performs communication between the laser printer 30 and the host computer 104. The controller 103 receives image information and a print command from the host computer 104, analyzes the received image information, and converts it into bitmap data. The controller 103 transmits bitmap data to the printer control unit 101 in synchronization with the TOP signal received from the printer control unit 101 during printing. The motor drive control unit 110 rotates a motor (not shown) that drives the photosensitive drum 1 and the drive roller 9 based on an instruction from the printer control unit 101. The primary transfer voltage control unit 112 controls the power supply of the primary transfer voltage applied between the primary transfer roller 6 and the photosensitive drum 1 based on an instruction from the printer control unit 101.

  The light emission control unit 113 controls the light emitting element (light emitting unit) 51 (see FIG. 2A) of the color misregistration detection sensor 41 based on an instruction from the printer control unit 101. The light emitting element 51 is, for example, an LED. In the first embodiment, the printer control unit 101 includes a PWM signal generation circuit (not shown). The printer control unit 101 turns on the light emitting element 51 by transmitting a PWM signal to the light emission control unit 113. The printer control unit 101 can change the light amount of the light emitting element 51 by changing the duty setting of the PWM signal.

  The printer control unit 101 can set the duty of the PWM signal in 201 steps in increments of 0.5% from 0% to 100%. The light reception control unit 114 converts a signal from the light receiving element (light receiving unit) 52 (see FIG. 2A) of the color misregistration detection sensor 41 into an electrical signal. The comparator 115 binarizes the output value of the color misregistration detection sensor 41 ((c-1) in FIG. 2C) output from the light reception control unit 114 ((c-2) in FIG. 2C). A binarized signal is input to the printer control unit 101. Further, the A / D converter 116 converts the output value of the color misregistration detection sensor 41 ((c-1) in FIG. 2C) output from the light reception control unit 114 into a 10-bit digital signal, and performs printer control. Output to the unit 101.

  The circumference detection sensor light receiving unit 111 detects the circumference detection mark 43 disposed in the vicinity of the side edge of the intermediate transfer belt 8 with the circumference detection sensor 42 (see FIG. 2B), and the detection signal is printer-controlled. Input to the unit 101. Note that the printer control unit 101 manages a control sequence to be described later using, for example, a counter. Further, for example, a timer may be used instead of the counter. Each function of the printer control unit 101 may be realized by the CPU executing various control programs, or a part or all of the function may be performed by a dedicated circuit (ASIC) for a specific application.

<Color shift detection sensor and color shift correction>
FIG. 2A is a diagram for explaining the configuration of the color misregistration detection sensor 41. The color misregistration detection sensor 41 includes a light emitting element 51 that is an LED, a light receiving element 52 that is a photodiode, an arithmetic processing unit (IC) (not shown) that processes a detection signal, and a holder (not shown) that accommodates these. Is done. The light emitting element 51 irradiates the intermediate transfer belt 8 with light 53. The light receiving element 52 detects the reflected light intensity by receiving the reflected light 54 from the intermediate transfer belt 8. The light receiving element 52 receives reflected light from the color misregistration detection toner image when a later-described color misregistration detection toner image is formed on the intermediate transfer belt 8.

  FIG. 2B is an arrangement diagram for explaining an arrangement state of the color misregistration detection sensor 41. In FIG. 2B, the main configuration including the intermediate transfer belt 8 is viewed from the image forming unit 5 side (that is, obliquely from below in FIG. 1A). The color misregistration detection sensors 41 are respectively arranged in the vicinity of both side edges along the width direction of the intermediate transfer belt 8 (direction orthogonal to the circumferential direction). In FIG. 2B, a color misregistration detection sensor 41R is arranged in the vicinity of the side edge on the back side, and a color misregistration detection sensor 41L is arranged in the vicinity of the side edge on the near side. The two color misregistration detection sensors 41R and 41L are positions for detecting the color misregistration detection toner images 44R and 44L transferred onto the intermediate transfer belt 8 by the photosensitive drum 1, respectively.

  The color misregistration detection toner images 44R and 44L may be line images formed linearly along the width direction of the intermediate transfer belt 8, as shown in FIG. The color misregistration detection toner images 44R and 44L may be line images formed in a linear shape extending obliquely in the width direction and the circumferential direction of the intermediate transfer belt 8 (the arrow direction in FIG. 2B). . When the light receiving element 52 is a line sensor along the width direction of the intermediate transfer belt 8 and the color misregistration detection toner images 44R and 44L are diagonal line images, not only in the sub-scanning direction but also in the main scanning direction. Color misregistration can also be detected.

  The color misregistration detection sensor 41 according to the first embodiment is configured to detect regular reflection light. The surface of the intermediate transfer belt 8 is glossy. In a state where the surface of the intermediate transfer belt 8 is exposed (the toner amount is 0), the light receiving element 52 of the color misregistration detection sensor 41 detects reflected light of substantially regular reflection from the glossy surface of the intermediate transfer belt 8. . On the other hand, when a toner image is formed on the intermediate transfer belt 8, the reflected light intensity detected by the light receiving element 52 decreases as the toner density (toner amount) increases, and the regular reflection output of the light receiving element 52 decreases. . This is because the regular reflection light from the surface of the intermediate transfer belt 8 is reduced by the toner covering the surface of the intermediate transfer belt 8.

  (C-1) in FIG. 2C shows the output voltage when the light receiving element 52 detects the reflected light from the intermediate transfer belt 8, the vertical axis is the output voltage value, and the horizontal axis is the time. It is. The output voltage of the light receiving element 52 is proportional to the reflected light intensity detected by the light receiving element 52. In (c-1), the surface of the intermediate transfer belt 8 on which the toner image is not formed → the surface of the intermediate transfer belt 8 on which the toner image is formed (hereinafter referred to as a toner image portion) → the toner image is formed. A state in which the light receiving element 52 detects reflected light in the order of the surface of the intermediate transfer belt 8 that has not been detected is shown. The “toner image portion” means a portion where the color misregistration detection toner image is transferred onto the intermediate transfer belt 8.

  A signal from the light receiving element 52 is input to the comparator 115 and compared with a predetermined threshold level TH. The comparator 115 converts the signal level from the light receiving element 52 to 1 (on) when the signal level is equal to or higher than a predetermined threshold level TH, and converts it to 0 (off) when the signal level is lower than the predetermined threshold level TH. Is input to the unit 101 ((c-2) in FIG. 2C). The printer control unit 101 detects the timing (T1) at which the front end of the toner image portion is detected from the output of the comparator 115 and the timing (T2) at which the rear end is detected, and the center of gravity position (T2) of the toner image portion based on these timings T1 and T2. T3) is determined. In the color misregistration correction control described later, the printer control unit 101 obtains the color misregistration amount from the barycentric position for each toner image portion generated by each image forming unit 5.

<Control process for color misregistration correction>
In the laser printer 30 having the color misregistration detection sensor 41, color misregistration correction control for correcting color misregistration between the image forming units 5 is executed. During the standby state of the laser printer 30, a test pattern image for color misregistration detection is transferred onto the intermediate transfer belt 8. The transferred test pattern image is detected by the color misregistration detection sensor 41, color misregistration in the sub-scanning direction (rotating direction of the intermediate transfer belt 8) between the image forming units 5, and main scanning direction (perpendicular to the sub-scanning direction). Color misregistration) is detected. The detected color misregistration information is notified to the controller 103 by the printer control unit 101.

  The controller 103 electrically corrects the bitmap data based on the color misregistration information notified from the printer control unit 101 and performs control for reducing the color misregistration on the transfer material P. The information notified to the controller 103 by the printer control unit 101 is how much the laser emission timing of the other colors is delayed with respect to the laser emission timing of the reference color (TOP signal output timing) in the sub-scanning direction. Have information. The reference color in the sub-scanning direction in the first embodiment is yellow (Y). The controller 103 delays the timing for transmitting the bitmap data to the printer control unit 101 according to the information notified from the printer control unit 101.

  The information notified to the controller 103 by the printer control unit 101 includes information on how much the laser emission timings of other colors are advanced or delayed with respect to the laser emission timings of the reference colors in the main scanning direction. . The reference color in the main scanning direction in the first embodiment is black (K). The controller 103 adjusts the timing for transmitting the bitmap data to the printer control unit 101 according to the information notified from the printer control unit 101.

<Effect of unevenness of belt surface condition on color shift detection>
FIG. 3A shows the output of the circumference detection sensor 42 when the intermediate transfer belt 8 is rotated, the TOP signal, the intensity of specular reflection detected by the light receiving element 52, and the light emission intensity of the light emitting element 51. A timing chart is shown. In FIG. 3A, T202 and T204 indicate the timing when the circumference detection sensor 42 detects the circumference detection mark 43. That is, the timing T202 to T204 indicates the rotation (circulation) of the intermediate transfer belt 8 for one rotation.

  In FIG. 3A, the light intensity of the light emitting element 51 of the color misregistration detection sensor 41 is constant, and the reflected light from the intermediate transfer belt 8 is received by the light receiving element 52. If the surface state of the intermediate transfer belt 8 and the thickness of the surface layer vary, the intensity of specular reflection light from the surface within the circumference of the intermediate transfer belt 8 is increased as shown at timings T202 to T204 in FIG. Unevenness may occur. The unevenness of the regular reflection light intensity may affect the accuracy of color misregistration detection.

  FIG. 3B shows how the test pattern image is detected by the color misregistration detection sensor 41 when the intensity of specular reflection light on the surface of the intermediate transfer belt 8 is relatively high (background level is large). FIG. 3C shows how the test pattern image is detected by the color misregistration detection sensor 41 when the intensity of specularly reflected light on the surface of the intermediate transfer belt 8 is relatively small (background level is small). 3B and 3C, the vertical axis represents an output voltage value or a compare value (on / off value), and the horizontal axis represents time. In FIG. 3, the on / off polarity of the compare value is shown inverted from that in FIG. Here, the detected test pattern image is the same in both the case of FIG. 3B and the case of FIG. Further, in FIG. 3, the vertical axes are aligned at the same time timing.

  The position at which the test pattern image reaches the detection range of the color misregistration detection sensor 41 by the rotation of the intermediate transfer belt 8 and the detection of the test pattern image starts is referred to as “the tip of the test pattern image”. Further, the position where the test pattern image moves out of the detection range of the color misregistration detection sensor 41 and the detection of the test pattern image ends is referred to as “the rear end of the test pattern image”.

  In the case of FIG. 3C where the intensity of specular reflection light on the surface of the intermediate transfer belt 8 is small, the light receiving element 52 of the test pattern image is compared with the case of FIG. 3B where the intensity of specular reflection light is large. The time from when the tip is detected until the regular reflected light waveform reaches a predetermined threshold level TH is short. That is, even when the same test pattern image is detected, the timing (T1) at which the comparator 115 switches from off to on is shifted if the regular reflection light intensity on the belt surface is different.

  Further, the regular reflection light waveform returning to the regular reflection intensity on the surface of the intermediate transfer belt 8 near the rear end of the test pattern image is also affected by the regular reflection light intensity on the surface of the intermediate transfer belt 8. In other words, the path of the specularly reflected light waveform at the leading edge and the trailing edge of the test pattern image differs depending on whether the intensity of the specularly reflected light on the surface of the intermediate transfer belt 8 is large or small. The center of gravity (T3) position of the test pattern image to be matched does not match. Therefore, if there is uneven regular reflected light intensity on the belt surface during one rotation of the intermediate transfer belt 8 shown at timings T202 to T204 in FIG. 3A, the detected barycentric position is shifted for each test pattern image. As a result, an error may occur in color misregistration detection.

  Further, when the intensity of specular reflection light on the surface of the intermediate transfer belt 8 is too large, the specular reflection light intensity at the time of detecting the test pattern image may not be lowered to the threshold level TH. When the intensity of specular reflection light on the surface of the intermediate transfer belt 8 is too small, if the potential difference between the output voltage and the threshold level TH is small, the sensor output voltage varies due to scratches on the intermediate transfer belt 8. There is a possibility that the test pattern image is erroneously detected.

  Note that irregularities in the regular reflection light intensity on the surface of the intermediate transfer belt 8 are caused by irregularities in the thickness of the surface layer of the belt, and therefore the fluctuation period is sufficiently larger than the period of the detection signal of the test pattern image.

<Light amount adjustment in color misregistration correction control>
In the first embodiment, the light amount of the light emitting element 51 is adjusted in accordance with the unevenness of the regular reflection light intensity from the surface of the intermediate transfer belt 8, thereby reducing the influence of the unevenness of the regular reflection light intensity on the color shift detection. In the first embodiment, in parallel with the detection of the surface state unevenness of the intermediate transfer belt 8 and the detection of the test pattern image for color misregistration detection, the unevenness of the regular reflection light intensity on the surface of the intermediate transfer belt 8 is reduced. The light amount of the light emitting element 51 is adjusted.

  The first embodiment will be described with reference to the flowcharts of FIGS. 4A and 4B and the timing charts of FIGS. 5A and 5B. FIG. 5A shows a TOP signal, a waveform graph of regular reflection light intensity in the conventional color misregistration correction control, and a waveform graph of light emission intensity by the light emitting element 51. FIG. 5B shows a TOP signal, a waveform graph of regular reflection light intensity in the color misregistration correction control of the first embodiment, and a waveform graph of light emission intensity by the light emitting element 51. In the conventional color misregistration correction control shown in FIG. 5A, the light emission intensity by the light emitting element 51 is constant. Therefore, if the surface state of the intermediate transfer belt 8 or the thickness of the surface layer varies, the regular reflection light intensity detected by the light receiving element 52 varies as a whole. A test pattern image detection signal is output so as to be superimposed on the regular reflected light intensity unevenness. In the color misregistration correction control of the first embodiment shown in FIG. 5B, the light emission intensity of the light emitting element 51 is adjusted corresponding to the irregular reflection light intensity unevenness (T111 to T113). Therefore, regular reflection light intensity unevenness caused by variations in the surface state of the intermediate transfer belt 8 and the thickness of the surface layer is removed from the reflection light intensity detected by the light receiving element 52. Hereinafter, the color misregistration correction control according to the first embodiment will be described with respect to the color misregistration detection sensor 41L. However, in the color misregistration correction control, the printer control unit 101 performs the same control for the color misregistration detection sensor 41R. .

  In step (hereinafter referred to as S) 101, the printer control unit 101 starts rotating the intermediate transfer belt 8. In step S102, the printer control unit 101 turns on the light emitting element 51 at timing T110 with the initial light amount of the light emitting element 51 stored in advance in the ROM 201a. In S103, it waits for a predetermined time (for example, 5 seconds) until the light emission intensity of the light emitting element 51 is stabilized (until rising). In step S104, the printer control unit 101 outputs a TOP signal to the controller 103 at timing T111. The controller 103 transmits a video signal for generating a test pattern image for color misregistration detection to the printer control unit 101 in synchronization with the TOP signal. Thereby, a test pattern image is formed in the image forming unit 5.

  In step S110, between timings T111 and T113, the printer control unit (adjustment unit) 101 outputs a TOP signal, and then performs feedback control for adjusting the light amount of the light emitting element 51 based on the reflected light intensity on the surface of the intermediate transfer belt 8. Do. However, since the reflected light intensity from the test pattern image is lower than the reflected light intensity from the surface of the intermediate transfer belt 8, adjusting the light intensity of the light emitting element 51 according to the reflected light intensity from the test pattern image results in excessive light emission intensity. It will improve. Therefore, the above feedback control is performed after removing the reflected light intensity fluctuation when the test pattern image passes the detection range by the filter. As the filter, for example, a calculation method using a moving average, a technique such as a low-pass filter, or the like can be used. The feedback control (the process of S110 in FIG. 4A) for adjusting the amount of emitted light will be described with reference to the flowchart of FIG.

  In the first embodiment, the amount of emitted light is sequentially adjusted using the method shown in the flowchart of FIG. A counter m is prepared that increments by 1 every 10 ms, with the light intensity adjustment starting point being 0. It is assumed that the regular reflection light intensity is V, the moving average result of the regular reflection light intensity is Vave, and the filtered regular reflection light intensity corresponding to the counter value is N [m]. The adjustment start time is set to Vave = V.

  The patch judgment threshold value Vthr, the target voltage value Vtgt, and the change threshold value Vch are set in advance in the ROM 201a. The patch determination threshold value Vthr is a numerical value with which the absolute value of the difference between the specular reflection light intensity V and the moving average value Vave is compared, and the specular reflection light intensity V is stored in the filtered specular reflection light intensity N [m]. Or a moving average value Vave. The target voltage value Vtgt is a reference value for determining whether it is necessary to increase or decrease the amount of emitted light of the light emitting element 51 by comparing with the moving average value Vave. The change threshold value Vch is a reference value for determining whether or not the light emission amount of the light emitting element 51 needs to be adjusted by comparing the difference between the moving average value Vave and the target voltage value Vtgt.

  In step S150, the printer control unit 101 determines whether 10 ms has elapsed by referring to the timer. If the printer control unit 101 determines in step S150 that 10 ms has not elapsed, the process of step S150 is repeated. If the printer control unit 101 determines that 10 ms has elapsed in S150, the value of the counter m is incremented by 1 in S151 (m = m + 1). In step S152, the printer control unit 101 determines whether the absolute value of the difference between the regular reflection light intensity V and the moving average value Vave at this time is smaller than a predetermined patch determination threshold value Vthr. If the printer control unit 101 determines in S152 that the absolute value of the difference is less than the patch determination threshold, the specularly reflected light of the light receiving element 52 is added to the specularly reflected light intensity N [m] at the counter m in S153. Store strength V. If the printer control unit 101 determines in S152 that the absolute value of the difference is equal to or greater than the patch determination threshold, in S154, the printer controller 101 stores the moving average value Vave in the specular reflected light intensity N [m] at the counter m. Keep it. Since the specular reflection light intensity significantly decreases in the test pattern image portion, the printer control unit 101 determines whether the test pattern image is being detected based on the difference amount between the specular reflection light intensity V and the moving average value Vave.

  The patch determination threshold value Vthr is an A / D value corresponding to an output voltage of, for example, 0.25 V in the first embodiment. In step S <b> 155, the printer control unit 101 includes the most recently reflected light intensity (N [m] to N [m−9) corresponding to the counter values from m−9 to m including the current counter value m. ]) And the moving average value Vave is updated.

  In step S156, the printer control unit 101 compares the moving average value Vave with the A / D value (target voltage value) Vtgt corresponding to the received light intensity 2.5V. Specifically, in step S156, the printer control unit 101 determines whether the difference between the moving average value Vave and the target voltage value Vtgt is equal to or greater than the change threshold value Vch. If the printer control unit 101 determines in S156 that the difference between the moving average value Vave and the target voltage value Vtgt is greater than or equal to the change threshold value Vch, the moving average value Vave is sufficiently larger than the target voltage value Vtgt. Proceed to processing. In step S157, the printer control unit 101 reduces the light amount of the light emitting element 51 by, for example, 0.5% (light amount reduction), and returns to the processing of step S150. If the printer control unit 101 determines in S156 that the difference between the moving average Vave and the target voltage value Vtgt is less than the change threshold Vch, the process proceeds to S158. In step S158, the printer control unit 101 compares the target voltage value Vtgt with the moving average value Vave. Specifically, in S158, the printer control unit 101 determines whether or not the difference between the target voltage value Vtgt and the moving average value Vave is equal to or greater than the change threshold value Vch. If the printer control unit 101 determines in S158 that the difference between the target voltage value Vtgt and the moving average value Vave is greater than or equal to the change threshold value Vch, the moving average value Vave is sufficiently smaller than the target voltage value Vtgt, and therefore the process of S159 Proceed to In step S159, the printer control unit 101 increases the light amount of the light emitting element 51 by, for example, 0.5% (light amount increase), and returns to the process of step S150.

  If the printer control unit 101 determines in S158 that the difference between the target voltage value Vtgt and the moving average value Vtgt is less than the change threshold value Vch, the process returns to S150 without changing the amount of emitted light. The change threshold Vch is set to 0.1 V in the first embodiment. When the difference between the moving average value Vave and the target voltage value Vtgt does not exceed the change threshold value Vch, the light emission amount is not changed, so that the light amount change frequency of the light emitting element 51 is reduced and the light amount is easily converged. Designed to be

  The intensity of the regular reflection light on the surface of the intermediate transfer belt 8 is not only influenced by unevenness of the surface state of the belt, but also by the surface state of the secondary transfer counter roller 10 facing the color misregistration detection sensor 41 and scratches on the belt. Also affected by. In order to reduce the influence, a reflected light intensity filter using a moving average is effective. Since the frequency of the unevenness of the surface state of the intermediate transfer belt 8 is relatively low, even if the high frequency component is removed by moving average, the influence thereof is small.

  By repeatedly executing this color misregistration correction control in parallel with the detection of the test pattern image for color misregistration detection, the detection value of the surface of the intermediate transfer belt 8 (the portion without the test pattern image) detected by the light receiving element 52 is detected. The voltage level can be flattened. In the first embodiment, the detection value of the test pattern image is filtered from the specular reflection light intensity by a calculation method using a moving average. However, the detection value of the test pattern image may be removed by a circuit such as a low-pass filter.

  In S111, along with the feedback control of the light amount adjustment in S110, the printer control unit 101 detects all four color test patterns Y, M, C, and K. In step S112, the printer control unit 101 turns off the light emitting element 51 at the end timing of color misregistration detection. In step S <b> 113, the printer control unit 101 stops the rotation of the intermediate transfer belt 8. In step S <b> 114, the printer control unit 101 calculates the color misregistration amount based on the detection result of the test pattern image, that is, the deviation of the center of gravity, and notifies the controller 103 of the color misregistration amount to perform image correction.

<Effect of Example 1>
According to the laser printer 30 of the first embodiment, even when the intensity of the regular reflection light from the intermediate transfer belt 8 is uneven, the unevenness of the regular reflection light intensity is detected when detecting the test pattern image for color misregistration detection. Therefore, color misregistration detection can be performed stably and accurately. In addition, it is possible to prevent the intensity of the regular reflection light from the surface of the intermediate transfer belt from becoming excessively high or from being too low to be close to the comparator threshold level. Even if there is some unevenness in the regular reflection intensity from the surface of the intermediate transfer belt, stable and highly accurate color misregistration detection can be realized by adjusting the light amount. The degree of freedom can be increased.

  In the first exemplary embodiment, “regular reflection light from the surface of the intermediate transfer belt” means regular reflection light from “a portion where the test pattern image is not formed” on the intermediate transfer belt. It does not necessarily mean only reflected light from the outermost surface of the intermediate transfer belt, but also includes reflected light from the inner layer of the intermediate transfer belt and interference light between the reflected light and the reflected light on the outermost surface. .

  As described above, according to this embodiment, even when there is unevenness in the intensity of reflected light from an image carrier such as an intermediate transfer belt, color misregistration can be detected stably and accurately.

  Example 2 will be described below. Since the configuration of the image forming apparatus and the schematic configuration of the control system of the second embodiment are the same as those of the first embodiment, the description thereof will be omitted, and the description will be given below using the same reference numerals. In the second embodiment, the intensity of regular reflection light on the surface of the intermediate transfer belt 8 is stored for one round before the color misregistration correction control is executed. During execution of the color misregistration correction control, the light amount of the light emitting element 51 is sequentially adjusted based on the stored specular reflection light intensity, and irregularities in the specular reflection light intensity from the intermediate transfer belt 8 during the color misregistration correction control are performed. Reduce.

<Light amount adjustment in color misregistration correction control>
The process of color misregistration correction control in the second embodiment will be described with reference to the flowchart of FIG. 6 and the timing chart of FIG. Hereinafter, the color misregistration correction control according to the second embodiment will be described with respect to the color misregistration detection sensor 41L. However, in the color misregistration correction control, the printer control unit 101 performs the same control for the color misregistration detection sensor 41R. .

  In step S <b> 200, the printer control unit 101 measures an output potential (hereinafter, dark potential Vd) of the light receiving element 52 while the light emitting element 51 is turned off. In step S201, the printer control unit 101 determines an initial light amount Pini of the light emitting element 51 in the color misregistration correction control. The procedure for determining the initial light amount Pini is as follows. That is, the printer control unit 101 checks the output voltage of the light receiving element 52 while increasing the duty of the PWM signal by 0% to 0.5%, and emits light when the output voltage of the light receiving element 52 exceeds 2.5V. Let the light quantity of the element 51 be an initial light quantity Pini.

  The output voltage value of 2.5 V is determined in consideration of the maximum value of the fluctuation width assumed as the reflected light intensity on the surface of the intermediate transfer belt 8 in the sub-scanning direction. A value of 2.5 V is employed as a voltage having a sufficient margin for both 3.3 V as the maximum detectable voltage and 1.2 V as the comparator threshold. Further, as the duty of the PWM signal is increased from 0%, the light quantity corresponding to the duty at which the output voltage of the light receiving element 52 starts to change from the dark potential Vd is stored as the light quantity intercept P0.

  In step S <b> 202, the printer control unit 101 starts rotating the intermediate transfer belt 8. In S203, the printer control unit 101 turns on the light emitting element 51 with the initial light amount Pini determined in S201. In S204, a predetermined time (for example, 5 seconds) is waited until the light emission intensity of the light emitting element 51 is stabilized. The printer control unit 101 waits until the circumference detection mark 43 arranged near the side edge of the intermediate transfer belt 8 is detected by the circumference detection sensor 42. If the circumference detection sensor 42 detects a circumference detection mark at timing T202 (see FIG. 3A) in S205, the process proceeds to S210 and S211.

  In S210, after the detection of the circumference detection mark 43, the printer control unit 101 sequentially stores the 10-bit A / D value of the regular reflection light intensity on the surface of the intermediate transfer belt 8 in a cycle of 10 ms. The printer control unit 101 prepares a counter that increments by 1 every 10 ms by setting the timing T202 for detecting the circumference detection mark 43 to 0, and stores the specular reflection light intensity N [m] every time the counter value advances by 1. To go. The regular reflected light intensity N [m] is stored for one rotation of the intermediate transfer belt 8 (until timing T204). Along with the processing of S210, in S211, the printer control unit 101 determines whether or not a predetermined TOP signal output timing has come with reference to the timing T202 of detecting the circumference detection mark 43. If the printer control unit 101 determines in S211 that it is not the output timing of the TOP signal, it repeats the processing in S211. As shown in FIG. 7, since the light emission intensity of the light emitting element 51 is constant between the timings T202 and T204, the intensity of the regular reflection light of the intermediate transfer belt 8 is uneven.

  If the printer control unit 101 determines in S211 that the output timing of the TOP signal is reached, the printer control unit 101 outputs the TOP signal to the controller 103 in S212. The controller 103 transmits a video signal for generating a test pattern image for color misregistration detection to the printer control unit 101 in synchronization with the TOP signal. Thereby, a test pattern image is formed in the image forming unit 5. Note that the output timing of the TOP signal is set so that the test pattern image for color misalignment detection reaches the detection range of the light receiving element 52 after the circumference detection sensor 42 detects the next circumference detection mark 43. It is determined in advance.

  In step S213, the printer control unit 101 detects the circumference detection mark 43 again by the circumference detection sensor 42 at the timing T204 after the belt travels. In S220, the light amount of the light emitting element 51 is adjusted based on the regular reflection light intensity and the initial light amount Pini of the surface of the intermediate transfer belt 8 stored in S210. By adjusting the light amount of the light emitting element 51, as shown at timings T204 to T205 in the timing chart of FIG. 7, unevenness of the regular reflection light amount from the intermediate transfer belt 8 during test pattern image detection is reduced.

  In the second embodiment, the amount of emitted light is adjusted using the method shown in the flowchart of FIG. A counter m that increments by 1 every 10 ms is prepared with the timing T202 at which the circumference detection sensor 43 detects the circumference detection mark 43 as 0. In step S230, the printer control unit 101 determines whether 10 ms has elapsed by referring to the timer. If it is determined that 10 ms has not elapsed, the process of step S230 is repeated. If the printer control unit 101 determines in step S230 that 10 ms has elapsed, in step S231, the value of the counter m is incremented by one. The printer control unit 101 sets the intensity of regular reflection light from the intermediate transfer belt 8 corresponding to the counter value m to N [m]. In step S232, the printer control unit 101 includes the current counter value m and the latest 10 reflected light intensities corresponding to the counter values from m-9 to m (N [m] to N [m-9]. ]) Is calculated.

In step S233, the printer control unit 101 calculates the light amount Padj using the following calculation formula based on the moving average value Vave, the dark potential Vd initially measured, the initial light amount Pini, and the light amount intercept P0. Vtgt is an A / D value corresponding to a received light intensity of 2.5V.
Padj = P0 + (Pini−P0) × (Vtgt−Vd) / (Vave−Vd) (Equation 1)
In step S <b> 234, the printer control unit 101 changes the amount of light emitted from the light emitting element 51 to the amount of light calculated by Equation 1 above.

  In step S221, the printer control unit 101 detects all four colors of test patterns Y, M, C, and K while adjusting the amount of light in step S220. Since the process of S222-S224 is the same as the process of S112-S114 of FIG. 4, description is abbreviate | omitted.

<Effect of Example 2>
In the second embodiment, prior to color misregistration correction control, a control process for reducing unevenness of the regular reflection light intensity of the intermediate transfer belt 8 is executed as a separate process. Therefore, the amount of light emitted from the light emitting element 51 can be adjusted with higher accuracy. It can be carried out. Further, in Example 2, even when a large number of test pattern images are arranged on the intermediate transfer belt 8 without interruption, the reflected light intensity from the intermediate transfer belt 8 is detected before the test pattern image is detected. Therefore, it is possible to adjust the amount of emitted light with high accuracy.

  As described above, according to the second embodiment, even when the reflected light intensity from the image carrier such as the intermediate transfer belt is uneven, the color misregistration can be detected stably and accurately.

  Example 3 will be described below. The configuration of the apparatus according to the third embodiment is substantially the same as that of the first embodiment except for the printer control unit 101. In addition, about the structure similar to Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted. In the first embodiment, the printer control unit 101 adjusts the light amount of the light emitting element 51, but in the third embodiment, the printer control unit 101 adjusts the gain (light receiving sensitivity) of the light receiving element 52.

  FIG. 8A is a flowchart for explaining the third embodiment. In the flowchart of FIG. 8A, steps S301 to S304 are the same as steps S101 to S104 of the first embodiment. In step S <b> 310, the printer control unit (adjusting unit) 101 outputs a TOP signal, and then performs feedback control for adjusting the gain (light receiving sensitivity) of the light receiving element 52 based on the reflected light intensity on the surface of the intermediate transfer belt 8. However, since the reflected light intensity from the test pattern image is lower than the reflected light intensity from the surface of the intermediate transfer belt 8, if the gain of the light receiving element 52 is adjusted in accordance with the reflected light intensity from the test pattern image, the detected light quantity becomes excessive. It will improve. Therefore, the above feedback control is performed after removing the reflected light intensity fluctuation when the test pattern image passes the detection range by the filter. As the filter, for example, a calculation method using a moving average, a technique such as a low-pass filter, or the like can be used. Since the same technique as that described in the first embodiment can be used for the arithmetic processing using the moving average and the low-pass filter, the description thereof will be omitted.

  In step S311, along with the feedback control for gain adjustment in step S310, the printer control unit 101 detects test pattern images for all four colors Y, M, C, and K. Since steps S312 to S314 are the same as steps S112 to S114 of the first embodiment, the description thereof is omitted.

  In the third embodiment, when the intensity of reflected light from the surface of the intermediate transfer belt 8 received by the light receiving element 52 is increased, the gain of the light receiving element 52 is reduced and the reflected light intensity is decreased. In addition, it is preferable to increase the gain of the light receiving element 52. Also in the third embodiment, it is possible to adopt the method as in the second embodiment. That is, before executing the color misregistration correction control, the regular reflection light intensity on the surface of the intermediate transfer belt 8 is stored in advance for one round. Then, the gain of the light receiving element 52 is sequentially adjusted based on the stored regular reflection light intensity, and unevenness of the regular reflection light intensity from the intermediate transfer belt 8 during the color misregistration correction control can be reduced.

<Effect of Example 3>
In the third embodiment, the same effect as that of the first or second embodiment can be obtained by adjusting the gain of the light receiving element 52. According to the third embodiment, even when the reflected light intensity from the image carrier such as the intermediate transfer belt is uneven, the color misregistration detection can be performed stably and accurately.

  Hereinafter, Example 4 will be described. The configuration of the apparatus of the fourth embodiment is substantially the same as that of the first embodiment except for the printer control unit 101. In addition, about the structure similar to Example 1, the same code | symbol is attached | subjected and description is abbreviate | omitted. In the first embodiment, the printer control unit 101 adjusts the light amount of the light emitting element 51, but in the fourth embodiment, the printer control unit 101 adjusts the detection intensity of the light receiving element 52. Here, “adjustment of detection intensity” means performing correction such as adding / subtracting / subtracting a predetermined number to the detection result as an output value after A / D conversion of the detection result of the light receiving element 52. To do.

  FIG. 8B is a flowchart for explaining the fourth embodiment. In the flowchart of FIG. 8B, the steps S401 to S404 are the same as the steps S101 to 104 of the first embodiment. In step S <b> 410, the printer control unit (correction unit) 101 outputs a TOP signal, and then performs feedback control to adjust the output value as the detection result of the light receiving element 52 based on the reflected light intensity on the surface of the intermediate transfer belt 8. However, since the reflected light intensity from the test pattern image is lower than the reflected light intensity from the surface of the intermediate transfer belt 8, adjusting the output value of the light receiving element 52 in accordance with the reflected light intensity from the test pattern image The output value becomes excessively large. Therefore, the above feedback control is performed after removing the reflected light intensity fluctuation when the test pattern image passes the detection range by the filter. As the filter, for example, a calculation method using a moving average, a technique such as a low-pass filter, or the like can be used. Since the same technique as that described in the first embodiment can be used for the arithmetic processing using the moving average and the low-pass filter, the description thereof will be omitted.

  In step S411, along with the feedback control for output value adjustment in step S410, the printer control unit 101 detects test patterns for all four colors Y, M, C, and K. The steps S412 to S414 are the same as the steps S112 to S114 of the first embodiment, and thus description thereof is omitted.

  In Example 4, when the intensity of reflected light from the surface of the intermediate transfer belt 8 received by the light receiving element 52 is increased, the output value of the light receiving element 52 is reduced and the reflected light intensity is decreased. In this case, it is preferable to increase the output value of the light receiving element 52. Also in the fourth embodiment, the method as in the second embodiment can be adopted. That is, before executing the color misregistration correction control, the regular reflection light intensity on the surface of the intermediate transfer belt 8 is stored in advance for one round. Then, the output value of the light receiving element 52 is sequentially adjusted based on the stored regular reflection light intensity, and unevenness of the regular reflection light intensity from the intermediate transfer belt 8 during execution of the color misregistration correction control can be reduced.

<Effect of Example 4>
In the fourth embodiment, the same effect as that of the first or second embodiment can be obtained by adjusting the output value of the light receiving element 52. Further, it is possible to adjust the digital after A / D conversion, not the adjustment by the amplifier circuit. According to the fourth embodiment, even when the reflected light intensity from an image carrier such as an intermediate transfer belt is uneven, color misregistration detection can be performed stably and accurately.

[Other embodiments]
Even in an image forming apparatus that forms a test pattern image for color misregistration detection and a pattern image for density detection in one rotation of the intermediate transfer belt, the present invention is limited to the position where the test pattern image is arranged. It is possible to carry out the light intensity adjustment process of the invention. In the first to fourth embodiments, the image forming apparatus having the intermediate transfer belt 8 is described. However, the present invention is also applied to an image forming apparatus that employs a method of directly transferring a toner image formed on a photosensitive drum onto a transfer material. The invention can be applied. That is, the intermediate transfer belt can be replaced with a transfer material conveyance belt (recording material carrier), and the light quantity adjustment process of the present invention can be applied to the transfer material conveyance belt (image carrier). In an image forming apparatus using a transfer material conveyance belt, a transfer material conveyed by a feeding and conveying unit is conveyed by a transfer material conveyance belt to a position where a toner image is transferred onto the transfer material by the transfer unit. A toner image corresponding to the color component of each color formed on the photosensitive drum corresponding to each color is transferred onto the transfer material being conveyed by the transfer material conveyance belt. As described above, also in other embodiments, even when the intensity of reflected light from an image carrier such as an intermediate transfer belt is uneven, color misregistration can be detected stably and accurately.

5, 5Y, 5M, 5C, 5K Image forming unit (image forming means)
8 Intermediate transfer belt (image carrier)
30 Laser printer (image forming device)
41, 41R, 41L Color shift detection sensor (detection means)
44L, 44R Color misregistration detection toner images (color misregistration correction toner images)
51 Light emitting element (light emitting means)
52 Light receiving element (light receiving means)
101 Printer control unit (adjustment means)

Claims (10)

An image forming apparatus,
A plurality of image forming means each having a photosensitive drum and forming a toner image on each photosensitive drum;
An image carrier to which a toner image on the photosensitive drum is transferred;
A light emitting means for emitting light toward the image carrier and a light receiving means for receiving reflected light from the image carrier, and detecting a toner image for color misregistration correction formed on the image carrier. Detecting means for
When detecting the toner image for color misregistration correction, depending on the plurality of positions of the image carrier based on the intensity of reflected light from the plurality of positions of the image carrier received by the light receiving means. Adjusting means for adjusting the light emission intensity of the light emitted by the light emitting means. A feeding and conveying means for conveying the transfer material;
Transfer means for transferring a toner image corresponding to each color on the photosensitive drum onto the transfer material;
The image carrier is an intermediate transfer belt for transferring the toner image transferred onto the image carrier to the transfer material conveyed by the feeding and conveying unit by the transfer unit. The image forming apparatus according to claim 1. A feeding and conveying means for conveying the transfer material;
Transfer means for transferring a toner image corresponding to each color on the photosensitive drum onto the transfer material;
2. The image according to claim 1, wherein the image carrier is a transfer material conveyance belt that conveys the transfer material conveyed by the feeding and conveying unit to a position where the transfer unit transfers the toner image. Forming equipment. The adjusting means includes
When the intensity of the reflected light from the image carrier received by the light receiving means increases, the light emission intensity by the light emitting means is reduced, and the reflection from the image carrier received by the light receiving means 4. The image forming apparatus according to claim 1, wherein when the light intensity decreases, the light emission intensity of the light emitting unit is increased. 5.   In parallel with receiving the reflected light from the image carrier by the light receiving means, the adjustment means adjusts the light emission intensity of the light by the light emitting means according to the intensity of the reflected light from the image carrier. 5. The image forming apparatus according to claim 1, wherein the detection unit detects the toner image for color misregistration correction. 6.   Based on the intensity of the reflected light from the image carrier previously received by the light receiving means, the adjustment means adjusts the light emission intensity by the light emitting means according to the intensity of the reflected light from the image carrier. 5. The image forming apparatus according to claim 1, wherein the detection unit detects the toner image for color misregistration correction. 6. In order to detect the rotational position of the image carrier in the form of an endless belt, a circumference detection mark disposed near a side edge of the image carrier;
The image forming apparatus according to any one of claims 1 to 6, further comprising a circumference detection unit for detecting the circumference detection mark.   The adjusting means corresponds to the reflected light from the image carrier received by the light receiving means, the reflected light from the color misregistration correction toner image transferred to the image carrier removed by a filter. The image forming apparatus according to claim 1, wherein the light emission intensity of the light emitting unit is adjusted. An image forming apparatus,
A plurality of image forming means each having a photosensitive drum and forming a toner image on each photosensitive drum;
An image carrier to which a toner image on the photosensitive drum is transferred;
A light emitting means for emitting light toward the image carrier and a light receiving means for receiving reflected light from the image carrier, and detecting a toner image for color misregistration correction formed on the image carrier. Detecting means for
When detecting the toner image for color misregistration correction, depending on the plurality of positions of the image carrier based on the intensity of reflected light from the plurality of positions of the image carrier received by the light receiving means. And an adjusting means for adjusting the light receiving sensitivity of the light receiving means. An image forming apparatus,
A plurality of image forming means each having a photosensitive drum and forming a toner image on each photosensitive drum;
An image carrier to which a toner image on the photosensitive drum is transferred;
A light emitting means for emitting light toward the image carrier and a light receiving means for receiving reflected light from the image carrier, and detecting a toner image for color misregistration correction formed on the image carrier. Detecting means for
When detecting the toner image for color misregistration correction, depending on the plurality of positions of the image carrier based on the intensity of reflected light from the plurality of positions of the image carrier received by the light receiving means. An image forming apparatus comprising: a correcting unit that corrects a light detection result by the light receiving unit.

Images