JP2023108662A - Image forming apparatus - Google Patents

Abstract

To prevent a shift in image position between images on a transfer target material even if the operating speed of an optical deflector of optical writing means is changed.SOLUTION: An image forming apparatus repeatedly scans surfaces of a plurality of photoreceptors 504 along a main scanning direction by optical writing means that deflects writing light according to image information by an optical deflector 202, writes latent images according to the image information on the surfaces of the plurality of photoreceptors, and transfers images obtained by visualizing the latent images on the surfaces of the plurality of photoreceptors so that the images overlap each other on a transfer target material. The image forming apparatus has optical deflector control means 350 that controls the operating speed of the optical deflector, and transfer timing changing means 350 that changes the timing to start transfer of the image on at least one photoreceptor of the plurality of photoreceptors to the transfer target material from one at a reference operating speed so as to reduce a shift in image position on the transfer target material between the images on the plurality of photoreceptors occurring due to a change in the operating speed of the optical deflector from the reference operating speed.SELECTED DRAWING: Figure 4

Description

The present invention relates to an image forming apparatus.

Conventionally, a latent image written on the surface of a moving photoreceptor is visualized by repeatedly scanning the surface of the moving photoreceptor in the main scanning direction using an optical writing means that deflects writing light with an optical deflector. 2. Description of the Related Art There is known an image forming apparatus that transfers a printed image onto a transfer material.

For example, Japanese Patent Laid-Open No. 2002-101002 discloses a writing drive control method for controlling the number of rotations (operating speed) of a polygon mirror (optical deflector) in order to finely adjust the image magnification in the sub-scanning direction (direction of surface movement of a photoreceptor). An image forming apparatus having means (optical deflector control means) is disclosed. In this image forming apparatus, the write clock frequency is also controlled by the write drive control means in order to cancel the change in the image magnification in the main scanning direction caused by this fine adjustment. More specifically, the write drive control means establishes a correspondence relationship between the sub-scanning direction magnification adjustment value and the main scanning direction magnification adjustment value for canceling the change in the image magnification in the main scanning direction due to each sub-scanning direction magnification adjustment value. Use a magnification correction table that describes The write drive control means controls the number of rotations of the polygon mirror according to the sub-scanning direction magnification adjustment value, and controls the write clock frequency according to the corresponding main scanning direction magnification adjustment value.

However, in a conventional image forming apparatus, each image is visualized from the latent images on the surface of a plurality of photoreceptors and is superimposed on a transfer material. However, there has been a problem that it is not possible to suppress the color shift that occurs when transferring in such a manner.

In order to solve the above-described problems, the present invention provides an optical writing device that deflects writing light according to image information by an optical deflector, and writes the surface of a plurality of moving photosensitive bodies along the main scanning direction. By repeatedly scanning, latent images corresponding to the image information are written on the surfaces of the plurality of photoreceptors, and the latent images on the surfaces of the plurality of photoreceptors are visualized so that the images are superimposed on a transfer material. and an optical deflector control means for controlling the operating speed of the optical deflector; and the plurality of photoreceptors generated by changing the operating speed of the optical deflector from a reference operating speed. The transfer start timing of the image of at least one photoreceptor of the plurality of photoreceptors to the transfer material is set to the reference so that the image position deviation on the transfer material between the images of the and transfer timing changing means for changing the operating speed.

According to the present invention, even if the operating speed of the optical deflector of the optical writing means is changed from the reference operating speed, the image position shift (color shift) on the transfer material between the images on the plurality of image carriers can be prevented. can be suppressed.

1 is a schematic diagram showing the main configuration of a color printer according to an embodiment; FIG. FIG. 4 is a schematic diagram showing the layout of the incident optical system of the MY unit in the same color printer; FIG. 4 is a schematic diagram showing the layout of the scanning optical system of the same MY unit; FIG. 4 is an explanatory diagram showing the configuration of a write control unit in the same color printer; (a) is a diagram showing an original image to be formed. (b) is a diagram showing a state in which the image of (a) is extended in the sub-scanning direction. FIG. 7C is a diagram showing a state in which the extension of the image in the sub-scanning direction is canceled (a state in which the image is extended in the main scanning direction in conjunction with this). 8A is an explanatory diagram showing the relationship between the write clock and the position on the photosensitive drum when the image is extended in the main scanning direction; FIG. (b) is an explanatory diagram showing the relationship between the write clock and the position on the photosensitive drum in a state where the main scanning magnification is adjusted for the image of (a). 4 is a flowchart showing an overview of the control flow of the write control unit; 4A and 4B are explanatory diagrams showing how an image position shift (color shift) occurs for each main scanning line of a photoreceptor drum on an intermediate transfer belt before and after changing the number of rotations of an optical deflector. (a) is a timing chart showing the write start timing of each photoreceptor before correction after the number of revolutions of the optical deflector is changed. (b) is a timing chart showing write start timing of each photoreceptor after correction after the number of revolutions of the optical deflector is changed. 4 is a flow chart showing the flow of correction processing for write start timing of each photoreceptor drum in the embodiment. FIG. 5 is an explanatory view showing an example of a color matching correction pattern for each color formed on the intermediate transfer belt while the optical deflector is operated at the reference number of rotations;

An embodiment in which the present invention is applied to a color printer as an image forming apparatus will be described below.

FIG. 1 is a schematic diagram showing the main configuration of a color printer 500 according to this embodiment.
The color printer 500 is a tandem-type multicolor printer capable of forming a full-color image by superimposing black, cyan, magenta, and yellow toner images. This color printer 500 comprises an optical writing device 100 as an optical writing means and four photosensitive drums 501 , 502 , 503 and 504 . It also has four cleaning units 605Y, 605M, 605C and 605K and four charging devices 602Y, 602M, 602C and 602K. It also has four developing devices 604Y, 604M, 604C and 604K each having developing rollers 603Y, 603M, 603C and 603K. In addition, an intermediate transfer belt 606, a secondary transfer roller 613, a fixing device 610, a paper feed roller 608, a pair of registration rollers 609, a paper discharge roller 612, a paper discharge tray 611, etc. there is

The photosensitive drum 501, cleaning unit 605K, charging device 602K, developing roller 603K, and developing device 604K constitute an image station (hereinafter referred to as "K station") for forming a black image. The photosensitive drum 502, cleaning unit 605C, charging device 602C, developing roller 603C, and developing device 604C constitute an image station (hereinafter referred to as "C station") for forming a cyan image. The photosensitive drum 503, cleaning unit 605M, charging device 602M, developing roller 603M, and developing device 604M constitute an image station (hereinafter referred to as "M station") for forming a magenta image. The photosensitive drum 504, cleaning unit 605Y, charging device 602Y, developing roller 603Y, and developing device 604Y constitute an image station (hereinafter referred to as "Y station") for forming a yellow image.

Each of the photosensitive drums 501, 502, 503 and 504 has a photosensitive layer on its peripheral surface and is driven to rotate in the direction of the arrow in FIG. 1 by a rotating mechanism. Each charging device 602Y, 602M, 602C, 602K uniformly charges the surface of the corresponding photosensitive drum 501, 502, 503, 504.

The optical writing device 100 includes a KC unit 100A that exposes and scans a photosensitive drum 501 for black and a photosensitive drum 502 for cyan, and an M-unit that exposes and scans a photosensitive drum 503 for magenta and a photosensitive drum 504 for yellow. Y unit 100B. The optical writing device 100 irradiates writing light (scanning light) with lighting control based on image data on the corresponding photosensitive drum surface as a surface to be scanned, thereby forming an electrostatic latent image on the photosensitive drum surface. do. As the photosensitive drums 501, 502, 503, and 504 rotate, the electrostatic latent images formed here are conveyed to developing regions facing the developing rollers of the developing devices 604Y, 604M, 604C, and 604K.

Each developing device 604Y, 604M, 604C, 604K has a developing roller carrying charged toner. A predetermined developing bias is applied to the developing roller, and the toner on the developing roller adheres to the electrostatic latent image on the photosensitive drum due to the action of the developing electric field formed thereby. As a result, images to which toner is attached (hereinafter referred to as “toner images”) are formed on the photosensitive drums 501 , 502 , 503 and 504 .

The toner image thus formed is conveyed to the primary transfer area facing the intermediate transfer belt 606 as the photosensitive drums 501 , 502 , 503 and 504 rotate. The yellow, magenta, cyan, and black toner images on the photoreceptor drums 501, 502, 503, and 504 are primarily transferred onto the intermediate transfer belt 606 at timings in which they overlap each other. As a result, a multicolor image is formed on the intermediate transfer belt 606 . Each cleaning unit 605Y, 605M, 605C, 605K removes transfer residual toner remaining on the surface of the corresponding photosensitive drum 501, 502, 503, 504 without being transferred.

On the other hand, the recording paper 510 , which is a recording material, is conveyed sheet by sheet to a registration roller pair 609 by a paper feed roller 608 . The registration roller pair 609 feeds the recording paper 510 to the secondary transfer area where the intermediate transfer belt 606 and the secondary transfer roller 613 face each other at a predetermined timing. In this secondary transfer area, the multicolor toner image on the intermediate transfer belt 606 is secondarily transferred to the recording paper 510 . Recording paper 510 onto which the multicolor toner image has been transferred is then sent to fixing device 610 . The fixing device 610 fixes the toner image on the recording paper 510 to the recording paper with heat and pressure. After fixing, the recording paper 510 is ejected onto a paper ejection tray 611 via a paper ejection roller 612 .

Next, the configuration and operation of the optical writing device 100 will be described.
Since the KC unit 100A and the MY unit 100B that constitute the optical writing device 100 have the same basic configuration, the configuration of the optical writing device 100 will be described using the MY unit 100B in the following description. and operation will be described. In the following description, Y, M, C, and K, which are color-coding codes, are omitted as appropriate.

FIG. 2 is a schematic diagram showing the layout of the incident optical system of the MY unit 100B.
The light source unit 101 has a light source 102 such as a surface-emitting laser that emits linearly polarized laser light, and a quarter-wave plate 105 that converts the laser light emitted from the light source 102 into circularly polarized light. It also has a collimating lens 106 for collimating the laser beam circularly polarized by the quarter-wave plate 105 and an aperture 107 for cutting the laser beam collimated by the collimating lens 106 . These optical components 102, 105, 106, 107 are positioned at predetermined positions with respect to the light source holder and integrally assembled. A laser beam emitted from the light source unit 101 is incident on an optical deflector 202 as optical scanning means via an incident optical system.

The incident optical system includes a polarizing beam splitter (PBS) 203 that splits the laser beam emitted from the light source unit 101 into two in the sub-scanning direction (the front-rear direction of the paper surface in FIG. 2). It also has a quarter-wave plate 204 that converts the polarization characteristics of the two split laser beams L1 and L2 from linearly polarized light to circularly polarized light. Also provided is a cylindrical lens 205 that forms images of the circularly polarized laser beams L1 and L2 on the mirror surfaces of two rotating polygon mirrors (polygon mirrors) 202a and 202b mounted on the optical deflector 202. there is The cylindrical lens 205 has a function of condensing the circularly polarized laser light only in the sub-scanning direction.

The laser beams L1 and L2 formed into predetermined laser profiles by such an incident optical system are imaged on the mirror surfaces of the rotary polygon mirrors 202a and 202b of the optical deflector 202, respectively. The optical deflector 202 stably drives the rotating polygon mirrors 202a and 202b integrally at a predetermined rotational speed (operating speed) about a rotating shaft parallel to the sub-scanning direction. When the laser beams L1 and L2 are incident on the mirror surfaces of the rotating rotary polygon mirrors 202a and 202b, the laser beams L1 and L2 are scanned in the main scanning direction as shown in FIG.

In this embodiment, a leading edge synchronization sensor 311 is provided upstream of each of the photosensitive drums 501, 502, 503, and 504 in the main scanning direction. When the tip synchronization sensor 311 detects the laser beams L1 and L2, the tip synchronization sensor 311 outputs a tip synchronization signal. A write control unit, which will be described later, starts lighting control based on the image data based on the timing at which the leading end synchronization signal is output, and determines the timing to start writing the latent image and the writing of each scanning line in the main scanning direction. Synchronize the loading start timing.

FIG. 3 is a schematic diagram showing the layout of the scanning optical system of the MY unit 100B.
One of the laser beams scanned by the optical deflector 202, the laser beam L1 (the laser beam scanned by the mirror surface of the upper rotating polygon mirror 202a) passes through the scanning lens 301 and the elongated lens 302, and passes through the dust-proof glass 305. pass through. Then, the surface of the photosensitive drum 504 is scanned at a constant speed. Mirrors 303a, 303b, and 303c are installed on this optical path to turn back the laser beam L1. The other laser beam L2 (laser beam scanned by the mirror surface of the lower rotary polygon mirror 202b) passes through the scanning lens 301 and the elongated lens 302, passes through the dust-proof glass 305, and reaches the surface of the photosensitive drum 503. is scanned at a constant speed. A mirror 304 is installed on this optical path to turn back the laser beam L2.

The incident optical system, the optical deflector 202, and the scanning optical system described above are all integrally provided in an optical housing 400 as a holding member shown in FIG.

Next, a method for adjusting the magnification in the sub-scanning direction of an image (hereinafter referred to as "sub-scanning magnification") will be described.
FIG. 4 is an explanatory diagram showing the configuration of the write control unit 350. As shown in FIG.
When adjusting the sub-scanning magnification of an image, it is also possible to adjust the sub-scanning magnification by performing data processing of image data for generating writing light. However, if the sub-scanning magnification is changed significantly, the memory capacity for storing image data will increase, and the processing load on the data processing unit 351 such as an ASIC that performs data processing will also increase. can be

Therefore, the write control unit 350 employs an inexpensive data processing unit 351 that does not have a function of adjusting the sub-scanning magnification by data processing. by adjusting the For example, when the sub-scanning magnification is to be decreased, the rotational speed of the optical deflector 202 is increased to narrow the interval between the scanning lines of the writing light on the photosensitive drum 504. When the sub-scanning magnification is to be increased, the light The number of rotations of the deflector 202 is decreased to widen the interval between the scanning lines of the writing light on the photosensitive drum 504 . The adjustment of the sub-scanning magnification by the data processing unit 351 and the adjustment of the sub-scanning magnification by adjusting the rotational speed of the optical deflector 202 may be used together.

As a specific example, when an image is formed based on the image data of the image shown in FIG. 5A, the image is formed extending in the sub-scanning direction as shown in FIG. 5B. (B2>B1), the rotational speed of the optical deflector 202 is increased to reduce the sub-scanning magnification. In this case, since the interval between the scanning lines of the writing light on the photosensitive drum 504 is narrowed, the sub-operation magnification is reduced. As a result, as shown in FIG. 5C, the extension of the image in the sub-scanning direction can be canceled.

When adjusting the sub-scanning magnification by adjusting the rotational speed of the optical deflector 202, the scanning speed in the main scanning direction is also changed. In this case, as shown in FIG. 4, the interval of one dot of the electrostatic latent image written for each clock pulse of the writing light, which is a repetitive pulse light, changes. main scanning magnification") is also changed. For example, if the number of rotations of the optical deflector 202 is increased to reduce the sub-scanning magnification, the scanning speed of the writing light increases, so the main scanning magnification increases. When the number of revolutions is decreased, the scanning speed of the writing light decreases, so the main scanning magnification decreases.

In the specific example shown in FIGS. 5A to 5C, when the rotational speed of the optical deflector 202 is increased in order to cancel the extension of the image in the sub-scanning direction, the scanning speed of the writing light increases. , the interval of one dot of the electrostatic latent image written for each clock pulse of the writing light is widened. As a result, the main scanning magnification increases, and the image is stretched in the main scanning direction (A2>A1), as shown in FIG. 5(c).

In this way, when the sub-scanning magnification is adjusted by adjusting the rotational speed of the optical deflector 202, the main scanning magnification changes accordingly, so it is necessary to cancel the change in the main scanning magnification. Therefore, for example, when the sub-scanning magnification is adjusted by adjusting the rotation speed of the optical deflector 202, the write control unit 350 adjusts the main scanning magnification by adjusting the write clock frequency. to cancel.

FIGS. 6A and 6B are explanatory diagrams for adjusting the main scanning magnification by adjusting the write clock frequency.
As in the specific examples shown in FIGS. 5A to 5C, when the rotational speed of the optical deflector 202 is increased in order to cancel the extension of the image in the sub-scanning direction, writing is performed for each clock pulse of the writing light. The one-dot interval of the electrostatic latent image that is formed is widened. Therefore, as shown in FIG. 6A, the image length in the main scanning direction becomes A2, which is longer than the original A1, and the main scanning magnification increases.

In order to cancel this change in the main scanning magnification, the write clock frequency of the write light should be increased. According to this, even if the scanning speed of the writing light increases due to the increase in the rotation speed of the optical deflector 202, the write clock frequency of the writing light increases. The interval of one dot of the electrostatic latent image written at each clock pulse is narrowed. As a result, the image length in the main scanning direction returns to the original A1, canceling the change in the main scanning magnification.

FIG. 7 is a flow chart showing an overview of the control flow of the write control unit 350. As shown in FIG.
If the number of rotations (operating speed) of the optical deflector 202 is changed during the writing of the electrostatic latent image (during the period of writing the latent image), the sub-scanning magnification and the main scanning magnification will change within one image, resulting in image deterioration. Distortion will occur. Therefore, generally, the rotation speed of the optical deflector 202 for adjusting the sub-scanning magnification is changed during the non-latent image writing period (between pages). Specifically, the control unit 352 of the write control unit 350 monitors the paper gate signal (S1), and at the timing of negation (Yes in S1), rotates the optical deflector 202 for adjusting the sub-scanning magnification. The number is changed (S2). At this time, the control unit 352 adjusts the optical deflector 202 based on the input sub-scanning magnification information so that the number of rotations of the optical deflector 202 corresponds to the sub-scanning magnification indicated by the sub-scanning magnification information. to control the motor 202c.

The controller 352 also adjusts the main scanning magnification in order to cancel the change in the main scanning magnification caused by the change in the rotational speed of the optical deflector 202 (S3). At this time, the control unit 352 controls the light source 102 based on the changed rotational speed of the optical deflector 202 so that the write clock frequency corresponds to the changed rotational speed.

Here, as described above, when the number of rotations (operating speed) of the optical deflector 202 is changed, the positional deviation of the images on the intermediate transfer belt 606 ( color shift) can occur. Specifically, when the number of rotations of the optical deflector 202 is changed from the reference number of rotations (reference operating speed), writing of the latent image onto each of the photosensitive drums 501, 502, 503, and 504 is started in accordance with this change. If the timing is changed, color misregistration will occur.

FIG. 8 shows the image positions (formed so as to overlap each other) for each main scanning line of the photosensitive drums 501, 502, 503, and 504 on the intermediate transfer belt 606 before and after the rotation speed of the optical deflector 202 is changed. 2 is an explanatory diagram showing the position of each image to be processed (for example, the tip position of each image); FIG.

Before the rotation speed of the optical deflector 202 is changed, that is, when the rotation speed of the optical deflector 202 is the reference rotation speed (reference operating speed), the intermediate transfer belt 606 illustrated in the lower part of FIG. As shown, no color shift occurs. However, in this embodiment, the timing to start writing the latent image onto each of the photosensitive drums 501, 502, 503, and 504 is controlled based on the number of scans by the optical deflector 202 from a predetermined print start timing. . Specifically, the write control unit 350 counts the number of times the leading end synchronization sensor 311 detects the laser beam, and determines that the write start timing has arrived when the count reaches a predetermined count.

In order to control the writing start timing of each of the photosensitive drums 501, 502, 503 and 504 in this way, when the number of rotations of the optical deflector 202 is changed, each of the photosensitive drums 501 and 502 is controlled in accordance with this change. , 503 and 504 will change. As a result, for example, when the rotational speed of the optical deflector 202 is changed to be slower, color misregistration occurs as shown in the intermediate transfer belt 606 illustrated in the upper side of FIG. This is because, with respect to the transfer positions Pm, Pc, and Pk of the photosensitive drums 501, 502, and 503 on the downstream side, the photosensitive drums 501, 502, and 503 on the upstream side of the image leading edges Tm, Tc, and Tk on the photosensitive drums 501, 502, and 503 are transferred. This is because the leading edges Ty, Tm, and Tc of the images transferred from the body drums 502, 503, and 504 on the intermediate transfer belt 606 reach earlier.

Therefore, in the present embodiment, the transfer start timing of the image on at least one photosensitive drum onto the intermediate transfer belt 606 is changed (corrected) so that the amount of color misregistration caused by changing the rotational speed of the optical deflector 202 is reduced. )do. Specifically, for example, the write start timing (image formation start timing) of the electrostatic latent image by the optical writing device 100 onto each of the photosensitive drums 501, 502, 503, and 504 is changed (corrected) with respect to the print start timing. )do.

FIGS. 9A and 9B are timing charts before and after correcting the writing start timings of the photosensitive drums 501, 502, 503, and 504 after changing the rotational speed of the optical deflector 202. FIG. .
FIG. 9A is a timing chart before correction of the write start timing, and FIG. 9B is a timing chart after correction of the write start timing.

The timing chart shown in FIG. 9A is before the rotation speed of the optical deflector 202 is changed, that is, when the rotation speed of the optical deflector 202 is the reference rotation speed. That is, in this timing chart, writing to each of the photosensitive drums 501, 502, 503, and 504 is started at the print start timing so that color misregistration does not occur when the number of rotations of the optical deflector 202 is the reference number of rotations. The timing has been decided.

At this time, if the number of rotations of the optical deflector 202 is changed from the reference number of rotations, the latent images of the photosensitive drums 501, 502, 503, and 504 are formed at the writing start timing according to the timing chart of FIG. When writing (image formation) is started, color misregistration occurs as described above. Therefore, in the present embodiment, the photoreceptor drums 501, 502, 503, and 504 are arranged so as to reduce the image position shift (color shift) between the images on the intermediate transfer belt 606 caused by this change. , 502, 503, and 504 are changed (corrected).

For example, when the number of rotations of the optical deflector 202 is changed to be slower, the write start timings for the photoreceptor drums 501, 502, 503, and 504 with respect to the print start timing are set as shown in the timing chart of FIG. 9(b). Change (correction) to that of As a result, the transfer start timings of the images on the downstream M, C, and K photosensitive drums 501, 502, and 503 onto the intermediate transfer belt 606 are advanced, and the images on the photosensitive drums 501, 502, 503, and 504 are transferred earlier. Image misregistration (color misregistration) on the intermediate transfer belt 606 is reduced or eliminated.

In this embodiment, the write start timing for each of the photosensitive drums 501, 502, 503, and 504 is determined based on the print start timing signal. Specifically, based on the print start timing signal, the timing to start writing to the K-color photosensitive drum 504 is determined, and based on the determined timing to start writing to the K-color photosensitive drum 501 to determine the write start timing for each of the other photosensitive drums 502 , 503 , 504 . The writing start timing to each of the other photoreceptor drums 502, 503, 504 depends on the inter-photoreceptor drum distance between the K-color photoreceptor drum 501 and each of the other photoreceptor drums 502, 503, 504. can be obtained from Lky, Lkm, and Lkc (distances between primary transfer positions) and the process speed (the surface moving speed of the photosensitive drum).

When the number of rotations of the optical deflector 202 is changed from the reference number of rotations, the write start timings (the write start timings before correction) of the photosensitive drums 501, 502, 503, and 504 described above are changed. The writing start timing of each photosensitive drum is corrected by multiplying by a correction coefficient corresponding to the subsequent rotation speed. That is, the writing start timings of the respective photosensitive drums 501, 502, 503, and 504 are corrected according to the following equation (1).
Write start timing after correction=write start timing before correction×correction coefficient (1)

Note that the correction coefficient (adjustment parameter) is obtained from the ratio between the number of revolutions of the optical deflector 202 before change (reference number of revolutions) and the number of revolutions after change, for example, as in the following equation (2). .
Correction coefficient = post-change rotation speed / reference rotation speed (2)

FIG. 10 is a flow chart showing the flow of processing for correcting the write start timing of each of the photosensitive drums 501, 502, 503, and 504 in this embodiment.
When an image forming instruction (print job) is input, the control unit 352 drives the photosensitive drums 501, 502, 503, and 504 at a predetermined surface moving speed, and moves the intermediate transfer belt 606 at a reference speed. The driving motor is controlled in such a manner as to start the image forming operation (S10). At this time, the writing start timing of each of the photosensitive drums 501 , 502 , 503 and 504 is determined using the value of the reference writing start timing (timing determination parameter) stored in the storage section of the control section 352 .

This reference write start timing value is initially a value calculated from an ideal design value so as not to cause color misregistration. This is the write start timing value corrected by the write start timing correction processing.

When the conditions for executing the reference write start timing correction process are satisfied, the control unit 352 executes the reference write start timing correction process while operating the optical deflector 202 at the reference rotation speed. In the reference write start timing correction process, first, a pattern image for correcting the reference write start timing (hereinafter referred to as "color matching correction pattern") is formed on the intermediate transfer belt 606 (S12). Then, the color matching correction pattern formed on the intermediate transfer belt 606 is detected by the pattern detection sensor 26 as detection means (S13).

FIG. 11 is an explanatory diagram showing an example of color matching correction patterns TPy, TPm, TPc, and TPk of respective colors formed on the intermediate transfer belt 606 with the optical deflector 202 operated at the reference rotational speed.
The reference K color matching correction pattern TPk is formed by writing at a predetermined reference write start timing (fixed timing). On the other hand, the color matching correction patterns TPy, TPm, and TPc of the other colors are arranged on the intermediate transfer belt 606 at regular intervals in the sub-scanning direction according to the value of the reference writing start timing stored in the storage section of the control section 352. is formed to open.

The transfer start timing (intermediate position on the transfer belt 606 in the sub-scanning direction) can change over time. For example, errors occur due to mounting position errors (errors in the distance between the photosensitive drums) of the photosensitive drums 501, 502, 503, and 504, and part dimensional changes due to temperature changes, wear, and the like. can change. The reference write start timing correction process described above is performed to correct such changes over time.

Based on the detection result of the pattern detection sensor 26 of the color matching correction patterns TPy, TPm, TPc, and TPk formed on the intermediate transfer belt 606, the control unit 352 adjusts the color of the photosensitive drums 502, 503, and 504 for colors other than K. The value of the reference write start timing is corrected (S14). Specifically, the controller 352 sets the intervals between the color matching correction pattern TPk of the K-color photoconductor drum 501 and the color matching correction patterns TPy, TPm, and TPc of the corresponding photoconductor drums 502, 503, and 504 to specified values. Calculate pattern correction values (reference alignment parameters) that can be spaced. Then, each pattern correction value is added to the values of the reference write start timings of the photosensitive drums 502, 503, and 504, and the reference write start timings of the photosensitive drums 502, 503, and 504 for colors other than K are calculated. Correct the value. As a result, even if color misregistration occurs due to changes over time, such as errors in the distance between the photoreceptor drums, temperature changes, and part dimensional changes due to wear, etc., by executing the reference write start timing correction processing, The occurrence of color misregistration is suppressed.

Here, the controller 352 changes the rotation speed of the optical deflector 202 from the reference rotation speed when a predetermined optical deflector rotation speed change condition is satisfied (Yes in S15). As the predetermined optical deflector rotational speed change condition, a condition for executing processing for correcting a sub-scanning magnification error such that the length of the formed image in the sub-scanning direction becomes longer or shorter than the original image, or the like. mentioned. In this case, by changing the number of rotations of the optical deflector 202 to a number of rotations corresponding to the magnitude of the sub-scanning magnification error, the scanning line spacing on each of the photosensitive drums 501, 502, 503, and 504 ( scan line spacing) is changed to correct for image stretching.

However, at this time, the timing at which the tip synchronization sensor 311 detects the laser light changes as the rotational speed of the optical deflector 202 changes, so the time interval at which the tip synchronization sensor 311 detects the laser light also changes. Therefore, the time until the count value of the number of times the leading end synchronization sensor 311 detects the laser light changes to reach the predetermined count number, and the timing at which the writing start timing of each of the photosensitive drums 501, 502, 503, and 504 arrives. It will change. As a result, the latent image writing start timing for each of the photosensitive drums 501, 502, 503, and 504 changes, and the intermediate transfer belt 606 between the images on the photosensitive drums 501, 502, 503, and 504 is changed as described above. An upper image position shift (color shift) occurs. In order to suppress this color shift, in the present embodiment, the write start timings of the photosensitive drums 501, 502, 503, and 504 are corrected according to the rotation speed after the optical deflector 202 is changed, as described above. A correction coefficient for this is calculated (S16).

After that, the controller 352 corrects the reference write start timing using the calculated correction coefficient (S17). Then, the controller 352 starts the image forming operation. At this time, the post-correction write start timing corrected in processing step S17 is used as the write start timing for each of the photosensitive drums 501, 502, 503, and 504. FIG.

As for the write start timing after correction in the present embodiment, the write start timing matches the print start timing for the reference K color, so correction is not particularly necessary. On the other hand, the post-correction writing start timings for the other colors that need to be corrected are given by the following equations (3-1) to (3-3).
Write start timing after correction (color C) =
(C-color reference write start timing + pattern correction value) x correction coefficient (3-1)
Write start timing after correction (M color) =
(M-color reference write start timing + pattern correction value) x correction coefficient (3-2)
Write start timing after correction (Y color) =
(Y-color reference write start timing + pattern correction value) x correction coefficient (3-3)

In the present embodiment, the write start timing after correction by the correction coefficient is calculated for all of the photosensitive drums 502, 503, and 504 that require correction, but only for the photosensitive drums used for image formation. The write start timing after correction may be calculated. In this case, the processing load on the control unit 352 can be reduced.

Further, in the present embodiment, a tandem image forming apparatus having four stations for superimposing toner images of four colors of black, cyan, magenta, and yellow to form an image has been described as an example. is not limited to For example, in addition to these stations, a tandem-type image forming apparatus having five stations including one station using toner other than these colors (hereinafter referred to as "special color toner") may be used. The special color toner mentioned here includes a transparent toner, a white toner, a gold toner, and the like.

What has been described above is only an example, and each of the following aspects has a unique effect.
[First aspect]
In the first mode, a plurality of photoreceptors 501, 502, 503, 504 that move on the surface are driven by an optical writing means (for example, an optical writing device 100) that deflects writing light according to image information by an optical deflector 202. The surface is repeatedly scanned in the main scanning direction to write latent images corresponding to the image information on the surfaces of the plurality of photoreceptors, and the latent images on the surfaces of the plurality of photoreceptors are visualized. on a transfer material (e.g., intermediate transfer belt 606) so as to overlap each other (e.g., color printer 500), wherein the optical deflector controls the operating speed (e.g., number of rotations) of the optical deflector Control means (for example, write control unit 350) and image positional deviation on the transfer material between the images of the plurality of photoreceptors caused by changing the operating speed of the optical deflector from the reference operating speed transfer timing changing means (e.g., writing speed) for changing the transfer start timing of the image on at least one of the plurality of photoreceptors to the transfer material from that at the reference operating speed so as to decrease the transfer timing. and a loading control unit 350).
Conventionally, in an image forming apparatus that visualizes a latent image written by an optical writing means and transfers the image formed on a photoreceptor to a transfer material, the operating speed of the optical deflector of the optical writing means is It may be changed from the standard operating speed. For example, in such an image forming apparatus, an image that is elongated or shrunk in the surface movement direction (sub-scanning direction) of the photoreceptor or transfer material from the original image may be formed due to various factors. . Such expansion and contraction of an image is called a sub-scanning magnification error. When such a sub-scanning magnification error occurs, by changing the operating speed of the optical deflector of the optical writing means from the reference operating speed, the latent image formed on the photosensitive member is expanded or contracted in the sub-scanning direction. It can be written, and it is possible to cancel the sub-scanning magnification error.
However, in some image forming apparatuses, latent images written on the surface of a plurality of photoreceptors by an optical writing means are visualized, and each image is transferred onto a transfer material so as to be superimposed on each other. There is an image forming apparatus that forms an image by In this image forming apparatus, when the operating speed of the optical deflector of the optical writing means is changed from the reference operating speed, the writing start timing of the latent image onto each photoreceptor changes along with this change. , image position shift (color shift) occurs between images on a plurality of photoreceptors. For example, when controlling the start timing of writing a latent image on each photoreceptor based on the number of scans by the optical deflector from a predetermined print start timing, if the operating speed of the optical deflector is changed, this change Accordingly, the timing to start writing the latent image onto each photoreceptor changes. At this time, for example, if the operating speed of the optical deflector is changed so as to be slower than the reference operating speed (operating speed before change), the corresponding photosensitive member will be transferred to the transfer position of the photosensitive member downstream in the direction of movement of the surface of the transferred material. The leading edge of the image transferred from the photoreceptor on the upstream side in the moving direction of the surface of the transfer material reaches earlier than the leading edge of the image on the transfer material. As a result, image misalignment (color misalignment) occurs on the transfer material between the images on the plurality of photoreceptors.
Therefore, in the present embodiment, one of the plurality of photoreceptors is arranged so as to reduce the image positional deviation on the transfer material between the images of the plurality of photoreceptors caused by such a change in the operating speed of the optical deflector. is changed from that at the reference operating speed. Accordingly, even if the operating speed of the optical deflector is changed from the reference operating speed, it is possible to suppress image positional deviation (color deviation) on the transfer material between the images of the plurality of photoreceptors.

[Second aspect]
According to a second aspect, in the first aspect, the transfer timing changing means changes the writing start timing of the latent image on the at least one photosensitive member to start transferring the image onto the transfer material. It is characterized by changing the timing.
According to this, it is possible to change the transfer start timing with a simple configuration.

[Third aspect]
According to a third aspect, in the first or second aspect, when the operating speed is the reference operating speed, the transfer timing changing means changes the image on the transfer material between the images on the plurality of photoreceptors. Using a reference alignment parameter (e.g., reference write start timing) for matching positions, a transfer start timing of the image of the at least one photoreceptor onto the transfer material is determined, and the optical deflector is controlled. When the means changes the operating speed from the reference operating speed, using an adjustment parameter (e.g., a correction coefficient) corresponding to the changed operating speed, transferring the image of the at least one photoreceptor to the transfer material. It is characterized by determining the start timing.
According to this, it is possible to change the transfer start timing by simple control.

[Fourth aspect]
In a fourth aspect based on the third aspect, the reference registration parameter is a timing determination parameter (reference write start timing before correction) that determines the transfer start timing of the image of the at least one photoreceptor onto the transfer material. ), and the adjustment parameter is a correction coefficient to be multiplied by the reference alignment parameter.
According to this, it is possible to change the transfer start timing by simpler control.

[Fifth aspect]
According to a fifth aspect, in the third or fourth aspect, the transfer timing changing means adjusts the transfer start timing of the image of the at least one photoreceptor onto the transfer material using an adjustment parameter different for each photoreceptor. It is characterized by determining
According to this, by changing the adjustment parameter for each photoreceptor, it is possible to cope with the deviation over time.

26: pattern detection sensor 100: optical writing device 100A: KC unit 100B: MY unit 101: light source unit 102: light source 202: optical deflector 202a: upper rotary polygon mirror 202b: lower rotary polygon mirror 202c: motor 204: Four-wave plate 205: Cylindrical lens 301: Scanning lens 302: Elongated lenses 303a to 303c, 304: Mirror 305: Dustproof glass 311: Tip synchronization sensor 350: Write controller 351: Data processor 352: Controller 400 : Optical housing 500 : Color printers 501 to 504 : Photoreceptor drum 510 : Recording paper 602 : Charging device 603 : Developing roller 604 : Developing device 605 : Cleaning unit 606 : Intermediate transfer belt 608 : Paper feed roller 609 : Registration roller pair 610 : fixing device 611 : discharge tray 612 : discharge roller 613 : secondary transfer rollers L1, L2: laser light

JP-A-2005-059602

Claims (5)

The surface of a plurality of moving photosensitive members is repeatedly scanned in the main scanning direction by an optical writing means that deflects writing light according to image information by an optical deflector, thereby forming latent images according to the image information. are respectively written on the surfaces of the plurality of photoreceptors, and each image obtained by visualizing the latent images on the surfaces of the plurality of photoreceptors is transferred onto a transfer material so as to overlap each other,
optical deflector control means for controlling the operating speed of the optical deflector;
of the plurality of photoreceptors so as to reduce an image position shift on the transfer material between the images on the plurality of photoreceptors caused by changing the operating speed of the optical deflector from the reference operating speed. and transfer timing changing means for changing the transfer start timing of the image of at least one of the photoreceptors to the transfer material from that at the reference operating speed. The image forming apparatus according to claim 1,
The transfer timing changing means changes the timing to start transferring the image onto the transfer material by changing the timing to start writing the latent image onto the at least one photoreceptor. forming device. The image forming apparatus according to claim 1 or 2,
When the operation speed is the reference operation speed, the transfer timing changing means uses a reference registration parameter for matching the image positions on the transfer material between the images of the plurality of photoreceptors. to determine the transfer start timing of the image of the at least one photoreceptor onto the transfer material, and when the optical deflector control means changes the operation speed from the reference operation speed, the operation speed after the change is determined. An image forming apparatus, wherein a timing for starting transfer of an image on said at least one photoreceptor to said transfer material is determined using a corresponding adjustment parameter. The image forming apparatus according to claim 3,
The reference alignment parameter is an addition value to be added to a timing determination parameter for determining the transfer start timing of the image of the at least one photoreceptor onto the transfer material,
The image forming apparatus, wherein the adjustment parameter is a correction coefficient to be multiplied by the reference alignment parameter. The image forming apparatus according to claim 3 or 4,
The image forming apparatus according to claim 1, wherein the transfer timing changing means determines the transfer start timing of the image of the at least one photoreceptor onto the transfer material using an adjustment parameter that differs for each photoreceptor.

Images