JP2009204670A - Image forming apparatus and control method - Google Patents

Abstract

An image forming apparatus and a control method capable of suppressing a transfer image shift amount and realizing a good image quality by correcting a transfer image shift with high accuracy.
An image forming apparatus includes a first photosensitive drum 21 to a fourth photosensitive drum 24, a first exposure unit 31 to a fourth exposure unit 34, and the like. The length of the scanning line of the electrostatic latent image scanned on the photosensitive drum is adjusted according to the amount of movement of the photosensitive drum. Further, the length of the scanning line of the electrostatic latent image is adjusted by changing the clock frequency of the image forming signal for each scanning of the laser beam with respect to the photosensitive drum. Further, the length of the scanning line of the electrostatic latent image is adjusted by changing the total number of clocks of the image forming signal for each scanning of the laser beam with respect to the photosensitive drum. Further, the length of the scanning line of the electrostatic latent image is adjusted by dividing the scanning range of the laser beam on the photosensitive drum into a plurality of parts.
[Selection] Figure 3

Description

  The present invention relates to an image forming apparatus including a plurality of image forming units and a control method.

  Conventionally, an electrophotographic tandem-type color that has a plurality of image forming units and transfers a toner image formed by developing an electrostatic latent image formed by exposing a photosensitive member to each image forming unit to a recording medium. There is an image forming apparatus. The tandem type image forming apparatus includes a plurality of image forming units (photosensitive drums and developing units as photoconductors) corresponding to the respective colors (yellow Y, magenta M, cyan C, and black Bk) for speeding up. I have. When forming an image, images of different colors are sequentially transferred onto a recording medium held on an intermediate transfer belt or a conveyance belt.

  The tandem type image forming apparatus having a plurality of image forming units as described above has the following problems. For each color, the speed fluctuations of multiple photosensitive drums and intermediate transfer belts, and the relationship between the movement of the outer peripheral surface of the photosensitive drum and the intermediate transfer belt and recording medium at the transfer position of each image forming unit, due to mechanical accuracy, etc. It occurs separately. For this reason, when the images of the respective colors are overlaid, they do not coincide with each other, and color misregistration (positional misregistration) occurs.

  Therefore, as disclosed in, for example, Patent Document 1 and the like, a visible image of a position detection mark corresponding to the image information of the original is formed in the image forming unit of each color, transferred to the moving member, and moved by the detecting unit. The position detection mark is detected. Further, each image forming unit is controlled based on the detection signal of the detection means to correct the transfer image deviation (sampling correction method).

  In general, in an image forming apparatus, the position and size of each image forming unit itself and the mounting positions and sizes of components constituting the image forming unit slightly change due to temperature changes inside the apparatus and external force applied to the apparatus. That is, this sampling correction method detects a color transfer image shift (color registration shift) having a constant size and orientation caused by the change, and corrects the detected transfer image shift with an image formed later. is there. Color registration (hereinafter referred to as color registration) is to match the formation positions of a plurality of color images having different colors.

  However, in color registration misalignment, in addition to the above-mentioned components that change over a long period of time, the color registration that changes mainly in the rotating body such as the photosensitive drum and the belt drive roll, and whose size and direction change in a short time. Misalignment is also included. The sampling correction method is not a correction target for the color registration misalignment component in a short time.

  That is, since color registration misalignment of an image formed in the past is detected and corrected in the next image formation, fluctuation in a short time cannot be corrected.

  Further, in Patent Document 2, a first image forming unit forms a visible image of a position detection mark corresponding to image information of a document, transfers the image to the intermediate transfer belt, and then uses a detection unit to detect the position of the intermediate transfer belt. Is detected. Further, the writing scanning timing of the second image forming unit is adjusted based on the detection signal of the detecting means. That is, since the second to fourth image forming units perform the second to fourth image formations in accordance with the image formed by the first image forming unit, respectively, it is possible to detect a relatively short time variation. Correction is possible.

  However, the position detection mark formed at the first image forming unit and then transferred onto the intermediate transfer belt is detected, and the writing operation timing of the second image forming unit is adjusted based on the detection signal. . For this reason, the fluctuation component generated within the time from when the second image is written to the second image forming unit until the second image is transferred to the intermediate transfer belt cannot be detected or corrected. I didn't have enough to correct the misregistration.

  In Patent Document 3, a tandem type electrophotographic image forming apparatus writes a pattern on a first photosensitive drum by a recording unit, and the pattern is copied to an intermediate transfer belt by a transfer unit. A technique for matching the speeds of the intermediate transfer belt and the photosensitive drum in the transfer unit from the pattern copied on the intermediate transfer belt and the pattern written on the second and subsequent photosensitive drums is disclosed (FIGS. 10 and 10). 11).

However, since the pattern is written at equal intervals in time or at equal intervals in distance, the color registration misalignment cannot be corrected accurately because it does not correspond to the image position written by exposure. It was. That is, since the fluctuation information of the writing position due to fluctuation factors such as polygon wow and jitter is not recorded, these errors cannot be erased. Further, there has been a problem that the deviation of the writing position due to the scanning timing of the first and second stations, the polygon rotation speed difference, the phase difference, etc. cannot be erased.
JP-A 64-6981 JP-A-5-241457 JP 2004-145077 A

  A so-called tandem that has a plurality of image forming portions and sequentially transfers images of different colors (black Bk, cyan C, magenta M, yellow Y) onto an intermediate transfer belt or a recording material held on a conveyance belt. The type color image forming apparatus has the following problems. That is, variations in the writing position, the position of the photosensitive drum, the rotational speed of the photosensitive drum, the running speed of the intermediate transfer belt, and the like are detected, and the transfer image shift (color registration shift) cannot be corrected based on the detected results. Therefore, there is a problem that a large transfer image shift remains.

  An object of the present invention is to provide an image forming apparatus and a control method capable of suppressing a transfer image shift amount and realizing a good image quality by correcting transfer image shift with high accuracy.

  In order to achieve the above-mentioned object, the present invention provides a rotating first image carrier, first electrostatic image forming means for forming an electrostatic image on the first image carrier, and the first image carrier. A first developing means for developing a first color toner image by developing the electrostatic image formed on the toner with a toner, and transferring the first color toner image on the first image carrier to a moving conveyance body A first transfer unit that rotates, a rotating second image carrier, a second electrostatic image forming unit that forms an electrostatic image on the second image carrier, and the static image formed on the second image carrier. A second developing unit that develops an electric image with toner to form a second color toner image; and the second color toner image on the second image carrier is transferred to the first color carrier. And a second transfer section that transfers the toner image on the toner image, and the transport of the first color toner image on the transport body. A transport body position index detecting unit that detects a transport body position index corresponding to a position in the direction of the transport body upstream of the second transfer unit, and the second color toner in the second image carrier. A second image carrier position index detecting means for detecting a second image carrier position index corresponding to a position in the rotation direction of the image at a position between the second developing means and the second transfer section; An adjustment unit that adjusts the position of the two-image carrier, and the adjustment unit is controlled based on the detection results of the conveyance-body-position-index detection unit and the second-image-carrier-position-index detection unit; The second electrostatic image forming unit is configured to reduce the amount of positional deviation between the first color toner image and the second color toner image in the moving direction of the carrier and to control the adjustment unit. To control the shape of the second image carrier. And a control means for changing the longitudinal size of the second image bearing member an electrostatic image which is characterized by comprising a.

  According to the present invention, the size of the electrostatic image formed on the second image carrier in the longitudinal direction of the second image carrier is changed. Therefore, in an image forming apparatus that transfers an image formed on each image carrier to the conveyance body, it is possible to correct the phenomenon that the transferred image from each image carrier is shifted with high accuracy. As a result, it is possible to reduce the transfer image deviation amount, and thus it is possible to realize a good image quality.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a configuration diagram showing an overall schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

  In FIG. 1, an image forming apparatus 1 includes a document reading unit (image reader unit) 1R that reads an image from a document and an image output unit (printer unit) 1P that forms and outputs an image on a recording medium such as paper. The image forming apparatus is configured as a copying machine that performs image formation. The document reading unit 1R reads an image from a document placed on a document table via a document cover (pressure plate) 19 and outputs an image reading signal. The image output unit 1P includes an image forming unit 10, an intermediate transfer belt 11, a fixing device 3, a manual feed cassette 2a, paper feed cassettes 2b and 2c, a paper discharge tray 5, and a control unit 70.

  The image forming unit 10 includes a first photosensitive drum 21 to a fourth photosensitive drum 24, a first primary charger 21 to a fourth primary charger, a first exposure unit 31 to a fourth exposure unit 34, and a first developing unit 35 to a fifth developer. Four developing devices 38 are provided. That is, the image forming unit 10 has a configuration in which the first to fourth image forming units (process units) are arranged in parallel.

  The first image forming unit includes a first photosensitive drum 21 (first image carrier), a first primary charger 25, a first exposure unit 31 (first electrostatic image forming unit), and a first developing unit 35 (first Developing means). The second image forming unit includes a second photosensitive drum 22 (second image carrier), a second primary charger 26, a second exposure unit 32 (second electrostatic image forming unit), and a second developing unit 36 (second Developing means). The third image forming unit includes a third photosensitive drum 23, a third primary charger 27, a third exposure unit 33, and a third developer 37. The fourth image forming unit includes a fourth photosensitive drum 24, a fourth primary charger 28, a fourth exposure unit 34, and a fourth developer 38.

  The first photosensitive drum 21 to the fourth photosensitive drum 24 are arranged along the belt surface of the intermediate transfer belt 11 (conveyance body), and the center is pivotally driven and rotationally driven in the direction of the arrow, and the electrostatic latent image is displayed. An image carrier to be formed. The first photosensitive drum 21 to the fourth photosensitive drum 24 are configured to be movable (shifted) relative to the intermediate transfer belt 11. The first photosensitive drum 21 to the fourth photosensitive drum 24 are moved (shifted) by a photosensitive drum shift actuator (moving means) described later.

  Around the first photosensitive drum 21 to the fourth photosensitive drum 24, the first to fourth cleaning units 6 to 9, the first primary charger 21 to the fourth primary charger in the rotation direction facing the outer peripheral surface, respectively. 25, the 1st exposure part 31-the 4th exposure part 34, the 1st developing device 35-the 4th developing device 38 are arrange | positioned.

  The first primary charger 21 to the fourth primary charger 25 apply a uniform charge amount to the surfaces of the first photosensitive drum 21 to the fourth photosensitive drum 24, respectively. The first exposure unit 31 to the fourth exposure unit 34 irradiate and scan the first photosensitive drum 21 to the fourth photosensitive drum 24 with laser beams modulated according to the image capturing signal output from the document reading unit 1R, respectively. This is an optical scanning unit. Thereby, electrostatic latent images are formed on the first photosensitive drum 21 to the fourth photosensitive drum 24. The first exposure unit 31 to the fourth exposure unit 34 include a scanner (see FIG. 2) that irradiates laser light onto the first photosensitive drum 21 to the fourth photosensitive drum 24, respectively.

  The first developing unit 35 to the fourth developing unit 38 respectively store four color developers (toners) of yellow (Y), cyan (C), magenta (M), and black (K). The first developing unit 35 to the fourth developing unit 38 develop the electrostatic latent images on the first photosensitive drum 21 to the fourth photosensitive drum 24 with toner, respectively, to visualize (visualize) them as toner images.

  The intermediate transfer belt 11 is disposed in contact with the outer peripheral surfaces of the first photosensitive drum 21 to the fourth photosensitive drum 24, and is circulated and driven (running driving) in the arrow direction (specified direction) via a plurality of rollers. This is an endless belt. A first transfer area Ta to a fourth primary transfer area Td are formed between the intermediate transfer belt 11 and the first photosensitive drum 21 to the fourth photosensitive drum 24. A secondary transfer region Te is formed between the intermediate transfer belt 11 and the secondary transfer unit 13.

  In the first transfer area Ta to the fourth primary transfer area Td, the toner images on the first photosensitive drum 21 to the fourth photosensitive drum 24 are sequentially transferred to the intermediate transfer belt 11. The first to fourth cleaning units 6 to 9 are disposed downstream of the first transfer area Ta to the fourth primary transfer area Td, respectively, and scrape off residual toner on the first photosensitive drum 21 to the fourth photosensitive drum 24. .

  The manual cassette 2a is used when the recording medium P is manually fed. The paper feed cassettes 2b and 2c store the recording medium P. The recording medium P fed from one of the manual feed cassette 2a and the paper feed cassettes 2b and 2c is supplied to the secondary transfer area Te. In the secondary transfer region Te, the toner image on the intermediate transfer belt 11 is transferred to the recording medium P. The fixing device 3 fixes the toner image on the recording medium P conveyed from the secondary transfer region Te. The recording medium P on which image formation has been completed is discharged to the paper discharge tray 5. The control unit 70 will be described with reference to FIG.

  Next, the operation of the image forming apparatus will be described. In the image forming unit 10, an image formation start signal is issued from the CPU (see FIG. 2). Accordingly, the toner image formed on the first photosensitive drum 21 located on the most upstream side in the rotation direction of the intermediate transfer belt 11 is primarily transferred to the intermediate transfer belt 11 in the first primary transfer area Ta (first). 1 transfer part). The toner image primarily transferred onto the intermediate transfer belt 11 is conveyed to the next second primary transfer region Tb.

  In the second primary transfer region Tb, image formation is performed with a delay by a time during which the toner image on the intermediate transfer belt 11 is conveyed between the image forming portions. That is, the next toner image is transferred onto the formed toner image by aligning the position (second transfer portion, transfer means). Matching the formation positions of a plurality of color images having different colors in this way is called registration. The same process is repeated thereafter, and finally the four color toner images are primarily transferred onto the intermediate transfer belt 11.

  Thereafter, when the fed recording medium P enters the secondary transfer area Te and contacts the intermediate transfer belt 11, a high voltage is applied to the secondary transfer unit 13 in accordance with the passing timing of the recording medium P. Then, the four color toner images formed on the intermediate transfer belt 11 are transferred to the surface of the recording medium P. The recording medium P onto which the toner image has been transferred is fixed by the fixing device 3 and then discharged to the paper discharge tray 5.

  FIG. 2 is a block diagram illustrating a configuration of a control system of the image output unit 1P of the image forming apparatus.

  In FIG. 2, the image output unit 1P includes a CPU 401 (control means), a ROM 402, a RAM 403, a load control ASIC (Application Specified IC) 404, a motor 405, and a controller unit 416. Further, the image output unit 1P includes a scanner control ASIC 406, a scanner Y 701a, a scanner M 701b, a scanner C 701c, and a scanner K 701d. The CPU 401, ROM 402, RAM 403, load control ASIC 404, controller unit 416, and scanner control ASIC 406 are mounted on the control unit 70.

  The CPU 401 is a microcomputer that performs various types of control including control of the drive target load of the image output unit 1P. The CPU 401 executes a control program and sets a drive target load control signal to the load control ASIC 404 to drive a motor 405 that rotationally drives the shafts of the first photosensitive drum 21 to the fourth photosensitive drum 24.

  Further, the CPU 401 designates a parameter such as a magnification in the scanner control ASIC 406. Accordingly, the scanner control ASIC 406 controls the magnification used by the scanner M • 701b, the scanner C • 701c, and the scanner K • 701d. Further, the CPU 401 executes processing shown in each flowchart described later based on the control program. The ROM 402 stores the control program such as firmware. The RAM 403 is used as a temporary storage area or a work area.

  The controller unit 416 receives a copy start instruction by pressing the copy start button on the operation panel 418 (input of a print job), issues a print command to the image output unit 1P, and transmits image data. Further, the controller unit 416 has a function of receiving an image reading signal through communication with the document reading unit 1R and receiving a signal indicating that the document cover (pressure plate) 19 is opened from the document reading unit 1R.

  FIG. 3 is a block diagram illustrating a schematic configuration of the first exposure unit 31 to the fourth exposure unit 34 of the image forming apparatus.

  In FIG. 3, the first exposure unit 31 includes a semiconductor laser 311, a collimator lens 312, an aperture 313, a rotary polygon mirror 314, an f-θ lens 315, and a beam detect sensor (hereinafter referred to as BD sensor) 316. Furthermore, the first exposure unit 31 includes a laser drive control unit 321 (light emission control unit), an image signal generation unit 322 (generation unit), a correction unit 323, and an input unit 324, respectively. In addition, since the 2nd exposure part 32-the 4th exposure part 34 are also the same, description is abbreviate | omitted.

  The laser drive control unit 321 emits laser light by drivingly controlling the semiconductor laser 311 with a drive (light emission) signal 306. The semiconductor laser 311 incorporates a PD (photodiode) sensor that detects a part of the emitted laser light. The detection signal of the PD sensor is used for auto power control (APC) control of the semiconductor laser 311. The laser light emitted from the semiconductor laser 311 is converted into substantially parallel laser light by the collimator lens 312 and the aperture 313 and then enters the rotating polygon mirror (polygon mirror) 314 with a predetermined beam diameter.

  The rotary polygon mirror 314 is rotated at an equal angular speed in the direction of the arrow. The incident laser light is converted into a deflected beam that continuously changes its angle as the rotary polygon mirror 314 rotates, and is reflected. The laser beam converted into the deflected beam is focused by the f-θ lens 315. Further, the f-θ lens 315 corrects the distortion aberration so as to guarantee the temporal linearity of scanning with respect to the laser light. As a result, the laser beam is coupled and scanned on the first photosensitive drum 21 at a constant speed.

  The BD sensor 316 detects laser light that passes through the f-θ lens 315 from the rotary polygon mirror 314. The detection signal 303 of the BD sensor 316 is used as a synchronization signal for synchronizing the rotation of the rotary polygon mirror 314 and the formation (writing) of the electrostatic latent image corresponding to the image data on the first photosensitive drum 21. The image signal generation unit 322 generates an image formation signal 305 and outputs it to the laser drive control unit 321.

  The input unit 324 outputs a data signal 304 indicating the movement amount (shift amount) of the photosensitive drum 21 with respect to the intermediate transfer belt 11 to the correction unit 323. The correction unit 323 generates a BD mask signal 301 in synchronization with the detection signal 303 of the BD sensor 316 and outputs the BD mask signal 301 to the laser drive control unit 321. Further, the correction unit 323 outputs light amount end correction data 302 corresponding to the scanning position of the laser beam with respect to the photosensitive drum 21 to the laser drive control unit 321.

  The laser drive control unit 321 performs digital / analog (D / A) conversion on the light amount edge correction data 302 input from the correction unit 323. The laser drive control unit 321 is a semiconductor laser based on the image forming signal 305 and the light amount end correction data 302 input from the image signal generating unit 322 in the image section where the electrostatic latent image is formed on the photosensitive drum 21. The current value and drive time of the 311 drive signal 306 are controlled.

  The laser light emitted from the semiconductor laser 311 is converted into substantially parallel light by the collimator lens 312 and the aperture 313 as described above, and then enters the rotary polygon mirror 314 with a predetermined beam diameter.

  In the present embodiment, the following control is performed. The length of the scanning line of the electrostatic latent image scanned on the photosensitive drum is adjusted according to the movement amount (shift amount) of the photosensitive drum. Further, the length of the scanning line of the electrostatic latent image scanned on the photosensitive drum is set to the clock frequency of the image forming signal output from the image signal generation unit 322 to the laser drive control unit 321 for each scanning of the laser beam on the photosensitive drum. Adjust by changing. Further, the length of the scanning line of the electrostatic latent image scanned on the photosensitive drum is adjusted by changing the total number of clocks of the image forming signal. Further, the length of the scanning line of the electrostatic latent image scanned on the photosensitive drum is adjusted for each section obtained by dividing the scanning range of the laser beam on the photosensitive drum into a plurality of sections. Each control will be described later.

  Next, image alignment control, which is a feature of the present embodiment, will be described.

  FIG. 4 is a diagram illustrating the configuration of the intermediate transfer belt 11, the first and second image forming units, and the control system of the image forming apparatus.

  In FIG. 4, the intermediate transfer belt 11, the first image forming unit, and the second image forming unit are illustrated. Since the third image forming unit and the fourth image forming unit may operate elements having the same functions as those of the second image forming unit with the same configuration, illustration and description are omitted to avoid complication.

  The control system includes a first recording unit 41, an image position information reading unit 51, a transcription control unit 60, a transcription unit 61, an image position information erasing unit 81, a second recording unit 42, a second image position information reading unit 52, and a first. An image position information reading unit 72 is provided. Further, the image position information erasing unit 82, the first image position information erasing unit B85, the first exposure scanning timing generation unit 101, the first recording control unit 111, the second exposure scanning timing generation unit 102, the second recording control unit 112, An image position information comparison unit 122 and a second drum control unit 132 are provided.

  Hereinafter, a control process for aligning the first image (first color toner image) and the second image (second color toner image) will be described with reference to FIGS. 9a and 9b. The processing shown in FIGS. 9 a and 9 b is executed by the CPU 401 of the control unit 70. First, first image position information D201 and second image position information D202 based on an image are created (step S900), and the process proceeds to steps S904 and S914, respectively. Regarding the first image, after the first raster scanning information based on the image is created (step S901), the processing of step S902 to step S909 is performed. For the second image, after the second raster scanning information based on the image is created (step S911), the processing of steps S912 to S916 is performed.

  The first photosensitive drum 21 of the first image forming unit is rotated at a substantially constant rotational speed by a motor (not shown) in the direction of the broken arrow (counterclockwise). The photoreceptor on the surface of the first photosensitive drum 21 is uniformly charged by the first primary charger 25 (FIG. 1).

  The first exposure unit 31 irradiates and scans the first photosensitive drum 21 with laser light, and forms a first electrostatic latent image by changing the potential of the laser light irradiated portion on the surface of the first photosensitive drum (step). S902). Yellow (Y) toner is attached to the portion of the first photosensitive drum 21 where the potential has changed due to laser light irradiation by the first developing device 35 (FIG. 1), thereby forming a first image. The toner for forming the first image is transferred onto the intermediate transfer belt 11 in the first primary transfer area Ta where the first photosensitive drum 21 and the intermediate transfer belt 11 are in contact with each other.

  The first photosensitive drum 21 is coated with an information recording medium such as a magnetic material at a location outside the image forming area. The place outside the image forming area is, for example, a portion where an image is not formed in the vicinity of the axial end portion of the surface of the photosensitive drum, an end surface portion of the photosensitive drum, or an inner surface portion of the photosensitive drum.

  The first exposure scanning timing generation unit 101 generates a raster scanning timing signal for the first exposure unit 31 (step S903) and sends it to the first recording control unit 111. The first recording control unit 111 controls the first recording unit 41 according to the raster scanning timing, and records the position information of the first image on the recording medium.

  FIG. 5 is a diagram showing a positional relationship between the first image and the first image position information when the first photosensitive drum 21 is developed.

  In FIG. 5, the first image position information D201 (FIG. 4) includes a first image position information start mark D211, a first image position mark D221, and a first image position information end mark D231. These marks are written on the first photosensitive drum 21 by the first recording unit 41 in accordance with the raster scanning timing signal synchronized with the laser emission (step S904).

  The formation pitch of the image position information as described above is required to be about 1 μm when the color shift of the transfer image to be corrected is 10 μm. By processing the output signals from the two read heads that are spatially shifted in phase by 90 degrees, for example, a scale of 10 μm pitch can be realized by dividing into 64 or 128 divisions.

  Returning to FIG. 4, the first recording unit 41 is disposed at a position that coincides with the laser exposure scanning position on the surface of the first photosensitive drum in the rotation direction of the first photosensitive drum 21. Ideally, the time from when the raster scanning timing signal is generated until the first recording control unit 111 records the position information of the first image by the first recording unit 41 is zero. However, there is actually some time delay.

  For example, when the process speed is 300 mm / sec, if the time delay is about 30 μsec, a positional shift of about 1 μm occurs. When the color shift of the transfer image to be corrected is 10 μm, it is acceptable if the time delay is 30 μsec or less. If a large time delay is unavoidable, the first recording unit 41 is disposed downstream of the laser exposure scanning position on the surface of the first photosensitive drum in the rotational angle direction of the first photosensitive drum 21 by a distance corresponding to the time delay. do it. Thereby, the position error due to time delay can be eliminated.

  The first image position information D201 reaches the first primary transfer area Ta where the first photosensitive drum 21 comes into contact with the intermediate transfer belt 11 as the first photosensitive drum 21 rotates (step S905). In the first primary transfer area Ta, the toner image on the first photosensitive drum 21 is transferred to the intermediate transfer belt 11. At the same time, the first image position information D201 on the first photosensitive drum 21 is transferred to the intermediate transfer belt 11 to form the first image position information B200.

  Further, a method for transferring the first image position information D201 will be described in detail. The first image position information D201 on the first photosensitive drum 21 that has reached the first primary transfer area Ta is read by the image position information reading unit 51 on the first photosensitive drum 21 (step S906), and the read signal is transferred and controlled. Sent to the unit 60. The transcription control unit 60 controls the transcription unit 61 according to the read signal to write the first image position information B200 on the intermediate transfer belt 11 (step S907). Similar to the first photosensitive drum 21, the intermediate transfer belt 11 is coated with an information recording medium such as a magnetic material at a location outside the image forming area, and the first image position information B 200 is written by the transcription unit 61.

  FIG. 6 is a diagram for explaining the transfer of the first image position information D201 to the intermediate transfer belt 11. In FIG.

  In FIG. 6, an information recording medium such as a magnetic material is applied to the back side (inside) of the intermediate transfer belt 11, and the first image position information B <b> 200 is written by the transcription unit 61. The transcription unit 61 is disposed at a position that coincides with the position of the image position information reading unit 51 on the first photosensitive drum 21 in the rotation angle direction of the first photosensitive drum 21. Ideally, the time from reading the image position information to posting is zero. However, there is actually some time delay.

  For example, when the process speed (such as the rotational speed of the photosensitive drum) is 300 mm / sec, if the time delay is about 30 μsec, a positional shift of about 1 μm occurs. When the color shift of the transferred image to be corrected is set to 10 μm or less, a time delay of 30 μs or less is acceptable. If a large time delay is inevitably generated, the transcription unit 61 is moved downstream by a distance corresponding to the time delay from the position of the image position information reading unit 51 on the first photosensitive drum in the rotation angle direction of the first photosensitive drum 21. What is necessary is just to arrange. Thereby, the position error due to the delay can be eliminated.

  FIG. 7 is a diagram showing the relationship between the first image transferred to the intermediate transfer belt 11 and the first image position information B200 transferred to the intermediate transfer belt 11.

  In FIG. 7, the first image position information B200 (conveyor position index) on the intermediate transfer belt 11 is composed of a first image position information start mark B241, a first image position mark B251, and a first image position information end mark B261. Has been.

  With respect to the movement direction of the intermediate transfer belt 11, the positional relationship between the first image and the first image position information is maintained between the first image on the first photosensitive drum 21 and the first image position information shown in FIG. Yes. When the surface on which the first image is transferred and the surface on which the first image position information B200 is transferred are different as shown in FIG. 6, there is no problem even if the first image position information overlaps the image area in the front and back direction. However, when the transfer surface and the transfer surface are the same as shown in FIG. 5, the first image position information is preferably outside the image region.

  The first image and the first image position information B200 recorded on the intermediate transfer belt 11 move as the intermediate transfer belt 11 travels, and the second primary transfer area where the intermediate transfer belt 11 contacts the second photosensitive drum 22. Tb is reached (step S908).

  On the other hand, a second image (magenta (M): developed with toner of the second color) is formed on the second photosensitive drum 22 in the same process as the first image (yellow (Y): developed with toner of the first color). This is done (step S912), which is the same as the conventional tandem type image forming apparatus.

  Also on the second photosensitive drum 22, an information recording medium such as a magnetic material is applied to a place outside the image forming area. The place outside the image forming area is, for example, a portion where an image is not formed in the vicinity of the axial end portion of the surface of the photosensitive drum, an end surface portion of the photosensitive drum, or an inner surface portion of the photosensitive drum.

  Returning to FIG. 4, the second exposure scanning timing generation unit 102 generates a raster scanning timing signal of the second exposure unit 32 and sends it to the second recording control unit 112 (step S913). The second recording control unit 112 controls the second recording unit 42 according to the raster scanning timing, and records the position information of the second image on the recording medium.

  FIG. 8 is a diagram showing a positional relationship between the second image and the second image position information D202 when the second photosensitive drum 22 is developed.

  In FIG. 8, the second image position information D202 (second image carrier position index) is composed of a first image position information start mark D212, a first image position information D222, and a first image position information end mark D232. . These marks are written on the second photosensitive drum 22 by the second recording unit 42 in accordance with the raster scanning timing signal synchronized with the laser emission (step S914).

  As the second photosensitive drum 22 rotates, the second image position information D202 reaches the second primary transfer region Tb where the second photosensitive drum 22 contacts the intermediate transfer belt 11 (step S915). Hereinafter, a method for aligning the positions of the first image and the second image in the second primary transfer region will be described.

  The second image position information reading unit 52 (second image carrier position index detection means, image carrier position index detection means) reads the second image position information on the second photosensitive drum 22 (step S916). Specifically, when the second image position information start mark D212 is detected, the second image position mark D222 is counted and a count signal is output to the image position information comparison unit 122. When the second image position information end mark D232 is detected, the counting is ended.

  The first image position information reading unit 72 (conveyor position index detection unit) on the intermediate transfer belt 11 reads the first image position information on the intermediate transfer belt 11 (step S909). Specifically, when the first image position information start mark B 241 is detected, the first image position mark B 251 is counted and a count signal is output to the image position information comparison unit 122. When the first image position information end mark B261 is detected, the counting ends.

  The image position information comparison unit 122 compares the count value sent from the second image position information reading unit 52 with the count value sent from the first image position information reading unit 72 on the intermediate transfer belt 11. (Step S921). As a result of the comparison, the image position information comparison unit 122 outputs the difference signal or a signal corresponding to the difference to the second drum control unit 132. Accordingly, the second drum control unit 132 (adjustment unit) performs control to shift the axis of the second photosensitive drum 22 so that the difference between the count values becomes zero (step S922), so that the first image and the first image are adjusted. The positions of the two images can be accurately aligned.

  It is desirable that the second image position information reading unit 52 and the first image position information reading unit 72 on the intermediate transfer belt 11 are arranged at the same position with respect to the traveling direction of the intermediate transfer belt 11.

  However, if it is known that an error due to time delay has occurred in the first recording unit 41, the second recording unit 42, or the transcription unit 61, the error can be eliminated. In other words, the error can be eliminated by shifting the positions of the second image position information reading unit 52 and the first image position information reading unit 72 on the intermediate transfer belt 11 by an amount corresponding to the error.

  FIG. 10 is a flowchart showing an overall control process including tasks 1 to 5 (recording of first and second image position information on the first and second photosensitive drums, second photosensitive drum control).

  In FIG. 10, the CPU 401 of the control unit 70 performs the following processing. First, the creation of the first image, the first image position information D201, the second image, and the second image position information D202, the start to start the rotation of the first photosensitive drum 21 and the second photosensitive drum 22, the running of the intermediate transfer belt 11 Preparation processing such as start-up is started (step S1001). Next, task 1 is started at time t = 0 (step S1002), and it is determined whether time t = θ / w has elapsed from the start of task 1 (step S1003).

  If time t = θ / w has elapsed, task 3 is started (step S1004), and it is determined whether time t = l / v has elapsed since the start of task 3 (step S1005). When the time t = 1 / v has elapsed, the task 2 is started (step S1006), and it is determined whether the time t = (θ / w) + (l / v) has elapsed since the start of the task 2 (step S1006). Step S1007). When the time t = (θ / w) + (l / v) has elapsed, task 4 and task 5 are started (step S1008). When the task 5 is finished (step S1009), this process is finished.

  Task 1 is a task for recording the first image position information D201 on the first photosensitive drum 21. The first exposure scanning timing generation unit 101 generates a timing signal synchronized with the raster scanning of the first exposure unit 31, and the first recording control unit 111 controls the first recording unit 41 according to the raster scanning timing to perform the first. Image position information D201 is recorded.

  Task 2 is a task for recording the second image position information D202 on the second photosensitive drum 22. The second exposure scanning timing generation unit 102 generates a timing signal synchronized with the raster scanning of the second exposure unit 32, and the second recording control unit 112 controls the first recording unit 42 in accordance with the raster scanning timing to perform the second. Image position information D202 is recorded.

  Task 3 is a task for creating the first image position information B200 by transferring the first image position information D201 to the intermediate transfer belt 11 by the transfer unit 61.

  Task 4 is a task in which the second image position information reading unit 52 reads the second image position information D202 on the second photosensitive drum 22. As image information, image position information and mark detection time described later are stored in a register.

  Task 5 reads the first image position information B200 on the intermediate transfer belt 11 and compares it with the second image position information D202 on the second photosensitive drum 22 read in task 4, and the second photosensitive drum according to the difference. 22 is a task for controlling 22.

  “Θ” is an angle from the first exposure position of the first photosensitive drum 21 to the first transfer position, and an angle from the second exposure position of the second photosensitive drum 22 to the second transfer position. “W” is the rotational angular velocity of the first photosensitive drum 21 and the second photosensitive drum 22. “L” is the distance from the first transfer position to the second transfer position. “V” is the traveling speed of the intermediate transfer belt 11. The time t = 0 at which the task 1 starts must be set before the first exposure scanning timing generation unit 101 issues a start signal.

  FIG. 11 is a flowchart showing task 1.

  In FIG. 11, this process is executed by the CPU 401 of the control unit 70. The raster scanning timing signal is derived from a start signal that is issued a predetermined time earlier than the start of image drawing, a signal that is synchronized with raster scanning of the first exposure unit 31, and an end signal that is output immediately after the end of image drawing. Become.

  First, it is determined whether there is a raster scanning timing signal (step S1101). If there is a raster scanning timing signal, it is determined whether it is a start signal (step S1102) or an end signal (step S1103). In the case of the start signal, the first image position information start mark D211 (FIG. 5) is recorded (written) on the first photosensitive drum 21 (step S1104). If it is not an end signal, the first image position mark D221 is recorded on the first photosensitive drum 21 (step S1105), and the process returns to step S1101.

  In the case of the end signal, the first image position information end mark D231 is recorded on the first photosensitive drum 21 (step S1106). Next, it is determined whether or not three first image position information end marks D231 are recorded on the first photosensitive drum 21 (step S1107). If three are not recorded, the process returns to step S1101, and three is recorded. Ends this processing.

  FIG. 12 is a flowchart showing the task 2.

  In FIG. 12, this process is executed by the CPU 401 of the control unit 70. The raster scanning timing signal is based on a start signal that is issued a predetermined time earlier than the start of image drawing, a signal that is synchronized with raster scanning of the second exposure unit 32, and an end signal that is output immediately after the end of image drawing. Become.

  First, it is determined whether there is a raster scanning timing signal (step S1201). If there is a raster scanning timing signal, it is determined whether it is a start signal (step S1202) or an end signal (step S1203). In the case of the start signal, the second image position information start mark D212 (FIG. 8) is recorded (written) on the second photosensitive drum 22 (step S1204). If it is not an end signal, the second image position mark D222 is recorded on the second photosensitive drum 22 (step S1205), and the process returns to step S1201.

  In the case of the end signal, the second image position information end mark D232 is recorded on the second photosensitive drum 22 (step S1206). Next, it is determined whether or not three second image position information end marks D232 have been recorded on the second photosensitive drum 22 (step S1207). If three are not recorded, the process returns to step S1201, and three are recorded. Ends this processing.

  FIG. 13 is a flowchart showing the task 3.

  In FIG. 13, this process is executed by the CPU 401 of the control unit 70. First, it is determined whether there is a reading signal at the first transfer position from the first image position information reading unit 51 on the first photosensitive drum 21 (step S1301). If there is a read signal, it is determined whether it is a signal of the first image position information start mark D211 (FIG. 5) (step S1302) or a signal of the first image position information end mark D231 (step S1303).

  In the case of the signal of the first image position information start mark D211, the first image position information start mark B241 (FIG. 8) is recorded (written) on the intermediate transfer belt 11 (step S1304). If it is not the signal of the first image position information end mark D231, the first image position mark B251 is recorded on the intermediate transfer belt 11 (step S1305), and the process returns to step S1301.

  In the case of the signal of the first image position information end mark D231, the first image position information end mark B261 is recorded on the intermediate transfer belt 11 (step S1306). Next, it is determined whether or not three first image position information end marks B261 have been recorded on the intermediate transfer belt 11 (step S1307). If three are not recorded, the process returns to step S1301, and if three are recorded. This process ends.

  FIG. 14 is a flowchart showing the task 4.

  In FIG. 14, this process is executed by the CPU 401 of the control unit 70. First, the second drum mark D counter that counts the number of marks D detected on the second photosensitive drum 22 is cleared to 0 (step S1401), and the presence / absence of the second image position information start mark D212 on the second photosensitive drum 22 is determined. It is detected (step S1402). When there is the second image position information start mark D212, the second drum detection mark D number register for storing the number of the detected mark D on the second photosensitive drum 22 is cleared to 0, and the second drum mark D counter is set. Count up by one (step S1403).

  Next, the presence / absence of the second image position mark D222 on the second photosensitive drum 22 is detected (step S1404). When there is the second image position mark D222, the count value of the second drum mark D counter is stored in the second drum detection mark D number register. Further, the current time is stored in the second drum detection time register that stores the mark D detection time on the second photosensitive drum 22 (step S1405). Next, the second drum mark D counter is incremented by 1 (step S1406), and the process returns to step S1404.

  If there is no second image position mark D222 in step S1404, the presence / absence of the second image position information end mark D232 on the second photosensitive drum 22 is detected (step S1407). If there is no second image position information end mark D232, the process returns to step S1404. If there is a second image position information end mark D232, this process ends.

  FIG. 15 is a flowchart showing the task 5.

  In FIG. 15, this process is executed by the CPU 401 of the control unit 70. First, the presence / absence of the second image position information start mark B241 (FIG. 7) on the intermediate transfer belt 11 is detected (step S1501). When there is the second image position information start mark B241, the belt detection mark B number register for storing the number of the detected mark B on the intermediate transfer belt 11 is cleared to zero. Further, the belt mark B counter for counting the number of marks B detected on the intermediate transfer belt 11 is incremented by 1 (step S1502).

  Next, the presence or absence of the first image position mark B251 on the intermediate transfer belt 11 is detected at the second transfer position (step S1503). When there is the first image position mark B251, the count value of the belt mark B counter is stored in the belt detection mark B number register, and the current time is stored in the belt detection time register that stores the mark B detection time on the intermediate transfer belt 11. Is stored (step S1504). Next, the belt mark B counter is incremented by 1 (step S1505).

  If there is no second image position information start mark B251 in step S1503, the presence / absence of the second image position information start mark B251 on the intermediate transfer belt 11 is detected (step S1506). If there is no second image position information start mark B251, the process returns to step S1503. If there is a second image position information start mark B251, this process ends.

  After step S1505, it is determined whether or not the second drum detection mark D number register (FIG. 14) is not 0, that is, whether or not reading of the second image position mark D222 on the second photosensitive drum 22 has started (step S1507). ). If reading of the second image position mark D222 on the second photosensitive drum 22 has not yet started, the process waits. If reading of the second image position mark D222 has started, the value of the second drum detection mark D number register is compared with the value of the belt detection mark B number register (step S1508).

  If the values in both registers match, the correction amount is calculated from the time difference between the time value stored in the second drum detection time register and the time value stored in the belt detection time register (step S1509). If the values in both registers do not match, the correction amount is calculated from the difference between the count value of the second drum mark D counter and the count value of the belt mark B counter (step S1510). Thus, the shift amount (movement amount) of the shaft of the second photosensitive drum 22 is controlled based on the correction amount (step S1511).

  Next, an outline of a method for shifting the axis of the second photosensitive drum 22 will be described with reference to FIG.

  FIG. 16 is a diagram illustrating a method for shifting the axis of the second photosensitive drum 22.

  In FIG. 16, the first image position information 200a, 200b on the intermediate transfer belt 11 and the second image position information 202a, 202b on the second photosensitive drum 22 are recorded on both sides (front side and back side), respectively. Yes. Of course, the recording (transcription) of the first image position information 200a and 200b on the intermediate transfer belt 11 is also performed separately on the near side and the far side. Accordingly, the first image position information reading units 72a and 72b and the second image position information reading units 52a and 52b on the intermediate transfer belt 11 are also arranged on the front side and the back side.

  The CPU 401 of the control unit 70 causes the second photosensitive drum shift actuators 92a and 92b (moving means) so that the difference between the count values of the first image position information 200a and 200b and the second image position information 202a and 202b becomes zero. ) To control. Thereby, the difference between the near side and the far side (for example, the difference in the diameter of the photosensitive drum, the difference in the traveling speed / the amount of expansion / contraction of the intermediate transfer belt 11) can be accurately corrected to match the images.

  As the second photosensitive drum shift actuators 92a and 92b, linear drive type actuators such as a laminated type piezoelectric actuator and a voice coil type linear actuator are suitable. Further, a photosensitive drum shift actuator is provided corresponding to each of the first photosensitive drum 21 to the fourth photosensitive drum 24. FIG. 16 illustrates the second photosensitive drum shift actuators 92a and 92b.

  When the charger, the developing unit, and the cleaning unit necessary for forming the toner image on the second photosensitive drum 22 move integrally with the shaft of the second photosensitive drum 22, the image forming condition does not change and a stable image is obtained. Formation can be performed.

  Next, a specific example of a shift mechanism for shifting the second photosensitive drum 22 will be described with reference to FIGS. 17, 18, and 19.

  FIG. 17 is a cross-sectional view showing the configuration of the shift mechanism of the second photosensitive drum 22. FIG. 8 is a diagram illustrating a configuration of the shift mechanism of the second photosensitive drum 22 as viewed from the upstream side of the intermediate transfer belt. FIG. 19 is a diagram illustrating a configuration of the shift mechanism of the second photosensitive drum 22 as viewed from above.

  17 to 19, an image forming unit (process unit) 500 for one color (magenta) having the second photosensitive drum 22 is shown. As described above, the image forming unit 10 includes first to fourth image forming units (process units) corresponding to the respective colors (yellow, magenta, cyan, and black). In the process unit 500 serving as a second image forming unit, a second primary charger 26, a second exposure unit 32, a second developing unit 36, and a second cleaning unit 7 are sequentially arranged around the second photosensitive drum 22. . These parts are supported by a U-shaped process unit chassis 508. The other image forming units (process units) are the same, but are not shown.

  The laser light emitted from the second exposure unit 32 according to the image formation signal passes through the opening 508a of the process unit chassis 508 and is scanned on the surface of the second photosensitive drum 22. The shaft of both ends of the second photosensitive drum 22 is supported by the process unit chassis 508 via a bearing A 514a and a bearing B 514b. One side of the shaft of the second photosensitive drum 22 is connected to a drum driving unit 509 supported by the process unit chassis 508. As a result, the second photosensitive drum 22 is rotationally driven by the drum drive unit 509.

  The process unit 500 that supports the components is rotatably supported by a U-shaped intermediate moving chassis 511 via a bearing C513. In the upper center of the process unit chassis 508, a bearing shaft C512 is provided. The intermediate moving chassis 511 is supported by the side chassis A521a and the side chassis B521b via linear guides 515a and 515b that can move only in the conveying direction of the intermediate transfer belt 11 at both ends. Since the side chassis A521a and the side chassis B521b are fixed to the chassis (not shown) of the image forming apparatus, the intermediate movement chassis 511 is movable in parallel with the conveyance direction of the intermediate transfer belt 11.

  The side chassis A521a and the side chassis B521b are provided with second photosensitive drum shift linear actuators 525a and 525b capable of driving the process unit chassis 508 in the actuator driving direction 532, respectively. As the linear actuator, a laminated type piezoelectric actuator, a voice coil type linear actuator, or the like is suitable.

  Compression springs 522a (not shown) and 522b for urging the process unit chassis 508 toward the linear actuator are provided at portions of the side chassis A521a and the side chassis B521b facing the linear actuator. Displacement sensors 524a and 524b for measuring the displacement of the displacement measurement surfaces 523a and 523b of the process unit chassis 508 are provided above the side chassis A521a and the side chassis B521b.

  On the other hand, the first image position information reading units 72a and 72b and the second image position information reading units 52a and 52b are supported by support members 526a and 526b fixed to the side chassis A521a and the side chassis B521b, respectively. The first image position information reading units 72a and 72b read the first image position information B200a and 200b on the intermediate transfer belt 11. The second image position information reading units 52 a and 52 b read the second image position information 202 a and 202 b on the second photosensitive drum 22.

  By configuring the shift mechanism for shifting the second photosensitive drum 22 as described above, both ends of the process unit 500 including the second photosensitive drum 22 can be independently moved in the intermediate transfer belt conveyance direction. Accordingly, not only can the second photosensitive drum 22 be translated in the transport direction of the intermediate transfer belt 11, but also the angle can be changed within a plane parallel to the intermediate transfer belt 11.

  Further, displacement sensors 524a and 524b are provided at both ends of the process unit 500, and outputs thereof are fed back to the linear actuators 525a and 525b. Thereby, highly accurate position control of the process unit 500 can be performed.

  In the present embodiment, the first image position information reading units 72 a and 72 b and the second image position information reading units 52 a and 52 b are arranged slightly before the transfer position. You may arrange in a position.

  The intermediate transfer belt 11 to which the first color (yellow) toner image is transferred in the first primary transfer area Ta and the second color (magenta) toner image is transferred in the second primary transfer area Tb is further circulated and driven downstream. It contacts the third photosensitive drum 23 corresponding to the primary transfer region Tc. Accordingly, the toner image of the third color (cyan C) is transferred to the intermediate transfer belt 11 in the third primary transfer region Tc.

  The CPU 401 of the control unit 70 compares the third image position information on the third photosensitive drum 23 and the first image position information on the intermediate transfer belt 11 created in the same manner as the above process, and the third image position information on the intermediate transfer belt 11 is compared with the third image position information. The axial movement of the photosensitive drum 23 is controlled. As a result, image alignment is performed on the third photosensitive drum 23. Similarly, image alignment is performed for the fourth photosensitive drum 24.

  As described above, by combining the second, third, and fourth image position information with the first image information on the intermediate transfer belt 11 as a reference, it is possible to accurately match the images of all colors.

  Further, after the image position information on the first photosensitive drum 21 to the fourth photosensitive drum 24 is read in each primary transfer region, the image position information erasing unit corresponding to each of the first photosensitive drum 21 to the fourth photosensitive drum 24. It is erased at 81, 82, 83, 84 (FIG. 4). The image position information erasing units 83 and 84 are not shown. Further, the first image position information on the intermediate transfer belt 11 is erased by the first image position information erasing unit B85 (FIG. 4) after passing through the final fourth primary transfer region Td.

  In this embodiment, the image position information 201 and 202 on the first photosensitive drum 21 and the second photosensitive drum 22 are transferred to an information recording medium such as a magnetic material by the first recording unit 41 and the second recording unit 42, respectively. The case of writing is given as an example, but the present invention is not limited to this. As described with reference to FIG. 9, the first exposure unit 31 and the second exposure unit 32 may be used to write image position information outside the image area on the photosensitive drum surface simultaneously with image drawing.

  Further, for example, a method of writing image position information as shown in FIG. 20 may be used (in FIG. 20, the second photosensitive drum 22 and the second exposure unit 32 are illustrated). That is, the scale 272 is attached (or engraved) in advance so as to rotate integrally with the second photosensitive drum 22 (or the intermediate transfer belt 11). Using the scale 272, the position information of the second photosensitive drum 22 (or the intermediate transfer belt 11) can be acquired and determined.

  The image position information on the second photosensitive drum 22 created from the raster scanning timing signal by the exposure scanning timing generator is stored in correspondence with the address of the scale 272 of the second photosensitive drum 22 (or the intermediate transfer belt 11). This may be an alternative to the method of writing image position information simultaneously with image formation using a magnetic material or laser.

  Next, based on the relationship between the resolution in the main scanning direction and the number of pixels in the main scanning direction, the pixel conversion main scanning magnification obtained by converting the length change amount Δl of the electrostatic latent image on the second photosensitive drum 22 into the number of pixels. The error will be described with reference to FIGS.

  First, image alignment when the axis of the second photosensitive drum 22 is shifted will be described.

  When the control of shifting the axis of the second photosensitive drum 22 is performed, the image writing due to the irradiation of the laser beam on the second photosensitive drum 22 by the second exposure unit 32 is affected. That is, in the main scanning direction, since the distance between the second photosensitive drum 22 and the second exposure unit 32 changes, the optical path length changes and appears as an expansion and contraction of the image in the main scanning direction. In the sub-scanning direction, the exposure position of the laser light emitted from the second exposure unit 32 that intersects the circumference of the second photosensitive drum 22 changes, so that it appears as an expansion and contraction of the image in the sub-scanning direction.

  FIG. 21A is a diagram illustrating a configuration of the second photosensitive drum viewed from the axial direction, and FIG. 21B is a diagram illustrating a configuration in which a part of FIG. 21A is enlarged.

  In FIG. 21A and FIG. 21B, first, the influence that occurs in the sub-scanning direction will be described. The incident angle of the laser light applied to the second photosensitive drum 22 from the second exposure unit 32 (FIG. 1) is γ, the line connecting the exposure position and the center of the second photosensitive drum 22 and the vertical line of the second photosensitive drum 22. Let Φ be the angle between Also, assuming that the center of the second photosensitive drum 22 before the shift is the origin, the horizontal direction is the y axis, the vertical direction is the z axis, and the radius of the second photosensitive drum 22 is r, the second photosensitive drum before the shift is performed. The circumference DR1 of 22 can be expressed by the following equation.

y ² + z ² = r ² [1]
Further, if the shift amount of the second photosensitive drum 22 is a, the circumference DR2 of the shifted second photosensitive drum 22 can be expressed by the following equation.

(Ya) ² + z ² = r ² (2)
The y-coordinate and z-coordinate of the exposure position A before shifting can be expressed by the following equations, respectively.

y _A = r × cos (Φ−π / 2) [3]
z _A = r × cos (Φ−π / 2) [4]
On the other hand, a line connecting the exposure position and the center of the second photosensitive drum 22 can be expressed by the following equation.

z = tan (Φ−π / 2) × y (5)
Further, the z coordinate of the laser light irradiated from the second exposure unit 32 to the second photosensitive drum 22 can be expressed by the following equation.

z = −tan (3π / 2−Φ−γ) × y + b (6)
However, b = r × (sinΘ ₁ + cosΘ ₁ × tanΘ ₂ ), Θ ₁ = Φ−π / 2, Θ ₂ = 3π / 2−Φ−γ
Accordingly, the y coordinate and the z coordinate of the exposure position B of the laser beam irradiated to the second photosensitive drum 22 shifted from the second exposure unit 32 by a from the equations [2] and [6] are expressed by the following equations, respectively. Can do.

また、aだけシフトした第２感光ドラム２２上における本来の露光位置Ｃのｙ座標、ｚ座標はそれぞれ下式で表すことができる。

Further, the y-coordinate and z-coordinate of the original exposure position C on the second photosensitive drum 22 shifted by a can be expressed by the following equations, respectively.

y _C = formula [3] + a
= r × cos (Φ−π / 2) + a (9)
z _C = Formula [4]
= r × cos (Φ−π / 2) ・ ・ ・ [10]
Therefore, the exposure position deviation amount when the second photosensitive drum 22 is shifted by a can be expressed by the following equation.

Δy = y _B −y _C [11]
Δz = z _B −z _C (12)
A displacement amount J on the circumference of the writing position when the second photosensitive drum 22 is shifted by a (FIG. 21B) is obtained. Now, if the angle formed by the point B ′ moved from the point B to the circle of DR1 is Φ ′, it can be expressed by the following equation.

変位量Jは下式で表すことができる。

The displacement amount J can be expressed by the following equation.

J = (2r × π) × ((Φ′−Φ) / 360) [14]
Accordingly, the electrostatic latent image deviation amount ΔJ on the drum circumference when the second photosensitive drum 22 is shifted by a can be expressed by the following equation.

ΔJ = a−J
= A − ((2r × π) × ((Φ′−Φ) / 360)) [15]
However, since the change in the electrostatic latent image in the sub-scanning direction is also recorded in the image position information, the second image on the second photosensitive drum 22 affected by this influence also reaches the second primary transfer region Tb. Image alignment can be performed accurately.

  Next, the influence that occurs in the main scanning direction will be described.

  FIG. 22 is a diagram illustrating a configuration of the second photosensitive drum as viewed from a direction orthogonal to the laser beam (in the direction of arrow G in FIG. 21A).

In FIG. 22, the length of the second photosensitive drum 22 is now L, and the length of the image formed on the second photosensitive drum 22 is l. Further, the scanning angle from the writing side of the laser beam irradiated to the second photosensitive drum 22 from the second exposure unit 32 to the image center is θ ₁ , and the scanning angle from the image center to the end of scanning is θ ₂ . Further, in order to align the positions of the first image and the second image on the intermediate transfer belt 11, the axis of the second photosensitive drum 22 is shifted by aL on the writing side and aR on the scanning end side.

  At this time, the second photosensitive drum 22 is inclined by an angle θ, and the angle θ can be expressed by the following equation.

θ = tan ⁻¹ ((aR−aL) / (l + ((L−l) / 2)) [16]
Therefore, if the intersection of the line passing through the left end of the second photosensitive drum 22 and the center of the second photosensitive drum 22 before the shift is the origin, the main scanning direction is the x-axis, and the sub-scanning direction is the y-axis, the shifted second The center line of the axis of the photosensitive drum 22 can be expressed by the following equation.

y = tan θ × x + (aR−aL) [17]
Further, the laser beam irradiated from the second exposure unit 32 to the second photosensitive drum 22 can be expressed by the following expression with respect to the y coordinate of the writing position.

y = −tan (π / 2−θ ₁ ) × x + b ₁ ... [18]
Where b ₁ = y _A + ((L−1) / 2) × tan (π / 2−θ ₁ )
The y coordinate of the scanning end position can be expressed by the following equation.

y = tan (π / 2−θ ₂ ) × x + b ₂ [19]
Where b ₂ = y _A − ((L + 1) / 2) × tan (π / 2−θ ₂ )
On the other hand, the y coordinate of the laser beam irradiated onto the second photosensitive drum 22 before being shifted from the second exposure unit 32 can be expressed by the following equation.

y = y _A ... [20]
That is, the scanning line of the electrostatic latent image drawn on the second photosensitive drum 22 is expressed by the equation [20].

On the other hand, the laser beam irradiated onto the second photosensitive drum 22 whose axis is inclined by shifting by aL on the writing side and aR on the scanning end side has the inclination tanθ, and the point γ (−y _A × sinθ, If it is a straight line passing through y _A × cos θ + aL), the y coordinate can be expressed by the following equation.

y = tan θ × x + c [21]
However, c = y _A × cos θ + aL + y _A × sin θ × tan θ
That is, the scanning line of the electrostatic latent image drawn on the second photosensitive drum 22 whose axis is shifted is expressed by the equation [21].

  Therefore, the x-coordinate and the y-coordinate of the scanning start deviation B1 after the shift of the second photosensitive drum 22 at the image end on the laser light writing side with respect to the second photosensitive drum 22 and the scanning end deviation B2 of the image end on the scanning end side. Can be represented by the following formulas.

x _B1 = (b ₁ −c) / (tan θ + tan (π / 2−θ ₁ )) [22]
x _B2 = (b ₂ −c) / (tan θ−tan (π / 2−θ ₂ )) [23]
Equations [22] and [23] are substituted into equations [18] and [19], respectively, and the y-coordinates of B1 and B2 can be expressed by the following equations, respectively.

y _B1 = −tan (π / 2−θ ₁ ) × ((b ₁ −c) / (tan θ + tan (π / 2−θ ₁ ))) + b ₁ ... [24]
y _B2 = tan (π / 2−θ ₂ ) × ((b ₂ −c) / (tan θ−tan (π / 2−θ ₂ ))) + b ₂ ... [25]
Therefore, the length l ′ of the electrostatic latent image drawn on the shifted second photosensitive drum 22 can be expressed by the following equation.

シフトする前の第２感光ドラム２２上に描かれる静電潜像の長さｌに対して、下式で表すΔｌだけ長さが変化する。

The length changes by Δl expressed by the following equation with respect to the length l of the electrostatic latent image drawn on the second photosensitive drum 22 before the shift.

即ち、主走査方向の倍率誤差が発生することになる。

That is, a magnification error in the main scanning direction occurs.

  Although the change amount Δl obtained by the equation [27] is slight, it is desirable to correct the change amount Δl in order to improve the image quality of the image forming apparatus. That is, the count value sent from the second image position information reading unit 52 is compared with the count value sent from the first image position information reading unit 72 on the intermediate transfer belt 11. When the axis of the second photosensitive drum 22 is shifted so that the difference between the count values becomes zero, the electrostatic latent image drawn on the second photosensitive drum 22 shifted in accordance with the value obtained from Equation [27]. Adjust the length. Thus, it is effective to control so that Δl≈0.

  As a method for adjusting the length of the electrostatic latent image formed on the second photosensitive drum 22, an image forming signal output to the laser drive control unit 321 for each scanning of the laser beam on the surface to be scanned of the second photosensitive drum 22. There is a method of changing the clock frequency. As shown in FIG. 25, let us consider a case where one pixel information is communicated by a clock having a period of, for example, 16 divisions. When the axis of the second photosensitive drum 22 is not shifted, that is, when the second photosensitive drum 22 is at the reference position, the clock cycle is T, and the length of the electrostatic latent image on the second photosensitive drum 22 is l.

  On the other hand, when the axis of the second photosensitive drum 22 is shifted by aL on the writing side and aR on the scanning end side, the length of the electrostatic latent image is l '. Accordingly, by adjusting the clock cycle T ′ so that the length of the electrostatic latent image changes by the amount of change Δl that is the difference between l ′ and l, control is performed so that Δl≈0.

  Based on the relationship between the resolution in the main scanning direction and the number of pixels in the main scanning direction, the pixel conversion main scanning magnification error E obtained by converting the length change amount Δl of the electrostatic latent image into the number of pixels can be expressed by the following equation. .

E = (25.4 [mm] / P) ÷ Δl [mm] ・ ・ ・ [28]
Where P is the main scanning output resolution [dpi]
Therefore, if the image forming range is Q [inch], the clock cycle T ′ to be corrected according to the change amount Δl can be expressed by the following equation.

T ′ = T × ((P + E) ÷ P) [29]
FIG. 23 is a block diagram illustrating a configuration of the correction unit 323 included in the first exposure unit 31 to the fourth exposure unit 34 of the image forming apparatus.

  In FIG. 23, the correction unit 323 (control unit, generation unit) includes a CPU 3231, a clock selection unit 3232, a plurality of clock generation units 3233, and an image data output unit 3234. The function of each part will be described with reference to the flowchart of FIG.

  FIG. 24 is a flowchart showing a color misregistration correction sequence.

  In FIG. 24, this processing is executed by the CPU 3231 of the correction unit 323. When the shaft shift amount (aL, aR) of the second photosensitive drum 22 is input from the input unit 324 of the second exposure unit 32 (step S2401), the CPU 3231 executes the following processing based on the program stored in the ROM 202. To do. First, the CPU 3231 calculates the length change amount Δl of the electrostatic latent image from the above equation [27] (step S2402). Next, the CPU 3231 determines whether or not the length change amount Δl of the electrostatic latent image is 0 (step S2403).

  If the length change amount Δl of the electrostatic latent image is not 0, the CPU 3231 calculates a pixel-converted main scanning magnification error E converted from the length change amount Δl of the electrostatic latent image, and sends the pixel to the clock selection unit 3232. A converted main scanning magnification error E is given (step S2404). If the length change amount Δl of the electrostatic latent image is 0, no main scanning magnification error occurs, so the pixel-converted main scanning magnification error E is 0, and the clock cycle remains the reference clock cycle (step S2407). ).

  The clock selection unit 3232 selects a clock cycle corresponding to the image data output unit 3234 from a plurality of clock generation units 3233 that generate a plurality of different clock cycles (step S2405). The plurality of clock generators 3233 have clocks CLK1, CLK2, CLK3, CLK5, CLK6, which have image widths of +3 pixels, +2 pixels, +1 pixel, −1 pixel, −2 pixels, and −3 pixels, with CLK4 as a reference clock. Seven data clocks of CLK7 are generated.

  The multiple clock generation units 3233 determine the clock cycle Tn (step S2406). That is, each clock cycle T1, T2, T3, T5, T6, and T7 can be expressed by the following equations, where each clock cycle in the reference clock CLK4 is T4.

T1 = T4 × 9603/9600 [30]
T2 = T4 × 9602/9600 [31]
T3 = T4 × 9601/9600 (32)
T5 = T4 × 9599/9600 [33]
T6 = T4 × 9598/9600 [34]
T7 = T4 × 9597/9600 (35)
The image data output unit 3234 outputs the BD mask signal 301 corrected to the selected clock cycle Tn to the laser drive control unit 321, and changes the clock cycle according to the change amount Δl of the length of the electrostatic latent image. In step S2408, the main scanning magnification error is corrected.

  For example, as shown in FIG. 25, it is assumed that by shifting the second photosensitive drum 22, the length l ′ of the electrostatic latent image is longer by Δl = 21.2 μm than the length l when the electrostatic latent image is not shifted. If the output resolution in the main scanning direction of the image forming apparatus is 1200 dpi and the image width is 8 inches, the main scanning direction is 9600 pixels. The pixel-converted main scanning magnification error E is obtained as E≈1 from the equation [28].

  Therefore, the clock selection unit 3232 can correct the main scanning magnification error by selecting CLK3 and supplying it to the image data output unit 3234. When the optical path length is changed by changing the distance between the second photosensitive drum 22 and the second exposure unit 32 in the main scanning direction, image defects due to expansion / contraction of the image in the main scanning direction are transferred from the photosensitive drum to the intermediate transfer belt 11. It can be corrected in advance before transferring the image on top.

  In this embodiment, the transfer image misalignment correction related to the second photosensitive drum 22 is taken as an example, but the present invention is not limited to this. For the third photosensitive drum 23 and the fourth photosensitive drum 24, the effect caused by shifting the third photosensitive drum 23 and the fourth photosensitive drum 24 is corrected by adjusting the length of the electrostatic latent image in the same process. can do.

  As described above, according to the present embodiment, in a tandem type image forming apparatus that includes a plurality of image forming units and sequentially transfers images of different colors onto an intermediate transfer belt, transfer image misalignment (transfer of each color) It is possible to correct a color shift (image shift) with high accuracy. As a result, the amount of shift of the transferred image can be reduced (reduced), so that a good image quality can be realized.

[Second Embodiment]
The second embodiment of the present invention is different from the first embodiment in the points described below. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1 to 3), description thereof is omitted.

  In the first embodiment, the control for adjusting (changing) the length of the electrostatic latent image in the main scanning direction by changing the clock frequency of the image forming signal has been described.

  On the other hand, in the present embodiment, control for adjusting (changing) the length of the electrostatic latent image in the main scanning direction by changing the total number of clocks of the image forming signal will be described. A method for adjusting the length of the electrostatic latent image will be described with reference to FIG.

  FIG. 26 is a diagram illustrating a method for adjusting the length of the electrostatic latent image when the second photosensitive drum of the image forming apparatus according to the present embodiment is moved (shifted).

  In FIG. 26, when the length 1 'of the electrostatic latent image is shorter than the length l when the second photosensitive drum 22 is not shifted, the following adjustment is performed. The length of the electrostatic latent image is adjusted to 1 by inserting a clock into the clock train of the image forming signal at a certain pixel position. On the other hand, when the length 1 'of the electrostatic latent image is longer than the length 1 when the second photosensitive drum 22 is not shifted, the following adjustment is performed. The length of the electrostatic latent image is adjusted to 1 by removing (deleting) the clock from the clock train of the image forming signal at a certain pixel position.

  In this embodiment, the clock of the image forming signal is inserted and removed in this way. That is, the total number of clocks of the image forming signal is changed. Thereby, when the optical path length changes due to the change in the distance between the second photosensitive drum 22 and the second exposure unit 32 in the main scanning direction, it is possible to suppress image defects due to the expansion and contraction of the image in the main scanning direction. .

  As described above, according to the present embodiment, it is possible to correct the transfer image shift with high accuracy in the tandem type image forming apparatus. As a result, the amount of shift of the transferred image can be reduced (reduced), so that a good image quality can be realized.

[Third Embodiment]
The third embodiment of the present invention differs from the first embodiment in the points described below. Since the other elements of the present embodiment are the same as the corresponding ones of the first embodiment (FIGS. 1 to 3), description thereof is omitted.

  In the first and second embodiments, the length of the electrostatic latent image in the main scanning direction is adjusted (changed) as follows. The total length of the electrostatic latent image in the scanning range of the laser beam on the surface to be scanned of the photosensitive drum was adjusted by changing the clock frequency of the image forming signal or the total number of clocks. As a result, the total length of the electrostatic latent image in the scanning range could be corrected to l. However, the length l ′ of the electrostatic latent image that is changed by shifting the second photosensitive drum 22 is longer than the length l in the case where the electrostatic exposure image is not shifted within the scanning range by the second exposure unit 32. There are cases where there are mixed sections and shorter sections.

  For example, as shown in FIG. 27, the second photosensitive drum 22 is brought closer to the second exposure unit 32 by a distance aL1 on the left end side in the image writing area р and away from the second exposure unit 32 by a distance aR1 on the right end side. When shifted, it becomes as follows. In the l′ L region on the left side, the electrostatic latent image line tilted by the shift of the second photosensitive drum 22 intersects the electrostatic latent image line horizontal to the bus line of the second photosensitive drum 22 before the shift. The image is relatively short, and the image is relatively long in the right l′ R region.

  In contrast, in the present embodiment, when adjusting (changing) the length of the electrostatic latent image of the second photosensitive drum 22 in the main scanning direction, the scanning range of the laser beam with respect to the second photosensitive drum 22 is divided into a plurality of parts. More accurate correction is performed by changing the correction value for each section. For example, the electrostatic latent image line inclined by shifting the second photosensitive drum 22 according to the shift amount of the second photosensitive drum 22 is horizontal to the bus line of the second photosensitive drum 22 before the shift. Find the point that intersects the line.

  Further, the length of the electrostatic latent image changed by shifting the second photosensitive drum 22 for each of the left and right sections from that point is set to the length when the shift is not performed. to correct. As a result, image expansion and contraction in one raster scan of the electrostatic latent image that can be caused by shifting the second photosensitive drum 22 can be reduced, and image quality can be improved.

  In the above-described method, when changing the length of the electrostatic latent image in the main scanning direction, the correction value is changed for each section, so that the electrostatic latent image is not shifted according to the shift amount of the second photosensitive drum 22. The positional relationship with the raster is obtained, and the optimum section division is performed and correction is performed each time. It is of course effective to gradually change the divided sections in accordance with the shift amount as described above, but a method as shown in FIG. 27 may be adopted to simplify the control.

  The image writing area р is divided into an image writing area рL from the writing side of the laser beam irradiated to the second photosensitive drum 22 from the second exposure unit 32 to the image center, and an image writing area рR from the image center to the end of scanning. Divide into two areas. In other words, it is also effective to adopt a method in which sections to be divided in advance are fixed and the length of the electrostatic latent image in the main scanning direction is adjusted for each section. In addition, the image quality can be improved by increasing the number of divisions of the image writing area р more than two divisions (three divisions, four divisions, etc.), but in a form according to the required performance of the image forming apparatus. The system can be designed.

  As described above, according to the present embodiment, it is possible to correct the transfer image shift with high accuracy in the tandem type image forming apparatus. As a result, the amount of shift of the transferred image can be reduced (reduced), so that a good image quality can be realized.

[Other embodiments]
In each of the above embodiments, the first image position information D201 and the second image position information D202 are recorded on the first photosensitive drum 21 and the second photosensitive drum 22 respectively, and the first image transferred onto the intermediate transfer belt 11 is recorded. The position information was compared with the second image position information. Further, the transfer image shift is corrected by aligning the positions of the first image and the second image by shifting the axis of the second photosensitive drum 22 so that the difference becomes zero. Is not to be done.

  As another method for correcting the positional deviation of the image by shifting the photosensitive drum, the following method can be considered. The rotation of the intermediate transfer belt and the photosensitive drum is controlled at an equal angular speed, and each photosensitive drum is shifted in accordance with the variation in the arrival time corresponding to each image forming unit due to the variation in the speed of the intermediate transfer belt. This is a method of correcting misalignment.

  Further, the intermediate transfer belt may be displaced in the main scanning direction at the transfer position corresponding to each image forming unit due to meandering or the like. In order to further improve the image quality, it can be considered to control the intermediate transfer belt 11 to reduce color misregistration in the main scanning direction due to the influence of meandering by shifting the photosensitive drum in the main scanning direction. In this case, the shift amount of the photosensitive drum in the main scanning direction is sent from the input unit 324 of the exposure unit to the correction unit 323, and the data writing timing change (advance / delay) is adjusted in accordance with the shift of the photosensitive drum in the sub-scanning direction. To do. As a result, color misregistration in both the main scanning direction and the sub-scanning direction can be prevented, and image quality can be further improved.

  In each of the above embodiments, the image forming apparatus using the intermediate transfer belt has been described as an example, but the present invention is not limited to this. The present invention is a system in which images of different colors are sequentially transferred from each photosensitive drum directly to a recording medium held by a conveying belt that conveys the recording medium to a transfer position corresponding to each photosensitive drum without using an intermediate transfer belt. It is also effective for an image forming apparatus.

  In each of the above embodiments, the case where the image forming apparatus is a copying machine has been described as an example. However, the present invention is not limited to this and can be applied to a printer.

  In each of the above embodiments, specific examples have been described in order to understand various concepts such as the superordinate concept, intermediate concept, and subordinate concept of the present invention. However, the technical scope of the present invention depends on each of the above embodiments. It is not limited. Of course, other embodiments than the above-described embodiments may be used as long as they embody the gist of the present invention, and various combinations of the above-described embodiments are possible. It is possible to design a system with a combination that takes into consideration the performance and price of the image forming apparatus.

1 is a configuration diagram showing an overall schematic configuration of an image forming apparatus according to a first embodiment of the present invention. 2 is a block diagram illustrating a configuration of a control system of an image forming unit of the image forming apparatus. FIG. It is a block diagram which shows the typical structure of the 1st exposure part-4th exposure part of an image forming apparatus. 2 is a diagram illustrating a configuration of an intermediate transfer belt, first and second image forming units, and a control system of the image forming apparatus. FIG. It is a figure which shows the positional relationship of the 1st image at the time of expand | deploying a 1st photosensitive drum, and 1st image position information. FIG. 6 is a diagram for explaining transcription of first image position information on an intermediate transfer belt. FIG. 6 is a diagram illustrating a relationship between a first image transferred to an intermediate transfer belt and first image position information transferred to the intermediate transfer belt. It is a figure which shows the positional relationship of the 2nd image at the time of expand | deploying a 2nd photosensitive drum, and 2nd image position information. It is a flowchart which shows the control process for aligning a 1st image and a 2nd image. It is a flowchart which shows the control process for aligning a 1st image and a 2nd image. It is a flowchart which shows the whole control process which consists of tasks 1-5 (recording of the 1st and 2nd image position information with respect to a 1st and 2nd photosensitive drum, 2nd photosensitive drum control). 3 is a flowchart showing a task 1; 10 is a flowchart showing a task 2. 10 is a flowchart showing a task 3. 10 is a flowchart showing a task 4. 10 is a flowchart showing a task 5. It is a figure explaining the shift method of the axis | shaft of a 2nd photosensitive drum. It is sectional drawing which shows the structure of the shift mechanism of a 2nd photosensitive drum. FIG. 4 is a diagram illustrating a configuration of a shift mechanism of a second photosensitive drum as viewed from an upstream direction of an intermediate transfer belt. It is a figure which shows the structure which looked at the shift mechanism of the 2nd photosensitive drum from upper direction. It is a figure which shows a structure at the time of attaching the 2nd photosensitive drum angle scale to the 2nd photosensitive drum. (A) is a figure which shows the structure which looked at the 2nd photosensitive drum from the axial direction, (b) is a figure which shows the structure which expanded a part of (a). It is a figure which shows the structure which looked at the 2nd photosensitive drum from the direction orthogonal to a laser beam. It is a block diagram which shows the structure of the correction | amendment part with which the 1st exposure part-the 4th exposure part of an image forming apparatus are provided. 6 is a flowchart illustrating a color misregistration correction sequence. It is a figure explaining the adjustment method of the length of an electrostatic latent image when a 2nd photosensitive drum is moved. It is a figure explaining the adjustment method of the length of an electrostatic latent image when the 2nd photosensitive drum of the image forming apparatus which concerns on the 2nd Embodiment of this invention is moved. It is a figure explaining the adjustment method of the length of an electrostatic latent image when the 2nd photosensitive drum of the image forming apparatus which concerns on the 3rd Embodiment of this invention is moved.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Intermediate transfer belt 21-24 Photosensitive drum 31-34 Exposure part 321 Laser drive control part 322 Image signal generation part 401 CPU

Claims (14)

A rotating first image carrier;
First electrostatic image forming means for forming an electrostatic image on the first image carrier;
First developing means for developing an electrostatic image formed on the first image carrier with toner to form a first color toner image;
A first transfer unit that transfers the first color toner image on the first image carrier to a moving carrier;
A rotating second image carrier;
Second electrostatic image forming means for forming an electrostatic image on the second image carrier;
Second developing means for developing the electrostatic image formed on the second image carrier with toner to form a second color toner image;
A second transfer unit that transfers the second color toner image on the second image carrier over the first color toner image transferred to the transport body;
In an image forming apparatus comprising:
A transport body position for detecting a transport body position index corresponding to a position of the transport body in the moving direction of the first color toner image on the transport body on the upstream side of the transport direction of the transport body relative to the second transfer unit; Index detection means;
A second image carrier position index corresponding to a position in the rotation direction of the second color toner image on the second image carrier is detected at a position between the second developing unit and the second transfer unit. Two-image carrier position index detection means;
Adjusting means for adjusting the position of the second image carrier;
Based on the detection results of the conveyance body position index detection means and the second image carrier position index detection means, the adjusting means is controlled to control the first color toner image and the second image on the conveyance body. The second electrostatic image forming unit is controlled based on the control of the adjusting unit to reduce the amount of positional deviation of the color toner image in the moving direction of the conveying member, and the second image bearing member Control means for changing the longitudinal size of the second image carrier of the electrostatic image to be formed;
An image forming apparatus comprising: A rotating first image carrier;
First electrostatic image forming means for forming an electrostatic image on the first image carrier;
First developing means for developing an electrostatic image formed on the first image carrier with toner to form a first color toner image;
A first transfer unit that transfers the first color toner image on the first image carrier to a recording material carried on a carrier;
A rotating second image carrier;
Second electrostatic image forming means for forming an electrostatic image on the second image carrier;
Second developing means for developing the electrostatic image formed on the second image carrier with toner to form a second color toner image;
A second transfer unit that transfers the second color toner image on the second image carrier in an overlapping manner with the first color toner image transferred to the recording material;
In an image forming apparatus comprising:
A transport body position for detecting a transport body position index corresponding to a position of the transport body in the moving direction of the first color toner image on the transport body on the upstream side of the transport direction of the transport body relative to the second transfer unit; Index detection means;
A second image carrier position index corresponding to a position in the rotation direction of the second color toner image on the second image carrier is detected at a position between the second developing unit and the second transfer unit. Two-image carrier position index detection means;
Adjusting means for adjusting the position of the second image carrier;
Based on the detection results of the conveyance body position index detection means and the second image carrier position index detection means, the adjustment means is controlled so that the first color toner image and the second color on the recording material are controlled. The second electrostatic image forming unit is controlled based on the control of the adjusting unit to reduce the amount of positional deviation of the color toner image in the moving direction of the conveying member, and the second image bearing member Control means for changing the longitudinal size of the second image carrier of the electrostatic image to be formed;
An image forming apparatus comprising: A rotating image carrier;
Electrostatic image forming means for forming an electrostatic image on the image carrier;
A developing unit capable of developing the electrostatic image formed on the image carrier with a first color toner and a second color toner to form first and second color toner images;
Transfer means for sequentially transferring the first color toner image and the second color toner image sequentially formed on the image carrier onto the moving carrier;
In an image forming apparatus comprising:
Conveyance body position index detection for detecting a conveyance body position index corresponding to a position of the first color toner image in the conveyance body in the movement direction of the conveyance body on the upstream side of the transfer unit in the movement direction of the conveyance body. Means,
An image carrier position index detection unit that detects an image carrier position index corresponding to a position of the image carrier in the rotation direction of the second color toner image at a position between the developing unit and the transfer unit;
Adjusting means for adjusting the position of the image carrier;
The first color toner image and the second color toner image on the recording material are controlled by controlling the adjustment unit based on the detection results of the conveyance body position index detection unit and the image carrier position index detection unit. Of the electrostatic image formed on the image carrier by controlling the electrostatic image forming unit based on the control of the adjusting unit. Control means for changing the longitudinal size of the image carrier;
An image forming apparatus comprising: The first electrostatic image forming unit and the second electrostatic image forming unit are respectively provided with a light emission control unit that controls light emission of laser light based on an image formation signal and an image formation signal that is output to the light emission control unit. Generating means for generating,
The control means includes scanning lines of electrostatic latent images that scan the first image carrier and the second image carrier by the first electrostatic image forming means and the second electrostatic image forming means, respectively. The length is adjusted by changing the clock frequency of the image forming signal output from the generation unit to the light emission control unit for each scan of the laser beam for the first image carrier and the second image carrier, respectively. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The electrostatic image forming unit includes: a light emission control unit that controls emission of laser light based on an image formation signal; and a generation unit that generates an image formation signal to be output to the light emission control unit,
The control means controls the light emission control of the scanning line length of the electrostatic latent image scanned on the image carrier by the electrostatic image forming means from the generation means for each scan of the laser beam on the image carrier. 4. The image forming apparatus according to claim 3, wherein adjustment is performed by changing a clock frequency of an image forming signal output to the means. The first electrostatic image forming unit and the second electrostatic image forming unit are respectively provided with a light emission control unit that controls light emission of laser light based on an image formation signal and an image formation signal that is output to the light emission control unit. Generating means for generating,
The control means includes scanning lines of electrostatic latent images that scan the first image carrier and the second image carrier by the first electrostatic image forming means and the second electrostatic image forming means, respectively. The length is adjusted by changing the total number of clocks of the image forming signal output from the generating unit to the light emission control unit for each scanning of the laser beam for the first image carrier and the second image carrier, respectively. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. The electrostatic image forming unit includes: a light emission control unit that controls emission of laser light based on an image formation signal; and a generation unit that generates an image formation signal to be output to the light emission control unit,
The control means controls the light emission control of the scanning line length of the electrostatic latent image scanned on the image carrier by the electrostatic image forming means from the generation means for each scan of the laser beam on the image carrier. 4. The image forming apparatus according to claim 3, wherein the adjustment is made by changing the total number of clocks of the image forming signal output to the means.   The control means includes scanning lines of electrostatic latent images that scan the first image carrier and the second image carrier by the first electrostatic image forming means and the second electrostatic image forming means, respectively. 3. The image forming apparatus according to claim 1, wherein the length is adjusted for each section obtained by dividing the scanning range of the laser beam for the first image carrier and the second image carrier into a plurality of sections.   The control unit adjusts the length of the scanning line of the electrostatic latent image scanned on the image carrier by the electrostatic image forming unit for each section obtained by dividing the scanning range of the laser beam on the image carrier into a plurality of sections. The image forming apparatus according to claim 3.   The transfer body includes an intermediate transfer belt for transferring an image formed on the first image carrier and the second image carrier, and transferring the transferred image to a recording medium. 3. The image forming apparatus according to claim 1, further comprising: an image carrier and a conveyance belt that conveys the image carrier to a transfer position corresponding to the second image carrier.   The conveyance body is an intermediate transfer belt for transferring an image formed on the image carrier and transferring the transferred image to a recording medium, and a conveyance belt for conveying the recording medium to a transfer position corresponding to the image carrier. 4. The image forming apparatus according to claim 3, further comprising: A rotating first image carrier;
First electrostatic image forming means for forming an electrostatic image on the first image carrier;
First developing means for developing an electrostatic image formed on the first image carrier with toner to form a first color toner image;
A first transfer unit that transfers the first color toner image on the first image carrier to a moving carrier;
A rotating second image carrier;
Second electrostatic image forming means for forming an electrostatic image on the second image carrier;
Second developing means for developing the electrostatic image formed on the second image carrier with toner to form a second color toner image;
A second transfer unit that transfers the second color toner image on the second image carrier over the first color toner image transferred to the transport body;
In a method for controlling an image forming apparatus comprising:
A transport body position for detecting a transport body position index corresponding to a position of the transport body in the moving direction of the first color toner image on the transport body on the upstream side of the transport direction of the transport body relative to the second transfer unit; An indicator detection step;
A second image carrier position index corresponding to a position in the rotation direction of the second color toner image on the second image carrier is detected at a position between the second developing unit and the second transfer unit. A two-image carrier position index detection step;
An adjustment step of adjusting the position of the second image carrier;
Based on the detection results of the conveyance body position index detection step and the second image carrier position index detection step, the adjustment step is controlled so that the first color toner image and the second color on the conveyance body are controlled. The amount of displacement of the color toner image in the moving direction of the transport body is reduced, and the second electrostatic image forming unit is controlled based on the control of the adjustment step, so that the second image carrier A control step of changing the size of the electrostatic image to be formed in the longitudinal direction of the second image carrier;
A control method comprising: A rotating first image carrier;
First electrostatic image forming means for forming an electrostatic image on the first image carrier;
First developing means for developing an electrostatic image formed on the first image carrier with toner to form a first color toner image;
A first transfer unit that transfers the first color toner image on the first image carrier to a recording material carried on a carrier;
A rotating second image carrier;
Second electrostatic image forming means for forming an electrostatic image on the second image carrier;
Second developing means for developing the electrostatic image formed on the second image carrier with toner to form a second color toner image;
A second transfer unit that transfers the second color toner image on the second image carrier in an overlapping manner with the first color toner image transferred to the recording material;
In a method for controlling an image forming apparatus comprising:
A transport body position for detecting a transport body position index corresponding to a position of the transport body in the moving direction of the first color toner image on the transport body on the upstream side of the transport direction of the transport body relative to the second transfer unit; An indicator detection step;
A second image carrier position index corresponding to a position in the rotation direction of the second color toner image on the second image carrier is detected at a position between the second developing unit and the second transfer unit. A two-image carrier position index detection step;
An adjustment step of adjusting the position of the second image carrier;
The adjustment step is controlled based on the detection results of the conveyance body position index detection step and the second image carrier position index detection step, and the first color toner image and the second image on the recording material are controlled. The amount of displacement of the color toner image in the moving direction of the conveying member is reduced, and the second electrostatic image forming unit is controlled based on the control of the adjusting step, so that the second image bearing member A control step of changing the size of the electrostatic image to be formed in the longitudinal direction of the second image carrier;
A control method comprising: A rotating image carrier;
Electrostatic image forming means for forming an electrostatic image on the image carrier;
Developing means capable of developing the electrostatic image formed on the image carrier with first and second color toners to form first and second color toner images;
Transfer means for sequentially transferring the first color toner image and the second color toner image sequentially formed on the image carrier onto the moving carrier;
In a method for controlling an image forming apparatus comprising:
Conveyance body position index detection for detecting a conveyance body position index corresponding to a position of the first color toner image in the conveyance body in the movement direction of the conveyance body on the upstream side of the transfer unit in the movement direction of the conveyance body. Steps,
An image carrier position index detection step of detecting an image carrier position index corresponding to a position in the rotation direction of the second color toner image on the image carrier at a position between the developing unit and the transfer unit;
An adjustment step of adjusting the position of the image carrier;
Based on the detection results of the conveyance body position index detection step and the image carrier position index detection step, the adjustment step is controlled so that the first color toner image and the second color toner image on the recording material. Of the electrostatic image formed on the image carrier by controlling the electrostatic image forming means based on the control of the adjustment step. A control step of changing the size of the image carrier in the longitudinal direction;
A control method comprising:

Images