JP2010214737A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming device capable of optically and properly correcting the subscanning positional displacement of a light beam when forming color images in a simple (inexpensive) constitution with good accuracy. <P>SOLUTION: The light beam scanning device of the color image forming apparatus is equipped with a synchronous detecting sensor 21 as the first light beam detector in the front end in the main scanning direction and a rear end sensor 22 as the second light beam detector in the rear end of the main scanning direction. The light beam entering the rear end sensor 22 is used as a reference beam for correcting the subscanning positional displacement by the detected signal of the synchronous detecting sensor 21 and the detected signal of the rear end sensor 22 and other light beams of a plurality of light beams entering the synchronous detecting sensor 21 is used for correcting the subscanning positional displacement by referring the table (schematic illustration) showing the correlation with the reference beam. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a color image forming apparatus capable of optically accurately and accurately correcting a sub-scanning position deviation of a light beam during color image formation with a simple configuration.

  Conventionally, as a well-known technique related to the correction of the sub-scanning position deviation of the light beam at the time of this type of color image formation, a general-purpose photo IC is used on the rear end side of the light beam scanning without using an expensive special photo IC It is possible to reduce the frequency of correcting the color misregistration by correcting the sub-scanning position deviation of the light beam, creating a color misregistration pattern, and detecting the color misregistration pattern with the color misalignment photosensor. And a laser beam detection method in the optical scanning device (see Patent Document 1).

  In addition, as a well-known technique related to color misregistration correction here, a stable and accurate position can be obtained at low cost by avoiding erroneous recognition of scratches, foreign matter, and surface irregularities on the transfer belt as misregistration correction patterns. A color misregistration correction method (see Patent Document 2) that enables misregistration correction.

  The correction of the sub-scanning position deviation of the light beam at the time of color image formation described above is based on the heat generated by the polygon motor in the light beam scanning apparatus provided in the (color) image forming apparatus, and various optical elements and members supporting them. Alternatively, it may be caused by thermal deformation of the surrounding housing, etc., but the technique disclosed in Patent Document 1 or Patent Document 2 can be obtained with a light beam detector provided at the rear end position or the front end position on the scanning surface. Since the sub-scanning position deviation of the light beam is corrected based on the detected (detection) signal, the quantity and quality provided for the positional deviation information as the optical system device are insufficient, and the sub-scanning position deviation There is a problem that correction cannot be performed accurately and accurately with a simple configuration.

  The present invention has been made to solve such problems, and its technical problem (objective) is to correct a sub-scanning position deviation of a light beam during color image formation with a simple (inexpensive) configuration. It is another object of the present invention to provide a color image forming apparatus that can be accurately and accurately performed.

  The present invention solves the above technical problem, and the invention according to claim 1 includes a light source device that generates a light beam, a deflection unit that deflects the light beam emitted from the light source device, and a deflection unit. And a light beam scanning device for condensing the deflected light beam on the scanning surface, and a first light beam provided parallel to the sub-scanning direction at a tip position on the scanning surface of the light beam scanning device. Correction of the sub-scanning beam position deviation based on the result of detecting the sub-scanning beam position by the detector and the second light beam detector provided in the rear end position on the scanning surface in parallel with the sub-scanning direction The light beam incident on the first light beam detector is a plurality of light beams, and the light beam incident on the second light beam detector is incident on the first light beam detector. What out of multiple light beams A color image forming apparatus that is a single light beam, and the light beam incident on the second light beam detector is detected by the detection signal of the first light beam detector and the detection of the second light beam detector. The other light beams of the plurality of light beams that are used as a reference beam for correcting the sub-scanning position deviation by the signal and incident on the first light beam detector are referred to the table showing the correlation with the reference beam. By doing so, it is used for correcting the sub-scanning position deviation.

  According to a second aspect of the present invention, in the color image forming apparatus, the light beam not incident on the first light beam detector corrects the sub-scanning position deviation by referring to a table showing a correlation with the reference beam. It is used for performing.

  According to a third aspect of the present invention, in the color image forming apparatus, the other light beams of the plurality of light beams incident on the first light beam detector include a black light beam for black exposure, and the first light The beam detector and the second light beam detector detect the reference beam during monochrome printing, and the black light beam corrects the sub-scanning position deviation by referring to a table showing the correlation with the reference beam. It is used for this purpose.

  According to a fourth aspect of the present invention, in the color image forming apparatus, the first light beam detector and the second light beam detector detect the reference beam from the first page of the monochrome print job. .

  According to a fifth aspect of the present invention, in the color image forming apparatus, the first light beam detector and the second light beam detector detect the reference beam from the last page of the monochrome print job, and the reference beam When the sub-scanning position shift amount is larger than a specified value, color shift correction is performed immediately after the monochrome print job is finished.

  The invention according to claim 6 is characterized in that, in any one of the color image forming apparatuses, the second light beam detector is disposed at a rear position after passing through all the optical systems.

  According to a seventh aspect of the present invention, in the color image forming apparatus, the light beam incident on the second light beam detector is a light beam that passes through an optical system nearest to the deflecting unit.

  According to an eighth aspect of the present invention, in any one of the above color image forming apparatuses, the table is stored in advance as to whether the table is a sub-scanning color misregistration detection amount stored in a storage device and the number of printed sheets from color misregistration correction. The sub-scanning color misregistration detection amount stored in the apparatus and the operating time of the deflecting means, the sub-scanning color misregistration detection amount stored in the storage device and the internal temperature change, or the storage device in advance. The accumulated data can be updated based on at least one of the sub-scanning color misregistration detection amount and the elapsed time.

  The invention according to claim 9 is characterized in that, in any one of the color image forming apparatuses, the correction of the sub-scanning position deviation is performed every time one page printing or one job printing is performed.

  According to the color image forming apparatus of the first aspect, the sub-scanning position deviation of the light beam is based on the detection (detection) signals obtained by the light beam detectors provided at both the front end position and the rear end position on the scanning surface. In particular, the second light beam detector at the rear end position on the scanning plane is provided non-parallel to the sub-scanning direction, and the first light beam detector provided at the front end position on the scanning plane is provided. A table indicating the correlation with the reference beam, which is used as a reference beam for correcting any sub-scanning position deviation by making any one of the incident light beams incident thereon. Therefore, the quantity of optical system device misregistration information is abundant and the quality is sufficiently improved. As a result, the sub-scanning misregistration can be corrected. Simple (cheap) configuration It is possible to perform the optically accurately accurately. Therefore, even if a general-purpose synchronous detection sensor (photo IC) is used for the first light beam detector, the sub-scanning position deviation of the light beams of other colors can be corrected only by the photo IC for one color of the light beam. Therefore, an image forming apparatus having a function to perform the above function can be configured at low cost.

  According to the color image forming apparatus of the second aspect, in addition to the above effect, it is possible to effectively correct the sub-scanning position deviation for a light beam that is not incident on the first light beam detector.

  According to the color image forming apparatus of the third aspect, even when the color printing is monochrome printing, the same effect as that of the first aspect can be obtained.

  According to the color image forming apparatus of the fourth aspect, it is possible to quickly correct the sub-scanning position deviation when the color printing is monochrome printing.

  According to the color image forming apparatus of the fifth aspect, when the color printing is monochrome printing, the color misregistration correction can be accurately performed after the monochrome printing when the sub-scanning position deviation amount is excessively large.

  According to the color image forming apparatus of the sixth aspect, in addition to any one of the above effects, the second light beam detector (photo IC) is disposed at the rear stage position after passing through all the optical systems, so that various optical The influence of the element on the sub-scanning position deviation of the light beam can be effectively corrected.

  According to the color image forming apparatus of the seventh aspect, in addition to the above effect, the light beam incident on the second light beam detector (photo IC) is applied to the vicinity of the deflecting means such as a polygon motor (the influence of the heat source is reduced). By detecting the light beam passing through the largest optical system, the effect of correcting the sub-scanning position deviation can be remarkably improved.

  According to the color image forming apparatus of the eighth aspect, in addition to any one of the above effects, the correction accuracy of the sub-scanning position deviation can be improved more easily.

  According to the color image forming apparatus of the ninth aspect, in addition to any one of the above effects, the correction accuracy of the sub-scanning position deviation can be improved more accurately and appropriately.

1 is a diagram illustrating a basic configuration of a color image forming apparatus according to Embodiment 1 of the present invention. It is the figure which showed the basic composition of the light beam scanning apparatus with which the color image forming apparatus shown in FIG. 1 is equipped. FIG. 3 is a functional block diagram illustrating a detailed configuration that is included in the color image forming apparatus illustrated in FIG. 1 and that is a main part of the light beam scanning apparatus illustrated in FIG. 2. 3 is a table showing the correlation between the sub-scanning position deviation amount for the other color of the light beam and the sub-scanning position deviation amount for one color of the light beam measured using the synchronization detection sensor and the rear end sensor described in FIG. It is the figure which illustrated data contents. 6 is a flowchart showing an example of a processing operation for updating the data content of the table described in FIG. 4 in the color image forming apparatus according to Embodiment 2 of the present invention.

  In the following, the color image forming apparatus of the present invention will be described in detail with reference to the drawings by giving some examples.

  FIG. 1 is a diagram illustrating a basic configuration of a color image forming apparatus according to Embodiment 1 of the present invention. This color image forming apparatus has a configuration in which parts corresponding to the respective colors are arranged along the transfer belt 5 and is called a tandem type.

  Specifically, the transfer belt 5 is a belt wound around a drive roller 7 and a driven roller 8 that are rotationally driven. The drive roller 7 is rotationally driven by a drive motor (not shown), and the drive motor, the drive roller 7, and the driven roller 8 function as drive means for moving the transfer belt 5. A plurality of image forming units 6BK, 6M, 6C, and 6Y are arranged along the transfer belt 5 in order from the upstream side in the traveling direction. The plurality of image forming units 6BK, 6M, 6C, and 6Y have the same internal configuration except that the colors of the toner images to be formed are different. The image forming unit 6BK forms a black image, the image forming unit 6M forms a magenta image, the image forming unit 6C forms a cyan image, and the image forming unit 6Y forms a yellow image.

  Therefore, for the sake of simplicity, the black image forming unit 6BK will be described in detail below. Since the image forming units 6M, 6C, and 6Y of other colors have the same configuration as the image forming unit 6BK, they are distinguished by reference signs and description thereof is omitted.

  The image forming unit 6BK includes a photosensitive drum 9BK as a photosensitive member, a charger 10BK disposed around the photosensitive drum 9BK, a light beam scanning device (exposure unit) 11, a developing unit 12BK, and a photosensitive member cleaner (not shown). 1), and the static eliminator 13BK. The light beam scanning device 11 is configured to irradiate laser beams 14BK, 14M, 14C, and 14Y that are light for exposure corresponding to image colors formed by the image forming units 6BK, 6M, 6C, and 6Y.

  At the time of image formation, the outer peripheral surface of the photosensitive drum 9BK is uniformly charged by the charger 10BK in the dark, and is then exposed by the laser beam 14BK corresponding to the black image from the light beam scanning device 11, thereby electrostatic latent An image is formed. The developing device 12BK visualizes the electrostatic latent image with black toner, thereby forming a black toner image on the photosensitive drum 9BK. The toner image is transferred onto the transfer belt 5 by the action of the transfer unit 15BK at a position where the photosensitive drum 9 and the transfer belt 5 are in contact with each other. After the transfer of the toner image is completed, unnecessary toner remaining on the outer peripheral surface of the photoreceptor drum 9BK is wiped off by the photoreceptor cleaner, and then the charge is removed by the charge eliminator 13BK and stands by for the next image formation.

  The transfer belt 5 moves to the next image forming unit 6M in order to form the next image on the belt. In the image forming unit 6M, a magenta toner image on the photosensitive drum 9M is formed by a process similar to the image forming process in the image forming unit 6BK, and the toner image is converted into a black image formed on the transfer belt 5. Superimposed and transferred.

  The transfer belt 5 further moves to the next image forming units 6C and 6Y, and a cyan toner image formed on the photosensitive drum 9C and a yellow toner formed on the photosensitive drum 9Y are moved in the same manner. The image is transferred while being superimposed on the transfer belt 5. Thus, a full-color image is formed on the transfer belt 5.

  The full-color toner image on the transfer belt 5 is transferred to the paper 4 at the portion where the transfer belt 5 and the paper 4 are in contact with the paper 4 separated and fed from the paper feed tray 1 by the paper feed roller 2 and the separation roller 3. As a result, a full-color toner image is formed on the paper 4. The paper 4 on which the full-color superimposed image is formed is discharged to the outside of the image forming apparatus after the image is fixed by the fixing device 16.

  TM sensors 17 and 18 for detecting a color misregistration pattern formed on the transfer belt 5 are provided in the vicinity of the image forming unit 6Y having the above configuration. The TM sensors 17 and 18 are mounted as two left and right pattern detection sensors on one support plate. The TM sensors 17 and 18 are used for detecting a color misregistration pattern. Based on the color misregistration information detected by the TM sensors 17 and 18, the color misregistration of each color is corrected.

  These functional configurations are well known as disclosed in Patent Document 2 except for the detailed configuration of a light beam scanning device (exposure device) 11 to be described later. The technique disclosed in Document 2 can be applied.

  FIG. 3 is a functional block diagram illustrating a detailed configuration that is included in the color image forming apparatus and that is a main part of the light beam scanning device 11.

  The basic operation of the light beam scanning device 11 will be described. The light beam from the LD (BK) and LD (Y) of the light source (LD) as the light source device is below the two-stage polygon mirror 23 which is a deflecting means. The light beam is deflected by being incident on the surface and rotating the polygon mirror 23, passes through the fθ lens 24, is folded back by the first mirror 19, and the second and third mirrors (not shown), and is emitted from the device. Then, the photosensitive drums 9BK and 9Y are irradiated.

  Further, light beams from LD (M) and LD (C) of the light source (LD) are incident on the polygon mirror 23, and the polygon mirror 23 is rotated to deflect the light beam and pass through the fθ lens 25. The first mirror 20 and the second and third mirrors (not shown) are folded back, emitted from the apparatus, and irradiated onto the photosensitive drums 9M and 9C.

  Further, the light beam scanning device 11 is provided with a synchronization detection sensor 21 as a first light beam detector at the front end in the main scanning direction, and the light beam passing through the fθ lenses 24 and 25 is totally reflected. It is folded by the mirrors 26 and 27 and enters the synchronization detection sensor 21 through a lens (not shown). The synchronization detection sensor 21 plays a role for detecting a synchronization detection signal on the writing start side. In addition, a rear end sensor 22 as a second light beam detector is provided at the rear end portion in the main scanning direction, and the light beam that has passed through the fθ lenses 24 and 25 is the first mirrors 19 and 20. It is folded by a second mirror and a third mirror (not shown) and enters the rear end sensor 22.

  The light beam incident on the rear end sensor 22 passes through the optical system closest to the polygon mirror 23 (heat source), and the light beam is incident on the synchronization detection sensor 21 and has a color for detecting the synchronization detection signal. It is a beam. This light beam is used as a reference beam for correcting the sub-scanning position shift. In the case of the first embodiment, the light beam is positioned at the rear end of the scanning line of the light beam of the light source (LD) LD (C). Yes. Further, the light beam receiving part 22a of the rear end sensor 22 has a rectangular shape and is disposed so as to hold an angle of 45 degrees with respect to the light beam scanning line.

  FIG. 3 is a functional block diagram showing a detailed configuration that is a main part of the light beam scanning device 11. Here, the light beam receiving portion 21a of the synchronization detection sensor 21 is also rectangular with respect to the previous rear end sensor 22, but is different in that it is arranged so as to maintain an angle parallel to the light beam scanning line. is doing.

  In the light beam scanning device 11, as an operation function, the light beam emitted from the LD (C) of the light emitting source (LD) passes through the fθ lens, is reflected by the first to third mirrors, and is a photosensitive member (photosensitive drum). Is irradiated. The synchronization detection sensor 21 is disposed at the tip in the main scanning direction of the path between the fθ lenses 24 and 25 and the first to third mirrors in the path. A rear end sensor 22 is disposed at the rear end portion in the main scanning direction of the path between the first to third mirrors and the photosensitive member.

  Light emission using the output signal of the synchronization detection sensor 21 (which can also be regarded as a detection signal or detection signal) and the output signal of the rear end sensor 22 (which can also be regarded as a detection signal or detection signal) in such a configuration. Beam position deviation correction (sub-scanning position deviation correction) in the sub-scanning direction of LD (C) of the source (LD) is performed. For the details of the sub-scanning position deviation correction, the technique disclosed in Patent Document 1 may be applied.

  Although the sub-scanning position shift of the light beam of the LD (C) of the light emission source (LD) can be corrected by the above method, the LD (BK), LD of the light emission source (LD) where the light beam is not incident on the rear end sensor 22. (M) and LD (Y) light beams cannot be corrected. Therefore, the positional deviation amount of the light beam of the light source (LD) in the sub-scanning direction and the position of the light source (LD) in the sub-scanning direction of the light beam (LD), LD (M), LD (Y). A table showing the correlation with the shift amount is provided in the storage unit in the color image forming apparatus, and the LD (BK), LD (M), LD ( Y) correction of the positional deviation in the light beam sub-scanning direction is performed.

  FIG. 4 shows a sub-scanning position shift amount (1 in FIG. 4) for one color of the light beam (light beam of LD (C) of the light emission source (LD)) measured using the synchronization detection sensor and the rear end sensor. Data contents of a table indicating the correlation of the sub-scanning position shift amount for the other colors of the light beam (light source (LD) LD (BK), LD (M), LD (Y) light beam)) FIG.

  The sub-scanning position shift amount of the light beam of the light source (LD) LD (BK), LD (M), and LD (Y) as shown in this table is experimentally disclosed in Patent Document 2 in advance. It can be determined from the amount of sub-scanning position deviation with respect to LD (C) of the light source (LD) obtained by the color misregistration correction of the technique.

  In the second embodiment, in the color image forming apparatus having the same configuration as that of the first embodiment, the positional deviation in the sub-scanning direction of the light beam of the light source (LD) LD (BK), LD (M), LD (Y). The present invention relates to an embodiment for updating data contents stored in a table for correcting the amount. The update of the data contents of the table includes the cyan C color obtained by detecting and calculating the pattern when the TM sensor 17 and 18 shown in FIG. The sub-scanning color misregistration amounts of other colors are stored in the storage device. Then, the sub-scanning color misregistration detection amount stored when reaching a certain number of printed sheets (for example, 100 sheets, 200 sheets, etc.) after the color misregistration correction and the number of prints (printing from the color misregistration correction) are stored. The data content stored in the table is updated by performing a calculation based on the number of images.

  FIG. 5 is a flowchart illustrating an example of a processing operation for updating the data contents of the table described above in the color image forming apparatus according to the second embodiment.

  Here, when the processing operation is started, after color misregistration correction (step S1) is performed, the sub scanning color misregistration amount is stored in the storage device to perform sub scanning color misregistration amount storage (step S2), and then printing is performed. Start (step S3). Thereafter, for example, it is determined whether or not 100 sheets have been printed (step S4). If 100 sheets have not been printed, the process returns to repeat the determination process. If 100 sheets have been printed, the table is returned. The table is updated to update the data content (step S5), and the processing operation is repeated.

  In the third embodiment, in the color image forming apparatus having the same configuration as that of the first embodiment, the positional deviation in the sub-scanning direction of the light beams of the light source (LD) LD (BK), LD (M), and LD (Y). The present invention relates to another form of updating the table for correcting the amount. The update of the data contents of the table is the cyan obtained by detecting and calculating the pattern when the TM sensors 17 and 18 detect the pattern and perform color misregistration correction as in the case described in the second embodiment. And the sub-scanning color misregistration amount of other colors are stored in the storage device. Then, the sub-scanning color misregistration amount stored when the operation time (for example, 10 minutes, 20 minutes, etc.) of the polygon mirror 23 of the deflecting means after the color misregistration correction is reached and the operation of the polygon motor 23 are stored. The calculation is performed based on the time, and the data content stored in the table is updated.

  In the fourth embodiment, in the color image forming apparatus having the same configuration as that of the first embodiment, the positional deviation in the sub-scanning direction of the light beams of the light source (LD) LD (BK), LD (M), and LD (Y). The present invention relates to another form of updating a table for correcting the amount. The update of the data contents of the table is the cyan obtained by detecting and calculating the pattern when the TM sensors 17 and 18 detect the pattern and perform color misregistration correction as in the case described in the second embodiment. And the sub-scanning color misregistration amount of other colors are stored in the storage device. Then, calculation is performed based on the sub-scanning color misregistration amount and the in-machine temperature change amount stored according to the in-machine temperature change (for example, + 5 ° C., −5 ° C., etc.) after the color misregistration correction, The content of data stored in is updated. Incidentally, the temperature change in the apparatus refers to the output value of the temperature sensor provided in the color image forming apparatus.

  In the fifth embodiment, in the color image forming apparatus having the same configuration as that of the first embodiment, the positional deviation in the sub-scanning direction of the light beams of the light source (LD) LD (BK), LD (M), and LD (Y). The present invention relates to still another form of updating the table for correcting the amount. The update of the data contents of the table is the cyan obtained by detecting and calculating the pattern when the TM sensors 17 and 18 detect the pattern and perform color misregistration correction as in the case described in the second embodiment. And the sub-scanning color misregistration amount of other colors are stored in the storage device. Then, calculation is performed based on the stored sub-scanning color misregistration amount and the elapsed time according to the elapsed time after the color misregistration correction (for example, 10 minutes, 20 minutes, etc.), and the table is accumulated. The contents of data to be updated are updated.

  In the sixth embodiment, in the color image forming apparatus having the same configuration as that of the first embodiment, a plurality of parameters for the number of printed sheets, the operation time of the polygon motor 23, the temperature change in the apparatus, and the elapsed time described in the second to fifth embodiments are set. In addition to the combination, calculation is performed based on the sub-scanning color misregistration amount stored in the storage device, and the data content stored in the table is updated.

  In the seventh embodiment, in the color image forming apparatus having any one configuration of the first to fifth embodiments, the correction of the sub-scanning position deviation of the light beam of each color is performed every time one page is printed or 1 This is executed every time job printing is performed.

  In the eighth embodiment, in the color image forming apparatus of the first embodiment, the color printing is monochrome printing, and the other light beams incident on the synchronization detection sensor 21 are black light beams for black exposure. The synchronization detection sensor 21 and the rear end sensor 22 detect the reference beam during monochrome printing.

  The black light beam here is used to correct the sub-scanning position deviation by referring to a table showing the correlation with the reference beam. The reference beam detection by the synchronization detection sensor 21 and the rear end sensor 22 may be performed from the first page of the monochrome print job or from the last page of the monochrome print job. In the latter case, color misregistration correction is performed immediately after the end of the monochrome print job when the amount of deviation of the sub-scanning position of the reference beam is larger than a specified value.

DESCRIPTION OF SYMBOLS 1 Paper feed tray 2 Paper feed roller 3 Separation roller 4 Paper 5 Transfer belt 6BK, 6M, 6C, 6Y Image formation part 7 Drive roller 8 Driven roller 9BK, 9M, 9C, 9Y Photosensitive drum 10BK, 10M, 10C, 10Y Charge 11 Light beam scanning device (exposure device)
12BK, 12M, 12C, 12Y Developer 13BK, 13M, 13C, 13Y Static eliminator 14BK, 14M, 14C, 14Y Laser light 15BK, 15M, 15C, 15Y Transfer device 16 Fixing device 17, 18 TM sensor 19, 20 First Mirror 21 Synchronization detection sensor 21a, 22a Light beam receiving part 22 Rear end sensor 23 Polygon mirror 24, 25 fθ lens 26, 27 Total reflection mirror

JP 2007-225844 A JP 2008-225163 A

Claims (9)

A light source device for generating a light beam, a deflecting unit for deflecting the light beam emitted from the light source device, and a light beam scanning device for condensing the light beam deflected by the deflecting unit on a scanning surface A first light beam detector provided parallel to the sub-scanning direction at the front end position on the scanning surface of the light beam scanning device, and the sub-scanning direction at the rear end position on the scanning surface. The sub-scanning beam position deviation can be corrected based on the result of detecting the sub-scanning beam position by the second light beam detector provided non-parallel to the first light beam detector, and is incident on the first light beam detector. The light image is a plurality of light beams, and the light beam incident on the second light beam detector is any one of the plurality of light beams incident on the first light beam detector. With forming equipment I,
The light beam incident on the second light beam detector is used to correct the sub-scanning position deviation based on the detection signal of the first light beam detector and the detection signal of the second light beam detector. Used as a reference beam for
The other light beams of the plurality of light beams incident on the first light beam detector are used for correcting the sub-scanning position deviation by referring to a table showing the correlation with the reference beam. A color image forming apparatus.   2. The color image forming apparatus according to claim 1, wherein the light beam not incident on the first light beam detector corrects the sub-scanning position deviation by referring to a table showing a correlation with the reference beam. And a color image forming apparatus.   The color image forming apparatus according to claim 1, wherein the other light beams of the plurality of light beams incident on the first light beam detector include a black light beam for black exposure, and the first light beam detection. And the second light beam detector detect the reference beam at the time of monochrome printing, and the black light beam refers to a table indicating a correlation with the reference beam, thereby detecting the sub-scanning position deviation. A color image forming apparatus, which is used for correction.   4. The color image forming apparatus according to claim 3, wherein the first light beam detector and the second light beam detector detect the reference beam from the first page of a monochrome print job. Image forming apparatus.   4. The color image forming apparatus according to claim 3, wherein the first light beam detector and the second light beam detector detect the reference beam from the last page of a monochrome print job, and detect the reference beam. A color image forming apparatus, wherein color misregistration correction is performed immediately after completion of the monochrome print job when a scanning position deviation amount is larger than a specified value.   6. The color image forming apparatus according to claim 1, wherein the second light beam detector is disposed at a subsequent position after passing through all the optical systems. Forming equipment.   7. The color image forming apparatus according to claim 6, wherein the light beam incident on the second light beam detector is a light beam passing through an optical system nearest to the deflecting means. apparatus.   8. The color image forming apparatus according to claim 1, wherein the table is a sub-scanning color misregistration detection amount stored in a storage device in advance and a number of printed sheets from color misregistration correction. The sub-scanning color misregistration detection amount stored in the storage device and the operation time of the deflection means, the sub-scanning color misregistration detection amount stored in the storage device in advance, and the in-machine temperature change, or the storage device in advance A color image forming apparatus, wherein the accumulated data can be updated based on at least one of the sub-scanning color misregistration detection amount and the elapsed time stored in.   9. The color image forming apparatus according to claim 1, wherein the correction of the sub-scanning position deviation is performed every time one page is printed or every time one job is printed. Image forming apparatus.

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