JP4492344B2 - Image forming apparatus - Google Patents

Description

  The present invention includes a plurality of light sources and a plurality of image carriers, and scans a light beam modulated based on a plurality of different image signals and emitted from each light source, whereby different originals are provided on each image carrier. The present invention relates to an image forming apparatus that forms an image and forms the image by multiply transferring the original images to the same transfer region.

  In recent years, an original image corresponding to each of the four colors of black (K), yellow (Y), magenta (M), and cyan (C) is formed, and finally these four original images are superimposed. Accordingly, an electrophotographic image forming apparatus that forms one color image has become widespread.

  As such an image forming apparatus, laser beams modulated on the basis of image signals corresponding to the respective colors of four colors are mutually reciprocally centered on the rotary polygon mirror for each two colors by one rotary polygon mirror as a deflecting unit. There is known an image forming apparatus in a form (hereinafter referred to as a bidirectional spray paint method) in which a scanning exposure apparatus that performs exposure scanning in the main scanning direction is provided. In this bidirectional spray paint type image forming apparatus, each photosensitive drum is exposed and scanned by deflecting the laser beam corresponding to each color by one rotating polygon mirror, so that the scanning exposure apparatus itself has a relatively compact configuration. be able to.

  However, in the image forming apparatus as described above, due to variations in the optical characteristics of the laser light for each color emitted from the exposure apparatus, positional deviation may occur when the original images are superimposed. As a result, the quality of the formed image may be deteriorated. Therefore, it is necessary to perform appropriate alignment control between the original images of each color.

As a technique for performing appropriate alignment, for example, a scanning start position detection sensor that detects a scanning start position of a light beam in a first main scanning direction and a second main scanning direction that is opposite to the first main scanning direction. (Hereinafter referred to as an SOS sensor) and a scanning end position detecting sensor (hereinafter referred to as an EOS sensor) for detecting the scanning end position of the light beam scanned in the second scanning direction. Based on the result, an image forming apparatus that corrects a deviation in the writing position (side registration) of a scanning line in the main scanning direction has been proposed (see, for example, Patent Document 1).
JP 2002-267970 A

  However, it is not sufficient to correct the misregistration in the main scanning direction by simply correcting the side registration deviation. For example, the writing end position of the scanning line in the main scanning direction or the print width (hereinafter referred to as magnification) may fluctuate due to environmental influences such as temperature rise due to the operation of the image forming apparatus or external air temperature fluctuations. Since positional deviation occurs when the original images are superimposed, it is necessary to correct the magnification fluctuation.

  Here, this magnification fluctuation will be specifically described with reference to FIG.

  FIG. 22 is a view showing a schematic configuration of an exposure apparatus (ROS) 300 for forming an electrostatic latent image with a light beam. The ROS 300 includes a semiconductor laser 302 that emits a light beam, a collimator lens 304 that collimates the light beam emitted from the semiconductor laser 300, and a rotating polygon mirror 306 that deflects the light beam via the collimator lens 304. It has been. When the scanning rotation motor (not shown) rotates, the rotary polygon mirror 306 rotates in the direction of arrow A, and the laser light incident on the rotary polygon mirror 306 via the collimator lens 304 is reflected on the circumferential surface of the rotary polygon mirror 306. The light is reflected by the surface and irradiated to the photoreceptor 310 through the fθ lens 308. An SOS sensor 312 is provided at the left end of the photoreceptor 310, and an EOS sensor 314 is provided at the right end. When the scanning laser light passes through the SOS sensor 312 and the EOS sensor 314, an SOS signal and an EOS signal indicating that the scanning laser light has been detected are output. Print image data, which is image data, is output after a predetermined time has elapsed from the timing at which the SOS signal is output from the SOS sensor 312.

  Here, when the temperature inside the image forming apparatus rises, the temperature of the semiconductor laser 302 that emits laser light also rises. As a result, the wavelength of the laser light emitted from the semiconductor laser 302 changes. Since the fθ lens 308 has a characteristic that the refractive index changes according to the wavelength of the incident laser light, when the laser light having a changed wavelength is incident on the fθ lens 308, a normal case (solid line in FIG. 22). ) Is refracted compared with () (broken line in FIG. 22). As a result, the laser beam is scanned with a wider scanning width than in a normal case. If an image is printed in such a state, the output timing of the SOS signal in the SOS sensor 312 will not only fluctuate, but the image will be formed in a state extending in the main scanning direction.

  Further, when the temperature inside the image forming apparatus is lowered, the laser beam is scanned with a scanning width narrower than that in the normal case (one-dot chain line in FIG. 22). That is, the image is shrunk.

  Since each of the Y, M, C, and K semiconductor lasers has a different distance from the fixing device as a heat source, as shown in FIG. 23, the temperature rise measured by a temperature sensor provided in the vicinity of the fixing device. In contrast, the amount of misregistration (MAG) due to the magnification variation of each of the Y, M, C, and K semiconductor lasers differs. As a result, a positional shift occurs when the original images are overlaid. Normally, when outputting an image signal corresponding to the light beam, the output frequency of the image signal is changed or the phase shift of the output clock of the image signal is performed. Etc. to correct the magnification.

  However, the conventional image forming apparatus as disclosed in Patent Document 1 does not consider magnification fluctuations at all, and magnification fluctuations are corrected as side registration fluctuations, which may be overcorrected. The image quality may be deteriorated.

  Hereinafter, this point will be described in detail with reference to the drawings.

  FIG. 24 is an explanatory diagram showing a correction state when the conventional image forming apparatus corrects misalignment for the C color and the M color whose scanning directions are opposite to each other when the variation in the scanning magnification of each color is the same.

  FIG. 24A shows a state in which there is no positional deviation between the two colors of C and M. Here, as shown in FIG. 24B, when the same amount of magnification variation occurs in the two colors C and M, the conventional image forming apparatus detects the magnification variation as the side registration variation, and the side registration variation. As corrected. That is, in the conventional image forming apparatus, the variation DMT_MAG of the output time interval from the M color SOS signal to the EOS signal is used as it is as a shift amount to be corrected for the M color, so that the correction result of FIG. Thus, the C color writing end position and the M color writing end position coincide with each other, and the C color writing end position and the M color writing end position coincide with each other. In this example, since the M-color magnification variation DTM_MAG = C-color magnification variation DTC_MAG, even if the magnification variation is corrected as a side registration variation, the positional deviation is eliminated.

  FIG. 25 is an explanatory diagram showing a correction state when the above-described conventional image forming apparatus corrects the positional deviation for the C and M colors whose scanning directions are opposite to each other when the variation in the scanning magnification of each color is different.

  FIG. 25A shows a state in which there is no positional deviation between the two colors of C and M. Here, as shown in FIG. 25 (B), when magnification variations of different amounts occur in the two colors of C and M, if correction is performed by the conventional image forming apparatus, the EOS signal is converted from the M color SOS signal. Since the variation DMT_MAG of the output time interval is used as it is as a shift amount to be corrected for M color, in this example, the magnification variation DTM_MAG for M color is larger than the magnification variation DTC_MAG for C color, and the positional deviation is not eliminated. As a result, as shown in FIG. 25C, the writing end position of the C color and the writing start position of the M color do not coincide with each other, and a positional deviation occurs. In this state, even if an attempt is made to perform magnification correction to match the magnification of M color to the magnification of C color, the M color writing position is excessively corrected. The image expands toward the scanning end side (in the magnification correction, the displacement amount increases toward the writing end position), the C writing start position and the M writing end position shift, and the image quality further deteriorates.

  In general, since a color image forming apparatus includes a plurality of light sources, the apparatus itself becomes large, and a difference in temperature distribution around the exposure apparatus increases. In particular, since the temperature difference between the portion near the fixing device, which is a heat source, and the portion away from the fixing device becomes larger, there is a large difference in the magnification fluctuation amount depending on the location of the semiconductor laser. For this reason, erroneous detection of the correction amount due to the magnification fluctuation difference is an amount that cannot be ignored.

  In addition, even when a minute position variation of the laser light reflecting mirror occurs, a magnification variation difference is generated in the same manner as the wavelength variation of the semiconductor laser.Therefore, in a portion close to the fixing device and a portion away from the fixing device, Furthermore, a magnification difference will occur.

  The present invention has been made to solve the above-described problems, and an image forming apparatus capable of forming a high-quality image by correcting not only a positional shift caused by side registration fluctuations but also a positional deviation caused by magnification fluctuations. The purpose is to provide.

The image forming apparatus according to claim 1 in order to achieve the above object, a plurality of light sources, a plurality of image bearing members, and provided with a rotary polygon mirror which rotates in a predetermined direction, several different including one reference image signal A light beam modulated based on an image signal and emitted from each of the light sources is deflected by the rotary polygon mirror, and the reference image signal is supplied to each of the image carriers corresponding to each of the image signals. while scanning the light beam to the first main scanning direction corresponding to a plurality of image signals including, a light beam corresponding to the remaining image signals, prior Symbol second main of the first main scanning direction and the reverse direction By scanning in the scanning direction, different original images are formed on each of the image carriers corresponding to the respective image signals, and the images are formed by multiply transferring the original images to the same transfer region. In the forming device, A reflective surface for reflecting a reference light beam corresponding to the reference image signal deflected by the rotary polygon mirror and a reflective surface for reflecting at least one light beam scanned in the second main scanning direction are provided on one substrate. A first reflecting means provided near the scanning start position of the reference light beam and near the scanning end position of the at least one light beam, and reflected by the first reflecting means A first scanning start position detecting means for outputting a scanning start signal by detecting a reference light beam corresponding to the reference image signal, and the at least one light beam reflected by the first reflecting means. or unless the scanning end position detecting means for outputting a scan termination signal by detecting, the reference light beams corresponding to the reference image signal is deflected by the rotary polygonal mirror A plurality of second reflecting means provided near each scanning start position of each light beam so as to reflect each light beam including the at least one light beam, and reflected by the second reflecting means A plurality of second scan start position detecting means for outputting respective scan start signals by detecting the respective light beams, and a magnification for detecting a magnification variation of the original image formed on each of the image carriers. Detection means;
Based on the magnification fluctuation detected by the magnification detection means, the magnification error calculation means for calculating the magnification error and the writing position of each original image by the light beam scanned in the same direction are aligned based on the scanning start signal. Based on the scanning start signal of the light beam scanned in the second main scanning direction, the scanning end signal of the light beam scanned in the second main scanning direction, and the magnification error. Light that scans in the second main scanning direction so that the writing start position of the original image by the light beam scanning in the main scanning direction and the writing end position of the original image by the light beam scanning in the second main scanning direction are aligned. An original image other than the reference original image is controlled so that the magnification of each of the original images other than the reference original image becomes the magnification of the reference original image based on the magnification error and the writing position of the original image by the beam is controlled. By correcting the respective magnification of the image, and a, and control means for controlling so that the main scanning direction across the original image to be formed on each of the image bearing member are aligned.
The invention according to claim 2 includes a plurality of light sources, a plurality of image carriers, and a rotating polygon mirror that rotates in a predetermined direction, and is modulated based on a plurality of different image signals including one reference image signal. The light beam emitted from each of the light sources is deflected by the rotary polygon mirror, and corresponds to a plurality of image signals including the reference image signal for each of the image carriers corresponding to each of the image signals. And scanning the light beam corresponding to the remaining plurality of image signals in the second main scanning direction opposite to the first main scanning direction. In the image forming apparatus for forming different original images on the respective image carriers corresponding to the respective image signals, and forming the images by multiply transferring the original images to the same transfer region, By mirror A reflective surface that reflects a reference light beam corresponding to the directed reference image signal and a reflective surface that reflects at least one light beam that scans in the second main scanning direction are provided on one substrate or integrally therewith. A first reflecting means formed near the scanning end position of the reference light beam and near the scanning start position of the at least one light beam, and the at least one reflected by the first reflecting means. A first scanning start position detecting means for outputting a scanning start signal by detecting two light beams and a reference light beam corresponding to the reference image signal reflected by the first reflecting means for scanning. Scanning end position detecting means for outputting an end signal; and the base corresponding to the reference image signal except for the at least one light beam deflected by the rotary polygon mirror. A plurality of second reflecting means provided near each scanning start position of each light beam so as to reflect each light beam including the light beam, and each of the light reflected by the second reflecting means. A plurality of second scanning start position detecting means for outputting a scanning start signal by detecting each light beam; a magnification detecting means for detecting a magnification fluctuation of an original image formed on each of the image carriers; Based on the magnification fluctuation detected by the magnification detection means, the magnification error calculation means for calculating the magnification error and the writing position of each original image by the light beam scanned in the same direction are aligned based on the scanning start signal. Based on the scanning start signal and the scanning end signal of the light beam that scans in the first main scanning direction, and the writing position of the original image by the light beam that scans in the first main scanning direction and the second Lord of Controlling the writing position of the original image by the light beam scanning in the second main scanning direction so that the writing end position of the original image by the light beam scanning in the scanning direction is aligned, and based on the magnification error, It is formed on each of the image carriers by correcting the magnification of each of the original images other than the reference original image so that the magnification of each of the original images other than the reference original image becomes the magnification of the reference original image. Control means for controlling so that both ends of the original image in the main scanning direction are aligned .

As a result, it is possible to correct not only the positional deviation due to the side registration fluctuation but also the positional deviation due to the magnification fluctuation, and form a high-quality image. According to another aspect of the present invention, when position variation (side registration variation) of the first reflecting means occurs, a scanning start signal in the first main scanning direction and a scanning end signal in the second main scanning direction. Since the output timing of the image data fluctuates by the same amount, it can be easily controlled so that the writing position and writing end position of the original image formed on each image carrier are aligned. According to a second aspect of the present invention, when a position variation (side registration variation) of the first reflecting means occurs, a scanning start signal in the second main scanning direction and a scanning end signal in the first main scanning direction. Since the output timing of the image data fluctuates by the same amount, it can be easily controlled so that the writing position and writing end position of the original image formed on each image carrier are aligned .

  The transfer area may be an area on the intermediate transfer member or an area on a recording medium.

Normally, when magnification correction is performed by frequency control or phase shift of an image signal, the original image is corrected so as to expand (or contract) from the writing side toward the writing end side (magnification correction is performed at the end of scanning. , The displacement becomes larger). Thus, for the correction between the light beam scanning in the same direction, if Soroere the writing position of the light beam of the reference side to write the position of the reference side of the light beam of the light beam, the magnification of the reference side of the original image When the correction is made, it is possible to align the writing end positions of the original images.

  In addition, for correction between light beams scanned in different directions, the scanning end position of the reference side light beam (light beam scanned in the first main scanning direction) and the direction opposite to the reference side light beam are scanned. When the magnification of the original image on the reference side is corrected by aligning the writing position of the reference side light beam (light beam scanned in the second main scanning direction), both ends of both original images are Can be aligned.

  Since the magnification correction is performed based on the magnification error calculated by the magnification error calculation means, the magnification correction can be easily performed. The magnification correction method is not particularly limited. For example, the magnification correction may be performed by changing the output frequency of the image signal, or the magnification correction may be performed by phase shifting the output clock of the image signal.

Further, in the image forming apparatus according to claim 1 or 2, as in claim 3, the magnification detection unit is arranged in the same transfer region by scanning in the first and second main scanning directions. A positional deviation detection unit configured to detect a positional deviation amount from the plurality of positional deviation detection patterns formed, and based on the positional deviation amount detected by the positional deviation detection unit, the original formed on each of the image carriers. It is possible to detect image magnification fluctuations.

  Thereby, it is possible to easily detect the magnification variation of each original image.

  The transfer area on which the misregistration detection pattern is formed may be an area on the intermediate transfer member or an area on the recording medium.

According to a fourth aspect of the present invention, the magnification detection unit includes a temperature detection unit that detects a temperature in the apparatus, and each image carrier is provided on the basis of the temperature detected by the temperature detection unit. It is possible to detect the magnification fluctuation of the original image to be formed.

  Since the magnification varies depending on the temperature, it is possible to perform magnification correction corresponding to the temperature variation by providing a temperature detecting means for detecting the temperature.

  It should be noted that when magnification correction is performed based on the temperature detected by the temperature detection means, it is not necessary to stop the image forming operation. Therefore, productivity is improved compared to a method of detecting a magnification variation by forming a detection pattern. A good image can be obtained.

The image forming apparatus according to claim 5, a plurality of light sources, a plurality of image bearing members, and provided with a rotary polygon mirror which rotates in a predetermined direction, based on several different image signal including one of the reference image signal A plurality of images including the reference image signal for each of the image carriers corresponding to each of the image signals is deflected by the rotary polygon mirror by deflecting the light beam modulated and emitted from each of the light sources. while scanning the light beam corresponding to the signal to the first main scanning direction, the light beam corresponding to the remaining plurality of image signals, Previous Stories second main scanning direction of the first main scanning direction and the reverse direction In an image forming apparatus that forms a different original image on each of the image carriers corresponding to each of the image signals by scanning, and forms the image by multiple transfer of the original images to the same transfer region , Rotating multi-face A reflection surface for reflecting a reference light beam corresponding to the reference image signal deflected by a mirror and a reflection surface for reflecting at least one light beam scanned in the second main scanning direction are provided on one substrate; or A first reflecting means formed integrally near a scanning start position of the reference light beam and near a scanning end position of the at least one light beam; and the reflected by the first reflecting means. A first scanning start position detecting means for outputting a scanning start signal by detecting a reference light beam corresponding to a reference image signal; and detecting the at least one light beam reflected by the first reflecting means. in the first scanning end position detecting means, the reflecting surface及for reflecting the reference light beams corresponding to the reference image signal is deflected by the rotary polygon mirror for outputting a scan termination signal A reflection surface that reflects the at least one light beam is provided on one substrate or integrally formed, and is provided in the vicinity of the scanning end position of the reference light beam and in the vicinity of the scanning start position of the at least one light beam. Second reflection means, second scanning start position detection means for outputting a scanning start signal by detecting the at least one light beam reflected by the second reflection means, and the second reflection. A second scanning end position detecting means for outputting a scanning end signal by detecting a reference light beam corresponding to the reference image signal reflected by the means; and corresponding to the reference image signal deflected by the rotary polygon mirror Provided in the vicinity of each scanning start position of each light beam so as to reflect each light beam except the reference light beam and the at least one light beam. A plurality of third reflecting means, a plurality of third scanning start position detecting means for outputting a scanning start signal by detecting each of the light beams reflected by the third reflecting means, and the scanning Based on the start signal, control is performed so that the writing position of each original image by the light beam scanned in the same direction is aligned, and based on the scan start signal and the scan end signal of the light beam scanned in the first main scanning direction. The second main scanning so that the writing end position of the original image by the light beam scanning in the first main scanning direction is aligned with the writing position of the original image by the light beam scanning in the second main scanning direction. The writing start position of the original image by the light beam scanning in the direction, and the output time interval between the scanning start signal and the scanning end signal of the light beam scanning in the first main scanning direction, and the second main scanning direction. Scan direction Based on the output time interval between the scanning start signal and the scanning end signal of the light beam to be scanned, the magnification of each of the original images other than the reference original image becomes the magnification of the reference original image. Control means for correcting the respective magnifications of the original images so as to align both ends of the original image formed on each of the image carriers in the main scanning direction.

  As a result, it is possible to correct not only the positional deviation due to the side registration fluctuation but also the positional deviation due to the magnification fluctuation, and form a high-quality image.

As described above, when the magnification correction is performed, the original image is corrected so as to expand (or contract) from the writing side toward the writing end side. Thus, for the correction between the light beam scanning in the same direction, if Soroere position out can 該書, can be aligned when the correction of the magnification of the reference side of the original image, the positions writing end of each original image . In addition, for correction between light beams scanned in different directions, the scanning end position of the reference side light beam (light beam scanned in the first main scanning direction) and the direction opposite to the reference side light beam are scanned. When the magnification of the original image on the reference side is corrected by aligning the writing position of the reference side light beam (light beam scanned in the second main scanning direction), both ends of both original images are Can be aligned.

  With such a configuration, when the position variation of the reflecting means (side registration variation) occurs, the output timings of the scanning start signal in the first main scanning direction and the scanning end signal in the second main scanning direction are the same. Since it varies by the amount, it can be easily controlled so that the writing position and writing end position of the original image formed on each image carrier are aligned. Further, since the output timing of the scanning start signal in the second main scanning direction and the scanning end signal in the first main scanning direction fluctuate by the same amount, the writing position of the original image formed on each image carrier and It can be easily controlled so that the writing end positions are aligned.

  For example, the output time interval between the scanning start signal and the scanning end signal of the light beam scanned in the first main scanning direction includes a positional deviation amount and a magnification variation due to a side registration variation of the light beam scanned in the first main scanning direction. The amount of misalignment due to is included. Further, the output time interval between the scanning start signal and the scanning end signal of the light beam scanned in the second main scanning direction includes a positional deviation amount and a magnification variation due to a side registration variation of the light beam scanned in the second main scanning direction. The amount of misalignment due to is included.

Here, if the first and second reflecting means as described above are provided, the amount of positional deviation due to the side registration fluctuation of the light beam scanned in the first and second main scanning directions becomes equal. A magnification error between the original images can be obtained, and based on this, the magnification of the original image formed on each image carrier can be easily corrected.

  As described above, according to the image forming apparatus of the present invention, a high-quality image can be formed with high productivity by correcting not only the position shift due to the side registration variation but also the position shift due to the magnification variation at the time of multiple image formation. There is an excellent effect of being able to.

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

[First Embodiment]
FIG. 1 schematically shows an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 includes four developing units (yellow developing unit Y, magenta developing unit M, cyan developing unit C, and black developing unit) corresponding to Y, M, C, and K color signals for forming a color image. K). Each developing unit has the same configuration and includes a photosensitive drum 12 as an image carrier.

  Further, the image forming apparatus 10 includes a scanning exposure device 11 for irradiating the photosensitive drum 12 included in each developing unit with a laser beam.

  FIG. 2 shows an outline of the scanning exposure apparatus 11 viewed from the direction of arrow A in FIG. The scanning exposure apparatus 11 includes an fθ lens 36 composed of a plano-convex lens and a plano-concave lens with a rotating polygon mirror (polygon mirror) 22 rotating at a constant speed in the direction of arrow S in FIG. It is arranged in each. The scanning exposure apparatus 11 also includes laser light corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black), which is modulated based on each color signal constituting the image data signal. Are provided with four laser diodes 30. The laser light emitted from each laser diode 30 is converted into parallel light by the corresponding collimator lens 34 and refracted in the optical path by the reflection mirror 29, and then transmitted through the fθ lens 36 to be rotated by the rotary polygon mirror 22. Are incident on each.

  Each laser beam incident on the rotating polygon mirror 22 is reflected by the reflecting surface of the rotating polygon mirror 22, passes through the fθ lens 36 again, is refracted by the mirror 27 disposed on the optical path different from the incident time, and is a cylindrical mirror. Each light is guided to 28 (see FIG. 1). The laser light guided to the cylindrical mirror 28 is refracted by the cylindrical mirror 28 so as to irradiate the exposure scanning position 13 on the surface of the photosensitive drum 12 (hereinafter referred to as the drum surface) of each developing unit. It has become. Therefore, the laser beam is scanned on the drum surface at a constant speed by the action of the fθ lens 36. The optical paths of the laser beams of the respective colors are indicated by arrows 15Y, 15M, 15C and 15K, respectively.

  In each developing unit, the photosensitive drum 12 is rotated at a predetermined speed in the direction of arrow P in FIG. 1 by a motor (not shown). As a result, each laser beam emitted from the scanning exposure device 11 is repeatedly scanned along the axial direction (main scanning direction) of the photosensitive drum 12 on the drum surface.

  In each developing unit, a charger 14 is provided slightly upstream of the exposure scanning position 13 along the drum rotation direction indicated by an arrow P in FIG. 1, so that the drum surface is uniformly charged. . As a result, the surface of the drum uniformly charged by the charger 14 is exposed and scanned with laser light, thereby removing the charged charges other than the image portion and leaving the charge in the image portion. A latent image is formed.

  Further, a developing device 16 is provided slightly downstream of the exposure scanning position 13 along the drum rotation direction indicated by an arrow P in FIG. The developing device 16 is filled with toner charged to a polarity opposite to that of the electrostatic latent image, and the electrostatic latent image formed on the drum surface is colored in each color (Y, M, C, K). A visible image (toner image) is formed by electrostatically adhering toner as charged fine particles.

  Further, a transfer unit 18 is provided below the photosensitive drum 12 in FIG. 1, and a transfer belt 18 </ b> A for transferring the toner image is sandwiched between the transfer unit 18 and the photosensitive drum 12. The transfer belt 18A is conveyed in order by the drive roller in the direction of the arrow Q in FIG. 1 in the developing units Y, M, C, and K. Further, the transfer unit 18 in each developing unit applies charges to the transfer belt 18A, and sequentially transfers the toner images for each color to the transfer belt 18A by the electrostatic force.

  Further, a fixing device 24 is disposed on the downstream side in the arrow Q direction of FIG. 1 of the transfer belt 18A to which the toner image for each color is transferred. In the fixing device 24, the toner image transferred to the transfer belt 18 A is fused to the recording medium 26 by applying heat or pressure while sandwiching the recording medium 26 for recording an image and conveying it in the direction of arrow R in FIG. It comes to wear.

  A cleaner 20 for removing toner remaining on the photosensitive drum 12 after transfer is provided at the rear end of the rotation direction of the photosensitive drum 12 of each developing unit (the direction of arrow P in FIG. 1). .

  In addition, a pair of misalignment detection units 50 is provided on the downstream side in the arrow Q direction of the transfer belt 18A and at a position (both ends in the width direction) perpendicular to the width direction of the transfer belt 18A. The misregistration detection unit 50 reads each misregistration detection color component pattern (hereinafter, misregistration detection pattern) sequentially transferred onto the transfer belt 18A, and detects misregistration of other colors with respect to the reference color. . Thereby, a variation in the ratio of the length of the image recording range along the main scanning direction by the laser beam for each color (hereinafter referred to as magnification or scanning magnification) is detected.

  In addition, as shown in FIG. 2, in the scanning exposure apparatus 11, laser light is respectively present near the scanning start position in the main scanning direction (arrows C and K in FIG. 2) of the laser light corresponding to C color and K color. SOS sensors 40C and 40K for detecting laser light are arranged in order to synchronize the timing of start of scanning (Start Of Scan; SOS). Further, in the main scanning direction (arrows Y and M in FIG. 2) of the laser light corresponding to the Y color and the M color, the SOS sensors 40Y and 40M are arranged in the vicinity of the scanning start position, respectively, and the scanning end position In the vicinity, EOS sensors 41Y and 41M for detecting the laser beam are arranged in order to synchronize the timing of the end of main scanning (End Of Scan; EOS) by the laser beam. Each of the SOS sensors 40C to 40K outputs an SOS signal indicating the scanning start position of the laser light when detecting the laser light, and each of the EOS sensors 41Y and 41M indicates an EOS signal indicating the scanning end position of the laser light when detecting the laser light. Is output.

  The EOS sensor is provided corresponding to a reference color that is different from the reference color in the scanning direction. In this embodiment, since the C color is used as the reference color, EOS sensors are provided for the Y color and the M color, which are different from the C color scanning direction.

  The SOS sensor 40K, SOS sensor 40C and EOS sensors 41M and 41Y detect the laser beams picked up by the corresponding pickup mirrors 38K, 38CM and 38Y, respectively, as shown in FIG. It has become. Here, one pickup mirror 38CM is provided in common to the SOS sensor 40C and the EOS sensor 41M. As another embodiment, as shown in FIG. 3B, the pickup mirrors 38C and 38M may be held by a common holder 39 so as to function as a unit. In addition, the laser beams picked up by the common pickup mirror 38CM or the like may have different scanning directions, and one of them may be a reference color. As the pickup mirror is integrally displaced in this way, a shift amount equivalent to the shift amount of the reference color (C color) is developed on the reference color (M color), so that the reference color (C color) is developed. ) Can be easily determined based on whether or not there is a deviation.

  That is, when attention is paid to the scanning laser beams of C color and M color, as shown in FIG. 4A which is a schematic view seen from the direction of arrow A in FIG. Since this is due to the displacement of the pickup mirror, if the mirror drawn by the solid line is displaced like the mirror drawn by the dotted line, a deviation occurs at the point to be picked up. That is, in FIG. 4A, the pickup is picked up at a position changed by Δθ as the scanning angle. As a result, as shown in FIG. 4B, the output timing of the C color SOS sensor before the change is advanced by Δt, and at the same time, the output timing of the M color EOS sensor is delayed by the same amount of Δt. Moreover, since the moving direction of the output timing is the reverse direction, it is convenient for correction.

  FIG. 5 shows a schematic diagram of a registration control unit (hereinafter referred to as a “resin control unit”) for aligning an image formed by laser light corresponding to each color of the image forming apparatus 10. This regicon unit is positioned for laser light (Y and M colors, and C and K colors) whose scanning directions are the same direction, and laser light (C color and M colors) whose scanning directions are different directions, respectively. The shift is corrected, and the position shift is corrected as a whole.

  The main control circuit 68 calculates magnification information (magnification fluctuation amount) of the image by the laser light emitted from each laser diode 30 based on the positional deviation information detected by the positional deviation detection unit 50, and the magnification Information is output to the magnification error calculation unit 80 and the image processing circuit 72.

  The main control circuit 68 is connected to a commander 76 for setting a counter value that is an output timing between line sync signals output from the line sync counters 70Y to 70C. The counter value set by the commander 76 is stored in a RAM (not shown) provided in the main control circuit 68, and is stored in a counter value from the commander 76 and a data register 66 described later. Are used for adjustment at the time of initial shipment and readjustment after shipment.

  When magnification information is input from the main control circuit 68, the magnification error calculation unit 80 calculates a magnification error based on the magnification information, outputs it to the image processing circuit 72, and uses a line sync counter with a correction value corrected by the magnification error. The line sync signal generation timing (described later) of 70Y to 70K is corrected.

  The image processing circuit 72 outputs print data generated by performing image processing on the input image data to the laser driving circuit 74 in accordance with the output timing of the line sync signals from the line sync counters 70Y to 70K. The frequency of the print data output from the image processing circuit 72 is changed by the magnification error input from the magnification error calculation unit 80. By changing the frequency of the image signal, the interval between dots irradiated with laser light along the main scanning direction changes, and the length (magnification) of the image recording range along the main scanning direction with the laser light changes. (Correction). Here, the magnification correction is performed on the image signal of the reference color so that the length of the recording range of the reference color image is equal to the length of the recording range of the reference color image.

  Further, the registration control circuit 60 for correcting the registration error includes a selector 62, a registration control counter 64, and a data register 66 (including an arithmetic unit).

  The selector 62 selects each SOS signal output from each of the SOS sensors 40Y to 40K and the EOS signal output from the EOS sensors 41M and 41Y, and outputs them to the register control counter 64.

  The regicon counter 64 measures the time difference between the SOS signal and the EOS signal output from the selector 62 and outputs the measured value to the data register 66.

  The data register 66 accumulates the measurement value output from the register control counter 64, and calculates and outputs a correction value from the measurement value by an arithmetic unit. A main control circuit 68 is connected to the data register 66, and the data register 66 operates according to an instruction from the main control circuit 68.

  Next, the operation of the regicon unit will be briefly described. Here, the C and K color scanning directions are referred to as forward scanning, and the Y and M scanning directions are referred to as reverse scanning.

  First, normal scanning will be described. Since the reference color is C, in order to measure the time difference in the output timing of the SOS signal from the reference color K, the two SOS signals are selected by the selector 62 and measured by the register control counter 64. . The measured value at the register control counter 64 is stored in the data register 66.

  Similarly, the reverse-scanning Y color and M color SOS signals are selected by the selector 62, and the measured value of the time difference between the output timings of the SOS signals is stored in the data register 66. In this reverse scanning, a value based on the M color is held.

  Further, the time difference between the output timings of the C-color SOS signal for normal scanning and the M-color SOS signal for reverse scanning is measured by the register control counter 64, and the measured value is stored in the data register 66.

  The data register 66 calculates a correction value for correcting the positional deviation based on each data stored in this manner by the calculator and outputs the correction value to the magnification error calculation unit 80. As described above, the magnification error calculation unit 80 obtains a magnification error based on the magnification information, calculates a final correction value obtained by adding the obtained magnification error to the correction value output from the data register 66, and Output to the line sync counters 70Y to 70K.

  When the correction value is input to each of the line sync counters 70Y to 70K, a line sync signal that is a signal for starting scanning of each laser beam corresponding to each color is output. The image processing circuit 72 sends print data generated by image processing of the image data to the laser drive circuit at the output timing of the line sync signal. The laser drive circuit 74 modulates the laser light emitted from each laser diode 30 according to the print data, and performs printing with the laser diode 30.

  As described above, the deviation in the main scanning direction between the laser beams corresponding to the respective colors is corrected by correcting the timing at which the scanning of the laser beams corresponding to the respective colors is started in accordance with the line sync signal.

  Next, the processing at the time of misalignment correction in the present embodiment will be described in detail.

  First, correction values (correction values that do not consider misalignment due to magnification fluctuations) calculated by the data register 66 will be described.

  In the positional deviation correction process between laser beams whose scanning directions are the same, the correction value is calculated and corrected by the data register 66 as follows. Below, C color and K color are given as examples.

  FIG. 6A shows a timing chart of the SOS signals output from the SOS sensors 40C and 40K in the initial state and the line sync signals output from the line sync counters 70C and 70K.

  Based on the SOS signal output from each of the SOS sensor 40C and the SOS sensor 40K, line sync signals L / S (C) and L / S ( K) is generated and output.

  The generation timing of the line sync signals L / S (C) and L / S (K) (the time from the output of the SOS signal to the output of the line sync signal) is LSTK (Line Sync Timing of K) and LSTC (Line Sync), respectively. Held as Timing of C). In addition, the time difference between the SOS signals is held as SDTKC (Same Direction Timing of K and C). Hereinafter, LSTK, LSTC, and SDTKC in the initial state are referred to as OLD_LSTK, OLD_LSTC, and OLD_SDTKC, respectively.

  Here, as shown in FIG. 6B, when the output of the SOS signal from the C color SOS sensor 40C is shifted by Δ seconds, the writing position of the laser beam corresponding to the C color changes. Here, when the changed writing position is not corrected at all, a color shift of Δ seconds occurs.

  At this time, since the value of SDTKC changes, the data register 66 calculates the amount of SDTKC fluctuation corresponding to Δ from the value before and after fluctuation of SDTKC, and the line sync counter 70K corresponding to K color By correcting the count value, the color shift is eliminated.

  Here, if the SDTKC when the SOS signal output from the SOS sensor 40C of laser light corresponding to the C color is displaced with a delay is NEW_SDTKC, NEW_SDTKC is expressed by the following equation.

NEW_SDTKC = OLD_SDTKC + Δ
Therefore, the time (LCTC, LSTK) until the generation of the respective line sync signals corresponding to the C color and the K color is expressed as LSTC = OLD_LSTC
LSTK = NEW_LSTK = OLD_LSTK + Δ
By doing so, the print image writing position can be aligned.

On the other hand, when the output of the C color SOS signal advances and is displaced (time interval decreases),
NEW_SDTKC = OLD_SDTKC−Δ
Therefore, the time from the output of the SOS signal of each color to the generation of the line sync signal is expressed as LSTC = OLD_LSTC
LSTK = NEW_LSTK = OLD_LSTK−Δ
By doing so, it is possible to align the image writing position in the same way.

  Further, as shown in FIG. 6C, even when the output of the SOS signal from the K color SOS sensor 40K is shifted by Δ seconds, it is output from the line sync counter 70K corresponding to the K color in the same manner as described above. Correct the output timing of the line sync signal.

That is, when the output of the K color SOS signal advances and is displaced,
NEW_SDTKC = OLD_SDTKC + Δ
Therefore, the time from the output of the SOS signal of each color to the generation of the line sync signal is
LSTC = OLD_LSTC
LSTK = NEW_LSTK = OLD_LSTK + Δ
By doing so, the print image writing position can be aligned.

When the output of the K color SOS signal is displaced with a delay (time interval is reduced),
SDTKC = NEW_SDTKC = OLD_SDTKC−Δ
Therefore, the time from the output of the SOS signal of each color to the generation of the line sync signal is
LSTC = OLD_LSTC
LSTK = NEW_LSTK = OLD_LSTK−Δ
By doing so, the print image writing position can be aligned.

  Further, as shown in FIG. 4D, the output of the C color and K color SOS signals may fluctuate simultaneously. Even in this case, since the variation of SDTKC is the amount of color misregistration, the output timing of the line sync signal of the line sync counter for the reference color is corrected by the variation of SDTKC.

Therefore, when the output of the K color SOS signal is displaced with a delay from the output of the C color SOS signal (the time interval increases),
NEW_SDTKC = OLD_SDTKC + Δ
The time from the generation of the SOS signal of each color to the generation of the line sync signal is expressed as LSTC = OLD_LSTC
LSTK = NEW_LSTK = OLD_LSTK + Δ
When the output of the K color SOS signal is displaced with respect to the output of the C color SOS signal (the time interval is reduced), the sign of the shift amount is changed,
LSTC = OLD_LSTC
LSTK = NEW_LSTK = OLD_LSTK−Δ
And Thereby, the output timing of the line sync signal is corrected.

  The Y color and the M color are corrected in the same manner as described above.

  Next, a process for correcting misalignment between laser beams performed by the data register 66 in which the scanning direction is different will be described with reference to FIG.

  FIG. 7 also shows print images at each timing in (1) to (6) of the timing chart.

  In the initial state, as shown in (1) and (2), the output timing of the C color SOS signal coincides with the output timing of the SOS signal corresponding to the M color, and the print image corresponding to the C color is written out. The position coincides with the writing position of the print image corresponding to the M color. Here, the time interval from the output timing of the SOS signal corresponding to the M color to the output timing of the EOS signal is referred to as DDSETM (Different Direction Sos to Eos Time of M). Hereinafter, DDSETM in the initial state is referred to as OLD_DDSETM.

  (3) to (5) in FIG. 7 are timing charts when the position of the pickup mirror or the like common to the C color and the M color is changed, and the pickup mirror on the SOS sensor side corresponding to the M color is also changed. is there. Due to the effect of the common structure of the pickup mirror described above, the output timing of the EOS signal of the EOS sensor 41M on the M color side changes by the same amount as ΔC, which is the deviation of the reference color C, as shown in (3).

  On the other hand, the output timing of the SOS signal output from the SOS sensor 40M corresponding to the M color varies independently of these and changes by ΔM. In this case, as shown in (3), since the output timing of the SOS signal corresponding to the C color advances and the print image writing position corresponding to the C color is displaced, the print image corresponding to the C color is written out. It is shifted by ΔC in the direction (left direction). In addition, since the scanning direction of the laser beam corresponding to the M color is opposite to the scanning direction of the laser beam corresponding to the C color, the print image corresponding to the M color is written at the writing position corresponding to the M color. It is shifted by ΔM in the direction (right direction). Therefore, in order to match the side registration of the print image corresponding to the C color and the print image corresponding to the M color, the output timing of the SOS signal corresponding to the M color is corrected so as to be shifted by ΔC + ΔM in the left direction.

Here, assuming that DDSETM after the change from the initial state is NEW_DDSETM, the change in the print image writing position by the pickup mirror that reflects the laser beam corresponding to M color to the SOS sensor 40M corresponding to M color is displayed in NEW_DDSETM. ΔM, and ΔC, which is the amount of change in the print image writing position by the common pickup mirror of the C color SOS sensor 40C on the EOS sensor 41M side, is included, so the difference from OLD_DDSETM, DDTM (Different Direction Time of M)
DDTM = NEW_DDSETM-OLD_DDSETM = ΔM + ΔC
It becomes. This corresponds to a deviation amount of the print image writing position corresponding to the M color.

  Therefore, this result is reflected in the correction of the M line sync signal generation timing.

If the C color does not change, the correction method by monitoring the time interval between the SOS sensors, which is the basis of the registration correction, may be applied to the C color and the M color. However, whether or not the C color has changed is corrected. It is necessary to monitor when performing the process, which makes the process extremely complicated. Even if this determination process is not performed, if the variation of DDSETM is monitored, it can be automatically corrected. That is, in the correction based on the SOS to EOS time of M color, ΔC becomes zero if C color does not change.
DDTM = NEW_DDSETM-OLD_DDSETM = ΔM
Thus, only ΔM is corrected. Accordingly, it is possible to automatically correct by ΔM without monitoring ΔC.

  In the present embodiment, the line sync signal generation timing is further corrected by correcting the correction value calculated in the data register 66 with the magnification error due to the magnification fluctuation and calculating the final correction value as described above. Correct the misalignment.

  Normally, when magnification correction is performed by controlling the frequency of the image signal, the image is corrected so that the image expands (or contracts) from the writing side to the writing end side. growing).

  Regarding correction between light beams scanned in the same direction, if the reference side write position is aligned with the reference side light beam start position, the magnification of the reference side original image is corrected to match the reference color. In addition, since both writing end positions are aligned, if the writing positions are aligned as described above, the writing end positions can be aligned when the magnification is corrected.

  However, with respect to correction between light beams scanned in different directions, if the correction value calculated above is used, as shown in FIG. 24, the writing position of the reference side light beam and the light beam on the reference side are displayed. Since the writing end position of the light beam on the reference side that scans in the opposite direction is aligned, there is a further misalignment when the magnification of the original image on the reference side is corrected to match the reference color. End up. Therefore, when correcting the positional shift due to magnification fluctuation, it is necessary to align the writing end position of the reference side light beam and the writing position of the reference side light beam that scans in the direction opposite to the reference side light beam. There is.

  In the following, a description will be given of a misregistration correction process in consideration of misregistration due to magnification fluctuation. Here, as a representative example, correction of positional deviation between the reference color C and the reference color M will be described.

  First, a pair of misregistration detection patterns as shown in FIGS. 8A and 8B is formed at both ends in the width direction of the transfer belt 18A. The misregistration detection unit 50 reads the pair of misregistration detection patterns formed on the transfer belt 18A, and calculates misregistration amounts of other colors with respect to the reference color from conversion of the pattern transit time for each color. . The amount of positional deviation is output to the main control circuit 68.

  The main control circuit 68 calculates magnification information for each color with respect to the reference color based on the positional deviation amount, and outputs it to the magnification error calculation unit 80.

  The magnification error calculator 80 calculates a correction value based on the magnification information. Here, the time interval OLD_DDSETM in the initial state from the output of the M color SOS signal to the output of the EOS signal is multiplied by the calculated magnification fluctuation amount to obtain a correction value (magnification error) MAG_ERR due to the magnification fluctuation of the M color. Ask for.

The magnification error MAG_ERR is subtracted from the DDTM to obtain a final correction value. That is, the final correction value in the laser beam whose scanning direction is the reverse direction is
DDTM = NEW_DDSETM − OLD_DDSETM − MAG_ERR
It becomes.

  Based on this DDTM, the magnification error calculation unit 80 sets the M line sync signal generation timing (LSTM) and outputs the set value to the line sync counter 70M.

  FIG. 9 is an explanatory diagram showing a correction state when the misregistration is corrected as described above for the C and M colors whose scanning directions are contradictory.

  FIG. 9A shows a state in which there is no positional deviation between the two colors of C and M. Here, as shown in FIG. 9B, when different amounts of magnification variation occur in the two colors of C and M, the MAG_ERR is calculated as described above to correct the line sync signal generation timing. As a result, as shown in FIG. 9C, the M color writing position is shifted to the left side (scanning end side) by just the C color position shift amount (DTC) from the original writing position (see FIG. 9A). In this state, the C color writing end position and the M color writing end position are corrected so as to coincide with each other.

  As shown in FIG. 9C, the M color writing end position and the C color writing start position cause a color shift due to the difference in magnification variation between the M color and the C color. MAG_ERR is output to the image processing circuit 72, and the image processing circuit 72 corrects the magnification of the reference color M so that the color shift corresponding to MAG_ERR is eliminated. The position and the C color export position also match. Note that the magnification correction process in the case of correcting the positional deviation between the laser beams having the same scanning direction is performed in the same manner.

  In this way, by correcting the magnification in accordance with the writing start position of the reference color in accordance with the writing end position of the reference color, a high-quality image with no positional deviation can be obtained.

  The image processing circuit 72 performs magnification correction by changing the frequency of the print data to be output in accordance with the magnification error (MAG_ERR) calculated by the magnification error calculation unit 80. By this magnification correction, the C color is corrected. There is a case where the writing end position and the M writing start position are shifted.

  FIG. 10A is a diagram showing an M color print image at the time when the line sync signal generation timing is corrected as shown in FIG. 9C. The M color writing position is corrected to a state shifted to the left side from the original writing position by the C color position shift amount (DTC). In this state, magnification correction is performed for the M color of the reference color. For example, when the image is expanded α times, the M color start position is also shifted to the left by DTC ′ that is α times the original start position. End up. Therefore, the magnification error calculation unit 80 calculates the difference between DTC and DTC ′ in advance so that the M color writing position matches the C color writing position after the magnification correction, and the difference is subtracted from the DDTC. The obtained value may be obtained as a final correction value. As a result, the positional deviation can be corrected more accurately. If the amount of DTC is small, the writing position does not vary greatly even if the magnification is corrected, and thus such correction can be omitted.

  As described above, the misalignment detection unit 50 is provided, and the correction information for correcting the misalignment is calculated by calculating the magnification information from the detected misalignment amount. In addition, it is possible to form a high-quality image by correcting misalignment due to magnification fluctuation.

  In the above-described embodiment, the case where the image processing circuit 72 corrects the magnification by changing the output frequency of the print data has been described. However, the present invention is not limited to this, and the magnification correction is performed by the phase shift of the output clock of the print data. You may do it.

  In the above-described embodiment, the case where the image processing circuit 72 corrects the magnification based on the magnification error calculated according to the detection result of the positional deviation detection unit 50 has been described. A temperature sensor that measures the temperature of the image forming apparatus is provided separately from the misregistration detection unit 50, and a variation amount of the magnification is obtained from the temperature measured by the temperature sensor, and the image processing circuit 72 is based on the variation amount of the magnification. You may make it perform magnification correction.

  In the above-described embodiment, the example in which the positional deviation detection pattern formed on the transfer belt 18A is read to calculate the positional deviation amount has been described. However, the positional deviation detection pattern formed on the recording medium is read. Thus, the amount of positional deviation may be calculated.

  As a modification of the configuration of the SOS sensor, the EOS sensor, and the pickup mirror according to the present embodiment shown in FIG. 3, as shown in FIG. 11, laser light having the same scanning direction is used as a common sensor. (40CK, 41YM) may be detected. This example is an integral type using a holder 39A as shown in FIG. 3B, but each pickup mirror 38M, 38C is set at a predetermined angle so that two laser beams are incident on one sensor. It is designed to be installed with an inclination of minutes. By comprising in this way, the number of sensors can be reduced and cost reduction can be achieved. In the case of this modification, if laser light is incident at the same time, it may not be possible to determine which color of the laser light is. It is necessary to provide a slight offset in the incident angle to the mirror 22 so that the sensor is incident in time series. Further, it is necessary to provide separation circuits 78A to 78C for separating the sensor signal outputs so as to be convenient for subsequent processing. FIG. 12 shows a schematic configuration of the regicon unit in this case.

[Second Embodiment]
In the present embodiment, a case will be described in which a temperature sensor is provided in the image forming apparatus and a correction process is performed by obtaining a magnification from a measurement value measured by the temperature sensor.

  The schematic configuration of the image forming apparatus of the present embodiment is a configuration in which the positional deviation detection unit 50 is omitted from the image forming apparatus 10 shown in FIG. 1 of the first embodiment and a temperature sensor 52 is provided. Illustration and description are omitted.

  FIG. 13 is a schematic diagram of the registration control unit (resin control unit) of the present embodiment. In FIG. 13, the same or equivalent parts as those in FIG. 5 of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 13, a temperature sensor 52 is connected to the main control circuit 68 instead of the misregistration detection unit 50, and the measurement result of the temperature sensor 52 that measures the internal temperature of the image forming apparatus is input to the main control circuit 68. It is the composition which is done.

  A magnification table 54 is connected to the main control circuit 68. The magnification table 54 stores in advance the amount of change in scanning magnification with respect to temperature for each color. The main control circuit 68 calculates the change amount (magnification information) of the magnification of the image by the laser light emitted from each laser diode 30 based on the measurement value measured by the temperature sensor 52 and the magnification table 54. The magnification error calculation unit 80 calculates a magnification error from the magnification information. The calculated magnification error is used to correct the line sync signal generation timing of the line sync counters 70Y to 70K, and is output to the image processing circuit 72 to be used for magnification correction.

  Next, the misregistration correction process in the present embodiment will be described.

  As for the misregistration correction without taking the magnification fluctuation into consideration, the correction between the laser beams in the same scanning direction and the correction between the laser beams in the opposite directions are the same as those in the first embodiment (FIGS. 6 to 7). Therefore, explanation is omitted.

In the present embodiment, the final correction value in consideration of the positional deviation due to the magnification variation between the laser beams whose scanning directions are opposite to each other is obtained as follows. Here, as a representative example, correction of positional deviation between the reference color C and the reference color M will be described. (Note that the correction between the laser beams in the same scanning direction does not require the following correction because the writing positions of the two are aligned.)
Usually, the variation in magnification depends on the temperature change around the scanning exposure apparatus 11. Therefore, in this embodiment, the positional deviation is corrected using the temperature measurement result of the temperature sensor 52.

  First, the time interval from the output of the SOS signal in the initial state of M color (the state without color misalignment) to the output of the EOS signal is OLD_DDSETM. The time interval until output is NEW_DDSETM.

The difference DTM between the time interval OLD_DDSETM from the output of the SOS signal to the output of the EOS signal and the time interval NEW_DDSETM from the output of the SOS signal to the output of the EOS signal in the state where the magnification fluctuation occurs is
DTM = OLD_DDSETM − NEW_DDSETM
It can be expressed as.

Note that DTM is a displacement amount including a displacement amount due to M-color side registration variation and a displacement amount due to magnification variation. Therefore, if the misregistration amount due to M-color side registration variation is DTM_SIDE and the misregistration amount due to magnification variation is DTM_MAG,
DTM = DTM_SIDE + DTM_MAG
It can be expressed as.

  Here, the main control circuit 68 obtains the change amount of magnification (magnification information) with respect to the temperature based on the measurement result of the temperature sensor 52 and the magnification table 54 in order to eliminate the influence of DTM_MAG.

  From this magnification information, the magnification error calculation unit 80 calculates a correction value (magnification error) MAG_ERR) due to magnification fluctuation. This correction value can be obtained in the same manner as in the first embodiment.

The final correction value is obtained by subtracting the magnification error MAG_ERR from the DTM. That is, the final correction value in the laser beam whose scanning direction is the reverse direction is
DTM = DTM_SIDE + DTM_MAG − MAG_ERR
It becomes.

  Based on this DTM, the magnification error calculation unit 80 newly sets an M color line sync signal generation timing (LSTM) and outputs the set value to the line sync counter 70M.

  As described above, as described with reference to FIG. 9 in the first embodiment, the M color writing position matches the C color writing end position.

  Similar to the first embodiment, even if the M color writing position and the C color writing end position coincide with each other, the M color writing end position and the C color writing position are the magnifications of the M color and the C color. The color difference of the variation difference occurs. This color shift is equal to MAG_ERR. Therefore, MAG_ERR is output to the image processing circuit 72, and the image processing circuit 72 uses the M color as the reference color based on MAG_ERR. By executing the magnification correction, the end position of the M color and the start position of the C color coincide with each other.

  Further, in consideration of the variation in the M color writing position after the magnification correction, as described with reference to FIG. 10 in the first embodiment, the variation is calculated in advance and the M color is corrected after the magnification correction. The final correction value may be calculated such that the writing position of the color coincides with the writing position of the C color.

  As described above, the temperature sensor 52 is provided, and the correction value for correcting the positional deviation is calculated by calculating the magnification from the temperature measurement result. Therefore, not only the positional deviation caused by the side registration fluctuation but also the position caused by the magnification fluctuation. A high quality image can be formed by correcting the shift.

  In the above-described embodiment, the case where the image processing circuit 72 corrects the magnification by changing the output frequency of the print data has been described. However, the present invention is not limited to this, and the magnification correction is performed by the phase shift of the output clock of the print data. You may do it.

  Also in this embodiment, as a modification of the configuration of the SOS sensor, the EOS sensor, and the pickup mirror according to this embodiment, as shown in FIG. You may make it detect with a sensor (40CK, 41YM). FIG. 14 shows a schematic configuration of the regicon unit in this case.

[Third Embodiment]
In this embodiment, as shown in FIG. 15, the M-color and Y-color EOS sensors are omitted, and instead, C-color and K-color EOS sensors 40C and 40K are provided to perform misalignment correction. In this embodiment, the misregistration of the M color is corrected using the SOS signal and EOS signal on the C color side, which is the reference color, and the SOS signal of the M color.

  The schematic configuration of the image forming apparatus of the present embodiment is a configuration in which the positional deviation detection unit 50 is omitted from the image forming apparatus 10 shown in FIG. 1 of the first embodiment and a temperature sensor 52 is provided. Illustration and description are omitted.

  The configuration of the scanning exposure apparatus 11 includes a pickup mirror for reflecting laser light toward the C-color EOS sensor 41C and a pickup mirror for reflecting laser light toward the M-color SOS sensor 40M. As shown in FIG. 16, the pickup mirrors 38C and 38M are respectively held by a common holder 39, and are configured to function as a unit. Moreover, it is good also as a structure provided with one common pick-up mirror. In FIG. 16, the laser beam having the same scanning direction is detected by a common sensor (40YM, 41CM).

  Further, as shown in FIG. 17, the magnification error calculation unit 80 is not provided in the register unit of the present embodiment, and the correction value output from the data register 66 is directly input to the line sync counters 70Y to 70K. Further, the temperature sensor 52 is connected to the main control circuit 68, and the measurement result of the temperature sensor 52 that measures the internal temperature of the image forming apparatus is input to the main control circuit 68. In the present embodiment, the main control circuit 68 calculates the magnification error and outputs it to the image processing circuit 72.

  The positional deviation correction process between laser beams whose scanning directions are the same is the same as that in the first embodiment, and thus the description thereof will be omitted. Here, the positional deviation correction process between laser beams whose scanning directions are opposite to each other is omitted. Will be described in detail by taking C color (reference color) and M color (reference color) as examples. The following processing is performed by the data register 66.

  The time interval from the output of the SOS signal to the output of the EOS signal in the initial state of C color (state without color misalignment) is OLD_DDSETC, and the time interval from the output of the SOS signal to the output of the EOS signal when color misregistration occurs NEW_DDSETC.

The difference DTC between the time interval OLD_DDSETC from the output of the SOS signal to the output of the EOS signal and the time interval NEW_DDSETC from the output of the SOS signal to the output of the EOS signal in the state where the magnification fluctuation occurs is
DTC = OLD_DDSETC − NEW_DDSETC
It can be expressed as.

Note that DTC is a misalignment amount including a misalignment amount due to a C color side registration variation and a misalignment amount due to a magnification variation. Therefore, if the misregistration amount due to C-color side registration variation is DTC_SIDE and the misregistration amount due to magnification variation is DTC_MAG,
DTC = DTC_SIDE + DTC_MAG
It can be expressed as.

  Since DTC is the displacement amount of the C color writing end position, in order to match the C color writing end position with the M color writing position, this DTC is used as it is as a correction value for the M color writing position. That's fine. By correcting the M color writing position with DTC (that is, correcting the line sync signal generation timing with DTC), as shown in FIG. 9C, the M color writing position and the C color writing end position are set. Can be matched.

  In the present embodiment, the correction value (magnification error) MAG_ERR due to the magnification variation is not obtained in the correction of the line sync signal generation timing, but the magnification correction process performed in the image processing circuit 72 requires a magnification error. Therefore, as in the second embodiment, the main control circuit 68 obtains the magnification change amount from the measurement value of the temperature sensor 52, obtains the magnification error (MAG_ERR) from the magnification change amount, and the image processing circuit. 72. The image processing circuit 72 performs magnification correction based on MAG_ERR, thereby matching the writing end position of the M color with the writing start position of the C color.

  Further, in consideration of the variation in the M color writing position after the magnification correction, as described with reference to FIG. 10 in the first embodiment, the variation is calculated in advance and the M color is corrected after the magnification correction. The correction value may be calculated so that the writing position of the color coincides with the writing position of the C color.

  Even with the configuration as described above, it is possible to correct not only the positional deviation due to the side registration fluctuation but also the positional deviation due to the magnification fluctuation, and form a high-quality image.

  Also in this embodiment, as a modification of the configuration of the SOS sensor, the EOS sensor, and the pickup mirror according to this embodiment, as shown in FIG. You may make it detect with a sensor (40CK, 41YM). A schematic configuration of the regicon unit in this case is shown in FIG.

  Further, in the present embodiment, the displacement detector 50 provided in the first embodiment is provided in place of the temperature sensor 52, and the displacement is detected by the displacement detector 50 to obtain the scanning magnification. The magnification error output to the image processing circuit 72 may be calculated.

[Fourth Embodiment]
In this embodiment, the EOS sensors provided for only the M and Y colors in the first embodiment are provided for the C and K colors, and the SOS signal and the EOS signal are provided for all colors. An image processing circuit configured to be obtained and correcting misregistration will be described as an example.

  The schematic configuration of the image forming apparatus according to the present embodiment is a configuration in which the misregistration detection unit 50 is omitted from the image forming apparatus 10 illustrated in FIG. 1 according to the first embodiment, and thus illustration and description thereof are omitted.

  FIG. 19 is a diagram showing an outline of the scanning exposure apparatus 11 in the present embodiment. As shown in FIG. 19, SOS sensors 40C and 40K are arranged in the vicinity of the scanning start position in the main scanning direction (arrows C and K in FIG. 2) of the laser light corresponding to the C color and the K color, EOS sensors 41C and 41K are disposed in the vicinity of the scanning end position. Further, in the main scanning directions (arrows Y and M in FIG. 2) of the laser beams corresponding to the Y color and the M color, SOS sensors 40Y and 40M are arranged in the vicinity of the scanning start position, and in the vicinity of the scanning end position. Are respectively provided with EOS sensors 41Y and 41M.

  A pickup mirror for reflecting laser light toward the C-color SOS sensor 40C and a pickup mirror for reflecting laser light toward the M-color EOS sensor 41M are provided in a common holder. It is hold | maintained and it comprises so that it may function as integral (for example, refer FIG. 3). In addition, a pickup mirror for reflecting the laser beam toward the C-color EOS sensor 41C and a pickup mirror for reflecting the laser beam toward the M-color SOS sensor 40M are provided in a common holder. Each is held and configured to function as a unit (see, for example, FIG. 16).

  Instead of providing each pickup mirror on a common holder, a configuration may be adopted in which one common pickup mirror is provided.

  FIG. 20 is a schematic diagram of a registration control unit (resin control unit) of the present embodiment. In FIG. 20, the same or equivalent parts as those in FIG. 5 of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  In this embodiment, the magnification error calculator 80 is not provided upstream of the line sync counters 70Y to 70K as in the first embodiment, and the correction value output from the data register 66 is directly applied to the line sync counter 70Y. It is configured so that it is input to ~ 70K. Furthermore, a magnification error calculation unit 56 is provided in the main control circuit 68. The magnification error calculator 56 calculates a magnification error from the time difference between the SOS signal and the EOS signal measured by the register control counter 64.

  The positional deviation correction process between laser beams whose scanning directions are the same is the same as that in the first embodiment, and thus the description thereof will be omitted. Here, the positional deviation correction process between laser beams whose scanning directions are opposite to each other is omitted. Will be described in detail by taking C color (reference color) and M color (reference color) as examples. The following processing is performed by the data register 66.

  The time interval from the output of the SOS signal to the output of the EOS signal in the initial state of C color (state without color misalignment) is OLD_DDSETC, and the time interval from the output of the SOS signal to the output of the EOS signal when color misregistration occurs NEW_DDSETC.

  The time interval from the output of the SOS signal in the initial state of M color (the state without color misalignment) to the output of the EOS signal is OLD_DDSETM, and the time from the output of the SOS signal to the output of the EOS signal when the color misregistration occurs Let the interval be NEW_DDSETM.

Further, the difference DTC between the time interval OLD_DDSETC from the output of the SOS signal to the output of the EOS signal in the C color and the time interval NEW_DDSETC from the output of the SOS signal to the output of the EOS signal in the state where the magnification change occurs is
DTC = OLD_DDSETC − NEW_DDSETC
It can be expressed as.

Further, the difference DTM between the time interval OLD_DDSETM from the output of the SOS signal to the output of the EOS signal in the M color and the time interval NEW_DDSETM from the output of the SOS signal to the output of the EOS signal in the state where the magnification change occurs is
DTM = OLD_DDSETM − NEW_DDSETM
It can be expressed as.

Here, the amount of misregistration due to side registration variation of C color is DTC_SIDE, the amount of misregistration due to variation in magnification is DTC_MAG, the amount of misregistration due to side registration variation of M color is DTM_SIDE, and the amount of misregistration due to variation in magnification is DTM_MAG.
DTM = DTM_SIDE + DTM_MAG
DTC = DTC_SIDE + DTC_MAG
It can be expressed as.

  However, the pickup mirror that guides the laser beam to the M color SOS sensor 40M and the C color EOS sensor 41C is held by a common holder or integrally formed as described above, and the M color EOS sensor. The pickup mirror for guiding the laser light to the 41M and C color SOS sensors 40C is held by a common holder or integrally formed. Therefore, the amount of misregistration DTM_SIDE due to M color side registration fluctuation and the amount of misregistration DTC_SIDE due to C color side registration fluctuation are the same.

  That is, DTM_SIDE = DTC_SIDE.

  Since DTC is the displacement amount of the C color scanning end position, in order to make the C color writing end position coincide with the M writing start position, this DTC is directly used as the correction value for the M writing start position. May be used. By correcting the M color writing position with DTC (that is, correcting the line sync signal generation timing with DTC), as shown in FIG. 9C, the M color writing position and the C color writing end position are set. Can be matched.

  On the other hand, the magnification error calculator 56 calculates DTC and DTM from the OLD_DDSETC, NEW_DDSETC, OLD_DDSETM, and NEW_DDSETM input from the register control counter 64 in the same manner as described above. Here, the difference between the positional deviation amount DTC_MAG due to the magnification variation included in the DTC and the positional deviation amount DTM_MAG due to the magnification variation included in the DTM is calculated as the magnification error MAG_ERR. That is, the magnification error MAG_ERR is expressed by the following equation.

MAG_ERR = DTM-DTC = DTM_MAG-DTC_MAG
Since the writing end position of the M color and the writing start position of the C color are shifted by the magnification error MAG_ERR, the main control circuit 68 uses a predetermined function equation based on the magnification error MAG_ERR to eliminate the deviation. A color magnification correction value is calculated, and the magnification correction value is output to the image processing circuit 72. The image processing circuit 72 performs magnification correction based on the magnification correction value, whereby the M color writing end position matches the C color writing start position.

  In consideration of the variation in the M color writing position after the magnification correction, as described with reference to FIG. 10 in the first embodiment, the variation is calculated in advance and the M color is corrected after the magnification correction. The M color writing position may be corrected so that the writing position of C matches the writing position of the C color.

  Even with the configuration as described above, it is possible to correct not only the positional deviation due to the side registration fluctuation but also the positional deviation due to the magnification fluctuation, and form a high-quality image.

  Also in this embodiment, as a modified example of the configuration of the SOS sensor, the EOS sensor, and the pickup mirror according to this embodiment, as shown in FIG. 11, a laser beam having the same scanning direction is shared. You may make it detect with a sensor (40CK, 41YM). FIG. 21 shows a schematic configuration of the regicon unit in this case.

1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment. It is a schematic block diagram of the scanning exposure apparatus of 1st Embodiment. (A) is a schematic diagram of an arrangement configuration of a pickup mirror, an SOS sensor, and an EOS sensor, and (B) is a schematic configuration of another example of the arrangement configuration shown in (A). (A) is a figure for demonstrating the mode of an installation position change of a pick-up mirror, a SOS sensor, and an EOS sensor, (B) is for demonstrating the mode of a change of the SOS signal accompanying the position change of (A). It is a timing chart. It is a schematic block diagram of the registration control part of 1st Embodiment. It is a timing chart explaining a correction process for side registration deviation between laser beams scanned in the same direction. It is a timing chart explaining a correction process for side registration deviation between laser beams scanned in different directions. It is an example of the pattern for position shift detection. It is explanatory drawing which shows the correction | amendment state when position shift is correct | amended about C color and M color which the scanning directions contradict. When the fluctuation is calculated in advance in consideration of the fluctuation of the M color writing position after the magnification correction, and the M color writing position after the magnification correction is corrected so as to coincide with the writing end position of the C color. It is explanatory drawing which shows the correction state. It is the schematic which showed an example of the arrangement structure of a pick-up mirror, a SOS sensor, and an EOS sensor in the case of detecting the laser beam whose scanning direction is the same direction with a common sensor. It is a modification of the registration control part shown in FIG. It is a schematic block diagram of the registration control part of 2nd Embodiment. It is a modification of the registration control part shown in FIG. It is a schematic block diagram of the scanning exposure apparatus of 3rd Embodiment. It is the schematic of the arrangement configuration of the pick-up mirror, SOS sensor, and EOS sensor in 3rd Embodiment. It is a schematic block diagram of the registration control part of 3rd Embodiment. It is a modification of the registration control part shown in FIG. It is a schematic block diagram of the scanning exposure apparatus in 4th Embodiment. It is a schematic block diagram of the registration control part of 4th Embodiment. 21 is a modification of the registration control unit shown in FIG. It is the figure which showed schematic structure of the exposure apparatus (ROS) for forming an electrostatic latent image with a light beam. An example of the amount of misalignment due to fluctuations in the scanning magnification of each of the Y, M, C, and K exposure apparatuses with respect to the temperature rise is shown. FIG. 9 is an explanatory diagram illustrating a correction state when a positional deviation is corrected by a conventional image forming apparatus when the variation in scanning magnification of each color is the same for C and M colors having opposite scanning directions. FIG. 10 is an explanatory diagram illustrating a correction state when a positional deviation is corrected by a conventional image forming apparatus when the variation in scanning magnification of each color is different for C and M colors having opposite scanning directions.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Scan exposure apparatus 12 Photosensitive drum 18A Intermediate transfer belt 22 Rotating polygon mirror 24 Fixing device 26 Recording medium 30 Laser diode 38 Pickup mirror 39 Holder 40 SOS sensor 41 EOS sensor 50 Position shift detector 52 Temperature sensor 54 Magnification Table 56 Magnification Error Calculation Unit 60 Registration Control Circuit 64 Register Control Counter 66 Data Register 68 Main Control Circuit 70 Line Sync Counter 72 Image Processing Circuit 74 Laser Drive Circuit 80 Magnification Error Calculation Unit

Claims (5)

A plurality of light sources, a plurality of image bearing members, and provided with a rotary polygon mirror which rotates in a predetermined direction, the light beam emitted from each of the light source is modulated on the basis of different image signals several including one reference image signal Are deflected by the rotary polygon mirror, and light beams corresponding to a plurality of image signals including the reference image signal are applied to each of the image carriers corresponding to each of the image signals by a first main scanning. while scanning direction, by scanning the light beam corresponding to the remaining image signal, Previous Stories second main scanning direction of the first main scanning direction and the opposite direction, corresponding to each of said image signal the In an image forming apparatus for forming different original images on each of the image carriers and forming the images by multiply transferring the original images to the same transfer region,
A reflective surface for reflecting a reference light beam corresponding to the reference image signal deflected by the rotary polygon mirror and a reflective surface for reflecting at least one light beam scanned in the second main scanning direction are provided on one substrate. Or a first reflecting means provided in the vicinity of the scanning start position of the reference light beam and in the vicinity of the scanning end position of the at least one light beam;
First scanning start position detecting means for outputting a scanning start signal by detecting a reference light beam corresponding to the reference image signal reflected by the first reflecting means ;
A scanning end position detecting means for outputting a scanning end signal by detecting the at least one light beam reflected by the first reflecting means ;
Excluding the reference light beam corresponding to the reference image signal deflected by the rotary polygon mirror and reflecting each light beam including the at least one light beam near each scanning start position of each light beam. A plurality of second reflecting means provided in each;
A plurality of second scanning start position detecting means for outputting a scanning start signal by detecting each of the light beams reflected by the second reflecting means;
Magnification detection means for detecting a variation in magnification of the original image formed on each of the image carriers;
A magnification error calculating means for calculating a magnification error based on the magnification fluctuation detected by the magnification detecting means;
Based on the scanning start signal, control is performed so that the writing position of each original image by the light beam scanning in the same direction is aligned, and the scanning start signal of the light beam scanning in the second main scanning direction, the second Based on the scanning end signal of the light beam scanned in the main scanning direction and the magnification error, the original image writing position by the light beam scanning in the first main scanning direction and the second main scanning direction are scanned. The writing position of the original image by the light beam scanned in the second main scanning direction is controlled so that the writing end position of the original image by the light beam is aligned, and other than the reference original image based on the magnification error By correcting the magnification of each of the original images other than the reference original image so that the magnification of each of the original images becomes the magnification of the reference original image, the main image of the original image formed on each of the image carriers is corrected. How to scan And control means for controlling so that both ends of aligned,
An image forming apparatus. A plurality of light sources, a plurality of image bearing members, and provided with a rotary polygon mirror which rotates in a predetermined direction, the light beam emitted from each of the light source is modulated on the basis of different image signals several including one reference image signal Are deflected by the rotary polygon mirror, and light beams corresponding to a plurality of image signals including the reference image signal are applied to each of the image carriers corresponding to each of the image signals by a first main scanning. while scanning direction, by scanning the light beam corresponding to the remaining plurality of image signals, Previous Stories second main scanning direction of the first main scanning direction and the opposite direction, corresponding to each of the image signals In the image forming apparatus that forms different original images on each of the image carriers and forms the image by multiply transferring the original images to the same transfer region,
A reflective surface for reflecting a reference light beam corresponding to the reference image signal deflected by the rotary polygon mirror and a reflective surface for reflecting at least one light beam scanned in the second main scanning direction are provided on one substrate. Or a first reflecting means provided in the vicinity of the scanning end position of the reference light beam and in the vicinity of the scanning start position of the at least one light beam;
A first scanning start position detecting means for outputting a scanning start signal by detecting said reflected at least one light beam by the first reflecting means,
Scanning end position detecting means for outputting a scanning end signal by detecting a reference light beam corresponding to the reference image signal reflected by the first reflecting means ;
Excluding the at least one light beam deflected by the rotary polygon mirror and reflecting each light beam including the reference light beam corresponding to the reference image signal, the vicinity of each scanning start position of each light beam. A plurality of second reflecting means provided in each;
A plurality of second scanning start position detecting means for outputting a scanning start signal by detecting each of the light beams reflected by the second reflecting means;
Magnification detection means for detecting a variation in magnification of the original image formed on each of the image carriers;
A magnification error calculating means for calculating a magnification error based on the magnification fluctuation detected by the magnification detecting means;
Based on the scanning start signal, control is performed so that the writing position of each original image by the light beam scanned in the same direction is aligned, and the scanning start signal and scanning end signal of the light beam scanned in the first main scanning direction are used. Based on this, the second image writing position by the light beam scanning in the first main scanning direction is aligned with the writing end position of the original image by the light beam scanning in the second main scanning direction. The writing position of the original image by the light beam scanned in the main scanning direction is controlled, and the magnification of each of the original images other than the reference original image is the magnification of the reference original image based on the magnification error. Control means for controlling the both ends of the original image formed on each of the image carriers to be aligned in the main scanning direction by correcting the magnification of each of the original images other than the reference original image ;
An image forming apparatus. The magnification detection means includes
A misregistration detecting means for detecting a misregistration amount from a plurality of misregistration detection patterns formed in the same transfer region by scanning in the first and second main scanning directions;
The image forming apparatus according to claim 1, wherein a magnification variation of an original image formed on each of the image carriers is detected based on a positional shift amount detected by the positional shift detection unit. The magnification detection means includes
Temperature detecting means for detecting the temperature in the apparatus,
The image forming apparatus according to claim 1, wherein a magnification variation of an original image formed on each of the image carriers is detected based on a temperature detected by the temperature detection unit. A plurality of light sources, a plurality of image bearing members, and provided with a rotary polygon mirror which rotates in a predetermined direction, the light beam emitted from each of the light source is modulated on the basis of different image signals several including one reference image signal Are deflected by the rotary polygon mirror, and light beams corresponding to a plurality of image signals including the reference image signal are applied to each of the image carriers corresponding to each of the image signals by a first main scanning. while scanning direction, by scanning the light beam corresponding to the remaining plurality of image signals, Previous Stories second main scanning direction of the first main scanning direction and the opposite direction, corresponding to each of the image signals In the image forming apparatus that forms different original images on each of the image carriers and forms the image by multiply transferring the original images to the same transfer region,
A reflective surface for reflecting a reference light beam corresponding to the reference image signal deflected by the rotary polygon mirror and a reflective surface for reflecting at least one light beam scanned in the second main scanning direction are provided on one substrate. Or a first reflecting means provided in the vicinity of the scanning start position of the reference light beam and in the vicinity of the scanning end position of the at least one light beam;
First scanning start position detecting means for outputting a scanning start signal by detecting a reference light beam corresponding to the reference image signal reflected by the first reflecting means ;
First scanning end position detecting means for outputting a scanning end signal by detecting the at least one light beam reflected by the first reflecting means ;
A reflective surface that reflects a reference light beam corresponding to the reference image signal deflected by the rotating polygon mirror and a reflective surface that reflects the at least one light beam are provided on or integrally formed on one substrate, and A second reflecting means provided near the scanning end position of the reference light beam and near the scanning start position of the at least one light beam;
Second scanning start position detecting means for outputting a scanning start signal by detecting the at least one light beam reflected by the second reflecting means;
Second scanning end position detecting means for outputting a scanning end signal by detecting a reference light beam corresponding to the reference image signal reflected by the second reflecting means ;
Each of the light beams except for the reference light beam corresponding to the reference image signal deflected by the rotating polygon mirror and the at least one light beam is reflected near each scanning start position. A plurality of provided third reflecting means;
A plurality of third scanning start position detecting means for outputting respective scanning start signals by detecting the respective light beams reflected by the third reflecting means;
Based on the scanning start signal, control is performed so that the writing position of each original image by the light beam scanned in the same direction is aligned, and the scanning start signal and scanning end signal of the light beam scanned in the first main scanning direction are used. On the basis of this, the second end position of the original image by the light beam scanning in the first main scanning direction is aligned with the start position of the original image by the light beam scanning in the second main scanning direction. An output time interval between a scanning start signal and a scanning end signal of the light beam that controls the writing position of the original image by the light beam that scans in the main scanning direction, and that scans in the first main scanning direction, and the second Based on the output time interval between the scanning start signal and the scanning end signal of the light beam scanned in the main scanning direction, the magnification of each of the original images other than the reference original image becomes the magnification of the reference original image. Base By correcting the respective magnification of the original image other than the original image, and control means for controlling so that the main scanning direction across the original image to be formed on each of the image bearing member are aligned,
An image forming apparatus.

Images