JP5309477B2 - Optical scanning apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to an exposure apparatus that performs optical writing in an image forming apparatus such as a printer or a copying machine.

  2. Description of the Related Art An electrophotographic color image forming apparatus such as a printer or a copying machine is known in which a photosensitive drum and an exposure device are arranged for each color. In such a color image forming apparatus, each exposure device scans and exposes each photosensitive drum with a laser beam modulated in accordance with image data for each color, and therefore the exposure position on the photosensitive drum in each exposure device is set. It is necessary to set in advance with high accuracy. Therefore, the exposure position on the photosensitive drum in each exposure apparatus is adjusted in the manufacturing process (for example, refer to Patent Document 1).

JP 2005-156914 A

  By the way, in a color image forming apparatus, a detection image is formed on a recording medium such as a recording sheet, and alignment correction (color registration correction) is performed at the detection timing of the detection image. That is, patch images (in which patches are formed in a row) are formed as detection images at both ends along the recording sheet conveyance direction, and the writing position is corrected based on this detection timing. Since such alignment correction is performed at a predetermined timing based on an empirical rule or the like, it may be performed even if the positional deviation does not actually occur, and the positional deviation occurs. Even if it is, it may not be done.

  An object of the present invention is to provide an optical scanning device and an image forming apparatus that detect the occurrence of a writing position shift and perform alignment correction based on the detection result.

  An optical scanning device to which the present invention is applied includes a plurality of light sources, an optical system that forms an image of a light beam from the plurality of light sources on a scanned object, and a part of each of the light beams from the plurality of light sources. Measurement for measuring the width of a pulse output by the synchronization light receiving element to which each of the light beams when the plurality of light sources emit light is incident, and the synchronization light receiving element that is incident every time the scanned object is scanned And correction means for correcting the alignment of the light beam based on the measurement result of the measurement unit.

  Here, it may further include an instruction unit that instructs the correction unit to start alignment correction when a measurement result by the measurement unit exceeds a predetermined value. In addition, it further includes a specifying unit that controls lighting of the plurality of light sources and specifies a light beam to be corrected by a combination of light beams incident on the synchronization light receiving element, and the correcting unit is specified by the specifying unit. It is possible to perform alignment correction on the light beam to be processed. In addition, it further includes a correction amount detection unit that controls lighting of the plurality of light sources and detects a correction amount by a combination of light beams incident on the synchronization light receiving element, and the correction unit includes the correction amount detection unit. It can be characterized by correcting the detected correction amount.

  An image forming apparatus to which the present invention is applied includes a plurality of image carriers, an exposure device that emits a plurality of light beams corresponding to the plurality of image carriers and scans and exposes the plurality of image carriers, and A detecting means for detecting misalignment between the plurality of light beams emitted from an exposure apparatus; and a correcting means for correcting alignment of the light beam based on a detection result of the detecting means, the detecting means comprising: A light receiving element for synchronization in which light in each non-image region of each of the plurality of light beams emitted from the exposure apparatus enters each time the plurality of image carriers are scanned; and one or more of the plurality of light beams And a measuring unit for measuring the width of a pulse obtained by being incident on the synchronizing light receiving element.

  Here, the detecting means may detect the presence or absence of a positional deviation based on a pulse width obtained by all of the plurality of light beams being incident on the synchronization light receiving element. The detecting means may detect a positional deviation amount based on a pulse width obtained when a predetermined combination of the plurality of light beams is incident on the synchronization light receiving element.

According to the first aspect of the present invention, it is possible to detect the occurrence of the write position deviation and perform the alignment correction based on the detection result. Further, it is possible to specify the color to be aligned and corrected during image formation.
According to the second aspect, it is possible to detect the occurrence of the write position deviation and perform the alignment correction based on the detection result. Further, it is possible to specify the color to be aligned and corrected during image formation.
According to claim 3 , it is possible to reduce the frequency of performing the alignment correction.
According to the fourth aspect of the present invention, it is possible to detect the occurrence of the write position deviation and perform the alignment correction based on the detection result. Further, it becomes possible to detect the correction amount to be aligned and corrected during image formation.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type digital color printer using an electrophotographic system. The image forming apparatus 1 includes an image forming process unit 70 that forms an image corresponding to the image data of each color, a control unit 80 that controls the operation of the entire image forming apparatus 1, and a personal computer (PC) 3 or a scanner, for example. An image processing unit 81 that performs predetermined image processing on the image data received from the image reading device 4 and the like, and a main storage unit 82 realized by, for example, a hard disk (Hard Disk Drive) in which processing programs, image data, and the like are stored. And.

In the image forming process unit 70, four image forming units 10Y, 10M, 10C, and 10K (hereinafter also collectively referred to as “image forming unit 10”) are arranged in parallel at regular intervals in the vertical direction (substantially vertical direction). . The image forming unit 10 develops a photosensitive drum 11 as an image holding member, a charging roll 12 that charges the surface of the photosensitive drum 11, and an electrostatic latent image formed on the photosensitive drum 11 with each color toner. A developing unit 13 and a drum cleaner 14 for cleaning the surface of the photosensitive drum 11 after transfer are provided.
Each image forming unit 10 is configured to be detachable from the main body of the image forming apparatus 1. For example, when the toner in the developing device 13 is consumed or the photosensitive drum 11 reaches the end of its life, It is exchanged in units of 10 image forming units.

The charging roll 12 is composed of a roll member in which a conductive elastic body layer and a conductive surface layer are sequentially laminated on a conductive metal core such as aluminum or stainless steel. Then, a charging bias voltage is supplied from a charging power source (not shown), and the surface of the photosensitive drum 11 is uniformly charged at a predetermined potential while being driven to rotate with respect to the photosensitive drum 11.
The developing device 13 holds a two-component developer composed of yellow (Y), magenta (M), cyan (C), and black (K) toners and a magnetic carrier in each of the image forming units 10, and is photosensitive. The electrostatic latent image formed on the body drum 11 is developed with each color toner.
The drum cleaner 14 brings a plate-like member formed of a rubber material such as urethane rubber into contact with the surface of the photosensitive drum 11 to remove toner, paper dust, and the like attached on the photosensitive drum 11.

Further, the image forming apparatus 1 of the present embodiment is provided with a laser exposure device 20 as an example of an exposure device that exposes the photosensitive drum 11 provided in each of the image forming units 10. The laser exposure device 20 acquires image data for each color from the image processing unit 81, and the laser light (light beam) controlled to be turned on based on the acquired image data, on the photosensitive drum 11 of each image forming unit 10. Are respectively subjected to scanning exposure.
Further, a paper transport belt 30 that transports the paper P that is a recording material (recording paper) is disposed so as to move in contact with the photosensitive drum 11 of each image forming unit 10. The paper transport belt 30 is formed of a film-like endless belt that electrostatically attracts the paper P. Then, a paper transport path M1 is formed that is stretched around the drive roll 32 and the idle roll 33 and circulates between the drive roll 32 and the idle roll 33, and transports the paper P from the lower side to the upper side in the substantially vertical direction. Yes.

Transfer rolls 31 are arranged at positions facing the respective photosensitive drums 11 inside the paper transport belt 30. Each transfer roll 31 forms a transfer electric field with the photosensitive drum 11, so that each color toner image formed by each image forming unit 10 is formed on the paper P held and transported by the paper transport belt 30. Transfer sequentially. Further, on the outer side of the paper conveying belt 30 and on the downstream side of each transfer roll 31, a static elimination lamp 35 that neutralizes the photosensitive drum 11 after the transfer is provided.
An adsorption roll 34 that charges the paper transport belt 30 is disposed at the most upstream portion of the paper transport belt 30 on the photosensitive drum 11 side. The surface of the paper transport belt 30 is electrostatically attracted to the paper P by being charged to a predetermined potential by the suction roll 34.
A fixing device 40 is provided on the downstream side of the paper transport belt 30 along the paper transport path M1 to perform a fixing process using heat and pressure on an unfixed toner image on the paper P.

Further, as a paper transport system other than the paper transport belt 30, a paper storage section 50 that stores the paper P and a paper P stored in the paper storage section 50 are taken out at a predetermined timing and transported to the paper feed side. A pickup roll 51, a conveyance roll 52 that conveys the paper P fed by the pickup roll 51, and a registration roll 53 that sends the paper P to the paper conveyance belt 30 in accordance with an image forming operation are provided.
On the other hand, on the paper discharge side, a paper discharge roll 54 that conveys the paper P fixed by the fixing device 40 is provided. Further, on the paper discharge side, in the case of single-sided printing, the paper P is discharged toward a paper discharge stacking unit 90 provided at the upper part of the apparatus main body, and in the case of double-sided printing, the paper discharge stacking unit 90 is at a predetermined timing. A reversing roll 55 is provided that feeds the paper P, one side of which has been fixed by the fixing device 40, toward the double-sided conveyance path M2 by reversing the rotation direction toward the reverse direction. In addition, the double-sided conveyance path M2 is provided with a plurality of conveyance rolls 56 along the double-sided conveyance path M2.

  In the image forming apparatus 1 of the present embodiment, the image forming process unit 70 performs an image forming operation under the control of the control unit 80. That is, the image data input from the PC 3 or the image reading device 4 is subjected to predetermined image processing by the image processing unit 81 and supplied to the laser exposure unit 20. For example, in the black (K) image forming unit 10 </ b> K, the surface of the photosensitive drum 11 uniformly charged at a predetermined potential by the charging roll 12 is based on the image data from the image processing unit 81 by the laser exposure unit 20. Then, scanning exposure is performed with the laser light whose lighting is controlled, and an electrostatic latent image is formed on the photosensitive drum 11. The formed electrostatic latent image is developed by the developing device 13, and a black (K) toner image is formed on the photosensitive drum 11. Similarly, in the image forming units 10Y, 10M, and 10C, yellow (Y), magenta (M), and cyan (C) toner images are formed.

On the other hand, when the formation of each color toner image in each image forming unit 10 is started, the paper P taken out from the paper container 50 is supplied to the paper transport belt 30 by the registration roll 53 in accordance with the toner image formation timing. Is done. The surface of the paper transport belt 30 is charged to a predetermined potential by the suction roll 34. As a result, the paper P is electrostatically attracted onto the paper transport belt 30 and is transported along the paper transport path M1 by the paper transport belt 30 that circulates and moves in the direction of the arrow in FIG. In the middle of the process, the color toner images are sequentially transferred onto the paper P by the transfer electric field formed by the transfer roll 31.
The sheet P on which each color toner image is electrostatically transferred is peeled from the sheet conveying belt 30 downstream of the image forming unit 10K and conveyed to the fixing device 40. When the paper P is conveyed to the fixing device 40, the unfixed toner image on the paper P is fixed to the paper P by receiving a fixing process using heat and pressure. The paper P on which the color toner images are fixed is stacked on a paper discharge stacking unit 90 provided in a discharge unit of the image forming apparatus 1. On the other hand, during double-sided printing, the same image forming operation is performed again via the double-sided conveyance path M2, and then the paper is stacked on the paper discharge stacking unit 90.

Next, the laser exposure device 20 of the present embodiment will be described.
FIG. 2 is a side view illustrating a schematic configuration of the laser exposure device 20 of the present embodiment. As shown in FIG. 2, the laser exposure device 20 includes a light source 21 composed of, for example, four semiconductor lasers. Furthermore, as an optical system, four collimator lenses 22 provided corresponding to each laser beam from the light source 21, a cylinder lens 23, a rotating polygon mirror (polygon mirror) 24 formed of, for example, a regular hexagonal plane, A plurality of folding mirrors 25, a polygon mirror side lens (not shown) constituting one of the fθ lenses, and four exit side lenses 26K, 26C, 26M, and 26Y constituting the other of the fθ lenses are provided. Further, the laser exposure device 20 is configured in a housing 27 as an example of a holding member, thereby suppressing leakage of laser light to the outside and adhesion of dust or the like to each optical member. Further, the laser exposure device 20 includes a support shaft (rotary shaft) 28 provided integrally with the upper portion of the housing 27 for installation in the image forming apparatus 1, and emission side lenses 26K, 26C, 26M, and 26Y. And a lens fixing frame 29 constituting a part of a holding member for fixing the lens. The deflection scanning direction by the rotation of the rotary polygon mirror 24 is referred to as a main scanning direction, and the direction orthogonal to the deflection scanning direction is referred to as a sub scanning direction.

In the laser exposure device 20 of the present embodiment, the four divergent laser beams emitted from the light source 21 are converted into parallel beams by the collimator lenses 22 and are converted by the cylinder lens 23 having a refractive power only in the sub-scanning direction. In the vicinity of the deflection reflection surface 24a of the polygon mirror 24, an image is formed as a long line image in the main scanning direction. Each laser beam is reflected by the deflecting / reflecting surface 24a of the polygon mirror 24 that rotates at a high speed at a constant speed, and is scanned at a constant angular velocity.
Each laser beam passes through a polygon mirror side lens that constitutes an fθ lens, and is redirected toward the surface of the photosensitive drum 11 by a plurality of folding mirrors 25, and is emitted from the exit side lenses 26K, 26C, 26M, and 26Y. The surface of the photosensitive drum 11 of the image forming unit 10 is scanned and exposed. Here, the polygon mirror side lens and the emission side lenses 26K, 26C, 26M, and 26Y constituting the fθ lens have a function of equalizing the scanning speed of the laser light spot on the photosensitive drum 11, respectively. Yes.
Further, the above-described line image is formed in the vicinity of the deflecting / reflecting surface 24a of the polygon mirror 24, and the fθ lens links the light spot on the surface of the photosensitive drum 11 with the deflecting / reflecting surface 24a as an object point in the sub-scanning direction. Since the image is formed, this scanning optical system (imaging optical system) has a function of correcting the tilting of the deflecting / reflecting surface 24a.

  In such a laser exposure device 20, the laser beams LK, LC, LM, and LY emitted from the emission side lenses 26K, 26C, 26M, and 26Y are photoconductive drums of the image forming units 10K, 10C, 10M, and 10Y, respectively. 11 is subjected to scanning exposure. Therefore, main scanning on the photosensitive drum 11 is performed so that the laser beams LK, LC, LM, and LY scan predetermined exposure positions of the photosensitive drum 11 provided in the image forming units 10K, 10C, 10M, and 10Y, respectively. The exposure position in the direction and the sub-scanning direction is set in the manufacturing process at the factory. The exposure position is set mainly by adjusting the set angle of each folding mirror 25. However, the exposure positions on the photosensitive drum 11 in the main scanning direction and the sub-scanning direction need to be set with extremely high accuracy. Therefore, in the final stage of setting the exposure position, the laser exposure device 20 is installed in the measuring apparatus, and the laser light exposure position is actually emitted from the exit side lenses 26K, 26C, 26M, and 26Y. While the angle is measured, the set angles of the exit side lenses 26K, 26C, 26M, and 26Y are finely adjusted, and adjustments are made to match the design values. Then, the exit side lenses 26K, 26C, 26M, and 26Y are fixed to the housing 27 in a state where the exposure position finally matches the design value. Thereby, the exposure positions in the main scanning direction and the sub-scanning direction in the laser exposure device 20 are set with high accuracy.

  Further, in the laser exposure device 20 of the present embodiment, the mirror 61 disposed at the scanning start position on each optical path of the laser beams LK, LC, LM, and LY, and the plurality of laser beams L reflected by the mirror 61. And a synchronization light receiving element (SOS (Start Of Scan) sensor) 62 having a size capable of simultaneously receiving -K, LC, LM, and LY. That is, for each scan, each of the laser beams LK, LC, LM, and LY at the scanning start position is reflected by the mirror 61 and simultaneously received by the synchronization light receiving element 62. The mirror 61 reflects the laser beams LK, LC, LM, and LY that pass through a predetermined position outside the image area.

FIG. 3 is a front view of the laser exposure device 20 as viewed from the image forming unit 10 side.
As shown in FIG. 3, emission side lenses 26 </ b> K, 26 </ b> C, 26 </ b> M, and 26 </ b> Y are arranged on the image forming unit 10 side of the laser exposure device 20. A synchronizing light receiving element 62 is disposed on the outer surface of the housing 27 of the laser exposure device 20, and laser beams L-K, L-C, L-M, L- are passed through holes (not shown) formed in the housing 27. Y is received. The synchronizing light receiving element 62 constitutes a part of pulse width measuring means (measuring part, instruction part, specifying part, correction amount detecting part, detecting part) for determining whether or not to perform alignment correction. To do.

FIG. 4 is a block diagram of the pulse width measuring means.
The pulse width measuring means shown in FIG. 4 includes a synchronization light receiving element 62, an amplifier 63 that amplifies the output signal output from the synchronization light receiving element 62, a reference voltage unit 64 that outputs a predetermined reference voltage, and an amplifier 63. And a comparator 65 that compares the output signal amplified by the reference voltage of the reference voltage unit 64 and outputs a synchronization detection signal (SOS detection signal, synchronization detection output) when the output signal exceeds the reference voltage. Yes. That is, the comparator 65 outputs a synchronization detection signal when the amount of received light energy exceeds a predetermined threshold value.

4 includes an oscillation circuit 66 that outputs a clock, a counter 67 that counts the synchronization detection signal output from the comparator 65, the count result of the counter 67, and the synchronization detection of the comparator 65. A control circuit 68 to which a signal is input and a storage unit 69 that stores information instructed by the control circuit 68 are provided.
Note that the control circuit 68 can be configured by, for example, a CPU, and the storage unit 69 can be configured by, for example, a memory. In addition to the count result of the counter 67 and the synchronization detection signal of the comparator 65, the information stored in the storage unit 69 can include whether or not alignment correction is necessary.

  Here, FIG. 5 is a time chart for explaining processing by the counter 67. As shown in FIG. 5, the counter 67 counts the number of clocks of the pulse width of the synchronization detection signal from the comparator 65 (see FIG. 4) using the clock of the oscillation circuit 66 (see FIG. 4). In the example shown in FIG. 5, the number of clocks of the pulse width of the synchronization detection signal is nine. As will be described later, the pulse width of the synchronization detection signal increases when the laser beams LK, LC, LM, and LY are misaligned.

[First Embodiment]
FIG. 6 is a flowchart of the first embodiment showing a series of processing procedures after receiving a print instruction.
As shown in FIG. 6, when the image forming apparatus 1 (see FIG. 1) receives a print instruction from the PC 3 or the image reading apparatus 4 (step 101), the control unit 80 (see FIG. 1) starts an image forming process. (Step 102). That is, the image forming operation is performed after predetermined image processing is performed in the image processing unit 81 (see FIG. 1). The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K). It is output to the laser exposure device 20. Thereafter, in the laser exposure unit 20, the laser light emitted from the light source 21 (see FIG. 2) is output from the image forming units 10Y, 10M, 10C, and 10K (see FIG. 1) according to the input color material gradation data. Each photosensitive drum 11 (see FIG. 1) is irradiated.

  At this time, the pulse width is measured by the above-described pulse width measuring means (step 103). That is, for each scan, each of the laser beams L-K, L-C, L-M, and L-Y at the scan start position is reflected by the mirror 61 (see FIG. 2), and the light-receiving element for synchronization 62 (see FIG. 2). 4)). The light receiving element for synchronization 62 outputs an output signal corresponding to the amount of energy of the laser beams LK, LC, LM, and LY incident simultaneously, and the number of clocks of the pulse width is detected based on the output signal. Is done. When the control circuit 68 (see FIG. 4) acquires the number of clocks of the pulse width, it is determined whether or not there is a mutual positional deviation between the laser beams LK, LC, LM, and LY (step 104).

  Here, FIG. 7 is a diagram for explaining the relationship between the positional relationship between the laser beams LK, LC, LM, and LY and the pulse width, and FIG. (B) shows a state in which there is a displacement. That is, as shown in FIG. 7B, if the laser beams LK, LC, LM, and LY are misaligned with each other, they enter the light receiving surface 62a of the synchronizing light receiving element 62. The beam position changes, so that the pulse width of the synchronization detection signal is wider than when there is no position shift (see FIG. 7A). Therefore, the control circuit 68 can determine whether or not there is a positional deviation based on the count number of the pulse width when there is no positional deviation. That is, the control circuit 68 determines that there is a positional deviation if the count number acquired from the counter 67 is larger than the count number when there is no positional deviation. A configuration is also conceivable in which the control circuit 68 determines that there is a positional deviation when the difference between the count number acquired from the counter 67 and the count number when there is no positional deviation exceeds a predetermined value.

  When it is determined that there is a positional deviation among the laser beams LK, LC, LM, and LY, the control circuit 68 indicates that the storage unit 69 (see FIG. 4) needs to be corrected. The storage unit 69 stores the information (step 105). If the control circuit 68 determines that there is no positional deviation among the laser beams LK, LC, LM, and LY, it is determined whether or not to end printing (step 109). If printing is not completed, the process returns to step 103. If printing is completed, the process proceeds to step 107.

  When the instructed printing is completed (step 106), the control circuit 68 determines whether correction is necessary (step 107). That is, the control circuit 68 determines whether or not information indicating that correction is necessary is stored in the storage unit 69. If such information is stored in the storage unit 69, the control circuit 68 determines that correction is necessary and performs alignment correction. (Step 108), if it is not stored, it is determined that correction is not necessary, and a series of processing is terminated.

Here, the alignment correction in the main scanning direction will be briefly described. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a light detection sensor 36 and a cleaner 37 used for the alignment correction. Is arranged. The light detection sensor 36 is for detecting an inspection pattern on the outer peripheral surface of the paper transport belt 30 in the vicinity of the drive roll 32 during alignment correction. The cleaner 37 is for removing the inspection pattern on the outer peripheral surface of the paper transport belt 30 at the time of alignment correction.
More specifically, at the time of alignment correction, a belt-like pattern corresponding to each color component of YMCK serving as a color misregistration detection pattern is formed on the outer peripheral surface of the paper transport belt 30. Then, the light detection sensor 36 determines the color misregistration amount to be corrected in the main scanning direction and the sub-scanning direction from the difference between the actual mutual distance obtained by detecting the position of the belt-like pattern and the calculated mutual distance. Get information. Based on the information, the color misregistration is corrected by controlling the image writing start timing.

[Second Embodiment]
FIG. 8 is a flowchart of the second embodiment showing a series of processing procedures after receiving a print instruction.
As shown in FIG. 8, when the image forming apparatus 1 (see FIG. 1) receives a print instruction (step 201), the control unit 80 (see FIG. 1) starts image forming processing (step 202), and measures pulse width. The pulse width is measured by the means (step 203). Then, based on the measurement result, it is determined whether or not there is a mutual positional deviation between the laser beams LK, LC, LM, and LY (step 204). Steps 201 to 204 correspond to steps 101 to 104 described above, and detailed description thereof is omitted.

  If it is determined in step 204 that there is a positional deviation among the laser beams LK, LC, LM, and LY, a positional deviation amount is detected (step 205). Note that, unlike the first embodiment, this misregistration amount is detected without waiting for the instructed printing to end. In other words, it is performed using a free time during printing.

  Here, FIGS. 9A and 9B are diagrams for explaining the detection procedure of the positional deviation amount in step 205. More specifically, FIG. 9A shows a case where the laser beams LK, LC, LM, and LY are incident on the light receiving surface 62a of the synchronization light receiving element 62, and FIG. b) shows the case where the laser beams L-C, L-M, and L-Y are incident on the light-receiving surface 62a of the light-receiving element 62 for synchronization. 9B shows a case where the laser beams LM and LY are incident on the light receiving surface 62a of the synchronization light receiving element 62, and FIG. 9B shows a case where the laser beam LY is incident. A case where the light enters the light receiving surface 62a of the synchronization light receiving element 62 is shown. In FIGS. 9A and 9B, the Y color is used as the reference color, but other colors may be used as the reference color.

  First, when the control unit 80 (see FIG. 1) controls so that the laser beams LK, LC, LM, and LY are emitted from the light source 21 (see FIG. 2), the laser beams LK, LC, LM, and LY are reflected on the respective mirrors 61. Reflected by (see FIG. 2), the laser beams LK, LC, LM, and LY are incident on the light receiving surface 62a of the synchronizing light receiving element 62 as shown in FIG. 9A. To do. The comparator 65 (see FIG. 4) outputs a synchronization detection signal based on the output signal of the synchronization light receiving element 62 at that time. The pulse width of the synchronization detection signal at this time is assumed to be ΔKCMY. The synchronization detection signal is counted by the counter 67 (see FIG. 4) and output to the control circuit 68 (see FIG. 4).

  Then, the control unit 80 performs control so that the laser beams LC, LM, and LY are emitted from the light source 21. That is, control is performed so that the laser beam LK is not emitted. As a result, the laser beams LC, LM, and LY are reflected by the mirrors 61, and the laser beams LC, LM, and LY are synchronized with the light receiving element 62 for synchronization, as shown in FIG. Is incident on the light receiving surface 62a. Then, the detection result of the received light energy at that time is output as an output signal of the synchronizing light receiving element 62. Let the pulse width of the synchronization detection signal at that time be ΔCMY. Based on the output signal, the synchronization detection signal of the comparator 65 is counted and output to the control circuit 68.

  Next, the control unit 80 performs control so that the laser beams LM and LY are emitted from the light source 21. That is, control is performed so that the laser beams LK and LC are not emitted. As a result, the laser beams LM and LY are reflected by the mirrors 61, and the laser beams LM and LY are incident on the light receiving surface 62a of the synchronization light receiving element 62, as shown in FIG. Then, a synchronization detection signal having a pulse width ΔMY is output by the comparator 65, and the synchronization detection signal is counted and output to the control circuit 68.

  Thereafter, the control unit 80 controls the laser light LY to be emitted from the light source 21. That is, control is performed so that the laser beams LK, LC, and LM are not emitted. As a result, the laser beam LY is reflected by the mirror 61, and when the laser beam LY is incident on the light receiving surface 62a of the synchronizing light receiving element 62 as shown in FIG. The detection signal is output by the comparator 65, and the synchronization detection signal is counted and output to the control circuit 68.

In this manner, four synchronization detection signals can be acquired by combining the patterns of the laser light incident on the light receiving surface 62a of the synchronization light receiving element 62. Based on the acquired synchronization detection signal, the laser beam L-K, L-C, L-M, and L-Y having the largest positional deviation amount can be grasped, and the positional deviation amount is The largest positional deviation of the laser beam can also be grasped.
More specifically, the pulse width ΔKCMY is the largest, the pulse width ΔCMY (see (b) of FIG. 9A) and the pulse width ΔMY (see (a) of FIG. 9B) are equal to each other, and the pulse width ΔY Is the smallest. Therefore, it can be seen that the amount of positional deviation of the laser beam LK is the largest with respect to the Y-color laser beam LY which is the reference color, and the amount of positional deviation is (ΔKCMY−ΔCMY). The control circuit 68 stores in the storage unit 69 (see FIG. 4) that the color deviation amount is the largest for the K color and the positional deviation amount.
In this way, a beam with a large amount of positional deviation is detected by combining patterns that turn on each color in such a manner that colors other than the reference color are erased.

Returning to FIG. When the positional deviation amount is detected in step 205, the one with the largest positional deviation amount is corrected (alignment correction) (step 206). Specifically, the correction is performed by adjusting the image writing start timing corresponding to the positional deviation amount for the K color.
Then, it is determined whether or not the instructed printing has been completed (step 207). If it is determined that the printing has not been completed, the process returns to step 203. If it is determined that the printing has been completed, the series of processing is terminated.

1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an exemplary embodiment. It is a side view explaining schematic structure of the laser exposure device of this Embodiment. It is the front view which looked at the laser exposure device from each image forming unit side. It is a block diagram of a pulse width measuring means. It is a time chart explaining the process by a counter. 3 is a flowchart of a first embodiment showing a series of processing procedures after receiving a print instruction. It is a figure for demonstrating the relationship between the positional relationship of a laser beam, and a pulse width. 10 is a flowchart of a second embodiment showing a series of processing procedures after receiving a print instruction. It is a figure for demonstrating the detection procedure of positional offset amount. It is a figure for demonstrating the detection procedure of positional offset amount.

Explanation of symbols

10Y, 10M, 10C, 10K ... image forming unit, 11 ... photosensitive drum, 20 ... laser exposure device, 21 ... light source, 30 ... paper conveying belt, 36 ... light detection sensor, 37 ... cleaner, 61 ... mirror, 62 ... Light receiving element for synchronization, 62a ... light receiving surface, 63 ... amplifier, 64 ... reference voltage unit, 65 ... comparator, 66 ... oscillator circuit, 67 ... counter, 68 ... control circuit, 69 ... memory unit, LK, LC, LM, LY, LK, LC, LM, LY ... laser light, [Delta] KCMY, [Delta] CMY, [Delta] MY, [Delta] Y ... pulse width

Claims (4)

Multiple light sources;
An optical system for forming an image of a light beam from the plurality of light sources on a scanned body;
A light receiving element for synchronization in which a part of each of light beams from the plurality of light sources is incident every time scanning is performed on the scanned object;
A measuring unit for measuring a width of a pulse output by the synchronization light-receiving element into which each light beam is incident when the plurality of light sources emit light; and
One reference light source among the plurality of light sources, when all of the plurality of light sources are turned on, when the number of light sources other than the reference light source is turned off and changed one by one , and the reference light source The light beam having the largest positional deviation with respect to the reference light source is identified by comparing the magnitude of each pulse width when the pulse width is measured by the measurement unit when one is turned on. Specific means,
Correction means for performing alignment correction of the light beam specified by the specifying means by adjusting the start timing corresponding to the amount of positional deviation;
Including an optical scanning device. The specifying means uses one of the plurality of light sources as a reference, turns on all of the plurality of light sources, measures the pulse width by the measurement unit, and then turns off the light sources other than the reference one by one. Change the number of light sources to be turned on one by one , measure the pulse width by the measurement unit while turning on, and finally turn on the reference light source and measure the pulse width by the measurement unit 2. The optical scanning device according to claim 1, wherein the light beam having the largest positional deviation with respect to the reference light source is identified by comparing the widths of the pulses.   The optical scanning apparatus according to claim 1, further comprising: an instruction unit that instructs the correction unit to start alignment correction when a measurement result by the measurement unit exceeds a predetermined value. A plurality of image carriers;
An exposure apparatus that scans and exposes the plurality of image carriers by emitting a plurality of light beams corresponding to the plurality of image carriers;
Detecting means for detecting misalignment between the plurality of light beams emitted from the exposure apparatus;
Correction means for correcting the alignment of the light beam based on the detection result of the detection means;
Including
The detection means includes
A light receiving element for synchronization in which light in each non-image region of each of the plurality of light beams emitted from the exposure apparatus enters each time scanning is performed on the plurality of image carriers;
A measurement unit that measures the width of a pulse obtained by one or more of the plurality of light beams being incident on the synchronization light-receiving element;
A case where one of the plurality of light beams is used as a reference and all of the plurality of light beams are turned on, and a case where the number of light beams to be turned on by turning off light beams other than the reference is changed one by one. By comparing the width of each pulse when the width of the pulse is measured by the measurement unit with the case where one light beam as a reference is turned on, the amount of positional deviation with respect to the reference light beam can be reduced. A specific means of identifying the most light beams,
Including
The correction unit performs alignment correction in the main scanning direction of the light beam specified by the specifying unit of the detection unit by adjusting an image writing start timing corresponding to a positional deviation amount. Image forming apparatus.

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