JP2006123181A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To always obtain an image without any magnification gap by carrying out magnification correction by an optimum manner to an electrostatic latent image formed on an image carrier. <P>SOLUTION: The optical scanner 22 which deflects and scans in a main scanning direction laser beams emitted from an LD 6 by a rotating polygon mirror 33 and optically writes the electrostatic latent image to a photoreceptor 21 which drives rotating in a sub scanning direction is equipped with a light detector 36 for detecting the laser beams deflected and scanned by the polygon mirror 33 and measuring its scanning time. The stable rotation of the polygon mirror 33 is detected. The scanning time is measured by the light detector 36 during the stable rotation. A time difference between the measured scanning time and a predetermined scanning time is obtained. The magnification correction in the main scanning direction of the electrostatic latent image is carried out on the basis of the time difference. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical scanning device and an image forming apparatus.

  In an electrophotographic image forming apparatus such as a digital copying machine or a laser printer, an electrostatic latent image is formed on an image carrier such as a photosensitive member by scanning a laser beam (laser beam) with a deflector such as a polygon mirror. Like to do. In such raster scanning, the synchronization in scanning is important, and if the synchronization between the main scans is not taken, the vertical lines of the formed image will be jagged. Preventing such pixel dot position shift in the main scanning direction is important for obtaining a highly accurate image.

  Therefore, in Patent Document 1, beam detectors are arranged at both ends of an effective scanning section of laser light, and a scanning time during which the laser light scans between these beam detectors is measured (measured), and based on the measurement result. Thus, a technique for locally correcting the dot position within the effective scanning section has been proposed. The correction method is a method of dynamically increasing or decreasing the pixel clock cycle using a clock having a frequency higher than that of the pixel clock. Patent Document 2 mentions that correction setup is performed between sheets at the time of outputting a plurality of sheets with the same configuration as Patent Document 1.

JP 2003-279873 A JP 2003-185953 A

  However, as in Patent Document 1, when the scanning time of the laser beam is measured every certain period and the magnification correction of the electrostatic latent image is performed during image formation based on the measurement result, The dot position is shifted before and after the start of magnification correction, and an image having a magnification shift is formed. Further, in Patent Document 2, correction is performed between sheets when outputting a plurality of sheets. However, since magnification correction cannot be performed during image formation, an image having a magnification shift is formed. That is, if the scanning time of the laser beam is always measured and the electrostatic latent image magnification cannot be corrected based on the measurement result, an image with a magnification shift is formed.

  In addition, when the scanning time of the laser beam is measured when the deflector is not rotating stably, and the electrostatic latent image is subjected to magnification correction based on the measurement result, the electrostatic latent image is accurately corrected for magnification. In other words, an image having a magnification shift is formed.

  An object of the present invention is to optimally correct the magnification of an electrostatic latent image formed on an image carrier and always obtain an image free from magnification shift.

  According to the first aspect of the present invention, optical scanning is performed in which an electrostatic latent image is optically written on an image carrier that is deflected and scanned in the main scanning direction with light emitted from a light source by a rotationally driven deflector and rotationally driven in the sub-scanning direction. In the apparatus, a light detector for detecting light deflected and scanned by the deflector and measuring a light scanning time by the deflector, means for detecting stable rotation of the deflector, and Means for measuring the scanning time by the photodetector during rotation stabilization, and obtaining a time difference between the measured scanning time and the predetermined scanning time, and based on the time difference in the main scanning direction of the electrostatic latent image Means for performing magnification correction.

  According to a second aspect of the present invention, in the optical scanning device according to the first aspect, the deflector is a polygon mirror having a plurality of reflecting surfaces that reflect the light from the light source and scan the light, respectively. The means for measuring time measures the scanning time for each reflecting surface of the deflector, and the means for correcting the magnification of the electrostatic latent image in the main scanning direction calculates the time difference for each reflecting surface of the deflector. It is characterized by seeking.

  According to a third aspect of the present invention, in the optical scanning device according to the first aspect, the deflector is a polygon mirror having a plurality of reflecting surfaces that reflect the light from the light source and scan the light, respectively. The means for measuring time measures the scanning time for each reflecting surface of the deflector, and the means for correcting the magnification of the electrostatic latent image in the main scanning direction is measured every rotation of the deflector. An average value is obtained from the plurality of scanning times, and a time difference between the obtained average value of the scanning times and the predetermined scanning time is obtained.

  According to a fourth aspect of the present invention, in the optical scanning device according to the first aspect, the means for correcting the magnification in the main scanning direction of the electrostatic latent image includes a plurality of measured values for each predetermined number of rotations of the deflector. An average value is obtained from the scanning time, and a time difference between the obtained average value of the scanning time and the predetermined scanning time is obtained.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording material by an electrophotographic method, an image carrier that carries an electrostatic latent image, and an optical scanning according to any one of the first to fourth aspects. And a device.

  According to the first aspect of the present invention, the scanning time is measured during the stable rotation of the deflector, the time difference between the scanning time and the ideal predetermined scanning time is obtained, and the electrostatic latent is determined based on the time difference. Since the magnification correction in the main scanning direction of the image is performed, the electrostatic latent image formed on the image carrier is optimally corrected for the magnification, and an image having no magnification deviation can be obtained at all times.

  According to the second aspect of the present invention, the magnification of the electrostatic latent image can be corrected with high accuracy.

  According to invention of Claim 3 or 4, the error by the dispersion | variation for every reflective surface of a deflector can be restrained small.

  According to invention of Claim 5, there exists an effect similar to the invention as described in any one of Claims 1 thru | or 4.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a digital copying machine which is an image forming apparatus according to the present embodiment.

  As shown in FIG. 1, a digital copying machine 1 includes a scanner 2 that is an image reading device that reads an image of a document, and a printer 3 that is an image forming unit that forms an image read by the scanner 2 on a recording material such as paper. And.

  The scanner 2 performs A / D conversion on an image signal corresponding to the read image and performs signal processing such as black offset correction, shading correction, and pixel position correction, and an image signal after A / D conversion. And an image processing circuit 5 that performs various image processing, and outputs the processed image signal to the printer 3. A VPU (Visual Processing Unit) or the like is used as the signal processing circuit 4, and an IPU (Image Processing Unit) or the like is used as the image processing circuit 5.

  The printer 3 forms an image on a recording material such as paper by an electrophotographic method based on an image signal (image data) from the scanner 2. The printer 3 includes a laser diode (LD) 6 that is a light emitting element for optically writing an electrostatic latent image on a photosensitive member 21 (see FIG. 2), an LD control unit 7 that controls the LD 6, and the printer 3. And a printer control unit 8 for controlling the whole.

  The digital copying machine 1 further includes a CPU 11, a ROM 12, a RAM 13, an image memory 14, a panel operation unit 15, and the like.

  The CPU 11 centrally controls the entire digital copying machine 1, the ROM 12 stores various control programs executed by the CPU 11, and the RAM 13 serves as a work area for the CPU 11 and temporarily stores various data. The image memory 14 stores image data read by the scanner 2. Data exchange of each unit is performed via the system bus 16, and the I / F 17 serves as an interface between the system bus 16 and the image processing circuit 5. The panel operation unit 15 displays various messages to the user and accepts various operations from the user. The panel operation unit 15 functions as a display unit and an operation unit.

  Here, when the image read by the scanner 2 is output as an electrostatic latent image to the photosensitive member 21 by the LD 6, the CPU 11 outputs a start signal to the printer control unit 8, and the printer control unit 8 uses the start signal as a reference. The image data is received from the image processing circuit 5, and the LD controller 7 turns on the LD 6 based on the image data. At this time, the CPU 11 also performs position control of the recording material in the sub-scanning direction.

  FIG. 2 is a block diagram showing a schematic configuration of the printer 3.

  As shown in FIG. 2, the printer 3 exposes and scans the surface of the charged photoreceptor 21, and a drum-shaped photoreceptor 21 that is driven to rotate, a charger (not shown) that charges the surface of the photoreceptor 21. An optical scanning device 22 for forming an electrostatic latent image on the surface is provided. The photosensitive member 21 is an image carrier that carries an electrostatic latent image. Further, the printer 3 supplies a toner to the electrostatic latent image on the photosensitive member 21 to form a toner image, a transfer device for transferring the toner image to a recording material such as paper, and a toner image on the recording material. Is provided with a fixing device (none of which is shown). The printer control unit 8 includes a dot position deviation detection / control unit 23, a pixel clock generation unit 24, an image processing unit 25, an LD drive data generation unit (laser drive data generation unit) 26, and the like.

  The optical scanning device 22 includes an LD 6 serving as a light source, a collimator lens 31, a cylinder lens 32, a polygon mirror 33 serving as a rotationally driven deflector, an fθ lens 34, a transparent member 35, a photodetector 36, and the like. The polygon mirror 33 is a rotating polygon mirror having a plurality of reflecting surfaces 33a that reflect the laser light from the LD 6 and scan the light respectively. The polygon mirror 33 is connected to a polygon control unit 37 that drives and controls the polygon mirror 33. The polygon control unit 37 sets a steady rotation flag (generates a steady rotation signal) when the rotation of the polygon mirror 33 becomes a steady rotation.

  Here, the laser light emitted from the LD 6 becomes a parallel light beam by the collimator lens 31 and enters the cylinder lens 32. The incident laser light is condensed by the cylinder lens 32 in the sub-scanning direction (the rotation direction of the photoconductor 21) and enters the polygon mirror 33. The laser beam is deflected and scanned by the polygon mirror 33 in the main scanning direction (in the rotational axis direction of the photosensitive member 21) parallel to the rotational axis direction of the photosensitive member 21. The laser light scanned in the main scanning direction is adjusted by the fθ lens 34 so that the scanning angle and the scanning distance are proportional to each other, and is condensed in the sub scanning direction, and is connected onto the photosensitive member 21 through the transparent member 35. Image. As a result, the surface of the photoreceptor 21 charged by the charger is exposed and scanned.

  The photodetector 36 is disposed outside the effective writing area on the surface of the photosensitive member 21, receives the laser beam deflected and scanned by the polygon mirror 33 and reflected by the transparent member 35, and receives the effective writing start position and the effective writing. The end position is detected. Detection signals (front end line synchronization signal and rear end line synchronization signal) output from the photodetector 36 are input to the dot position deviation detection / control unit 23.

  The dot position deviation detection / control unit 23 measures the scanning time of the laser beam between the two photodetectors 36, compares the measured scanning time with an ideal predetermined scanning time, and detects the deviation between them. A time difference, which is a quantity, is obtained, phase data for correcting the time difference is generated and output to the pixel clock generator 24. The detection signal output from the photodetector 36 is also output to the image processing unit 25 as a line synchronization signal. Note that the ideal predetermined scanning time is a scanning time measured when ideal laser scanning is performed, and is stored in advance in a memory such as the ROM 12 or the RAM 13.

  When the pixel clock generation unit 24 does not include a phase data storage circuit, the dot position deviation detection / control unit 23 outputs phase data to the pixel clock generation unit 24 for each line. On the other hand, when the pixel clock generation unit 24 includes a phase data storage circuit, the phase data is previously given to the pixel clock generation unit 24, for example, by obtaining phase data.

  Further, the dot position deviation detection / control unit 23 not only provides phase data (first phase data) for always performing the same correction for each line that corrects scanning unevenness caused by the characteristics of the scanning lens, but also the polygon mirror 33. When phase data (second phase data) corresponding to correction that changes for each line such as rotation unevenness of the pixel is also generated and the pixel clock generation unit 24 includes a phase data synthesis circuit, The phase data is also output to the pixel clock generator 24. Further, by providing a plurality of sets of photodetectors 36, it is possible to simultaneously generate phase data for a plurality of lines.

  The dot position deviation detection / control unit 23 changes the phase data based on the time difference between the measured scanning time and an ideal predetermined scanning time (phase correction), thereby controlling the pixel clock (LD6 lighting control). The phase of the clock is changed in one or a plurality of locations in the main scanning direction in units of 1 / n (n is an integer of 2 or more) of one cycle of the pixel clock, that is, by changing the phase of the pixel clock Perform magnification correction.

  The pixel clock generation unit 24 generates a pixel clock based on the phase data from the dot position deviation detection / control unit 23 and outputs the pixel clock to the image processing unit 25 and the LD drive data generation unit 26. The image processing unit 25 generates image data with reference to the pixel clock, and outputs the image data to the LD drive data generation unit 24. The LD drive data generation unit 26 generates LD drive data (modulation data) based on the image data with reference to the pixel clock, and outputs the LD drive data to the LD control unit 7. The LD control unit 7 controls driving of the LD 6 based on the LD driving data.

  Note that a method of changing the dot position to an arbitrary position by performing clock phase shift based on the phase data is well known, and thus the description thereof is omitted (see Japanese Patent Application Laid-Open No. 2003-279873). In addition, since a method for measuring the scanning time difference in which the laser beam is scanned is known, the description thereof is also omitted (see Japanese Patent Laid-Open No. 9-58053).

  With such a configuration, the rotation start processing and phase correction processing (magnification correction processing) of the polygon mirror 33 executed by the CPU 11 based on the program stored in the ROM 12 will be described with reference to FIGS. Various means are executed by this processing.

  FIG. 3 is a flowchart showing the flow of the rotation start process of the polygon mirror 33.

  As shown in FIG. 3, the CPU 11 rotates the polygon mirror 33 via the polygon control unit 37 (step S1), determines whether a steady rotation flag is set by the polygon control unit 37 (step S2), and It waits for the rotation flag to be reached, that is, for the rotation of the polygon mirror 33 to be a steady rotation (stable rotation) (N in step S2). When it is determined that the steady rotation flag is set, that is, the rotation of the polygon mirror 33 is a steady rotation (Y in step S2), a phase correction permission signal is generated (step S3).

  The CPU 11 confirms from the polygon control unit 37 whether the rotation of the polygon mirror 33 is a steady rotation at intervals of several ms. When it is determined that the rotation of the polygon mirror 33 is not normal rotation (steady rotation), that is, it is abnormal (N in Step S2), for example, a stop command for stopping the polygon mirror 33 is generated. At this time, the phase correction permission signal is not generated.

  FIG. 4 is a flowchart showing the flow of the phase correction process when the time difference is obtained for each reflection surface 33a of the polygon mirror 33.

  As shown in FIG. 4, it is determined whether or not a phase correction permission signal is being generated and whether or not a tip line synchronization signal has been generated (steps S11 and S12). It waits for generation | occurrence | production of a synchronizing signal (N of step S11 and N of step S12). When it is determined that the phase correction permission signal is being generated and the leading line synchronization signal has been generated (Y in step S11 and Y in step S12), measurement of the scanning time of the laser beam is started (step S13). Here, the counter is cleared when the phase correction permission signal is generated, and the scanning time is measured by turning the counter at the start of the measurement of the scanning time of the laser beam.

  Next, it is determined whether or not a phase correction permission signal is being generated and whether or not a rear end line synchronization signal has been generated (step S14 and step S15), and the system waits for generation of a rear end line synchronization signal (step S14). Y of S14 and N of step S15). When it is determined that the phase correction permission signal is not being generated (N in step S14), the process returns to step S11.

  When it is determined that the rear end line synchronization signal has been generated (Y in step S15), the measurement of the scanning time of the laser beam is ended (step S16). Here, the counter is stopped at the end of the measurement of the scanning time of the laser beam. The measured scanning time is compared with an ideal predetermined scanning time to obtain a time difference that is the amount of deviation between them, and phase data for correcting the time difference is generated to change the phase of the pixel clock (phase correction). The magnification correction in the main scanning direction of the electrostatic latent image is performed (step S17).

  Such processing will be described with reference to a timing chart as shown in FIG.

  FIG. 5 is a timing chart for obtaining a time difference for each reflection surface 33a of the polygon mirror 33. FIG.

  As shown in FIG. 5, when the polygon mirror 33 is in a steady rotation, a phase correction permission signal is generated (high level). While the phase correction permission signal is generated, the scanning time of the laser beam from the pulse (low level) of the leading end line synchronization detection signal to the pulse (low level) of the trailing end line synchronization detection signal is measured. A time difference between the measured scanning time and an ideal predetermined scanning time is calculated, phase data is generated by the dot position deviation detection / control unit 23 based on the time difference, and pixel clock generation is performed based on the phase data. A pixel clock is generated by the unit 24. Further, image data is generated by the image processing unit 25 based on the pixel clock, and LD drive data (LD lighting signal) is generated based on the image data, thereby forming an image without positional deviation. On the other hand, when the polygon mirror 33 does not rotate constantly, a phase correction permission signal is not generated (low level), and phase correction (magnification correction) is not performed.

  As described above, according to the present embodiment, the scanning time of the laser beam is measured during the stable rotation of the polygon mirror 33, and a time difference which is a deviation amount between the scanning time and an ideal predetermined scanning time is obtained. Since magnification correction in the main scanning direction of the electrostatic latent image is performed based on the time difference, the electrostatic latent image is optimally corrected for magnification, and an image that is always free from magnification deviation can be obtained. Further, since a time difference is obtained for each reflecting surface 33a of the polygon mirror 33, the magnification of the electrostatic latent image can be corrected with high accuracy.

  In this embodiment, the time difference is obtained for each reflection surface 33a of the polygon mirror 33. However, the present invention is not limited to this. For example, the measurement is performed for each reflection surface 33a every rotation of the polygon mirror 33. An average value may be obtained from a plurality of scanning times, and the average value of the obtained scanning times may be compared with an ideal predetermined scanning time to obtain a time difference therebetween, or a predetermined number of rotations of the polygon mirror 33 may be obtained. Each time, an average value is obtained from a plurality of scanning times measured for each reflecting surface 33a, and the average value of the obtained scanning times is compared with an ideal predetermined scanning time to obtain a time difference therebetween. .

  Here, for example, a case where a time difference is obtained for each rotation of the polygon mirror 33 using the polygon mirror 33 having the six reflecting surfaces 33a as the polygon mirror 33 will be described with reference to FIG. In this case, the phase correction process repeats step S13 to step S16 shown in FIG. 4 six times. At this time, the scanning time measured for each of the six reflecting surfaces 33a is stored in a memory such as the RAM 13 for each measurement.

  FIG. 6 is a timing chart for obtaining a time difference for each rotation of the polygon mirror 33 having six reflecting surfaces 33a.

  As shown in FIG. 6, when the polygon mirror 33 is in a steady rotation, a phase correction permission signal is generated (high level). While the phase correction permission signal is generated, the scanning time of the laser beam from the pulse (low level) of the leading end line synchronization detection signal to the pulse (low level) of the trailing end line synchronization detection signal is measured. This measurement is performed for every six reflecting surfaces 33a. Therefore, when the polygon mirror 33 rotates once, the scanning time for each of the six reflecting surfaces 33a is obtained, and the average value is obtained from the scanning time for each of the six reflecting surfaces 33a. A time difference, which is a deviation amount between the average value and an ideal predetermined scanning time, is calculated, and phase data is generated by the dot position deviation detection / control unit 23 based on the time difference, and a pixel is obtained based on the phase data. A pixel clock is generated by the clock generator 24. Further, image data is generated by the image processing unit 25 based on the pixel clock, and LD drive data (LD lighting signal) is generated based on the image data, thereby forming an image without positional deviation. On the other hand, when the polygon mirror 33 does not rotate constantly, a phase correction permission signal is not generated (low level), and phase correction (magnification correction) is not performed.

  In this way, since a time difference that is a shift amount is obtained for each rotation of the polygon mirror 33 having the six reflecting surfaces 33a, errors due to variations of the reflecting surfaces 33a of the polygon mirror 33 can be suppressed to be small.

  Next, a case where the time difference is obtained every three rotations of the polygon mirror 33 will be described with reference to FIG.

  FIG. 7 is a flowchart showing the flow of the phase correction process when the time difference is obtained every three rotations of the polygon mirror 33.

  As shown in FIG. 7, it is determined whether or not the phase correction permission signal is being generated and whether or not the tip line synchronization signal has been generated (step S21 and step S22), and the generation of the phase correction permission signal and the tip line are determined. It waits for generation | occurrence | production of a synchronizing signal (N of step S21 and N of step S22). When it is determined that the phase correction permission signal is being generated and the tip line synchronization signal has been generated (Y in step S21 and Y in step S22), measurement of the scanning time of the laser beam is started (step S23). Here, the counter is cleared when the phase correction permission signal is generated, and the scanning time is measured by turning the counter at the start of the measurement of the scanning time of the laser beam.

  Next, it is determined whether or not the phase correction permission signal is being generated and whether or not the rear end line synchronization signal has been generated (step S24 and step S25), and the system waits for the generation of the rear end line synchronization signal (step S24). Y in S24 and N in Step S25). When it is determined that the phase correction permission signal is not being generated (N in step S24), the process returns to step S21.

  When it is determined that the rear end line synchronization signal has been generated (Y in step S25), the measurement of the scanning time of the laser beam is ended (step S26). Here, the counter is stopped at the end of the measurement of the scanning time of the laser beam. Next, it is determined whether or not the polygon mirror 33 has rotated three times (N = 3) (step S27), and the laser beam scanning time measurement is repeated until the polygon mirror 33 has rotated three times (N in step S27). If it is determined that the polygon mirror 33 has rotated three times (Y in step S27), the average value is obtained from the scanning time of the laser beam measured so far, and the average value and the ideal predetermined scanning time are obtained. The time difference which is the amount of shift is compared and phase data for correcting the time difference is generated, the phase of the pixel clock is changed (phase correction), and the magnification of the electrostatic latent image in the main scanning direction is corrected (step) S28). Finally, N is cleared (N = 0), and the process returns to step S21.

  In this way, since a time difference that is a deviation amount is obtained every three rotations of the polygon mirror 33, an error due to variations of the reflection surfaces 33a of the polygon mirror 33 can be suppressed to a small value.

1 is a block diagram illustrating a schematic configuration of a digital copying machine that is an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a schematic configuration of a printer provided in a digital copying machine. It is a flowchart which shows the flow of a rotation start process of a polygon mirror. It is a flowchart which shows the flow of the phase correction process in the case of calculating | requiring a time difference for every reflective surface of a polygon mirror. It is a timing chart in the case of calculating | requiring a time difference for every reflective surface of a polygon mirror. It is a timing chart in the case of calculating | requiring a time difference for every rotation of the polygon mirror which has six reflective surfaces. It is a flowchart which shows the flow of a phase correction process in the case of calculating | requiring a time difference for every 3 rotations of a polygon mirror.

Explanation of symbols

1 Image forming device (digital copier)
6 Light source (LD)
21 Photosensitive body 22 Optical scanning device 33 Deflector (polygon mirror)
33a Reflecting surface 36 Photodetector

Claims (5)

In an optical scanning device that deflects and scans light emitted from a light source in a main scanning direction by a rotationally driven deflector and optically writes an electrostatic latent image on an image carrier that is rotationally driven in a sub-scanning direction.
A photodetector for detecting light deflected and scanned by the deflector and measuring a scanning time of the light by the deflector;
Means for detecting stable rotation of the deflector;
Means for measuring the scan time by the photodetector during rotation stabilization of the deflector;
Means for obtaining a time difference between the measured scanning time and the predetermined scanning time, and performing magnification correction in the main scanning direction of the electrostatic latent image based on the time difference;
An optical scanning device comprising: The deflector is a polygonal mirror having a plurality of reflecting surfaces that reflect light from the light source and scan the light respectively.
The means for measuring the scanning time measures the scanning time for each reflecting surface of the deflector,
The means for correcting the magnification of the electrostatic latent image in the main scanning direction obtains the time difference for each reflecting surface of the deflector.
The optical scanning device according to claim 1. The deflector is a polygonal mirror having a plurality of reflecting surfaces that reflect light from the light source and scan the light respectively.
The means for measuring the scanning time measures the scanning time for each reflecting surface of the deflector,
The means for correcting the magnification of the electrostatic latent image in the main scanning direction obtains an average value from the plurality of measured scanning times for each rotation of the deflector, and determines the average value of the obtained scanning times and a predetermined value. To obtain a time difference from the scanning time of
The optical scanning device according to claim 1. The means for correcting the magnification of the electrostatic latent image in the main scanning direction obtains an average value from the plurality of measured scanning times for each predetermined number of rotations of the deflector, and calculates the average value of the obtained scanning times. And obtaining a time difference between the predetermined scanning time,
The optical scanning device according to claim 1. In an image forming apparatus that forms an image on a recording material by electrophotography,
An image carrier for carrying an electrostatic latent image;
An optical scanning device according to any one of claims 1 to 4,
An image forming apparatus comprising:

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