JP2016130812A - Optical scanner and optical scanning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively reduce density unevenness resulting from a polygon mirror.SOLUTION: An optical scanner 2a includes: a polygon mirror A4 configured to deflect light flux emitted from a light source by a plurality of mirrors rotating around a rotation axis to repeat optical scanning in a main scanning direction; a position adjustment part 13 configured to change a height position of the light flux incidence in each mirror surface of the polygon mirror A4; and a control part 11 configured to periodically change the height position of the light flux by the position adjustment part 13 to set a cycle to change the height position to be longer than a rotation cycle of the polygon mirror A4.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an optical scanning device and an optical scanning method.

  In general, an electrophotographic image forming apparatus deflects a laser beam modulated based on original image data by a polygon mirror, and repeatedly scans a rotating photoconductor in a main scanning direction, thereby generating one page. A latent image is formed. An image is formed on a sheet by transferring a developed image by supplying a color material such as toner onto the photoreceptor on which the latent image is formed, and transferring the image onto the sheet via an image carrier such as an intermediate transfer belt. can do.

  The polygon mirror includes a plurality of mirrors that rotate about a rotation axis, and deflects the light beam in the main scanning direction by reflecting the light beam emitted from the light source on each mirror surface. If there are irregularities on the mirror surface, the scanning position of the light beam in the main scanning direction shifts, and this shift repeatedly occurs every rotation of the polygon mirror and may be observed as density unevenness.

  In order to reduce density unevenness caused by such mirror characteristics, a method has been proposed in which the height position of the polygon mirror in the rotation axis direction is adjusted to a height position in which the unevenness of each mirror surface is small and the scan position is least displaced. (For example, refer to Patent Document 1)

JP 2013-3183 A

  Although the density unevenness can also be reduced by the above adjustment method, all the mirror surfaces are hardly smooth, and it is difficult to completely eliminate the scanning position deviation only by adjusting the height position. When a scanning position shift occurs on any of the mirror surfaces, density unevenness with the same period as the rotation period of the polygon mirror occurs.

  An object of the present invention is to effectively reduce density unevenness caused by a polygon mirror.

According to the invention of claim 1,
A polygon mirror that repeats light scanning in the main scanning direction by deflecting a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis;
A position adjusting unit for changing the height position of the light beam incident on each mirror surface of the polygon mirror;
A control unit that periodically changes the height position of the luminous flux by the position adjustment unit, and sets the cycle for changing the height position to be longer than the rotation cycle of the polygon mirror;
An optical scanning device is provided.

According to invention of Claim 2,
2. The optical scanning device according to claim 1, wherein the control unit adds a white noise component to the height position that is periodically changed by the position adjustment unit.

According to invention of Claim 3,
A polygon mirror that repeats light scanning in the main scanning direction by deflecting a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis;
A position adjusting unit for changing the height position of the light beam incident on each mirror surface of the polygon mirror;
A control unit for aperiodically changing the height position of the luminous flux by the position adjustment unit;
An optical scanning device is provided.

According to invention of Claim 4,
The polygon mirror includes a plurality of coils arranged concentrically with the rotation shaft and a magnet arranged to face the plurality of coils in the rotation shaft direction, and a magnetic force between the coils and the magnet. An adjustment mechanism for raising and lowering each mirror of the polygon mirror in the direction of the rotation axis is attached by
The position adjustment unit switches the drive current supplied to the coil of the adjustment mechanism and changes the height position of each mirror of the polygon mirror in the rotation axis direction, thereby increasing the height of the light beam incident on each mirror surface. A position is changed, The optical scanning device as described in any one of Claims 1-3 characterized by the above-mentioned is provided.

According to the invention of claim 5,
The optical scanning device according to any one of claims 1 to 4, wherein the polygon mirror is an axial type or a radial type.

According to the invention of claim 6,
An optical scanning method that repeats optical scanning in the main scanning direction using a polygon mirror that deflects a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis,
Optical scanning characterized by periodically changing the height position of a light beam incident on each mirror surface of the polygon mirror, and changing the height position to a period longer than the rotation period of the polygon mirror. A method is provided.

According to the invention of claim 7,
An optical scanning method that repeats scanning in the main scanning direction using a polygon mirror that deflects a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis,
There is provided an optical scanning method characterized in that the height position at which the light beam enters each mirror surface of the polygon mirror is changed aperiodically.

  According to the present invention, density unevenness caused by a polygon mirror can be effectively reduced.

1 is a front view illustrating an outline of an image forming apparatus according to an embodiment. It is a perspective view which shows the outline | summary of the optical scanning device of FIG. It is a top view of an axial type polygon mirror. FIG. 3B is an end view taken along line Z1-Z1 in FIG. 3A. It is a top view of a radial type polygon mirror. FIG. 4B is an end view taken along line Z2-Z2 in FIG. 4A. It is a block diagram which shows the structure of the control system of an optical scanning device for every function. It is a figure which shows the scanning position of the main scanning direction which changes with the position of the thickness direction of a mirror surface. It is a figure which shows the change pattern in the case of changing periodically the height position where a light beam injects into a mirror surface. It is a graph which shows the change pattern at the time of adding a white noise component. It is a figure which shows the change pattern in the case of changing the height position where a light beam injects into a mirror surface aperiodically.

  Embodiments of an optical scanning device and an optical scanning method of the present invention will be described below with reference to the drawings.

FIG. 1 shows an outline of an image forming apparatus 1 in which the optical scanning device of the present embodiment is used.
As shown in FIG. 1, the image forming apparatus 1 includes an image forming unit 2, and an image is formed on a sheet by the image forming unit 2 based on original image data.
The image forming apparatus 1 also includes an image reading unit 3 that reads a document surface to generate original image data, an image generation unit 4 that generates original image data in response to an external image forming instruction, and a generated original image. An image processing unit 5 that performs image processing on data, an operation unit 6 as a user interface, a display unit 7 and the like are provided.

The image forming unit 2 forms an image composed of a plurality of colors on a sheet based on the original image data image-processed by the image processing unit 5.
As shown in FIG. 1, the image forming unit 2 includes four writing units 21, an intermediate transfer belt 22, a secondary transfer roller 23, a fixing device 24, a paper feed tray 25, and a reverse path 26.
Each writing unit 21 is arranged in series (tandem) along the belt surface of the intermediate transfer belt 22. The intermediate transfer belt 22 is an image carrier that is wound and rotated by a plurality of rollers. Among the plurality of rollers, a primary transfer roller 2f and a secondary transfer roller 23 are included. The secondary transfer roller 23 and the fixing device 24 are arranged on the conveyance path of the paper conveyed from the paper feed tray 25.

The four writing units 21 form images of C (cyan), M (magenta), Y (yellow), and K (black), respectively. Each writing unit 21 has the same configuration, and includes an optical scanning device 2a, a photoreceptor 2b, a developing unit 2c, a charging unit 2d, a cleaning unit 2e, and a primary transfer roller 2f as shown in FIG.
At the time of image formation, each writing unit 21 scans the photoconductor 2b with a light beam emitted from the light scanning device 2a based on the original image data after applying a voltage to the photoconductor 2b by the charging unit 2d and charging it. Thus, an electrostatic latent image is formed. When a color material such as toner is supplied from the developing unit 2c to develop the electrostatic latent image on the photoreceptor 2b, an image is formed on the photoreceptor 2b.

When an image of each color is formed on the photoreceptor 2b of each writing unit 21, the image is composed of a plurality of colors by sequentially transferring (primary transfer) on the intermediate transfer belt 22 by the respective primary transfer rollers 2f. Form. After the primary transfer, in each writing unit 21, the color material remaining on the photoreceptor 2b is removed by the cleaning unit 2e.
Next, the paper is fed by the paper feed tray 25 and the image on the intermediate transfer belt 22 is transferred onto the paper by the secondary transfer roller 23. The transferred paper is heated and pressed by the fixing device 24 to fix the image on the paper.
When images are formed on both sides of one sheet, the sheet is conveyed to the reversing path 26 to reverse the sheet surface, and then conveyed to the secondary transfer roller 23 again.

  The image generation unit 4 receives data in which the content of an image formation instruction is described in a page description language (PDL) from an external device such as a user terminal or a server on the network, and performs rasterization processing on the data. By carrying out the processing, original image data in the bitmap format is generated for each of C, M, Y, and K colors.

The image processing unit 5 performs color conversion on the original image data of R, G, and B colors generated by the image reading unit 3, and outputs original image data of each color of C, M, Y, and K.
The image processing unit 5 performs image processing such as gradation correction processing and halftone processing on the original image data after color conversion or the original image data generated by the image generation unit 4. The gradation correction process is a process for converting the gradation value of each pixel of the original image data into a gradation value corrected so that the density of the image formed on the paper matches the target density. The halftone processing is, for example, error diffusion processing, screen processing using a systematic dither method, or the like.

FIG. 2 shows a schematic configuration of the optical scanning device 2a.
As shown in FIG. 2, the light scanning device 2a includes a light source A1 and a polygon mirror A4. The light source A1 emits a laser beam by emitting light. The polygon mirror A4 includes a plurality of mirrors around the rotation axis, and reflects the light beam emitted from the light source A1 on each mirror surface that rotates about the rotation axis, thereby causing the photoconductor 2b to scan in the main scanning direction. The light beam is deflected so as to scan in x. Although FIG. 2 shows an example of the polygon mirror A4 in which six mirrors are arranged so as to form a regular hexagonal side, the number of mirror surfaces is not limited to six.

Between the light source A1 and the polygon mirror A4, a collimator lens A2 that converts laser light into parallel light, and the parallel light converges in the sub-scanning direction y that is orthogonal to the main scanning direction x on the photosensitive member 2b. A cylindrical lens A3 that forms an image on the mirror surface of the mirror A4 is disposed.
A lens group A5 is disposed between the polygon mirror A4 and the photoreceptor 2b. The lens group A5 has an fθ lens that corrects aberrations of the light beam so that the light beam deflected by the polygon mirror A4 scans the photoreceptor 2b at a constant speed, and has power (refractive power) in the sub-scanning direction y. It consists of a cylindrical lens or the like that forms an image on the photoreceptor 2b.
Near the start end in the main scanning direction x, a sensor A7 that detects a light beam that scans the start end side of the image area and a mirror A6 that guides the light beam to the sensor A7 are arranged.

  When the mirror that reflects and deflects the light beam from the light source A1 is switched by the rotation of the polygon mirror A4, the scanning position of the light beam returns to the starting end. Therefore, the photosensitive member 2b is rotated to shift the scanning position in the sub-scanning direction y. Thus, an electrostatic latent image of each scanning line can be formed on the photoreceptor 2b.

The polygon mirror A4 includes an axial type and a radial type, but any type can be used.
3A is a top view showing a configuration of an axial type polygon mirror A4, and FIG. 3B is an end view taken along the line Z1-Z1 shown in FIG. 3A.
In the axial type polygon mirror A4, as shown in FIGS. 3A and 3B, the rotation axis A41 is rotatably supported by an air bearing A421 provided in the center of the rotor A42, and a mirror portion A43 is provided on the rotor A42. It has been. The mirror part A43 is a pillar having a regular hexagonal cross section, and six mirrors A431 are arranged on the side surface. A substrate A45 is provided on the housing A47 of the rotation axis A41, and a plurality of coils A46 are arranged on the substrate A45 in an annular shape concentric with the rotation axis A41. On the other hand, an annular magnet A44 is disposed on the lower surface of the rotor A42 so as to be concentric with the rotation axis A41 so as to face the plurality of coils A46 in the axial direction (rotation axis direction) with a gap. .

4A is a top view showing the configuration of the radial type polygon mirror A4, and FIG. 4B is an end view taken along the line Z2-Z2 shown in FIG. 4A.
The radial type has the same basic configuration as the axial type except that the arrangement positions of the coil A46 and the magnet A44 that generate the rotational driving force are the same. Therefore, in FIGS. 4A and 4B, the axial types shown in FIGS. The same reference numerals are given to the same components as the type.
As shown in FIGS. 4A and 4B, in the radial type, a magnet A44 is fixed inside a rotor A42 formed in a concave cup shape, and a plurality of coils A46 are arranged to face the magnet A44 in the radial direction. Yes.

  In both the axial type and the radial type, the mirror portion A43 can be rotationally driven around the rotation axis A41 by the action of the magnetic field generated by supplying the drive current to the coil A46 and the magnetic field of the magnet A44.

As shown in FIGS. 3B and 4B, an adjustment mechanism B for the height position of the mirror portion A43 in the rotation axis direction is provided in both the axial type and the radial type. The adjustment mechanism B includes a substrate B1 fixed to the rotation axis A41 at the upper part of the mirror part A43, a plurality of coils B2 arranged on the substrate B1 in an annular shape concentric with the rotation axis A41, and each coil B2. And an annular magnet A44 provided on the mirror portion A43 so as to face in the axial direction.
By switching the drive current supplied to each coil B2 of the adjustment mechanism B, a magnetic force that repels or attracts between each coil B2 and the magnet B3 can be generated, and the mirror part A43 can be moved up and down in the direction of the rotation axis.

FIG. 5 is a block diagram showing the control system of the optical scanning device 2a for each function.
As shown in FIG. 5, the optical scanning device 2a includes a control unit 11, a storage unit 12, a position adjustment unit 13, a drive unit 14 for the light source A1, a drive unit 15 for the polygon mirror A4, and a drive unit 16 for the photoreceptor 2b. ing.

The control unit 11 controls the light emission drive of the light source A1 and the rotational drive of the polygon mirror A4 and the photosensitive member 2b to synchronize the scan start position in the main scan direction and the scan start position in the sub scan direction of each scan line.
For example, the control unit 11 outputs the detection signal of the light beam immediately before the start end of each scanning line output from the sensor A7 to the driving unit 14 as a horizontal synchronization signal indicating the scanning start timing of each scanning line in the main scanning direction. The light emission drive of the light source A1 is controlled.
In addition, the control unit 11 outputs a clock signal for rotational driving to the driving units 15 and 16, and controls the rotational speeds of the polygon mirror A4 and the photosensitive member 2b.

  Further, in order to effectively reduce density unevenness, the control unit 11 periodically changes the height position of the light beam incident on each mirror surface by the position adjustment unit 13, and sets the cycle for changing the height position as a polygon. The period is determined to be longer than the rotation period of the mirror A4.

The control unit 11 can be configured by a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like, and the above-described control can be realized by reading and executing a program stored in the storage unit 12. it can.
The storage unit 12 stores a program executed by the control unit 11. For example, the storage unit 12 stores a change pattern of the height position of the light beam.

  The position adjustment unit 13 changes the height position at which the light beam is incident on each mirror surface of the polygon mirror A4 at a cycle determined by the control unit 11. The position adjustment unit 13 can adjust the height position by switching the amount of drive current supplied to each coil B2 of the adjustment mechanism B attached to the polygon mirror A4.

  The driving unit 14 of the light source A1 performs pulse width modulation on the original image data output from the image processing unit 5 in synchronization with the clock signal output from the control unit 11, and generates a driving signal. The drive unit 14 outputs the generated drive signal to the light source A1, thereby driving the pulse of the light source A1 to emit a light beam.

The driving unit 15 of the polygon mirror A4 controls the driving voltage applied to the coil A46 of the polygon mirror A4 based on the clock signal for rotational driving of the polygon mirror A4 output from the control unit 11, and thereby the polygon mirror A4. Is rotated at a predetermined rotational speed.
Similarly, the drive unit 16 of the photoconductor 2b drives the photoconductor 2b to rotate at a predetermined rotation speed based on the clock signal for rotating the photoconductor 2b output from the control unit 11.

In the above-described polygon mirror A4, if the mirror surface is uneven, the deflection angle of the light beam fluctuates, so that the scanning position of the light beam varies in the main scanning direction.
FIG. 6 shows a case where the position in the thickness direction at a certain point on the mirror surface is 0.0 mm, and the position in the thickness direction is varied within 0.2 mm within a range of −1.0 to 1.0 mm. The detection result of the scanning position of the light beam in the main scanning direction is shown. The scanning position of the light beam was detected by sensors arranged at five reference positions X0 to X4 provided in the main scanning direction.
As shown in FIG. 6, it can be seen that the deviation of the scanning position of the light beam from the reference position in the main scanning direction differs depending on the position in the thickness direction of the mirror surface on which the light beam is incident.

When the height position of the light beam incident on the mirror surface in the rotation axis direction is fixed, the same deviation always occurs in the scanning line of the light beam deflected by the same mirror. It occurs repeatedly at the same cycle as the rotation cycle of the polygon mirror A4, and is easily observed as density unevenness.
In the optical scanning device 2a, in order to reduce such density unevenness, the position adjustment unit 13 periodically changes the height position of the light beam incident on each mirror surface of the polygon mirror A4, and the control unit 11 controls the polygon mirror A4. The cycle for changing the height position is determined so that the cycle is longer than the rotation cycle.

FIG. 7 shows an example of a change pattern when the height position of the light beam is periodically changed.
The change pattern shown in FIG. 7 is a pattern in which the height position is continuously raised and lowered within a range of −1.0 to 1.0 mm, with 24 rotation periods of the polygon mirror A4 as one period.
Specifically, the height position of the incident light is continuously raised from 0.0 mm to 1.0 mm while the polygon mirror A4 is rotated 1 to 6 times, and from 1.0 mm to 0 while the polygon mirror A4 is rotated 7 to 12 times. Lower continuously to 0 mm. Further, the height position of the incident light is continuously lowered from 0.0 mm to −1.0 mm while the polygon mirror A4 rotates 13 to 18 times, and from −1.0 mm to 0. Raise continuously to 0 mm.

The control unit 11 determines the height position according to the number of the mirror A431 that deflects the light beam and the number of rotations of the polygon mirror A4 based on the height position change pattern. As the change pattern, one stored in the storage unit 12 can be read and used.
The position adjustment unit 13 switches the drive current supplied to the coil B2 of the adjustment mechanism B according to the difference between the height position determined by the control unit 11 and the current height position. Thereby, the height position of each mirror A431 in the polygon mirror A4 in the rotation axis direction is changed, and the height position of the light beam incident on the mirror surface is changed to the height position determined by the control unit 11.

In this way, the height position at which the light beam enters each mirror surface is not fixed, but is constantly changed, thereby increasing the number of scanning position deviation patterns, and reducing density unevenness due to repeated deviation of the same pattern. Can do. As long as the change in the height position is a periodic change, the light flux enters the same height position of the same mirror A 431 and the same deviation pattern also periodically occurs. However, by setting the change cycle to a cycle longer than the rotation cycle of the polygon mirror A4, the cycle in which the same pattern shift occurs can also be set to a long cycle. The longer the cycle, the less the density unevenness.
It is difficult to completely smooth the mirror surface, and the scan position shift due to the characteristics occurs not a little, but even if the shift occurs, the above-mentioned change control of the height position of the light flux can be performed, and thus the density unevenness can be effectively obtained. Can be reduced.

  In order to further reduce the repetition of the shift of the scanning position peculiar to each mirror A 431, the control unit 11 can also add a white noise component to the height position that is periodically changed by the position adjustment unit 13. White noise refers to noise that exhibits the same level of intensity in the entire frequency band.

Specifically, the control unit 11 obtains the height position obtained from the white noise pattern by adding the height position obtained from the white noise pattern to the height position corresponding to the mirror number and the rotational speed obtained from the periodic change pattern. The height position is determined as the height position where the light beam enters. The white noise pattern stored in the storage unit 12 may be read and used.
The position adjustment unit 13 switches the drive current supplied to the coil B2 of the adjustment mechanism B in accordance with the difference between the height position determined by the control unit 11 and the current height position, so that each mirror A431 of the polygon mirror A4 is switched. Adjust the height position in the rotation axis direction.

FIG. 8 shows an example of a change pattern of the height position of the luminous flux when white noise is added.
In the change pattern shown in FIG. 8, like the change pattern shown in FIG. 7, the height position is a cycle within a range of −1.0 to 1.0 mm, with 24 rotation cycles of the polygon mirror A4 as one cycle. However, the height position fluctuates more finely in one cycle due to the addition of the white noise component.
Such fluctuations in the height position further increase the scanning position shift pattern, and the interval at which the same shift pattern occurs becomes aperiodic, so that density unevenness can be reduced more effectively.

  As described above, the optical scanning device 2a of the present embodiment deflects the light beam emitted from the light source A1 by the plurality of mirrors A431 that rotate about the rotation axis A41, and performs optical scanning in the main scanning direction x. The polygon mirror A4 to be repeated, the position adjusting unit 13 for changing the height position of the light beam incident on each mirror surface of the polygon mirror A4, and the position adjusting unit 13 periodically changing the height position of the light beam, And a control unit 11 that sets the cycle for changing the position to a cycle longer than the rotation cycle of the polygon mirror A4.

  By changing the height position of the light beam, it is possible to increase the scanning position shift pattern and reduce density unevenness due to repetition of the same shift. In addition, by setting the period of changing the height position of the light beam to a period longer than the rotation period of the polygon mirror A4, it is possible to extend the interval at which the same misaligned pattern appears periodically as an interval where it is difficult to observe as density unevenness. . Thereby, density unevenness caused by the polygon mirror A4 can be effectively reduced.

[Other Embodiments]
Since the density unevenness is caused by the periodic repetition of the deviation of the scanning position of the light beam, in the optical scanning device 2a of the above embodiment, the height position of the light beam incident on each mirror surface is changed aperiodically. Therefore, it is possible to reduce the repetition of the shift of the scanning position peculiar to each mirror A431.

FIG. 9 shows an example of a change pattern when the height position of the light beam is changed aperiodically.
The change pattern shown in FIG. 9 is a pattern that is changed to a height position that does not depend on the mirror number and the rotational speed of the polygon mirror A4 within a range of −1.0 to 1.0 mm.
Note that the height position change pattern shown in FIG. 9 is not limited as long as the height position can be changed aperiodically. In order to avoid instability of the operation of the polygon mirror A4 due to a sudden change in the height position, a random pattern from the random number generator is added to the sine wave as noise. It is preferable to determine.

Based on the change pattern as shown in FIG. 9, the control unit 11 determines the height position according to the mirror number for deflecting the light beam and the number of rotations of the polygon mirror A4, and the height position of the light beam is determined. The height adjustment position in the rotation axis direction of each mirror A431 of the polygon mirror A4 is adjusted by the position adjustment unit 13 so as to reach the vertical position.
By changing the height position of the light beam non-periodically, it is possible to prevent the deviation of the scanning position peculiar to each mirror A 431 from occurring periodically and to prevent the occurrence of density unevenness due to the repeated deviation. be able to.

  As described above, the optical scanning device 2a according to another embodiment deflects the light beam emitted from the light source A1 by the plurality of mirrors A431 that rotate about the rotation axis A41, and performs optical scanning in the main scanning direction x. , A position adjusting unit 13 that changes the height position of the light beam incident on each mirror surface of the polygon mirror A4, and a control unit that changes the height position of the light beam by the position adjusting unit 13 aperiodically. 11.

  Thereby, it is possible to prevent the deviation of the scanning position peculiar to each mirror A431 of the polygon mirror A4 from occurring periodically and to prevent the occurrence of density unevenness due to the repeated deviation.

The above-described embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
In the above-described embodiment, the adjustment mechanism B using the magnetic force of the coil and the magnet is used. However, the height position can be changed without using the adjustment mechanism B. For example, an elevator is installed under the polygon mirror A1 as the position adjustment unit 13, and the height position of the light beam incident on each mirror surface of the polygon mirror A4 is determined by raising and lowering the polygon mirror A4 in the rotation axis direction by this elevator. It may be changed.

  If the height position of the light beam incident on the mirror surface of the polygon mirror A4 can be changed, the height position of the light source A1 is raised by moving the light source A1 up and down in the direction of the rotation axis of the polygon mirror A4 instead of the polygon mirror A4. You may adjust.

  Further, as a computer-readable medium for the program, a non-volatile memory such as a ROM and a flash memory, and a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing program data via a communication line.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Image forming part 2a Optical scanning apparatus A1 Light source A4 Polygon mirror B Adjustment mechanism 11 Control part 13 Position adjustment part 2b Photoconductor 5 Image processing part

Claims (7)

A polygon mirror that repeats light scanning in the main scanning direction by deflecting a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis;
A position adjusting unit for changing the height position of the light beam incident on each mirror surface of the polygon mirror;
A control unit that periodically changes the height position of the luminous flux by the position adjustment unit, and sets the cycle for changing the height position to be longer than the rotation cycle of the polygon mirror;
An optical scanning device comprising:   The optical scanning device according to claim 1, wherein the control unit adds a white noise component to the height position that is periodically changed by the position adjustment unit. A polygon mirror that repeats light scanning in the main scanning direction by deflecting a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis;
A position adjusting unit for changing the height position of the light beam incident on each mirror surface of the polygon mirror;
A control unit for aperiodically changing the height position of the luminous flux by the position adjustment unit;
An optical scanning device comprising: The polygon mirror includes a plurality of coils arranged concentrically with the rotation shaft and a magnet arranged to face the plurality of coils in the rotation shaft direction, and a magnetic force between the coils and the magnet. An adjustment mechanism for raising and lowering each mirror of the polygon mirror in the direction of the rotation axis is attached by
The position adjustment unit switches the drive current supplied to the coil of the adjustment mechanism and changes the height position of each mirror of the polygon mirror in the rotation axis direction, thereby increasing the height of the light beam incident on each mirror surface. The position is changed, The optical scanning device as described in any one of Claims 1-3 characterized by the above-mentioned.   The optical scanning device according to claim 1, wherein the polygon mirror is an axial type or a radial type. An optical scanning method that repeats optical scanning in the main scanning direction using a polygon mirror that deflects a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis,
Optical scanning characterized by periodically changing the height position of a light beam incident on each mirror surface of the polygon mirror, and changing the height position to a period longer than the rotation period of the polygon mirror. Method. An optical scanning method that repeats scanning in the main scanning direction using a polygon mirror that deflects a light beam emitted from a light source by a plurality of mirrors that rotate about a rotation axis,
An optical scanning method, wherein a height position at which a light beam enters each mirror surface of the polygon mirror is changed aperiodically.

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