JP2006084637A - Image forming apparatus and image quality adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus capable of adjusting a distance from an exposure point to a transfer point and restraining the defect of image quality (density variation) associated with the speed variation of a photoreceptor, and an image quality adjusting method for the image forming apparatus. <P>SOLUTION: In an image forming unit 106, a positioning cam 158 is turned, whereby a print head 110 is turned around the shaft (shaft 140) of the photoreceptor, and the exposure point 122 is moved. The position of the exposure point 122 is set so that the distance from the exposure point 122 to the primary transfer point 128 may be the integral multiple of the the variation cycle of the rotational speed of the photoreceptor 108, and the variation in exposure and transfer may be negated each other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image quality adjusting method, and in particular, an image forming apparatus using an exposure device such as an LED print head having a plurality of light emitting points as an exposure device, and image quality adjustment in the image forming device. Regarding the method.

  2. Description of the Related Art In recent years, so-called tandem image forming apparatuses have been developed as image forming apparatuses for laser printers and digital multi-function peripherals, in which a plurality of image forming units are arranged in series to form a full color image in one pass. The four photoconductors are independently exposed and developed by Y, M, C, and K image data sent from the data control unit, and then sequentially transferred onto the intermediate transfer belt. The full-color image created on the intermediate transfer belt is batch-transferred onto the sheet at the secondary transfer position and then fixed on the sheet by a fixing device.

  In this tandem type image forming apparatus, an apparatus using an LED print head as an exposure device has been developed as means for realizing miniaturization of the apparatus itself.

  For example, Patent Document 1 describes an image forming apparatus in which four image forming units 14 are arranged below one intermediate transfer belt 12 as shown in FIG. When the image forming unit 14 is arranged below the intermediate transfer belt 12 in this way, the distance from the image forming unit 14K to the paper discharge unit 16 is shortened, and the time from the print instruction / copy instruction to the fixing image discharge can be shortened. There is an advantage.

  However, if an image forming unit such as an exposure device is disposed below the photoconductor, the image forming unit cannot be accessed from above the image forming apparatus, and the mounting / removing direction thereof is within a horizontal plane (a direction parallel to the arrangement of the image forming units). Therefore, the configuration is complicated from the viewpoint of assembly and maintenance.

  On the other hand, in Patent Document 1, as shown in FIG. 9, four LED arrays 20 are integrally held on one LED holding base 18, and this integrated holding base is horizontally attached to the apparatus main body. Describes a structure that is detachable.

  With such a configuration, the positional relationship of the LED array can be accurately maintained, but the mounting configuration becomes complicated and the cost is increased, and the occupied space including the holding base becomes large. In order to simplify the mounting configuration, it is desirable to mount the four LED arrays independently. However, there are items to be considered in order to suppress image quality defects caused by the positioning accuracy of the LED arrays.

  The first is image streaks that occur parallel to the paper transport direction. This is a phenomenon in which the exposure amount becomes non-uniform in the LED arrangement direction due to the difference in the amount of light between the dots of the LEDs, the transmission of the used SELFOC lens, and the variation in imaging characteristics, and the density unevenness becomes an image streak. Therefore, as a mounting configuration, it is important to position the relative distance between the LED print head having a shallow depth of focus and the photosensitive member with high accuracy.

  The second is density unevenness perpendicular to the paper transport direction. This image quality defect is not a problem inherent to an image forming apparatus using an LED print head, but also occurs when a laser scanning device is used as an exposure unit.

  FIG. 10 conceptually shows the configuration of the image forming unit using the LED print head. The LED print head 26 exposes the photosensitive member 24 charged by the charger (BCR) 22 by forming an image of the light beam emitted from the LED chip 28 on the photosensitive member 24 by the SELFOC lens array 30. Thereafter, the image is developed by the developing device 32 and transferred to the intermediate transfer belt 34. Density unevenness occurs due to the relationship between the speed fluctuation of the photoconductor 24 and the distance from the exposure point 36 to the transfer point 38.

  FIG. 11 is a diagram for explaining the mechanism of image formation. Here, for convenience of explanation, an LED print head 26 is disposed on the upper side of the photoconductor 24, and an intermediate transfer belt 34 is disposed on the lower side. An image exposed by the LED print head 26 at regular time intervals is formed as a latent image 40 on the photosensitive member 24, and is transferred onto the intermediate transfer belt 34 after rotating about 180 °. Here, if there is no change in the rotational speed of the photosensitive member 24, the transfer image 44 on the intermediate transfer belt 34 becomes an image at equal intervals as shown in FIG.

However, in practice, the period is determined by, for example, a drive transmission configuration from a motor that drives the photosensitive member 24, and the amplitude thereof varies due to variations in the accuracy of components. For example, when the speed unevenness as shown in FIG. 12A occurs, if the speed of the photosensitive member 24 increases at the timing of passing through the exposure point 36 (see FIG. 10), the interval between the images widens and the rough state is reached. When a latent image is formed and, on the contrary, the speed of the photosensitive member 24 is decreased, the interval between the images is narrowed to form a dense latent image. The density of the image pitch is canceled or the density is superimposed depending on the speed of the photosensitive member 24 when the latent image having the density reaches the transfer point 38 (see FIG. 10). . For example, as can be seen from a comparison between FIG. 12C and FIG. 12D, the timing at which the latent image in the state where the image interval is widened becomes slow (the state where the transfer target is relatively fast). When the transfer point 38 is reached, the interval between the transfer images is further increased. On the contrary, when the latent image with the image interval narrowed reaches the transfer point 38 at a timing when the speed is increased, the image interval of the transfer image is further narrowed. That is, if the distance from the exposure point 36 to the transfer point 38 (circumferential length of the photoconductor) is an integral multiple of the speed fluctuation cycle of the photoconductor, and exposure and transfer are performed in the same phase, the speed fluctuation of the photoconductor is When the phase is canceled and the phase is reversed, the speed variation is superimposed and the density of the transferred image is increased. Then, since the portion where the image pitch is dense becomes dark and the portion where the image pitch becomes coarse becomes thin, as shown in FIG. As described above, the density unevenness perpendicular to the paper transport direction occurs depending on the position of the exposure point 36, that is, the mounting positioning accuracy of the LED print head 26.
JP 2002-6588 A JP 10-166563 A

  In consideration of the above-described facts, the present invention can adjust the distance from the exposure point to the transfer point, and can suppress an image quality defect (density variation) due to the speed variation of the photosensitive member, and the image quality in the image forming device. An object is to obtain an adjustment method.

  According to the first aspect of the present invention, the photosensitive member having an outer peripheral surface that is a cylindrical surface to be exposed, and a plurality of light emitting points that are opposed to the surface to be exposed, emit light corresponding to image information. An exposure device that irradiates a surface to be exposed by irradiation from a point; a developing device that develops the exposed surface exposed by the exposure device; and a transfer member to which an image on the exposed surface by the developing device is transferred Holding means for holding the exposure device such that the light emitting point moves on a circumference around the central axis of the photoreceptor, and positioning means for positioning and fixing the exposure device at a predetermined fixed position. It is characterized by having.

  In this image forming apparatus, the exposure surface of the photosensitive member is exposed by an exposure device, and further developed by a developing device, and the obtained image is transferred to a transfer member.

  The exposure device is held by holding means so that the light emitting point moves on a circumference around the central axis of the photosensitive member. Therefore, by this movement, the exposure point is moved to an arbitrary position, and the distance from the exposure point to the transfer point (primary transfer point to the member to be transferred) is fixed at a position that is an integral multiple of the speed fluctuation cycle of the photoconductor. Thus, it is possible to obtain a good image state by suppressing the density fluctuation accompanying the speed fluctuation of the photoreceptor.

  According to a second aspect of the present invention, in the first aspect of the present invention, the holding means includes at least a holding unit that integrally holds the photosensitive member and the exposure device. Features.

  By thus unitizing the photoconductor and the exposure device by the holding unit, it is possible to maintain their relative positions with high accuracy.

  The invention according to claim 3 is characterized in that, in the invention according to claim 2, the positioning means is capable of adjusting the fixed position of the holding unit.

  By making it possible to adjust the fixing position of the holding unit, it is possible to absorb the variation between them and obtain a good image.

  The invention according to claim 4 is the invention according to any one of claims 1 to 3, further comprising a housing, wherein the positioning means is provided in the housing. .

  Generally, fluctuations in the speed of the photoreceptor that cause density unevenness occur in the drive unit of the image forming apparatus. The state of the transfer point is also affected by the distortion of the housing. As described above, there are many image quality fluctuation factors on the apparatus main body side. According to the fourth aspect of the present invention, when the positioning means is provided in the housing, the positioning reference for determining the exposure point remains in the housing. Therefore, even if the unitized photoconductor and the exposure device are replaced. Adjusted image quality is maintained.

  In addition, when the photosensitive member and the exposure device are unitized by the holding unit, the exposure device can be brought into and out of contact with the photosensitive member by attaching and detaching the unit to and from the housing. A mechanism (such as a retract mechanism) for releasing is not required, and the mounting structure can be simplified.

  The invention according to claim 5 is characterized in that, in the invention according to claim 4, the positioning means is provided on the holding unit attaching / detaching operation side of the housing.

  As a result, the positioning means is arranged on the side where the housing is easily accessible, so that the manufacturing process, the inspection process, and the maintenance process (such as density unevenness adjustment during use) can be easily performed.

  According to a sixth aspect of the present invention, there is provided an image forming unit comprising at least the photosensitive member, the exposure device, and the developing device according to any one of the first to fifth aspects. A plurality of photoconductors arranged in parallel with each other, and the transfer member is arranged so that the plurality of photoconductors are in contact with each other. .

  That is, this image forming apparatus is a tandem type image forming apparatus in which image forming units are arranged in tandem. Thereby, it is possible to form an image of a plurality of colors (for example, full color).

  Then, by adjusting the exposure point by moving the light emission point in each of the image forming units, it is possible to obtain a plurality of high-quality images.

  According to a seventh aspect of the invention, there is provided an image quality adjustment method for an image forming apparatus according to any one of the first to sixth aspects, wherein a predetermined density unevenness test pattern is output, and based on the output result. Then, the image quality is adjusted by rotating the exposure unit on the circumference.

  As the density unevenness test pattern, a pattern that can easily detect uneven rotation speed of the photosensitive member can be used. Then, by adjusting the image quality by rotating the exposure unit on the circumference based on the output result, the exposure point can be adjusted reliably and efficiently.

  Since the present invention is configured as described above, the distance from the exposure point to the transfer point can be adjusted, and image quality defects (density fluctuations) due to fluctuations in the speed of the photoreceptor can be suppressed.

  FIG. 1 shows an image forming apparatus 102 according to the first embodiment of the present invention. The image forming apparatus 102 is a so-called tandem type image forming.

  The image forming apparatus 102 includes an intermediate transfer belt 104 that is stretched substantially horizontally, and four image forming units 106 corresponding to different development colors are disposed below the intermediate transfer belt 104. In the following description, if it is necessary to distinguish between colors, Y (yellow), M (magenta), C (cyan), or K (black) is indicated after the reference sign. To do.

  As shown in FIGS. 2 to 4, the image forming unit 106 includes a housing 120, in which the photosensitive member 108, the charger (BCR) 109, the LED print head 110, and the cleaner 112 are accommodated. Has been unitized. Further, the exposed surface (outer peripheral surface) 108E of the photosensitive member 108 is partially exposed from the housing 120, and the developing unit 114 disposed outside the housing 120 develops in this exposed portion as shown in FIG. The roller is in contact. Further, the exposed surface 108E of the photoconductor 108 is in contact with the intermediate transfer belt 104 on the downstream side of the developing device 114 in the rotation direction (arrow R direction).

  The photoconductor 108 is an exposed surface 108E having at least an outer peripheral surface that is cylindrical, and an electrostatic latent image can be formed on the exposed surface 108E.

  The LED print head 110 includes a plurality of LEDs (light emitting points) 116 facing the exposed surface 108E, and these LEDs 116 are turned on based on image data transferred from a controller (not shown). Light from the LED 116 is irradiated to the exposure point 122 on the exposed surface 108E charged by the charger 109 via the Selfoc lens 118, and a latent image is formed on the exposed surface 108E. When the photoconductor 108 rotates counterclockwise, the latent image is developed into a developed image by the developing device 114 and is primarily transferred to the intermediate transfer belt 104 at the primary transfer point 128. The intermediate transfer belt 104 rotates clockwise in FIG. 1, and images corresponding to each color of Y (yellow), M (magenta), C (cyan), and K (black) are sequentially transferred and superimposed. After that, secondary transfer is performed at the secondary transfer point 130 onto the paper fed from the paper tray 132. The second-transferred paper is fixed by the fixing device 134 and stacked on the paper discharge tray 136. Further, the exposed surface 108E of the photoconductor 108 is cleaned by the cleaner 112 after passing the primary transfer point 128.

  As shown in FIGS. 3 and 4, a photoreceptor flange 138 is fitted on both sides of the photoreceptor 108 of the image forming unit 106, and a shaft 140 is inserted into the photoreceptor flange 138 to constitute a photoreceptor assay as a whole. Has been. A bearing 144 is fitted to the photoreceptor flange 138 of the photoreceptor assay, and this bearing 144 is supported by the housing 120 of the image forming unit.

  As shown in FIGS. 1 and 5, the image forming unit 106 can be inserted and mounted from the front side of the image forming apparatus 102 through an open hole 148 provided in the housing 146 of the image forming apparatus 102. In the mounted state, the shaft 140 constituting the shaft of the photoconductor 108 is supported by a rear frame and a front positioning frame (not shown), and the image forming unit 106 can rotate around the shaft 140.

  As shown in FIGS. 3 and 4, the LED print head 110 includes positioning pins 150 at both ends thereof. Further, a pressing spring 152 is fitted in a compressed state on the opposite side of the positioning pin 150 with the LED print head 110 interposed therebetween. By using the pressing force of the pressing spring 152 to abut the tip of the positioning pin 150 against the bearing 144, the LED print head 110 can be positioned in the optical axis direction with respect to the photoreceptor 108.

  Since the image forming unit 106 supports the photosensitive member 108 and the LED print head 110 with an integrally configured housing 120, the image forming unit 106 does not have a mechanism for releasing the pressure of the LED print head 110, and has a fitting hole provided in the housing 120. Since the position of the positioning pin 150 in the circumferential direction (exposure point) of the positioning pin 150 is regulated at 154, the LED print head 110 is abutted against the bearing 144 and positioned in a stable state.

  FIG. 5 shows the positioning portion of the image forming unit 106 in an enlarged manner. A contact portion 156 protrudes from one end of the housing 120, and the position of the image forming unit 106 with respect to the rotation shaft (shaft 140) of the photosensitive member 108 is brought into contact with the contact portion 156 by contacting the positioning cam 158. That is, the exposure point 122 can be determined.

  As shown in detail in FIG. 6, the positioning cam 158 is formed in a substantially fan shape and is rotatably attached to a support shaft 160 provided in the housing 146 of the image forming apparatus 102. A portion of the positioning cam 158 facing the contact portion 156 is a cam portion 162 whose distance from the support shaft 160 gradually changes in the circumferential direction, and a part of the cam portion 162 is a contact portion 156 at a contact point 164. In contact with. In the vicinity of the cam portion 162, an arc-shaped long hole 166 having a certain radius from the support shaft 160 is formed. The screw 172 inserted through the long hole 166 is screwed into the housing 146, and the posture of the positioning cam 158 is maintained.

  A gear portion 168 is provided on the opposite side of the cam portion 162 and meshes with an adjustment gear 170 that is rotatably attached to the housing 146. By rotating the adjustment gear 170, the positioning cam 158 also rotates, so that the position of the contact point 164 moves. As a result, the distance from the center of the support shaft 160 to the contact point 164 changes, and the housing 120 rotates about the shaft 140. Then, the posture of the image forming unit 106 is adjusted, and the position of the exposure point 122 on the exposed surface 108E on the photoconductor 108 is also adjusted. The position of the exposure point 122 is set such that the distance from the exposure point 122 to the primary transfer point 128 is an integral multiple of the fluctuation cycle of the rotation speed of the photoconductor 108, and fluctuations in exposure and transfer are canceled out.

  In the state where the adjustment is completed, the screw 172 inserted through the long hole 166 is tightened, and the positioning cam 158 is fixed in this posture. As described above, since the positioning cam 158 is fixed to the housing 146 at a predetermined adjustment position, the adjustment position is maintained even when the image forming unit 106 is attached or detached. The image forming unit 106 is pressed against the positioning cam 158 by pressing means (not shown) from the opposite side of the positioning cam 158, and the housing 120 is sandwiched between the pressing means and the positioning cam 158. The posture is to be maintained. The pressing means is not particularly limited, but it is preferable to use a spring such as a compression coil spring or a leaf spring because the structure is not complicated.

  In the image forming apparatus 102 according to the first embodiment having such a configuration, as described above, the distance from the exposure point 122 to the primary transfer point 128 is an integral multiple of the fluctuation cycle of the rotation speed of the photoconductor 108, and exposure is performed. The position of the exposure point 122 is set so that fluctuations in the transfer cancel each other. That is, in the state where the position of the exposure point 122 is not adjusted, for example, when the speed of the photoconductor 108 changes, the density of the image (transfer image at the primary transfer point 128) is adjusted as shown in FIG. This may cause density unevenness in the cycle of speed fluctuation. On the other hand, in the present embodiment, it is possible to suppress density unevenness accompanying the speed fluctuation of the photoconductor 108 and obtain a good image state. In particular, in the tandem type image forming apparatus as in this embodiment, by adjusting the position of the exposure point 122 in each of the image forming units 106, a high-quality image without color misregistration among a plurality of colors is recorded. It is also possible.

  For example, this position adjustment may be performed in advance in a predetermined position in the manufacturing process of the image forming apparatus 102. That is, in the image quality adjustment process, halftone samples are output to check density unevenness. If the determination criterion is exceeded, the positioning cam 158 is adjusted to suppress density unevenness.

  In this embodiment, as an example, since the speed variation period of the photoconductor 108 is 3 mm pitch, if the posture of the image forming unit 106 is adjusted so that the phase shift is within ± 0.75 mm corresponding to a quarter period. The density unevenness caused by the phase shift is within an allowable range.

  FIG. 7 partially shows the image forming apparatus according to the second embodiment of the present invention. In the second embodiment, since only the configuration of the positioning unit that positions the image forming unit 106 at a predetermined position is different from that of the first embodiment, the description of the overall configuration of the image forming apparatus is omitted, and the first embodiment is different from the first embodiment. Only the differences are described.

  In the second embodiment, the holding piece 174 is provided in the housing 146. The holding piece 174 is formed with a female screw, and an adjusting screw 176 is screwed into the holding piece 174. The tip of the adjustment screw 176 is in contact with the contact portion 156, and the posture of the image forming unit 106 can be adjusted by rotating the adjustment screw 176.

  In general, the housing 146 is often configured to include a sheet metal at least at a part thereof, and therefore the holding piece 174 can be configured by partially bending the sheet metal. Of course, the holding piece 174 may be configured by fixing a member formed separately from the housing 146 to the housing 146.

  In each embodiment of the present invention, at least the photosensitive member 108 and the LED print head 110 are unitized, so that the mechanism for pressing the LED print head 110 closer to or away from the photosensitive member 108, and pressing and pressing. Since a mechanism for releasing (retract mechanism) is not required, the structure can be simplified. In addition, the relative positional relationship between the photoconductor 108 and the LED print head 110 can be maintained with high accuracy by unitization.

  In such a configuration in which the photoconductor 108 and the LED print head 110 are integrally accommodated in the image forming unit 106, for example, if a long-life photoconductor such as an amorphous silicon photoconductor is used as the photoconductor 108, the image forming unit 106 is In many cases, the image forming apparatus 102 can be used until the lifetime of the apparatus. Further, when the life of the photoconductor is shorter than the life of the apparatus, the image forming unit 106 may be collected at the manufacturing factory, and only the photoconductor 108 may be replaced and re-supplied to the production line of the newly formed image forming apparatus. Further, the image forming unit 106 may be replaced only on the photoconductor 108 at the site where the image forming apparatus 102 is used.

  Of course, in the present invention, the photosensitive member 108 and the LED print head 110 need not be unitized. For example, the photosensitive member 108 and the LED print head 110 may be independently held by the housing 146. In such a separate configuration, for example, a member that holds the LED print head 110 in a movable manner (for example, the shaft 140 of the photoconductor 108 is formed around the shaft 140 and holds both end portions of the LED print head 110. Possible grooves or the like).

  Further, a member that contacts the positioning portion, that is, the contact portion 156 to position the housing 146 (image forming unit 106) at a predetermined position is also provided on the housing 146 side like the above-described positioning portion. For example, it may be provided on the housing 120 side. However, in general, the speed fluctuation of the photoconductor 108 often occurs in the drive unit of the image forming apparatus 102. Also, the state of the primary transfer point 128 may be affected by the distortion of the housing 146. Therefore, if the positioning unit is provided on the housing 146 side, the positioning reference for determining the exposure point remains on the housing 146 side. Therefore, even if the unitized photoconductor 108 and the LED print head 110 are replaced, The image quality after adjustment can be maintained.

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to a first embodiment of the present invention. 1 is a perspective view illustrating an image forming unit of an image forming apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating an image forming unit of an image forming apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view illustrating an image forming unit of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a front view illustrating an image forming unit of the image forming apparatus according to the first embodiment of the present invention and a positioning unit that positions the image forming unit. FIG. 2 is an enlarged front view showing a positioning cam of the positioning unit and the vicinity thereof in the image forming apparatus according to the first embodiment of the present invention. It is a front view which expands and shows the positioning cam of the positioning part which concerns on the image forming apparatus of 2nd Embodiment of this invention, and its vicinity. It is the schematic which shows the structure of the conventional image forming apparatus. It is a perspective view which shows the structure of the LED array of the conventional image forming apparatus. 1 is a schematic diagram illustrating an image forming unit and its vicinity of an image forming apparatus. It is explanatory drawing which shows the mechanism of the image formation in an image forming apparatus. FIG. 6 is an explanatory diagram showing a relationship between a speed fluctuation of a photosensitive member, a fluctuation of an image pitch, and uneven density of an image.

Explanation of symbols

102 Image forming apparatus 104 Intermediate transfer belt (member to be transferred)
106 Image forming unit 108 Photoconductor 110 LED print head (exposure device)
112 Cleaner 114 Developer 116 LED (light emitting point)
118 Selfoc lens 120 housing (holding unit, holding means)
122 Exposure point 128 Primary transfer point 130 Secondary transfer point 132 Paper tray 134 Fixing device 136 Paper discharge tray 138 Photosensitive flange 140 Shaft 144 Bearing 146 Housing 148 Open hole 150 Pin 152 Press spring 154 Fitting hole 156 Abutting portion 158 Cam (positioning means)
160 Support shaft 162 Cam portion 164 Contact point 166 Long hole 168 Gear portion 170 Adjustment gear 172 Screw 174 Holding piece 176 Adjustment screw

Claims (7)

A photoreceptor whose outer peripheral surface is a cylindrical exposed surface;
An exposure device that is arranged so that a plurality of light emitting points are opposed to the surface to be exposed, and that exposes the surface to be exposed by irradiating light corresponding to image information from the light emitting point
A developing unit for developing the exposed surface exposed by the exposure unit;
A transfer member to which an image on an exposed surface by the developing device is transferred;
Holding means for holding the exposure device such that the light emitting point moves on a circumference around the central axis of the photoreceptor;
Positioning means for positioning and fixing the exposure device at a predetermined fixed position;
An image forming apparatus comprising: A holding unit in which the holding means integrally holds at least the photosensitive member and the exposure unit;
The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 2, wherein the positioning unit is capable of adjusting the fixed position of the holding unit. A housing,
The image forming apparatus according to claim 1, wherein the positioning unit is provided in the housing.   The image forming apparatus according to claim 4, wherein the positioning unit is provided on the holding unit attaching / detaching operation side of the housing. A plurality of image forming units each including at least the photoconductor, the exposure unit, and the developing unit are provided, and the rotation axes of the respective photoconductors of the image forming unit are arranged in parallel,
6. The image forming apparatus according to claim 1, wherein the member to be transferred is arranged so that a plurality of the photoconductors are in contact with each other. An image quality adjustment method in an image forming apparatus according to any one of claims 1 to 6,
An image quality adjustment method comprising: outputting a predetermined density unevenness test pattern, and adjusting the image quality by rotating the exposure unit on the circumference based on the output result.

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