Optical scanning apparatus, method of manufacturing optical scanning apparatus, and image forming apparatus

Abstract

To provide an optical scanning apparatus that can prevent image defects while keeping manufacturing cost low.SOLUTION: An optical scanning apparatus comprising a light source having five or more light-emitting portions arrayed in a row, a cylindrical lens, a restricting portion, a polygon mirror, and a plurality of scanning lenses, wherein a plurality of the light sources are provided and each emits a light beam. The restricting portion has a plurality of first apertures that restrict the optical path width of the light beams along the sub-scanning direction. Each of the first apertures has a first opening that penetrates in the optical axis direction and allows the light beam to pass therethrough. The centers of the first openings in the sub-scanning direction are disposed displaced in the sub-scanning direction.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an optical scanning device, a method for manufacturing an optical scanning device, and an image forming apparatus. [Background technology]

[0002] A conventional optical scanning device is disclosed in Patent Document 1. This optical scanning device employs a multi-beam system and includes a light source having five or more light-emitting elements arranged in a row, a cylindrical lens, a regulating unit, a polygon mirror, and multiple scanning lenses. The cylindrical lens focuses the light beams emitted from each light-emitting element. The regulating unit regulates the optical path width of the light beams incident on the cylindrical lens. The polygon mirror has a deflecting surface that reflects the light beams that have passed through the cylindrical lens, and rotates around its axis to scan the scanned surface of an image carrier in the main scanning direction. The multiple scanning lenses form an image of the light beams reflected by the polygon mirror on the scanned surface of the image carrier.

[0003] Each light beam emitted from each light-emitting element is reflected by one deflection surface and forms an image on the surface to be scanned. When the image carrier rotates, each light beam is reflected by the next deflection surface and forms an image on the surface to be scanned. The formed light beams are aligned at a predetermined interval in the sub-scanning direction.

[0004] The scanning lens is formed in a non-arcuate shape in the sub-scanning cross section defined by a polynomial including an aspherical coefficient, thereby preventing scanning curvature and field curvature of each light beam imaged on the scanned surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-14953 Summary of the Invention [Problem to be solved by the invention]

[0006] In the configuration of Patent Document 1, if the rotation axis of the polygon mirror is tilted and axial tilt occurs, the angle of incidence of each light beam on the scanning lens changes. At this time, each light beam formed on the scanned surface is shifted in the sub-scanning direction. This causes uneven spacing between each formed light beam in the sub-scanning direction, which can lead to image defects such as color shift.

[0007] An object of the present invention is to provide an optical scanning device, a manufacturing method for an optical scanning device, and an image forming apparatus that can prevent the occurrence of image defects while suppressing manufacturing costs. [Means for solving the problem]

[0008] In order to achieve the above object, a first configuration of the present invention is an optical scanning device including a light source having five or more light-emitting elements arranged in a row, a cylindrical lens, a regulating unit, a polygon mirror, and multiple scanning lenses. The cylindrical lens focuses the light beams emitted from each light-emitting element. The regulating unit regulates the optical path width of the light beam incident on the cylindrical lens. The polygon mirror has a deflecting surface that reflects the light beam that has passed through the cylindrical lens and rotates around its axis to scan the light beam on the scanned surface of the image carrier in the main scanning direction. The multiple scanning lenses focus the light beam reflected by the polygon mirror on the scanned surface of the image carrier. Multiple light sources are provided, and each light source emits a light beam. The regulating unit has multiple first apertures that regulate the optical path width of each light beam in the sub-scanning direction. Each first aperture has a first opening that penetrates in the optical axis direction and through which the light beam passes. The centers of the first openings in the sub-scanning direction are positioned at different positions in the sub-scanning direction.

[0009] In order to achieve the above object, a second aspect of the present invention is a method for manufacturing an optical scanning device including a light source having five or more light-emitting elements arranged in a row, a cylindrical lens, a first aperture, a polygon mirror, and multiple scanning lenses. The cylindrical lens focuses the light beams emitted from each light-emitting element. The first aperture regulates the optical path width in the sub-scanning direction of the light beam incident on the cylindrical lens and is movable in the sub-scanning direction. The polygon mirror has a deflection surface that reflects the light beam that has passed through the cylindrical lens and rotates around its axis to scan the light beam in the main scanning direction on the scanned surface of the image carrier. The multiple scanning lenses focus the light beam reflected by the polygon mirror on the scanned surface of the image carrier. The method for manufacturing an optical scanning device includes a beam pitch adjustment process. The beam pitch adjustment step adjusts the interval in the sub-scanning direction between the light beams imaged on the scanned surface across the main scanning direction by moving the first aperture in the sub-scanning direction, by moving the light beams emitted from the light-emitting elements and imaged at one end of the scanned surface in the sub-scanning direction and the light beams imaged at the other end of the scanned surface in the sub-scanning direction. In the beam pitch adjustment step, the light beams emitted from the light-emitting elements and imaged at one end of the scanned surface in the sub-scanning direction and the light beams imaged at the other end of the scanned surface in the sub-scanning direction move in opposite directions in the sub-scanning direction at the upstream end and downstream end of the scanned surface in the main scanning direction. [Effects of the Invention]

[0010] According to the first and second aspects of the present invention, it is possible to provide an optical scanning device that can prevent the occurrence of image defects while suppressing manufacturing costs, and an image forming apparatus including the same. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 according to an embodiment of the present invention. [Figure 2] 1 is a top view of an optical scanning device 5 according to an embodiment of the present invention. [Figure 3] 1 is a cross-sectional view of an optical scanning device 5 according to an embodiment of the present invention; [Figure 4] FIG. 1 is a sub-scanning cross-sectional view showing an imaging state of a light beam D1 of an optical scanning device 5 according to an embodiment of the present invention. [Figure 5] FIG. 1 is a cross-sectional view showing a schematic configuration of an optical scanning device 5 according to an embodiment of the present invention. [Figure 6] FIG. 1 is a perspective view of a light source unit 26 of an optical scanning device 5 according to an embodiment of the present invention. [Figure 7] FIG. 1 is an explanatory diagram schematically illustrating a scanning line SL formed by an optical scanning device 5 according to an embodiment of the present invention. [Figure 8] FIG. 1 is an explanatory diagram schematically illustrating a scanning line SL formed by an optical scanning device 5 according to an embodiment of the present invention. [Figure 9] FIG. 1 is a sub-scanning cross-sectional view showing the optical paths of light beams LB1 and LB8 in an optical scanning device 5 according to an embodiment of the present invention. [Figure 10] FIG. 1 is a sub-scanning cross-sectional view showing the optical paths of light beams LB1 and LB8 in an optical scanning device 5 according to an embodiment of the present invention. [Figure 11] FIG. 1 is a sub-scanning cross-sectional view showing the optical paths of light beams LB1 and LB8 in an optical scanning device 5 according to an embodiment of the present invention. [Figure 12] FIG. 1 is an enlarged sub-scanning cross-sectional view showing the optical paths of light beams LB1 and LB8 in an optical scanning device 5 according to an embodiment of the present invention. [Figure 13] FIG. 1 is an enlarged sub-scanning cross-sectional view showing the imaging state of light beams LB1 and LB8 of an optical scanning device 5 according to an embodiment of the present invention. [Figure 14] FIG. 10 is a sub-scanning cross-sectional view showing the optical paths of the light beams LB1 and LB8 of the optical scanning device 5 according to a modified example of the embodiment of the present invention. [Figure 15] FIG. 10 is a sub-scanning cross-sectional view showing the optical paths of the light beams LB1 and LB8 of the optical scanning device 5 according to a modified example of the embodiment of the present invention. [Figure 16] FIG. 1 is an enlarged sub-scanning cross-sectional view showing the imaging state of light beams LB1 and LB8 of an optical scanning device 5 according to an embodiment of the present invention. [Figure 17] 1 is a plan view of an intermediate transfer belt 8 of an image forming apparatus 100 according to an embodiment of the present invention; [Figure 18]1 is a flowchart listing steps executed in a method for manufacturing an optical scanning device 5 according to an embodiment of the present invention. [Figure 19] FIG. 1 is an explanatory diagram schematically illustrating a scanning line SL formed by an optical scanning device 5 according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] 1. Configuration of Image Forming Apparatus 100 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a schematic cross-sectional view showing the overall configuration of an image forming apparatus 100 equipped with an optical scanning device 5 of the present invention. The image forming apparatus 100 includes the optical scanning device 5, photosensitive drums (image carriers) 1a-1d, charging devices 2a-2d, developing devices 3a-3d, primary transfer rollers 6a-6d, a secondary transfer roller 9, a paper cassette 16, a fixing device 13, an image density sensor 50, and a control unit 90.

[0013] Specifically, image forming apparatus 100 is a tandem color printer. Four image forming units Pa, Pb, Pc, and Pd are arranged in this order within the main body of image forming apparatus 100 from the upstream side in the transport direction (the right side in FIG. 1). These image forming units Pa to Pd are provided corresponding to images of four different colors (yellow, magenta, cyan, and black), and sequentially form images of yellow, magenta, cyan, and black through the processes of charging, exposure, development, and transfer, respectively.

[0014] The image forming apparatus 100 includes rotatable photosensitive drums 1a to 1d as image carriers. The photosensitive drums 1a to 1d are made of organic photosensitive materials (OPC photosensitive materials) having an organic photosensitive layer formed thereon, or amorphous silicon photosensitive materials having an amorphous silicon photosensitive layer formed thereon, etc. The photosensitive drums 1a to 1d are arranged in tandem corresponding to the colors yellow, magenta, cyan, and black.

[0015] A developing device 3a, a charging device 2a, and a cleaning device 7a are disposed around the photosensitive drum (image carrier) 1a. Similarly, developing devices 3b-3d, charging devices 2b-2d, and cleaning devices 7b-7d are disposed around each of the photosensitive drums 1b-1d. An optical scanning device 5 is disposed below the developing devices 3a-3d.

[0016] The developing devices 3a to 3d are disposed opposite the photosensitive drums (image carriers) 1a to 1d and have developing rollers (developer carriers) 21a to 21d. The developing devices 3a to 3d apply a predetermined developing voltage to the developing rollers (developer carriers) 21a to 21d to cause toner to adhere to the electrostatic latent images formed on the photosensitive drums (image carriers) 1a to 1d, thereby forming toner images. The developing devices 3a to 3d face the photosensitive drums 1a to 1d, respectively, and supply toner to the photosensitive drums 1a to 1d. The developing devices 3a to 3d have containers 4a to 4d, which contain magenta, cyan, yellow, and black toner.

[0017] The charging devices 2a to 2d are disposed upstream of the developing devices 3a to 3d in the rotation direction of the photosensitive drums 1a to 1d, and face the surfaces of the photosensitive drums 1a to 1d, respectively. The charging devices 2a to 2d uniformly charge the surfaces of the photosensitive drums 1a to 1d, respectively.

[0018] The cleaning devices 7a to 7d remove residual developer (toner) and the like from the photosensitive drums 1a to 1d.

[0019] In this embodiment, the optical scanning device 5 is disposed below the photosensitive drums 1a to 1d. The optical scanning device 5 irradiates (optically scans) the surfaces of the photosensitive drums 1a to 1d, which have been uniformly charged by the charging devices 2a to 2d, with light based on image data such as characters and pictures input to an image input unit from a personal computer or the like. As a result, electrostatic latent images are formed on the surfaces of the photosensitive drums 1a to 1d.

[0020] Intermediate transfer belt (belt) 8 is provided adjacent to each of the image forming stations Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred (primary transfer) onto the intermediate transfer belt 8, which moves while contacting each of the photosensitive drums 1a to 1d, and are superimposed.

[0021] The toner image that has been primarily transferred onto the intermediate transfer belt 8 is secondarily transferred onto a sheet of paper S (recording medium) as an example of a recording medium by a secondary transfer roller 9. Furthermore, the toner image on the sheet of paper S that has been secondarily transferred onto it is fixed by a fixing device 13, and then the sheet of paper S is discharged from the main body of the image forming apparatus 100.

[0022] The paper S onto which the toner image is secondarily transferred is stored in a paper cassette 16 located at the bottom of the main body of the image forming apparatus 100, and is transported via a paper feed roller 12a and a pair of registration rollers 12b to the nip between the secondary transfer roller 9 and the drive roller 11 of the intermediate transfer belt 8. In addition, a blade-shaped belt cleaner 19 is located downstream of the secondary transfer roller 9 to remove toner and other particles remaining on the surface of the intermediate transfer belt 8.

[0023] When image data is input from a host device such as a personal computer, the surfaces of the photosensitive drums 1a-1d are first uniformly charged by the charging devices 2a-2d. Next, the optical scanning device 5 irradiates light according to the image data, forming electrostatic latent images on the photosensitive drums 1a-1d in accordance with the image data. The developing devices 3a-3d are filled with a predetermined amount of two-component developer containing yellow, magenta, cyan, and black toner, respectively. If the toner content in the two-component developer in each developing device 3a-3d falls below a specified value due to the formation of a toner image (described below), toner is replenished from containers 4a-4d to each developing device 3a-3d. The toner in the developer is supplied to the photosensitive drums 1a-1d by the developing devices 3a-3d and electrostatically adheres to them. This results in the formation of a toner image corresponding to the electrostatic latent image formed by the exposure from the optical scanning device 5.

[0024] Then, primary transfer rollers 6a-6d apply an electric field at a predetermined transfer voltage between the primary transfer rollers 6a-6d and the photosensitive drums 1a-1d, and the yellow, magenta, cyan, and black toner images on the photosensitive drums 1a-1d are primarily transferred onto the intermediate transfer belt 8. These four color images are formed in a predetermined positional relationship for forming a predetermined full-color image. After that, toner and other substances remaining on the surfaces of the photosensitive drums 1a-1d after the primary transfer are removed by cleaning devices 7a-7d in preparation for the subsequent formation of a new electrostatic latent image.

[0025] The intermediate transfer belt 8 is stretched over a driven roller 10 on the upstream side and a drive roller 11 on the downstream side, and when the intermediate transfer belt 8 starts to rotate clockwise in accordance with the rotation of the drive roller 11 by a belt drive motor (not shown), the paper S is transported from the pair of registration rollers 12b to a nip portion (secondary transfer nip portion) between the drive roller 11 and a secondary transfer roller 9 provided adjacent thereto at a predetermined timing, and the full-color image on the intermediate transfer belt 8 is secondarily transferred onto the paper S. The paper S onto which the toner image has been secondarily transferred is transported to a fixing device 13.

[0026] The image density sensor 50 faces the driven roller 10 with the intermediate transfer belt 8 sandwiched therebetween. The image density sensor 50 is, for example, a specular reflection sensor that detects reflected light. The image density sensor 50 converts the measurement result into an electrical signal and outputs it to the control unit 90, which will be described later. The image density sensor 50 may be any sensor that can detect density information of a toner image, and may be, for example, a sensor that can detect density from an image obtained by capturing a toner image.

[0027] The paper S conveyed to the fixing device 13 is heated and pressurized by the fixing belt 21 and the pressure roller 22, and the toner image is fixed to the surface of the paper S, forming a predetermined full-color image. The paper S on which the full-color image has been formed is then directed to a different conveying direction by the branching section 30, which branches in multiple directions, and is then discharged directly (or after being sent to the double-sided conveying path 18 and having images formed on both sides) onto the discharge tray 17 by the discharge roller pair 15.

[0028] The control unit 90 comprehensively controls the image forming apparatus 100. Specifically, the control unit 90 controls the image forming unit, which includes an optical scanning device 5, photosensitive drums (image carriers) 1a to 1d, charging devices 2a to 2d, and developing devices 3a to 3d.

[0029] [2. Configuration of optical scanning device] Fig. 2 is a top view of the optical scanning device 5 with the cover removed. Fig. 3 is a cross-sectional view of the optical scanning device 5, without showing the scanning lens 49b. Fig. 4 is a sub-scanning cross-sectional view showing the imaging state of the light beam D1. In Fig. 3, the optical axes AX of the collimator lens 41, the cylindrical lens 42, and the multiple scanning lenses 49a and 49b are indicated by dashed lines.

[0030] The optical scanning device 5 includes a housing 39, a light source unit (light source) 26, a collimator lens 41, a cylindrical lens 42, a restriction portion 47, a polygon mirror 45, a plurality of scanning lenses 49a, 49b, exit mirrors 51a to 51d, and a reflecting mirror 52.

[0031] In this embodiment, four light source units 26 (light sources) and four collimator lenses 41 are provided corresponding to the image forming units Pa to Pd. Each light source unit (light source) 26 emits light beams D1 to D4 corresponding to the image forming units Pa to Pd, respectively (see FIG. 3). A plurality of light source units 26 (light sources) are provided, and a polygon mirror 45 reflects the plurality of light beams D1 to D4 emitted from each light source unit 26 to scan the scanned surfaces of the photosensitive drums (image carriers) 1a to 1d corresponding to each light source unit 26. This allows a single polygon mirror 45 to scan a plurality of photosensitive drums 1a to 1d, reducing the number of parts and the manufacturing cost of the optical scanning device 5.

[0032] The collimator lens 41 converts the light beams D1 to D4 emitted from the light source unit 26 into substantially parallel light beams (parallel light beams).

[0033] The cylindrical lens 42 has a predetermined refractive power only in the sub-scanning direction of the light beams D1 to D4, and condenses the light beams D1 to D4 emitted from the laser diodes LD1 to LD8 (light-emitting units) described below. The light source unit 26, the collimator lens 41, and the cylindrical lens 42 are arranged in a straight line.

[0034] The restricting portion 47 is a plate member disposed between the collimator lens 41 and the cylindrical lens 42. The restricting portion 47 restricts the optical path width of the light beams D1 to D4 that pass through the collimator lens 41 and enter the cylindrical lens 42. In this embodiment, the restricting portion 47 has a first aperture 43 and a second aperture 44. Four first apertures 43 are disposed, one for each light source unit 26 (light source). Furthermore, one second aperture 44 is disposed in common to all the light source units 26 (light source). This reduces the number of components of the second aperture 44, thereby reducing the manufacturing cost of the optical scanning device 5.

[0035] The polygon mirror 45 has a deflection surface 63 that reflects the light beams D1 to D4 that have passed through the cylindrical lens 42, and rotates around its axis to scan the light beams D1 to D4 on the scanned surfaces of the photosensitive drums (image carriers) 1a to 1d in the main scanning direction (X1-X2 direction) (see Figure 5).

[0036] The scanning lenses 49a and 49b are lenses having fθ characteristics. One scanning lens 49a is provided in common to each of the photosensitive drums 1a to 1d. Four scanning lenses 49b are provided corresponding to each of the photosensitive drums 1a to 1d (see FIGS. 2 and 3). The scanning lenses 49a and 49b are disposed between each of the photosensitive drums 1a to 1d and the polygon mirror 45, and focus the light beam LB reflected by the polygon mirror 45 on the scanned surface of each of the corresponding photosensitive drums (image carriers) 1a to 1d.

[0037] The light beams D1 to D4 are deflected and scanned in the main scanning direction (X1-X2 direction) by the polygon mirror 45. The light beams D1 to D4 scanned by the polygon mirror 45 are guided to exit mirrors 51a to 51d via optical elements such as scanning lenses 49a and 49b and reflecting mirrors 52a to 52c. The light beams D1 to D4 reflected by the exit mirrors 51a to 51d are then irradiated onto the photosensitive drums 1a to 1d of the image forming units Pa to Pd, respectively.

[0038] Fig. 5 is a cross-sectional view showing a schematic configuration of the optical scanning device 5, and Fig. 6 is a perspective view of the light source unit 26. Although the optical scanning device 5 performs optical scanning on each of the photosensitive drums 1a to 1d, only the optical scanning on the photosensitive drum 1a will be described here, and other descriptions will be omitted.

[0039] Each light source unit 26 (light source) has five or more laser diodes LD1 to LD8 (light-emitting units) and a beam generating unit 20. In this embodiment, eight laser diodes LD1 to LD8 (light-emitting units) are arranged in a row, but it is preferable to provide five or more laser diodes. Increasing the number of laser diodes can increase image resolution and reduce the rotation speed of the polygon mirror 45.

[0040] The light source unit 26 is rotatable in the circumferential direction about an axis (central axis J) that is normal to the light source unit 26 and passes through the center of the light source unit 26.

[0041] The laser diodes LD1 to LD8 are arranged linearly at equal intervals along the radial direction of the light source unit 26. Based on image information transmitted from the control unit 90, the beam generating unit 20 generates a light beam D1 (hereinafter also referred to individually as light beams LB1 to LB8) that is separately emitted from the laser diodes LD1 to LD8.

[0042] By rotating the light source unit 26, the spacing between the laser diodes LD1 to LD8 in the main scanning direction (X1-X2 direction) and the sub-scanning direction (Z1-Z2 direction) can be adjusted. When the laser diodes LD1 to LD8 are aligned in a line parallel to the sub-scanning direction (Z1-Z2 direction), the spacing between the laser diodes LD1 to LD8 in the main scanning direction (X1-X2 direction) is minimum, and the spacing between the laser diodes LD1 to LD8 in the sub-scanning direction (Z1-Z2 direction) is maximum. Conversely, when the laser diodes LD1 to LD8 are aligned in a line parallel to the main scanning direction (X1-X2 direction), the spacing between the laser diodes LD1 to LD8 in the main scanning direction (X1-X2 direction) is maximum, and the spacing between the laser diodes LD1 to LD8 in the sub-scanning direction (Z1-Z2 direction) is minimum (see the dashed line in FIG. 6 for both).

[0043] In this embodiment, the first aperture 43 is disposed closer to the collimator lens 41 than the second aperture 44. The first aperture 43 has a first opening 43a. The first opening 43a penetrates in the optical axis direction and allows the light beams LB1 to LB8 to pass through. The optical axis direction is a direction parallel to the direction in which the optical axis AX of the cylindrical lens 42 extends (see FIG. 3). The light beams LB1 to LB8 passing through the first opening 43a have their optical path widths in the sub-scanning direction (Z1-Z2 direction) restricted. That is, the first aperture 43 restricts the optical path widths of the light beams LB1 to LB8 in the sub-scanning direction (Z1-Z2 direction). The first aperture 43 is movable in the sub-scanning direction and is fixed at a predetermined position.

[0044] The second aperture 44 is disposed closer to the cylindrical lens 42 than the first aperture 43. The second aperture 44 has a second opening 44a. The light beams LB1 to LB8 that pass through the second opening 44a have their optical path widths regulated in the main scanning direction (X1-X2 direction). The beam widths of the light beams LB1 to LB8 that pass through the first aperture 43 and the second aperture 44 are regulated, stabilizing the beam spot diameters on the scanned surface of the photosensitive drum 1a.

[0045] The polygon mirror 45 is a regular polygonal prism (here, a regular hexagonal prism) with deflection surfaces 63 formed on each side. Each deflection surface 63 is a mirror surface and is capable of reflecting and deflecting the light beam D1 that has passed through the cylindrical lens 42. The polygon mirror 45 is supported so as to be rotatable about a central axis (not shown) that extends in the vertical direction (the direction of the paper in FIG. 2). The polygon mirror 45 is connected to a polygon motor (not shown) and rotates by the rotary driving force of the polygon motor.

[0046] The polygon mirror 45 is rotated at a constant speed in the clockwise direction by a polygon motor (not shown). Therefore, the light beam D1 is scanned at a constant speed in the main scanning direction (X2 direction) on the scanned surface of the photosensitive drum 1a. As a result, a scanning line SL extending linearly in the main scanning direction (X1-X2 direction) is formed on the scanned surface of the photosensitive drum 1a (see FIG. 5). One scanning line SL is drawn per deflection surface 63. As the polygon mirror 45 rotates, the light beam D1 is sequentially focused on adjacent deflection surfaces 63. As the photosensitive drum 1a rotates, multiple scanning lines SL are formed in the sub-scanning direction (Z1-Z2 direction), forming an electrostatic latent image.

[0047] The light beams LB1 to LB8 emitted from the light source unit 26 are incident on the collimator lens 41, the first aperture 43, the second aperture 44, and the cylindrical lens 42 in this order, and are each focused as a line image on the deflection surface 63. The light beams LB1 to LB8 focused on the deflection surface 63 are deflected and pass through the scanning lenses 49a and 49b, and are each focused on the photosensitive drum 1a with a spot diameter of a predetermined size.

[0048] 7 and 8 are explanatory diagrams schematically showing scanning lines SL. As shown in FIG. 7, one scanning line SL is formed by light beams LB1 to LB8 focused on the scanned surface of the photosensitive drum 1a. In one scanning line SL, the intervals W1 between the focused light beams LB1 to LB8 in the sub-scanning direction (Z1-Z2 direction) can be changed by rotating the light source unit 26 about the central axis J in accordance with a predetermined image resolution (see FIG. 6). For example, if the resolution is 1200 dpi, the intervals W1 between the focused light beams LB1 to LB8 in the sub-scanning direction (Z1-Z2 direction) are set to approximately 21 μm.

[0049] When the rotation axis of the polygon mirror 45 is tilted and axial tilt occurs, the intervals W1 between the focused light beams LB1 to LB8 in the sub-scanning direction (Z1-Z2 direction) change. Specifically, when the polygon mirror 45 is tilted, the reflection angles of the light beams LB1 to LB8 on the deflection surface 63 change, and the angles of incidence on the scanning lenses 49a and 49b also change. At this time, the image positions of the light beams LB1 to LB8 on the scanned surface shift in the sub-scanning direction (Z1-Z2 direction). This changes the intervals W1 between the focused light beams LB1 to LB8 in the sub-scanning direction (Z1-Z2 direction). This also changes the width of the scan line SL in the sub-scanning direction (Z1-Z2 direction).

[0050] At this time, the interval W2 between adjacent scanning lines SL (the interval between adjacent light beams LB1 and LB8 in the sub-scanning direction (Z1-Z2 direction)) also changes. As a result, the sizes of the intervals W1 and W2 differ, and the intervals between the images of the light beams LB1 to LB8 repeatedly aligned in the sub-scanning direction (Z1-Z2 direction) become non-uniform. This may result in image defects.

[0051] For example, when the interval W1 increases, the interval W2 decreases. On the other hand, when the interval W1 decreases, the interval W2 increases. Furthermore, as the number of light beams LB emitted from the light source unit 26 increases, the non-uniformity of the intervals W1 and W2 increases.

[0052] Furthermore, as shown in Figure 8, when the gap W1 increases toward the downstream side X2 in the main scanning direction, there is a possibility that the light beams LB1 and LB8 will reverse direction in the sub-scanning direction (Z1-Z2 direction) at the end of the downstream side X2 in the main scanning direction.

[0053] In contrast, in this embodiment, the first aperture 43 is moved in the sub-scanning direction (Z1-Z2 direction) to shift the image positions of the light beams LB1 to LB8 formed on the scanned surface in the sub-scanning direction (Z1-Z2 direction), thereby changing the reflection angles of the light beams LB1 to LB8 on the deflection surface 63 and adjusting the intervals W1 and W2.

[0054] More specifically, the light beam LB1 emitted from each laser diode LD1 to LD8 (light-emitting unit) and focused at the upper end of the scanned surface in the sub-scanning direction (end on one side Z1 of the sub-scanning direction) and the light beam LB8 focused at the lower end of the scanned surface in the sub-scanning direction (end on the other side Z2 of the sub-scanning direction) are moved in opposite directions in the sub-scanning direction (Z1-Z2 direction) at the end on the upstream side X1 of the scanned surface in the main scanning direction and the end on the downstream side X2 of the scanned surface in the main scanning direction. That is, in each scan line SL, the light beams LD1 to LD4 and the light beams LD5 to LD8 are moved in a direction separating them (arrow Z3 in FIG. 8) at the end on the upstream side X1 of the scanned surface in the main scanning direction, and are moved in a direction approaching them (arrow Z4 in FIG. 8) at the end on the downstream side X2 of the scanned surface in the main scanning direction.

[0055] As a result, the interval W1 between the light beams LB1 to LB8 becomes larger at the end on the upstream side X1 in the main scanning direction, and the interval W1 between the light beams LB1 to LB8 becomes smaller at the end on the downstream side X2 in the main scanning direction. Therefore, the intervals between the images of the light beams LB1 to LB8 repeatedly lined up in the sub-scanning direction (Z1-Z2 direction) can be made uniform across the main scanning direction (X1-X2 direction).

[0056] In this embodiment, the focal points of the light beams LB1 to LB8 on the scanning lenses 49a and 49b are shifted from each other in the optical axis direction. The amount of axial shift of the focal points of the light beams LB1 to LB8 varies across the main scanning direction (X1-X2 direction).

[0057] 9 to 12, 14, and 15 are sub-scanning cross sections showing the optical paths of the light beams LB1 and LB8, and FIGS. 13 and 16 are sub-scanning cross sections showing enlarged images of the light beams LB1 and LB8 of the optical scanning device 5. FIGS. 9 and 10 show the state of the light beams LB1 and LB8 from when they are emitted until they are incident on the polarization surface 63. FIGS. 11, 12, 14, and 15 show the state of the light beams LB1 and LB8 reflected by the polarization surface 63 until they are imaged on the scanned surface of the photosensitive drum 1a. FIGS. 11 and 12 show the optical paths of the light beams LB1 and LB8 at the end on the upstream side X1 in the main scanning direction. FIGS. 14 and 15 show the optical paths of the light beams LB1 and LB8 at the end on the downstream side X2 in the main scanning direction.

[0058] 9, 11, and 14 show the state before first aperture 43 is moved downward (the other side of the sub-scanning direction Z2), and FIGS. 10, 12, and 15 show light beams LB1 and LB8 after first aperture 43 is moved downward (the other side of the sub-scanning direction Z2). In FIGS. 9 to 16, light beam LB1 is indicated by a solid line, and light beam LB8 is indicated by a dashed line. In FIGS. 11 and 12, scanning lenses 49a and 49b are shown as a single unit, and second aperture 44 is not shown in FIGS. 9 and 10.

[0059] The optical axis direction (Y1-Y2 direction) is the direction in which the optical axis AX (see FIG. 4) of the scanning lenses 49a, 49b extends, and the optical axis direction (Y1-Y2 direction) is perpendicular to the main scanning direction (X1-X2 direction) and the sub-scanning direction (Z1-Z2 direction). The upstream side in the traveling direction of the light beams LB1, LB8 is referred to as the upstream side Y1 in the optical axis direction, and the downstream side in the traveling direction of the light beams LB1, LB8 is referred to as the downstream side Y2 in the optical axis direction.

[0060] In this embodiment, the scanning lenses 49a and 49b are arranged such that a first focal point F1 of the light beam LB1, which is focused on the upper end (the end on one side of the sub-scanning direction Z1) of the scanned surface of the photosensitive drum 1a among the light beams LB1 to LB8 emitted from the laser diodes LD1 to LD8 (light-emitting units), and a second focal point F8 of the light beam LB8, which is focused on the lower end (the end on the other side of the sub-scanning direction Z2) of the scanned surface of the photosensitive drum 1a, are positioned on opposite sides of the scanned surface in the optical axis direction. That is, the first focal point F1 of the light beam LB1 and the second focal point F8 of the light beam LB8 are positioned offset from each other in the optical axis direction.

[0061] Furthermore, the deviation in the optical axis direction between the first focal point F1 and the second focal point F8 of the scanning lenses 49a, 49b varies across the main scanning direction (X1-X2 direction). Specifically, the first focal point F1 at the end of the scanning lenses 49a, 49b on the upstream side X1 in the main scanning direction is located on the side farther from the scanning lens 49b (one side in the optical axis direction) than the second focal point F8 (see FIGS. 11 and 12), and the first focal point F1 at the end of the scanning lenses 49a, 49b on the downstream side X2 in the main scanning direction is located on the side closer to the scanning lens 49b than the second focal point F8 (the other side in the optical axis direction) (see FIGS. 14 and 15).

[0062] More specifically, the focal points of the light beams LB1 to LB4 are positioned at different positions in the optical axis direction, and in this embodiment, the focal points of the light beams LB1 to LB4 that are imaged on the scanned surface and the focal points of the light beams LB5 to LB8 that are imaged on the scanned surface are positioned on opposite sides of the scanned surface in the optical axis direction.

[0063] Furthermore, at the end of the upstream side X1 in the main scanning direction, the focal points of the light beams LB1 to LB4 are located farther from the scanning lens 49b than the scanned surface (one side in the optical axis direction), and the focal points of the light beams LB5 to LB8 are located closer to the scanning lens 49b than the scanned surface (the other side in the optical axis direction). Furthermore, at the end of the downstream side X2 in the main scanning direction, the focal points of the light beams LB1 to LB4 are located closer to the scanning lens 49b than the scanned surface (the other side in the optical axis direction), and the focal points of the light beams LB5 to LB8 are located farther from the scanning lens 49b than the scanned surface (one side in the optical axis direction). In other words, the positional relationship between the focal points of the light beams LB1 to LB4 and the focal points of the light beams LB5 to LB8 at the end of the upstream side X1 in the main scanning direction is reversed in the optical axis direction (Y1-Y2 direction) from the positional relationship between the focal points of the light beams LB1 to LB4 and the focal points of the light beams LB5 to LB8 at the end of the downstream side X2 in the main scanning direction. The light beams LB1 to LB8 are each focused in a blurred state on the surface to be scanned on the photosensitive drum 1a.

[0064] When the center in the sub-scanning direction of the first opening 43a of the first aperture 43 is shifted downward (in one direction in the sub-scanning direction) with respect to the optical axis, the light beams LB1 to LB8 passing through the first opening 43a are shifted downward (in the other direction Z2 in the sub-scanning direction) and enter the cylindrical lens 42. The light beams LB1 to LB8 that have passed through the cylindrical lens 42 are focused on the polarization plane 63 (see FIGS. 9 and 10). The light beams LB1 to LB8 that have been focused on the polarization plane 63 are reflected and enter the scanning lens 49a (see FIGS. 11 and 12).

[0065] At this time, the light beams LB1 to LB8 are incident on the scanning lens 49a while shifting downward (to the other side of the sub-scanning direction Z2), and the incident angle to the scanning lens 49a becomes smaller. In this embodiment, the light beam LB1, which is the first beam incident on the end of the scanning lens 49a on the upstream side X1 in the main scanning direction, is directed toward a first focal point F1, which is located farther from the scanning lens 49b than the scanned surface of the photosensitive drum 1a (see FIGS. 10 and 11). At this time, the light beam LB1 that is incident on the scanning lens 49a while shifting downward (to the other side of the sub-scanning direction Z2) is shifted upward (to one side of the sub-scanning direction Z1) on the scanned surface of the photosensitive drum 1a (see FIG. 13). Furthermore, although not shown, the light beams LB2 to LB4 that form images on the scanned surface are also shifted upward (to one side of the sub-scanning direction Z1).

[0066] Meanwhile, the light beam LB8, which is the last beam incident on the end of the scanning lens 49a on the upstream side X1 in the main scanning direction, is directed toward a second focal point F8 located closer to the scanning lens 49b than the scanned surface of the photosensitive drum 1a (see FIGS. 11 and 12). At this time, the light beam LB8, which is shifted downward (the other side of the sub-scanning direction Z2) and incident on the scanning lens 49a, is shifted downward (the other side of the sub-scanning direction Z2) on the scanned surface of the photosensitive drum 1a (see FIG. 13). Although not shown, the light beams LB5 to LB7 that form images on the scanned surface are also shifted downward (the other side of the sub-scanning direction Z2). Therefore, in each scanning line SL, the light beams LD1 to LD4 and the light beams LD5 to LD8 can be moved away from each other (arrow Z3 in FIG. 8) at the end of the scanned surface on the upstream side X1 in the main scanning direction.

[0067] Furthermore, the light beam LB1, which is the first beam incident on the end of the scanning lens 49a on the downstream side X2 in the main scanning direction, is directed toward a first focal point F1 located closer to the scanning lens 49b than the scanned surface of the photosensitive drum 1a (see FIGS. 14 and 15). At this time, the light beam LB1, which is shifted downward (the other side of the sub-scanning direction Z2) and incident on the scanning lens 49a, is shifted downward (the other side of the sub-scanning direction Z2) on the scanned surface of the photosensitive drum 1a (see FIG. 16). Furthermore, although not shown, the light beams LB2 to LB4 that form images on the scanned surface are also shifted downward (the other side of the sub-scanning direction Z2).

[0068] On the other hand, the light beam LB8, which is the last beam incident on the end of the scanning lens 49a on the downstream side X2 in the main scanning direction, is directed toward a second focal point F8, which is located farther from the scanning lens 49b than the scanned surface of the photosensitive drum 1a (see FIGS. 14 and 15). At this time, the light beam LB8, which is shifted downward (the other side of the sub-scanning direction Z2) and incident on the scanning lens 49a, is shifted upward (one side of the sub-scanning direction Z1) on the scanned surface of the photosensitive drum 1a (see FIG. 16). Although not shown, the light beams LB5 to LB7 that form images on the scanned surface are also shifted upward (one side of the sub-scanning direction Z1). Therefore, in each scanning line SL, the light beams LD1 to LD4 and the light beams LD5 to LD8 can be moved toward each other (arrow Z4 in FIG. 8) at the end of the scanned surface on the downstream side X2 in the main scanning direction.

[0069] As a result, on the upstream side X1 in the main scanning direction of the scanned surface of the photosensitive drum 1a, the intervals W1 in the sub-scanning direction (Z1-Z2 direction) between the imaged light beams LB1 to LB8 become larger (see FIG. 13). Therefore, when the intervals W2 between adjacent scan lines SL become larger on the upstream side X1 in the main scanning direction of the scanned surface of the photosensitive drum 1a due to the axial tilt of the polygon mirror 45, the sizes of the intervals W1 and W2 can be made uniform by moving the first aperture 43 downward (to the other side Z2 in the sub-scanning direction).

[0070] On the other hand, on the downstream side X2 in the main scanning direction of the scanned surface of the photosensitive drum 1a, the intervals W1 in the sub-scanning direction (Z1-Z2 direction) between the focused light beams LB1 to LB8 become smaller (see FIG. 16). Therefore, when the intervals W2 between adjacent scan lines SL become larger due to the axial tilt of the polygon mirror 45 on the downstream side X2 in the main scanning direction of the scanned surface of the photosensitive drum 1a, the first aperture 43 can be moved downward (to the other side Z2 in the sub-scanning direction) to equalize the sizes of the intervals W1 and W2. This makes it possible to equalize the intervals between the focused images of the light beams LB1 to LB8 that are repeatedly aligned in the sub-scanning direction (Z1-Z2 direction), thereby preventing image defects. Furthermore, by making the intervals between the focused images of the light beams LB1 to LB8 uniform across the main scanning direction (X1-X2 direction), it is possible to further prevent image defects.

[0071] In this embodiment, a plurality of light source units (light sources) 26 are provided, and each light source unit (light source) 26 emits a light beam. A plurality of first apertures 43 are provided corresponding to the respective light source units (light sources) 26, and the centers of the respective first openings 43a in the sub-scanning direction are shifted in the sub-scanning direction in each first aperture 43. More specifically, the centers of the respective first openings 43a in the sub-scanning direction are shifted in the sub-scanning direction from the respective optical axes AX of the cylindrical lenses 42. In other words, the amounts of shift in the sub-scanning direction from the optical axes AX of the cylindrical lenses 42 differ. This makes it possible to prevent image defects in the light source units (light sources) 26 of each color by moving each first aperture 43.

[0072] Next, a method for detecting image defects will be described. Image defects caused by axial tilt of polygon mirror 45 can be easily detected by forming a patch image used for calibration on intermediate transfer belt 8, detecting the density of the patch image with image density sensor (image sensor) 50, and having control unit 90 monitor the detection result.

[0073] 17 is a plan view of a color misregistration patch image formed on the intermediate transfer belt 8. The patch image (development pattern) P is arranged at the end of the intermediate transfer belt 8 in the main scanning direction. For example, the patch image P consists of reference images Y, M, C, and K of the respective colors of yellow, magenta, cyan, and black.

[0074] The patch images P are formed in reference image forming areas Rs that are located at both ends in the main scanning direction (belt width direction). The reference image forming areas Rs are formed within the readable range of the image density sensor 50 and outside the effective image forming area Rg in the main scanning direction. The effective image forming area is capable of forming images up to the maximum paper width (e.g., 13 inches) used in the image forming apparatus 100.

[0075] The secondary transfer roller 9 (see FIG. 1) has an axial length equivalent to the width L1 of the effective image forming area Rg so as to prevent the patch image P from adhering thereto. The primary transfer rollers 6a to 6d (see FIG. 1) have an axial length equivalent to the width L2 of the intermediate transfer belt 8, which is the sum of the effective image forming area Rg and the reference image forming area Rs, because they are required to perform the primary transfer of the patch image P to the reference image forming area Rs.

[0076] The patch image P has a configuration in which a plurality of straight lines parallel to the main scanning direction (X1-X2 direction) corresponding to the above-mentioned scanning lines SL are arranged at regular intervals in the sub-scanning direction (belt travel direction Z1).

[0077] An image density sensor (image sensor) 50 detects the image density of a patch image (developed pattern) P formed at an end in the main scanning direction (X1-X2) of the intermediate transfer belt (belt) 8. Based on the detection result of the patch image (developed pattern) P by the image density sensor 50, a control unit 90 detects image defects such as color misalignment of the toner image formed on the recording medium.

[0078] Specifically, when axial tilt of polygon mirror 45 occurs, the spacing in the sub-scanning direction (belt travel direction) of the parallel lines that make up reference images Y to K and extend in the main scanning direction (X1-X2) becomes uneven, resulting in image defects (see FIG. 8). At this time, the image density of reference images Y to K detected by image density sensor 50 indicates an abnormality. Control unit 90 determines the occurrence of image defects based on the detection result of image density sensor 50. This makes it possible to easily detect the occurrence of image defects by monitoring the density change of patch image P.

[0079] Next, a method for manufacturing the optical scanning device 5 will be described. Fig. 18 is a flowchart sequentially listing the steps executed in the method for manufacturing the optical scanning device 5. The method for manufacturing the optical scanning device 5 includes the following steps S1 to S5. First, the light source unit (light source) 26, the collimator lens 41, the cylindrical lens 42, the restriction portion 47, the polygon mirror 45, and the plurality of scanning lenses 49a, 49b are arranged in their respective predetermined design positions on the housing 39 (step S1).

[0080] Next, optical axis adjustment is performed in the main scanning and sub-scanning directions (step S2). For example, an imaging sensor is used to perform optical axis adjustment so that the spots of the light beams LB1 to LB8 are positioned at predetermined positions. At this time, the light source unit 26 is moved in the sub-scanning direction (Z1-Z2 direction) to align the light beams LB1 to LB8 in the sub-scanning direction (Z1-Z2 direction). The light source unit 26 is also moved in the main scanning direction (X1-X2 direction) to align the light beams LB1 to LB8 in the main scanning direction (X1-X2 direction).

[0081] Next, focus adjustment is performed in the main scanning direction and the sub-scanning direction (step S3). For example, the light source unit 26 is moved in the optical axis direction so that the light beams LB1 to LB8 that have passed through the collimator lens 41 become parallel rays. Furthermore, the light source unit 26 and the collimator lens 41 are moved together in the optical axis direction while maintaining their positional relationship so that the light beams LB1 to LB8 are focused as beam spots of a predetermined size on the scanned surfaces of the photosensitive drums 1a to 1d. This adjusts the focus position.

[0082] Next, the beam pitch is adjusted (step S4). The light source units 26 are rotated to adjust the beam pitch so that the interval W1 in the sub-scanning direction (Z1-Z2 direction) between the light beams LB1 to LB8 emitted from each light source unit 26 corresponds to the specified resolution. Furthermore, even if the rotation axis of the polygon mirror 45 is tilted, causing axial tilt and resulting in uneven beam pitch, the first aperture 43 is moved downward (to the other side of the sub-scanning direction, Z2), as described above, to make the intervals W1 and W2 between the light beams LB1 to LB8 uniform. This prevents image defects from occurring.

[0083] Next, the light source unit (light source) 26, the collimator lens 41, the cylindrical lens 42, the restricting portion 47, the polygon mirror 45, and the plurality of scanning lenses 49a and 49b are fixed to the housing 39 (step S5).

[0084] According to the manufacturing method of the optical scanning device 5 described above, the light beam LB1 emitted from each of the laser diodes LD1 to LD8 (light-emitting units) and focused at the upper end of the scanned surface in the sub-scanning direction (the end on one side of the sub-scanning direction Z1) and the light beam LB8 focused at the lower end of the scanned surface in the sub-scanning direction (the end on the other side of the sub-scanning direction Z2) are moved in opposite directions in the sub-scanning direction (Z1-Z2 direction) between the end on the upstream side X1 of the main scanning direction and the end on the downstream side X2 of the main scanning direction (beam pitch adjustment process). This moves the first aperture 43 in the sub-scanning direction (Z1-Z2 direction), thereby adjusting the spacing in the sub-scanning direction (Z1-Z2 direction) of the light beams LB1 to LB8 focused on the scanned surfaces of the photosensitive drums 1a to 1d.

[0085] More specifically, when the first aperture 43 is moved in the sub-scanning direction (Z1-Z2 direction), the light beams LB1 and LB8 are separated in the sub-scanning direction (Z1-Z2 direction) at the upstream X1 end of the scanned surface in the main scanning direction, and the light beams LB1 and LB8 are brought closer in the sub-scanning direction (Z1-Z2 direction) at the downstream X2 end of the main scanning direction (see Figure 8).

[0086] As a result, even if the rotation axis of the polygon mirror 45 is tilted, causing axis tilt and making the beam pitch uneven, the intervals W1 and W2 of the light beams LB1 to LB8 can be made uniform in the main scanning direction (X1-X2 direction), preventing color shift from occurring. Therefore, it is possible to provide an optical scanning device 5 that can prevent image defects from occurring while suppressing manufacturing costs.

[0087] Furthermore, in the beam pitch adjustment process, when the first aperture 43 is moved in the sub-scanning direction, the distance by which the light beams LB1 and LB8 approach or move away from each other in the sub-scanning direction (Z1-Z2 direction) is greater at the end on the downstream side X2 in the main scanning direction than at the end on the upstream side X1 in the main scanning direction. As a result, even if the interval W1 increases toward the downstream side X2 in the main scanning direction (see FIG. 8), the intervals W1 and W2 between the light beams LB1 to LB8 can be made uniform across the main scanning direction (X1-X2 direction), preventing color misregistration.

[0088] Furthermore, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in this embodiment, the spacing between the light beams LB1 to LB8 is adjusted by moving the first aperture 43 downward (the other side of the sub-scanning direction Z2), but the spacing between the light beams LB1 to LB8 may also be adjusted by moving the first aperture 43 upward (one side of the sub-scanning direction Z1).

[0089] Furthermore, in this embodiment, the first focus F1 of the light beam LB1 and the second focus F8 of the light beam LB8 are located on opposite sides of the optical axis across the scanned surface of the photosensitive drum 1a, but the first focus F1 of the light beam LB1 and the second focus F8 of the light beam LB8 do not have to be located on opposite sides of the optical axis across the scanned surface of the photosensitive drum 1a.

[0090] Furthermore, in this embodiment, the first aperture 43 is moved in the sub-scanning direction (Z1-Z2 direction), and the light beams LB1 and LB8 are separated in the sub-scanning direction (Z1-Z2 direction) on the upstream side X1 of the main scanning direction of the scanned surface, and the light beams LB1 and LB8 are brought closer to each other in the sub-scanning direction (Z1-Z2 direction) on the downstream side X2 of the main scanning direction, but the light beams LB1 and LB8 may be brought closer to each other in the sub-scanning direction (Z1-Z2 direction) only on the downstream side X2 of the main scanning direction.

[0091] 19 is an explanatory diagram schematically showing the scan line SL. When the rotation axis of the polygon mirror 45 is tilted, causing axial tilt, the interval W1 may become smaller toward the downstream side X2 in the main scanning direction. In this case, the first aperture 43 may be moved in the sub-scanning direction (Z1-Z2 direction) to bring the light beams LB1 and LB8 closer to each other in the sub-scanning direction (Z1-Z2 direction) on the upstream side X1 of the main scanning direction of the scanned surface, and to separate the light beams LB1 and LB8 in the sub-scanning direction (Z1-Z2 direction) on the downstream side X2 of the main scanning direction. This makes it possible to make the intervals W1 and W2 between the light beams LB1 to LB8 uniform across the main scanning direction (X1-X2 direction), preventing color shifts, even when the interval W1 becomes smaller toward the downstream side X2 in the main scanning direction. The light beam LB1 and the light beam LB8 may be spaced apart in the sub-scanning direction (Z1-Z2 direction) only on the downstream side X2 in the main scanning direction.

[0092] In addition, in the above embodiment, a color printer as shown in FIG. 1 was used as an example of image forming apparatus 100, but the image forming apparatus is not limited to a color printer and may be other image forming apparatuses such as monochrome and color copiers, digital multifunction machines, facsimiles, etc. [Industrial Applicability]

[0093] The present invention can be used in an optical scanning device and an image forming apparatus that employ a multi-beam system in which a photosensitive drum is scanned with light beams from a multi-beam laser having a plurality of light emitters. [Explanation of symbols]

[0094] 1a to 1d Photosensitive drum 2a~2d Charging device 3a~3d developing device 4a~4d Toner container 5 Optical scanning device 6a~6d Primary transfer roller 7a~7d Cleaning device 8 Intermediate transfer belt 9 Secondary transfer roller 10 driven roller 11 Drive roller 12a Paper feed roller 12b Registration Roller Pair 13 Fixing device 15 Discharge Roller Pair 16 Paper cassette 17 Output tray 18-sided conveyor 19 Belt cleaner 20 Beam generation unit 21 Fixing belt 22 Pressure roller 26 Light source unit (light source) 27 Exit surface 30 Branch 39 Case 40 Main motor 41 Collimator lens 42 Cylindrical Lens 43 First Aperture 43a 1st opening 44 Second Aperture 44a 2nd opening 45 Polygon Mirror 46 Polygon Motor 47 Regulatory Department 49a, 49b Scanning lenses 50 Image density sensor (image sensor) 51a~51d Exit mirrors 52a~52c Reflective mirror 63 Deflection surface 70 Image input unit 71 Voltage control circuit 80 Control section 81 LCD display section 82 LED 90 Control Unit 91 CPU 92 ROM 93 RAM 94 Temporary storage 95 Counter 97 Correction Unit 100 Image forming device C center F1 1st focal point F8 2nd focal point L optical axis D1~D4 Light beam LB1~LB8 Light beams LD1~LD8 Laser diodes Pa, Pb, Pc Image forming section Pa~Pd Image forming section S paper SL Scan Line W1 spacing W2 spacing Z1 Sub-scanning direction one side Z2 Other side of sub-scanning direction J center axis

Claims

1. a light source having five or more light-emitting units arranged in a row; a cylindrical lens that focuses the light beams emitted from the light-emitting units; a restricting portion that restricts the optical path width of the light beam incident on the cylindrical lens; a polygon mirror having a deflection surface that reflects the light beam that has passed through the cylindrical lens, and rotating about an axis to scan the light beam in a main scanning direction on a surface to be scanned of an image carrier; a plurality of scanning lenses that form an image of the light beam reflected by the polygon mirror on a surface to be scanned of an image carrier; a plurality of light sources are provided, and each of the light sources emits a light beam; the regulating section has a plurality of first apertures that regulate the optical path width of each of the light beams in the sub-scanning direction; a plurality of the first apertures are provided corresponding to the light sources, each having a first opening penetrating in an optical axis direction and through which the light beam passes; The optical scanning device, wherein the centers of the first openings in the sub-scanning direction are positioned so as to be shifted in the sub-scanning direction.

2. 2. The optical scanning device according to claim 1, wherein the centers of the first openings in the sub-scanning direction are positioned so as to be shifted in the sub-scanning direction from the optical axes of the cylindrical lenses.

3. the scanning lens is configured so that a first focal point of the light beam emitted from each of the light-emitting units, which is focused at one end of the scanned surface in the sub-scanning direction, and a second focal point of the light beam, which is focused at the other end of the scanned surface in the sub-scanning direction, are positioned so as to be shifted in the optical axis direction; 2. The optical scanning device of claim 1, wherein the first focus at the upstream end in the main scanning direction is located on one side of the optical axis direction relative to the second focus, and the first focus at the downstream end in the main scanning direction is located on the other side of the optical axis direction relative to the second focus.

4. A plurality of the light sources are provided, The optical scanning device according to any one of claims 1 to 3, wherein the polygon mirror reflects the plurality of light beams emitted from each of the light sources to scan the scanned surface of the image carrier corresponding to each of the light sources.

5. 4. The optical scanning device according to claim 1, wherein the regulating portion further includes a second aperture that regulates the optical path width of the light beam in the main scanning direction.

6. The restriction portion is a plurality of the first apertures provided corresponding to the light sources; The optical scanning device according to claim 5 , further comprising: a second aperture provided in one location common to all of the light sources.

7. an optical scanning device according to any one of claims 1 to 3; a developing device that forms a toner image by visualizing the electrostatic latent image formed on the image carrier by the optical scanning device; an endless belt that moves along the developing device; an image sensor for detecting the image density of a developed pattern formed on an end of the belt in the main scanning direction; and a control unit that detects an image defect of the toner image formed on a recording medium based on a detection result of the development pattern by the image sensor.

8. a light source having five or more light-emitting units arranged in a row; a cylindrical lens that focuses the light beams emitted from the light-emitting units; a first aperture that regulates the optical path width in the sub-scanning direction of the light beam incident on the cylindrical lens and is movable in the sub-scanning direction; a polygon mirror having a deflection surface that reflects the light beam that has passed through the cylindrical lens, and rotating about an axis to scan the light beam in a main scanning direction on a surface to be scanned of an image carrier; a plurality of scanning lenses that form an image of the light beam reflected by the polygon mirror on the scanned surface, a beam pitch adjustment step of moving the first aperture in the sub-scanning direction to move the light beams emitted from the light emitting units and focused at one end of the scanned surface in the sub-scanning direction and the light beams focused at the other end of the scanned surface in the sub-scanning direction in the sub-scanning direction, thereby adjusting the interval in the sub-scanning direction between the light beams focused on the scanned surface across the main scanning direction; A method for manufacturing an optical scanning device, wherein in the beam pitch adjustment process, the light beam emitted from each light-emitting element and imaged at one end of the scanned surface in the sub-scanning direction and the light beam imaged at the other end of the scanned surface in the sub-scanning direction have opposite movement directions in the sub-scanning direction at the upstream end and downstream end of the scanned surface in the main scanning direction.

9. 9. A method for manufacturing an optical scanning device as described in claim 8, wherein in the beam pitch adjustment process, by moving the first aperture in the sub-scanning direction, the light beam emitted from each light-emitting element and imaged at one end of the scanned surface in the sub-scanning direction and the light beam imaged at the other end of the scanned surface in the sub-scanning direction are brought closer together at one of the upstream end or downstream end of the scanned surface in the main scanning direction, and are separated apart at the other of the upstream end or downstream end of the scanned surface in the main scanning direction.

10. A method for manufacturing an optical scanning device as described in claim 8 or claim 9, wherein, in the beam pitch adjustment process, when the first aperture is moved in the sub-scanning direction, the distance traveled in the sub-scanning direction by the light beam emitted from each light-emitting element and imaged at one end of the scanned surface in the sub-scanning direction and the light beam imaged at the other end of the scanned surface in the sub-scanning direction is greater at the downstream end of the scanned surface in the main scanning direction than at the upstream end of the scanned surface in the main scanning direction.

Images