Optical scanning apparatus and image forming apparatus equipped therewith

Abstract

The present invention provides an optical scanning device and an image forming apparatus equipped therewith, which can reduce the number of parts and assembly man-hours, and can also be made smaller in size. [Solution] The optical scanning device comprises a first light source unit and a second light source unit that emit a first beam of light and a second beam of light, a polygon mirror, a scanning lens, and a scanning optical system including a plurality of folding mirrors. The folding mirror consists of a first mirror that reflects the first beam of light and the second beam of light that have passed through the scanning lens, a second mirror that guides the first beam of light reflected by the first mirror onto the image carrier, and a third mirror and a fourth mirror that guide the second beam of light reflected by the first mirror onto the image carrier. The second and third mirrors are positioned closer to the polygon mirror than the first mirror when viewed from the main scanning direction, and the fourth mirror is positioned further from the polygon mirror than the first mirror when viewed from the main scanning direction.

Description

Technical Field

[0001] The present invention relates to an optical scanning device which is used in an image forming apparatus such as a copying machine, a printer, a facsimile machine and a multifunction peripheral thereof utilizing an electrophotographic system, for forming an electrostatic latent image by irradiating an image carrier with light, and to an image forming apparatus provided with the same.

Background Art

[0002] Conventionally, in an optical scanning device used for an image forming apparatus, beam light emitted from a light source such as a laser diode passes through a collimator lens, a cylindrical lens and an aperture, enters a deflector such as a polygon mirror and is deflected, then passes through a scanning lens and is guided to a photosensitive drum (image carrier), and exposes and scans the surface of the photosensitive drum to form an electrostatic latent image.

[0003] Further, when the beam light that has passed through the scanning lens cannot be directly guided to the photosensitive drum due to layout constraints of the image forming apparatus, it is common to adopt a configuration in which the beam light is reflected by using a folding mirror.

[0004] In an optical scanning device used for a color image forming apparatus, it is necessary to guide a plurality of beams of light to photosensitive drums corresponding to a plurality of colors. Therefore, the number of folding mirrors increases, which leads to problems such as enlargement of the optical scanning device and increase in cost.

[0005] Therefore, methods have been proposed to achieve miniaturization and cost reduction of optical scanning devices. For example, Patent Document 1 discloses an optical scanning device comprising a housing that accommodates multiple light sources, a single rotating polyhedron, a common imaging optical system, a common reflective mirror, and multiple folding mirrors, wherein at least one of the multiple optical paths from the common reflective mirror to the surface to be scanned has two or more folding mirrors on the optical path from the common reflective mirror to the surface to be scanned, and the folding mirrors that constitute the optical path from the common reflective mirror to one surface to be scanned do not overlap in the sub-scanning direction with the optical path formed by two or more folding mirrors on the optical paths from the common reflective mirror to other surfaces to be scanned. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2001-264655 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the optical scanning device described in Patent Document 1 had the problem that, in addition to the common mirror, two or more mirrors were required for both the inner (closer to the polygon mirror) optical path and the outer (farther from the polygon mirror) optical path, and furthermore, the size in the unit width direction became larger.

[0008] In view of the above problems, the present invention aims to provide an optical scanning device and an image forming apparatus equipped therewith that can reduce the number of parts and assembly man-hours, and can also be made smaller. [Means for solving the problem]

[0009] To achieve the above objective, the first configuration of the present invention is an optical scanning device comprising: a first light source unit that emits a first beam of light; a second light source unit that emits a second beam of light; a scanning optical system that scans the first beam of light and the second beam of light and guides them onto a corresponding image carrier; and a housing that holds the first light source unit, the second light source unit, and the optical elements constituting the scanning optical system, thereby forming an electrostatic latent image by exposing the surface of the image carrier and attenuating its charge. The scanning optical system includes a polygon mirror that deflects the first beam of light and the second beam of light at constant angular velocity; one or more scanning lenses that deflect the first beam of light and the second beam of light deflected at constant angular velocity by the polygon mirror at constant velocity; and a plurality of folding mirrors that guide the first beam of light and the second beam of light deflected at constant velocity by the scanning lenses onto the surface of the image carrier. The folding mirror consists of a first mirror that reflects the first and second beams of light that have passed through the scanning lens, a second mirror that guides the first beam of light reflected by the first mirror onto the image carrier, and a third and fourth mirror that guide the second beam of light reflected by the first mirror onto the image carrier. The second and third mirrors are positioned closer to the polygon mirror than the first mirror when viewed from the main scanning direction, and the fourth mirror is positioned further away from the polygon mirror than the first mirror when viewed from the main scanning direction.

[0010] According to the first configuration of the present invention, it is possible to configure two optical paths, a first beam and a second beam, with the minimum number of parts, thereby reducing the number of parts and assembly man-hours, and thus reducing the manufacturing cost of the optical scanning device. Furthermore, the horizontal arrangement space for the folding mirror inside the housing is also reduced, which contributes to the miniaturization of the optical scanning device. [Brief explanation of the drawing]

[0011] [Figure 1] A schematic cross-sectional view showing the overall configuration of the image forming apparatus 1 equipped with the optical scanning device 5 of the present invention. [Figure 2] Plan view showing the internal structure of an optical scanning device 5 according to one embodiment of the present invention. [Figure 3] A side cross-sectional view (section AA in Figure 2) showing the internal structure of the optical scanning device 5 of this embodiment. [Figure 4] A side cross-sectional view (BB section in Figure 2) showing the internal structure of the optical scanning device 5 of this embodiment. [Figure 5] Figure 3 shows a magnified partial view illustrating the optical paths of laser beams D1 and D2 from the polygon mirror 51 through the first scanning lens 56a and the second scanning lens 57a to the photoreceptor drums 1c and 1d. [Figure 6] A partially enlarged view showing the optical paths of laser beams D1 and D2 from the polygon mirror 51 to the photoreceptor drums 1c and 1d via the first scanning lens 56a and the second scanning lens 57a in the comparative example optical scanning apparatus 105. [Modes for carrying out the invention]

[0012] [1. Configuration of the image forming apparatus] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic cross-sectional view showing the internal structure of an image forming apparatus 100 equipped with the optical scanning device 5 of the present invention. The image forming apparatus 100 shown in Figure 1 is a so-called tandem color printer.

[0013] Inside the main body 7 of the image forming apparatus 100, image forming sections Pa to Pd are arranged horizontally. Each image forming section Pa to Pd sequentially forms yellow, magenta, cyan, and black images through the processes of charging, exposure, development, and transfer, respectively. Each image forming section Pa to Pd is provided to correspond to the image of each color. Below, only the image forming section Pa will be described, but the image forming sections Pb to Pd have basically the same configuration and will therefore not be described.

[0014] The image forming unit Pa is equipped with a photoreceptor drum 1a that carries a visible image (toner image). An optical scanning device 5 is positioned above the image forming unit Pa. The optical scanning device 5 emits an optical beam (laser light) toward the surface of the photoreceptor drums 1a to 1d to draw an electrostatic latent image. Around the photoreceptor drum 1a, a charging device 2a, a developing device 3a, and a cleaning device 23a are arranged in the direction of drum rotation (clockwise direction in Figure 1).

[0015] The charging device 2a is positioned opposite the photoreceptor drum 1a and can charge the surface of the photoreceptor drum 1a. The developing device 3a includes a developing container 4a, a developing roller 21a, and a supply roller 24a. The developing container 4a is filled with a predetermined amount of toner. The toners filled in the developing containers 4a to 4d are one of yellow, magenta, cyan, and black, for each of the developing devices 3a to 3d. The developing roller 21a is positioned opposite the photoreceptor drum 1a. The supply roller 24a supplies the toner from the developing container 4a to the outer surface of the developing roller 21a. The developing roller 21a is capable of supplying the toner supplied to its outer surface to the photoreceptor drum 1a.

[0016] An intermediate transfer unit 31 is provided below the photoreceptor drums 1a to 1d. The intermediate transfer unit 31 comprises a frame 30, a drive roller 10, a tension roller 11, an intermediate transfer belt 8, and primary transfer rollers 6a to 6d. The drive roller 10 and the tension roller 11 are rotatably supported at both ends of the frame 30 in the longitudinal direction.

[0017] The intermediate transfer belt 8 is an endless belt (preferably a seamless belt without seams). The intermediate transfer belt 8 is wound around the tension roller 11 and the drive roller 10 so as to be rotatable in the circumferential direction. When the drive roller 10 rotates due to the rotational driving force of a belt drive motor (not shown), the rotational driving force is transmitted to the intermediate transfer belt 8 by friction. As a result, the intermediate transfer belt 8 rotates in the same direction as the rotation of the drive roller 10. The primary transfer rollers 6a to 6d are rotatably supported on the frame 30 in a position opposite the photoreceptor drums 1a to 1d, with the intermediate transfer belt 8 in between.

[0018] A secondary transfer roller 9 is provided so as to face the drive roller 10 with the intermediate transfer belt 8 interposed therebetween. The secondary transfer roller 9 is pressed against the intermediate transfer belt 8 to form a secondary transfer nip N. The secondary transfer roller 9 secondarily transfers the toner image formed on the intermediate transfer belt 8 onto sheets S1 and S2 passing through the secondary transfer nip N.

[0019] Inside the image forming apparatus 100, at positions lateral to the image forming units Pa to Pd and the intermediate transfer belt 8, there are arranged a sheet conveying path 20, a pair of registration rollers 12, a sheet cassette 16, a sheet feeding unit 25, and a manual feed unit 26.

[0020] The sheet conveying path 20 is configured to include a main conveying path 28 and a duplex conveying path 18. The main conveying path 28 extends in the vertical direction. The pair of registration rollers 12, the secondary transfer roller 9, and a fixing device 13 are arranged at an intermediate position of the main conveying path 28. The main conveying path 28 conveys the sheet S1 or sheet S2 from the manual feed unit 26 and the sheet cassette 16, which will be described later, through the pair of registration rollers 12, the secondary transfer nip N, and the fixing device 13 in that order.

[0021] The pair of registration rollers 12 aligns the conveying direction of the sheets S1 and S2 such that the leading ends (the end on the downstream side with respect to the sheet conveying direction) of the sheets S1 and S2 are orthogonal to the sheet conveying direction, and corrects oblique conveyance (skew).

[0022] At the downstream end of the main conveying path 28 with respect to the sheet conveying direction, there is provided a sheet discharge port 15 communicating with the outside of the image forming apparatus 100. A pair of discharge rollers 22 is provided at the sheet discharge port 15.

[0023] A branching section 14 is provided between the discharge roller pair 22 and the fixing device 13 in the sheet conveying direction. The double-sided conveying path 18 branches off from the main conveying path 28 at a position that coincides with the branching section 14 of the main conveying path 28 in the sheet conveying direction, and rejoins the main conveying path 28 upstream of the resist roller pair 12. The branching section 14 can distribute the sheets S1 and S2 that have passed through the fixing device 13 to the sheet discharge port 15 or the double-sided conveying path 18.

[0024] The sheet cassette 16 and the manual feed unit 26 are located upstream of the main transport path 28 with respect to the sheet transport direction. Sheet S1 can be loaded into the sheet cassette 16, and sheet S2 can be loaded into the manual feed unit 26. The sheet feeding unit 25 is positioned between the main transport path 28 and the sheet cassette 16 and manual feed unit 26, and feeds sheets S1 and S2 to the main transport path 28.

[0025] The sheet cassette 16 is detachable from the main unit 7 of the device. Specifically, it can be pulled out from the main unit 7 of the device when it is inserted to the deepest part of the cassette housing in the horizontal direction (attached state).

[0026] The manual feed section 26 is mounted on the side of the main body 7, between the loading entrance 38 and the opening edge of the cassette storage section 29 in the vertical direction. The manual feed section 26 can feed sheets S2 (sheets used as recording media, including special-sized paper, cardboard, envelopes, OHP sheets, etc.) onto its upper surface. The loading entrance 38 is provided with a loading roller pair 40 and a sheet feeding roller 41. The sheet feeding roller 41 and the loading roller pair 40 rotate to load the sheets S2 into the manual feed path 39. The sheets S2 loaded into the manual feed path 39 are then transported toward the pickup roller 42 by a transport roller pair 47.

[0027] The sheet feeding unit 25 includes a pickup roller 42 and a pair of feeding rollers 43. The pickup roller 42 rotates in contact with the upper surface of the sheet S1 loaded on the sheet stacking plate 37 in the sheet cassette 16 and the sheet S2 that is fed from the manual feed unit 26 into the manual feed path 39. As a result, the sheets S1 and S2 are fed in the feeding direction and handed over to the pair of feeding rollers 43.

[0028] An operation panel 101 is located at the front of the image forming apparatus 100. The operation panel 101 is an operating unit for receiving various setting inputs. A control unit 102 is located inside the image forming apparatus 100. The control unit 102 oversees the operation of the entire image forming apparatus 100 and controls each part of the image forming apparatus 100.

[0029] Next, the image formation procedure in the image forming apparatus 100 will be described. When the user inputs the start of image formation, first, the photoreceptor drum 1a is rotated while the charging devices 2a to 2d uniformly charge the surfaces of the photoreceptor drums 1a to 1d. Then, the light scanning device 5 irradiates light onto the surfaces of the photoreceptor drums 1a to 1d, forming an electrostatic latent image on the photoreceptor drums 1a to 1d corresponding to the image signal.

[0030] Then, the toner in the developer of the developing devices 3a to 3d is supplied onto the photoreceptor drums 1a to 1d by the developing rollers 21a to 21d and adheres to them electrostatically. As a result, a toner image corresponding to the electrostatic latent image is formed on the photoreceptor drums 1a to 1d.

[0031] In this state, the drive roller 10 is rotated to start the counterclockwise rotation of the intermediate transfer belt 8. Then, the toner images of each color formed on the photoreceptor drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8. After the primary transfer is complete, any toner remaining on the photoreceptor drums 1a to 1d is removed by the cleaning devices 23a to 23d in preparation for the formation of a new electrostatic latent image. In addition, any residual charge remaining on the photoreceptor drums 1a to 1d is removed by a static eliminator (not shown).

[0032] Subsequently, at a predetermined timing, sheets S1 and S2 are fed from the sheet cassette 16 or manual feed section 26 to the main transport path 28, pass through the registration roller pair 12, and are then transported to the secondary transfer nip N. At this point, the toner image on the intermediate transfer belt 8 is secondarily transferred to sheets S1 and S2. Then, sheets S1 and S2 are transported to the fuser unit 13, where they are heated and pressurized by the fuser roller pair 13a of the fuser unit 13, fixing the toner image to the surface of sheets S1 and S2.

[0033] When printing on one side of sheets S1 and S2, the branching section 14 distributes sheets S1 and S2 that have passed through the fuser 13 to the sheet discharge port 15. Sheets S1 and S2 that reach the sheet discharge port 15 are discharged onto the sheet discharge tray 17 by the discharge roller pair 22.

[0034] When performing double-sided printing on sheets S1 and S2, the branching unit 14 distributes sheets S1 and S2, which have passed through the fuser unit 13, to the double-sided transport path 18. The double-sided transport path 18 then transports sheets S1 and S2 again to the registration roller pair 12, while reversing their front and back sides. Sheets S1 and S2 then pass through the secondary transfer nip N and fuser unit 13 again, and after the toner image is fixed to the back side, they are distributed to the sheet discharge port 15 by the branching unit 14.

[0035] [2. Configuration of the optical scanning device] Figure 2 is a plan view showing the internal structure of an optical scanning device 5 according to one embodiment of the present invention. Figures 3 and 4 are side cross-sectional views showing the internal structure of the optical scanning device 5 according to this embodiment, respectively. Figure 3 shows the AA section of Figure 2, and Figure 4 shows the BB section of Figure 2. Note that Figure 2 shows the state in which the cover portion 50b has been removed, making the inside of the optical scanning device 5 visible. Also, Figure 3 shows the state as seen from the rear side of Figure 1, and the arrangement of the photoreceptor drums 1a to 1d is reversed left to right compared to Figure 1. Furthermore, the direction of the arrow X in Figures 2 and 4 is the main scanning direction.

[0036] As shown in Figures 2 to 4, the optical scanning device 5 includes a housing 50. The housing 50 has a main body 50a and a lid 50b. A polygon mirror 51 is positioned in the center of the bottom surface of the main body 50a. In this embodiment, the polygon mirror 51 is a rotating polyhedron with a regular polygon (regular hexagon) having multiple deflection surfaces (reflecting surfaces) on its sides, and rotates at a predetermined speed by a polygon motor 52. The polygon motor 52 is fixed to the bottom surface of the main body 50a via a motor support plate 53.

[0037] Inside the housing 50 are light source units 55a to 55d, first scanning lenses 56a and 56b, second scanning lenses 57a and 57b, first mirrors 58a and 58b, second mirrors 59a and 59b, third mirrors 60a and 60b, and fourth mirrors 61a and 61b. Light source units 55a and 55b, and light source units 55c and 55d are arranged to overlap each other vertically.

[0038] As shown in Figure 4, the light source units 55a to 55d each include a laser light source 63, an aperture 64, and a lens unit 65. The lens unit 65 includes a collimator lens and a cylindrical lens (neither of which are shown).

[0039] The light source unit 55a (first light source) and the light source unit 55b (second light source) are mounted diagonally to the polygon mirror 51. The laser light D1 (first beam) emitted from light source unit 55a and the laser light D2 (second beam) emitted from light source unit 55b are incident on the polygon mirror 51 at the same angle in the vertical direction and are reflected by the polygon mirror 51 at the same angle in the vertical direction. The same applies to the laser light D3 (first beam) emitted from light source unit 55c (first light source) and the laser light D4 (second beam) emitted from light source unit 55d (second light source).

[0040] The first scanning lenses 56a, 56b and the second scanning lenses 57a, 57b have fθ characteristics and image the laser beams D1-D4, which have been deflected and reflected by the polygon mirror 51, onto the photoreceptor drums 1a-1d. In addition, the first mirrors 58a, 58b, the second mirrors 59a, 59b, the third mirrors 60a, 60b, and the fourth mirrors 61a, 61b are arranged in the optical path of each laser beam D1-D4 from the polygon mirror 51 to the photoreceptor drums 1a-1d (see Figure 1). The polygon mirror 51, the first scanning lenses 56a, 56b, the second scanning lenses 57a, 57b, and the first mirrors 58a, 58b to the fourth mirrors 61a-61b constitute a scanning optical system that scans the laser beams D1-D4 and guides them onto the photoreceptor drums 1a-1d.

[0041] As shown in Figures 2 and 3, the first scanning lenses 56a and 56b, the second scanning lenses 57a and 57b, the first mirrors 58a and 58b, the second mirrors 59a and 59b, the third mirrors 60a and 60b, and the fourth mirrors 61a and 61b are each positioned symmetrically on either side of the polygon mirror 51. More specifically, when viewed from the main scanning direction (the direction perpendicular to the plane of the paper in Figure 3), the mirrors are arranged in the following order from the side closest to the polygon mirror 51: first scanning lenses 56a and 56b, second mirrors 59a and 59b, second scanning lenses 57a and 57b, third mirrors 60a and 60b, first mirrors 58a and 58b, and fourth mirrors 61a and 61b.

[0042] In this embodiment, the first scanning lens 56a and the second scanning lens 57a are common to the upper and lower optical paths (laser beams D1 and D2). Also, the first scanning lens 56b and the second scanning lens 57b are common to the upper and lower optical paths (laser beams D3 and D4). Therefore, the optical path length from the reflection point at the polygon mirror 51 to the incident point on the photoreceptor drums 1a to 1d must be the same for each optical path. Furthermore, the optical path length must be such that it satisfies the fθ characteristics of the first scanning lenses 56a and 56b and the second scanning lenses 57a and 57b.

[0043] Figure 5 is a partially enlarged view showing the optical paths of laser beams D1 and D2 from the polygon mirror in Figure 3 through the first scanning lens 56a and the second scanning lens 57a to the photoreceptor drums 1c and 1d. The scanning operation of laser beams D1 and D2 by the optical scanning device 5 of this embodiment will be explained using Figure 5. In Figure 5, laser beam D1 is shown as a solid line and laser beam D2 as a dashed line. The scanning operation of laser beams D3 and D4 emitted from the laser light sources 63 of the light source units 55c and 55d is the same as that of laser beams D1 and D2, except that it is symmetrical.

[0044] The laser beams D1 and D2 emitted from the laser light sources 63 (see Figure 3) of the light source units 55a and 55b are given a predetermined optical path width by the aperture 64, and then made into approximately parallel beams by the collimator lens in the lens unit 65. Next, the approximately parallel beams D1 and D2 are incident on the cylindrical lens. The laser beams D1 and D2 incident on the cylindrical lens remain as parallel beams in the main scanning cross-section, and are emitted converged in the sub-scanning direction (vertical direction), forming a line image on the deflection plane of the polygon mirror 51. At this time, in order to facilitate the separation of the optical paths of the two deflected laser beams D1 and D2 by the polygon mirror 51, these laser beams D1 and D2 are configured to be incident on the deflection plane at different angles in the sub-scanning direction.

[0045] The laser beams D1 and D2 incident on the polygon mirror 51 are deflected at a constant angular velocity by the polygon mirror 51, and then deflected at a constant velocity by the first scanning lens 56a. The laser beams D1 and D2 that have passed through the first scanning lens 56a are incident on the second scanning lens 57a, and are deflected at a constant velocity by the second scanning lens 57a. The uniformly deflected laser beams D1 and D2 are then reflected by a common first mirror 58a. The laser beams D1 and D2 are configured to be incident on the reflective surface of the first mirror 58a at different positions in the sub-scanning direction. The width of the first mirror 58a in the sub-scanning direction is about 1.5 times larger than that of the second mirrors 59a to the fourth mirrors 61a. This ensures a region for reflecting the laser beams D1 and D2.

[0046] The laser beam D1, reflected by the first mirror 58a, is then reflected by the second mirror 59a, passes between the first scanning lens 56a and the second scanning lens 57a, and then passes through the window 70b formed on the bottom surface of the main body 50a to be distributed to the photoreceptor drum 1c. The laser beam D2, reflected by the first mirror 58a, is then reflected by the third mirror 60a and the fourth mirror 61a, and then passes through the window 70a formed on the bottom surface of the main body 50a to be distributed to the photoreceptor drum 1d.

[0047] If the first mirror 58a is positioned further from the polygon mirror 51 than the fourth mirror 61a when viewed from the main scanning direction (the direction perpendicular to the plane of the paper in Figure 5) (right side in Figure 5), the horizontal dimensions of the optical scanning device 5 (left-right direction in Figure 3) will increase, and it will become difficult to secure the optical path of the laser light D2 distributed to the photoreceptor drum 1d. Therefore, as shown in Figure 5, it is preferable to position the first mirror 58a closer to the polygon mirror 51 than the fourth mirror 61a when viewed from the main scanning direction (left side in Figure 5).

[0048] Figure 6 is a partially enlarged view showing the optical paths of laser beams D1 and D2 from the polygon mirror 51 to the photoreceptor drums 1a and 1b via the first scanning lens 56a and the second scanning lens 57a in the comparative example optical scanning device 105. In the optical scanning device 105 of Figure 6, the laser beam D1, which is deflected at a constant angular velocity by the polygon mirror 51 and then deflected at a constant velocity by the first scanning lens 56a and the second scanning lens 57a, is reflected by the first mirror 58a1 and the second mirror 59a before being distributed to the photoreceptor drum 1c.

[0049] Furthermore, the laser beam D2, which is deflected at a constant angular velocity by the polygon mirror 51 and then deflected at a constant velocity by the first scanning lens 56a and the first scanning lens 57a, is reflected by the first mirror 58a2, the third mirror 60a, and the fourth mirror 61a before being distributed to the photoreceptor drum 1d.

[0050] If, instead of using a common first mirror 58a as shown in Figure 5, first mirrors 58a1 and 58a2 are placed for each optical path of the laser beams D1 and D2 as shown in Figure 6, a total of five folding mirrors will be required for the optical paths of the laser beams D1 and D2. In addition, the number of fixing members such as leaf springs to secure each mirror will increase. Furthermore, the increased number of folding mirrors will reduce the mounting space, worsening the ease of mounting the folding mirrors with fixing members and compromising assembly efficiency. Moreover, the increase in mirror mounting surfaces (mounting locations) that require high dimensional accuracy will make it more difficult to achieve dimensional accuracy in the housing 50.

[0051] In the optical scanning device 5 of this embodiment, the laser beams D1 and D2 are reflected by a common first mirror 58a. The first mirror 58a is positioned closer to the polygon mirror 51 than the incident optical path to the photoreceptor drum 1d in the optical path of the laser beam D2 (outer optical path), and further from the polygon mirror 51 than the incident optical path to the photoreceptor drum 1d in the optical path of the laser beam D1 (inner optical path). In other words, the fourth mirror 61a is positioned further from the polygon mirror 51 than the first mirror 58a when viewed from the main scanning direction, and the second mirror 59a and the third mirror 60a are positioned closer to the polygon mirror 51 than the first mirror 58a when viewed from the main scanning direction.

[0052] This makes it possible to configure two optical paths, D1 and D2, with the minimum number of parts, reducing the number of parts and assembly steps, and thus lowering the manufacturing cost of the optical scanning device 5. In addition, the horizontal arrangement space for the folded mirrors within the housing 50 is also reduced, contributing to the miniaturization of the optical scanning device 5.

[0053] Furthermore, the present invention is not limited to the embodiments described above, and various modifications are possible without departing from the spirit of the invention. For example, although the above embodiment described a four-beam optical scanning device 5 equipped with four light source units 55a to 55d, the present invention is not limited to a four-beam optical scanning device, but is also applicable to a two-beam optical scanning device equipped with two light source units.

[0054] Furthermore, although the above embodiment described an image forming apparatus 100 equipped with an optical scanning device 5 using a tandem-type color printer as an example, the present invention is not limited to color printers and can be applied in exactly the same way to electrophotographic color image forming apparatuses such as color copiers and facsimile machines. [Industrial applicability]

[0055] The present invention can be used in an optical scanning device that forms an electrostatic latent image by irradiating an image carrier with light, and in an image forming apparatus equipped therewith. By using the present invention, it is possible to provide an optical scanning device and an image forming apparatus equipped therewith that can reduce the number of parts and assembly man-hours, and also enable miniaturization. [Explanation of Symbols]

[0056] 1a~1d Photoreceptor drum (image carrier) 2a~2d Charging device 3a~3d developing device 5. Optical scanning device 50 cabinets 50a Main body 50b Lid 51 Polygon Mirror 55a, 55c Light source unit (first light source section) 55b, 55d Light source unit (second light source section) 56a, 56b First scanning lens 57a, 57b Second scanning lens 58a, 58b First mirror (folding mirror) 59a, 59b Second mirror (folding mirror) 60a, 60b Third mirror (folding mirror) 61a, 61b Fourth mirror (folding mirror) 100 Image forming apparatus Pa~Pd Image Forming Unit D1, D3 laser light (first beam light) D2, D4 laser light (second beam light)

Claims

1. A first light source unit that emits a first beam of light, A second light source unit that emits a second beam of light, A scanning optical system that scans the first beam light and the second beam light and guides them onto the corresponding image carrier, A housing that holds the first light source unit, the second light source unit, and the optical elements constituting the scanning optical system, An optical scanning apparatus comprising the above, which forms an electrostatic latent image by exposing the surface of the image carrier to attenuate the charge, The scanning optical system is A polygon mirror that deflects the first beam light and the second beam light at a constant angular velocity, One or more scanning lenses that deflect the first beam light and the second beam light, which are deflected at a constant angular velocity by the polygon mirror, A plurality of folding mirrors that guide the first beam light and the second beam light, which are deflected at a constant velocity by the scanning lens, to the surface of the image carrier, Includes, The aforementioned folding mirror is A first mirror that reflects the first beam light and the second beam light that have passed through the scanning lens, A second mirror guides the first beam light reflected by the first mirror onto one of the image carriers, A third mirror and a fourth mirror guide the second beam light reflected by the first mirror onto the other image carrier, Composed of, An optical scanning apparatus characterized in that the second mirror and the third mirror are positioned closer to the polygon mirror than the first mirror when viewed from the main scanning direction, and the fourth mirror is positioned further from the polygon mirror than the first mirror when viewed from the main scanning direction.

2. The first beam light and the second beam light are incident on the first mirror at a predetermined interval in a sub-scanning direction perpendicular to the main scanning direction. The optical scanning apparatus according to claim 1, characterized in that the width of the first mirror in the sub-scanning direction is 1.5 times or more the width of the second mirror, the third mirror, and the fourth mirror.

3. The scanning lens comprises a first scanning lens positioned closer to the polygon mirror when viewed from the main scanning direction, and a second scanning lens positioned further away from the polygon mirror. The optical scanning apparatus according to claim 1, characterized in that, when viewed from the main scanning direction, the first scanning lens, the second mirror, the second scanning lens, the third mirror, the first mirror, and the fourth mirror are arranged in that order from the side closest to the polygon mirror.

4. The system comprises one pair each of the first light source unit and the second light source unit, The scanning lens and the folding mirror are each arranged in pairs symmetrically on either side of the polygon mirror when viewed from the main scanning direction. The optical scanning apparatus according to claim 1, characterized in that the first beam light and the second beam light are guided to the surface of four different image carriers.

5. An image forming apparatus comprising an optical scanning device according to any one of claims 1 to 4.

Images