Optical Scanning Device

Abstract

To provide an optical scanning device that can be suppressed from enlarging in size.SOLUTION: An optical scanning device is provided with a first scanning optical system LoY, a second scanning optical system LoM, a third scanning optical system LoC and a fourth scanning optical system LoK. Each of the scanning optical systems has a first scanning lens 60, at least one reflection mirror (first reflection mirror 81) and one second scanning lens 70 that collects beams in a sub scanning direction. In the first scanning optical system LoY and in the second scanning optical system LoM, centers C1 and C2 in the sub scanning direction of the second scanning lenses 70Y and 70M are offset to one side in a second direction with respect to beams BY and BM passing through the second scanning lenses 70Y and 70M. In the third scanning optical system LoC and in the fourth scanning optical system LoK, centers C3 and C4 in the sub scanning direction of the second scanning lenses 70C and 70K are offset to the other side in the second direction with respect to beams BC and BK passing through the second scanning lenses 70C and 70L.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an optical scanning device equipped with a polygon mirror. [Background technology]

[0002] Conventionally, an optical scanning device has been known that includes a light source, a polygon mirror that deflects the beam emitted from the light source, a motor that drives the polygon mirror, and a housing having a base wall and side walls (see Patent Document 1). This optical scanning device has four scanning optical systems, each of which has a first scanning lens, a second scanning lens, and a reflecting mirror. Four second scanning lenses corresponding to the four scanning optical systems are aligned in a row around the polygon mirror, with two located on one side of the polygon mirror and the remaining two on the other side. Each second scanning lens is positioned offset slightly from the center of the lens with respect to the emitted beam so as not to impair the optical properties of the lens. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-178605 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the optical scanning device of Patent Document 1, all of the second scanning lenses are offset in the same direction relative to the emitted beam, which results in a lack of space between the second scanning lens located on one side of the polygon mirror that is closest to the polygon mirror and the second scanning lens located on the other side of the polygon mirror that is closest to the polygon mirror, making it difficult to prevent the scanning optical device from becoming larger.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to prevent the scanning optical device from becoming large. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems, the scanning optical device according to the present invention includes a light source, a polygon mirror, a motor, a first scanning optical system, a second scanning optical system, a third scanning optical system, and a fourth scanning optical system. Equipped with. The light source emits a beam. The polygon mirror deflects the beam emitted from the light source. The motor rotates the polygon mirror around a rotation axis extending in the first direction. The first scanning optical system is arranged on one side of the polygon mirror in a second direction perpendicular to the first direction and emits the beam deflected by the polygon mirror toward a first image plane. The second scanning optical system is arranged on one side of the polygon mirror in the second direction and emits the beam deflected by the polygon mirror toward a second image plane. The second scanning optical system emits a beam toward the second image plane at a position closer to the polygon mirror in the second direction than the beam of the first scanning optical system. The third scanning optical system is arranged on the other side of the polygon mirror in the second direction and emits the beam deflected by the polygon mirror toward a third image plane. The fourth scanning optical system is arranged on the other side of the polygon mirror in the second direction and emits the beam deflected by the polygon mirror toward a fourth image plane. The fourth scanning optical system emits a beam toward a fourth image plane at a position farther from the polygon mirror in the second direction than the beam of the third scanning optical system. The first scanning optical system, the second scanning optical system, the third scanning optical system and the fourth scanning optical system each have a first scanning lens through which the beam deflected by the polygon mirror passes, at least one reflecting mirror that reflects the beam that has passed through the first scanning lens, and a second scanning lens that focuses the beam reflected by the reflecting mirror in the sub-scanning direction. In the first scanning optical system and the second scanning optical system, the center of the second scanning lens in the sub-scanning direction is offset to the one side in the second direction with respect to the beam passing through the second scanning lens. In the third scanning optical system and the fourth scanning optical system, the center of the second scanning lens in the sub-scanning direction is offset to the other side in the second direction with respect to the beam passing through the second scanning lens.

[0007] According to this configuration, the second scanning lenses of the first and second scanning optical systems are offset in the direction opposite to the offset direction of the second scanning lenses of the third and fourth scanning optical systems, which allows the distance between the second scanning lens of the second scanning optical system and the second scanning lens of the third scanning optical system to be increased. Therefore, the distance between the emitted beams does not increase, and the space between the second scanning lens of the second scanning optical system and the second scanning lens of the third scanning optical system is increased, thereby preventing the scanning optical device from becoming larger.

[0008] In the above-described scanning optical device, the second scanning lenses of the first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system may be arranged linearly in the second direction.

[0009] This makes it possible to make the distance from each second scanning lens to the image plane equal.

[0010] In addition, in the above-mentioned scanning optical device, the first scanning lens of the first scanning optical system and the first scanning lens of the second scanning optical system may be a single common lens, and the first scanning lens of the third scanning optical system and the first scanning lens of the fourth scanning optical system may be a single common lens.

[0011] According to this, by sharing the first scanning lens, the scanning optical device can be made smaller.

[0012] Furthermore, in the above-mentioned scanning optical device, the first scanning optical system and the fourth scanning optical system each may have a first reflecting mirror that reflects the beam toward the second scanning lens, and the second scanning optical system and the third scanning optical system each may have two reflecting mirrors: a first reflecting mirror that reflects the beam toward the second scanning lens and a second reflecting mirror that reflects the beam deflected by the polygon mirror toward the first reflecting mirror.

[0013] This allows the number of reflecting mirrors to be reduced.

[0014] In addition, the above-mentioned scanning optical device may further include a frame to which the motor, first scanning optical system, second scanning optical system, third scanning optical system, and fourth scanning optical system are fixed, the frame being open on one side in the first direction, the frame having a base wall to which the motor is fixed, and a side wall protruding from the base wall to one side in the first direction and surrounding the base wall, wherein the beam reflected by the polygon mirror travels obliquely with respect to a plane that passes through the polygon mirror and is perpendicular to the first direction, and in the first scanning optical system and the fourth scanning optical system, the beam reflected by the polygon mirror travels obliquely to the other side in the first direction with respect to the plane, and in the second scanning optical system and the third scanning optical system, the beam reflected by the polygon mirror travels obliquely to one side in the first direction with respect to the plane.

[0015] In the above scanning optical device, the optical surfaces of the second scanning lenses of the first scanning optical system, the second scanning optical system, the third scanning optical system and the fourth scanning optical system may be configured to be symmetrical with respect to the sub-scanning direction.

[0016] In addition, in the above-mentioned scanning optical device, a straight line parallel to the sub-scanning direction of each second scanning lens of the first scanning optical system and the second scanning optical system and a straight line parallel to the sub-scanning direction of each second scanning lens of the third scanning optical system and the fourth scanning optical system may be configured to form different angles with the second direction.

[0017] This allows the beam emitted from the second scanning lens to form an angle with respect to the first direction. [Effects of the Invention]

[0018] The present invention aims to prevent the scanning optical device from becoming large. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a perspective view of the scanning optical device according to the embodiment, as viewed from the other side in the first direction. [Figure 2] FIG. 2 is a perspective view showing the structure around the coupling lens. [Figure 3] FIG. 2 is a perspective view of the scanning optical device as seen from one side in a first direction. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Figure 5] FIG. 2 is a cross-sectional view of FIG. 1 . [Figure 6] 6 is a diagram for explaining in detail the position and angle of each second scanning lens in FIG. 5. FIG. [Figure 7] FIG. 2 is a perspective view of the frame as seen from the other side in the first direction. [Figure 8] FIG. 2 is a perspective view of the frame as seen from one side in the first direction. [Figure 9] FIG. 10 is a cross-sectional view showing a structure for attaching the reflecting mirror to the frame. DETAILED DESCRIPTION OF THE INVENTION

[0020] As shown in FIGS. 1 to 3, the scanning optical device 1 includes a frame F, an incident optical system Li, a deflector 50, and a scanning optical system Lo. The scanning optical device 1 is applied to an electrophotographic image forming apparatus. In the following description, a direction along the rotation axis X1 of the polygon mirror 51 shown in FIG. 3 is referred to as a "first direction." A direction perpendicular to the first direction, in which the polygon mirror 51 and the first scanning lens 60 shown in FIG. 3 are aligned, is referred to as a "second direction." A direction perpendicular to the first and second directions is referred to as a "third direction." In the scanning optical system Lo, the third direction corresponds to the main scanning direction, and the first direction corresponds to the sub-scanning direction. In the drawings, arrows indicating each direction indicate "one side" in each direction.

[0021] 2, the incident optical system Li includes four semiconductor lasers 10, four coupling lenses 20, an aperture plate 30, and a condenser lens 40. The semiconductor lasers 10 and the coupling lenses 20 are an example of a light source.

[0022] The semiconductor laser 10 is a device that emits light. Four semiconductor lasers 10 are provided corresponding to four photosensitive drums 200 (see FIG. 5) that are scanned and exposed by the scanning optical device 1. A toner image of a different color is formed on each photosensitive drum 200.

[0023] In this embodiment, the first color is "yellow (Y)," the second color is "magenta (M)," the third color is "cyan (C)," and the fourth color is "black (K)." In the following description, the names of components corresponding to the first color may be distinguished by adding "first" to the beginning of the name and adding "Y" to the end of the reference numerals of the components corresponding to the first color. Similarly, the names of components corresponding to the second, third, and fourth colors may be distinguished by adding "second," "third," and "fourth" to the beginning of the name and adding "M," "C," and "K" to the end of the reference numerals.

[0024] The first semiconductor laser 10Y is arranged in the first direction with a gap between them and the second semiconductor laser 10M. The first semiconductor laser 10Y is located on one side in the first direction with respect to the second semiconductor laser 10M.

[0025] The third semiconductor laser 10C is arranged adjacent to the second semiconductor laser 10M in the second direction at a distance. The third semiconductor laser 10C is located on the other side in the second direction relative to the second semiconductor laser 10M. The fourth semiconductor laser 10K is arranged adjacent to the third semiconductor laser 10C in the first direction at a distance, and is arranged adjacent to the first semiconductor laser 10Y in the second direction at a distance.

[0026] The coupling lens 20 is a lens that converts the light from the semiconductor laser 10 into a beam. The coupling lenses 20Y, 20M, 20C, and 20K corresponding to each color are arranged at positions facing the corresponding semiconductor lasers 10Y, 10M, 10C, and 10K.

[0027] 1, the diaphragm plate 30 is a portion having an aperture diaphragm 31 through which the beam from the coupling lens 20 passes, and is formed integrally with the frame F. The diaphragm plate 30 is located between the coupling lens 20 and the condenser lens 40.

[0028] The condenser lens 40 is a lens that condenses the beam from the coupling lens 20 onto the polygon mirror 51 in the sub-scanning direction. The condenser lens 40 is located on the opposite side of the diaphragm plate 30 from the coupling lens 20.

[0029] As shown in FIG. 3, the deflector 50 has a polygon mirror 51 and a motor 52. The polygon mirror 51 deflects the beam emitted from the light source. Specifically, the polygon mirror 51 deflects the beam that has passed through the condenser lens 40 in the main scanning direction. The polygon mirror 51 has five mirror surfaces that are equidistant from a rotation axis X1. The motor 52 rotates the polygon mirror 51 about the rotation axis X1 that extends in the first direction. The motor 52 is fixed to a frame F.

[0030] The scanning optical system Lo is an optical system that forms an image of the beam deflected by the deflector 50 on the surface of the photosensitive drum 200, which serves as an image plane. The scanning optical system Lo is fixed to a frame F. As shown in FIG. 5, the scanning optical system Lo has a first scanning optical system LoY corresponding to yellow, a second scanning optical system LoM corresponding to magenta, a third scanning optical system LoC corresponding to cyan, and a fourth scanning optical system LoK corresponding to black.

[0031] The first scanning optical system LoY and the second scanning optical system LoM are arranged on one side of the polygon mirror 51 in the second direction. The third scanning optical system LoC and the fourth scanning optical system LoK are arranged on the other side of the polygon mirror 51 in the second direction. A beam deflected in the main scanning direction by the polygon mirror 51 is incident on each of the scanning optical systems LoY, LoM, LoC, and LoK.

[0032] The first scanning optical system LoY, the second scanning optical system LoM, the third scanning optical system LoC and the fourth scanning optical system LoK each have a first scanning lens through which the beam deflected by the polygon mirror 51 passes, at least one reflecting mirror that reflects the beam that has passed through the first scanning lens, and a second scanning lens that focuses the beam reflected by the reflecting mirror in the sub-scanning direction. In this embodiment, the first scanning lens of the first scanning optical system LoY and the first scanning lens of the second scanning optical system LoM are a single common lens 60YM. Similarly, the first scanning lens of the third scanning optical system LoC and the first scanning lens of the fourth scanning optical system LoK are a single common lens 60CK. In this embodiment, the first scanning optical system LoY and the fourth scanning optical system LoK each have one reflecting mirror, and the second scanning optical system LoM and the third scanning optical system LoC each have two reflecting mirrors.

[0033] The first scanning optical system LoY emits the beam BY deflected by the polygon mirror 51 toward a first image plane of the first photosensitive drum 200Y. The first scanning optical system LoY has a first scanning lens 60YM, a second scanning lens 70Y, and a first reflecting mirror 81Y.

[0034] The first scanning lens 60YM is a lens that refracts the beam BY deflected by the deflector 50 in the main scanning direction to form an image on the image plane. The first scanning lens 60YM also has an fθ characteristic that causes the light scanned at a constant angular velocity by the deflector 50 to move at a constant velocity on the image plane. The first scanning lens 60YM is the scanning lens closest to the polygon mirror 51 in the first scanning optical system LoY.

[0035] The first reflecting mirror 81Y is a mirror that reflects the beam BY from the first scanning lens 60YM toward the second scanning lens 70Y. The second scanning lens 70Y is a lens that refracts the beam BY reflected by the first reflecting mirror 81Y in the sub-scanning direction to form an image on an image plane. The first reflecting mirror 81Y overlaps with the second scanning lens 70Y when viewed from the first direction. The second scanning lens 70Y is disposed on one side of the polygon mirror 51 in the first direction. The second scanning lens 70Y is the scanning lens closest to the image plane in the first scanning optical system LoY.

[0036] The second scanning optical system LoM emits the beam BM deflected by the polygon mirror 51 toward the second image surface of the second photosensitive drum 200M. The second scanning optical system LoM emits the beam BM toward the second image surface of the second photosensitive drum 200M at a position closer to the polygon mirror 51 in the second direction than the beam BY of the first scanning optical system LoY. The second scanning optical system LoM has a first scanning lens 60YM, a second scanning lens 70M, a first reflecting mirror 81M, and a second reflecting mirror 82M.

[0037] The first scanning lens 60YM of the second scanning optical system LoM is located between the polygon mirror 51 and the beam BM traveling from the first reflecting mirror 81M toward the second scanning lens 70M.

[0038] The second reflecting mirror 82M is a mirror that reflects the beam from the first scanning lens 60YM toward the first reflecting mirror 81M. The first reflecting mirror 81M is a mirror that reflects the beam BM from the second reflecting mirror 82M toward the second scanning lens 70M. The first reflecting mirror 81M overlaps with the second scanning lens 70M when viewed from the first direction. The second scanning lens 70M is a lens that refracts the beam reflected by the first reflecting mirror 81Y in the sub-scanning direction to form an image on an image plane. In the second scanning optical system LoM, the first scanning lens 60YM and the second scanning lens 70M overlap when viewed from the first direction. The second scanning lens 70M is disposed on one side of the polygon mirror 51 in the first direction. The second scanning lens 70M is the scanning lens in the second scanning optical system LoM that is closest to the image plane.

[0039] The third scanning optical system LoC emits the beam deflected by the polygon mirror 51 toward a third image plane of the third photosensitive drum 200C. The third scanning optical system LoC has a first scanning lens 60CK, a second scanning lens 70C, a first reflecting mirror 81C, and a second reflecting mirror 82C.

[0040] The first scanning lens 60CK is a lens that refracts the beam deflected by the deflector 50 in the main scanning direction to form an image on the image plane. The first scanning lens 60CK also has an fθ characteristic that causes the light scanned at a constant angular velocity by the deflector 50 to move at a constant velocity on the image plane. The first scanning lens 60CK is the scanning lens in the third scanning optical system LoC that is closest to the polygon mirror 51. The first scanning lens 60CK of the third scanning optical system LoC is located between the polygon mirror 51 and the beam BC that travels from the first reflecting mirror 81C toward the second scanning lens 70C.

[0041] The second reflecting mirror 82C is a mirror that reflects the beam from the first scanning lens 60CK toward the first reflecting mirror 81C. The first reflecting mirror 81C is a mirror that reflects the beam BC from the second reflecting mirror 82C toward the second scanning lens 70C. The first reflecting mirror 81C overlaps with the second scanning lens 70C when viewed from the first direction. The second scanning lens 70C is a lens that refracts the beam reflected by the first reflecting mirror 81C in the sub-scanning direction to form an image on an image plane. The second scanning lens 70C is disposed on the other side of the polygon mirror 51 in the first direction. The second scanning lens 70C is the scanning lens closest to the image plane in the third scanning optical system LoC.

[0042] The fourth scanning optical system LoK emits the beam deflected by the polygon mirror 51 toward the fourth image plane of the fourth photosensitive drum 200K. The fourth scanning optical system LoK emits the beam BK toward the fourth image plane of the fourth photosensitive drum 200K at a position farther from the polygon mirror 51 in the second direction than the beam BK of the fourth scanning optical system LoK. The fourth scanning optical system LoK has a first scanning lens 60CK, a second scanning lens 70K, and a first reflecting mirror 81K.

[0043] The first scanning lens 60CK is a lens that refracts the beam BK deflected by the deflector 50 in the main scanning direction to form an image on the image plane. The first scanning lens 60CK also has an fθ characteristic that causes the light scanned at a constant angular velocity by the deflector 50 to move at a constant velocity on the image plane. The first scanning lens 60CK is the scanning lens closest to the polygon mirror 51 in the fourth scanning optical system LoK.

[0044] The first reflecting mirror 81K is a mirror that reflects the beam BK from the first scanning lens 60CK toward the second scanning lens 70K. The first reflecting mirror 81K overlaps with the second scanning lens 70K when viewed from the first direction. The second scanning lens 70K is a lens that refracts the beam BK reflected by the first reflecting mirror 81K in the sub-scanning direction to form an image on an image plane. The second scanning lens 70K is disposed on the other side of the polygon mirror 51 in the first direction. The second scanning lens 70K is the scanning lens closest to the image plane in the fourth scanning optical system LoK.

[0045] The second scanning lenses 70Y, 70M, 70C, and 70K of the first scanning optical system LoY, the second scanning optical system LoM, the third scanning optical system LoC, and the fourth scanning optical system LoK are aligned linearly in the second direction. In other words, the second scanning lenses 70Y, 70M, 70C, and 70K are arranged so as to at least partially overlap one another when viewed from the second direction.

[0046] As shown in Fig. 6, the beam reflected by the polygon mirror 51 travels obliquely with respect to a plane HM that passes through the reflection point of the beam on the polygon mirror 51 and is perpendicular to the first direction. In the first scanning optical system LoY and the fourth scanning optical system LoK, the beam reflected by the polygon mirror 51 travels obliquely to the other side of the first direction (upper side in Fig. 6) with respect to the plane HM. In the second scanning optical system LoM and the third scanning optical system LoC, the beam reflected by the polygon mirror 51 travels obliquely to one side of the first direction (lower side in Fig. 6) with respect to the plane HM. The optical surfaces of the second scanning lenses 70Y, 70M, 70C, and 70K of the first scanning optical system LoY, second scanning optical system LoM, third scanning optical system LoC, and fourth scanning optical system LoK are symmetrical with respect to the sub-scanning direction.

[0047] In the first scanning optical system LoY and the second scanning optical system LoM, the centers C1, C2 of the optical surfaces of the second scanning lenses 70Y, 70M in the sub-scanning direction are offset to one side in the second direction (the left side in Figure 6) with respect to the beams BY, BM passing through the second scanning lenses 70Y, 70M. On the other hand, in the third scanning optical system LoC and the fourth scanning optical system LoK, the centers C3 and C4 of the optical surfaces of the second scanning lens 70C in the sub-scanning direction are offset to the other side in the second direction (the right side in Figure 6) with respect to the beams BC and BK passing through the second scanning lenses 70C and 70K. That is, the second scanning lenses 70Y, 70M of the first scanning optical system LoY and the second scanning optical system LoM, and the second scanning lenses 70C, 70K of the third scanning optical system LoC and the fourth scanning optical system LoK are arranged offset from each other.

[0048] A line L1 parallel to the sub-scanning direction of the second scanning lens 70Y of the first scanning optical system LoY is parallel to a line L2 parallel to the sub-scanning direction of the second scanning lens 70M of the second scanning optical system LoM. A line L3 parallel to the sub-scanning direction of the second scanning lens 70C of the third scanning optical system LoC is parallel to a line L4 parallel to the sub-scanning direction of the second scanning lens 70K of the fourth scanning optical system LoK. The straight lines L1 and L2 parallel to the sub-scanning direction of the second scanning lenses 70Y and 70M of the first scanning optical system LoY and the second scanning optical system LoM form angles with the second direction that are different from the straight lines L3 and L4 parallel to the sub-scanning direction of the second scanning lenses 70C and 70K of the third scanning optical system LoC and the fourth scanning optical system LoK. Specifically, the straight lines L3 and L4 parallel to the sub-scanning direction of the second scanning lenses 70C and 70K of the third scanning optical system LoC and the fourth scanning optical system LoK form a larger angle with the plane HM extending in the second direction than the straight lines L1 and L2 parallel to the sub-scanning direction of the second scanning lenses 70Y and 70M of the first scanning optical system LoY and the second scanning optical system LoM.

[0049] 4, the light emitted from each semiconductor laser 10Y to 10K is converted into beams BY to BK by passing through each coupling lens 20Y to 20K. After passing through corresponding aperture stops 31Y to 31K of diaphragm plate 30, beams BY to BK pass through condenser lens 40 and are then incident on polygon mirror 51. Collector lens 40 is a lens through which beams BY, BM, BC, and BK pass in common, and has a cylindrical entrance surface and a flat exit surface.

[0050] As shown in FIG. 5, the polygon mirror 51 deflects the beams BY to BK toward the corresponding scanning optical systems LoY to LoK. The beam BY toward the first scanning optical system LoY passes through the first scanning lens 60YM, is reflected by the first reflecting mirror 81Y, and passes through the second scanning lens 70Y to be emitted toward an image plane on one side in the first direction. The beam BY is emitted from the second scanning lens 70Y at a predetermined angle with respect to the first direction. The beam BY is focused on the first photosensitive drum 200Y and scanned in the main scanning direction.

[0051] The beam BM heading toward the second scanning optical system LoM passes through the first scanning lens 60YM, is reflected by the second reflecting mirror 82M and the first reflecting mirror 81M, and passes through the second scanning lens 70M to be emitted toward an image plane on one side in the first direction. The beam BM is emitted from the second scanning lens 70M at a predetermined angle with respect to the first direction. The beam BM is imaged on the second photosensitive drum 200M and scanned in the main scanning direction. Similarly, the beams BC and BK are also emitted toward an image plane on one side in the first direction by the corresponding scanning optical systems LoC and LoK, and are imaged on the corresponding photosensitive drums 200C and 200K to be scanned in the main scanning direction.

[0052] As shown in FIGS. 3 and 5, a polygon mirror 51, a motor 52, a first scanning optical system LoY, a second scanning optical system LoM, a third scanning optical system LoC, and a fourth scanning optical system LoK are fixed to a frame F. The frame F is made of resin and is integrally molded. The frame F has a first recess CP1 shown in FIG. 8 and a second recess CP2 shown in FIG. 7. The first recess CP1 opens to one side in the first direction. The second recess CP2 opens to the other side in the first direction. As shown in FIG. 5, a deflector 50 and a part of the scanning optical system Lo are disposed in the first recess CP1. Specifically, the components of the scanning optical system Lo, excluding the first reflecting mirrors 81, are disposed in the first recess CP1. As shown in FIG. 2, a coupling lens 20, an aperture plate 30, and a condenser lens 40 (see FIG. 1) are disposed in the second recess CP2.

[0053] 5, the scanning optical device 1 further includes a cover C. The cover C covers the deflector 50 and the first base wall Fb1 from one side in the first direction, and is fixed to the frame F with screws. More specifically, the cover C covers the opening of the first recess CP1. The first scanning lenses 60YM and 60CK and the second scanning lenses 70Y, 70M, 70C, and 70K are disposed between the first base wall Fb1 and the cover C and housed in the first recess CP1.

[0054] As shown in FIGS. 7 and 8, the frame F has a first base wall Fb1 as an example of a base wall located at the bottom of the first recess CP1, and a second base wall Fb2 located at the bottom of the second recess CP2.

[0055] The first base wall Fb1 and the second base wall Fb2 are walls that intersect with the first direction. More specifically, the first base wall Fb1 and the second base wall Fb2 are walls whose thickness directions are aligned with the first direction. In other words, the first base wall Fb1 and the second base wall Fb2 are walls having planes that are perpendicular to the first direction.

[0056] The second base wall Fb2 is positioned at a position offset to one side in the first direction with respect to the first base wall Fb1. As shown in FIG. 5, the deflector 50 and the aforementioned part of the scanning optical system Lo are directly or indirectly attached to the first base wall Fb1 from one side in the first direction. Therefore, the deflector 50 and part of the scanning optical system Lo are positioned on one side in the first direction with respect to the first base wall Fb1. In this embodiment, the deflector 50, i.e., the polygon mirror 51 and the motor 52, are fixed to the first base wall Fb1 with a plurality of screws N.

[0057] As shown in Figure 5, the second scanning lenses 70Y, 70M, 70C, and 70K of the scanning optical systems LoY, LoM, LoC, and LoK emit beams BY, BM, BC, and CK in directions from the first base wall Fb1 toward the second scanning lenses 70Y, 70M, 70C, and 70K.

[0058] 2, the semiconductor laser 10, the coupling lens 20, and the diaphragm plate 30 are located on the other side in the first direction with respect to the second base wall Fb2. Also, as shown in FIG. 1, the condenser lens 40 and the first reflecting mirror 81 are located on the other side in the first direction with respect to the second base wall Fb2.

[0059] 7, the frame F has a shape that exposes at least a portion of the first reflecting mirror 81 on the other side in the first direction of the first base wall Fb1 (the side opposite the opening of the first recess CP1). Specifically, the first reflecting mirror 81 is disposed near the first base wall Fb1 and is exposed on the other side in the first direction with respect to the first base wall Fb1. In other words, the first base wall Fb1 does not have a portion that is located on the other side in the first direction of the first reflecting mirror 81. As a result, the first reflecting mirror 81 is exposed on the other side in the first direction without being hidden by the first base wall Fb1, and can be attached to the frame F from the other side in the first direction.

[0060] The first base wall Fb1 has holes H that expose the reflective surfaces of the first reflecting mirrors 81 to one side (opening side) in the first direction (see also FIGS. 5 and 8). The holes H extend in the third direction, and four holes H are arranged corresponding to the first reflecting mirrors 81.

[0061] The frame F further includes a first partition wall F1 located between the first recess CP1 and the second recess CP2. The first partition wall F1 is connected to the first base wall Fb1 and the second base wall Fb2 (see also FIG. 8). The first partition wall F1 protrudes from the second base wall Fb2 to the other side in the first direction and from the first base wall Fb1 to one side in the first direction.

[0062] The first partition wall F1 has two first openings F11 and F12 through which the beams BY to BK pass from the aperture stops 31 of the diaphragm plate 30 toward the polygon mirror 51. The first openings F11 and F12 are formed in the shape of slits that are long in the first direction, penetrate in the third direction, and open to one side in the first direction (see FIG. 8). The first opening F11 passes the beams BY and BM. The first opening F12 passes the beams BC and BK.

[0063] 1, the condenser lens 40 is disposed so as to cover the first openings F11 and F12 shown in FIG.

[0064] 3 and 8, the frame F further has two second partition walls F2 located on either side of the polygon mirror 51 (see FIG. 3) in the second direction. The second partition wall F2 on one side in the second direction has a second opening F21 through which the beams BY and BM reflected by the polygon mirror 51 pass. The second partition wall F2 on the other side in the second direction has a second opening F22 through which the beams BC and BK reflected by the polygon mirror 51 pass. Each of the second openings F21 and F22 penetrates in the second direction and opens to one side in the first direction.

[0065] Each second partition wall F2 protrudes from the first base wall Fb1 to one side in the first direction. Each second partition wall F2 is connected to the first partition wall F1 and a first side wall F41 (described later). As a result, the first base wall Fb1, the first partition wall F1, each second partition wall F2, and the first side wall F41 form an accommodating recess CP3 for accommodating the polygon mirror 51.

[0066] The first scanning lens 60YM is disposed so as to block a portion of the second opening F21. The first scanning lens 60CK is disposed so as to block a portion of the second opening F22. The first scanning lenses 60YM and 60CK are fixed to a first lens seating surface B1, which is a portion of the first base wall Fb1. The first lens seating surface B1 is a surface shifted to one side in the first direction from the portion of the first base wall Fb1 where the deflector 50 is attached.

[0067] The frame F further includes a first side wall F41, a second side wall F42, a third side wall F43, and a fourth side wall F44 that form a substantially rectangular frame surrounding each of the recesses CP1 and CP2. The first side wall F41, the second side wall F42, the third side wall F43, and the fourth side wall F44 are examples of side walls that surround the first base wall Fb1. The first recess CP1 is surrounded by a first side wall F41, a third side wall F43, a fourth side wall F44, and the first partition wall F1. Also, as shown in Fig. 7, the second recess CP2 is surrounded by a second side wall F42, a third side wall F43, a fourth side wall F44, and the first partition wall F1. In this embodiment, the third side wall F43 and the fourth side wall F44 are offset in the second direction at portions corresponding to the first recess CP1 and the second recess CP2.

[0068] 3, the first side wall F41 is located on the opposite side of the deflector 50 from the semiconductor laser 10. The first side wall F41 protrudes from the first base wall Fb1 to one side in the first direction.

[0069] The second side wall F42 is located on the opposite side of the deflector 50 from the first side wall F41. More specifically, the second side wall F42 is located on the opposite side of the coupling lens 20 from the deflector 50. The second side wall F42 protrudes from the second base wall Fb2 to the other side in the first direction.

[0070] The third side wall F43 is located on the opposite side of the first scanning lens 60YM from the deflector 50. The third side wall F43 is connected to one end of the first side wall F41, the first base wall Fb1, the second base wall Fb2, and the second side wall F42 in the second direction. A part of the third side wall F43 protrudes from the first base wall Fb1 to one side in the first direction, and another part protrudes from the second base wall Fb2 to the other side in the first direction.

[0071] The fourth side wall F44 is located on the opposite side of the deflector 50 with respect to the first scanning lens 60CK. The fourth side wall F44 is connected to the other end portions in the second direction of the first side wall F41, the first base wall Fb1, the second base wall Fb2, and the second side wall F42. A part of the fourth side wall F44 protrudes from the first base wall Fb1 to one side in the first direction, and another part protrudes from the second base wall Fb2 to the other side in the first direction.

[0072] As shown in FIG. 9 , the scanning optical device 1 further includes a support member Fs that is detachable from the frame F, which includes the first recess CP1 and the second recess CP2. The support member Fs supports the first reflecting mirror 81. The support member Fs has a seat FsZ that supports the first reflecting mirror 81 and allows the angle of the first reflecting mirror 81 to be adjusted. The seat FsZ has a spherical protrusion Fs1 that can tiltably support the first reflecting mirror 81. The protrusion Fs1 protrudes toward the first reflecting mirror 81 and contacts the first reflecting mirror 81 to serve as a fulcrum when adjusting the orientation of the first reflecting mirror 81. The orientation of the first reflecting mirror 81 relative to the seat FsZ is fixed by a photocurable resin P. The photocurable resin P can be, for example, an ultraviolet-curable resin. The first reflecting mirror 81 and the support member Fs, which are fixed by the photocurable resin P, are attached to the frame F by a U-shaped leaf spring SP.

[0073] The leaf spring SP is an example of a spring, and is a spring that presses the first reflecting mirror 81 toward the seating surface FsZ. The leaf spring SP has an opening SPK through which light that cures the photocurable resin can pass (see FIG. 1). The frame F has a shape that exposes the portion of the first reflecting mirror 81 that overlaps with the seating surface FsZ in the thickness direction (the direction perpendicular to the reflecting surface) on the other side in the first direction. The first reflecting mirror 81 does not have a reflective film that forms a reflective surface on either end in the third direction. This allows light that passes through the opening SPK to reach the photocurable resin.

[0074] For each first reflecting mirror 81, one support member Fs and one leaf spring SP are arranged at each end in the longitudinal direction of the first reflecting mirror 81. A pair of support members Fs and a pair of leaf springs SP corresponding to one first reflecting mirror 81 are provided for each of the four first reflecting mirrors 81.

[0075] The frame F has a support surface Fm1 that supports the support member Fs. The support surfaces Fm1 are disposed at positions corresponding to the longitudinal ends of the four first reflecting mirrors 81 (see FIG. 7).

[0076] When attaching the first reflecting mirror 81 to the frame F, first, photocurable resin P is applied to both sides of the protrusion Fs1 of the support member Fs, and the support member Fs is attached to the support surface Fm1. Then, the first reflecting mirror 81 is brought into contact with the protrusion Fs1 of the support member Fs. At this time, the photocurable resin P is placed in contact with both the support member Fs and the first reflecting mirror 81. After that, a leaf spring SP is attached, and the first reflecting mirror 81 and the support member Fs are pressed toward the frame F. Next, with light emitted from the semiconductor laser 10, the angle of the first reflecting mirror 81 is adjusted by tilting the first reflecting mirror 81 from the protrusion Fs1 as a starting point while monitoring the position of the beam on the image plane. To adjust the angle of the first reflecting mirror 81, an arm AM, indicated by a two-dot chain line in FIG. 9, is pressed against the first reflecting mirror 81 to move it. After the angle adjustment is completed, the photocurable resin P is irradiated with light such as ultraviolet light, thereby fixing the first reflecting mirror 81 to the support member Fs.

[0077] As shown in FIGS. 3 and 8, the frame F further includes a first wall W1, a second wall W2, and a third wall W3.

[0078] The first wall W1 is a wall that supports the second scanning lenses 70Y, 70M, 70C, and 70K. The first wall W1 is a wall that rises from the first base wall Fb1 toward one side in the first direction. The first walls W1 are respectively disposed at both ends of the second scanning lenses 70Y, 70M, 70C, and 70K in the longitudinal direction (third direction). Each first wall W1 is formed with a second lens seating surface W11 that is recessed toward the other side in the first direction. Both ends of the second scanning lenses 70Y, 70M, 70C, and 70K in the longitudinal direction fit into each second lens seating surface W11. Each second scanning lens 70Y, 70M, 70C, and 70K is fixed to the frame by a spring (not shown) with both ends pressed against the seating surface of the second lens seating surface W11 facing one side in the first direction.

[0079] The second walls W2 are arranged on both sides of the second scanning lenses 70Y, 70M, 70C, and 70K in the longitudinal direction and extend parallel to the first wall W1. In this embodiment, the first partition wall F1 and the first side wall F41 form the second wall W2.

[0080] The third wall W3 is a wall extending in a direction perpendicular to the first direction and connects the first wall W1 and the second wall W2.

[0081] As described above, the following effects can be obtained in this embodiment. In each of the scanning optical systems LoY, LoM, LoC, and LoK of the scanning optical device 1 in this embodiment, the second scanning lenses 70Y, 70M, 70C, and 70K are disposed at positions closest to the respective image planes, thereby reducing the distance from the last scanning lens to the photosensitive drum 200. This reduces the tolerance sensitivity of the scanning optical device 1.

[0082] Furthermore, since the second scanning lenses 70Y, 70M, 70C, and 70K of each scanning optical system LoY, LoM, LoC, and LoK are arranged in a straight line in the second direction, the distance from each second scanning lens 70Y, 70M, 70C, and 70K to each image plane can be made equal.

[0083] Furthermore, the first scanning lens 60YM of the first scanning optical system LoY and the first scanning lens 60YM of the second scanning optical system LoM are one common lens, and the first scanning lens 60CK of the third scanning optical system LoC and the first scanning lens 60CK of the fourth scanning optical system LoK are one common lens, so the number of parts is reduced and the scanning optical device 1 can be made smaller.

[0084] Furthermore, in the second scanning optical system LoM, the first scanning lens 60YM and the second scanning lens 70M overlap when viewed from the first direction, so the second scanning lens 70M can be disposed close to the polygon mirror 51. This allows the scanning optical device 1 to be made smaller.

[0085] Furthermore, since the first scanning lens 60YM is positioned between the beam BM traveling from the first reflecting mirror 81M of the second scanning optical system LoM toward the second scanning lens 70M and the polygon mirror 51, the distance between the polygon mirror 51 and the first scanning lens 60YM can be shortened. Similarly, since the first scanning lens 60CK is positioned between the beam BC traveling from the first reflecting mirror 81C of the third scanning optical system LoC toward the second scanning lens 70C and the polygon mirror 51, the distance between the polygon mirror 51 and the first scanning lens 60CK can be shortened.

[0086] In addition, the first scanning optical system LoY and the fourth scanning optical system LoK have one reflecting mirror, while the second scanning optical system LoM and the third scanning optical system LoC have two reflecting mirrors, so the number of reflecting mirrors can be reduced.

[0087] Furthermore, since the frame F has the first wall W1 that supports the second scanning lenses 70Y, 70M, 70C, and 70K, the positional accuracy of the polygon mirror 51 and each of the second scanning lenses 70Y, 70M, 70C, and 70K can be improved.

[0088] Furthermore, the frame F has the third wall W3 that connects the first wall W1 and the second wall W2, thereby improving the strength of the first wall W1 that supports the second scanning lenses 70Y, 70M, 70C, and 70K.

[0089] In the first scanning optical system LoY and the second scanning optical system LoM, the centers C1 and C2 of the second scanning lenses 70Y and 70M in the sub-scanning direction are offset to one side in the sub-scanning direction relative to the beams BY and BM passing through the second scanning lenses 70Y and 70M. In the third scanning optical system LoC and the fourth scanning optical system LoK, the centers C3 and C4 of the second scanning lenses 70C and 70K in the sub-scanning direction are offset to the other side in the second direction relative to the beams BC and BK passing through the second scanning lenses 70C and 70K. This allows for a larger distance between the second scanning lens 70M of the second scanning optical system LoM and the second scanning lens 70C of the third scanning optical system LoC. As a result, the distance between the emitted beams BY, BM, BC, and BK is not increased, and the space between the second scanning lens 70M of the second scanning optical system LoM and the second scanning lens 70C of the third scanning optical system LoC is increased, thereby preventing the scanning optical device 1 from becoming larger.

[0090] Furthermore, the straight lines L1 and L2 parallel to the sub-scanning direction of the second scanning lenses 70Y and 70M of the first and second scanning optical systems LoY and LoM and the straight lines L3 and L4 parallel to the sub-scanning direction of the second scanning lenses 70C and 70K of the third and fourth scanning optical systems LoC and LoK form different angles with the second direction, so that the beams BY, BM, BC, and BK emitted from the second scanning lenses 70Y, 70M, 70C, and 70K can be configured to form angles with the first direction.

[0091] Furthermore, the frame F has a seating surface FsZ that supports the first reflecting mirror 81 and allows the angle of the reflecting mirror 81 to be adjusted, and is shaped to expose at least a portion of the first reflecting mirror 81 to the other side in the first direction (the side opposite to the opening in the first base wall Fb1). This allows the angle of the first reflecting mirror 81 to be adjusted from the side opposite to the beam emission direction. This makes it easy to adjust the angle of the first reflecting mirror 81 when assembling the scanning optical device 1.

[0092] Furthermore, since the seating surface FsZ of the support member Fs has the protrusion Fs1 that serves as a fulcrum when adjusting the orientation of the first reflecting mirror 81, the orientation of the first reflecting mirror 81 can be easily adjusted.

[0093] Furthermore, the frame F is configured to have a main frame Fm and a support member Fs. Therefore, if the angle of the first reflecting mirror 81 fails to be adjusted during assembly of the scanning optical device 1, the first reflecting mirror 81 can be removed without affecting the main frame Fm. As a result, even if the angle adjustment fails, the first reflecting mirror 81 can be reattached.

[0094] The present invention is not limited to the above-described embodiment, but can be used in various forms as exemplified below.

[0095] In the above embodiment, a part of the scanning optical system Lo is attached to one side of the first base wall Fb1 in the first direction, but the present invention is not limited to this. For example, the entire scanning optical system may be attached to one side of the first base wall Fb1 in the first direction.

[0096] In the above embodiment, the leaf spring SP is exemplified as an example of the spring, but the spring is not limited to the leaf spring and may be a wire spring or the like.

[0097] In the above embodiment, the frame F and the support member Fs having the seat surface FsZ are configured as different members, but the seat surface FsZ may be configured integrally with the frame F.

[0098] In the above embodiment, the second scanning lens 70 is fixed to the frame by a spring (not shown), but the method for fixing the second scanning lens 70 is not particularly limited, and the second scanning lens 70 may be fixed by adhesive using a photocurable resin or the like.

[0099] In the above embodiment, the semiconductor laser 10 has one light-emitting point, but the semiconductor laser 10 may have multiple light-emitting points. In this case, multiple light beams from the semiconductor laser 10 are converted into multiple beams by one coupling lens 20, and the multiple beams are imaged on the surface of the photosensitive drum 200 by corresponding scanning optical systems Lo. In this configuration, the beams BY, BM, BC, and BK in the above embodiment each include multiple beams.

[0100] The elements described in the above-described embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0101] 1. Scanning optical device 51 Polygon Mirror 52 Motor 60 First scanning lens 60YM, 60CK 1st scanning lens 70Y, 70M, 70C, 70K Second scanning lens 81 First reflecting mirror 82 Second reflecting mirror 200 Photosensitive drum BY,BM,BC,BK beam F Frame Fb1 1st base wall Fm1 Support surface Fs support member Fs1 protrusion FsZ seat H hole LoY, LoM, LoC, LoK First scanning optical system W1 1st wall W2 Second wall W3 Third Wall X1 rotation axis

Claims

1. a light source that emits a beam; a polygon mirror that deflects the beam emitted from the light source; a motor that rotates the polygon mirror about a rotation axis extending in a first direction; a first scanning optical system that is disposed on one side of the polygon mirror in a second direction orthogonal to the first direction and that emits the beam deflected by the polygon mirror toward a first image plane; a second scanning optical system that is disposed on one side of the polygon mirror in the second direction and that emits the beam deflected by the polygon mirror toward a second image plane, the second scanning optical system that emits the beam toward the second image plane at a position closer to the polygon mirror in the second direction than the beam of the first scanning optical system; a third scanning optical system that is disposed on the other side of the polygon mirror in the second direction and that emits the beam deflected by the polygon mirror toward a third image plane; a fourth scanning optical system that is disposed on the other side of the polygon mirror in the second direction and that emits the beam deflected by the polygon mirror toward a fourth image plane, the fourth scanning optical system that emits the beam toward the fourth image plane at a position farther from the polygon mirror in the second direction than the beam of the third scanning optical system; Equipped with The first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system are a first scanning lens through which the beam deflected by the polygon mirror passes; at least one reflecting mirror that reflects the beam that has passed through the first scanning lens; a second scanning lens that condenses the beam reflected by the reflecting mirror in the sub-scanning direction, In the first scanning optical system and the second scanning optical system, a center of the second scanning lens in the sub-scanning direction is offset to the one side in the second direction with respect to the beam passing through the second scanning lens, In the third scanning optical system and the fourth scanning optical system, a center of the second scanning lens in the sub-scanning direction is offset to the other side in the second direction with respect to the beam passing through the second scanning lens, In the first scanning optical system and the second scanning optical system, the beam passing through the second scanning lens is angled with respect to the first direction so as to approach the rotation axis; In the third scanning optical system and the fourth scanning optical system, the beam passing through the second scanning lens is angled with respect to the first direction so as to move away from the rotation axis; a scanning optical device characterized in that a straight line parallel to the sub-scanning direction of the second scanning lens of the third scanning optical system and the fourth scanning optical system forms a larger angle with a plane extending in the second direction than a straight line parallel to the sub-scanning direction of the second scanning lens of the first scanning optical system and the second scanning optical system.

2. 2. The scanning optical device according to claim 1, wherein the second scanning lenses of the first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system are aligned linearly in the second direction.

3. the first scanning lens of the first scanning optical system and the first scanning lens of the second scanning optical system are a single common lens, 3. The scanning optical device according to claim 1, wherein the first scanning lens of the third scanning optical system and the first scanning lens of the fourth scanning optical system are a single common lens.

4. the first scanning optical system and the fourth scanning optical system each include, as the reflecting mirror, one first reflecting mirror that reflects the beam toward the second scanning lens; 4. A scanning optical device according to claim 1, wherein the second scanning optical system and the third scanning optical system each have two reflecting mirrors: a first reflecting mirror that reflects the beam toward the second scanning lens, and a second reflecting mirror that reflects the beam deflected by the polygon mirror toward the first reflecting mirror.

5. a frame to which the motor, the first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system are fixed, the frame being open on one side in the first direction, the frame having a base wall to which the motor is fixed, and a side wall that protrudes from the base wall on the one side in the first direction and surrounds the base wall, the beam reflected by the polygon mirror travels obliquely with respect to a plane that passes through the polygon mirror and is perpendicular to the first direction, In the first scanning optical system and the fourth scanning optical system, the beam reflected by the polygon mirror travels obliquely toward the other side in the first direction with respect to the plane, 5. A scanning optical device according to claim 1, wherein in the second scanning optical system and the third scanning optical system, the beam reflected by the polygon mirror travels obliquely toward the one side of the first direction relative to the plane.

6. 6. The scanning optical device according to claim 1, wherein optical surfaces of the second scanning lenses of the first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system are symmetrical with respect to the sub-scanning direction.

7. The beam reflected by the polygon mirror travels obliquely with respect to a plane passing through the polygon mirror and perpendicular to the first direction, In the first scanning optical system and the fourth scanning optical system, the beam reflected by the polygon mirror travels obliquely with respect to the plane so as to move away from the first image plane and the fourth image plane in the first direction, 5. The scanning optical device according to claim 4, wherein in the second scanning optical system and the third scanning optical system, the beam reflected by the polygon mirror travels obliquely with respect to the plane so as to approach the second image plane and the third image plane in the first direction.

Images