JP7806471B2 - Optical Scanning Device - Google Patents

Description

The present invention relates to an optical scanning device equipped with a polygon mirror.

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 that has a base wall and side walls (see Patent Document 1).

JP 2014-178341 A

However, in the optical scanning device of Patent Document 1, the reflecting mirror is positioned closer to the photosensitive drum on which the beam is focused than the final scanning lens. This increases the distance from the final scanning lens to the photosensitive drum, resulting in a relatively large sub-scanning magnification. As a result, the increased sub-scanning magnification increases the optical scanning device's sensitivity to tolerances in the sub-scanning direction, which is a problem.

Therefore, the present invention aims to reduce the tolerance sensitivity of optical scanning devices.

In order to solve the above problem, the optical scanning device of the present invention comprises a light source, a polygon mirror, a motor, a first scanning optical system, a second scanning optical system, a third scanning optical system, a fourth scanning optical system, and a frame.
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 frame has a base wall to which the motor is fixed and a side wall that protrudes from the base wall to one side in the first direction and surrounds the base wall. The frame has an opening on one side in the first direction to which the first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system are fixed.
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 through which the beam reflected by the reflecting mirror passes.
The second scan lens emits the beam in a direction from the base wall toward the second scan lens.

With this configuration, the second scanning lens is positioned closest to the image plane, thereby reducing tolerance sensitivity.

Furthermore, in the above-mentioned 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 each be configured to be aligned linearly in the second direction.

This allows the distance from each second scanning lens to the image plane to be equal.

In the above-described scanning optical device, 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,
The first scanning lens of the third scanning optical system and the first scanning lens of the fourth scanning optical system may be configured as a single common lens.

By using a common first scanning lens, the scanning optical device can be made smaller.

Furthermore, in the above-mentioned scanning optical device, in at least one scanning optical system, the first scanning lens and the second scanning lens may be configured to overlap when viewed from the first direction.

This allows the second scanning lens in at least one scanning optical system to be positioned close to the polygon mirror.

Furthermore, in the above-mentioned scanning optical device, the reflecting mirror may include a first reflecting mirror that reflects the beam toward the second scanning lens, and in the second scanning optical system and the third scanning optical system, the first scanning lens may be positioned between the beam traveling from the first reflecting mirror toward the second scanning lens and the polygon mirror.

This allows the distance between the polygon mirror and the first scanning lens to be shortened.

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

This allows for fewer reflective mirrors to be used.

Furthermore, in the above-mentioned scanning optical device, the frame may be configured to have a first wall that supports the second scanning lens and that rises from the base wall in the first direction.

This allows for increased positional accuracy of the polygon mirror and second scanning lens.

Furthermore, in the above-mentioned scanning optical device, the frame may be configured to have second walls arranged on both sides of the second scanning lens in the longitudinal direction.

Furthermore, in the above-mentioned scanning optical device, the frame may be configured to have a third wall that is perpendicular to the first direction and connects the first wall and second wall.

This improves the strength of the first wall that supports the second scanning lens.

Furthermore, in the above-mentioned scanning optical device, the first wall may be configured to support multiple second scanning lenses.

This invention reduces tolerance sensitivity.

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. FIG. 2 is a perspective view showing the structure around the coupling lens. FIG. 2 is a perspective view of the scanning optical device as seen from one side in a first direction. FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 2 is a cross-sectional view taken along the line VV in FIG. 1. 6 is a diagram illustrating in detail the position and angle of each second scanning lens in FIG. 5 . FIG. 10 is a perspective view of the frame as seen from the other side in the first direction. FIG. 2 is a perspective view of the frame as seen from one side in a first direction. FIG. 10 is a cross-sectional view showing a structure for attaching the reflecting mirror to the frame.

As shown in Figures 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, the direction along the rotation axis X1 of the polygon mirror 51 shown in Figure 3 is referred to as the "first direction." Furthermore, the direction perpendicular to the first direction, in which the polygon mirror 51 and the first scanning lens 60 shown in Figure 3 are aligned, is referred to as the "second direction." Furthermore, the direction perpendicular to the first and second directions is referred to as the "third direction." Note that the third direction corresponds to the main scanning direction in the scanning optical system Lo, and the first direction corresponds to the sub-scanning direction. Furthermore, the arrows indicating each direction in the drawings will refer to "one side" in that direction.

As shown in FIG. 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.

The semiconductor laser 10 is a device that emits light. Four semiconductor lasers 10 are provided, corresponding to the four photosensitive drums 200 (see Figure 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.

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, parts corresponding to the first color may be distinguished by adding "first" to the beginning of their names and adding "Y" to the end of their reference numerals. Similarly, parts corresponding to the second, third, and fourth colors may be distinguished by adding "second," "third," and "fourth" to the beginning of their names and adding "M," "C," and "K" to the end of their reference numerals.

The first semiconductor laser 10Y is arranged with a gap in the first direction relative to the second semiconductor laser 10M. The first semiconductor laser 10Y is located on one side of the second semiconductor laser 10M in the first direction.

The third semiconductor laser 10C is aligned with the second semiconductor laser 10M at a distance in the second direction. The third semiconductor laser 10C is located on the other side of the second semiconductor laser 10M in the second direction. The fourth semiconductor laser 10K is aligned with the third semiconductor laser 10C at a distance in the first direction, and is aligned with the first semiconductor laser 10Y at a distance in the second direction.

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 positioned opposite the corresponding semiconductor lasers 10Y, 10M, 10C, and 10K.

As shown in FIG. 1, the aperture plate 30 is a part that has an aperture stop 31 through which the beam from the coupling lens 20 passes, and is formed integrally with the frame F. The aperture plate 30 is located between the coupling lens 20 and the condenser lens 40.

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.

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 the rotation axis X1. The motor 52 rotates the polygon mirror 51 around the rotation axis X1, which extends in the first direction. The motor 52 is fixed to the frame F.

The scanning optical system Lo is an optical system that focuses the beam deflected by the deflector 50 onto the surface of the photosensitive drum 200, which serves as an image plane. The scanning optical system Lo is fixed to the 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.

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.

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.

The first scanning optical system LoY emits the beam BY deflected by the polygon mirror 51 toward the 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.

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 in the first scanning optical system LoY that is closest to the polygon mirror 51.

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 the 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 positioned on one side of the polygon mirror 51 in the first direction. The second scanning lens 70Y is the scanning lens in the first scanning optical system LoY that is closest to the image plane.

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.

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

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 the 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 positioned 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.

The third scanning optical system LoC emits the beam deflected by the polygon mirror 51 toward the 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.

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 beam BC traveling from the first reflecting mirror 81C toward the second scanning lens 70C and the polygon mirror 51.

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 the image plane. The second scanning lens 70C is located 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.

The fourth scanning optical system LoK emits the beam deflected by the polygon mirror 51 toward the fourth image surface of the fourth photosensitive drum 200K. The fourth scanning optical system LoK emits the beam BK toward the fourth image surface 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.

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 in the fourth scanning optical system LoK that is closest to the polygon mirror 51.

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 the image plane. The second scanning lens 70K is positioned on the other side of the polygon mirror 51 in the first direction. The second scanning lens 70K is the scanning lens of the fourth scanning optical system LoK that is closest to the image plane.

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 that they at least partially overlap each other when viewed from the second direction.

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.

In the first scanning optical system LoY and the second scanning optical system LoM, the centers C1 and C2 of the optical surfaces of the second scanning lenses 70Y and 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 and BM passing through the second scanning lenses 70Y and 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.

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 have different angles with the second direction than 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.

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

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

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. Beam BM is emitted from the second scanning lens 70M at a predetermined angle with respect to the first direction. Beam BM is imaged on the second photosensitive drum 200M and scanned in the main scanning direction. Similarly, beams BC and BK are emitted toward an image plane on one side in the first direction by the corresponding scanning optical systems LoC and LoK, are imaged on the corresponding photosensitive drums 200C and 200K, and are scanned in the main scanning direction.

As shown in Figures 3 and 5, the frame F has 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 fixed thereto. The frame F is made of resin and is integrally molded. The frame F has a first recess CP1 shown in Figure 8 and a second recess CP2 shown in Figure 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 Figure 5, the deflector 50 and a portion of the scanning optical system Lo are disposed within the first recess CP1. Specifically, all components of the scanning optical system Lo, except for the first reflecting mirrors 81, are disposed within the first recess CP1. As shown in Figure 2, the coupling lens 20, the aperture plate 30, and the condenser lens 40 (see Figure 1) are disposed within the second recess CP2.

As shown in FIG. 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, 60CK and the second scanning lenses 70Y, 70M, 70C, 70K are disposed between the first base wall Fb1 and the cover C and are housed in the first recess CP1.

As shown in Figures 7 and 8, the frame F has a first base wall Fb1, which is an example of a base wall located at the bottom of the first recess CP1, and a second base wall Fb2, which is located at the bottom of the second recess CP2.

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 direction is along the first direction. In other words, the first base wall Fb1 and the second base wall Fb2 are walls having a plane that is perpendicular to the first direction.

The second base wall Fb2 is positioned offset to one side in the first direction relative 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 attached directly or indirectly 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 to one side in the first direction relative to the first base wall Fb1. In this embodiment, the deflector 50, i.e., the polygon mirror 51 and motor 52, are fixed to the first base wall Fb1 by multiple screws N.

As shown in FIG. 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, respectively.

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

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

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 Figures 5 and 8). The holes H extend in the third direction, and four holes H are arranged corresponding to each of the first reflecting mirrors 81.

The frame F further has 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 Figure 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.

The first partition wall F1 has two first openings F11 and F12 through which beams BY to BK pass as they travel from each aperture stop 31 on the diaphragm plate 30 toward the polygon mirror 51. The first openings F11 and F12 are formed as slits that are long in the first direction, penetrate in the third direction, and open to one side in the first direction (see Figure 8). The first opening F11 passes beams BY and BM. The first opening F12 passes beams BC and BK.

As shown in FIG. 1, the condenser lens 40 is positioned so as to cover the first openings F11 and F12 shown in FIG. 7. The condenser lens 40 is sandwiched between the first partition wall F1 and the aperture plate 30.

As shown in Figures 3 and 8, the frame F further has two second partition walls F2 located on either side of the polygon mirror 51 (see Figure 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.

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 below). 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 a storage recess CP3 for storing the polygon mirror 51.

The first scanning lens 60YM is positioned so as to block a portion of the second opening F21. The first scanning lens 60CK is positioned 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 part 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.

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 between the portions corresponding to the first recess CP1 and the second recess CP2.

As shown in FIG. 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.

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.

The third side wall F43 is located on the opposite side of the deflector 50 from the first scanning lens 60YM. 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 portion of the third side wall F43 protrudes from the first base wall Fb1 to one side in the first direction, and another portion protrudes from the second base wall Fb2 to the other side in the first direction.

The fourth side wall F44 is located on the opposite side of the deflector 50 from the first scanning lens 60CK. The fourth side wall F44 is connected to the other ends 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 portion of the fourth side wall F44 protrudes from the first base wall Fb1 to one side in the first direction, and another portion protrudes from the second base wall Fb2 to the other side in the first direction.

As shown in FIG. 9 , the scanning optical device 1 further includes a support member Fs that can be detached from the frame F, which includes the first recess CP1 and second recess CP2 described above. 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 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, fixed by the photocurable resin P, are attached to the frame F by a U-shaped leaf spring SP.

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 that allows light to pass through to cure the photocurable resin (see Figure 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 (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.

One support member Fs and one leaf spring SP are arranged for each first reflecting mirror 81, at each longitudinal end 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.

The frame F has a support surface Fm1 that supports the support member Fs. The support surface Fm1 is positioned at a position corresponding to each longitudinal end of the four first reflecting mirrors 81 (see Figure 7).

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. The first reflecting mirror 81 is then brought into contact with the protrusion Fs1 of the support member Fs. At this time, the photocurable resin P is positioned in contact with both the support member Fs and the first reflecting mirror 81. A leaf spring SP is then 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 while monitoring the beam position on the image plane. To adjust the angle of the first reflecting mirror 81, the arm AM, indicated by the two-dot chain line in Figure 9, is pressed against the first reflecting mirror 81 to move it. After the angle adjustment is complete, the first reflecting mirror 81 is fixed to the support member Fs by irradiating the photocurable resin P with light such as ultraviolet light.

As shown in Figures 3 and 8, the frame F further has a first wall W1, a second wall W2, and a third wall W3.

The first wall W1 supports the multiple second scanning lenses 70Y, 70M, 70C, and 70K. The first wall W1 rises from the first base wall Fb1 toward one side in the first direction. The first walls W1 are disposed at both ends of the second scanning lenses 70Y, 70M, 70C, and 70K in the longitudinal direction (third direction). Each first wall W1 has a second lens seating surface W11 that is recessed toward the other side in the first direction. Both longitudinal ends of each second scanning lens 70Y, 70M, 70C, and 70K 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 facing one side in the first direction of the second lens seating surface W11.

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 constitute the second wall W2.

The third wall W3 is a wall that extends in a direction perpendicular to the first direction. The third wall W3 connects the first wall W1 and the second wall W2.

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 surfaces, 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.

In addition, since the second scanning lenses 70Y, 70M, 70C, and 70K of each scanning optical system LoY, LoM, LoC, and LoK are aligned linearly in the second direction, the distances from each second scanning lens 70Y, 70M, 70C, and 70K to each image plane can be made equal.

In addition, 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 a single 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 a single common lens, which reduces the number of parts and allows the scanning optical device 1 to be made more compact.

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 positioned close to the polygon mirror 51. This allows the scanning optical device 1 to be made more compact.

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 located 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.

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, which allows for fewer reflecting mirrors.

Furthermore, since the frame F has a 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.

Furthermore, the frame F has a 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.

In addition, in the first scanning optical system LoY and the second scanning optical system LoM, the centers C1 and C2 in the sub-scanning direction of the second scanning lenses 70Y and 70M are offset to one side in the sub-scanning direction with respect 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 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 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 spacing between the emitted beams BY, BM, BC, and BK does not become large, 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 becomes wider, preventing the scanning optical device 1 from becoming larger.

Furthermore, 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 and 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 different angles with the second direction. Therefore, 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 respect to the first direction.

The frame F also 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 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 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.

In addition, the seating surface FsZ of the support member Fs has a protrusion Fs1 that serves as a fulcrum when adjusting the orientation of the first reflecting mirror 81, making it easy to adjust the orientation of the first reflecting mirror 81.

Furthermore, the frame F is composed of 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.

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

In the above embodiment, 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.

In the above embodiment, a leaf spring SP was used as an example of a spring, but the spring is not limited to a leaf spring and may be a wire spring, etc.

In the above embodiment, the frame F and the support member Fs having the seat surface FsZ were constructed from different members, but the seat surface FsZ may also be constructed integrally with the frame F.

In the above embodiment, the second scanning lens 70 was fixed to the frame by a spring (not shown), but the method for fixing the second scanning lens 70 is not particularly limited, and it may be fixed by adhesive such as photocurable resin.

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 a single coupling lens 20, and the multiple beams are imaged on the surface of the photosensitive drum 200 by the corresponding scanning optical system Lo. In this configuration, the beams BY, BM, BC, and BK in the above embodiment each include multiple beams.

The elements described in the above embodiments and variations may be implemented in any combination.

1 Scanning optical device 51 Polygon mirror 52 Motor 60 First scanning lens 60YM, 60CK First 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 First base wall Fm1 Support surface Fs Support member Fs1 Protrusion FsZ Seat surface H Hole LoY, LoM, LoC, LoK First scanning optical system W1 First wall W2 Second wall W3 Third wall X1 Rotation axis

Claims (10)

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;
a frame having a base wall to which the motor is fixed and a side wall that protrudes from the base wall toward one side in the first direction and surrounds the base wall, the frame having an opening toward the one side in the first direction and to which the first scanning optical system, the second scanning optical system, the third scanning optical system, and the fourth scanning optical system are fixed;
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 through which the beam reflected by the reflecting mirror passes,
the second scan lens emits a beam in a direction from the base wall toward the second scan lens;
the reflecting mirror includes a first reflecting mirror that reflects the beam from the base wall toward the second scanning lens;
the first reflecting mirror is attached to the base wall from the other side in the first direction,
A scanning optical device characterized in that the base wall has a hole extending in a third direction perpendicular to the first direction and the second direction, and exposing the reflective surface of the first reflective mirror to one side of the first direction. The scanning optical device described in claim 1, characterized in that 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 each aligned linearly in the second direction. 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. A scanning optical device according to any one of claims 1 to 3, characterized in that in at least one scanning optical system, the first scanning lens and the second scanning lens overlap when viewed from the first direction. 5. The scanning optical device according to claim 1, wherein in the second scanning optical system and the third scanning optical system, the first scanning lens is located between the beam traveling from the first reflecting mirror toward the second scanning lens and the polygon mirror. 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;
6. 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. A scanning optical device according to any one of claims 1 to 6, characterized in that the frame has a first wall that supports the second scanning lens and rises from the base wall in the first direction. A scanning optical device as described in claim 7, wherein the frame has second walls arranged on both sides of the second scanning lens in the longitudinal direction. A scanning optical device as described in claim 8, characterized in that the frame has a third wall that is perpendicular to the first direction and connects the first wall and the second wall. A scanning optical device according to claims 7 to 9, wherein the first wall supports a plurality of the second scanning lenses.