JP5891652B2 - Laser scanning optical device - Google Patents

Description

  The present invention relates to a laser scanning optical apparatus, and more particularly to a laser scanning optical apparatus that scans a surface to be scanned with a linearly polarized laser beam emitted from light source means that is modulated based on image data.

  Normally, in this type of laser scanning optical device, a laser beam is deflected by using a polarizer (polygon mirror). However, since the incident angle to the deflector changes linearly in one main scanning, the laser beam is deflected. The intensity of the light beam changes linearly according to the deflection angle, and finally the light amount unevenness (shading) on the surface to be scanned. In order to eliminate unevenness in the amount of light on the surface to be scanned, conventionally, the film configuration has been devised so as to cancel or alleviate the intensity distribution of the deflected light beam at the deflector on the reflecting member closest to the surface to be scanned. For example, see Patent Documents 1 and 2.

  However, in a laser scanning optical apparatus corresponding to a tandem type having a plurality of light source means and optical paths, in order to eliminate unevenness in the amount of light on each of the plurality of scanned surfaces when the arrangement angles of the light source means are different from each other, Each reflecting member corresponding to each light source means needs to have a film configuration having different polarization characteristics, which leads to an increase in cost.

Japanese Patent No. 2727572 JP 2009-169248 A

  An object of the present invention is to provide a laser scanning optical device that can reduce unevenness in the amount of light on a plurality of surfaces to be scanned by using a reflecting member in each optical path as a common film configuration.

A laser scanning optical device according to one aspect of the present invention is
A plurality of light source means for emitting a linearly polarized laser beam;
A single deflector for deflecting and scanning a light beam emitted from each of the plurality of light source means;
A scanning optical element that focuses the light beam deflected by the deflector onto a plurality of scanned surfaces corresponding to the respective light source means;
A reflecting member provided on each optical path between the deflector and the plurality of scanned surfaces, and configured to return the light beam deflected by the deflector in a sub-scanning direction;
In a laser scanning optical device comprising:
A plurality of the reflecting members are installed in at least one optical path,
The reflecting members arranged at positions closest to the scanning surface in the respective optical paths are composed of the same film,
The linearly polarized light oscillation directions of the plurality of light source means are + A ° and −A ° with respect to a plane perpendicular to the rotation axis of the deflector including the light emitting point, with the clockwise direction being positive with respect to the traveling direction of the light beam. There are two types
The reflecting member disposed at a position closest to the scanning surface in each of the optical paths has a reflectance gradient that cancels the reflectance gradient at the deflector due to a change in the deflection angle even with respect to a different vibration direction of linearly polarized light. As described above, when the scanning direction by the deflector is a Y axis, in the optical path composed of a plurality of reflecting members, the longitudinal direction of each reflecting member is parallel to the Y axis, and among the plurality of reflecting members of the optical path, In two consecutive reflecting members with no reflecting member in between, when the reflecting member close to the deflector on the optical path is a front reflecting member and the reflecting member close to the scanned surface is a rear reflecting member, it is perpendicular to the Y axis. The angle formed by the normal lines of the front reflecting member and the rear reflecting member on the plane is the angle of arrangement of the respective light source means when the incident angle to the front reflecting member on the plane perpendicular to the Y axis is α. Together, (90-α) ° to (18 -.alpha.) °, or between, (during the 180-α) ° ~ (270-α) °, that said reflecting member is disposed,
It is characterized by.

  In the laser scanning optical device, the reflection member is arranged in a U-shape or a Z-shape with respect to a plurality of light source means having different arrangement angles, so that the reflectance inclination in the deflector is caused by the reflectance inclination in the reflection member. By canceling or mitigating, the light quantity distribution inclination on each scanned surface is reduced. The U-shaped arrangement means that the angle formed by the normal line between the front reflecting member and the rear reflecting member on the plane perpendicular to the Y axis is the angle of incidence on the front reflecting member on the plane perpendicular to the Y axis. In other words, the reflecting member is arranged between (90-α) ° and (180-α) ° in accordance with the arrangement angle of each light source means. The Z-type arrangement means that the reflecting member is arranged between (180−α) ° and (270−α) °.

  In other words, the distribution of the P-polarization ratio of the light beam incident on the final reflecting member can be achieved by combining two arrangement modes of the reflecting member (the U-shaped arrangement and the Z-shaped arrangement) for different arrangement angles of the light source means. And an intensity distribution that cancels the intensity distribution of the light beam deflected by the deflector. Therefore, the reflecting members arranged at positions closest to the scanning surface in each optical path can have the same film configuration.

  According to the present invention, it is possible to reduce unevenness in the amount of light on a plurality of scanned surfaces by using a reflection member in each optical path as a common film configuration, thereby achieving cost reduction.

It is a perspective view which shows the laser scanning optical apparatus which is one Example. It is an elevation view of the laser scanning optical device in the sub-scanning direction. It is a graph which shows the change of the incident angle in the polygon mirror in the said laser scanning optical apparatus, and the change of a reflectance. It is explanatory drawing which shows Z shape arrangement | positioning and U shape arrangement | positioning of a reflecting member. It is explanatory drawing which shows the angle of the vibration direction of polarized light with respect to an entrance plane. It is a perspective view which shows the shift | offset | difference of the entrance plane in Z type | mold arrangement | positioning. It is a perspective view which shows the shift | offset | difference of the entrance plane in a U-shaped arrangement | positioning. It is explanatory drawing which shows the angle change of the vibration direction of the polarized light with respect to an entrance plane. It is explanatory drawing which shows the P polarization ratio change in the example 1 of the combination angle and arrangement | positioning of a light emitting element. It is explanatory drawing which shows the P polarization | polarized-light ratio change in the example 2 of the arrangement angle and arrangement | positioning of a light emitting element. It is explanatory drawing which shows the P polarization ratio change in the example 3 of the arrangement angle of a light emitting element, and arrangement | positioning. It is explanatory drawing which shows the P polarization | polarized-light ratio change in the example 4 of the arrangement angle and arrangement | positioning of a light emitting element. It is a graph which shows the polarized light reflectance of a final reflection member. It is a graph which shows the reflectance inclination in a polygon mirror, and the light quantity distribution in the to-be-scanned surface. It is a graph which shows the angle ((alpha) = 30 degrees) which the incident surface of a reflective member makes with respect to the angle which the normal line of a reflective member makes. It is explanatory drawing which shows the change of the vibration direction of a linearly polarized light with respect to the entrance plane at the time of providing three reflection members. It is explanatory drawing which shows the range of the angle which each reflection member of a U-shaped arrangement | positioning and a Z-type arrangement | positioning makes. It is a graph which shows the inclination of the reflectance of a reflection member by the arrangement angle of a light emitting element, and arrangement | positioning of a reflection member. It is a graph which shows the P polarization ratio at the time of incidence | injection of a back reflection member, and the reflectance of a back reflection member.

  Embodiments of a laser scanning optical apparatus according to the present invention will be described below with reference to the accompanying drawings. In addition, in each figure, the same code | symbol is attached | subjected to the same member, and the overlapping description is abbreviate | omitted.

(Laser scanning optical device, see FIGS. 1 and 2)
As shown in FIGS. 1 and 2, a laser scanning optical apparatus 1 according to an embodiment is used in a tandem color image forming apparatus. In FIGS. 1 and 2, y, m, c, k Means a member arranged in the optical path of each color of yellow, magenta, cyan, and black, and the description as a subscript is omitted when any color is applicable in the description.

  The laser scanning optical device 1 is configured to form yellow, magenta, cyan, and black images on four photosensitive drums 40y, 40m, 40c, and 40k, respectively. The four-color image (electrostatic latent image) formed on the photosensitive drum 40 is developed with toner, and then primary-transferred / combined on an intermediate transfer belt (not shown), and then secondary-transferred onto a recording material. The This type of image forming process is well known and will not be described.

  The light source optical system 10 mainly includes four light emitting elements 11y, 11m, 11c, and 11k formed of a laser diode array, collimator lenses 12y, 12m, 12c, and 12k, and apertures (diaphragms) 13y, 13m, 13c, and 13k. And the cylinder lens 16. Laser beams (diffused light) emitted from the light emitting elements 11 are converted into parallel light by the collimator lenses 12 and pass through the openings 13. The light beam By emitted from the light emitting element 11 y is reflected by the optical path combining mirror 14 y and travels toward the mirror 15. The light beam Bm emitted from the light emitting element 11m is reflected by the optical path combining mirror 14m and travels toward the mirror 15. The light beam Bc emitted from the light emitting element 11c is reflected by the optical path combining mirror 14c and travels toward the mirror 15. The light beam Bk emitted from the light emitting element 11k is reflected by the optical path combining mirror 14k and travels to the mirror 15. Here, the optical path combining mirror 14 is a reflecting member arranged so that the optical path of each light beam is in the same direction (x direction).

  Each light beam reflected by the mirror 15 passes through the cylinder lens 16 and is condensed in the sub-scanning direction z near the deflection surface of the polygon mirror 17. The polygon mirror 17 is rotationally driven at a predetermined speed, and each light beam is deflected and scanned in the main scanning direction y. Each light beam is incident on the deflecting surface at a predetermined different angle with respect to a surface perpendicular to the rotation axis of the polygon mirror 17.

  Regarding the traveling direction x of each light beam from the polygon mirror 17, the scanning optical system 20 includes a first scanning lens 21, a second scanning lens 22, third scanning lenses 23y, 23m, 23c, 23k, a reflecting member (mirror) 24y, 24m, 24c, 24k, 25y, 25m, 25c, 26c and parallel flat plates (dust-proof window glass) 28y, 28m, 28c, 28k are arranged.

  The respective light beams simultaneously deflected by the deflection surface (reflection surface) of the polygon mirror 17 are transmitted through the first scanning lens 21 and the second scanning lens 22. The light beam By is reflected by the reflecting member 24y, passes through the third scanning lens 23y, is further reflected by the reflecting member 25y, passes through the parallel plate 28y, forms an image on the photosensitive drum 40y, and is scanned in the main scanning direction y. To scan. The light beam Bm is reflected by the reflecting member 24m, passes through the third scanning lens 23m, is further reflected by the reflecting member 25m, passes through the parallel plate 28m, and forms an image on the photosensitive drum 40m, and the main scanning direction y To scan. The light beam Bc is reflected by the reflecting member 24c, passes through the third scanning lens 23c, is further reflected by the reflecting members 25c and 26c, passes through the parallel plate 28c, forms an image on the photosensitive drum 40c, and performs main scanning. Scan in direction y. The light beam Bk passes through the third scanning lens 23k, is reflected by the reflecting member 24k, passes through the parallel plate 28k, forms an image on the photosensitive drum 40k, and scans in the main scanning direction y.

  In the scanning optical system 20, the scanning lenses 21 and 22 are arranged in common for all the optical paths y, m, c, and k, and the scanning lens 23 is individually arranged in each optical path y, m, c, and k. Yes. Further, two reflection members 24 and 25 for turning the optical path are arranged on the optical path y, two on the optical path m, three on the optical path c, and one on the optical path k. As shown in FIG. 2, the reflecting members 24y, 25y, 24m, and 25m are arranged to form a Z-shaped optical path in the optical paths y and m, and the reflecting members 24c, 25c, and 26c are U-shaped in the optical path c. The optical path of the mold is arranged. In the optical path k, the reflecting member 24k is disposed so as to form a Z-shaped optical path.

  In the light source optical system 10, the arrangement angle of each light emitting element (laser diode array) 11 (the clockwise rotation of the light beam with respect to the deflection plane is positive) is as shown in Table 1 below. The element 11m is −45 °, the element 11c is 45 °, and the element 11k is −45 °.

  The change of the incident angle to the polygon mirror 17 according to the deflection angle is as shown in FIG. 3A, and the change of the reflectance according to the deflection angle is as shown in FIG. 3B.

  The cross-sectional configurations in the sub-scanning direction of the U-shaped arrangement and the Z-shaped arrangement of the reflecting members 24 and 25 are as shown in FIGS. In the Z-shaped arrangement (see FIG. 4A), the light beam emitted from the second reflective member 25 is directed to the first reflective member 24 with reference to a plane including incident light rays to the plurality of arbitrary second reflective members 25. On the opposite side of the incident beam. In the U-shaped arrangement (see FIG. 4B), the light beam emitted from the second reflection member 25 is directed to the first reflection member 24 with reference to a plane including light rays incident on the plurality of arbitrary second reflection members 25. The second reflecting member 25 is arranged so as to be on the same side as the incident light beam.

  FIG. 5 shows the angle of the polarization vibration direction with respect to the incident surface when entering the reflecting member, and the P-polarized component and the S-polarized component at that time. The light is projected onto a plane perpendicular to the optical axis, and the depth of the drawing is the traveling direction of the light beam. The vertical axis is the incident surface, the horizontal axis is a plane perpendicular to the incident surface, and the optical axis is the origin. When the polarization vibration direction at the time of incidence on the reflecting member represented by a double-line arrow is projected onto the incidence plane and a plane perpendicular to the incidence plane, the P polarization ratio and the S polarization ratio are obtained.

  By the way, an image scanning start point of main scanning by the polygon mirror 17 is referred to as SOI (start of image), and an image scanning end point is referred to as EOI (end of image). 6A and 6B three-dimensionally show the light rays incident on the first reflecting member 24 and the second reflecting member 25 in the Z-type arrangement in the SOI and EOI and the deviation of the incident surface in this embodiment. ing. This is the deviation of the incident surface when a plane where the incident surfaces of the reflecting members 24 and 25 intersect is considered. The deviation of the incident surface is represented by an angle of inclination from the incident surface of the first reflecting member 24 to the incident surface of the second reflecting member 25. The direction of deviation of the incident surface is opposite between the SOI side and the EOI side.

  7A and 7B, in this embodiment, the light rays incident on the first reflecting member 24 and the second reflecting member 25 in the U-shaped arrangement in the SOI and EOI and the deviation of the incident surface are three-dimensionally shown. Show. This is the deviation of the incident surface when a plane where the incident surfaces of the reflecting members 24 and 25 intersect is considered. The deviation of the incident surface is represented by an angle of inclination from the incident surface of the first reflecting member 24 to the incident surface of the second reflecting member 25. The direction of deviation of the incident surface is opposite between the SOI side and the EOI side.

  FIG. 8 shows an angular change in the vibration direction of polarized light with respect to the incident surface when the incident surface is shifted between the reflecting members 24 and 25. The light is projected onto a plane perpendicular to the optical axis, and the depth of the drawing is the traveling direction of the light beam. The vertical axis is the incident surface, the horizontal axis is a plane perpendicular to the incident surface, and the optical axis is the origin. Although the polarization vibration direction does not change spatially, the axis rotates 30 ° due to the deviation of the incident surface, and the angle of the polarization vibration direction with respect to the incident surface changes from 45 ° to 75 °.

  In FIG. 9, the arrangement angle of the light emitting element 11 is −45 °, and the reflection members 24 and 25 are in the Z-type arrangement optical path (combination example 1). The vibration direction angle and S polarization ratio are shown. Since the incident surface is shifted in the negative direction on the SOI side and in the positive direction on the EOI side, the angle change in the vibration direction of polarized light with respect to the incident surface is positive on the SOI side and negative on the EOI side. Therefore, the P-polarization ratio is high on the SOI side, and the P-polarization ratio is low on the EOI side.

  In FIG. 10, the arrangement angle of the light emitting element 11 is −45 °, and the polarization with respect to the incident surface when entering the second reflection member 25 in the optical path in which the reflection members 24 and 25 are U-shaped arrangement (combination example 2). The angle of the vibration direction and the S polarization ratio are shown. Since the deviation of the incident surface is positive on the SOI side and negative on the EOI side, the change in the angle of polarization oscillation relative to the incident surface is negative on the SOI side and positive on the EOI side. Therefore, the P-polarization ratio is low on the SOI side, and the P-polarization ratio is high on the EOI side.

  In FIG. 11, the arrangement angle of the light emitting element 11 is 45 °, and the polarization of the polarization with respect to the incident surface when entering the second reflecting member 25 in the optical path in which the reflecting members 24 and 25 are U-shaped (combination example 3). The vibration direction angle and S polarization ratio are shown. Since the deviation of the incident surface is positive on the SOI side and negative on the EOI side, the change in the angle of polarization oscillation relative to the incident surface is negative on the SOI side and positive on the EOI side. Therefore, the P-polarization ratio is high on the SOI side, and the P-polarization ratio is low on the EOI side.

  In FIG. 12, the arrangement angle of the light emitting element 11 is 45 °, and the vibration of the polarization with respect to the incident surface when entering the second reflecting member 25 in the optical path in which the reflecting members 24 and 25 are in the Z-type arrangement (combination example 4). The direction angle and S polarization ratio are shown. Since the incident surface is shifted in the negative direction on the SOI side and in the positive direction on the EOI side, the angle change in the vibration direction of polarized light relative to the incident surface is positive on the SOI side and negative on the EOI side. Therefore, the P-polarization ratio is low on the SOI side, and the P-polarization ratio is high on the EOI side.

  FIG. 13 shows the P-polarized reflectance and the S-polarized reflectance of the final reflecting member in this example. Here, the term “final” means that each optical path is disposed at a position closest to the scanned surface.

  FIG. 14A shows the reflectance inclination of the polygon mirror 17 and the second reflecting member 25 in this embodiment, and FIG. 14B shows the light amount distribution inclination on the surface to be scanned. In all the optical paths, the reflectance gradient of the reflecting member closest to the scanned surface cancels or reduces the reflectance gradient at the polygon mirror 17, and the light amount distribution gradient on the scanned surface is sufficiently small.

  FIG. 15 shows an angle formed by the incident surface of the front reflecting member and the incident surface of the rear reflecting member with respect to the angle formed by the normal line of the front reflecting member and the normal line of the rear reflecting member. Here, out of a plurality of reflecting members arranged in each optical path, the reflecting member close to the polygon mirror on the optical path is reflected near the front reflecting member and the surface to be scanned. The member is referred to as a back reflecting member. When the angle formed by the normal line of the front reflection member and the normal line of the rear reflection member is monotonically increased up to 180 °, the angle formed by the normal line of the front reflection member and the normal line of the rear reflection member is 180 °. The angle formed by the incident surface of the front reflecting member and the incident surface of the rear reflecting member is 180 °. At this time, the reflecting surfaces of both reflecting members are parallel, and the incident surfaces coincide. When the angle formed by the normal line of the front reflection member and the normal line of the rear reflection member exceeds 180 °, the angle decreases monotonously.

  FIG. 16 shows a straight line with respect to the incident surface of each reflecting member when three reflecting members are mixed in a U-shaped arrangement for the first and second reflecting members and a Z-shaped arrangement for the second and third reflecting members. The change of the vibration direction of polarized light is shown. When the vibration direction of the linearly polarized light with respect to the incident surface in the first reflecting member is + 45 °, if the change in the incident surface of the U-shaped arrangement is larger than the change in the incident surface of the Z-shaped arrangement, two arrangements are mixed in one optical path. Also good.

  FIG. 17 shows a range of angles formed by the front reflecting member 24 and the rear reflecting member 25 in the U-shaped arrangement and the Z-shaped arrangement.

  FIG. 18A shows angles formed by the incident surfaces of the reflecting members in the Z-shaped arrangement and the U-shaped arrangement. FIG. 18B shows the angle of the polarization vibration direction with respect to the incident plane when the arrangement angle of the light emitting element is 45 °, and FIGS. 19A and 19B are incident on the post-reflecting member in the same case. The P polarization ratio at the time and the reflectance of the rear reflecting member are shown. FIG. 18C shows the angle of the polarization vibration direction with respect to the incident plane when the arrangement angle of the light emitting element is −45 °, and FIGS. 19C and 19D show the same for the post-reflection member in the same case. The P polarization ratio at the time of incidence and the reflectance of the rear reflecting member are shown. Specific numerical values are as shown in Table 2 below.

  In the laser scanning optical device having the above configuration, when the light beam emitted from each light emitting element 11 is deflected by the polygon mirror 17, the incident angle to the polygon mirror 17 is determined by the deflection angle (the incident angle is the normal vector of the reflecting surface). Defined as an angle formed with the optical axis vector) monotonously increases or monotonously decreases (see FIG. 3A). Therefore, according to the angle characteristics of the reflecting surface of the polygon mirror 17 (reflectance characteristics with respect to the incident angle), the reflectance tilt in the polygon mirror 17 (the reflectance tilt is the difference in reflectance for each light beam traveling on the surface to be scanned is A state in which the deflection angle substantially increases or decreases substantially monotonically) (see FIG. 3B).

  In addition, the light beam incident on the reflecting member is often linearly polarized light and has a polarization vibration direction. The polarization oscillation direction does not change with respect to the optical axis. When the incident surface (the normal of the reflection surface and the plane including the incident light and the reflected light) is defined when reflecting, the angle of the polarization vibration direction with respect to the incident surface is defined. Is determined (see FIG. 5). The angle of the polarization oscillation direction with respect to the incident surface is positive in the clockwise direction of the light beam traveling direction. The ratio of the P-polarized light and the S-polarized light of the incident light beam is determined by the vibration direction of the polarized light with respect to the incident surface. Since P-polarized light and S-polarized light have different reflectance characteristics (see FIG. 13), if the polarization ratio of the incident light beam is inclined due to the deflection angle on the reflecting surface, the reflectance is inclined.

  Assuming that the vector in the longitudinal direction of the reflecting member is arranged substantially parallel to the scanning line, the inclination of the polarization ratio of the incident light beam due to the deflection angle occurs because the incident surface is different at each deflection angle of each reflecting member. In the optical path incident on the center of image (COI), the normal of each reflecting member and the incident light are always in a common plane, so the incident plane is the same, and the angle of the polarization oscillation direction with respect to the incident plane is almost the same. The polarization ratio of the incident light beam remains almost unchanged. The optical path incident on the surface to be scanned with a deflection angle other than COI changes depending on the rotation angle with the longitudinal vector of each reflecting member as an axis. Therefore, the incident surface defined by the normal of the reflecting surface and the incident ray is also Varies between reflecting members. The change of the incident surface according to the deflection angle is symmetrical between the SOI side and the EOI side with reference to the COI incident surface (see FIGS. 6 and 7), and the change is larger as the deflection angle is larger.

  Here, the Z-shaped arrangement and the U-shaped arrangement of the two reflecting members will be described in detail. The Z-shaped arrangement means that the longitudinal direction of each reflecting member is parallel to the Y axis in the optical path composed of a plurality of reflecting members, where the scanning direction by the polygon mirror is the Y axis, and among the plurality of reflecting members in the optical path In the case of two consecutive reflecting members with no reflecting member in between, when the reflecting member close to the polygon mirror is the front reflecting member and the reflecting member close to the scanned surface is the rear reflecting member, the plane is perpendicular to the Y axis. When the angle between the normal line of the front reflecting member and the normal line of the rear reflecting member is α ° when the incident angle to the front reflecting member is a plane perpendicular to the Y axis, This is when (180-α) ° to (270-α) ° according to the arrangement angle. At this time, the outgoing light beam of the rear reflecting member is on the side opposite to the incident light beam of the front reflecting member with reference to the incident light beam of the rear reflecting member when viewed in a plane perpendicular to the Y axis (see the right side view of FIG. 17). .

  On the other hand, the U-shaped arrangement means that the longitudinal direction of each reflecting member is parallel to the Y axis in the optical path composed of a plurality of reflecting members when the scanning direction of the polygon mirror is the Y axis, and the plurality of reflections of the optical path are reflected. Of the two consecutive reflecting members with no reflecting member in between, when the reflecting member close to the polygon mirror is the front reflecting member and the reflecting member close to the scanned surface is the rear reflecting member, it is perpendicular to the Y axis. When the angle between the normal line of the front reflecting member and the normal line of the rear reflecting member when considered in a plane is α ° when the incident angle to the front reflecting member when considered in a plane perpendicular to the Y axis is α °, This is when (90-α) ° to (180-α) ° according to the arrangement angle of the light-emitting elements. At this time, the outgoing light beam of the rear reflecting member is on the same side as the incident light beam of the front reflecting member with reference to the incident light beam of the rear reflecting member when viewed in a plane perpendicular to the Y axis (see the left side of FIG. 17). .

  At each deflection angle, the angle of the polarization vibration direction with respect to the incident surface changes due to the change of the incident surface between the reflecting members (see FIG. 8). In the case of the Z-type arrangement, the change in angle on the SOI side is positive and the EOI side is negative. On the other hand, in the case of the U-shaped arrangement, the rotation is reversed, and the angular change on the SOI side is negative and the EOI side is positive.

  In the light source means, the light emitting elements corresponding to the respective light paths y, m, c, k are arranged on the light source substrate at predetermined intervals. Then, in order to obtain a desired sub-scanning interval on the surface to be scanned, adjustment is performed by rotating the light source substrate. Since the optical magnification in the sub-scanning direction z is the same in each of the optical paths y, m, c, and k, the arrangement angle of a certain light-emitting element is A ° in order to make the sub-scanning direction intervals of the plurality of light-emitting elements on the light source substrate the same. Then, a possible arrangement interval of light emitting elements other than A ° is −A °.

  Here, a Z-type arrangement is considered when the arrangement angle of the light emitting elements is around −45 ° (see FIG. 9). If the angle of the oscillation direction of polarized light with respect to the incident surface of the first reflecting member having the Z-shaped arrangement is about −45 ° in all deflection angles (see the center diagram in FIG. 9), the SOI changes by 10 ° to 40 ° and is incident. The angle of the vibration direction of the polarized light with respect to the surface is −35 ° to −5 ° (see the left diagram in FIG. 9). On the other hand, in the EOI, the change of the incident surface is symmetric, and the angle of the polarization vibration direction with respect to the incident surface is −85 ° to −55 ° (see the right diagram in FIG. 9). When the absolute value of the vibration direction of polarized light with respect to the incident surface is less than 45 °, the P polarization ratio is high, and when it exceeds 45 °, the P polarization ratio is low. Since the P-polarized reflectance is lower than the S-polarized reflectance, when the P-polarized ratio is high, the reflectance is lower than when the P-polarized ratio is low. In other words, when the arrangement angle of the light emitting element is around −45 °, the reflectivity of SOI at the second reflecting member in the Z-type arrangement is low, the reflectivity of EOI is high, and the reflectivity is inclined.

  When the light emitting element is arranged on the SOI side, since the incident angle of the SOI optical path in the polygon mirror is small and the incident angle of the EOI optical path is large, the SOI optical path on the reflective surface of the polygon mirror is determined by the angle characteristics of the reflective surface of the polygon mirror. The reflectance of the EOI optical path is low, and the reflectance slope is opposite to that of the second reflecting member in the Z-type arrangement, thereby canceling or reducing the reflectance.

  Next, a U-shaped arrangement is considered in the case where the arrangement angle of the light emitting element is around −45 ° (see FIG. 10). If the angle of the polarization oscillation direction with respect to the incident surface of the first reflecting member having the U-shaped arrangement is about −45 ° in all deflection angles (see the center diagram in FIG. 10), the SOI changes −10 ° to −40 °. The angle of the polarization vibration direction with respect to the incident surface is −85 ° to −55 ° (see the left diagram in FIG. 10). On the other hand, in the EOI, the change of the incident surface is symmetric, and the angle of the polarization vibration direction with respect to the incident surface is −35 ° to −5 ° (see the right diagram in FIG. 10). That is, since the P-polarized light ratio on the SOI side is high, the reflectivity of SOI at the second reflecting member is high, the reflectivity of EOI is low, and a reflectivity gradient occurs. However, when the light emitting element is arranged on the SOI side, the reflectance inclination of the second reflecting member has the same tendency as the reflectance inclination of the polygon mirror, and the reflectance inclination is amplified.

  Therefore, a U-shaped arrangement is considered when the arrangement angle of the light emitting elements is around 45 ° (see FIG. 11). If the angle of the polarization oscillation direction with respect to the incident surface of the first reflecting member having the U-shaped arrangement is about 45 ° in all deflection angles (see the center diagram in FIG. 11), the SOI changes by −10 ° to −40 °. The angle of the polarization vibration direction with respect to the incident surface is 5 ° to 35 ° (see the left diagram in FIG. 11). On the other hand, in the EOI, the change of the incident surface is symmetric, and the angle of the polarization vibration direction with respect to the incident surface is 55 ° to 85 ° (see the right side of FIG. 10). That is, since the P-polarization ratio on the SOI side is high and the P-polarization ratio on the EOI side is low, the reflectivity of the SOI at the second reflecting member is low, the reflectivity of the EOI is high, and the reflectivity gradient occurs. . When the light emitting element is arranged on the SOI side, the reflectance inclination of the second reflecting member cancels or reduces the reflectance inclination of the polygon mirror.

  Further, a Z-type arrangement is considered in the case where the arrangement angle of the light emitting element is around 45 ° (see FIG. 12). If the angle of the oscillation direction of polarized light with respect to the incident surface of the first reflecting member in the Z-shaped arrangement is about 45 ° in all deflection angles (see the center diagram in FIG. 12), the SOI changes by 10 ° to 40 °, and the incident surface The angle of the vibration direction of the polarized light with respect to is 55 ° to 85 ° (see the left diagram in FIG. 12). On the other hand, in the EOI, the change of the incident surface is symmetric, and the angle of the polarization vibration direction with respect to the incident surface is 5 ° to 35 ° (see the right diagram in FIG. 12). That is, since the P-polarization ratio on the SOI side is low and the P-polarization ratio on the EOI side is high, the reflectivity of SOI at the second reflecting member is high, the reflectivity of EOI is low, and the reflectivity gradient occurs. . When the light emitting element is arranged on the SOI side, the reflectance inclination of the second reflecting member amplifies the reflectance inclination of the polygon mirror.

  Reflective members arranged at positions closest to the surface to be scanned in each of the optical paths y, m, c, and k by appropriately using the Z-shaped arrangement or the U-shaped arrangement for the arrangement angles of the respective light emitting elements. Even if the same film configuration is used, the reflectance gradient in the polygon mirror can be canceled or reduced, and the light amount distribution gradient in the scanned surface can be reduced (see FIG. 14). This eliminates the need for a plurality of reflecting members having different polarization characteristics in order to reduce the amount of light distribution gradient. In other words, the same film configuration can be obtained, leading to cost reduction.

  By the way, when three reflecting members are arranged in at least one optical path, the first reflecting member and the second reflecting member are arranged in a U shape, and the second reflecting member and the third reflecting member are in a Z shape. The angle formed between the normal line of the first reflecting member and the normal line of the second reflecting member is 45 ° or more, and the angle formed between the normal line of the second reflecting member and the normal line of the third reflecting member is 170. It is preferable that it is more than °. Specific arrangement angles, normal lines of the reflecting members, and angles formed by the incident surfaces are shown in Tables 3 and 4 below.

  The change in the angle of the vibration direction of polarized light with respect to the incident surface is opposite in sign between the U-shaped arrangement and the Z-shaped arrangement. Therefore, when the U-shaped arrangement and the Z-shaped arrangement are mixed, the angle change The influence of arrangement with a large absolute value of becomes dominant (see FIG. 16).

  In the case of the U-shaped arrangement, the angle formed between the normal line of the front reflection member and the normal line of the rear reflection member when projected on a plane perpendicular to the Y axis in the front reflection member and the rear reflection member is to the front reflection member. When the incident angle is α °, the angle is (90−α) ° to (180−α) ° (see the left diagram in FIG. 17). In this angle range, the angle formed by the incident surface of the front reflecting member and the incident surface of the rear reflecting member is always raised to the right with respect to the angle formed by the normal line of the front reflecting member and the normal line of the rear reflecting member. (See FIG. 15).

  When the angle formed by the incident surface of the front reflecting member and the incident surface of the rear reflecting member is 180 °, the respective incident surfaces coincide with each other, so that the vibration direction of the linearly polarized light with respect to the incident surface is not changed. Further, when the angle formed by the incident surface of the front reflecting member and the incident surface of the rear reflecting member is 90 °, the vibration direction is changed most.

  In the case of the Z-shaped arrangement, the angle formed by the normal line of the front reflection member and the normal line of the rear reflection member when projected on a plane perpendicular to the Y axis in the front reflection member and the rear reflection member having the U-shaped arrangement is When the incident angle to the front reflecting member is α °, the angle is (180−α) ° to (270−α) ° (see the right side of FIG. 17). Since this angle range always includes 180 °, at that time, the angle formed by the incident surface of the front reflecting member and the incident surface of the rear reflecting member is 180 °, and the respective incident surfaces coincide with each other and are straight lines with respect to the incident surface. Do not change the direction of polarization oscillation. Further, when the angle formed by the normal line of the front reflecting member and the normal line of the rear reflecting member when projected on a plane perpendicular to the Y axis is around 180 °, the incident surface of the front reflecting member and the incident surface of the rear reflecting member Is a value close to 180 °, and the change in the vibration direction of the linearly polarized light with respect to the incident surface is small.

  In order to make the angle formed by the entrance surface of the front reflecting member with the U-shaped arrangement and the entrance surface of the back reflecting member larger than the angle formed by the entrance surface of the front reflecting member with the Z-shaped arrangement and the entrance surface of the rear reflecting member The angle formed between the normal line of the front reflecting member and the normal line of the rear reflecting member in each arrangement is defined. First, the angle formed by the normal line of the front reflecting member and the normal line of the rear reflecting member in the U-shaped arrangement is set to 45 ° or more. At this time, the angle formed between the incident surface of the front reflecting member and the incident surface of the rear reflecting member in the U-shaped arrangement is 20 ° or more. Furthermore, the angle formed by the normal line of the front reflection member and the normal line of the rear reflection member in the Z-shaped arrangement is set to 170 ° or more. At this time, the angle formed by the incident surface of the front reflecting member with the Z-shaped arrangement and the incident surface of the rear reflecting member is 20 ° or less. Under this angle condition, the angle formed by the incident surface of the front reflecting member with the U-shaped arrangement and the incident surface of the rear reflecting member is always the angle between the incident surface of the front reflecting member with the Z-shaped arrangement and the incident surface of the rear reflecting member. It is larger than the angle it makes.

  In the present embodiment, in the optical path c, the first reflecting member and the second reflecting member have a U-shaped arrangement, and the second reflecting member and the third reflecting member have a Z-shaped arrangement. The angle formed between the normal line of the first reflection member and the normal line of the second reflection member when considered in a plane perpendicular to the Y axis is 92.17 °, and the incident surface of the first reflection member and the second reflection member The angle formed by the incident surface is 45.07 ° in SOI (see Table 4). Further, the angle formed by the normal line of the second reflecting member and the normal line of the third reflecting member when considered in a plane perpendicular to the Y axis is 203.66 °, and the incident surface of the second reflecting member and the third angle The angle formed by the incident surface of the reflecting member is 15.41 ° in SOI (see Table 4). The absolute value of the angle formed by the incident surface of each reflecting member is linearly polarized with respect to the incident surface because the U-shaped arrangement of the first reflecting member and the second reflecting member is larger than the Z-shaped arrangement of the second reflecting member and the third reflecting member. The optical path c is greatly influenced by the U-shaped arrangement with respect to the change in the vibration direction, and can be considered to be only the U-shaped arrangement.

  The laser scanning optical apparatus according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist thereof.

  As described above, the present invention is useful for a laser scanning optical device, and is particularly excellent in that it can reduce unevenness of light quantity on a plurality of scanned surfaces with a common film configuration of the reflecting member.

DESCRIPTION OF SYMBOLS 1 ... Laser scanning optical apparatus 10 ... Light source optical system 11 ... Light emitting element 17 ... Polygon mirror 20 ... Scanning optical system 21, 22, 23 ... Scanning lens 24, 25, 26 ... Reflective member 40 ... Photosensitive drum

Claims (4)

A plurality of light source means for emitting a linearly polarized laser beam;
A single deflector for deflecting and scanning a light beam emitted from each of the plurality of light source means;
A scanning optical element that focuses the light beam deflected by the deflector onto a plurality of scanned surfaces corresponding to the respective light source means;
A reflecting member provided on each optical path between the deflector and the plurality of scanned surfaces, and configured to return the light beam deflected by the deflector in a sub-scanning direction;
In a laser scanning optical device comprising:
A plurality of the reflecting members are installed in at least one optical path,
The reflecting members arranged at positions closest to the scanning surface in the respective optical paths are composed of the same film,
The linearly polarized light oscillation directions of the plurality of light source means are + A ° and −A ° with respect to a plane perpendicular to the rotation axis of the deflector including the light emitting point, with the clockwise direction being positive with respect to the traveling direction of the light beam. There are two types
The reflecting member disposed at a position closest to the scanning surface in each of the optical paths has a reflectance gradient that cancels the reflectance gradient at the deflector due to a change in the deflection angle even with respect to a different vibration direction of linearly polarized light. As described above, when the scanning direction by the deflector is a Y axis, in the optical path composed of a plurality of reflecting members, the longitudinal direction of each reflecting member is parallel to the Y axis, and among the plurality of reflecting members of the optical path, In two consecutive reflecting members with no reflecting member in between, when the reflecting member close to the deflector on the optical path is a front reflecting member and the reflecting member close to the scanned surface is a rear reflecting member, it is perpendicular to the Y axis. The angle formed by the normal lines of the front reflecting member and the rear reflecting member on the plane is the angle of arrangement of the respective light source means when the incident angle to the front reflecting member on the plane perpendicular to the Y axis is α. Together, (90-α) ° to (18 -.alpha.) °, or between, (180-α) ° ~ (270-α) that ° between the reflecting member is disposed,
A laser scanning optical device characterized by the above. 2. The laser according to claim 1 , wherein the vibration direction of the linearly polarized light of the plurality of light source means is 20 ° to 70 ° with respect to a plane that includes the light emitting point and is perpendicular to the rotation axis of the deflector. Scanning optical device.   3. The laser scanning optical apparatus according to claim 1, wherein the number of reflecting members arranged in each optical path is not the same.   The first reflecting member, the second reflecting member, and the third reflecting member are disposed in at least one optical path, and the first reflecting member and the second reflecting member are disposed in a U-shape, and the second reflecting member and the second reflecting member The three reflecting members are arranged in a Z shape, and the angle formed by the normal line of the first reflecting member and the normal line of the second reflecting member is 45 ° or more, and the normal line of the second reflecting member and the third reflecting member The laser scanning optical apparatus according to any one of claims 1 to 3, wherein an angle formed by the normal line is 170 ° or more.

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