JP2018036512A - Optical scanning device, and image formation device equipped with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical scanning device that achieves sufficient miniaturization.SOLUTION: An optical scanning device according to the present invention comprises: a deflector that deflects first and second light fluxes upon a first deflection surface to scan first and second scanned surfaces in a main scan direction, respectively, and deflects third and fourth light flexes upon a second deflection surface to scan third and fourth scanned surfaces in the main scan surface, respectively; first and second image formation optical systems that guide each of the first and second light fluxes deflected by the deflector to the first and second scanned surfaces; and third and fourth image formation optical systems that guide each of the third and fourth light fluxes deflected by the deflector to the third and fourth scanned surfaces. In a sub scanning cross-section, the number of crossing points between optical paths themselves of an on-axis light flux of the first and second light fluxes deflected by the deflector is more than that of the crossing points between optical paths themselves of an on-axis light flux of the third and fourth light fluxes deflected by the deflector.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an optical scanning apparatus, and is suitable for an image forming apparatus such as a laser beam printer (LBP), a digital copying machine, or a multifunction printer (MFP).

  Patent Document 1 employs a multistage imaging lens, and with a small number of mirrors, prevents each light beam from entering an image forming optical system that guides another light beam. An optical scanning device including a plurality of imaging optical systems that guide light to a plurality of scanned surfaces is disclosed.

JP-A-2015-108834

However, in the optical scanning device disclosed in Patent Document 1, in order to prevent the light beam incident on the photoconductor near the deflector from re-entering the imaging lens, the reflection angle of the light beam by the mirror is increased to some extent. Therefore, the overall size of the apparatus is not sufficiently reduced.
Therefore, an object of the present invention is to provide an optical scanning device that achieves a sufficiently small size.

  The optical scanning device according to the present invention deflects the first and second light beams by the first deflection surface to scan the first and second scanned surfaces in the main scanning direction, and the third and second 4 deflected by the second deflecting surface to scan each of the third and fourth scanned surfaces in the main scanning direction, and the first and second light beams deflected by the deflector, respectively. The first and second imaging optical systems for guiding the light to the first and second scanned surfaces, and the third and fourth light beams deflected by the deflector, respectively. And an intersection of the optical paths of the on-axis light beams of the first and second light beams deflected by the deflector in the sub-scan section. Of the third and fourth light beams deflected by the deflector is larger than the number of intersections between the optical paths of the axial light beams. The features.

  According to the present invention, it is possible to provide an optical scanning device that achieves a sufficiently small size.

FIG. 3 is a main scanning sectional view of the optical scanning device according to the first embodiment. FIG. 3 is a sub-scan sectional view of an imaging optical system of the optical scanning device according to the first embodiment. FIG. 3 is a sub-scan sectional view of an incident optical system of the optical scanning device according to the first embodiment. The figure which showed the main scanning direction position dependence of the curvature of field on each to-be-scanned surface by the optical scanning device which concerns on 1st embodiment. The figure which showed the main scanning direction position dependence of the f (theta) characteristic of each imaging optical system of the optical scanning device which concerns on 1st embodiment. The figure which showed the main scanning direction position dependence of the scanning line curve on each to-be-scanned surface by the optical scanning device which concerns on 1st embodiment. FIG. 7 is a main scanning sectional view of an optical scanning device according to a second embodiment. FIG. 9 is a sub-scanning sectional view of an imaging optical system of an optical scanning device according to a second embodiment. FIG. 10 is a sub-scan sectional view of an incident optical system of an optical scanning device according to a second embodiment. FIG. 9 is a main scanning sectional view of an optical scanning device according to a third embodiment. FIG. 10 is a sub-scan sectional view of an imaging optical system of an optical scanning device according to a third embodiment. FIG. 10 is a sub-scan sectional view of an incident optical system of an optical scanning device according to a third embodiment. The schematic diagram for demonstrating the physical meaning of the conditional expression of this invention. FIG. 6 is a cross-sectional view of a main part of a color image forming apparatus on which an optical scanning device according to any one of the first to third embodiments is mounted.

  Hereinafter, the optical scanning device according to the present embodiment will be described with reference to the drawings. It should be noted that the drawings shown below may be drawn at a scale different from the actual scale so that the present embodiment can be easily understood.

  In the following description, the main scanning direction (Y direction) corresponds to the direction perpendicular to the rotation axis of the deflector and the optical axis (X direction) of the optical system, and the sub-scanning direction (Z direction) is the deflector. Corresponds to the direction parallel to the rotation axis. The main scanning section corresponds to a section perpendicular to the sub scanning direction, and the sub scanning section corresponds to a section perpendicular to the main scanning direction.

[First embodiment]
FIGS. 1A and 1B are main scanning sectional views of the optical scanning device 100 according to the first embodiment. FIG. 2 shows a sub-scanning sectional view of the imaging optical system of the optical scanning device 100 according to the first embodiment. FIG. 3 shows a sub-scanning sectional view of the incident optical system of the optical scanning device 100 according to the first embodiment.
In FIGS. 1A and 1B, the optical path folded back by the mirror is developed and shown, and the mirror is not shown.

The optical scanning device 100 according to the present embodiment includes light sources 1a, 1b, 1c and 1d, aperture stops 2a, 2b, 2c and 2d, coupling lenses 3a, 3b, 3c and 3d, and cylindrical lenses 4a, 4b, 4c and 4d.
Further, the optical scanning device 100 includes a deflector 5, first imaging lenses 6 and 6 ′, second imaging lenses (first and second imaging optical elements) 7 and 7 ′, and mirrors (reflection optics). Elements) M1, M2, M3, M1 ′, M2 ′ and M3 ′, and a housing 9 are provided.

As the light sources 1a, 1b, 1c, and 1d, semiconductor lasers having light emitting points are used.
The aperture stops 2a and 2b have different aperture diameters in the sub-scanning direction so that the spot diameters on the scanned surfaces 8a and 8b are equal (1 / e ² slice diameter of the spot peak light quantity). The light beam diameters in the sub-scanning direction of the light beams RA and RB emitted from the light sources 1a and 1b are limited.
Similarly, the aperture stops 2c and 2d have different aperture diameters in the sub-scanning direction so that the spot diameters on the scanned surfaces 8c and 8d are equal to each other, and are emitted from the light sources 1c and 1d. The light beam diameter in the sub-scanning direction of the light beams RC and RD is limited.

The coupling lenses 3a and 3c respectively convert the light beams RA and RC emitted from the light sources 1a and 1c into a substantially parallel light beam in the sub-scanning section and a weakly convergent light beam in the main scanning section.
On the other hand, the coupling lenses 3b and 3d respectively convert the light beams RB and RD emitted from the light sources 1b and 1d into a substantially parallel light beam in the sub-scanning section and a weakly divergent light beam in the main scanning section.
Here, the exit surfaces of the coupling lenses 3a, 3b, 3c and 3d are anamorphic surfaces. The respective convergence degrees are set to desired values by making the radii of curvature in the main scanning section of the exit surfaces of the coupling lenses 3a and 3b and 3c and 3d different from each other.
Here, the substantially parallel light beam includes a weak divergent light beam, a weakly convergent light beam, and a parallel light beam.
The cylindrical lenses 4a, 4b, 4c and 4d each have a finite power (refractive power) in the sub-scan section, and the light beams RA, RB, RC passing through the coupling lenses 3a, 3b, 3c and 3d and RD is condensed only in the sub-scan section.

In this way, the light beams RA and RB emitted from the light sources 1a and 1b are collected only in the sub-scan section in the vicinity of the deflection surface 5a of the deflector 5, and are formed as a line image that is long in the main scanning direction. .
Further, the light beams RC and RD emitted from the light sources 1c and 1d are collected only in the sub-scan section in the vicinity of the deflection surface 5a ′ of the deflector 5 and formed as a line image that is long in the main scanning direction.
The aperture stop 2a, the coupling lens 3a, and the cylindrical lens 4a constitute an incident optical system (first incident optical system) LA of the optical scanning device 100 according to the present embodiment.
Further, the aperture stop 2b, the coupling lens 3b, and the cylindrical lens 4b constitute an incident optical system (second incident optical system) LB of the optical scanning apparatus 100 according to the present embodiment.
In addition, the aperture stop 2c, the coupling lens 3c, and the cylindrical lens 4c constitute an incident optical system (third incident optical system) LC of the optical scanning device 100 according to the present embodiment.
Further, the aperture stop 2d, the coupling lens 3d, and the cylindrical lens 4d constitute an incident optical system (fourth incident optical system) LD of the optical scanning device 100 according to the present embodiment.

As described above, each of the incident optical systems LA to LD of the optical scanning device 100 according to this embodiment has different aperture shapes of the aperture stops 2a and 2b and 2c and 2d, and the coupling lens 3a. Except for the shapes of the exit surfaces 3b and 3c and 3d being different from each other, they have the same configuration. The distances from the light sources 1a and 1b along the optical axes of the incident optical systems LA and LB to the deflection surface 5a and the light sources 1c and 1d along the optical axes of the incident optical systems LC and LD from the deflection surface 5a, respectively. Each distance to 'is the same as each other.
As a result, the arrangement of the optical components can be made common, the types of holding parts and the types of assembly tools for holding the optical components can be reduced, and productivity can be improved.

The incident optical systems LA to LD of the optical scanning apparatus 100 according to the present embodiment have an angle with respect to the deflection surfaces 5a and 5a ′ in the sub-scan section from an oblique direction (with respect to the normal lines of the deflection surfaces 5a and 5a ′). A sub-scanning oblique incidence optical system for entering the light beams RA to RD.
By adopting such a sub-scanning oblique incidence optical system, it becomes possible to separate and deflect each light beam while suppressing an increase in size of the deflecting surface of the deflector 5 along the sub-scanning direction. .
Here, as shown in FIGS. 1A and 1B, FIGS. 2 and 3, the main on-axis light beam among the light beams RA to RD on the deflection surfaces 5 a and 5 a ′ of the deflector 5. The deflection points (reference points) when the light beam is deflected are defined as C0 (first deflection point) and C0 ′ (second deflection point), respectively. A plane (reference plane) that includes the deflection points C0 and C0 ′ and is perpendicular to the rotation axis of the deflector 5 is defined as Fp.
In other words, the reference plane Fp (second plane) is a plane that includes a straight line (second straight line) passing through the deflection point C0 and the center of the deflector 5 and is parallel to the main scanning direction.
Here, if the oblique incidence angle of the light beam with respect to the reference plane Fp is too large, it becomes difficult to correct the spot collapse due to the wavefront aberration twist on the scanned surfaces 8a, 8b, 8c and 8d. On the other hand, if the oblique incident angle of the light beam with respect to the reference plane Fp is too small, it becomes difficult to separate the light beams RA to RD emitted from the light sources 1a to 1d.
In the optical scanning device 100 according to the present embodiment, the oblique incident angle α of the light beams RA and RC to the deflecting surface is −3.0 °, and the oblique incident angle α of the light beams RB and RD to the deflecting surface is + 3.0 °. The absolute value of the oblique incident angle is set to be the same. Thereby, it is possible to easily correct the collapse of the spot and separate the optical paths.

The deflector 5 is a rotating polygonal mirror (polygon mirror) having four deflecting surfaces with a circumscribed circle radius of 20 mm, and rotates at a constant speed in the direction of arrow A by a driving force generated by a driving unit (motor) (not shown). ing. Thereby, the light beams RA, RB, RC, and RD are deflected toward the scanned surfaces 8a, 8b, 8c, and 8d, respectively.
The first imaging lenses 6 and 6 ′ and the second imaging lenses 7 and 7 ′ are anamorphic imaging lenses having different powers in the main scanning section and the sub-scanning section, and are deflected by the deflector 5. The focused light beams RA to RD are condensed (guided) on the scanned surfaces 8a to 8d.
The mirrors M1, M2, M3, M1 ′, M2 ′ and M3 ′ are means for deflecting the light beam.

The first imaging lens 6, the second imaging lens 7, and the mirror M3 constitute an imaging optical system (first imaging optical system) SA of the optical scanning device 100 according to the present embodiment. .
Further, the first imaging lens 6, the second imaging lens 7, and the mirrors M1 and M2 form an imaging optical system (second imaging optical system) SB of the optical scanning device 100 according to the present embodiment. Composed.
Further, the first imaging lens 6 ′, the second imaging lens 7 ′, and the mirrors M1 ′ and M2 ′ are used to form an imaging optical system (third imaging optics) of the optical scanning device 100 according to the present embodiment. System) SC is configured.
Further, the first imaging lens 6 ′, the second imaging lens 7 ′, and the mirror M3 ′ form an imaging optical system (fourth imaging optical system) SD of the optical scanning device 100 according to the present embodiment. Composed.

The light beam (first light beam) RA emitted from the light source 1a passes through the aperture stop 2a, and the parallelism of the light beam is converted by the coupling lens 3a. The converted light beam RA is condensed only in the sub-scan section by the cylindrical lens 4a, and enters the deflection surface 5a (first deflection surface) of the deflector 5 from the upper side in the sub-scan direction.
The light beam (second light beam) RB emitted from the light source 1b passes through the aperture stop 2b, and the parallelism of the light beam is converted by the coupling lens 3b. Then, the converted light beam RB is collected only in the sub-scan section by the cylindrical lens 4b, and enters the deflection surface 5a of the deflector 5 from the lower side in the sub-scan direction.
The light beam (third light beam) RC emitted from the light source 1c passes through the aperture stop 2c, and the parallelism of the light beam is converted by the coupling lens 3c. The converted light beam RC is condensed only in the sub-scan section by the cylindrical lens 4c, and is incident on the deflection surface 5a ′ (second deflection surface) of the deflector 5 from the upper side in the sub-scan direction.
The light beam (fourth light beam) RD emitted from the light source 1d passes through the aperture stop 2d, and the parallelism of the light beam is converted by the coupling lens 3d. The converted light beam RD is condensed only in the sub-scan section by the cylindrical lens 4d, and enters the deflection surface 5a 'of the deflector 5 from the lower side in the sub-scan direction.

The light beam RA emitted from the light source 1a and incident on the deflecting surface 5a of the deflector 5 is deflected and scanned by the deflector 5, and then condensed on the scanned surface 8a by the imaging optical system SA to be scanned surface ( First surface to be scanned) 8a is scanned at a constant speed.
The light beam RB emitted from the light source 1b and incident on the deflecting surface 5a of the deflector 5 is deflected and scanned by the deflector 5, and then condensed on the scanned surface 8b by the imaging optical system SB. The surface (second surface to be scanned) 8b is scanned at a constant speed.
The light beam RC emitted from the light source 1c and incident on the deflecting surface 5a ′ of the deflector 5 is deflected and scanned by the deflector 5, and then condensed on the scanned surface 8c by the imaging optical system SC. The scanning surface (third surface to be scanned) 8c is scanned at a constant speed.
The light beam RD emitted from the light source 1d and incident on the deflecting surface 5a ′ of the deflector 5 is deflected and scanned by the deflector 5, and then condensed on the scanned surface 8d by the imaging optical system SD. The scanning surface (fourth surface to be scanned) 8d is scanned at a constant speed.
Since the deflector 5 rotates in the arrow A direction, the deflected and scanned light beams RA, RB, RC, and RD respectively scan the scanned surfaces 8a, 8b, 8c, and 8d in the arrow B direction.
In the present embodiment, photosensitive drums are used as the scanned surfaces 8a, 8b, 8c, and 8d.
Creation of the exposure distribution in the sub-scanning direction on the photosensitive drums 8a, 8b, 8c, and 8d is achieved by rotating the photosensitive drums 8a, 8b, 8c, and 8d in the sub-scanning direction for each main scanning exposure.
In this way, four-color images are simultaneously formed by exposing and scanning the photosensitive drums 8a to 8d corresponding to the four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). It becomes possible.
Further, in the optical scanning device 100 according to the present embodiment, the deflector 5 is shared by the four light sources 1a to 1d, thereby reducing the number of parts and reducing the cost of the device.
In the optical scanning device 100 according to the present embodiment, the optical axes of the incident optical systems LA to LD (or the principal rays of the light beams incident on the deflecting surfaces 5a and 5b) and the imaging optical system SA in the main scanning section. The angle β formed by each optical axis of SD to 90 is 90 °.

  Next, features of the imaging optical systems SA to SD of the optical scanning device 100 according to the present embodiment, particularly different configurations will be described.

As described above, the imaging optical systems SA to SD focus the light beams RA to RD deflected by the deflector 5 on the scanned surfaces 8a to 8d, thereby forming spot images.
The imaging optical systems SA and SB are configured such that the deflection surface 5a of the deflector 5 and the scanned surfaces 8a and 8b are optically conjugate in the sub-scan section.
Similarly, the imaging optical systems SC and SD are each configured such that the deflection surface 5a ′ of the deflector 5 and the scanned surfaces 8c and 8d are optically conjugate in the sub-scan section.
That is, the imaging optical systems SA to SD are surface tilt correction optical systems that correct the influence (surface tilt correction) due to the difference in tilt angle (surface tilt) of each deflection surface in the sub-scan section.

In the imaging optical systems SA to SD of the optical scanning device 100 according to the present embodiment, the first imaging lenses 6 and 6 ′ closest to the deflector 5 on the optical path are mirror-symmetric with respect to the reference plane Fp. The shape is the same (the same shape for the upper and lower light beams).
On the other hand, the second imaging lenses 7 and 7 ′ closest to the scanned surfaces 8a to 8d on each optical path have an asymmetric shape with respect to the reference plane Fp.
Specifically, in the second imaging lenses 7 and 7 ′, the shape of the upper lens portion and the shape of the lower lens portion with respect to the reference plane Fp are both in the main scanning section and in the sub scanning section. Are different from each other.
That is, the second imaging lenses 7 and 7 ′ are multistage lenses in which the first lens portions 7a and 7′a and the second lens portions 7b and 7′b are arranged in the sub-scanning direction, respectively. .
By employing such a multi-stage lens, the number of imaging lenses constituting each of the imaging optical systems SA to SD is reduced, and the optical scanning device 100 is reduced in size and cost.

A light beam RA emitted from the light source 1a and deflected by the deflection surface 5a of the deflector 5 is a first lens portion (first optical portion) 7a of the first imaging lens 6 and the second imaging lens 7. And is reflected by the mirror M3 (first reflective optical element) and enters the surface to be scanned 8a.
The light beam RB emitted from the light source 1b and deflected by the deflecting surface 5a of the deflector 5 is a second lens unit (second optical unit) of the first imaging lens 6 and the second imaging lens 7. ) 7b, is reflected by mirrors M1 (second reflective optical element) and M2 (third reflective optical element), and enters the scanned surface 8b.
Further, the light beam RC emitted from the light source 1c and deflected by the deflecting surface 5a ′ of the deflector 5 is a second lens portion (a third lens portion) of the first imaging lens 6 and the second imaging lens 7 ′. The light is condensed by the optical unit 7′b, is reflected by the mirrors M1 ′ (fourth reflective optical element) and M2 ′ (fifth reflective optical element), and enters the scanned surface 8c.
The light beam RD emitted from the light source 1d and deflected by the deflecting surface 5a ′ of the deflector 5 is a first lens portion (fourth lens) of the first imaging lens 6 and the second imaging lens 7 ′. The light is condensed by the optical part) 7′a, reflected by the mirror M3 ′ (sixth reflective optical element), and incident on the scanned surface 8d.

Generally, when the optical scanning device is arranged in the image forming apparatus main body, one end of the optical scanning device along the arrangement direction of the plurality of photosensitive drums is close to the paper discharge or paper feed path. .
Therefore, if the height at one end of the optical scanning device can be reduced, the size of the image forming apparatus can be reduced accordingly.
For example, FIG. 14 shows a sub-scan sectional view of the image forming apparatus 50 on which the optical scanning device 150 according to the present embodiment or the second or third embodiment described below is mounted. The lower left end of the apparatus 150 is close to the paper feed path of the image forming apparatus 50.

Therefore, in the optical scanning device 100 according to the present embodiment, as shown in FIG. 2, the intersection PA between the scanned surfaces 8a to 8d and the optical axes of the imaging optical systems SA to SD (first Plane (first line) P connecting the intersection points), PB (second intersection), PC (third intersection), and PD (fourth intersection), and parallel to the main scanning direction (first 1 plane) The rotation axis of the deflector 5 is inclined (non-parallel) to the normal line of Fd.
In the optical scanning device 100 according to the present embodiment, the points PA to PD are equally spaced from each other along the direction P, and pass through the point PE between the point PB and the point PC or between the point PA and the point PD. The normal line of the plane Fd is Fd0, and the intersection of the normal line Fd0 and the reference plane Fp is O.
At this time, in the optical scanning device 100 according to the present embodiment, the deflector 5 is disposed at a position shifted from the intersection point O. In other words, when the intersection of the rotation axis of the deflector 5 and the reference plane Fp is P0, the deflector 5 is arranged so that the point P0 is shifted to the right with respect to the point O in FIG.
Furthermore, in other words, in the optical scanning device 100 according to the present embodiment, the intersection (the fifth normal) between the normal line (first normal line) Fd2 perpendicular to the plane Fd and passing through the center of the deflector 5 and the plane Fd. The distance between the intersection point PF and the intersection point PB is shorter than the distance between the intersection point PA and the intersection point PF, and the distance between the intersection point PC and the intersection point PF is between the intersection point PD and the intersection point PF. Shorter than the distance. The rotational axis of the deflector 5 and the normal line Fd2 are not parallel to each other, and the center of the deflector 5 is not in the vertical bisector of the line segment connecting the intersection point PB and the intersection point PC. The deflector 5 is arranged. The center of the deflector 5 is an intersection point P0 between the rotation axis of the deflector 5 and the reference plane Fp.
That is, by disposing the deflector 5 on the one end side (right side in FIG. 2) along the straight line P in the optical scanning device 100, the other end side (see FIG. 2), the height in the Fd0 direction can be reduced. As a result, the optical scanning device 100 can be reduced in size, and the size of the image forming apparatus on which the optical scanning device 100 is mounted can be reduced.

As described above, in the optical scanning device 100 according to the present embodiment, the rotation axis of the deflector 5 is inclined with respect to the normal line of the plane Fd, and the deflector 5 is shifted.
Thus, the optical path lengths from the deflector 5 to the outer scanned surfaces 8a and 8d are the same.

In the optical scanning device 100 according to the present embodiment, in order to reduce the size of the first imaging lenses 6 and 6 ′ and the second imaging lenses 7 and 7 ′ and reduce the manufacturing cost, Each lens is arranged on the deflector 5 side with respect to the mirrors M1 to M3 ′ on the optical path.
In this case, the degree of freedom of the arrangement of the mirrors M1 to M3 ′ becomes low, and even if the rotation axis of the deflector 5 is tilted with respect to the normal line of the plane Fd, all the mirrors are not chamfered and the optical scanning device is not required. It is difficult to reduce the height.
Therefore, in the optical scanning device 100 according to the present embodiment, the outer imaging is performed with respect to the imaging optical systems SA and SB on one end side along the straight line P, that is, on the side where the deflector 5 is shifted. The distance from the deflection point C0 on the deflection surface 5a along the optical axis of the optical system SA to the scanned surface 8a is measured from the deflection point C0 on the deflection surface 5a along the optical axis of the inner imaging optical system SB. The distance is shorter than the distance to the scanning surface 8b.
Thus, even if the first imaging lenses 6 and 6 ′ and the second imaging lenses 7 and 7 ′ are arranged on the deflector 5 side with respect to the mirrors M1 to M3 ′ on the optical path, all the mirrors Thus, the height of the optical scanning device 100 can be reduced.

Further, in the optical scanning device 100 according to the present embodiment, the optical path of the axial light beam of the light beam RA deflected by the deflector 5 and the light beam RB deflected by the deflector 5 in the sub-scan section. The optical path of the axial light beam intersects with each other at at least one intersection (two intersections in FIG. 2).
Similarly, in the sub-scan section, the optical path of the axial light beam of the light beam RC deflected by the deflector 5 and the optical path of the axial light beam of the light beam RD deflected by the deflector 5 are at least 1. Two intersections (one intersection in FIG. 2) intersect each other.
Here, in the optical scanning device 100 according to the present embodiment, the number of the intersections on the side of one end along the straight line P, that is, the side where the deflector 5 is shifted is set to the side of the other end. The mirrors M1 to M3 ′ are arranged so as to be larger than the number of the intersections.
In other words, in the optical scanning device 100 according to the present embodiment, the number of intersections between the optical paths of the axial light beams of the light beams RA and RB deflected by the deflector 5 is determined by the deflector 5 in the sub-scan section. It is larger than the number of intersections between the optical paths of the axial light beams of the deflected light beams RC and RD.
In this way, it is possible to prevent all the mirrors from being chamfered and prevent a light beam incident on a scanning surface from entering a mirror for reflecting the light beam toward other scanning surfaces. Can minimize the number of mirrors. As a result, the optical scanning device 100 can be reduced in size.
Further, in the optical scanning device disclosed in Patent Document 1, the first mirror that reflects the light beam incident on the photoconductor on the side close to the deflector prevents the light beam incident on the photoconductor on the side far from the deflector from vignetting. In order to do so, processing such as chamfering the end portion of the first mirror is required. This increases the manufacturing cost of the mirror, leading to an increase in the cost of the optical scanning device.
On the other hand, in the optical scanning device 100 according to the present embodiment, since all the mirrors can be chamfered, cost reduction of the optical scanning device is also achieved.

Further, in the optical scanning device 100 according to the present embodiment, the intersection is set to 1 on both sides of the one end along the straight line P, that is, the side where the deflector 5 is shifted and the other end. The mirrors M1 to M3 ′ are arranged so that two or more are provided.
As a result, the mirror M1 that reflects the light beam to the inner scanned surface 8b faces the optical path of the light beam incident on the outer scanned surface 8a, and the mirror M1 ′ that reflects the light beam to the inner scanned surface 8c Facing the optical path of the light beam incident on the scanned surface 8d.
As a result, it is not necessary to provide a large chamfered portion on the mirror in order to prevent a light beam incident on a certain scanned surface from passing through a mirror for making the light beam incident on other scanned surfaces. Can be suppressed.

With the above configuration, the optical scanning device 100 according to the present embodiment can reduce the number of mirrors while minimizing the need for chamfering all the mirrors as compared with the conventional optical scanning device that does not have the intersection. Miniaturization of the optical scanning device 100 can be achieved.
Further, by reducing the intervals between the points PA, PB, PC, and PD, the arrangement intervals of the plurality of photosensitive drums provided in the image forming apparatus can be reduced.
The height of one end along the straight line P connecting the points PA to PD in the optical scanning device 100 can be reduced, thereby reducing the size of the image forming apparatus in which the optical scanning device 100 is provided. Can do.

In general, a mirror is used to pass the light beam between the deflector and the imaging lens so that the optical path of the light beam deflected by the deflector and incident on the scanned surface intersects its own optical path. A method of arrangement is also conceivable.
However, normally, a motor of the deflector, a substrate for controlling the motor, a seating surface for attaching the imaging lens, and the like are densely arranged between the deflector and the imaging lens.
For this reason, the method of intersecting with its own optical path has a problem that there is no redundancy with respect to the photosensitive drum pitch, and the drum pitch cannot be narrowed below a certain value.

On the other hand, in the optical scanning device 100 according to the present embodiment, the mirrors M1 to M3 ′ are arranged so that the optical path of the axial light beam among the light beams RA to RD does not intersect with its own light path in the sub-scan section. Is arranged.
Thereby, the intervals between the points PA, PB, PC, and PD can be arbitrarily set, that is, the arrangement intervals of the plurality of photosensitive drums provided in the image forming apparatus on which the optical scanning device 100 is mounted are arbitrarily set. can do.

である。
そして、Ｄｐは、点ＰＡと点ＰＢ、点ＰＢと点ＰＣ、及び点ＰＣと点ＰＤとの間の距離であり、αは、光軸を含む副走査断面内における偏向面５ａ及び５ａ’の法線に対する偏向器５からの軸上光束の出射角度である。また、φは、平面Ｆｄの法線Ｆｄ０が偏向器５の回転軸に対してなす角度、Ｌｐは、偏向器５の中心と偏向点Ｃ０との間の距離である。 The optical scanning device 100 according to the present embodiment satisfies the following conditional expression (1) corresponding to the above configuration.
1.05 <(Tci-Tco) / A <1.90 (1)
Here, Tci is the optical path length from the deflection point C0 of the axial beam of the deflector 5 to the inner scanned surface 8b or 8c in the sub-scan section including the optical axis. Tco is the optical path length from the deflection point C0 of the axial beam of the deflector 5 to the outer scanned surface 8a or 8d in the sub-scan section including the optical axis. Also

It is.
Dp is the distance between the point PA and the point PB, the point PB and the point PC, and the point PC and the point PD, and α is the deflection surface 5a and 5a ′ in the sub-scan section including the optical axis. This is the outgoing angle of the axial beam from the deflector 5 with respect to the normal. Φ is the angle formed by the normal Fd0 of the plane Fd with respect to the rotation axis of the deflector 5, and Lp is the distance between the center of the deflector 5 and the deflection point C0.

FIG. 13 is a schematic diagram for explaining the physical meaning of conditional expression (1).
In FIG. 13, only the relationship between the imaging optical system SA for condensing the light beam on the outer scanned surface 8a and the imaging optical system SB for condensing the light beam on the inner scanned surface 8b is shown. ing.

となる。 In FIG. 13, in the sub-scan section including the optical axis, the reflection point C1 of the axial light beam of the mirror M1 that reflects the light beam toward the inner scanned surface 8b is on the axis on which the outer scanned surface 8a is incident. The case where it exists on the optical path of a light beam is shown.
In such a case, as derived and shown in detail later, (Tci-Tco) is substantially the same as A, that is,

It becomes.

If (Tci−Tco) / A falls below the lower limit of the conditional expression (1), an axial light beam incident on the outer scanned surface 8a enters the mirror M1.
Alternatively, in the sub-scan section, the mirror M1 is disposed on the deflector 5 side so that the optical path of the axial light beam of the light beam RA and the optical path of the axial light beam of the light beam RB do not intersect each other. It will be. In this case, it is necessary to provide a large chamfer on the mirror M1, leading to an increase in cost.
On the other hand, when (Tci−Tco) / A exceeds the upper limit of the conditional expression (1), the mirror M1 is unnecessarily separated from the deflector 5 with respect to the optical path of the axial light beam of the light beam RA. Will be placed.
As a result, the width in the direction perpendicular to the main scanning direction in the reference plane Fp of the optical scanning device 100 becomes unnecessarily long.
In addition, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b and the deflection point on the deflection surface 5a 'along the optical axis of the imaging optical system SC. When the distance from C0 ′ to the scanned surface 8c is made equal, as shown in FIG. 2, the axis incident on the scanned surface 8d to the mirror M1 ′ that reflects the light beam toward the scanned surface 8c. There is a high possibility that the upper luminous flux will be incident.

In addition, it is more preferable that the optical scanning device 100 according to the present embodiment satisfies the following conditional expression (1a).
1.10 <(Tci-Tco) / A <1.50 (1a)

By satisfying conditional expression (1a), the optical scanning device 100 according to the present embodiment can reduce the size of the optical scanning device 100 and the image forming apparatus on which the optical scanning device 100 is mounted and the number of mirrors to the minimum. In addition, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SA to the surface to be scanned 8a and the deflection surface 5a 'along the optical axis of the imaging optical system SD. The distance from the deflection point C0 ′ to the scanned surface 8d is equal to each other, and the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b The distance from the deflection point C0 ′ on the deflection surface 5a ′ along the optical axis of the optical system SC to the scanned surface 8c can be made equal to each other.
Accordingly, the second imaging lens 7 having the first lens portion 7a and the second lens portion 7b, and the second imaging having the first lens portion 7′a and the second lens portion 7′b. The lens 7 ′ can be manufactured in the same shape, and the types of molds for forming the imaging lens can be minimized.

In the optical scanning device 100 according to the present embodiment, as shown in Tables 1 to 8 below, α = 3 degrees, φ = 13 degrees, Tci = 206.114 mm, Tco = 161.114 mm, Dp = 60 mm and Lp = 5.683 mm are set.
Accordingly, A = 34.48 mm, that is, (Tci−Tco) /A=45/34.48=1.31, and the optical scanning device 100 according to the present embodiment has the conditional expressions (1) and (1a). It can be seen that

  Next, the derivation of A included in conditional expression (1) will be described.

First, as shown in FIG. 13, the intersection between the optical path of the axial light beam of the light beam RA deflected by the deflector 5 and the reference plane Fp is defined as C4, and the distance between the intersection C4 and the point O is shown. When L is L0, the following equation (2) is obtained.
L0 = 1.5Dp / cosφ (2)

Next, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SA to the scanned surface 8a and the deflection point on the deflection surface 5a 'along the optical axis of the imaging optical system SD. When the distance from C0 ′ to the surface to be scanned 8d is the same, the distance L3 between the point O and the point P0 is expressed by the following equation (3).

Then, the distance L2 between the point C0 and the point C4 is expressed as the following expression (4) using the expressions (2) and (3).
L2 = L0-L3-Lp
= 1.5Dp / cosφ−1.5Dp × tan (α + φ) −Lp (4)

Next, when the reflection point of the axial light beam of the mirror M3 that reflects the light beam toward the scanned surface 8a is C3, the distance L4 between the point C1 and the point C3 is expressed by the following equation (5). It is expressed in

The reflection point of the on-axis light beam of the mirror M2 that reflects the light beam toward the scanned surface 8b is C2, the plane that includes the point C2 and is parallel to the plane Fd is Fd1, and the light beam RA deflected by the deflector 5 is Let L5 be the distance between the plane Fd1 and the point C1 along the optical path of the axial light beam.
At this time, when the optical scanning device 100 is disposed in the image forming apparatus, it is desirable that the height of the optical scanning device 100 in the Fd0 direction is smaller than the distance Dp.
In particular, it is most ideal when the distance between the plane Fd1 and the point C3 along the optical path of the axial light beam among the light beams RA deflected by the deflector 5, that is, L4 + L5 is 0.5 times the interval Dp. Is.
Therefore, the optical scanning device 100 according to the present embodiment is designed so as to satisfy the following expression (6) and is arranged in the image forming apparatus.
L5 = 0.5Dp-L4 (6)

Next, the distance L6 between the point C1 and the point C2 is expressed by the following equation (7) using the equations (5) and (6).

When the distance between the point C0 and the point C1 is L7 and the distance between the point C0 and the point C3 is L8, in the optical scanning device 100 according to this embodiment, the tilt angle φ is sufficiently small. It can be approximated as L7≈L8.
At this time, assuming that the distance between the plane Fd and the plane Fd1 along the optical path of the axial beam of the light beam RA or RB deflected by the deflector 5 is Lc, the optical path lengths Tci and Tco are respectively (8) and (9).
Tci = L7 + L6 + Lc (8)
Tco = L7 + L4 + L5 + Lc (9)

Here, as shown in FIG. 13, in the sub-scan section including the optical axis, the reflection point C1 of the on-axis light beam of the mirror M1 that reflects the light beam toward the inner scanned surface 8b is Assuming that it is on the optical path of the axial light beam incident on the surface to be scanned 8a, the difference A between the optical path length Tci and the optical path length Tco is expressed by the following equation using equations (4), (6) and (7). It is expressed as (10).

  Next, a specific arrangement and design of the optical scanning device 100 according to the present embodiment will be described.

Table 1 shows the specification values and optical arrangement of the incident optical system LA and the imaging optical system SA, and Table 2 shows the lens shapes of the incident optical system LA and the imaging optical system SA.
Table 3 shows the specification values and optical arrangement of the incident optical system LB and the imaging optical system SB, and Table 4 shows the lens shapes of the incident optical system LB and the imaging optical system SB.
Table 5 shows the specification values and optical arrangement of the incident optical system LC and the imaging optical system SC, and Table 6 shows the lens shapes of the incident optical system LC and the imaging optical system SC.
Table 7 shows the specification values and the optical arrangement of the incident optical system LD and the imaging optical system SD, and Table 8 shows the lens shapes of the incident optical system LD and the imaging optical system SD.

In Table 1, Table 3, Table 5, and Table 7, the coordinates of the surface vertex and the reflection point are those with the reference point P0 as the origin (0, 0, 0), and the unit is millimeter.
The reflection point of the mirror is the reflection point of the axial light beam, and the direction of the optical axis of the mirror corresponds to the direction of the surface normal of the reflection surface of the mirror.

The exit surfaces of the cylindrical lenses 4a, 4b, 4c, and 4d of the optical scanning device 100 according to the present embodiment are configured as diffractive surfaces on which diffraction gratings are formed.
The cylindrical lenses 4a to 4d are formed by injection molding using a plastic material, and a temperature compensation optical system that compensates for changes in refractive power caused by environmental fluctuations by changes in diffraction power caused by wavelength changes of the semiconductor laser. It has become.
Here, the outgoing diffraction surfaces of the cylindrical lenses 4a to 4d are defined by a phase function ψ = 2πM / λ (C3Z ² ) where M is the diffraction order and λ is the design wavelength.
Note that since the first-order diffracted light is used in the optical scanning device 100 according to the present embodiment, the diffraction order M = 1, the design wavelength λ = 790 nm, and C3 is a coefficient.

  The first imaging lenses 6 and 6 ′, the first and second lens portions 7a and 7b of the second imaging lens 7, and the second imaging lens 7 ′ of the optical scanning device 100 according to the present embodiment. The generatrix shapes (shapes in the main scanning section) of the entrance and exit surfaces of the first and second lens portions 7′a and 7′b are both aspherical shapes represented by functions up to the 12th order. It has become.

Here, when the intersection of each lens surface (optical surface) and each optical axis is the origin, the optical axis is the X axis, and the axis (main scanning direction) orthogonal to the X axis in the main scanning section is the Y axis, The bus bar shape X is represented by the following formula (11).

Here, R is a curvature radius (bus curvature radius) in the main scanning section, K is an eccentricity, and B4, B6, B8, B10, and B12 are aspherical coefficients.
The aspheric coefficient Bi (i = 4, 6, 8, 10, 12) is the side opposite to the light source with respect to the optical axis (Table 2, Table 4, Table 6, and 8). Numerical values are different from each other on the + Y side in FIGS. 1A and 1B and the light source side (the −Y side in FIGS. 1A and 1B). The subscript u is added to the coefficient on the + Y side (ie, Bi_u), and the subscript l is attached to the coefficient on the −Y side (ie, Bi_l).
As a result, the bus shape can be asymmetric in the main scanning direction with respect to the optical axis.

なお、子線形状Ｓは、主走査方向における各位置での母線上の面法線を含む主走査断面に垂直な断面内での面形状を示しており、式におけるｍ_ｊｋは非球面係数である。 In addition, the first imaging lenses 6 and 6 ′ of the optical scanning device 100 according to the present embodiment, the first and second lens portions 7 a and 7 b of the second imaging lens 7, and the second imaging lens 7 are used. The sub-line shape S (the shape in the sub-scanning section) of the entrance surface and the exit surface of the first and second lens portions 7'a and 7'b is represented by the following formula (12).

The sub-line shape S indicates a surface shape in a section perpendicular to the main scanning section including the surface normal on the generatrix at each position in the main scanning direction, and m _jk in the equation is an aspheric coefficient. is there.

Here, the aspheric coefficient m _jk (i = 2, 4, 6, 8, 10, and k = 1) is expressed with respect to the optical axis as shown in Tables 2, 4, 6, and 8. On the opposite side to the light source (the + Y side in FIGS. 1A and 1B) and the light source side (the −Y side in FIGS. 1A and 1B), the numerical values are different from each other. The subscript u is attached to the coefficient on the + Y side (ie, mi_k_u), and the subscript l is attached to the coefficient on the −Y side (ie, mi_k_l).
Further, the first-order (k = 1) term of Z is a term that contributes to the tilt amount (child tilt amount) of the lens surface in the sub-scan section.
Therefore, the amount of tilt of the child line can be changed asymmetrically in the main scanning direction.

ここで、ｒは光軸上での子線曲率半径であり、Ｅ２、Ｅ４、Ｅ６、Ｅ８、Ｅ１０は子線変化係数である。 Further, r ′ represents the radius of curvature (sub-wire curvature radius) in the sub-scanning section at a position Y apart from the optical axis in the main scanning direction, and is represented by the following formula (13).

Here, r is the radius of curvature of the strand on the optical axis, and E2, E4, E6, E8, and E10 are the strand change coefficients.

In addition, as shown in Table 2, Table 4, Tables 6 and 8, the subline change coefficient Ei (i = 2, 4, 6, 8, 10) is opposite to the light source with respect to the optical axis. The numerical values are different from each other on the + Y side in FIGS. 1A and 1B and the light source side (the −Y side in FIGS. 1A and 1B). The subscript u is attached to the coefficient on the + Y side (ie, Ei_u), and the subscript l is attached to the coefficient on the −Y side (ie, Ei_l).
As a result, the aspherical amount of the child line shape can be changed asymmetrically in the main scanning direction.
In the optical scanning device 100 according to the present embodiment, the shape of each lens surface is defined by the above expression, but is not limited thereto, and may be defined by another expression.

In the optical scanning device 100 according to the present embodiment, as shown in Table 2, Table 4, Table 6, and Table 8, the first and second lens portions 7a and 7b of the second multistage imaging lens 7 are used. The bus line shape and the child wire shape (the child wire curvature and the child wire tilt amount) of the entrance and exit surfaces of the first and second lens portions 7′a and 7′b of the second multistage imaging lens 7 ′ are as follows. They are different from each other, that is, they are asymmetric.
As a result, the imaging optical systems SA and SB and the imaging optical systems SC and SD satisfy both different imaging performances, while the imaging optical systems SA and SB second imaging lenses and imaging By integrating the second imaging lenses of the optical systems SC and SD, the lens cost can be reduced.

In the optical scanning device 100 according to the present embodiment, since the light beam that has passed through the multistage imaging lens is bent by a mirror, it is a problem to suppress the height of the optical scanning device 100 and to reduce the number of mirrors.
Therefore, in the optical scanning device 100 according to the present embodiment, as described above, the number of mirrors is minimized by tilting the deflector 5 or adjusting the optical path length of the light beam corresponding to each imaging optical system. However, the height of the optical scanning device 100 is reduced.

On the other hand, in order to correspond to the different optical path lengths, the first and second lens portions 7a and 7b of the second multistage imaging lens 7 and the first and second lenses of the second multistage imaging lens 7 ′ are used. If the shape difference between the two lens portions 7′a and 7′b is too large, it becomes difficult to integrally mold each of them.
Therefore, in the optical scanning device 100 according to the present embodiment, the first and second lens portions 7a and 7b of the second multi-stage imaging lens 7 and the second multi-stage imaging are formed with different imaging performances. In order to reduce the shape difference between the first and second lens portions 7′a and 7′b of the lens 7 ′, the main light fluxes emitted from the light sources 1a to 1d that enter the deflection surfaces 5a and 5a ′ are reduced. The degree of convergence in the scanning section (the degree of convergence of the imaging optical systems SA to SD) is set appropriately.
Specifically, in the main scanning section, the optical distance (optical path length) from the rear main plane of the imaging optical systems SA to SD to the scanned surfaces 8a to 8D is Sk (mm), and the imaging optical system When the focal length of SA to SD is f (mm), the convergence degree of the imaging optical systems SA to SD can be expressed as m = 1−Sk / f.
Depending on the degree of convergence m, the state of the light beam emitted from the light sources 1a to 1d incident on the deflecting surfaces 5a and 5a ′ in the main scanning section differs, that is, when m = 0, a parallel light beam, m <0. Is a divergent beam, and m> 0 is a convergent beam.

In the optical scanning device 100 according to the present embodiment, the light beam RA emitted from the light source 1a and passed through the coupling lens 3a is a weakly convergent light beam in the main scanning section. In the imaging optical system SA, Sk = 135. 848, f = 136.966, and m = + 0.008.
Similarly, in the main scanning section, the light beam RB emitted from the light source 1b and passed through the coupling lens 3b is a weakly divergent light beam. In the imaging optical system SB, Sk = 179.361, f = 134.224, m = −0.336.
In the main scanning section, the light beam RC emitted from the light source 1c and passed through the coupling lens 3c is a weakly divergent light beam. In the imaging optical system SC, Sk = 179.361, f = 134.224, m = -0.336.
Similarly, in the main scanning section, a light beam RD emitted from the light source 1d and passed through the coupling lens 3d is a weakly convergent light beam. In the imaging optical system SD, Sk = 135.848, f = 136.966, m is set to +0.008.

The second multistage imaging lenses 7 and 7 ′ of the optical scanning device 100 according to the present embodiment are respectively the boundary between the first and second lens portions 7 a and 7 b and the first and second lens portions 7. The external center position in the sub-scanning direction corresponding to the boundary between 'a and 7'b is arranged so as to be included in the reference plane Fp.
In the second multistage imaging lens 7, the optical axes of the first and second lens portions 7a and 7b are shifted by 2.24 mm downward and upward in the sub-scanning direction with respect to the reference plane Fp, respectively. It is arranged to come to.
In the second multistage imaging lens 7 ′, the optical axes of the first and second lens portions 7′a and 7′b are 2.24 mm above and below the reference plane Fp in the sub-scanning direction, respectively. It is arranged so that it is in a position shifted only by that.
Accordingly, the first and second lens portions 7a and 7b of the second multistage imaging lens 7, and the first and second lens portions 7′a and 7′b of the second multistage imaging lens 7 ′ are obtained. These optical axes can be provided in the vicinity of the incident position of the light beam on the respective lens portions.
Therefore, it becomes easy to take correspondence between the surface shape and the imaging performance, and the surface shape at the time of molding can be easily evaluated.

In general, when the scanning image height is Y (mm) and the scanning field angle corresponding to the scanning image height Y is θ (rad), the scanning characteristics (Kθ characteristics) of the imaging optical systems SA to SD are Y = It is expressed by the equation Kθ. The coefficient K, which is the value of the ratio of the scanning field angle θ to the scanned image height Y, is called the Kθ coefficient.
In the optical scanning device 100 according to the present embodiment, the imaging optical systems SA and SB and the imaging optical systems SC and SD are made different from each other while satisfying the equal velocity, respectively. The shape difference between the first and second lens portions 7a and 7b of the second multi-stage imaging lens 7, and the first and second lens portions 7'a and 7 of the second multi-stage imaging lens 7 '. The difference in shape from 'b' can be reduced.

Further, in the optical scanning device 100 according to the present embodiment, the deflector 5 is disposed so as to face each other, and the different deflection surfaces 5a and 5a ′ of the deflector 5 are inclined at the same angle in the sub-scan section. The imaging optical systems that collect incident and deflected light beams are set to have different imaging performance.
Specifically, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b is on the deflection surface 5a ′ along the optical axis of the imaging optical system SD. Is set to be longer than the distance from the deflection point C0 ′ to the scanned surface 8d.
Further, the distance from the deflection point C0 'on the deflection surface 5a' along the optical axis of the imaging optical system SC to the scanned surface 8c, the deflection point on the deflection surface 5a along the optical axis of the imaging optical system SA. It is set longer than the distance from C0 to the surface to be scanned 8a.
This minimizes the number of mirrors that reflect the light beam RB to the scanned surface 8b and the mirror that reflects the light beam RC to the scanned surface 8c, and eliminates the need for chamfering.
In particular, the height on the imaging optical system SD side of the optical scanning device 100 can be reduced.

Further, in the optical scanning device 100 according to the present embodiment, the rotational axis of the deflector 5 is tilted in order to reduce the height of one end of the optical scanning device 100. Then, in order to compensate for the asymmetry of the positional relationship between the deflector 5 and the outer scanned surfaces 8a and 8d caused by tilting the rotation axis of the deflector 5, the deflector 5 is shifted from the center position.
Thereby, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SA to the scanned surface 8a and the deflection on the deflection surface 5a 'along the optical axis of the imaging optical system SD. The distance from the point C0 ′ to the scanned surface 8d can be made the same.
For this reason, the imaging optical systems SA and SD can be optically equivalent to each other, and the color misalignment when the optical scanning device 100 is used in the image forming apparatus is minimized by unifying the design performance. Can be suppressed.
Further, since the Kθ characteristics can be made the same between the imaging optical systems SA and SD, the image clock can be made common and the cost of the circuit board can be suppressed.

Furthermore, in the optical scanning device 100 according to the present embodiment, the distance from the deflection point C0 on the deflection surface 5a to the scanned surface 8b along the optical axis of the imaging optical system SB, and the optical axis of the imaging optical system SC. The deflection on the deflection surface 5a along the optical axis of the imaging optical system SA is the same as the distance from the deflection point C0 'on the deflection surface 5a' to the scanned surface 8c. The distance from the point C0 to the scanned surface 8a is longer than the distance from the deflection point C0 ′ on the deflection surface 5a ′ along the optical axis of the imaging optical system SD to the scanned surface 8d.
Further, the sub-scanning oblique incident angle of the light beam RA on the deflecting surface 5a of the deflector 5 is the same as the sub-scanning oblique incident angle of the light beam RC on the deflecting surface 5a ′ of the deflector 5, while the deflection of the light beam RD is performed. The sign is opposite to the sub-scanning oblique incident angle on the deflecting surface 5a 'of the device 5.
Similarly, the sub-scanning oblique incident angle of the light beam RB on the deflecting surface 5a of the deflector 5 is opposite in sign to the sub-scanning oblique incident angle of the light beam RC on the deflecting surface 5a ′ of the deflector 5, The sub-scanning oblique incidence angle of the light beam RD on the deflecting surface 5a ′ of the deflector 5 is the same.
Accordingly, the second multi-stage imaging lenses 7 and 7 'can be made the same shape as each other while being asymmetrical in the vertical direction, and can be produced with only one type of lens molding die. It is possible to reduce the resources to be applied.

As described above, in the optical scanning device 100 according to the present embodiment, the sub-scanning oblique incident angle of the light beam RA onto the deflecting surface 5a of the deflector 5 and the sub-scanning of the light beam RD onto the deflecting surface 5a ′ of the deflector 5 are performed. The oblique incident angle has opposite signs, and the sub-scan oblique incident angle of the light beam RB to the deflecting surface 5a of the deflector 5 and the sub-scan oblique incident light of the light beam RC to the deflecting surface 5a 'of the deflector 5 are the same. The angles are opposite in sign.
Thereby, the height of one end of the optical scanning device 100 along the arrangement direction of the plurality of scanned surfaces 8a to 8d is reduced.
Furthermore, in the optical scanning device 100 according to the present embodiment, the rotational axis of the deflector 5 is tilted and the deflector 5 is shifted from the center position in accordance with such an arrangement. Further, as described above, the optical path length of each light beam emitted from each of the light sources 1a to 1d and condensed on each of the scanned surfaces 8a to 8d by the imaging optical systems SA to SD is adjusted. This effectively achieves both a reduction in the height of one end of the optical scanning device 100 and a reduction in the cost of the mirror.
Further, in the optical scanning device 100 according to the present embodiment, the second multistage imaging lenses 7 and 7 ′ each having an asymmetric shape in the sub-scanning direction are disposed to face each other with the deflector 5 interposed therebetween, and both lenses Are arranged in the same shape and rotated 180 degrees around the main scanning direction.
Specifically, in the inner imaging optical systems SB and SC, the second lens unit 7b of the second imaging lens 7 and the second lens unit 7′b of the second imaging lens 7 ′. Only the coefficient m _{0_1} corresponding to the _sub- line tilt amount has the same absolute value and the _opposite sign, and the other aspheric coefficients are set to be the same.
Similarly, in the outer imaging optical systems SA and SD, the first lens unit 7a of the second imaging lens 7 and the first lens unit 7'a of the second imaging lens 7 ' Only the coefficient m _{0_1} corresponding to the line tilt amount has the same absolute value and the sign is inverted, and the other aspheric coefficients are set to be the same.

In the optical scanning device 100 according to the present embodiment, the deflector 5 is shifted to the scanning surface 8a side in the arrangement direction of the plurality of scanning surfaces 8a to 8d, and on the opposite side, the optical axis of the imaging optical system SC. The distance from the deflection point C0 'on the deflection surface 5a' to the scanned surface 8c along the axis is from the deflection point C0 'on the deflection surface 5a' along the optical axis of the imaging optical system SD to the scanned surface 8d. The optical scanning device 100 is designed so as to be longer than the above distance.
This prevents the light beam RD deflected by the deflecting surface 5a ′ of the deflector 5 from entering the mirror M1 ′ and the light beam RC reflected by the mirror M1 ′ from re-entering the second imaging lens 7 ′. However, the height of the optical scanning device 100 can be reduced.

  As described above, the optical scanning device 100 according to the present embodiment can achieve downsizing and cost reduction by reducing the height in the sub-scanning direction.

FIG. 4A shows the position dependency of the field curvature (defocus) in the main scanning direction and the sub-scanning direction on the surface 8a to be scanned by the optical scanning apparatus 100 according to the present embodiment in the main scanning direction. FIG. 4B shows the position dependence of the curvature of field (defocus) in the main scanning direction and the sub-scanning direction on the scanned surface 8b by the optical scanning apparatus 100 according to the present embodiment in the main scanning direction. Yes.
As shown in FIGS. 4A and 4B, it can be seen that the curvature of field on the scanned surfaces 8a and 8b is well corrected.
As described above, in the optical scanning device 100 according to the present embodiment, the imaging optical systems SA and SD are optically equivalent to each other, and the imaging optical systems SB and SC are also optically equivalent to each other. It is.
For this reason, description of the scanned surfaces 8c and 8d is omitted, but the field curvature is similarly corrected well on the scanned surfaces 8c and 8d.

FIGS. 5A and 5B show the position dependence of the fθ characteristics dy1 of the imaging optical systems SA and SB of the optical scanning apparatus 100 according to the present embodiment in the main scanning direction, respectively.
Here, the fθ characteristic dy1 means the difference between the position where the light beam actually reaches (actual image height) and the design value (ideal image height) on the surface to be scanned.
As shown in FIGS. 5A and 5B, the fθ characteristics dy1 of the imaging optical systems SA and SB are corrected well.
As described above, in the optical scanning device 100 according to the present embodiment, the imaging optical systems SA and SD are optically equivalent to each other, and the imaging optical systems SB and SC are also optically equivalent to each other. It is.
Therefore, the description of the imaging optical systems SC and SD is omitted, but the fθ characteristic dy1 is similarly corrected in the imaging optical systems SC and SD.

FIGS. 6A and 6B show the position dependence of the scanning line bend dz on the scanned surfaces 8a and 8b by the optical scanning apparatus 100 according to the present embodiment in the main scanning direction.
Here, the scanning line curve dz means the difference between the imaging position in the sub-scanning direction at each image height and the imaging position in the sub-scanning direction at the axial image height on the surface to be scanned. .
As shown in FIGS. 6A and 6B, the scanning line curve dz is 10 μm or less on both the scanned surfaces 8a and 8b, and is not of a level that affects the formed image. I understand that.
As described above, in the optical scanning device 100 according to the present embodiment, the imaging optical systems SA and SD are optically equivalent to each other, and the imaging optical systems SB and SC are also optically equivalent to each other. It is.
Therefore, the description of the scanned surfaces 8c and 8d is omitted, but the scanning line curve dz is not at a level that affects the image to be formed on the scanned surfaces 8c and 8d as well.

[Second Embodiment]
FIGS. 7A and 7B are main scanning sectional views of the optical scanning device 200 according to the second embodiment. FIG. 8 shows a sub-scanning sectional view of the imaging optical system of the optical scanning device 200 according to the second embodiment. FIG. 9 shows a sub-scanning sectional view of the incident optical system of the optical scanning device 200 according to the second embodiment.
In FIGS. 7A and 7B, the optical path folded back by the mirror is developed and shown, and the mirror is not shown.

  The optical scanning device 200 according to the second embodiment is qualitatively the same as the optical scanning device 100 according to the first embodiment, and is quantitatively different.

  Hereinafter, a specific arrangement and design of the optical scanning device 200 according to the present embodiment will be described.

Table 9 shows the specification values and the optical arrangement of the incident optical system LA and the imaging optical system SA, and Table 10 shows the lens shapes of the incident optical system LA and the imaging optical system SA.
Table 11 shows the specification values and the optical arrangement of the incident optical system LB and the imaging optical system SB, and Table 12 shows the lens shapes of the incident optical system LB and the imaging optical system SB.
Table 13 shows the specification values and optical arrangement of the incident optical system LC and the imaging optical system SC, and Table 14 shows the lens shapes of the incident optical system LC and the imaging optical system SC.
Table 15 shows the specification values and the optical arrangement of the incident optical system LD and the imaging optical system SD, and Table 16 shows the lens shapes of the incident optical system LD and the imaging optical system SD.

In the optical scanning device 200 according to the present embodiment, as shown in Tables 9 to 16, α = 3 degrees, φ = 18 degrees, Tci = 199.114 mm, Tco = 161.114 mm, Dp = 60 mm, Lp = 5.683 mm is set.
Therefore, A = 34.73 mm, that is, (Tci−Tco) /A=38/34.73=1.09, and the optical scanning device 200 according to this embodiment satisfies the conditional expression (1). I understand that.
From this, in the optical scanning device 200 according to the present embodiment, the conditional expression (1) is satisfied, so that the optical scanning device 200, and thus the image forming apparatus on which the optical scanning device 200 is mounted, can be sufficiently downsized. can do.
Further, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b, and the deflection point on the deflection surface 5a ′ along the optical axis of the imaging optical system SC. The distance from C0 ′ to the scanned surface 8c can be made to coincide with each other. At the same time, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SA to the scanned surface 8a and the deflection on the deflection surface 5a 'along the optical axis of the imaging optical system SD. The distance from the point C0 ′ to the surface to be scanned 8d can also be made to coincide with each other.
Accordingly, the second multi-stage imaging lenses 7 and 7 'can be made the same shape as each other while being asymmetrical in the vertical direction, and can be produced with only one type of lens molding die. It is possible to reduce the resources to be applied.

[Third embodiment]
FIGS. 10A and 10B are main scanning sectional views of an optical scanning device 300 according to the third embodiment. FIG. 11 shows a sub-scanning sectional view of the imaging optical system of the optical scanning device 300 according to the third embodiment. FIG. 12 shows a sub-scanning sectional view of the incident optical system of the optical scanning device 300 according to the third embodiment.
In FIGS. 10A and 10B, the optical path folded back by the mirror is developed and shown, and the mirror is not shown.

In the optical scanning device 100 according to the first embodiment, the distance from the deflection point C0 ′ on the deflection surface 5a ′ to the scanned surface 8c along the optical axis of the imaging optical system SC is the light of the imaging optical system SD. It was designed to be longer than the distance from the deflection point C0 ′ on the deflection surface 5a ′ along the axis to the scanned surface 8d.
On the other hand, the optical scanning device 300 according to this embodiment includes the distance from the deflection point C0 ′ on the deflection surface 5a ′ to the scanned surface 8c along the optical axis of the imaging optical system SC, and the imaging optics. The distance from the deflection point C0 ′ on the deflection surface 5a ′ to the scanned surface 8d along the optical axis of the system SD is designed to be the same.
Thereby, the imaging optical system SC and the imaging optical system SD can be optically equivalent to each other.
Therefore, the first and second lens portions 7′a and 7′b of the second multistage imaging lens 7 ′ are mirror-symmetrical with respect to the reference plane Fp (the same shape for the upper and lower two light beams). Therefore, the second multistage imaging lens 7 ′ can be easily molded.

In addition, from the above, in the optical scanning device 300 according to the present embodiment, the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SA to the scanned surface 8a, and the imaging optics The distance from the deflection point C0 ′ on the deflection surface 5a ′ along the optical axis of the system SC to the scanned surface 8c and the deflection point C0 ′ on the deflection surface 5a ′ along the optical axis of the imaging optical system SD. The distance to the surface to be scanned 8d is the same.
The distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b is longer than the other optical path lengths.
As a result, the four imaging optical systems SA to SD can be configured with only two optical design values, the inspection during development and manufacturing can be simplified, and the manufacturing cost of the optical scanning device can be suppressed.

  Hereinafter, a specific arrangement and design of the optical scanning device 300 according to the present embodiment will be described.

Table 17 shows the specification values and optical arrangement of the incident optical system LA and the imaging optical system SA, and Table 18 shows the lens shapes of the incident optical system LA and the imaging optical system SA.
Table 19 shows the specification values and the optical arrangement of the incident optical system LB and the imaging optical system SB, and Table 20 shows the lens shapes of the incident optical system LB and the imaging optical system SB.
Table 21 shows specification values and optical arrangements of the incident optical system LC and the imaging optical system SC, and Table 22 shows lens shapes of the incident optical system LC and the imaging optical system SC.
Table 23 shows the specification values and the optical arrangement of the incident optical system LD and the imaging optical system SD, and Table 24 shows the lens shapes of the incident optical system LD and the imaging optical system SD.

In the optical scanning device 300 according to the present embodiment, as shown in Tables 17 to 24, α = 3 degrees, φ = 6 degrees, Tci = 221.114 mm, Tco = 161.114 mm, Dp = 60 mm, Lp = 5.683 mm is set.
Therefore, A = 34.11 mm, that is, (Tci−Tco) /A=60/34.11=1.76, and the optical scanning device 200 according to this embodiment satisfies the conditional expression (1). I understand that.
From this, in the optical scanning device 300 according to the present embodiment, the conditional expression (1) is satisfied, so that the optical scanning device 300, and thus the image forming apparatus on which the optical scanning device 300 is mounted, can be sufficiently downsized. can do.

In the optical scanning device 300 according to the present embodiment, as compared with the optical scanning device 100 according to the first embodiment, the deflector 5 with respect to the normal line of the plane Fd including the arrangement direction of the plurality of scanned surfaces and the main scanning direction. Conditional expression (1) is satisfied by reducing the angle (inclination angle) φ formed by the rotation axis of, while increasing the optical path length difference (Tci−Tco).
This suppresses asymmetry between the imaging optical systems SA to SD of the optical scanning device 300 as much as possible, reduces the deformation of the housing due to heat during printing, and reduces the height of one end of the optical scanning device 300. It is effectively reduced.

Further, if the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b is increased, the deflection surface 5a 'along the optical axis of the imaging optical system SC is extended. If the distance from the deflection point C0 ′ to the surface to be scanned 8c is also increased, the mirror M1 ′ will jump out of the optical path of the light beam RD collected on the surface to be scanned 8d. This causes problems such as interference between mirrors and an increase in the lateral width of the optical scanning device 300.
Therefore, in the optical scanning device 300 according to the present embodiment, the distance from the deflection point C0 on the deflection surface 5a to the scanned surface 8a along the optical axis of the imaging optical system SA, and the optical axis of the imaging optical system SC. The distance from the deflection point C0 'on the deflection surface 5a' to the scanned surface 8c along the optical axis and the deflection point C0 'on the deflection surface 5a' along the optical axis of the imaging optical system SD to the scanned surface 8d. And the optical path lengths thereof are shorter than the distance from the deflection point C0 on the deflection surface 5a along the optical axis of the imaging optical system SB to the scanned surface 8b. The problem is solved.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various combination, a deformation | transformation, and a change are possible within the range of the summary.

  For example, in the optical scanning device according to the first to third embodiments, two mirrors that reflect the light beams RB and RC emitted from the light sources 1b and 1c, respectively, and the light beams RA and RD emitted from the light sources 1a and 1d, respectively. Although one mirror for reflecting each is provided, the present invention is not limited to this. If the number of mirrors that reflect the light beams RB and RC emitted from the light sources 1b and 1c, respectively, is greater than the number of mirrors that reflect the light beams RA and RD emitted from the light sources 1a and 1d, respectively. The effects according to the embodiment can be sufficiently obtained.

Further, in the optical scanning device according to the first to third embodiments, the light is emitted from the light source 1a condensed by the imaging optical system SA on the side where the deflector 5 is shifted, that is, in the sub-scanning section. The number of intersections between the optical path of the axial light beam among the light beams and the optical path of the axial light beam among the light beams emitted from the light source 1b collected by the imaging optical system SB is two.
On the other hand, on the opposite side, that is, in the sub-scan section, the optical path of the axial light beam of the light beam RC deflected by the deflector 5 and the optical path of the axial light beam of the light beam RD deflected by the deflector 5 The number of intersections with is one.
However, the present invention is not limited to this. For example, the number of intersections on the side where the deflector 5 is shifted may be three, and the number of intersections on the opposite side may be two. If the number of intersections is larger than the number of the intersections on the opposite side, the effects according to the first to third embodiments can be sufficiently obtained.

In the optical scanning device according to the first to third embodiments, the second imaging lenses 7 and 7 ′ are configured by multistage lenses. However, the present invention is not limited to this. Two imaging lenses may be provided independently one by one.
In each of the imaging optical systems SA to SD, the number of imaging lenses is not limited to two, but may be only one or three or more.

In the optical scanning device according to the first to third embodiments, the first and second lens portions 7a and 7b of the second multistage imaging lens 7, and the first and second lenses of the second multistage imaging lens 7 ′ are used. The second lens portions 7'a and 7'b are formed such that the boundary between their optical surfaces is discontinuous and there is a step between them, but this is not a limitation. .
For example, in the vicinity of the boundary portion, each optical surface is splined (for example, the incident surfaces of the first and second lens portions 7a and 7b are connected to each other by a spline function), and the boundary portion having continuity is formed. It may be formed.
Alternatively, each optical surface of each lens portion of the second multistage imaging lenses 7 and 7 ′ may be expressed by a power polynomial relating to the main scanning direction and the sub scanning direction.

  Further, as the light sources 1a to 1d, monolithic multi-beam lasers having a plurality of light emitting points may be used.

[Image forming apparatus]
FIG. 14 is a main-part sub-scan sectional view of the color image forming apparatus 50 on which the optical scanning device 150 according to any of the first to third embodiments is mounted.

The image forming apparatus 50 is a tandem type color image forming apparatus that records image information on each photosensitive drum surface as an image carrier using the optical scanning device 150 according to any one of the first to third embodiments. is there.
The image forming apparatus 50 includes an optical scanning device 150 according to any of the first to third embodiments, photosensitive drums 21, 22, 23, and 24 as image carriers, and developing units 31, 32, 33, and 34. Yes. Further, the image forming apparatus 50 includes a conveyance belt 51, a printer controller 53, and an intermediate transfer body 54.

  The image forming apparatus 50 receives R (red), G (green), and B (blue) color signals (code data) output from an external device 52 such as a personal computer. The input color signal is converted into C (cyan), M (magenta), Y (yellow), and K (black) image data (dot data) by a printer controller 53 in the image forming apparatus 50. Each converted image data is input to the optical scanning device 150. The optical scanning device 150 emits light beams 41, 42, 43, and 44 that are modulated according to each image data, and the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 are exposed by these light beams. Is done.

  A charging roller (not shown) for uniformly charging the surfaces of the photosensitive drums 21, 22, 23, and 24 is provided so as to contact the surface. Then, light beams 41, 42, 43, and 44 are irradiated by the optical scanning device 150 onto the surfaces of the photosensitive drums 21, 22, 23, and 24 charged by the charging roller.

  As described above, the light beams 41, 42, 43, 44 are modulated based on the image data of each color, and the photosensitive drums 21, 22, 23 are irradiated with the light beams 41, 42, 43, 44. , 24 are formed on the surface. The formed electrostatic latent image is developed as a toner image by developing devices 31, 32, 33, and 34 arranged so as to contact the photosensitive drums 21, 22, 23, and 24.

  The toner images developed by the developing devices 31 to 34 are multiple-transferred onto an unillustrated sheet (a material to be transferred) conveyed on the conveying belt 51 by an intermediate transfer member (transfer device) 54, and one full color. An image is formed.

  The sheet on which the unfixed toner image is transferred as described above is further conveyed to a fixing device (not shown) behind the photosensitive drums 21 to 24. The fixing device includes a fixing roller having a fixing heater therein and a pressure roller disposed so as to be in pressure contact with the fixing roller. The conveyed sheet is heated while being pressed at the pressure contact portion between the fixing roller and the pressure roller, whereby the unfixed toner image on the sheet is fixed. Further, a paper discharge roller (not shown) is disposed behind the fixing roller, and the paper discharge roller discharges the fixed paper to the outside of the image forming apparatus 50.

In the color image forming apparatus 50, the optical scanning device 150 records image signals (image information) on the photosensitive surfaces of the photosensitive drums 21, 22, 23, and 24 corresponding to the colors C, M, Y, and K, and It prints images at high speed.
As the external device 52, for example, a color image reading device including a CCD sensor may be used. In this case, the color image reading apparatus and the color image forming apparatus 50 constitute a color digital copying machine.
The printer controller 53 not only converts the data described above, but also controls each part in the image forming apparatus 50 such as a motor.

5 Deflectors 5a, 5a 'Deflection surfaces (first and second deflection surfaces)
8a, 8b, 8c, 8d Scanned surfaces (first, second, third, and fourth scanned surfaces)
100 Optical scanning device RA, RB, RC, RD Light flux (first, second, third, fourth light flux)
SA, SB, SC, SD imaging optical system (first, second, third and fourth imaging optical systems)

Claims (16)

The first and second light beams are deflected by the first deflection surface to scan the first and second scanned surfaces in the main scanning direction, and the third and fourth light beams are scanned to the second deflection surface. A deflector that deflects the first and fourth surfaces to be scanned in the main scanning direction;
First and second imaging optical systems for guiding the first and second light beams deflected by the deflector to the first and second scanned surfaces, respectively.
A third and a fourth imaging optical system for guiding the third and fourth light beams deflected by the deflector to the third and fourth scanned surfaces, respectively.
In the sub-scan section, the number of intersections between the optical paths of the on-axis light beams of the first and second light beams deflected by the deflector is the third and fourth deflected by the deflector. An optical scanning device characterized in that there are more than the number of intersections between the optical paths of axial light beams among the light beams.   The distance from the first deflection point on the first deflection surface along the optical axis of the first imaging optical system to the first scanned surface is the light of the second imaging optical system. The optical scanning device according to claim 1, wherein the optical scanning device is shorter than a distance from the first deflection point along the axis to the second scanned surface. The first and second imaging optical systems and the third and fourth imaging optical systems are arranged to face each other across the deflector,
The intersections of the first to fourth scanned surfaces and the optical axes of the first to fourth imaging optical systems are defined as first, second, third, and fourth intersections, respectively. A plane that includes the first straight line passing through the first to fourth intersections and that is parallel to the main scanning direction is defined as the first plane, is perpendicular to the first plane, and passes through the center of the deflector. When the normal is the first normal, the distance between the fifth intersection that is the intersection of the first normal and the first plane and the second intersection is the first intersection. And the distance between the third intersection point and the fifth intersection point is less than the distance between the fourth intersection point and the fifth intersection point. Shorter than distance,
The rotation axis of the deflector and the first normal line are not parallel to each other;
3. The optical scanning device according to claim 1, wherein the center of the deflector is not within a perpendicular bisector of a line segment connecting the second intersection and the third intersection. 4. Each of the first and third light beams has an angle of + α degrees with respect to a main scanning section perpendicular to the rotation axis of the deflector in the sub-scanning section, and the first and second deflection surfaces. Obliquely incident on the
The second and fourth light beams have an angle of −α degrees with respect to the main scanning section perpendicular to the rotation axis of the deflector in the sub-scanning section, respectively. Obliquely incident on the surface,
The distance from the first deflection point on the first deflection surface along the optical axis of the second imaging optical system to the second scanned surface is Tci, and the distance of the first imaging optical system is The distance from the first deflection point on the first deflection surface along the optical axis to the first scanned surface is Tco, and the distance between the second intersection point and the third intersection point is When Dp, the angle formed by the rotation axis of the deflector with respect to the first normal line is φ, and the distance between the center of the deflector and the first deflection point is Lp,

The optical scanning device according to claim 3, wherein:   The distance between the second intersection and the fifth intersection is shorter than the distance between the third intersection and the fifth intersection. Optical scanning device.   Within the sub-scan section, the number of intersections between the optical paths of the axial light beams of the first and second light beams deflected by the deflector, and the third and fourth light beams deflected by the deflector. 6. The optical scanning device according to claim 1, wherein the number of intersections between the optical paths of the on-axis light beam among the light beams is one or more.   Within the sub-scan section, the number of intersections between the optical paths of the axial light beams of the first and second light beams deflected by the deflector, and the third and fourth light beams deflected by the deflector. The optical scanning device according to any one of claims 1 to 6, wherein the number of intersections between the optical paths of the on-axis light beams of the light beams is two and one, respectively.   8. The optical path of the axial light beam among the first, second, third, and fourth light beams deflected by the deflector does not intersect with its own light path, respectively. The optical scanning device according to any one of the above. The distance from the first deflection point on the first deflection surface to the first scanned surface along the optical axis of the first imaging optical system, and the light of the third imaging optical system A distance from the second deflection point on the second deflection surface along the axis to the third scanned surface is different from each other, and
The distance from the first deflection point to the second scanned surface along the optical axis of the second imaging optical system and the second along the optical axis of the fourth imaging optical system 9. The optical scanning device according to claim 1, wherein a distance from the deflection point to the fourth surface to be scanned is different from each other.   The distance from the first deflection point on the first deflection surface to the first scanned surface along the optical axis of the first imaging optical system, and the light of the fourth imaging optical system 10. The distance from the second deflection point on the second deflection surface along the axis to the fourth scanned surface is equal to each other, 10. Optical scanning device.   The distance from the second deflection point on the second deflection surface along the optical axis of the third imaging optical system to the third scanned surface is the light of the fourth imaging optical system. 11. The optical scanning device according to claim 1, wherein the optical scanning device is longer than a distance from the second deflection point along the axis to the fourth surface to be scanned. 11. The distance from the first deflection point on the first deflection surface along the optical axis of the first imaging optical system to the first scanned surface is the light of the second imaging optical system. Shorter than the distance from the first deflection point along the axis to the second scanned surface;
The distance from the second deflection point on the second deflection surface along the optical axis of the third imaging optical system to the third scanned surface is the light of the fourth imaging optical system. Longer than the distance from the second deflection point along the axis to the fourth scanned surface;
The distance from the first deflection point along the optical axis of the first imaging optical system to the first scanned surface, and the second along the optical axis of the fourth imaging optical system The distance from the deflection point to the fourth scanned surface is the same as each other,
The distance from the first deflection point along the optical axis of the second imaging optical system to the second scanned surface, and the second along the optical axis of the third imaging optical system The optical scanning device according to claim 1, wherein a distance from the deflection point to the third surface to be scanned is the same as each other. A first imaging optical element including first and second optical units through which each of the first and second light beams deflected by the deflector passes;
Each shape of the first and second optical units is a second shape passing through a first deflection point of an axial light beam of the first light beam on the first deflection surface and a center of the deflector. 13. The second plane including a straight line and parallel to the main scanning direction is different from each other in both the main scanning section and the sub-scanning section. Optical scanning device. A second imaging optical element including a third and a fourth optical unit through which the third and fourth light beams deflected by the deflector pass, respectively.
The optical scanning according to claim 13, wherein the first and second imaging optical elements have the same shape and are arranged in a relationship rotated by 180 degrees about the main scanning direction. apparatus.   15. The optical scanning device according to claim 1, and a developing unit that develops, as a toner image, electrostatic latent images formed on the first to fourth scanned surfaces by the optical scanning device. An image forming apparatus comprising: a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material.   15. The optical scanning device according to claim 1, and a printer controller that converts code data output from an external device into an image signal and inputs the image signal to the optical scanning device. Image forming apparatus.

Images