阅读说明：本技术 光学扫描装置和图像形成装置 (Optical scanning device and image forming apparatus ) 是由 寺村昌泰 宫岛悠 于 2019-08-20 设计创作，主要内容包括：本发明涉及光学扫描装置和图像形成装置。根据本发明的光学扫描装置包括：偏转单元,被配置为通过偏转在副扫描截面中相对于主扫描截面以不同角度入射在第一偏转表面上的第一光束和第二光束,在主扫描方向上扫描第一被扫描表面和第二被扫描表面；以及第一光学元件,包括第一光学部分和第二光学部分,其被配置为将由偏转单元偏转的第一光束和第二光束分别引导到第一被扫描表面和第二被扫描表面。第一光学元件的入射表面在包括该入射表面上的表面顶点的副扫描截面中在该表面顶点的位置处朝向偏转单元最突出。第一光学部分的第一出射表面和第二光学部分的第二出射表面中的至少一个是弧矢倾斜表面。在包括轴上光线的入射位置的副扫描截面中的第一出射表面上的表面顶点与第二出射表面上的表面顶点之间的距离大于在包括最外侧轴外光线的入射位置的副扫描截面中的第一出射表面上的表面顶点与第二出射表面上的表面顶点之间的距离。(The invention relates to an optical scanning device and an image forming apparatus. An optical scanning device according to the present invention includes: a deflection unit configured to scan the first scanned surface and the second scanned surface in the main scanning direction by deflecting the first light beam and the second light beam incident on the first deflection surface at different angles with respect to the main scanning section in the sub-scanning section; and a first optical element including a first optical portion and a second optical portion configured to guide the first light beam and the second light beam deflected by the deflection unit to the first scanned surface and the second scanned surface, respectively. An incident surface of the first optical element is most protruded toward the deflection unit at a position of a surface vertex on the incident surface in a sub-scanning section including the surface vertex. At least one of the first exit surface of the first optical portion and the second exit surface of the second optical portion is a sagittal inclined surface. The distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the on-axis ray is larger than the distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the outermost off-axis ray.)

1. An optical scanning device, comprising:

a deflection unit configured to: scanning the first scanned surface and the second scanned surface in the main scanning direction by deflecting the first light beam and the second light beam incident on the first deflecting surface at different angles with respect to the main scanning section in the sub-scanning section; and

a first optical element including a first optical portion and a second optical portion configured to guide the first and second light beams deflected by the deflection unit to the first and second scanned surfaces, respectively, wherein

An incident surface of the first optical element is most protruded toward the deflecting unit at a position of a surface vertex on the incident surface in a sub-scanning section including the surface vertex,

at least one of the first exit surface of the first optical part and the second exit surface of the second optical part is a sagittal inclined surface, and

the distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the on-axis ray is larger than the distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the outermost off-axis ray.

2. An optical scanning device according to claim 1, wherein at least one of the incident surface of the first optical portion and the incident surface of the second optical portion is a sagittal inclined surface.

3. The optical scanning device according to claim 1, wherein a surface vertex on the first exit surface in the sub-scanning section including the incident position of the light ray on the axis is located on an opposite side of the first optical portion with respect to the main scanning section including the surface vertex on the incident surface of the first optical element.

4. The optical scanning device of claim 1, further comprising:

a second optical element including a third optical portion and a fourth optical portion configured to guide the third light beam and the fourth light beam deflected by the deflection unit to a third scanned surface and a fourth scanned surface, respectively, wherein

The deflection unit scans the third scanned surface and the fourth scanned surface in the main scanning direction by deflecting the third light beam and the fourth light beam incident on the second deflection surface at different angles with respect to the main scanning section in the sub-scanning section,

at least one of the third exit surface of the third optical portion and the fourth exit surface of the fourth optical portion is a sagittal inclined surface, and

the shapes of the first optical element and the second optical element are different from each other.

5. The optical scanning device according to claim 4, wherein the incident surface of the second optical element is most protruded toward the deflecting unit at a position of a surface vertex on the incident surface in a sub-scanning section including the surface vertex.

6. An optical scanning device according to claim 4, wherein the distance between the on-axis deflection point on the first deflection surface and the entrance surface of the first optical element is equal to the distance between the on-axis deflection point on the second deflection surface and the entrance surface of the second optical element.

7. The optical scanning device according to claim 4, wherein a distance between a surface vertex on the third exit surface and a surface vertex on the fourth exit surface in the sub-scanning section including the incident position of the on-axis ray is larger than a distance between the surface vertex on the third exit surface and the surface vertex on the fourth exit surface in the sub-scanning section including the incident position of the outermost off-axis ray.

8. An optical scanning device according to claim 4, wherein the following condition is satisfied:

| Ps1| < or equal to | Ps3|, and

|Ts1|≤|Ts3|，

where Ps1 and Ts1 denote a refractive power in the sub-scanning section of the first optical portion and a sagittal tilt amount on the first exit surface, respectively, and Ps3 and Ts3 denote a refractive power in the sub-scanning section of the third optical portion and a sagittal tilt amount on the third exit surface, respectively.

9. The optical scanning device according to claim 1, wherein the incident surface of the first optical element has a positive refractive power.

10. The optical scanning device according to claim 1, wherein the exit surface of the first optical element has a negative refractive power.

11. The optical scanning device according to claim 1, wherein the first optical element has a positive refractive power.

12. An image forming apparatus, comprising:

an optical scanning device according to any one of claims 1 to 11;

a developing unit configured to develop an electrostatic latent image formed on a scanned surface with an optical scanning device into a toner image;

a transfer unit configured to transfer the developed toner image to a transfer material; and

a fixing unit configured to fix the transferred toner image to the transfer material.

13. An image forming apparatus, comprising:

an optical scanning device according to any one of claims 1 to 11, and

a printer controller configured to convert a signal output from an external device into image data and input the image data to the optical scanning device.

14. An optical scanning device, comprising:

a deflection unit configured to scan the first scanned surface and the second scanned surface in the main scanning direction by deflecting the first light beam and the second light beam incident on the first deflection surface at different angles with respect to the main scanning section in the sub-scanning section, and configured to scan the third scanned surface and the fourth scanned surface in the main scanning direction by deflecting the third light beam and the fourth light beam incident on the second deflection surface at different angles with respect to the main scanning section in the sub-scanning section;

a first optical element including a first optical portion and a second optical portion configured to guide the first and second light beams deflected by the deflection unit to the first and second scanned surfaces, respectively;

a second optical element including a third optical portion and a fourth optical portion configured to guide the third light beam and the fourth light beam deflected by the deflection unit to a third scanned surface and a fourth scanned surface, respectively, wherein

At least one of the first exit surface of the first optical part and the second exit surface of the second optical part is a sagittal inclined surface, and

the shapes of the first optical element and the second optical element are different from each other.

15. The optical scanning device according to claim 14, wherein the incident surface of the first optical element is most protruded toward the deflecting unit at a position of a surface vertex on the incident surface in a sub-scanning section including the surface vertex, and

an incident surface of the second optical element is most protruded toward the deflection unit at a position of a surface vertex on the incident surface in a sub-scanning section including the surface vertex.

16. The optical scanning device according to claim 14, wherein a distance between a surface vertex on the first exit surface and a surface vertex on the second exit surface in the sub-scanning section including the incident position of the on-axis ray is larger than a distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the outermost off-axis ray, and

a distance between a surface vertex on the third exit surface of the third optical portion and a surface vertex on the fourth exit surface of the fourth optical portion in the sub-scanning section including the incident position of the on-axis ray is larger than a distance between the surface vertex on the third exit surface and the surface vertex on the fourth exit surface in the sub-scanning section including the incident position of the outermost off-axis ray.

17. An image forming apparatus, comprising:

an optical scanning device according to any one of claims 14 to 16;

a developing unit configured to develop an electrostatic latent image formed on a scanned surface with an optical scanning device into a toner image;

a transfer unit configured to transfer the developed toner image to a transfer material; and

a fixing unit configured to fix the transferred toner image to the transfer material.

18. An image forming apparatus, comprising:

an optical scanning device according to any one of claims 14 to 16; and

a printer controller configured to convert a signal output from an external device into image data and input the image data to the optical scanning device.

Technical Field

The present invention relates to an optical scanning apparatus which is particularly suitable for an image forming apparatus such as a Laser Beam Printer (LBP), a digital copying machine, and a multifunction printer (MFP).

Background

In recent years, in order to achieve size reduction of a color image forming apparatus, a small-sized optical scanning apparatus has been developed.

However, such a reduction in the size of the optical scanning device leads to a reduction in the space inside the optical scanning device, thereby complicating the arrangement of optical elements therein to avoid mutual interference.

Japanese patent application laid-open No. 2004-102050 discloses an optical scanning apparatus including an f θ lens having a sagittal inclined surface, in which a plurality of light beams are obliquely incident on a deflection unit at angles different from each other in a sub-scan section, and the light beams deflected by the deflection unit are refracted by the f θ lens to expand an interval between the light beams. According to this device, it is possible to achieve a reduction in size of the entire device by adopting a configuration in which a plurality of light beams are deflected by a common deflection unit, and to ensure a sufficient space for arranging optical elements located downstream of the f θ lens to avoid mutual interference.

However, in the optical scanning device disclosed in japanese patent application laid-open No. 2004-102050, the light beam is obliquely incident on the deflection unit. As a result, a track (scanning line) on each optical element formed by the light beam deflected by the deflecting unit is curved in the sub-scanning direction. Therefore, it is difficult for the apparatus to reduce the size of each optical element in the sub-scanning direction.

In view of such a situation, an object of the present invention is to provide an optical scanning device capable of achieving further reduction in size by reducing the amount of bending of a scanning line in the sub-scanning direction.

Disclosure of Invention

An optical scanning device according to the present invention includes: a deflection unit configured to: scanning the first scanned surface and the second scanned surface in the main scanning direction by deflecting the first light beam and the second light beam incident on the first deflecting surface at different angles with respect to the main scanning section in the sub-scanning section; and a first optical element including a first optical portion and a second optical portion configured to guide the first and second light beams deflected by the deflection unit to the first and second scanned surfaces, respectively. An incident surface of the first optical element is most protruded toward the deflection unit at a position of a surface vertex on the incident surface in a sub-scanning section including the surface vertex. At least one of the first exit surface of the first optical portion and the second exit surface of the second optical portion is a sagittal inclined surface. The distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the on-axis ray is larger than the distance between the surface vertex on the first exit surface and the surface vertex on the second exit surface in the sub-scanning section including the incident position of the outermost off-axis ray.

Further features of the invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

Drawings

Fig. 1A is an expanded view of a main scanning section of an optical scanning device according to a first embodiment.

Fig. 1B is an expanded view of a sub-scanning section of an incident optical system included in an optical scanning device according to the first embodiment.

Fig. 1C is an expanded view of a sub-scanning section of a scanning optical system included in an optical scanning device according to the first embodiment.

Fig. 2 is a sub-scanning sectional view of a scanning optical system included in the optical scanning device according to the first embodiment.

Fig. 3A is a diagram illustrating an influence on the separation of outgoing light beams according to the shape of the f θ lens.

Fig. 3B is a diagram illustrating an influence on the separation of outgoing beams according to another shape of the f θ lens.

Fig. 3C is a graph illustrating an influence on the separation of outgoing beams according to another shape of the f θ lens.

Fig. 3D is a graph illustrating an influence on the separation of outgoing beams according to another shape of the f θ lens.

Fig. 4A is a diagram illustrating an influence of the shape of the incident surface of the f θ lens on ghost light (ghost light).

Fig. 4B is a diagram illustrating an influence of another shape of the incident surface of the f θ lens on ghost light.

Fig. 5A is a diagram illustrating a positional change of a surface vertex on an incident surface of the first f θ lens in the main scanning direction of the first embodiment.

Fig. 5B is a diagram showing changes in respective positions of surface vertexes on the exit surfaces of the first optical portion and the second optical portion of the first f θ lens of the first embodiment in the main scanning direction.

Fig. 5C is a view showing a sub-scanning section of the first f θ lens of the first embodiment at the scanning start end.

Fig. 5D is a view showing a sub-scanning section of the first f θ lens of the first embodiment at a central portion.

Fig. 5E is a view showing a sub-scanning section of the first f θ lens of the first embodiment at the scanning termination end.

Fig. 6A is a diagram illustrating the influence of sagittal tilt on the exit surfaces of the first optical part and the second optical part on the curvature of the scanning line of the first embodiment.

Fig. 6B is a graph showing the influence of the sagittal inclination on the exit surfaces of the first optical portion and the second optical portion of the conventional example on the curvature of the scanning line.

Fig. 7 is a diagram showing an alternative shape of the first f θ lens.

Fig. 8A is an expanded view of a main scanning section of an optical scanning device according to a second embodiment.

Fig. 8B is an expanded view of a sub-scanning section of an incident optical system included in an optical scanning device according to the second embodiment.

Fig. 8C is an expanded view of sub-scanning sections of a plurality of incident optical systems included in the optical scanning device according to the second embodiment.

Fig. 8D is an expanded view of a sub-scanning section of a scanning optical system included in an optical scanning device according to the second embodiment.

Fig. 9 is a sub-scanning sectional view of a scanning optical system included in an optical scanning device according to a second embodiment.

Fig. 10 shows a sub-scanning sectional view of the first f θ lens included in the optical scanning device according to the second embodiment.

Fig. 11 is a sub-scanning sectional view showing a main part of the color image forming apparatus according to the embodiment.

Detailed Description

An optical scanning device according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. Note that, for convenience of understanding of the embodiments, the drawings shown below may be shown in a size different from the actual size.

In the following description, the main scanning direction is a direction perpendicular to the rotation axis of the deflection unit and the optical axis of the optical system. The sub-scanning direction is a direction parallel to the rotation axis of the deflection unit. The main scanning section is a cross section perpendicular to the sub scanning direction. The sub-scanning section is a cross section perpendicular to the main scanning direction.

Therefore, it should be noted that, in the following description, the main scanning direction and the sub-scanning section in the incident optical system are different from those in the imaging optical system.

[ first embodiment ]

Fig. 1A shows an expanded view of a main scanning section of an optical scanning device 1 according to a first embodiment. Fig. 1B and 1C show developed views of sub-scanning sections of the incident optical system and the scanning optical system included in the optical scanning device 1 according to the first embodiment, respectively. Fig. 2 shows a sub-scanning sectional view of a scanning optical system included in the optical scanning device 1 according to the first embodiment.

The optical scanning device 1 of the present embodiment includes a first light source 101 and a second light source 201, a first collimating lens 102 and a second collimating lens 202, a first cylindrical lens 103 and a second cylindrical lens 203, and a first aperture stop 104 and a second aperture stop 204.

Further, the optical scanning device 1 of the present embodiment includes a deflection unit 10, a first f θ lens 106 (first optical element), second f θ lenses 107 and 207, and reflection members 109, 209, and 210.

A semiconductor laser or the like is used for each of the first light source 101 and the second light source 201.

The first and second collimating lenses 102 and 202 convert light beams LA and LB (first and second light beams) emitted from the first and second light sources 101 and 201 into parallel light beams. Here, the parallel light beam includes not only a strictly parallel light beam but also a substantially parallel light beam such as a weakly divergent light beam and a weakly convergent light beam.

Each of the first cylindrical lens 103 and the second cylindrical lens 203 has a finite optical power (refractive power) in a sub-scan section. The light beams LA and LB passing through the first and second collimator lenses 102 and 202 are converged in the sub-scanning direction by the first and second cylindrical lenses 103 and 203.

The first aperture stop 104 and the second aperture stop 204 limit the beam diameters of the light beams LA and LB passing through the first cylindrical lens 103 and the second cylindrical lens 203.

Therefore, the light beams LA and LB emitted from the first and second light sources 101 and 201 are converged in the sub-scanning direction only in the vicinity of the deflecting surface 105 of the deflecting unit 10, and are formed into linear images each of which is long in the main scanning direction.

The deflecting unit 10 is rotated in the direction of an arrow a in fig. 1A by a not-shown driving unit (e.g., a motor), thereby deflecting the light beams LA and LB incident on the deflecting unit 10. Here, the deflection unit 10 is formed of, for example, a polygon mirror.

Each of the first f θ lens 106 and the second f θ lenses 107 and 207 is an anamorphic imaging lens having different powers in the main scanning section and in the sub-scanning section. Further, each of the first and second f θ lenses 106 and 107 and 207 is configured to converge (guide) the light beams LA and LB deflected by the deflecting surface 105 of the deflecting unit 10 onto the first and second scanned surfaces 108 and 208.

Here, the first f θ lens 106 is a multi-stage lens in which the first optical portion 106a and the second optical portion 106b are arranged side by side in the sub scanning direction. Specifically, the incident surface of the first f θ lens 106 is formed by the incident surface of the first optical part 106a and the incident surface of the second optical part 106b, and the exit surface of the first f θ lens 106 is formed by the exit surface (first exit surface) of the first optical part 106a and the exit surface (second exit surface) of the second optical part 106 b. Further, the exit surfaces of the first optical portion 106a and the second optical portion 106b are sagittal-tilt variable surfaces having shapes in which sagittal-tilt amounts are different from each other, and each of the sagittal-tilt amounts varies in the main scanning direction.

The reflecting members 109, 209, and 210 are units for reflecting light beams, which employ deposited mirrors or the like.

In the optical scanning device 1 of the present embodiment, the first incident optical system 75a is formed by the first collimating lens 102, the first cylindrical lens 103, and the first aperture stop 104. Further, the second incident optical system 75b is formed by a second collimator lens 202, a second cylindrical lens 203, and a second aperture stop 204.

Meanwhile, in the optical scanning device 1 of the present embodiment, the first scanning optical system 85a is formed by the first optical portion 106a of the first f θ lens 106 and the second f θ lens 107. Also, the second scanning optical system 85b is formed by the second optical portion 106b of the first f θ lens 106 and the second f θ lens 207.

Meanwhile, in the optical scanning device 1 of the present embodiment, the first reflective optical system 95a is formed by the reflective member 109, and the second reflective optical system 95b is formed by the reflective members 209 and 210.

Incidentally, in the optical scanning device 1 of the present embodiment, the optical axes of the first incident optical system 75a and the second incident optical system 75b form angles of +3.0 degrees and-3.0 degrees, respectively, in the sub-scanning section with respect to the main scanning section.

Note that the expression "angles different from each other" in the present embodiment also includes such angles having the same absolute value but having opposite signs from each other.

The light beam LA emitted from the light emitting point of the first light source 101 is converted into a parallel light beam by the first collimating lens 102.

Then, the converted light beam LA is converged in the sub-scanning direction by the first cylindrical lens 103, passes through the first aperture stop 104, and is incident on the deflecting surface 105 of the deflecting unit 10 from the lower side in the sub-scanning direction.

Thereafter, the light beam LA emitted from the first light source 101 and incident on the deflecting surface 105 of the deflecting unit 10 is deflected by the deflecting unit 10, and then condensed on the first scanned surface 108 by the first scanning optical system 85a, thereby scanning the first scanned surface 108 at a uniform speed.

The light beam LB emitted from the light emitting point of the second light source 201 is converted into a parallel light beam by the second collimating lens 202.

Then, the converted light beam LB is converged in the sub-scanning direction by the second cylindrical lens 203, passes through the second aperture stop 204, and is incident on the deflecting surface 105 of the deflecting unit 10 from the upper side in the sub-scanning direction.

The light beam LB emitted from the second light source 201 and incident on the deflecting surface 105 of the deflecting unit 10 is deflected by the deflecting unit 10 and then condensed on the second scanned surface 208 by the second scanning optical system 85b, thereby scanning the second scanned surface 208 at a uniform speed.

Here, the deflecting unit 10 rotates in the direction a in fig. 1A. Accordingly, the deflected light beams LA and LB scan the first scanned surface 108 and the second scanned surface 208, respectively, in the direction B in fig. 1A.

Meanwhile, reference symbol C0 denotes a deflection point on the deflection surface 105 of the deflection unit 10 (on-axis deflection point) with respect to the principal ray of the on-axis light beam. In terms of the sub-scanning direction, the light beams LA and LB emitted from the first light source 101 and the second light source 201 intersect each other at the deflection point C0. Meanwhile, the deflection point C0 serves as a reference point for the first scanning optical system 85a and the second scanning optical system 85 b.

Note that, in the present embodiment, the first photosensitive drum 108 and the second photosensitive drum 208 function as the first scanned surface 108 and the second scanned surface 208.

Meanwhile, forming the exposure distribution in the sub-scanning direction on the first photosensitive drum 108 and the second photosensitive drum 208 is achieved by rotating the first photosensitive drum 108 and the second photosensitive drum 208 in the sub-scanning direction during each main-scanning exposure.

Next, characteristics of the first and second incident optical systems 75a and 75b and the first and second scanning optical systems 85a and 85b of the optical scanning device 1 of the present embodiment will be listed in tables 1 to 3 below.

Note that in tables 1 to 3, the direction of the optical axis, the axis orthogonal to the optical axis in the main-scanning section, and the axis orthogonal to the optical axis in the sub-scanning section in the case where the intersection point of each lens surface and the optical axis is defined as the origin are defined as the x-axis, the y-axis, and the z-axis, respectively. In tables 2 and 3, the formula "E-x" represents ". times.10^-x”。

The aspherical shape (meridional shape) in the main scanning cross section of each lens surface of the first optical portion 106a and the second optical portion 106b of the first f θ lens 106 and the second f θ lenses 107 and 207 of the optical scanning device 1 of the present embodiment is defined by the following expression (1):

wherein R is the radius of curvature, k is the eccentricity, and B_i(i-4, 6, 8, 10, 12) is an aspherical coefficient. Here, the coefficient B of the positive side and the negative side_iWith respect to y, the index u is added to the coefficient on the positive side (i.e., B)_iu) And an index l is added to the coefficient on the negative side (i.e., B)_il)。

Meanwhile, the aspherical shape (sagittal shape) in the sub-scanning cross section of each lens surface of the first optical portion 106a and the second optical portion 106b of the first f θ lens 106 and the second f0 lenses 107 and 207 is defined by the following formula (2):

wherein M is_jk(j-0 to 12, and k-1) is an aspheric coefficient.

Note that the sagittal gradient in the present embodiment corresponds to the value M₀₁. Thus, the sagittal inclined surface means having a value M different from 0₀₁And the sagittal inclination variable surface represents having a value M not equal to 0_j1(j ═ 1 to 12).

Meanwhile, the radius of curvature r' in the sub-scanning section continuously changes according to the y-coordinate of the lens surface, as defined in (3) below:

wherein r is the radius of curvature on the optical axis, and E_i(j ═ 1 to 10) is a coefficient of variation.

Next, effects of the optical scanning device 1 of the present embodiment will be described.

Fig. 3A to 3D are diagrams illustrating an influence on the separation of outgoing light beams according to the shape of an f θ lens.

Specifically, fig. 3A shows the case of an f θ lens 501 having a convex incident surface and a concave exit surface, and fig. 3B shows the case of an f θ lens 502 having a concave incident surface and a convex exit surface. Meanwhile, fig. 3C shows the case of the f θ lens 503 having a concave incident surface and a concave exit surface, and fig. 3D shows the case of the first f θ lens 106 included in the optical scanning device 1 of the present embodiment.

In the f θ lens 501 shown in fig. 3A, a light beam incident on the incident surface 5010 is refracted due to convex power, thereby reducing the interval therebetween. Then, the light beam emitted from the exit surface 5011 is refracted due to the concave power, thereby increasing the interval therebetween.

In the f θ lens 502 shown in fig. 3B, the light beam incident on the incident surface 5020 is refracted due to the concave optical power, thereby increasing the interval therebetween. Then, the light beam emitted from the exit surface 5021 is refracted due to the convex power, thereby reducing the interval therebetween.

In the f θ lens 503 shown in fig. 3C, the light beam incident on the incident surface 5030 is refracted due to the concave power, thereby increasing the interval therebetween. Then, the light beam emitted from the exit surface 5031 is refracted due to the concave optical power, thereby further increasing the interval therebetween.

In the first f θ lens 106 shown in fig. 3D, the light beam incident on the incident surface 1060 is refracted due to the convex power, thereby reducing the interval therebetween. Then, the light beams emitted from the exit surface 1061 of the first optical part 106a and the exit surface 1062 of the second optical part 106b are refracted due to the concave optical power, thereby increasing the interval therebetween.

In other words, the light beam incident on the incident surface of the first optical portion 106a and the light beam incident on the incident surface of the second optical portion 106b are refracted in such a manner as to reduce the interval therebetween. Meanwhile, the light beam emitted from the exit surface 1061 of the first optical part 106a and the light beam emitted from the exit surface 1062 of the second optical part 106b are refracted in such a manner as to increase the interval therebetween.

Further, the first f θ lens 106 may refract the light beam in such a manner as to increase the interval between the exit surface 1061 and the exit surface 1062 by using sagittal tilt on them.

As a result, the light beams can be split while reducing the height of the first f θ lens 106.

Fig. 4A and 4B are diagrams illustrating the influence of the shape of the incident surface of the f θ lens on ghost light.

More specifically, fig. 4A shows the case of the f θ lens having the concave incident surface 601, and fig. 4B shows the case of the first f θ lens 106 of the present embodiment having the convex incident surface 1060.

Note that a broken line in each of fig. 4A and 4B indicates a part of ghost light generated by the incident surface of the f θ lens.

Meanwhile, a component 9 such as a motor constituting a part of the deflecting unit 10 is also shown in each of fig. 4A and 4B.

When the incident surface 601 of the f θ lens is formed as a concave surface, the light beam reflected from the incident surface 601 can be further reflected from the deflecting surface of the deflecting unit 10 or reflected from the member 9, and therefore ghost light that may reach the scanned surface is easily generated.

On the other hand, when the incident surface is formed to be convex, as in the case of the incident surface 1060 of the first f θ lens 106 of the present embodiment, the light beam reflected from the incident surface 1060 is diffused as shown in fig. 4B. For this reason, the reflected light beam is less likely to reach the deflection unit 10. As a result, even if ghost light is generated, the adverse effect thereof is reduced as compared with the case where the incident surface is formed to be concave.

As described above, with the f θ lens having the concave incident surface and the concave exit surface as shown in fig. 3C, the light beams incident thereon can be caused to exit in such a manner that the interval therebetween is increased to the maximum.

However, in the case of using the above-described f θ lens, ghost light reaching the surface to be scanned may be generated as shown in fig. 4A.

In addition, such an f θ lens has a large negative refractive power in the sub-scanning section, and thus increases the sensitivity of the optical system. Therefore, such a configuration is not preferable in view of optical performance including imaging performance and the like.

Meanwhile, the negative refractive power in the sub-scan section can be reduced using the f θ lens having the concave incident surface and the convex incident surface as shown in fig. 3B, as compared with the f θ lens of fig. 3C.

However, as with the f θ lens of fig. 3C, the lens is likely to produce ghost light reaching the surface being scanned. Also, the lens reduces the interval between the outgoing beams as compared to the f θ lens of fig. 3C.

Meanwhile, the use of an f θ lens having a convex incident surface and a concave exit surface as shown in fig. 3A is not preferable because the lens cannot increase the interval between the exiting light beams.

In view of such a situation, the optical scanning device 1 of the present embodiment solves the above-described problem by using the first f θ lens 106, the first f θ lens 106 including the first optical part 106a and the second optical part 106b, each having the exit surface formed as a sagittal inclination variable surface.

Specifically, the amount of beam splitting, i.e., the spacing between the exiting beams, can be controlled by adjusting the amount of sagittal tilt of the respective exit surfaces 1061 and 1062 of the first and second optical portions 106a and 106 b.

Further, the sub-scanning magnification, i.e., the refractive power in the sub-scanning section, can be controlled by adjusting the sagittal curvature of the respective exit surfaces 1061 and 1062 of the first optical part 106a and the second optical part 106 b.

Further, the incident surface 1060 of the first f θ lens 106 is formed to be convex (which is most protruded toward the deflection unit 10 at the position of the surface vertex on the incident surface of the first f θ lens 106 in the sub-scanning section including the surface vertex), which is preferable because the incident surface 1060 can thus suppress the generation of ghost light reaching the scanned surface.

Therefore, as shown in fig. 2, the optical scanning device 1 of the present embodiment can avoid the light beam LA emitted from the first optical portion 106a of the first f θ lens 106 from interfering with the reflection member 209, so that the second f θ lenses 107 and 207 can be appropriately arranged.

Next, the influence of the change in the sagittal inclination in the first f θ lens 106 of the present embodiment will be described.

As described above, each lens surface of the first f θ lens 106 of the present embodiment has a refractive power in the sub-scan section, that is, the incident surface 1060 has a positive refractive power, and each of the exit surfaces 1061 and 1062 in the first optical part 106a and the second optical part 106b has a negative refractive power. Also, the first f θ lens 106 has a positive refractive power as a whole.

Therefore, each lens surface is formed as a curved surface in the sub-scanning section, and thus has a surface apex.

Fig. 5A to 5E are diagrams illustrating changes in sagittal inclination on the respective exit surfaces 1061 and 1062 of the first optical part 106a and the second optical part 106b of the first f θ lens 106 of the present embodiment.

Specifically, fig. 5A shows a change in the position of the surface vertex on the incident surface 1060 of the first f θ lens 106 in the main scanning direction. Meanwhile, fig. 5B shows a change in the respective positions of the surface vertices on the exit surfaces 1061 and 1062 of the first optical part 106a and the second optical part 106B of the first f θ lens 106 in the main scanning direction.

On the other hand, fig. 5C shows a sub-scanning sectional view of the first f θ lens 106 at the scanning start end, that is, at a position in the main scanning direction where the light beam directed to the outermost off-axis image height on the side opposite to the light source passes through the first f θ lens 106 (the passing position (incident position) of the outermost off-axis light ray). Meanwhile, fig. 5D shows a sub-scanning sectional view of the first f θ lens 106 at a central portion, that is, at a position in the main scanning direction where the light beam guided to the on-axis image height passes through the first f θ lens 106 (a passing position (incident position) of the light beam on the axis).

Meanwhile, fig. 5E shows a sub-scanning sectional view of the first f θ lens 106 at the scanning end, that is, at a position in the main scanning direction where the light beam directed to the outermost off-axis image on the light source side is high passes through the first f θ lens 106 (a passing position (incident position) of the outermost off-axis light ray).

As shown in fig. 5A, since the incident surface 1060 of the first f θ lens 106 does not adopt sagittal tilt, the position of the surface vertex on the incident surface 1060 is located at the central portion in the sub-scanning direction regardless of the position in the main scanning direction. In other words, the position of the surface vertex is constant, as shown by the dashed line 700.

On the other hand, as shown in fig. 5B, the exit surfaces 1061 and 1062 of the first and second optical portions 106a and 106B of the first f θ lens 106 adopt sagittal tilt, which varies with the position in the main scanning direction, and are each formed as a sagittal tilt variable surface.

Thus, the respective positions of the surface apexes on the exit surfaces 1061 and 1062 vary with the position in the main scanning direction, as indicated by broken lines 701 and 702.

Meanwhile, as shown in fig. 5C to 5E, the interval between the positions of the surface apexes on the respective exit surfaces 1061 and 1062 is widest at the central portion and decreases toward each end in the main scanning direction.

Further, the position of the surface vertex on the exit surface 1061 is located on the exit surface 1062 side in the sub-scanning direction (the opposite side of the first optical portion 106a across the center in the sub-scanning direction of the first f θ lens 106, or the opposite side of the first optical portion 106a with respect to the main scanning cross section including the surface vertex on the incident surface of the first f θ lens 106) over the entire area in the main scanning direction. Meanwhile, the position of the surface vertex on the exit surface 1062 is located on the exit surface 1061 side in the sub-scanning direction (the opposite side of the second optical portion 106b across the center in the sub-scanning direction of the first f θ lens 106, or the opposite side of the second optical portion 106b with respect to the main scanning cross section including the surface vertex on the incident surface of the first f θ lens 106) over the entire area in the main scanning direction.

As described above, the surface vertex cited herein denotes a surface vertex on a virtual curved surface obtained by extending each of the exit surfaces 1061 and 1062.

Fig. 6A and 6B are diagrams illustrating the influence of sagittal inclination on the exit surfaces 1061 and 1062 of the first and second optical parts 106A and 106B of the first f θ lens 106 in the optical scanning device 1 according to the first embodiment on the curvature of the scanning line.

Specifically, fig. 6A shows scan lines 802 and 803 originating from light beams LA and LB respectively emerging from exit surfaces 1061 and 1062 on a cross section 1, which cross section 1 includes a reflection point of an on-axis ray on the reflecting member 209 and is perpendicular to the main-scan section and the sub-scan section, as shown in fig. 2.

On the other hand, fig. 6B shows scan lines 804 and 805 on the cross section 1 derived from the light beams LA and LB emitted from the exit surface in the case where the conventional f θ lens and the conventional reflecting member 1209 not employing sagittal tilt are arranged instead of the first f θ lens 106 and the reflecting member 209.

As described above, the interval between the positions of the surface apexes on the respective exit surfaces 1061 and 1062 is widest at the central portion, and decreases toward each end in the main scanning direction (i.e., close to the central portion in the sub-scanning direction of the first f θ lens 106).

In other words, the sagittal inclination amount of the exit surfaces 1061 and 1062 decreases toward each end in the main scanning direction.

In summary, as the amount of sagittal tilt on the respective exit surfaces 1061 and 1062 becomes smaller toward the end in the main scanning direction, the intervals between the light beams LA and LB respectively emitted from the exit surfaces 1061 and 1062 become narrower.

As a result, the interval between the scanning lines 802 and 803 originating from the light beams LA and LB becomes narrower toward each end in the main scanning direction, so that the amount of bending of the respective scanning lines 802 and 803 can be reduced.

As described above, according to the optical scanning device 1 of the present embodiment, by forming each of the exit surfaces 1061 and 1062 of the first optical part 106a and the second optical part 106b of the first f θ lens 106 as the sagittal inclination variable surface, the amount of bending of the scanning line can be reduced.

As a result, the size of the reflection member for reflecting the light beam emitted from the first f θ lens 106 can be reduced, thereby reducing the area of the reflection surface of the reflection member.

The optical scanning device 1 of the present embodiment can reduce the amount of curvature of the scanning line by using the above-described first f θ lens 106, thereby providing an optical scanning device that achieves further reduction in size.

In addition, the optical scanning device 1 can suppress interference between optical members by adjusting the beam split amount while maintaining optical performance with respect to sub-scanning magnification, generation of ghost light, and the like.

Although the optical scanning device 1 of the present embodiment employs the first f θ lens 106 having a convex incident surface, the present invention is not limited to only this configuration. For example, by using the f θ lens 901 as shown in fig. 7, it is also possible to expect a similar effect by forming the incident surfaces of the first optical portion 106a and the second optical portion 106b into inclined surfaces, and forming the f θ lens 901 into such a shape that the central portion of the first f θ lens 106 protrudes toward the incident side.

[ second embodiment ]

Fig. 8A shows an expanded view of a main scanning section of the optical scanning device 2 according to the second embodiment. Fig. 8B and 8C respectively show development views of sub-scanning sections of an incident optical system included in the optical scanning device 2 according to the second embodiment. Fig. 8D shows an expanded view of a sub-scanning section of a scanning optical system included in the optical scanning device 2 according to the second embodiment.

Fig. 9 shows a sub-scanning sectional view of a scanning optical system included in the optical scanning device 2 according to the second embodiment.

The optical scanning device 2 of the present embodiment includes a first light source 101, a second light source 201, a third light source 301, and a fourth light source 401, and a first collimator lens 102, a second collimator lens 202, a third collimator lens 302, and a fourth collimator lens 402. Further, the optical scanning device 2 of the present embodiment includes the first cylindrical lens 103, the second cylindrical lens 203, the third cylindrical lens 303, and the fourth cylindrical lens 403, and the first aperture stop 104, the second aperture stop 204, the third aperture stop 304, and the fourth aperture stop 404.

Further, the optical scanning device 2 of the present embodiment includes the deflection unit 10, first f θ lenses 106 and 206 (first optical element and second optical element), second f θ lenses 107, 207, 307, and 407, and reflection members 109, 209, 210, 309, 310, and 409.

A semiconductor laser or the like is used for each of the first light source 101, the second light source 201, the third light source 301, and the fourth light source 401.

The first, second, third, and fourth collimating lenses 102, 202, 302, and 402 convert light beams LA, LB, LC, and LD (first, second, third, and fourth light beams) emitted from the first to fourth light sources 101 to 401 into parallel light beams. Here, the parallel light beam includes not only a strictly parallel light beam but also a substantially parallel light beam such as a weakly divergent light beam and a weakly convergent light beam.

Each of the first cylindrical lens 103, the second cylindrical lens 203, the third cylindrical lens 303, and the fourth cylindrical lens 403 has a finite optical power (refractive power) in a sub-scan section. The light beams LA to LD passing through the first to fourth collimator lenses 102 to 402 are converged in the sub-scanning direction by the first to fourth cylindrical lenses 103 to 403.

The first aperture stop 104, the second aperture stop 204, the third aperture stop 304, and the fourth aperture stop 404 limit the beam diameters of the light beams LA to LD that pass through the first cylindrical lens 103 to the fourth cylindrical lens 403.

Therefore, the light beams LA and LB emitted from the first and second light sources 101 and 201 are converged only in the sub-scanning direction near the first deflecting surface 105 of the deflecting unit 10, and are formed into linear images each of which is long in the main scanning direction.

Meanwhile, the light beams LC and LD emitted from the third and fourth light sources 301 and 401 are converged only in the sub-scanning direction near the second deflection surface 205 of the deflection unit 10, and are formed into linear images each of which is long in the main scanning direction.

The deflection unit 10 is rotated in the direction of an arrow a in fig. 8A by a not-shown driving unit (e.g., a motor), thereby deflecting the light beams LA to LD incident on the deflection unit 10. Here, the deflection unit 10 is formed of, for example, a polygon mirror.

Each of the first f θ lens 106 and the second f θ lenses 107 and 207 is an anamorphic imaging lens having different powers in the main scanning section and in the sub-scanning section. Further, each of the first and second f θ lenses 106 and 107 and 207 condenses (guides) the light beams LA and LB deflected by the first deflecting surface 105 of the deflecting unit 10 onto the first and second scanned surfaces 108 and 208.

Meanwhile, each of the first f θ lens 206 and the second f θ lenses 307 and 407 is an anamorphic imaging lens having different powers in the main scanning section and in the sub-scanning section. Further, each of the first f θ lens 206 and the second f θ lenses 307 and 407 condenses (guides) the light beams LC and LD deflected by the second deflection surface 205 of the deflection unit 10 onto the third scanned surface 308 and the fourth scanned surface 408.

Here, the first f θ lens 106 is a multi-stage lens in which the first optical portion 106a and the second optical portion 106b are arranged side by side in the sub scanning direction. Specifically, the incident surface of the first f θ lens 106 is formed by the incident surface of the first optical part 106a and the incident surface of the second optical part 106b, and the exit surface of the first f θ lens 106 is formed by the exit surface of the first optical part 106a and the exit surface of the second optical part 106 b. Further, the exit surfaces of the first optical portion 106a and the second optical portion 106b are sagittal-tilt variable surfaces having shapes in which sagittal-tilt amounts are different from each other, and each of the sagittal-tilt amounts varies in the main scanning direction.

Meanwhile, the first f θ lens 206 is a multi-stage lens in which a first optical portion 206a (third optical portion) and a second optical portion 206b (fourth optical portion) are arranged side by side in the sub-scanning direction. Specifically, the incident surface of the first f θ lens 206 is formed by the incident surface of the first optical part 206a and the incident surface of the second optical part 206b, and the exit surface of the first f θ lens 206 is formed by the exit surface (third exit surface) of the first optical part 206a and the exit surface (fourth exit surface) of the second optical part 206 b. Further, the exit surfaces of the first optical portion 206a and the second optical portion 206b are sagittal-tilt-variable surfaces having shapes in which sagittal-tilt amounts are different from each other, and each of the sagittal-tilt amounts varies in the main scanning direction.

The reflecting members 109, 209, 210, 309, 310, and 409 are units for reflecting light beams, which employ deposited mirrors or the like.

In the optical scanning device 2 of the present embodiment, the first incident optical system 75a is formed by the first collimating lens 102, the first cylindrical lens 103, and the first aperture stop 104. Further, the second incident optical system 75b is formed by a second collimator lens 202, a second cylindrical lens 203, and a second aperture stop 204.

Meanwhile, the third incident optical system 75c is formed by a third collimator lens 302, a third cylindrical lens 303, and a third aperture stop 304. Further, the fourth incident optical system 75d is formed by a fourth collimator lens 402, a fourth cylindrical lens 403, and a fourth aperture stop 404.

Meanwhile, in the optical scanning device 2 of the present embodiment, the first scanning optical system 85a is formed by the first optical portion 106a of the first f θ lens 106 and the second f θ lens 107. Also, the second scanning optical system 85b is formed by the second optical portion 106b of the first f θ lens 106 and the second f θ lens 207.

Meanwhile, the third scanning optical system 85c is formed by the first optical portion 206a of the first f θ lens 206 and the second f θ lens 307. Also, the fourth scanning optical system 85d is formed by the second optical portion 206b of the first f θ lens 206 and the second f θ lens 407.

Meanwhile, in the optical scanning device 2 of the present embodiment, the first reflective optical system 95a is formed by the reflective member 109, and the second reflective optical system 95b is formed by the reflective members 209 and 210.

Meanwhile, the third reflective optical system 95c is formed by the reflective members 309 and 310, and the fourth reflective optical system 95d is formed by the reflective member 409.

Incidentally, in the optical scanning device 2 of the present embodiment, the optical axes of the first incident optical system 75a and the second incident optical system 75b form angles of +3.0 degrees and-3.0 degrees, respectively, in the sub-scanning section with respect to the main scanning section.

Meanwhile, the optical axes of the third incident optical system 75c and the fourth incident optical system 75d form angles of +3.0 degrees and-3.0 degrees, respectively, in the sub-scanning section with respect to the main scanning section.

The light beam LA emitted from the light emitting point of the first light source 101 is converted into a parallel light beam by the first collimating lens 102.

Then, the converted light beam LA is converged in the sub-scanning direction by the first cylindrical lens 103, passes through the first aperture stop 104, and is incident on the first deflecting surface 105 of the deflecting unit 10 from the lower side in the sub-scanning direction.

Thereafter, the light beam LA emitted from the first light source 101 and incident on the first deflecting surface 105 of the deflecting unit 10 is deflected by the deflecting unit 10, and then condensed on the first scanned surface 108 by the first scanning optical system 85a, thereby scanning the first scanned surface 108 at a uniform speed.

The light beam LB emitted from the light emitting point of the second light source 201 is converted into a parallel light beam by the second collimating lens 202.

Then, the converted light beam LB is converged in the sub-scanning direction by the second cylindrical lens 203, passes through the second aperture stop 204, and is incident on the first deflecting surface 105 of the deflecting unit 10 from the upper side in the sub-scanning direction.

The light beam LB emitted from the second light source 201 and incident on the first deflecting surface 105 of the deflecting unit 10 is deflected by the deflecting unit 10 and then condensed on the second scanned surface 208 by the second scanning optical system 85b, thereby scanning the second scanned surface 208 at a uniform speed.

The light beam LC emitted from the light emitting point of the third light source 301 is converted into a parallel light beam by the third collimator lens 302.

Then, the converted light beam LC is converged in the sub-scanning direction by the third cylindrical lens 303, passes through the third aperture stop 304, and is incident on the second deflecting surface 205 of the deflecting unit 10 from the lower side in the sub-scanning direction.

Thereafter, the light beam LC emitted from the third light source 301 and incident on the second deflecting surface 205 of the deflecting unit 10 is deflected by the deflecting unit 10, and then condensed on the third scanned surface 308 by the third scanning optical system 85c, thereby scanning the third scanned surface 308 at a uniform speed.

A light beam LD emitted from a light emitting point of the fourth light source 401 is converted into a parallel light beam by the fourth collimator lens 402.

Then, the converted light beam LD is condensed in the sub-scanning direction by the fourth cylindrical lens 403, passes through the fourth aperture stop 404, and is incident on the second deflecting surface 205 of the deflecting unit 10 from the upper side in the sub-scanning direction.

The light beam LD emitted from the fourth light source 401 and incident on the second deflecting surface 205 of the deflecting unit 10 is deflected by the deflecting unit 10, and then condensed on the fourth scanned surface 408 by the fourth scanning optical system 85d, thereby scanning the fourth scanned surface 408 at a uniform speed.

Here, the deflecting unit 10 rotates in the direction a in fig. 8A. Accordingly, the deflected light beams LA and LB scan the first scanned surface 108 and the second scanned surface 208, respectively, in the direction B in fig. 8A. Further, the deflected light beams LC and LD scan the third scanned surface 308 and the fourth scanned surface 408, respectively, in the direction D in fig. 8A.

Meanwhile, reference symbol C0 denotes a deflection point on the first deflection surface 105 of the deflection unit 10 (on-axis deflection point) with respect to the principal ray of the on-axis light beam. In terms of the sub-scanning direction, the light beams LA and LB emitted from the first light source 101 and the second light source 201 intersect each other at the deflection point C0. Meanwhile, the deflection point C0 serves as a reference point for the first scanning optical system 85a and the second scanning optical system 85 b.

On the other hand, reference numeral E0 denotes a deflection point on the second deflection surface 205 of the deflection unit 10 (on-axis deflection point) with respect to the principal ray of the on-axis light beam. In terms of the sub-scanning direction, the light beams LC and LD emitted from the third light source 301 and the fourth light source 401 cross each other at the deflection point E0. Meanwhile, the deflection point E0 serves as a reference point for the third scanning optical system 85c and the fourth scanning optical system 85 d.

Note that, in the present embodiment, the first photosensitive drum 108, the second photosensitive drum 208, the third photosensitive drum 308, and the fourth photosensitive drum 408 serve as the first scanned surface 108, the second scanned surface 208, the third scanned surface 308, and the fourth scanned surface 408.

Meanwhile, forming the exposure distribution in the sub-scanning direction on the first to fourth photosensitive drums 108 to 408 is achieved by rotating the first to fourth photosensitive drums 108 to 408 in the sub-scanning direction during each main-scanning exposure.

Next, the characteristics of the third incident optical system 75c and the fourth incident optical system 75d and the third scanning optical system 85c and the fourth scanning optical system 85d of the optical scanning device 2 of the present embodiment will be listed in tables 4 to 6 below.

Note that the characteristics of the first and second incident optical systems 75a and 75b and the first and second scanning optical systems 85a and 85b are the same as those of the optical scanning device 1 according to the first embodiment listed in tables 1 to 3. Therefore, duplicate lists will be omitted here.

Note that in tables 4 to 6, the direction of the optical axis, the axis orthogonal to the optical axis in the main-scanning section, and the axis orthogonal to the optical axis in the sub-scanning section in the case where the intersection point of each lens surface and the optical axis is defined as the origin are defined as the x-axis, the y-axis, and the z-axis, respectively. In tables 5 and 6, the formula "E-x" represents ". times.10^-x”。

The aspherical shape (meridional shape) in the main scanning cross section of each lens surface of the first optical portion 206a and the second optical portion 206b of the first f θ lens 206 and the second f θ lenses 307 and 407 of the optical scanning device 2 of the present embodiment is defined by the above expression (1).

Meanwhile, the aspherical shape (sagittal shape) in the sub-scanning cross section of each lens surface of the first and second optical portions 206a and 206b of the first f θ lens 206 and the second f θ lenses 307 and 407 is defined by the above equation (2).

Meanwhile, the radius of curvature r' in the sub-scanning section continuously changes according to the y-coordinate of the lens surface, as defined in the above formula (3).

Next, effects of the optical scanning device 2 of the present embodiment will be described. Note that explanation of the same effects as those of the optical scanning device 1 of the first embodiment will be omitted.

In the optical scanning device 2 of the present embodiment, a single deflection unit 10 can scan the four scanned surfaces 108, 208, 308, and 408.

Also, the distance on the optical path from the deflection point C0 to each incident surface of the second f θ lenses 107 and 207 is different from the distance on the optical path from the deflection point E0 to each incident surface of the second f θ lenses 307 and 407.

As a result, interference between the f θ lens and the reflecting member can be avoided as shown in fig. 9, thereby obtaining a compact optical scanning device.

Fig. 10 shows a sub-scanning cross-sectional view of the first f θ lenses 106 and 206 included in the optical scanning device 2 of the present embodiment.

As described above, the distance on the optical path from the deflection point to each of the second f θ lenses 107 and 207 is different from the distance on the optical path from the deflection point to each of the second f θ lenses 307 and 407.

Thus, in the optical scanning device 2 of the present embodiment, the first f θ lens 106 and the first f θ lens 206 have different shapes from each other, as shown in fig. 10.

In other words, the incident surface 1060 of the first f θ lens 106 and the incident surface 2060 of the first f θ lens 206 have different shapes from each other. Also, each of the exit surfaces 1061 and 1062 of the first and second optical parts 106a and 106b of the first f θ lens 106 has a different shape from each of the exit surfaces 2061 and 2062 of the first and second optical parts 206a and 206b of the first f θ lens 206.

Specifically, the characteristics of the first f θ lenses 106 and 206 are respectively configured as listed in table 7 below.

[ Table 7]

Assuming that the refractive powers in the sub-scanning sections of the first f θ lenses 106 and 206 are Ps1 and Ps2, respectively, the optical scanning device 2 of the present embodiment generates | Ps1| -0.0020 and | Ps2| -0.0209, as shown in table 7.

Meanwhile, as shown in table 7, in both the first f θ lenses 106 and 206 included in the optical scanning device 2 of the present embodiment, each incident surface has a positive refractive power in the sub-scanning section, and each exit surface has a negative refractive power in the sub-scanning section. Further, both the first f θ lenses 106 and 206 have positive optical power in the sub-scanning section as the entire system.

As described above, the positive refractive power Ps2 in the sub-scan section of the first f θ lens 206 is larger than the positive refractive power Ps1 in the sub-scan section of the first f θ lens 106.

Therefore, in order to convert the light beam emitted from the first f θ lens 106The amount of separation (in other words, the interval between them) is set to be substantially equal to the amount of separation of the light beams emitted from the first f θ lens 206, and it is only necessary to set the amount of arc tilt Ts2 (the value M of each of the exit surfaces 2061 and 2062) on each of the exit surfaces 2061 and 2062 of the first optical portion 206a and the second optical portion 206b of the first f θ lens 206₀₁) The sagittal inclination amount Ts1 on each of the exit surfaces 1061 and 1062 of the first optical part 106a and the second optical part 106b disposed to be larger than the first f θ lens 106 (the value M of each of the exit surfaces 1061 and 1062)₀₁)。

More specifically, in the optical scanning device 2 of the present embodiment, the absolute value | M of the amount of sagittal tilt on each of the exit surfaces 1061 and 1062 of the first optical part 106a and the second optical part 106b of the first f θ lens 106₀₁| is set to 0.0384. Meanwhile, the absolute value | M of the amount of sagittal tilt on each of the exit surfaces 2061 and 2062 of the first optical part 206a and the second optical part 206b of the first f θ lens 206₀₁| is set to 0.0810.

Therefore, the optical scanning device 2 of the present embodiment is configured to satisfy the conditions defined as | Ps1| ≦ | Ps2| and | Ts1| ≦ | Ts2 |.

As described above, the optical scanning device 2 of the present embodiment can reduce the amount of bending of the scanning line by using the above-described first f θ lenses 106 and 206, thereby providing an optical scanning device that achieves further reduction in size.

In addition, the optical scanning device 2 can suppress interference between optical members by adjusting the beam split amount while maintaining optical performance with respect to sub-scanning magnification, generation of ghost light, and the like.

Although preferred embodiments of the present invention have been described above, it should be understood that the present invention is not limited to only these embodiments, but various modifications and changes can be made within the scope of the present invention.

[ image Forming apparatus ]

Fig. 11 shows a sub-scanning sectional view of a main part of a color image forming apparatus 90 in which an optical scanning apparatus 11 according to a second embodiment is mounted.

The image forming apparatus 90 is a tandem-type color image forming apparatus including the optical scanning apparatus 11 according to the second embodiment, and is configured to record image information on respective photosensitive drums serving as image carriers.

The image forming apparatus 90 includes the optical scanning device 11 according to the second embodiment, photosensitive drums (photosensitive bodies) 23, 24, 25, and 26 serving as image carriers, and developing units 15, 16, 17, and 18. Further, the image forming apparatus 90 includes a conveyor belt 91, a printer controller 93, and a fixing unit 94.

Signals (code data) of respective colors of R (red), G (green), and B (blue) output from an external device 92 such as a personal computer are input to the image forming device 90. The input color signals are converted into respective image data (dot data) of C (cyan), M (magenta), Y (yellow), and K (black) by a printer controller 93 in the image forming apparatus 90.

The converted image data are input to the optical scanning devices 11, respectively. Then, light beams 19, 20, 21, and 22 modulated according to the respective image data are emitted from the optical scanning device 11, respectively, and the photosensitive surfaces of the photosensitive drums 23, 24, 25, and 26 are exposed to these light beams.

Charging rollers (not shown) configured to uniformly charge the surfaces of the photosensitive drums 23, 24, 25, and 26 are provided in contact with the respective surfaces thereof. Further, the optical scanning device 11 irradiates the surfaces of the photosensitive drums 23, 24, 25, and 26 charged by the charging rollers with the light beams 19, 20, 21, and 22.

As described above, the light beams 19, 20, 21, and 22 are modulated according to the image data of the respective colors, and electrostatic latent images are formed on the surfaces of the photosensitive drums 23, 24, 25, and 26 as a result of irradiation of the light beams 19, 20, 21, and 22. The thus formed electrostatic latent images are developed into toner images by the developing units 15, 16, 17, and 18, and the developing units 15, 16, 17, and 18 are arranged in contact with the photosensitive drums 23, 24, 25, and 26.

The toner images developed by the developing units 15 to 18 are transferred multiple times onto an unillustrated sheet (transferred material) conveyed on the conveying belt 91 by unillustrated transfer rollers (transfer units) arranged face to face with the photosensitive drums 23 to 26, thereby forming a single full-color image thereon.

The sheet having the unfixed toner image transferred as described above is further conveyed to a fixing unit 94 located downstream (left side in fig. 11) of the photosensitive drums 23, 24, 25, and 26. The fixing unit 94 includes a fixing roller having a built-in fixing heater (not shown), and a pressure roller disposed in pressure contact with the fixing roller. The sheet conveyed from the transfer unit is pressurized and heated by a pressure contact portion of the fixing roller and the pressure roller, thereby fixing an unfixed toner image on the sheet. Further, an unillustrated sheet discharge roller is disposed behind the fixing roller. The sheet discharge roller discharges the fixed sheet to the outside of the image forming apparatus 90.

The color image forming apparatus 90 is configured to print a color image at high speed by recording image signals (image information) on the photosensitive surfaces of the photosensitive drums 23, 24, 25, and 26 corresponding to the respective colors of C, M, Y and K by using the optical scanning apparatus 11.

For example, a color image reading device provided with a CCD sensor may be used as the external device 92. In this case, the color image reading apparatus and the color image forming apparatus 90 together constitute a color digital copying machine.

Meanwhile, a pair of optical scanning devices according to the first embodiment may be used instead of the optical scanning device 11 of the second embodiment.

According to the present invention, it is possible to provide an optical scanning device capable of achieving further reduction in size by reducing the amount of bending of the scanning line in the sub-scanning direction.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.