JPH08122673A - Optical scanning device - Google Patents

Abstract

PURPOSE: To provide a small-sized image formation device which has no color slurring and provides a color image at a low cost and the optical scanning device which is suitable to this device. CONSTITUTION: This optical scanning device 1 has a 1st lens 27 which has its incidence surface and outgoing surface made toric and is so prescribed that the power in a subscanning direction is negative, a 2nd lens 29 which has its incidence surface and outgoing surface made toric and is so prescribed that the power in the subscanning direction is positive, and a 3rd lens 31 which has the incidence surface made toric and the outgoing surface formed into a rotationally symmetrical surface and is so prescribed that the power in the subscanning direction is positive. The optical scanning device 5 optimizes image formation characteristics such as decoloration, curvature of image surface, distortion of image surface, and lateral magnification power over the entire range in the subscanning direction of scanning light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-beam optical scanning device for scanning a plurality of laser beams, which is applicable to a multi-drum type color printer, a multi-drum type color copying machine, a high speed laser printer, a digital copying machine and the like. The present invention relates to an image forming apparatus using the multi-beam optical scanning device.

[0002]

2. Description of the Related Art For example, in an image forming apparatus such as a multi-drum type color printer or a multi-drum type color copier, a plurality of image forming sections corresponding to color separated color components and a color image forming section An optical scanning device (laser exposure device) that provides image data corresponding to the component, that is, a plurality of laser beams is used.

In this type of image forming apparatus, there are an example in which a plurality of optical scanning devices are arranged corresponding to each image forming section, and a multi-beam optical scanning device formed so as to be able to provide a plurality of laser beams. It is known that they are arranged.

In the conventional multi-beam optical scanning device, as shown in Japanese Unexamined Patent Publication No. 5-83485, when the number of multi-beams is N, a semiconductor laser element which is a light source, a cylinder lens and a glass f.theta. There is an example in which N sets and N / 2 polygon mirrors are used. Therefore, in the case of four laser beams, four sets of laser elements, cylinder lenses, and glass fθ lens groups and two polygon mirrors are used. An example in which some lenses of the fθ lens group are commonly used is also widely known.

In Japanese Patent Application Laid-Open No. 62-232344, f
An example is shown in which a lens in which at least a part of the lens surface of the θ lens is formed as a toric surface is commonly used. This Japanese Patent Laid-Open No. 62-232344 proposes that some of the fθ lenses are made of plastic to improve the degree of freedom in design of each lens surface and improve the aberration characteristic at the image forming position. This publication also discloses a method in which all the lenses are used in common and all the laser beams pass through the respective lenses. JP-A-5-346
Japanese Unexamined Patent Publication No. 12 discloses a method of making laser beams from a plurality of light sources incident on one polygon mirror using a half mirror.

[0006]

[Patent Document 1] Japanese Patent Application Laid-Open No. 5-83485
When the multi-beam optical scanning device seen in the publication is used, compared with the case where a plurality of optical scanning devices are used,
Although the size of the space occupied by the optical scanning device is reduced, as the optical scanning device alone, the cost of parts and assembly increases due to the increase in the number of lenses or mirrors, or the optical scanning device alone. There is an increase in size and weight. Also, due to the shape error of the fθ lens, the individual error, the mounting error, or the like, the bending of the main scanning line of the laser beam for each color component, or fθ
It is known that the deviation of the aberration characteristic represented by the characteristic and the like on the image plane becomes non-uniform.

On the other hand, in the example in which the first fθ lens is commonly used for each laser beam, the second fθ lens arranged for each laser beam is shown, but the shape error of the second fθ lens is shown. Alternatively, due to an individual error or an attachment error, the same inconvenience as in the example disclosed in Japanese Patent Laid-Open No. 5-83485 is caused.

Further, in the example disclosed in Japanese Patent Laid-Open No. 62-232344, since only the toric surface whose shape is not optimized is arranged, it is mainly applied to any one of a plurality of laser beams. There is a problem that scan line bending occurs. An example in which a part of the laser beam directed to the deflecting device is controlled in the optical axis direction has been proposed in connection with the above-mentioned Japanese Patent Laid-Open No. 62-232344, but the aberration characteristics are sufficiently sufficient in all imaging regions. Is difficult to correct.

Further, in the example disclosed in Japanese Patent Laid-Open No. 62-232344, since the amount of change in the refractive index of the lens made of plastic due to temperature change is relatively large, a wide range of environmental conditions (particularly , Temperature conditions)
Below, there is a problem that characteristics such as field curvature, main scanning line curvature, or fθ characteristics vary greatly. In this example, however, various conditions such as achromaticity, field curvature, field distortion, and lateral magnification must be satisfied, especially in the entire area in the sub-scanning direction, so that there is a problem that the number of lenses is increased. At the same time, in order to ensure the parallelism of the main scanning lines of each laser beam, the accuracy of the housing must be made extremely high, which increases the cost.

On the other hand, in the example disclosed in Japanese Unexamined Patent Publication No. 5-34612, the light intensity (light quantity) of the laser beam that passes through the most half mirrors must be sufficiently secured, and the light source is large. Will be done. In addition, in this type of optical scanning device, there is a problem that the optical system at the subsequent stage of the deflecting device for separating the laser beam deflected by one deflecting device tends to be large.

An object of the present invention is to provide an image forming apparatus capable of providing a small color image without color shift at low cost and a multi-beam optical scanning apparatus suitable for the image forming apparatus.

[0012]

The present invention has been made on the basis of the above-mentioned problems, and includes an optical scanning means for scanning a plurality of lights in a predetermined direction, and a light scanning means in order from the side closer to the optical scanning means.
The optical scanning means includes first to third toric lenses whose powers in the sub-scanning direction orthogonal to the scanning direction of the respective lights are defined as negative, positive and positive, respectively, and the optical scanning means is provided. The present invention provides an optical scanning device having an image forming optical means for giving a predetermined image forming characteristic to each light scanned by the optical scanning device.

According to the present invention, the light scanning means for scanning a plurality of lights in a predetermined direction and the light scanning means are arranged in order from the side closer to the light scanning means, and the respective light scanning means scan the respective lights. The power of the sub-scanning direction orthogonal to the main scanning direction is negative and the rotational symmetry axis of the surface on which the light scanned by the optical scanning means is incident is in the main scanning direction and the exit surface from which the incident light is emitted. The first double-sided toric lens whose rotational symmetry axis is defined in the sub-scanning direction, and the rotational symmetry axis of the surface on which the power scanned in the sub-scanning direction is positive and the light scanned by the optical scanning means is incident, are the main scanning. Direction, and a second double-sided toric lens in which the rotational symmetry axis of the emitting surface from which the incident light is emitted is defined in the sub-scanning direction, and the power in the sub-scanning direction is positive, and the light is scanned by the optical scanning means. Incident light Is a toric surface, the axis of rotational symmetry is in the main scanning direction and the exit surface from which the incident light is emitted includes a single-sided toric lens defined as a rotational symmetry surface, and each is scanned by the optical scanning means. And an image forming optical unit for giving a predetermined image forming characteristic to the light.

Further, according to the present invention, the light scanning means for scanning a plurality of light beams in a predetermined direction and the light scanning means are arranged in order from the side closer to the light scanning means, and the respective light beams are scanned by the light scanning means. The power in the sub-scanning direction orthogonal to the main scanning direction is negative and the rotational symmetry axis of the surface on which the light scanned by the optical scanning means is incident is in the sub-scanning direction and the exit surface from which the incident light is emitted. The first double-sided toric lens whose rotational symmetry axis is defined in the sub-scanning direction, and the rotational symmetry axis of the surface on which the power scanned in the sub-scanning direction is positive and the light scanned by the optical scanning means is incident, are the main scanning. Direction and a second double-sided toric lens in which the rotational symmetry axis of the emitting surface from which the incident light is emitted is defined in the main scanning direction, and the power in the sub-scanning direction is positive and is scanned by the optical scanning means. Incident light The surface is a toric surface, the axis of rotational symmetry is in the main scanning direction, and the exit surface through which the incident light is emitted includes a single-sided toric lens defined as a rotationally symmetric surface, and is scanned by the optical scanning means. An optical scanning device is provided which has an image forming optical means for giving a predetermined image forming characteristic to each light.

[0015]

The optical scanning device of the present invention has the first to third lenses which give the light scanned by the optical scanning means a predetermined image forming characteristic. The first lens has a negative power in the sub-scanning direction orthogonal to the light scanning direction. The second lens has a positive power in the sub-scanning direction orthogonal to the light scanning direction. The third lens has a positive power in the sub-scanning direction orthogonal to the direction in which light is scanned. This maximizes the scanning angle of the light scanned by the optical scanning means.

According to the optical scanning device of the present invention, the entrance surface and the exit surface of the first lens are respectively toric surfaces, and the entrance surface and the exit surface of the second lens are respectively toric surfaces. , The entrance surface of the third lens is defined as a toric surface, and the exit surface of the third lens is defined as a rotationally symmetric surface. Therefore, it is possible to optimally maintain the image forming characteristics of the light scanned by the light scanning unit at a predetermined position at any position. As a result, image forming characteristics such as achromaticity, field curvature, field distortion, and lateral magnification in the entire area in the sub-scanning direction are improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. 1 and 2 are a schematic plan view and a schematic sectional view of a multi-beam optical scanning device according to an embodiment of the present invention. In a color laser beam printer, usually, yellow = Y, magenta = M, cyan = C.
And four sets of various devices for forming an image for each color component corresponding to each of Y, M, C and B, and four types of image data color-separated for each color component of black and black = B are used. Therefore, Y, M, C, and B are added to each reference code to identify the image data for each color component and the corresponding device.

According to FIGS. 1 and 2, the multi-beam optical scanning device 1 generates first to fourth laser beams (light beams) LY, LM, LC and LB corresponding to image data for each color component. Semiconductor laser (ie light source,
Hereinafter referred to as laser element) 3Y, 3M, 3C and 3
B and the laser beam L (Y, M, C and B) emitted from each of the laser elements 3 (Y, M, C and B) is used as an image plane (imaging object arranged at a predetermined position). , For example, a (only) optical deflecting device (scanning means) 5 for deflecting toward the photosensitive drum surface S at a predetermined linear velocity.

The respective laser elements 3Y, 3M, 3C and 3B are arranged at a predetermined angle with respect to the optical deflector 5 and are separated by 3 degrees.
They are arranged in the order of Y, 3M, 3C and 3B. In the laser element 3B, that is, the laser element corresponding to the B (black) image, the laser beam LB directed to the reflecting surface of the light deflecting device 5 can be directly incident on the light deflecting device 5 (without being reflected). Will be placed.

Between each laser element 3 (Y, M, C and B) and the optical deflecting device 5, the laser element 3 (Y,
M, C and B), a light source side optical system for adjusting the sectional beam spot shape of the laser beam L (Y, M, C and B) to a predetermined shape, that is, pre-deflection optical systems 7Y, 7M and 7C
And 7B are arranged.

The optical deflecting device 5 includes, for example, a polygon mirror body 5a in which eight plane reflecting mirrors (planes) 5α to 5ε and 5κ to 5μ are arranged in a regular polygonal shape, and a polygon mirror body 5a.
Is constituted by a motor 5m for rotating the motor in a predetermined direction at a constant speed. The polygonal mirror body 5a is, for example,
It is formed of an aluminum alloy. Also, the polygon mirror 5a
Each of the reflecting surfaces 5α to 5ε and 5κ to 5μ of is cut out along a plane orthogonal to the plane including the direction in which the polygonal mirror body 5a is rotated, and then, for example, S _i
It is provided by depositing a surface reflective layer such as O ₂ .

Pre-deflection optical system 7 (Y, M, C and B)
Is the laser beam L (Y, M, C and B) from each laser element 3 (Y, M, C and B),
The direction in which the laser beam L (Y, M, C and B) is deflected by the optical deflector 5 (that is, the first direction, hereinafter,
Finite focus lenses 9Y, 9M, 9C and 9B, which provide a predetermined convergence in both the main scanning direction) and the second direction (hereinafter, referred to as the sub scanning direction) orthogonal to the first direction, respectively, Hybrid cylinder lenses 11Y, 11M, 11C and 11B for further converging the laser beam L (Y, M, C and B) passing through the focusing lens 9 (Y, M, C and B) only in the sub-scanning direction. , And the four laser beams L (Y, M, C, and B) that have passed through the respective hybrid cylinder lenses 11 (Y, M, C, and B), each deflection surface (reflection surface) of the optical deflector 5. 5α to 5ε and 5κ to 5
It has a (only) pre-deflection folding mirror block (multistage reflecting means) 13 which is bent toward μ. The laser element 3 (Y, M, C and B), the finite focus lens 9 (Y, M, C and B), the hybrid cylinder lens 11 (Y, M, C and B), and the mirror block (folding mirror). ) 13 is integrally arranged on a holding member 15 formed of, for example, an aluminum alloy.

Finite focus lens 9 (Y, M, C and B)
Are each formed by an aspherical glass lens or a spherical glass lens on which an aspherical surface is bonded with UV curable plastic. In addition, each lens is fixed on the holding member 15 via a lens barrel (lens holding ring) (not shown) formed of a material having substantially the same thermal expansion coefficient as the holding member 15.

Hybrid cylinder lens 11 (Y,
M, C and B) include plastic cylinder lenses 17Y, 17M, 17C and 17B and glass cylinder lenses 19Y, 19M, 19C and 19B, respectively (shown in detail in FIGS. 3 and 5). .

Each plastic cylinder lens 1
7 (Y, M, C and B) and glass cylinder lens 19
(Y, M, C, and B) have substantially the same curvature in the sub-scanning direction. Each plastic cylinder lens 17 (Y, M, C and B) is made of a material such as PMMA (polymethylmethacryl). Glass cylinder lens 19 (Y, M,
C and B) are formed of a material such as SFS1. Further, each of the cylinder lenses 17 and 19 is fixed on the holding member 15 via a lens barrel (lens holding ring) (not shown) formed of a material having substantially the same coefficient of thermal expansion as the holding member 15. The finite focus lens 9 (Y, M, C and B) and the hybrid cylinder lens 11 (Y, M, C and B) may be held by the same lens barrel.

The mirror block 13 is formed of a material having a small coefficient of thermal expansion, for example, an aluminum alloy, and a block body 13a. The mirror block 13 is formed on a predetermined surface of the block body 13a. The number of colors is 1) less than the number of colors (1), and a plurality of reflecting surfaces 13Y, 13M, and 13C are arranged (see FIG. 4, which will be described later).

Between the light deflecting device 5 and the image plane S, the respective reflecting surfaces 5α to 5ε and 5κ to 5μ of the light deflecting device 5 are provided.
The image plane side optical system, that is, the post-deflection optical system 21 and the post-deflection optical system for forming the laser beam L (Y, M, C and B) deflected by Each laser beam L passed through the system 21
(Only one) horizontal sync detector 23 for detecting a part of (Y, M, C and B), and post-deflection optical system 21
Between the laser beam and the horizontal synchronization detector 23, a part of the four laser beams L (Y, M, C and B) that have passed through the post-deflection optical system 21 are reflected toward the horizontal synchronization detector 23. A (only one) folding mirror 25 for horizontal synchronization is arranged.

The post-deflection optical system 21 has a wide scanning width (that is, the laser beam L scanned on the image plane by the optical deflector 5).
(Lengths of Y, M, C and B in the main scanning direction on the image plane S) The four laser beams L deflected by the respective reflection surfaces 5α to 5ε and 5κ to 5μ of the optical deflector 5 over the entire area. (Y, M, C, and B) is given a predetermined aberration characteristic, and the first for suppressing fluctuation of the image plane of each laser beam L (Y, M, C, and B) within a certain range. To third imaging lenses 27, 29 and 31.

Between the third imaging lens (lens closest to the image plane) 31 and the image plane S of the post-deflection optical system 21, the four laser beams LY, LM, LC passed through the lens 31.
And the first folding mirrors 33Y, 33M, 33C and 33B that bend the LB toward the image plane S, and the second folding mirrors LY, LM and LC that are folded by the first folding mirrors 33Y, 33M and 33C. The folding mirrors 35Y, 35M and 35C and the third folding mirrors 37Y, 37M and 37C are arranged. As is clear from FIG. 2, the laser beam L corresponding to the B (black) image
After being folded back by the first folding mirror 33B, B is guided to the image surface S without passing through other mirrors. That is, the second folding mirrors 35Y, 35M and 3
The 5C and the third folding mirrors 37Y, 37M and 37C are arranged in three pieces with respect to the four laser beams, respectively.

The first, second and third imaging lenses 27,
29 and 31, the first folding mirror 33 (Y, M,
C and B) and the second folding mirror 35 (Y,
M and C) are fixed to a plurality of fixing members (not shown) formed integrally with the intermediate base 1a of the optical scanning device 1 by adhesion or the like. The third folding mirror 37 (Y, M and C) is moved in at least one direction related to the sub-scanning direction by the fixing rib and the tilt adjusting mechanism which are integrally formed on the intermediate base 1a. Can be arranged (Fig. 1
0).

The third folding mirrors 37Y, 37M and 37C, and the first folding mirror 33B and the image plane S.
Between the respective mirrors 33B, 37Y, 3
At the position where the four laser beams L (Y, M, C and B) reflected via 7M and 37C are emitted from the optical scanning device 1, dustproof for further dustproofing the inside of the optical scanning device 1 is provided. Glasses 39Y, 39M, 39C and 39B are arranged.

Referring to FIG. 2, each laser beam LY,
LM, LC and LB are the third folding mirror 37
The light is emitted to the outside of the optical scanning device 1 at approximately equal intervals by the Y, 37M, and 37C and the first folding mirror 33B. That is, the laser beam LB (black)
Is emitted from the optical scanning device 1 by an optical path including the first folding mirror 33B (only one sheet). The laser beams LY, LM, and LC are respectively reflected by the third folding mirrors 37Y, 37M, and 37C (each 3
The light is emitted from the optical scanning device 1 through an optical path including The number of mirrors in each optical path is 1 and 3
Since it is a sheet, it is unified as an odd number. This can provide the same phase (direction) in the direction of the curve of the main scanning line of each laser beam L (Y, M and C) that reaches the image plane due to the inclination of the lens.

Next, the pre-deflection optical system will be described in detail. FIG. 3 is a partial sectional view in which the folding mirror and the like of the pre-deflection optical system 7 are omitted. Further, Table 1 shows lens data of each lens of the pre-deflection optical system 7. In FIG. 3, only the optical components for one laser beam LY (Y = corresponding to a yellow image) are shown as a representative. In addition, the remaining laser beams LM, LC and LB
In the figure, only the outermost shell of the laser beam L (M, C and B) after passing through the last optical component of the pre-deflection optical system 7 and the optical axis of the optical system are shown. The pre-deflection optical systems 7Y and 7B, 7M and 7C are the same finite lens 9 and the same hybrid cylinder lens 11 respectively.
And the distance from each laser element 3 to the polygon mirror is equal, and they are formed symmetrically with respect to the optical axis O.

Here, the distance between the finite focus lens 9Y and the hybrid cylinder lens 11Y and the distance between the finite focus lens 9B and the hybrid cylinder lens 11B are formed to be the same. In addition, the finite focus lens 9M and the hybrid cylinder lens 11M
And the distance between the finite focus lens 9C and the hybrid cylinder lens 11C are formed to be the same. In this case, the distance between the lenses 9Y and 11Y is defined to be slightly longer than the distance between the lenses 9M and 11M.

On the other hand, the hybrid cylinder lens 11Y
And the reflecting surface of the light deflecting device 5 and the distance between the hybrid cylinder lens 11B and the reflecting surface of the light deflecting device 5 are the same. Also,
The distance between the hybrid cylinder lens 11M and the reflecting surface of the light deflecting device 5 and the distance between the hybrid cylinder lens 11C and the reflecting surface of the light deflecting device 5 are formed to be the same. In this case, the distance between the lens 11Y and the light deflecting device 5 is defined to be slightly longer than the distance between the lens 11M and the light deflecting device 5.
The distance between the light emitting point 3 and the finite focus lens 9 is
Y, M, C and B are formed equally. (Less than,
Table 1 shows the lens data of the pre-deflection optical system, and Table 2
In the same manner, lens data of an optical system that has been conventionally used is shown as a comparative example. )

[0036]

[Table 1]

[0037]

[Table 2]

According to FIG. 3, the laser beam LY emitted from the laser element 3Y is caused by the finite focus lens 9Y.
Generally, it is converted into a laser beam focused on the image plane S. The laser beam LY that has passed through the lens 9Y is collected on the reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflecting device 5 in the sub-scanning direction by the hybrid cylinder lens 11Y having a power only in the sub-scanning direction. Be illuminated.

The hybrid cylinder lens 11Y includes a PMMA cylinder lens 17Y and a glass cylinder lens 19Y having substantially the same curvature in the sub-scanning direction.
It is formed by and. A surface of the PMMA cylinder lens 17Y that contacts air is formed to be substantially flat. Each cylinder lens 17Y and cylinder lens 19Y
Is provided by bonding the exit surface of the cylinder lens 17Y and the entrance surface of the cylinder lens 19Y, or by integrally molding the cylinder lens 17Y on the entrance surface of the cylinder lens 19Y. Also, the cylinder lens 19Y
The cylinder lens 17Y may be pressed by a positioning member (not shown) from a predetermined direction. The material of the cylinder lens 17Y, PMMA, is formed of a material having substantially the same optical characteristics as those of the first to third imaging lenses 27, 29 and 31 used in the post-deflection optical system 21.

Next, the hybrid cylinder lens 11Y
The optical characteristics of will be described in detail. Post-deflection optical system 21, that is, first to third imaging lenses 27, 29 and 31
Is formed of plastic, for example PMMA, the ambient temperature (of the optical scanning device) changes, for example, between 0 ° C. and 50 ° C., so that the refractive index n changes from 1.4876. It is known to change up to 1.4789. In this case, the image plane on which the laser beam L (Y, M, C and B) having passed through the first to third image forming lenses 27, 29 and 31 is actually condensed, that is, the image forming position in the sub-scanning direction Fluctuates by about ± 12 mm. Here, a lens made of the same material as that of the lens used for the post-deflection optical system 21 is incorporated in the pre-deflection optical system 7 in a state in which the curvature is optimized, so that a change in the refractive index n due to a temperature change is caused. Variation of the image plane caused by
It can be suppressed to about 0.5 mm. That is, the pre-deflection optical system 7 is a glass lens, and the post-deflection optical system 21 is PM.
It is possible to correct chromatic aberration in the sub-scanning direction caused by a change in the refractive index of the lens of the post-deflection optical system 21 due to a temperature change, as compared with a conventional optical system including a lens formed of MA.

As is apparent from FIG. 3, the respective laser beams LY, LM, LC and LB are incident symmetrically with respect to the optical axis of the optical scanning device 1 (the optical axis of the system) in the sub-scanning direction. Has been done. That is, the laser beams LY and LB are incident on the polygon mirror 5a symmetrically with respect to the optical axis O. Similarly, the laser beams LM and LC are symmetrical with respect to the optical axis O and the laser beams LY and L.
The optical axis O side of B is guided by the polygon mirror 5a. This indicates that the post-deflection optical system 21 can be optimized at two positions in the sub-scanning direction for each laser beam L (Y, M, C, and B). Therefore, the characteristics such as field curvature and astigmatism of each laser beam L (Y, M, C, and B) can be further improved, and the number of lenses of the post-deflection optical system 21 can be reduced.

According to FIG. 4, the mirror block 13 has the first to fourth laser beams LY, LM, LC and L.
B as a laser beam Lo of one bundle
Are used to guide each of the reflecting surfaces 5α to 5ε and 5κ to 5μ. Specifically, the mirror block 13
Is used to return the laser beam LY emitted from the laser element 3Y in order to make the laser beam incident on the reflecting surface 5 of the optical deflector 5.
The first reflecting surface 13Y for guiding α to 5ε and 5κ to 5μ, the laser beam LM from the laser element 3M, and the laser beam LC from the laser element 3C are respectively reflected on the reflecting surfaces 5α to 5ε of the optical deflecting device 5. 5κ
Through the second and third reflecting surfaces 13M and 13C, which are turned back toward 5μ to 5μ, and a passage region for guiding the laser beam LB from the laser element 3B to the reflecting faces 5α to 5ε and 5κ to 5μ of the optical deflecting device 5 as they are. Thirteen
Have B.

Reflecting surfaces 13Y, 13M and 1 respectively
3C is provided by cutting out a position corresponding to each reflecting surface of the block body 13a at a predetermined angle, and then coating or vapor depositing a material having a high reflectance such as aluminum on the cutting surface. . The positions corresponding to the respective reflection surfaces of the block body 13a may be mirror-finished by polishing after cutting.

According to the mirror block shown in FIG. 4, since the reflecting surfaces 13Y, 13M and 13C are cut out from one block body 13a, the relative tilt error of each mirror is reduced. Also, the block body 1
By manufacturing 3a by die casting, for example,
A highly accurate mirror block can be provided.

As already described, the laser beam LB from the laser element 3B does not intersect with the mirror block 13 and passes through the passage area 13 on the block body 13a.
After passing through B, each of the reflecting surfaces 5α to 5 of the light deflecting device 5
Directly guided in ε and 5κ to 5μ.

Here, each laser beam L (Y, Y which is reflected by the mirror block 13 and guided to the optical deflector 5 is shown.
M and C) and the intensity (light quantity) of the laser beam LB directly guided to the light deflector 5 will be considered.

As already described in the section of the prior art, Japanese Patent Application Laid-Open No. 5-34612 discloses a method of making two or more laser beams into a bundle of laser beams to enter the reflecting surface of the optical deflector. The method of stacking laser beams in order is shown by the half mirror. However, since a plurality of half mirrors are used, the amount of light of the laser beam emitted from each laser is reduced to 5 times for each reflection and transmission (every time passing through the half mirror).
It is known that 0% is wasted. In this case, even if the transmittances and reflectances of the half mirrors are optimized for each laser beam, the intensity of one laser beam that passes through all the half mirrors
(Light intensity) is about 25% of the light intensity output from the laser element
Will be reduced to. Further, due to the fact that the half mirror exists in the optical path in a tilted manner in the optical path, and the number of the half mirrors through which each laser beam passes is different, etc. It is known that the characteristics differ for each laser beam. The characteristics such as curvature of field and astigmatism that are different for each laser beam make it difficult to form all the laser beams on the image plane only with the same finite focus lens and cylinder lens.

On the other hand, according to the mirror block 13 shown in FIG. 4, the respective laser beams LY,
LM and LC are the former stages of incidence on the polygonal mirror 5a of the optical deflector 5, and are laser beams LY, LM and LC.
Is an area separated in the sub-scanning direction (shown by shading in FIG. 3) and is folded by a normal mirror. Therefore, the light is supplied (reflected) toward the image surface S by the polygon mirror 5a.
The amount of light of each laser beam L (Y, M, C, and B) that is generated can be maintained at approximately 90% or more of the amount of emitted light. This not only can reduce the output of each laser, but also can uniformly correct the aberration of the light reaching the image surface S, so that the laser beam can be narrowed down and high definition can be dealt with. Laser element 3B corresponding to B (black)
Is guided by the polygon mirror 5a after passing through the passage region 13B of the mirror block 13, so that not only the output capacity of the laser can be reduced, but also the incident angle of the polygon on the polygon mirror 5a due to the reflection on the reflecting surface is reduced. The error is eliminated.

Next, referring to FIGS. 5 to 7, a bundle of laser beams L reflected by the polygon mirror 5a of the optical deflector 5 is shown.
The relationship between o and the post-deflection optical system 21 will be described. In Table 3, each lens of the post-deflection optical system 21, that is, the first to third plastic lenses 27, 29 and 3 is shown.
Lens data of 1 is shown.

[0050]

[Table 3]

A surface in which the curvature of the sub-scan is "-" is a lens shape when the surface is rotated about the optical axis, and a surface in which the curvature is shown is 1 / toric rotation in the z-axis direction of the local coordinates. It shows a shape rotated about an axis parallel to the direction shown in the column of the toric rotation target axis in a plane separated by the curvature in the direction shown in the column of the target axis. (Hereinafter, in Table 4, the lens data of the post-deflection optical system shown in Table 2 for the pre-deflection optical system conventionally used as a comparative example are shown by the same method. The busbar shape is expressed by the equation (1). Shall be shown.)

[0052]

[Table 4]

FIG. 5 is a development view of an optical path obtained by cutting the optical scanning device described with reference to FIGS. 1 and 2 along the optical axis O. Note that in FIG. 5, only the optical components for one laser beam LY (Y = corresponding to a yellow image) are shown as a representative,
For the remaining laser beams LM, LC and LB,
Only the outermost shell of each laser beam L (M, C and B) and the respective optical axes are shown. Also, the first to third folding mirrors 33B, 35Y, 35M, 35C, 37.
Y, 37M and 37C are omitted. FIG.
It is a schematic perspective view which shows the rotating shaft of the toric surface of the 1st thru | or 3rd imaging lens in the optical path shown in FIG. Note that, according to FIG. 6, the laser beam L (Y, M, C and B) passing through each lens is omitted. Figure 7
FIG. 6 is a development view of the optical path shown in FIG. 5 viewed from a direction orthogonal to the sub-scanning direction on each reflection surface of the light deflecting device 5.

According to FIGS. 5 to 7, the post-deflection optical system 2 is shown.
1 denotes the first to third plastic toric lenses 27, 29 and 31, and each laser beam L (Y,
M, C and B), dust-proof glasses 39Y, 39M, 39C and 39B are arranged correspondingly.

The first to third plastic toric lenses 27, 29 and 31 are used for the pre-deflection optical system 7 (Y,
M, C and B) as described above, the plastic cylinder lens 1 used in the hybrid cylinder lens 11 (Y, M, C and B), respectively.
7 (Y, M, C and B), which is substantially the same as the material such as PMMA (polymethylmethacryl). The laser beams LY, LM, and LC that are bundled into one bundle of laser beams Lo before the optical deflector 5 are included.
And LB are generally in the same bundle state, and are the first to third plastic toric lenses 2 respectively.
7, 29 and 31 are passed.

First plastic toric lens 27
Is a toric lens in which both the entrance surface (optical deflector 5 side) 27 _in and the exit surface (image surface S side) 27 _ra are toric surfaces. The toric rotational symmetry axis of each surface of the lens 27 extends _{in the} sub-scanning direction (FIG. 6, R27 _in ) with respect to the incident surface 27 _{in and in the} sub-scanning direction (FIG. 6, R27 _ra ) with respect to the exit surface 27 _ra . ing. The combined power in the sub-scanning direction by the entrance surface 27 _in and the exit surface 27 _ra is specified to be negative.

Second plastic toric lens 29
Is a toric lens in which both the incident surface (light deflector 5 side) 29 _in and the emission surface (image surface S side) 29 _ra are toric surfaces. The toric rotational symmetry axis of each surface of the lens 29 extends _{in the} sub-scanning direction (FIG. 6, R29 _in ) with respect to the entrance surface 29 _{in and in the} main scanning direction (FIG. 6, R29 _ra ) with respect to the exit surface 29 _ra . ing. The combined power of the incident surface 29 _in and the exit surface 29 _{ra in the} sub-scanning direction is positively defined.

In the third plastic toric lens (final lens) 31, the entrance surface (light deflector 5 side) 31 _in is a toric surface and the exit surface (image surface S side) 31 _ra is a rotationally symmetric aspherical surface. It is a single-sided toric lens.
The toric rotational symmetry axis of the incident surface 31 _in of the lens 31 is
It extends in the main scanning direction (R31 _{in in} FIG. 6). It goes without saying that the emitting surface 31 _ra is rotated about the optical axis O. In addition, the combined power in the sub-scanning direction by the incident surface 31 _in and the exit surface 31 _ra is positively defined.

Next, consideration will be given to the toric axis of the first to third plastic lenses, and the fluctuation and aberration characteristics of the image plane. In the conventional optical scanning devices, the toric axes of all toric lenses are defined along the main scanning direction. In this case, as described above, the aberration characteristics such as spherical aberration, coma aberration, field curvature or magnification error in the image plane cannot be set independently in the sub-scanning direction.

On the other hand, by independently defining the toric rotational symmetry axes of the first plastic lens 27 and the second plastic lens 27, spherical aberration, coma aberration, field curvature or magnification error in the sub-scanning direction. Etc. can be independently optimized by the first to third plastic lenses 27, 29 and 31. In addition,
Exit surface of third toric lens 31 (rotating aspherical surface) 3
1 _ra suppresses the influence on the characteristics in the sub-scanning direction,
It is used for fine adjustment of various characteristics in the main scanning direction. In addition, the combined powers of the first plastic lens 27, the second plastic lens 29, and the third plastic lens 31 in the sub-scanning direction are given in order.
When negative, positive, and positive, the reflection angle of the laser beam reflected by each reflection surface of the optical deflector 5 can be maximized. According to FIG. 5, further, the respective laser beams LY, LM, LC and LB reflected by the polygon mirror 5a of the optical deflecting device 5 are the materials of the respective lenses 27, 29 and 31 of the post-deflection optical system 21. In order to reduce the positional deviation of the PMMA in the sub-scanning direction on the image surface S due to the refractive index change due to the temperature change or the thermal expansion, the position closer to the image surface S side than the combined node position of the post-deflection optical system 21 on the optical axis. It is passed through a slightly shifted position and guided to the image plane S. That is, the polygon mirror 5a
Each of the laser beams LY, LM, LC reflected by
The lens surface passing positions of LB and LB in the sub scanning direction are the first
The distance between the entrance surface 27 _in of the lens 27 and the exit surface 31 _ra of the third lens 31 is regulated in the opposite direction with the optical axis interposed.
As an example, referring to the laser beam LC, the laser element 3C is arranged above the optical axis O at a predetermined angle with respect to the optical axis O. Laser beam LC from laser element 3C
Is passed above the optical axis O by the polygonal mirror 5a, is passed above the optical axis O and in the vicinity of the optical axis O at the incident surface 27 _in of the first toric lens 27, and is emitted from the first toric lens 27. The surface 27 _ra and the incident surface 2 of the second toric lens 29
At 9 _in, it passes near the optical axis O and below the optical axis O.
To the toric lens 31 of. This lens 27
The passing position between the lens 31 and the lens 31 in the sub-scanning direction is the finite focus lens 9Y of the pre-deflection optical systems 7Y, 7M, 7C and 7B.
This is easily achieved by optimally arranging the respective optical axes of 9M, 9C and 9B and the hybrid cylinder lenses 11Y, 11M, 11C and 11B.

According to FIG. 7, each laser element 3Y, 3M,
Laser beams LY and L emitted from 3C and 3B
Each of M, LC and LB passes through the corresponding pre-deflection optical system and is rotated at a predetermined speed.
After deflection via, deflect toward the optical system (continuously reflected)
To be done. As already described, each laser beam L (Y, M, C and B) incident on the polygon mirror 5a is supplied to the pre-deflection optical system 7 (Y, M, C and B) and the polygon mirror 5a (optical deflector). 5) and the mirror block 13 disposed between the mirror block 13 and
Is guided to the polygon mirror 5a.

Each laser beam L (Y, M, C) reflected by the polygonal mirror 5a of the optical deflector 5 and passed through the post-deflection optical system 21, that is, the first to third toric lenses 27, 29 and 31. And B) as a part of the laser beam L (Y, M,
C and B) are reflected to the (only) horizontal sync detector 23 via the (only) horizontal sync folding mirror 25.

FIGS. 8A and 8B show laser beams L which are deflected to the image plane S through the optical path shown in FIG.
A folding mirror for horizontal synchronization is shown which can guide Y, LM, LC and LB to only one horizontal synchronization detector.

As shown in FIG. 8 (a), the horizontal synchronization folding mirror 25 includes the respective laser beams LY, LM, and L.
In order to reflect C and LB to the horizontal sync detector 23 in the main scan direction at different timings, and to provide substantially the same height on the horizontal sync detector 23 in the sub scan direction, the main scan direction is provided. And the first to fourth folding mirror surfaces 25 formed at different angles in both the sub-scanning direction
It has Y, 25M, 25C and 25B, and a mirror block 25a that integrally holds the respective mirrors 25 (Y, M, C and B).

The mirror block 25a is made of, for example, glass-filled PC (polycarbonate). Each mirror 25 (Y, M, C and B) is formed by vapor-depositing a metal such as aluminum at a corresponding position of the block 25a molded at a predetermined angle.

In this way, each laser beam LY, LM, LC and LB deflected by the optical deflector 5 can be made incident on one detector 23, and, for example, the detector It is possible to eliminate the deviation of the horizontal synchronizing signal due to the sensitivity or the positional deviation of each detector, which is a problem when a plurality of detectors are arranged. It should be noted that the horizontal synchronization detector 23 is provided with a horizontal synchronization folding mirror 25 so that the horizontal scanning direction 1
Laser beams LY, LM, LC and LB per line
Needless to say, is incident a total of four times. Further, the mirror block 25a is designed so that one mirror surface of the mold can be created by cutting from the block, and is devised so that it can be removed from the mold without requiring an undercut.

FIG. 8 (b) shows a modification of the horizontal synchronization folding mirror 25 shown in FIG. 8 (a). Folding mirror 26 for horizontal synchronization (designated as 26)
As shown in FIG. 8B, even if the four mirrors 26Y, 26M, 26C and 26B are sequentially attached to the fixing member 1b integrally formed at a predetermined position of the intermediate base 1a. Good. Also in this case, the shape of the mirror holding surface is devised so that the undercut is not necessary.

By using the horizontal sync detecting folding mirror 25 (or 26) shown in FIGS. 8A and 8B, the electric components required for detecting the horizontal sync signal can be The number can be reduced. In addition, the laser beams LY, LM, LC, and L
B is incident one by one. Therefore, it suffices that the detector 23 can detect the incidence of the laser beams L (Y, M, C and. This means that the reflecting surfaces 5α to 5ε and 5κ to 5μ of the optical deflector 5 are sub-scanned. Even if the flatness in the direction is insufficient, each laser beam L (Y, M,
It shows that the writing position of C and B) can be accurately detected.

Next, referring to FIG. 2 again, the laser beam L (Y, M,
C and B) and the optical system 21 through the post-deflection optical system 21.
Of the laser beams LY, LM, LC and LB emitted to the outside of the mirror and folding mirrors 33B, 37Y and 37
The relationship between M and 37C will be described.

As described above, the laser beams LY, LM, which are reflected by the polygonal mirror 5a of the optical deflector 5 and are given predetermined aberration characteristics by the first to third plastic lenses 27, 29 and 31. LC and LB are the first folding mirrors 33Y, 33M and 33C, respectively.
And 33B to be folded back in a predetermined direction.

At this time, the laser beam LB is reflected by the first folding mirror 33B and then guided to the image surface S through the dustproof glass 39B as it is. In contrast,
The remaining laser beams LY, LM and LC are supplied to the second folding mirrors 35Y, 35M and 35C, respectively.
And is guided by the second folding mirrors 35Y, 35M and 35C.
After being reflected toward M and 37C and further reflected by the third folding mirrors 37Y, 37M and 37C, dust-proof glasses 39Y, 39M and 39, respectively.
By C, images are formed on the image surface S at substantially equal intervals. In this case, the laser beam LB emitted from the first folding mirror 33B and the laser beam LC adjacent to the laser beam LB are also imaged on the image surface S at substantially equal intervals.

By the way, the laser beam LB is emitted from the optical scanning device 1 toward the image plane S only after being emitted from the laser element 3B and then being reflected by the polygon mirror 5a and the folding mirror 33B. Therefore, the laser beam LB guided substantially by only one folding mirror 33B can be secured.

When a plurality of mirrors are present in the optical path, this laser beam LB is varied (multiplied) according to the number of mirrors, and changes in various aberration characteristics of the image on the image plane or main scanning line bending, etc. , It is useful as a reference ray for relatively correcting the remaining laser beams L (Y, M and C).

When a plurality of mirrors are present in the optical path, it is preferable that the number of mirrors used for each of the laser beams LY, LM, LC and LB is made even or even. That is, according to FIG. 2, the number of mirrors involved in the laser beam LB is one (odd number) except for the polygon mirror 5a of the optical deflector 5,
The number of mirrors involved in C, LM and LY is 3 (odd number) respectively. Here, regarding any one of the laser beams LC, LM and LY, the second mirror 3
Assuming that No. 5 is omitted, the direction of the main scanning line bending due to the inclination of the lens of the laser beam passing through the optical path (the number of mirrors is an even number) where the second mirror 35 is omitted is different from that of the other laser beam. The number of mirrors is the opposite of the direction of the main scanning line bending due to the tilt or the like of an odd number of lenses, which causes a color shift which is a harmful problem when reproducing a predetermined color.

Therefore, the four laser beams LY, LM,
When a predetermined color is reproduced by superimposing LC and LB, the number of mirrors arranged in the optical path of each laser beam LY, LM, LC and LB is substantially unified into an odd number or an even number.

FIG. 9 shows the third folding mirrors 37Y and 3Y.
It is a schematic perspective view which shows the support mechanism of 7M and 37C.
According to FIG. 9, each of the third folding mirrors 37 (Y, M and C) has a fixing portion 41 integrally formed with the intermediate base 1a at a predetermined position of the intermediate base 1a of the optical scanning device 1. (Y, M and C) and the fixed part 41 (Y, M
M and C) are held by mirror pressing leaf springs 43 (Y, M and C) which are opposed to each other with the corresponding mirror interposed therebetween.

A pair of fixed portions 41 (Y, M and C) are formed at both ends (main scanning direction) of each mirror 37 (Y, M and C). Two protrusions 45 (Y, M and C) for holding the mirror 37 (Y, M and C) at two points are formed on one of the fixed portions 41 (Y, M and C), respectively. . The two protrusions 45 (Y, M
And C) are the ribs 46 (Y,
M and C).

The remaining fixing portion 41 (Y, M and C) has a set screw 47 for movably supporting the mirror held by the protrusion 45 (Y, M and C) along the optical axis.
(Y, M and C) are arranged.

As is clear from FIG. 9, each mirror 37
(Y, M and C) are set screws 47 (Y, M and C)
Is moved forward and backward, the protrusion 45 (Y, M and C) is used as a fulcrum to move in the optical axis direction.

FIGS. 10 to 12 show FIGS.
An example of a post-deflection optical system different from the post-deflection optical system 21 shown in FIG. With reference to FIGS. 10 to 12, the post-deflection optical system 121 includes first to third plastic lenses 127, 129, and 131. Table 5 shows lens data of each lens in the same manner as in Table 3.

[0081]

[Table 5]

The shape of the generatrix is assumed to be represented by the equation (1). Hereinafter, Table 6 shows lens data of an optical system conventionally used as a comparative example in the same manner. It should be noted that the shape of the generatrix is similarly expressed by the equation (1).

[0083]

[Table 6]

First plastic toric lens 12
7 is an incident surface (on the side of the optical deflector 5) 127 _in and an exit surface
(Image side S side) Both 127 _ra are toric lenses formed on a toric surface. The toric rotational symmetry axis of each surface of the lens 127 extends _{in the} main scanning direction (R127 _in ) with respect to the entrance surface 127 _{in and in the} sub scanning direction (R127 _ra ) with respect to the exit surface 127 _ra . The combined power in the sub-scanning direction by the entrance surface 127 _in and the exit surface 127 _ra is specified to be negative.

Second plastic toric lens 12
Reference numeral 9 denotes an incident surface (on the side of the optical deflector 5) 129 _in and an emitting surface.
(Image side S side) Both 129 _ra are toric lenses formed on a toric surface. The toric rotational symmetry axis of each surface of the lens 129 extends _{in the} main scanning direction (R129 _in ) with respect to the incident surface 129 _{in and in the} sub-scanning direction (R129 _ra ) with respect to the exit surface 129 _ra . The combined power of the incident surface 129 _in and the exit surface 129 _{ra in the} sub-scanning direction is positively defined.

The third plastic toric lens (final lens) 131 is an incident surface (light deflector 5 side) 131.
_in is a toric surface and an emission surface (image surface S side) 131 _ra
Is a single-sided toric lens formed on a rotationally symmetric aspherical surface. The toric rotational symmetry axis of the incident surface 131 _in of the lens 31 extends _{in the} main scanning direction (R131 _in ). Needless to say, the emission surface 131 _ra is rotated about the optical axis O. In addition, the incident surface 131 _in
The combined power in the sub-scanning direction by the emission surface 131 _ra is positively defined.

According to the lens arrangements shown in FIGS. 10 to 12, aberration characteristics such as spherical aberration, coma aberration, field curvature or magnification error in the image plane are compared with the examples shown in FIGS. , Can be more optimized.

FIG. 13 shows the reflection of each laser beam LY, LM, LC and LB of the optical deflector 5 obtained from the characteristics in the sub-scanning direction of the post-deflection optical system 21 shown in FIGS. 10 to 12 and Table 5. The incident conditions on the surface are shown.

As is apparent from FIG. 13, each laser guided to each reflecting surface of the optical deflecting device 5 by optimizing the power of the first to third plastic lenses 27, 29 and 31 in the sub-scanning direction. The beams LY, LM, LC and LB are largely separated in the sub scanning direction.

Below, as shown in FIG. 13, the respective laser beams LY, LM, LC and LB are sub-corresponding to the first to third plastic lenses 127, 129 and 131 shown in FIG. 10 to FIG. The post-deflection optical system suitable for the state of being largely separated in the scanning direction is the lens data of each lens of the pre-deflection optical system 7 of Table 5 (the lens arrangement is the same as the example of FIGS. 1 to 7). Shown in
(In addition, Table 8 shows the lens data of the optical system shown in Table 6 which is a conventionally used post-deflection optical system as a comparative example in the same manner).

[0091]

[Table 7]

[0092]

[Table 8] Next, the separation amounts of the laser beams LY, LM, LC and LB shown in FIG. 13 in the sub-scanning direction are shown more specifically in Tables 9 and 10.

[0093]

[Table 9]

[0094]

[Table 10]

Table 9 shows each laser beam L (Y, M, for the examples shown in Tables 1 and 3 and Tables 2 and 4).
C and B) shows the amount of separation in the sub-scanning direction, and Table 10 shows each laser beam L (Y, M, C and C for the examples shown in Tables 7 and 9 and Tables 8 and 10). B)
The amount of separation in the sub-scanning direction is shown.

As is apparent from Tables 9 and 10, in the examples in which the post-deflection optical system is optimized as shown in FIGS. 10 to 12 and Table 5, each laser beam L (Y, M,
It is recognized that the amount of separation of C and B) in the sub-scanning direction is maximized.

As a result, the folding mirror 33B and the second folding mirrors 37Y, 37M and 3 shown in FIG.
It will be appreciated that various restrictions on the spacing and position of each mirror as the 7C is placed can be relaxed.

[0098]

As described above, the optical scanning device of the present invention has the first to third lenses that give the light scanned by the optical scanning means a predetermined image forming characteristic. First
The lens has a negative power in the sub-scanning direction orthogonal to the direction in which light is scanned. The second lens has a positive power in the sub-scanning direction orthogonal to the light scanning direction. The third lens has a positive power in the sub-scanning direction orthogonal to the direction in which light is scanned. This maximizes the scanning angle of the light scanned by the optical scanning means.

According to the optical scanning device of the present invention, the entrance surface and the exit surface of the first lens are respectively toric surfaces, and the entrance surface and the exit surface of the second lens are respectively toric surfaces. , The entrance surface of the third lens is defined as a toric surface, and the exit surface of the third lens is defined as a rotationally symmetric surface. Therefore, it is possible to optimally maintain the image forming characteristics of the light scanned by the light scanning unit at a predetermined position at any position.

Further, according to the optical scanning device of the present invention,
The rotational symmetry axes of the entrance surface of the first lens and the entrance surface of the second lens are the same as those of the exit surface of the first lens, the exit surface of the second lens and the entrance surface of the third lens in the sub-scanning direction. The axis of rotational symmetry is defined in the direction in which the light is scanned. As a result, image forming characteristics such as achromaticity, field curvature, field distortion, and lateral magnification in the entire area in the sub-scanning direction are improved.

Therefore, an image forming apparatus capable of providing a small color image without color shift at low cost and a multi-beam optical scanning apparatus suitable for the image forming apparatus are provided. As a result, a low cost image forming apparatus is provided.

[Brief description of drawings]

FIG. 1 is a partial plan view of an optical scanning device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the optical scanning device shown in FIG. 1 taken along the optical axis extending from the optical deflecting device toward the image plane.

3 is an optical path diagram in which a pre-deflection optical system portion of the optical scanning device shown in FIG. 1 is developed.

4 is a schematic perspective view of a pre-deflection folding mirror block of the optical scanning device shown in FIG.

5 is an optical path diagram in a state where a folding mirror and the like of the optical scanning device shown in FIG. 1 are omitted.

6 is a schematic perspective view showing a rotation axis of a toric surface of each lens of a post-deflection optical system portion of the optical scanning device shown in FIG.

7 is a schematic plan view showing the arrangement of each optical member of the optical scanning device shown in FIG.

8 is a schematic perspective view of a folding mirror for horizontal synchronization detection of the optical scanning device shown in FIG.

9 is a schematic perspective view showing an adjusting mechanism of an emission mirror of the optical scanning device shown in FIG.

10 is an optical path diagram showing a modification of the optical path diagram of the optical scanning device shown in FIG.

11 is a schematic perspective view showing a rotation axis of a toric surface of each lens in the post-deflection optical system portion of the optical scanning device shown in FIG.

12 is a schematic plan view showing the arrangement of each optical member of the optical scanning device shown in FIG.

13 is a schematic diagram showing a state in which the separation amount of the pre-deflection optical system is increased by the optical scanning device shown in FIGS.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Multi-beam optical scanning device, 3 ... Semiconductor laser element, 5 ... Optical deflecting device, 7 ... Pre-deflection optical system, 9 ... Finite focus lens, 11
... Hybrid cylinder lens, 13 ... Mirror block, 15 ... Holding member, 17 ... Plastic cylinder lens, 19 ... Glass cylinder lens, 2
DESCRIPTION OF SYMBOLS 1 ... Post-deflection optical system, 23 ... Horizontal synchronization detector, 25 ... Horizontal synchronization folding mirror, 27 ... First imaging lens, 29 ... Second imaging lens,
31 ... Third imaging lens, 33 ... First folding mirror, 35 ... Second folding mirror, 37 ... Third
Folding mirror, 39 ... Dustproof glass, 41 ...
Fixed part, 43 ... Mirror pressing leaf spring, 45 ... Protrusion, 47 ... Set screw.

Claims (4)

[Claims] 1. A light scanning means for scanning a plurality of lights in a predetermined direction, and a sub-scanning direction orthogonal to a direction in which the respective light is scanned by the light scanning means in order from the side closer to the light scanning means. Of the first to third toric lenses whose respective powers are defined as negative, positive and positive, respectively, and image forming optical means for giving a predetermined image forming characteristic to each light scanned by the optical scanning means. And an optical scanning device having. 2. A plurality of light sources, a first optical means for collecting a plurality of light beams from the plurality of light sources into a light ray group that can be regarded as a bundle of light rays, and a first optical means. Scanning means for scanning the light ray group in a predetermined direction, and first to third lenses arranged in order from the side closer to the scanning means, the light ray group being orthogonal to the scanning direction by the scanning means. A first lens having a negative power in the sub-scanning direction, a second lens having a positive power in the sub-scanning direction, and a third lens having a positive power in the sub-scanning direction. A second optical means for separating the light ray group collected by the first optical means into the original number of light rays and for forming each light ray into a substantially linear image at a predetermined position; Is passed through at least part of the optical means of And a third optical means for guiding the light beam group to approximately one point. 3. A plurality of light sources, a first optical means for collecting a plurality of light from the plurality of light sources into a light ray group that can be regarded as a bundle of light rays, and a first optical means. A scanning means for scanning the light ray group in a predetermined direction, and first to third lenses arranged in order from the side close to the scanning means, wherein the entrance surface and the exit surface are each formed in a toric shape, The rotational symmetry axis of the entrance surface is defined in the main scanning direction in which the light beam group is scanned by the scanning means, and the rotational symmetry axis of the exit surface is defined in the sub-scanning direction orthogonal to the main scanning direction. The first lens whose power in the direction is regulated to be negative and the shape of the entrance surface and the exit surface are formed toric, respectively, and the axis of rotational symmetry of the entrance surface is in the main scanning direction and the axis of rotational symmetry of the exit surface is in the sub-direction. scanning With defined respectively in direction, a second lens which the sub-scanning direction power is defined positively,
The entrance surface is formed in a toric shape and the exit surface is formed in a rotationally symmetric surface, the rotational symmetry axis of the incident surface is defined in the main scanning direction, and the power in the sub-scanning direction is positively defined. Second optical means including three lenses, for separating the light rays grouped by the first optical means into the original number of light rays and for forming each light ray into a substantially linear image at a predetermined position. And an optical scanning device comprising: a third optical unit that guides the light beam group that has passed through at least a part of the second optical unit to approximately one point. 4. A plurality of light sources, a first optical means for collecting a plurality of lights from the plurality of light sources into a light ray group that can be regarded as a bundle of light rays, and a first optical means. A scanning means for scanning the light ray group in a predetermined direction, and first to third lenses arranged in order from the side close to the scanning means, wherein the entrance surface and the exit surface are each formed in a toric shape, The rotational symmetry axis of the entrance surface is defined in the sub-scanning direction orthogonal to the main scanning direction in which the light beam group is scanned by the scanning means, and the rotational symmetry axis of the exit surface is defined in the sub-scanning direction. The first lens whose power in the direction is regulated to be negative and the shapes of the entrance surface and the exit surface are formed in a toric shape, and the rotational symmetry axis of the entrance surface is in the main scanning direction and the rotational symmetry axis of the exit surface is the main axis. scanning With defined respectively in direction, a second lens which the sub-scanning direction power is defined positively,
The entrance surface is formed in a toric shape and the exit surface is formed in a rotationally symmetric surface, the rotational symmetry axis of the incident surface is defined in the main scanning direction, and the power in the sub-scanning direction is positively defined. Second optical means including three lenses, for separating the light rays grouped by the first optical means into the original number of light rays and for forming each light ray into a substantially linear image at a predetermined position. And an optical scanning device comprising: a third optical unit that guides the light beam group that has passed through at least a part of the second optical unit to approximately one point.