JP2006145868A - Optical scanner and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a new optical scanner which is suitable for low-cost, low-power consumption, and miniaturization, and which causes little color shift generation, even when the temperature changes. <P>SOLUTION: To miniaturize a deflector, a group of a luminous flux parallel to a horizontal plane and a luminous flux tilted with respect to the horizontal plane by a prescribed angle are made incident on the same position on a deflection reflecting surface, and another similar group in the same phase is made incident on another deflection reflecting surface. For each luminous flux group, the luminous flux parallel to the horizontal plane is acutely bent by a loop back mirror and is made incident on the deflection reflecting surface, and the luminous flux tilted the prescribed angle is made incident thereon, without being bent, as is. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical scanning device such as a digital copying machine, a laser printer, and a laser facsimile, and an image forming apparatus using the same.

FIG. 9 is a diagram for explaining the outline of the optical system of the optical scanning device.
In the figure, reference numeral 101 denotes a light source, 105 denotes a coupling lens, 106 denotes a cylindrical lens, 107 denotes a folding mirror, 108 denotes a polygon mirror as an optical deflector, 109 denotes a first scanning lens, 110 denotes a second scanning lens, and 114 denotes A photoconductor as a surface to be scanned is shown.
First, referring to FIG. 1 for the basic configuration of the scanning optical system, a divergent light beam emitted from a semiconductor laser 101 as a light source is converted into a light beam form suitable for the subsequent optical system by a coupling lens 105. The form of the light beam converted by the coupling lens 105 can be a parallel light beam, or a light beam with weak divergent or weak convergence.
The light beam from the coupling lens 105 is condensed in the sub-scanning direction by the cylindrical lens 106 and enters the deflecting / reflecting surface of the rotary polygon mirror that rotates the polygon mirror 108 via the folding mirror 107 as necessary. The light beam reflected by the deflecting and reflecting surface is deflected at a constant angular velocity as the polygon mirror 108 rotates at a constant speed, passes through the first scanning lens L1 and the second scanning lens L2, and reaches the photosensitive member 114. The scanning lenses L1 and L2 constitute a scanning imaging optical system, and collect the deflected light beam toward the photosensitive member 114. As a result, the deflected light beam forms a light spot on the photosensitive member 114 and performs optical scanning of the surface to be scanned. At this time, the direction in which the light spot moves due to the rotation of the optical deflector is called the main scanning direction, and the direction perpendicular thereto is called the sub-scanning direction. These two directions are applied not only to the surface to be scanned but also to any position of the optical system. In other words, in the figure, a direction parallel to the paper surface is defined as being enlarged in the main scanning direction, and a direction perpendicular to the paper surface is defined as the sub-scanning direction. Further, since the rotation axis of the polygon mirror is most stable when installed vertically, the present invention will be described assuming that the rotation axis is arranged in the vertical direction for convenience of explanation.
Therefore, in the same figure, the direction orthogonal to the paper surface may be called the vertical direction, and the direction parallel to the paper surface may be called the horizontal direction.
The coupling lens 105, the cylindrical lens 106, the first scanning lens L1, and the second scanning lens L2 may be sequentially referred to as a first optical system, a second optical system, a third optical system, and a fourth optical system, respectively.

FIG. 10 is a diagram for explaining an example of an image forming apparatus using an optical scanning device.
In the figure, reference numeral 1 denotes an image forming apparatus main body, 2 a transfer belt, 3 a photosensitive member, 4 a charging charger, 5 a scanning optical system, 6 a developing device, 7 a transfer charger, 8 a cleaning device, and 9 a resist. A roller pair, 10 is a belt charging charger, 11 is a peeling charger, 12 is a static elimination charger, 13 is a belt cleaner, 14 is a fixing unit, 15 is a discharge tray, and 16 is a discharge roller pair. Subscripts Y, M, C, and K are codes indicating development colors, and indicate yellow, magenta, cyan, and black, respectively.
This image forming apparatus is a tandem full-color laser printer.
In the figure, a transfer belt 2 is provided on the lower side of the apparatus for transferring a transfer paper (not shown) fed from a paper feed cassette 21 arranged in a horizontal direction to transfer an image. . On this transfer belt 2, a photosensitive member 3Y for yellow Y, a photosensitive member 3M for magenta M, a photosensitive member 3C for cyan C, and a photosensitive member 3K for black K are sequentially arranged from the upstream side in the transfer paper conveyance direction. They are arranged at intervals. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoreceptors 3Y, 3M, 3C, and 3K are all formed to have the same diameter, and process members that perform each process according to the electrophotographic process are sequentially arranged around the photoreceptors. Taking the photoconductor 3Y as an example, a charging charger 4Y, an optical scanning optical system 5Y, a developing device 6Y, a transfer charger 7Y, a cleaning device 8Y, and the like are sequentially arranged. However, since the scanning optical system 5 includes a plurality of optical elements and is dispersed in position, the scanning optical system 5 is represented by a light beam passing through the optical system.

The same applies to the other photoconductors 3M, 3C, 3K. That is, in this laser printer, the surfaces of the photoreceptors 3Y, 3M, 3C, and 3K are used as scanned surfaces or irradiated surfaces set for the respective colors, and the optical scanning optical system 5Y is applied to each photoreceptor. 5M, 5C, and 5K are provided in a one-to-one correspondence.
However, the first scanning lens L1 is commonly used for M and Y, and is commonly used for K and C. Further, a registration roller 9 and a belt charging charger 10 are provided around the transport belt 2 upstream of the photosensitive member 5Y, and are positioned downstream of the photosensitive member 5K in the rotation direction of the belt 2. A belt separation charger 11, a static elimination charger 12, a cleaning device 13 and the like are provided in this order. Further, a fixing device 14 is provided downstream of the belt separation charger 11 in the transfer paper conveyance direction, and is connected to a paper discharge tray 15 by a paper discharge roller 16.

  In such a configuration, for example, in the full color mode (multiple color mode), the respective photoreceptors 3Y, 3M, 3C, and 3K are respectively based on the image signals of the colors Y, M, C, and K. An electrostatic latent image corresponding to each color signal is formed on the surface of each photosensitive member by optical scanning of the light beam by the optical scanning optical systems 5Y, 5M, 5C, and 5K. These electrostatic latent images are developed with color toners by the corresponding developing devices to form toner images, which are superposed by being sequentially transferred onto transfer paper that is electrostatically attracted onto the transfer belt 2 and conveyed. As a result, a full-color image is formed on the transfer paper. This full-color image is fixed by the fixing device 14 and then discharged to the discharge tray 15 by the discharge roller 16.

As described above, an optical scanning device widely known in connection with a laser printer or the like generally deflects a light beam from a light source side by an optical deflector and scans a surface to be scanned by a scanning imaging optical system such as an fθ lens. A light spot is formed on the surface to be scanned by focusing toward the surface, and the surface to be scanned is optically scanned (main scan) with this light spot. What constitutes the surface to be scanned is a photosensitive surface of a photosensitive medium such as a photoconductive photosensitive member.
As an example of a full-color image forming apparatus, four photoconductors are arranged in the conveyance direction of the recording paper, and light beams emitted from a plurality of light source devices corresponding to the photoconductors are deflected by one deflecting unit. A plurality of scanning imaging optical systems corresponding to the respective photoconductors are scanned and simultaneously exposed to the respective photoconductors to form latent images, and these latent images are developed with different colors such as yellow, magenta, cyan, and black. After the visible image is developed by a developing device using the above, these visible images are sequentially superimposed and transferred and fixed on the same recording paper so that a color image can be obtained. As described above, an image forming apparatus that obtains a two-color image, a multicolor image, a color image, or the like by using two or more combinations of optical scanning devices and photoreceptors is known as a “tandem image forming apparatus”. Yes. As such a tandem image forming apparatus, a system in which a plurality of photosensitive media share a single optical deflector is disclosed (see, for example, Patent Document 1 and Patent Document 2).
As described above, when the optical deflectors are shared by a plurality of scanned surfaces, it is possible to reduce the number of optical deflectors, thereby reducing the size and cost of the image forming apparatus.

Patent Document 2 discloses a full-color tandem type image forming apparatus using a one-side scanning optical system. In the optical scanning device used in such an image forming apparatus, it is necessary to make a light beam traveling from one side of the deflector toward a different surface to be scanned enter the deflection scanning surface, which has a great layout restriction. In this patent document, the light beams from the light source devices directed to different scanning surfaces are combined in the main scanning direction to achieve a compact layout. However, beam combining means such as a prism for combining light beams is expensive, and there is a problem in reducing the cost of the apparatus.
For the purpose of improving the scanning characteristics, the use of a special surface typified by an aspherical surface has become common for the optical element of the optical scanning device, and such a special surface can be easily formed, and the cost is low. “Resin optical elements” are frequently used. In particular, in the tandem type image forming apparatus described above, since the number of optical elements used is large, the cost reduction effect by using resin optical elements is very large.

However, when a resinous optical element is used in the optical scanning device, the resinous optical element has a larger coefficient of thermal expansion than glass, so that a large change in shape occurs due to a temperature change, and the optical characteristics change.
When the temperature inside the optical box rises due to deflection means such as polygon mirrors that generate a large amount of heat, heat is uniformly transferred due to the airflow created by the rotation of the polygon mirror and the difference in shape inside the optical box. In addition, the temperature inside the optical box has a temperature distribution.
Also in the scanning lens, a uniform temperature change does not occur due to a difference in heat transmission method, a difference in lens shape (a difference in installation area on the optical box), and the like, and a temperature difference due to the location of the scanning lens occurs.
In the tandem type image forming apparatus, the light fluxes directed to the respective photoconductors pass through different scanning lenses, and due to the temperature distribution in the optical box holding the scanning lenses, different temperature distributions are generated between the respective scanning lenses. The shape change, the refractive index change, and the like are not uniform, and the amount of change in the scanning length and the change in isokineticity of each photoconductor are different. These latent images are visualized with a developing device using different color developers such as yellow, magenta, cyan, and black, and then these visible images are sequentially superimposed and transferred onto the same recording paper. When a color image is obtained by fixing, so-called “color shift” occurs. In particular, when the scanning lens closest to the deflecting means such as a polygon mirror that generates a large amount of heat in the optical box is made of resin, the change in optical characteristics becomes large.

As a method of dealing with the problem of the “scan length change”, a light receiving unit is provided on each of the writing start side and the writing end side, and the image frequency of each light beam is adjusted based on the difference in the light receiving time of each light receiving unit. (For example, refer to Patent Document 3). If this method is adopted in the above-described tandem type image forming apparatus that “shared a plurality of scanned surfaces with an optical deflector”, light is received on the write end side. Since a space for arrangement of means is required, it becomes more difficult to secure an effective write width.
Further, in the method of arranging the light receiving means on the writing start side and the writing end side and adjusting the image frequency of each light beam based on the difference in the light receiving time of each light receiving means, the length of the scanning line on each photoconductor However, it is impossible to correct a change in isokineticity due to the temperature distribution of each scanning lens. For this reason, for example, even if the dot positions in the main scanning direction at the start and end of writing are corrected by each photoconductor, the dot positions in the main scanning direction in the middle do not match, and color misregistration occurs. .
In the tandem optical scanning device, in order to solve the above problem, there are many examples in which the material of the scanning lens closest to the deflecting means such as a polygon mirror that generates a large amount of heat is made of glass. Compared to this, the cost will increase significantly.

More recently, as a means for reducing the cost of a single optical deflector in an optical scanning device of a color image forming apparatus, an oblique light beam is incident on the deflecting reflection surface of the optical deflector at an angle in the sub-scanning direction. An incident optical system is known (see, for example, Patent Document 4). In the oblique incidence optical system, after a plurality of light beams are deflected and reflected by the deflecting / reflecting surfaces, they are separated and guided to corresponding scanning surfaces (photoconductors) by folding mirrors or the like. At this time, the angle of each light beam in the sub-scanning direction (the angle at which the light beam obliquely enters the optical deflector) is set to an angle at which each light beam can be separated by the mirror. By using this oblique incidence optical system, it is possible to separate the intervals between adjacent light beams in the sub-scanning direction without increasing the size of the optical polarizer (increasing the number of polygon mirrors in the sub-scanning direction and increasing the thickness). Become.
However, when a full-color tandem image forming apparatus is configured with an oblique incidence optical system, an oblique incidence angle is obtained when an attempt is made to secure a distance in the sub-scanning direction necessary to separate the luminous flux into the corresponding scanned surface. However, there is a problem that the optical performance described below deteriorates.

The oblique incidence method has a problem that “scan line bending” is large. The amount of occurrence of the scanning line bending varies depending on the oblique incident angle of each light beam in the sub-scanning direction, and appears as a color shift when a latent image drawn with each light beam is superimposed and visualized with each color toner. End up. In addition, the oblique incident light causes the light beam to be twisted into the scanning lens, thereby increasing the wavefront aberration. Especially, the optical performance is significantly deteriorated at the peripheral image height, the beam spot diameter is increased, and the image quality is improved. It becomes a factor to prevent.
As a method of correcting the “large scanning line bending” inherent to the oblique incidence method, the scanning imaging optical system “changes the intrinsic inclination of the lens surface in the sub-scanning section in the main scanning direction so as to correct the scanning line bending”. Including a lens having a lens surface that has been adjusted (see, for example, Patent Document 5), or a scanning imaging optical system in which “the intrinsic inclination of the reflecting surface in the sub-scanning cross section is corrected so as to correct the scanning line curvature. A method of including a “corrected reflecting surface having a reflecting surface changed in the scanning direction” (see, for example, Patent Document 6) has been proposed.
Another problem with the oblique incidence method is that the wavefront aberration is likely to be greatly deteriorated at the peripheral image height (near both ends of the scanning line) due to the light beam skew. When such wavefront aberration occurs, the spot diameter of the light spot increases at the peripheral image height. If this problem cannot be solved, “high-density optical scanning”, which has been strongly demanded recently, cannot be realized. In the optical scanning device described in the above-mentioned patent document, a large scanning line curve peculiar to the oblique incidence method is corrected very well, but the correction of the wavefront aberration is not sufficient.

As an optical scanning device that can satisfactorily correct the above-mentioned “scan line bending and wavefront aberration degradation”, which can be said to be a problem with the oblique incidence method, the scanning imaging optical system includes a plurality of rotationally asymmetric lenses, and the lens surfaces of these rotationally asymmetric lenses. There has been proposed one in which the shape of the bus connecting the child line vertices is curved in the sub-scanning direction (see, for example, Patent Document 7).
However, since the lens having the above-mentioned “lens surface obtained by curving the shape of the generatrix connecting the vertexes of the child lines in the sub-scanning direction” has a curved generatrix, it is necessary to increase the lens width in the sub-scanning direction. In particular, on a lens surface having a large curvature, the amount of curve of the bus for correcting the scanning line curve becomes large, and the lens width must be considerably increased.
In addition, since the lens has a curvature in the sub-scanning direction, the wavefront aberration is greatly deteriorated when the lens rotates about the optical axis.
In addition, when the toric surface has a curvature in the sub-scanning direction different from that in the main scanning direction, the shape of the main scanning direction changes greatly for each height in the sub-scanning direction due to a change in temperature, When the incident position of the light beam is deviated in the sub-scanning direction due to the assembling error, a large variation in magnification error occurs, and in a color machine, the beam spot position is deviated between colors and color misregistration occurs.

JP-A-9-54263 JP 2001-4948 A Japanese Patent Laid-Open No. 9-58053 JP 2003-5114 A Japanese Patent Laid-Open No. 11-14932 Japanese Patent Laid-Open No. 11-38348 Japanese Patent Laid-Open No. 10-73778

It is an object of the present invention to realize a novel optical scanning device that is suitable for low cost, low power consumption, miniaturization, and has little occurrence of color misregistration even during temperature fluctuations.
For this purpose, in an optical scanning device having a plurality of light source devices, light beams from the respective light source devices are deflected by a common optical deflector and then condensed on the corresponding scanned surface by a scanning optical system. The first object is to make the optical system compact and to reduce the size of the apparatus.
A second object of the present invention is to realize an optical scanning device capable of obtaining a stable optical performance with a small color misregistration toward a higher quality of color images.
In addition, the realization of a low-cost optical scanning device in consideration of the environment, such as downsizing of the rotary polygon mirror, which is an optical deflector, and reduction of power consumption due to a reduction in the rotation speed of the rotary polygon mirror by multi-beam, and the above Another object is to realize an image forming apparatus that achieves the object.

According to the first aspect of the present invention, the light source device includes a plurality of light source devices, an optical deflector including a rotating polygon mirror, a scanning optical system including a lens and the like, and a plurality of scanned surfaces. In the optical scanning device that deflects the light beam by the optical deflector and condenses it on the scanned surface corresponding to each of the plurality of light beams through the scanning optical system, the light beam from at least one light source device and at least another One light beam is in a plane direction (this direction is called a main scanning direction and a direction perpendicular to this plane is called a sub-scanning direction) drawn by rotation of the normal line of the deflection reflection surface, and the main beam to the deflection reflection surface is drawn. The incident angles in the scanning direction are different from each other.
According to a second aspect of the present invention, in the optical scanning device according to the first aspect, at least one lens of the scanning optical system is shared by light beams from a plurality of light source devices.

According to a third aspect of the present invention, in the optical scanning device according to the first or second aspect, the optical deflector includes a plurality of deflection reflection surfaces having the same phase, and an incident angle in the main scanning direction with respect to the deflection reflection surface. Are different from each other, and are incident on different deflecting reflecting surfaces.
According to a fourth aspect of the present invention, in the optical scanning device according to any one of the first to third aspects, the optical scanning device includes a plurality of light beams incident on the deflection reflection surface at the same angle in a main scanning direction. The plurality of light beams include a light beam parallel to a plane drawn by rotation of the normal line of the deflecting reflection surface and a light beam having a predetermined angle with respect to the plane.

According to a fifth aspect of the present invention, in the optical scanning device according to the fourth aspect, the light beam parallel to the plane is incident on the deflecting / reflecting surface after passing through a folding mirror.
According to a sixth aspect of the present invention, in the optical scanning device according to the fifth aspect, the angle formed between the incident light beam and the reflected light beam on the folding mirror is an acute angle.

According to a seventh aspect of the present invention, in the optical scanning device according to any one of the first to sixth aspects, the lens surface of at least one scanning lens of the scanning optical system is a main surface to the deflecting reflection surface. It is characterized by having different shapes between light beams having different incident angles in the scanning direction.
According to an eighth aspect of the present invention, in the optical scanning device according to any one of the first to seventh aspects, a multi-beam light source device that emits a plurality of light beams is used as the plurality of light source devices. And

  According to a ninth aspect of the invention, there is provided an image forming apparatus using the optical scanning device according to any one of the first to eighth aspects.

The present invention has a plurality of light source devices, and a light beam from each light source device is deflected by a common light deflector and then condensed on a corresponding scanned surface by a scanning optical system. It is possible to reduce the size of the apparatus by configuring the previous optical system compactly.
Furthermore, it is possible to realize an optical scanning device capable of obtaining a stable optical performance with a small color misregistration toward an increase in image quality of a color image.
In addition, the realization of a low-cost optical scanning device in consideration of the environment, such as downsizing of the rotary polygon mirror, which is an optical deflector, and reduction of power consumption due to a reduction in the rotation speed of the rotary polygon mirror by multi-beam, and the above An image forming apparatus that achieves the object can be realized.

FIG. 1 is a diagram showing an embodiment of the present invention. FIG. 4A is a plan view, and FIG. 4B is an optical path side sectional view after the deflector.
In the figure, reference numerals 101 to 104 denote light sources A to D, 108 denotes a light polarizer, 109 denotes a first scanning lens (L1), 110 to 113 denotes a second scanning lens (L2), 114 to 117 denote photosensitive members, and LA. ˜LD indicates light beams from the light sources A to D, respectively.
This figure is a combination of four scanning optical systems shown in FIG. The four light sources are indicated by light sources A to D, respectively. A coupling lens and a cylindrical lens are also used but are not shown in the figure. In this embodiment, the light source A and the light source B share one folding mirror 107AB, and the light source C and the light source D share the other folding mirror 107CD. The light beam LA from the light source A and the light beam LD from the light source D are emitted in the horizontal direction, and the light beam LB from the light source B and the light beam LC from the light source C are inclined at a predetermined angle ± βs1 opposite to each other in the horizontal direction. And inject.
The two light beams sharing the folding mirror are incident and deflected at substantially the same position of the optical polarizer. The deflected light fluxes LA and LD travel horizontally, the light flux LB travels upward at an angle βs1, and the light flux LC travels downward at an angle βs1. Each light beam passes through the first scanning lens 109 (lens L1), and then reaches the photoconductors 114 to 117 via the individual second scanning lenses 110 to 113 (lens L2). A folding mirror (not shown) is provided between the lens L1 and the photosensitive member as necessary to reduce the size of the apparatus.
With this configuration, the height of the polygon, that is, the height in the sub-scanning direction can be greatly reduced as compared with the deflection unit of the conventional optical scanning device in which all the light beams are horizontal. .

FIG. 2 is a diagram showing a difference in height of a polygon due to a difference in method. FIG. 4A is a diagram according to the present invention, FIG. 4B is a diagram according to a conventional system, and FIG. 4C is a diagram according to another conventional system.
In the figure, reference numerals h1 to h3 denote the heights of the polygons, z denotes the beam interval necessary for separating the light beams, and βs1 to βs3 denote the inclination angles of the light beams.
Each light beam enters the individual lens L2 after passing through the first scanning lens 109, but each lens L2 has a considerably larger outer shape than the cross-sectional size of the light beam. Otherwise, the lens L2 interferes with the adjacent light flux. Thus, receiving the light flux individually by the lens L2 is called separation of the light flux for convenience. Let z be the minimum beam interval required for the separation of the luminous flux. z is practically about 3 to 5 mm.
If the same beam interval z is to be obtained, the polygon height h1 according to the present invention is approximately one half of the conventional polygon height h2 in which all light beams are deflected horizontally. Can be. As another conventional method, the height h3 of the polygon in which all the light beams are inclined with respect to the horizontal plane can be reduced to a quarter or less of h2, but instead, the maximum inclination angle βs3 of the light beam is Approximately 1.5 times the inclination angle βs1 of the present invention is required. Note that βs3 is approximately one half of βs1.

As the height h of the polygon increases, friction loss with the air accompanying rotation, so-called wind loss increases, so it is better to make h as small as possible. When the windage loss is large, problems such as increase in power consumption, increase in noise, and cost increase occur. In particular, in the components of the optical scanning device, the cost ratio of the deflecting means is high, so the cost cannot be ignored. Therefore, the method of inclining the luminous flux is advantageous because the height h of the polygon can be reduced.
In FIG. 5B, the distance from the highest light beam incident point to the upper surface of the polygon and the distance from the lowest light beam incident point to the lower surface of the polygon are both set to be smaller than half of z. I can do it. Therefore, in FIG. 2A, the polygon does not need to be continuous between the two light beam incident points. That is, as long as the reflection surface is on the same surface (this may be referred to as the same phase), the upper reflection point and the lower reflection point can be formed as two different polygons. By doing so, the axial length (thickness in the sub-scanning direction) of the deflecting / reflecting surface can be reduced even when the two steps are added, the inertia as the rotating body can be reduced, and the start-up time can be shortened.

FIG. 3 is a diagram for explaining a problem in the case where the light beam is incident obliquely.
The light beams from a plurality of light source devices are reduced in size to a rotating polygon mirror as an optical deflector by making this a light beam incident horizontally on the deflecting reflection surface of the optical deflector and a light beam incident at an angle. Reduction of power consumption, noise, and cost can be achieved. Further, since the incident angle of the obliquely incident light beam can be set to a small angle with respect to the normal line of the deflecting / reflecting surface, it is an advantageous system in view of optical performance.
However, before entering the deflecting / reflecting surface, as shown in the figure, the interval between the light beams having an angle with respect to the horizontal plane is the direction in which the distance in the sub-scanning direction is separated after the deflecting / reflecting, and the corresponding scanned object. Although it can be separated into planes, if it follows the pre-deflection, it will approach the opposite, making it difficult to arrange the light source device.
It is substantially difficult to arrange the light source devices so as to overlap in the sub-scanning direction due to an increase in the size of the device and deterioration of optical performance due to an increase in the tilt angle of the light beam. For this reason, it is necessary to arrange | position a some light source device so that it may not interfere in a horizontal surface. At this time, in order to make the light beams from the respective light source devices enter the deflecting reflection surface, it is necessary to synthesize each light beam in the main scanning direction (same optical path in plan view), but it is synthesized by a folding mirror. In this case, as described above, the interval in the sub-scanning direction of each light beam is narrow (particularly, the distance between the light beam LB and the light beam LC becomes narrower), making it difficult to arrange the folding mirror.
Therefore, as in the present invention, by making the incident angle of the light flux from each light source device to the deflection reflection surface in the horizontal plane different from each other, the interference of the light flux from each light source device can be prevented, thereby solving the above-mentioned problem. be able to. The configuration shown in FIG. 1 is an example, and has two pairs of a light beam having an inclination angle with respect to the horizontal plane and a pair of horizontal light beams, and the incident angle (in the main scanning direction in the horizontal scanning direction) to each deflecting reflection surface. This is an optical scanning device with different incidence angles.

The distance in the sub-scanning direction between the horizontal light beam and the light beam having an inclination angle spreads from the deflection reflection surface toward the light source device. For this reason, it is possible to separate the deflected light beams by using the mirrors before the deflection in the same manner as in the sub-scanning direction by the folding mirror to guide the deflected light beams to the corresponding scanned surfaces. Separable means that the light source device is viewed from the optical deflector side, that is, it is possible to combine light beams from the light source device arranged without interfering in the main scanning direction toward the deflecting reflection surface. It is.
In such a configuration having two pairs of light beams from two sets of light source devices (four light source devices), each pair of light beam groups is incident on the deflection reflection surface at different incident angles in the main scanning direction. Is done. For this reason, even if the interval between the light beams having an angle with respect to the horizontal plane (inclined in the sub-scanning direction) approaches as described above, the light source device can be disposed without interfering with each other because the distance is in the main scanning direction. Become. The paired light beam groups can be combined using a mirror, and the light beam groups have a distance in the main scanning direction and do not interfere with each other, so that the light beams from the respective light source devices can be combined in a compact and easy manner.
In the present embodiment, the light beam having an angle with respect to the horizontal plane and the horizontal light beam have been described. However, the light beams are incident on the same deflecting reflection surface of the optical deflector or different deflecting reflecting surfaces having the same phase (such as polygons arranged in two stages). In the one-side scanning method, downsizing of the optical system until it enters the optical deflector becomes a problem. That is, the present invention is not applied only to the present embodiment, but can also be applied to the case where the light beams from all the light source devices have an angle with respect to the horizontal plane or are horizontal. Furthermore, in the present embodiment, the light beam groups having different incident angles in the main scanning direction on the deflecting reflection surface are paired with a light beam having an angle with respect to the horizontal plane and a horizontal light beam. However, the present invention is not limited to this.

Incidentally, as mentioned before, it is known that the amount of various aberrations increases and the optical performance deteriorates in the oblique incidence method in which the light is incident obliquely with respect to the horizontal plane. In this method of oblique incidence, there is a problem that “scan line bending” is large. The amount of scan line bending varies depending on the inclination angle of each light beam, and appears as color misregistration when the latent images drawn with each light beam are superimposed and visualized with toner of each color. In addition, the oblique incident light causes the light beam to be twisted and incident on the scanning lens, thereby increasing the wavefront aberration. Particularly, the optical performance is significantly deteriorated at the peripheral image height, the beam spot diameter is increased, and the image quality is improved. It becomes a factor to prevent.
In the present invention, a special tilt eccentric surface is employed to correct wavefront aberration and scanning line bending. Correction of scanning line bending and wavefront aberration can be corrected by tilting the lens surface in the sub-scanning direction. By balancing the scanning position in the sub-scanning direction between image heights and the amount of deteriorated wavefront aberration, the scanning position and wavefront aberration at each image height are corrected, and the scanning line curve on the scanned surface is corrected. Thickening of the beam spot diameter due to the wavefront aberration deterioration is corrected well.
However, the amount of degradation of wavefront aberration due to the amount of twist (skew) of the light beam incident on the lens surface, the amount of change in the sub-scanning direction of the object point between the image heights due to oblique incidence on the rotating polygon mirror, and the deflection reflection surface Since the distance from the lens surface to the lens surface differs between image heights, it is impossible to completely correct wavefront aberrations and scanning line bending. Therefore, according to the present invention, it is possible to more appropriately correct the wavefront aberration and the scanning line bending by adopting the special tilt eccentric surface.

The special tilt eccentric surface is a special surface having a different eccentric angle (tilt amount) in the lens lateral direction (sub-scanning direction) depending on the lens height in the lens longitudinal direction (main scanning direction).
The tilt amount (eccentric angle) of the special tilt eccentric surface refers to an inclination angle in a short direction with respect to a surface orthogonal to the optical axis (center axis) of the lens. When the tilt amount is 0, the surface is orthogonal to the optical axis. The special tilt eccentric surface is formed so as to correct “scanning line bending and wavefront aberration” on the surface to be scanned.
The surface shape of the lens surface is according to the following shape formula. However, the content of the present invention is not limited to the following shape formula, and the same surface shape can be specified using another shape formula.
The shape formula of the “special toroidal surface” used in the numerical examples described later is shown below.
The paraxial radius of curvature in the “main scanning section” which is a plane section including the optical axis and parallel to the main scanning direction is RY, the distance from the optical axis in the main scanning direction is Y, and the higher order coefficients are A, B, C, D ...
Let RZ be the paraxial radius of curvature in the “sub-scan section” orthogonal to the main scan section.

X (Y, Z) = (Y ² · Cm) / (1 + √ [1- (1 + K) · (Y · Cm) ² ])
+ A ・ Y ⁴ + B ・ Y ⁶ + C ・ Y ⁸ + D ・ Y ¹⁰ + E ・ Y ¹²・ ・
+ CS (Y) · Z ² / (1 + √ [1- (CS (Y) · Z) ² ])
+ (F0 + F1 · Y + F2 · Y ² + F3 · Y ³ + F4 · Y ⁴ + ··) Z
However, Cm = 1 / RY and CS (Y) = 1 / RZ.
(F0 + F1 · Y + F2 · Y ² + F3 · Y ³ + F4 · Y ⁴ + ···) Z is a portion representing the tilt amount, and when there is no tilt amount, F0, F1, F2, ··· are all 0. .
When F1, F2,... Are not 0, the tilt amount changes in the main scanning direction.
In a scanning lens shared by the light beams from a plurality of light sources, the passing position of the light beam having an angle with respect to the horizontal plane is a position separated from the center in the short direction (sub scanning direction) of the lens in the sub scanning direction. pass.
The surface shape at this time includes a position where the light flux toward the image height 0 passes through the special tilt eccentric surface, and a line horizontal to the normal line of the deflecting / reflecting surface is the optical axis used in the description of the above formula.

FIG. 4 is a diagram illustrating an example of a state in which the tilt amount of the sub-scanning cross-sectional shape changes in the main scanning direction.
In the figure, the Y direction indicates the main scanning direction, and the Z direction indicates the sub scanning direction. Further, in order to make the shape of the special tilt surface easy to understand, the shape in the main scanning direction is flat and the tilt amount is exaggerated more than the actual. The inclination of the surface in the sub-scanning direction changes depending on the position in the main scanning direction.
Further, the color shift can be reduced by making the surface shape of the special tilt eccentric surface in the sub-scanning direction a planar shape having no curvature.
If the bus bar is curved in the case of a toric surface having a curvature in the sub-scanning direction different from that in the main scanning direction, the shape in the main scanning direction changes greatly for each height in the sub-scanning direction, resulting in temperature fluctuations and optical element assembly errors. As a result, when the incident position of the light beam is shifted in the sub-scanning direction, a large variation in magnification error occurs. In a color machine, the beam spot position between colors is shifted and color shift occurs, but the surface shape of the special tilt eccentric surface in the sub-scanning direction is a planar shape having no curvature as in the present invention. As a result, the shape error in the main scanning direction can be reduced for each height in the sub-scanning direction, the variation in magnification error when the incident position of the light beam is shifted in the sub-scanning direction can be reduced, and the occurrence of color misregistration can be suppressed. be able to.

When the scanning lens closest to the optical deflector is shared with a horizontal light beam (horizontal light beam) and a light beam having an angle with respect to a horizontal plane (an oblique light beam) as in the present embodiment, one surface of the passing position of the oblique light beam is used. Is the special tilt eccentric surface, but the main scanning shape at the center of the special tilt eccentric surface in the sub-scanning direction (the optical axis in the explanation formula of the special tilt eccentric surface) is the same as the horizontal light beam (that is, the special tilt When the amount of tilt eccentricity of the eccentric surface is 0, the sub-scan section of the passing position of the horizontal light beam and the oblique light beam is a plane), and the main scanning direction of the scanning lens is affected by the heat generated by the optical deflector or the like. Even in the case of having a temperature distribution, the refractive power change is almost the same, the amount of beam spot position deviation in the main scanning direction is the same on all scanned surfaces, and the color change and color deviation during continuous printing are the same. Occurrence can be suppressed. Strictly speaking, the optical path length in the lens differs between the light beam that passes through the shared lens obliquely and the light beam that passes horizontally, but this is a very small difference, and the effect on the main scanning beam spot position deviation on the scanned surface is not affected. Very small.
By integrally forming the scanning lens shared by the plurality of light beams, it is possible to realize a scanning optical system that is low in cost and has a small incident angle of the light beam with respect to the normal line of the deflecting reflection surface of the polygon mirror. it can. Even if the scanning lens is divided in the sub-scanning direction and overlapped, the same effect can be obtained by using an eccentric surface. However, an increase in the number of scanning lenses causes an increase in cost.

Since the refractive power in the sub-scanning direction of the scanning lens closest to the deflecting unit is almost zero, the scanning lens closest to the surface to be scanned has a strong positive refractive index. As a result, the sub-scanning magnification of the scanning imaging optical system becomes a reduction system, and performance degradation due to component assembly errors, component shape errors, and the like can be suppressed. In the sub-scanning direction, it is needless to say that the base point of the deflecting unit and the surface to be scanned are in a conjugate relationship and has a function of correcting the surface tilt of the deflecting unit.
The light beam having an angle on the deflecting / reflecting surface may be disposed by tilting the light source device, the first optical system (coupling optical system), and the second optical system (cylindrical lens system) at a desired angle. An angle may be given using. Further, the light beam directed toward the deflecting / reflecting surface may be angled by shifting the optical axis of the first optical system in the sub-scanning direction.

In an optical scanning device having a horizontal light beam and an oblique light beam, it is desirable to provide a folding mirror for combining the light beams from the light source device in the horizontal light beam.
As described above, the obliquely incident light beam is greatly deteriorated in wavefront aberration. For this reason, in an optical scanning device having a horizontal light beam and an oblique light beam, the optical performance differs slightly depending on the method. The wavefront aberration is corrected well by using the special tilt eccentric surface, but the fluctuation of the optical performance due to the attachment of the optical element is slightly large and the stability is slightly inferior. Therefore, it is desirable to provide a folding mirror for the horizontal light beam, in which the wavefront aberration is corrected more satisfactorily and to improve the stability of the optical performance, and the oblique light beam is directly incident on the optical deflector.
Furthermore, the folding mirror deteriorates the wavefront aberration when tilted in the sub-scanning direction. This is because the light beam that is deflected and scanned by the deflecting reflecting surface and incident on the scanning lens is twisted due to the tilt of the folding mirror. The amount of twist increases as the angle formed between the incident light and the emitted light on the mirror increases, and the deterioration of wavefront aberration also increases. When the wavefront aberration is deteriorated, the beam spot diameter is increased and the image quality is deteriorated.
Therefore, it is desirable to arrange the mirror so that the angle formed between the incident light and the emitted light to the mirror is an acute angle. As described above, in the present invention, since the incident angle in the main scanning direction on the deflecting reflecting surface is made different, the degree of freedom in designing the mirror arrangement is high.

In the present embodiment, among the lenses constituting the scanning optical system, the scanning lens L1 closest to the polygon mirror as the deflecting means is configured to allow a plurality of light beams traveling toward different scanning surfaces to pass. For this reason, it is possible to suppress image degradation due to color shift and color between different scanned surfaces. The scanning lens L1 closest to the deflecting unit has a strong positive refractive power in the main scanning direction and corrects constant velocity. By passing a plurality of light beams directed to different scanning surfaces through this lens, the beam spot position deviation in the main scanning direction due to processing variations of the scanning lens becomes almost the same on the different scanning surfaces, thereby suppressing the occurrence of color misregistration. can do.
Furthermore, the polygon mirror as the deflecting means generates a large amount of heat due to the motor unit that drives the polygon mirror to rotate at high speed and its circuit board. With regard to the substrate, it is possible to reduce the temperature fluctuation in the optical box by taking it out of the optical box, but it is difficult to release the heat generated by the motor part to the outside. The temperature rise inside cannot be avoided. The heat generated in the motor unit or the like propagates through the optical box, thereby generating a temperature distribution in the lens constituting the scanning optical system, particularly the scanning lens L1 closest to the polygon mirror. This temperature distribution is generated because a uniform temperature change does not occur in the scanning lens due to the air current in the optical box by the polygon mirror, the shape of the scanning lens, and the like. As a result, in a tandem color image forming apparatus of the opposite scanning method in which the beam toward each scanned surface passes through a different scanning optical element, the beam in the relative main scanning direction on each scanned surface during continuous printing. The spot position fluctuates and the color changes. The generation of this temperature distribution can be improved by sealing the polygon mirror and allowing the light flux to enter and exit the polygon mirror through the parallel flat glass. However, in the counter scanning method, it is difficult to completely match the temperature distribution between the left and right scanning lenses with the polygon mirror interposed therebetween, which causes color shift and color change.
Therefore, in an optical scanning device according to another embodiment of the present invention, the scanning lens closest to the deflecting unit is configured so that all light beams directed to different scanning surfaces pass through. This is referred to herein as a one-side scanning method. In the one-side scanning method, even when the scanning lens has a temperature distribution in the main scanning direction, the shape in the main scanning direction is the same between the light beams directed to different scanned surfaces. The refractive power change (surface shape change) is the same, and the beam spot position deviation in the main scanning direction is almost the same on different scanned surfaces, and it is possible to suppress changes in color and occurrence of color deviation during continuous printing. .

In order to satisfactorily correct the field curvature in the sub-scanning direction, it is desirable that the scanning optical system includes at least one surface whose curvature in the sub-scanning direction changes according to the image height.
The special tilt eccentric surface is a surface having no curvature and does not have a function of condensing light in the sub-scanning direction. Therefore, when a special tilt decentered surface is used for wavefront aberration correction and scanning line bending correction by using a surface (hereinafter referred to as a special toroidal surface) whose curvature in the sub-scanning direction changes according to the image height. In this case, the curvature of field at each image height can be efficiently corrected without increasing the number of lenses.
The surface shape of the lens surface of the special toroidal surface is according to the following shape formula. However, the content of the present invention is not limited to the following shape formula, and the same surface shape can be specified using another shape formula.
The paraxial radius of curvature in the “main scanning section” which is a plane section including the optical axis and parallel to the main scanning direction is RY, the distance from the optical axis in the main scanning direction is Y, and the higher order coefficients are A, B, C, D ...
Let RZ be the paraxial radius of curvature in the “sub-scan section” orthogonal to the main scan section.

X (Y, Z) = (Y ² · Cm) / (1 + √ [1- (1 + K) · (Y · Cm) ² ])
+ A ・ Y ⁴ + B ・ Y ⁶ + C ・ Y ⁸ + D ・ Y ¹⁰ + E ・ Y ¹²・ ・
+ CS (Y) · Z ² / (1 + √ [1- (CS (Y) · Z) ² ])
However,
Cm = 1 / RY
CS (Y) = 1 / RZ + aY + bY ² + cY ³ + dY ⁴ + eY ⁵ + fY ⁶ + gY ⁷ + hY ⁸
+ IY ⁹ + jY ¹⁰ ..

  Between the light beams having different incident angles in the main scanning direction on the deflecting reflecting surface, the rotational position of the polarizing reflecting surface at the start of scanning slightly differs. Therefore, since the influence of the sag generated on the deflecting / reflecting surface is different, the optical performance (particularly the sub-scanning image surface curvature) is different between the light beams. For this reason, it is possible to obtain good imaging performance for each light flux by correcting the special toroidal surface with different lens surface shapes. Also, the special tilt eccentric surface also has an optimum shape for each because the scanning line bends differently. Higher quality optical performance can be achieved by optimizing the surface shape as in the present invention.

FIG. 5 is a diagram showing an example of a light source unit constituting the multi-beam light source device.
In the figure, reference numeral 400 denotes a light source unit. Other symbols are quoted from time to time in the description.
This figure is a diagram showing a first embodiment of a light source unit.
In the optical scanning device according to the present invention, the light source is, for example, a semiconductor laser array having a plurality of light emitting points, or a multi-beam light source device using a single light emitting point or a plurality of light sources having a plurality of light emitting points, and a plurality of light beams. May be configured to simultaneously scan the surface of the photoconductor. By doing so, it is possible to configure an optical scanning device and an image forming apparatus that are increased in speed and density, and even when such an optical scanning device and an image forming apparatus are configured, the same effects as described above are obtained. The effect of can be obtained.

In the figure, semiconductor lasers 403 and 404 are individually fitted in fitting holes 405a and 405b (not shown) formed on the back side of the base member 405, respectively. The fitting holes 405a and 405b are inclined by a predetermined angle in the main scanning direction, in the embodiment, by about 1.5 °, and the semiconductor lasers 403 and 404 fitted in the fitting holes are also arranged in the main scanning direction. Inclined by 1.5 °. The semiconductor lasers 403 and 404 have notches formed in the cylindrical heat sink parts 403a and 404a, and the protrusions 406a and 407a formed in the center round holes of the holding members 406 and 407 are formed in the notch parts of the heat sink part. By aligning, the arrangement direction of the light emitting sources is adjusted. The holding members 406 and 407 are fixed to the base member 405 with screws 412 from the back side thereof, so that the semiconductor lasers 403 and 404 are fixed to the base member 405. Further, the collimating lenses 408 and 409 are adjusted in the optical axis direction along the outer circumferences of the semicircular mounting guide surfaces 405d and 405e of the base member 405, and the divergent beams emitted from the light emitting points become parallel light beams. So that it is positioned and glued.
In the above embodiment, since the light beams from the respective semiconductor lasers are set so as to intersect within the main scanning plane, the fitting holes 405a and 405b and the semicircular mounting guide surfaces 405d and 405e are inclined along the light beam direction. Formed. By engaging the cylindrical engagement portion 405c of the base member 405 with the holder member 410 and passing the screw 413 through the through holes 410b and 410c and screwing into the screw holes 405f and 405g, the base member 405 is engaged with the holder member 410. It is fixed and constitutes a light source unit.

  The holder member 410 of the light source unit has a cylindrical portion 410a fitted in a reference hole 411a provided in the mounting wall 411 of the optical housing, and a spring 611 is inserted from the front side of the mounting wall 411 so that the stopper member 612 protrudes from the cylindrical portion. By engaging with 410c, the light source unit is held in close contact with the back side of the mounting wall 411. One end of the spring 611 is hooked on the protrusion 411b of the mounting wall 411, and the other end of the spring 611 is hooked on the light source unit, thereby generating a rotational force with the center of the cylindrical portion as the rotation axis. An adjustment screw 613 provided to lock the rotational force of the light source unit is provided, and the adjustment screw 613 can rotate the entire unit in the θ direction around the optical axis to adjust the pitch. It is configured as follows. An aperture 415 is disposed in front of the light source unit, and the aperture 415 is provided with a slit corresponding to each semiconductor laser, and is configured to be attached to the optical housing to define the emission diameter of the light beam.

FIG. 6 is a view showing another example of the light source unit constituting the multi-beam light source device. 2A is an exploded view of the optical system, and FIG. 2B is a view showing the inside of the semiconductor laser container.
In the figure, reference numeral 700 denotes a light source unit, and 801 denotes a light emitting element having four light emitting sources.
The figure shows a second embodiment of the light source unit.
Each light beam from the semiconductor laser 703 that emits four light beams is configured to be combined using beam combining means. Reference numeral 706 denotes a pressing member, 705 denotes a base member, 708 denotes a collimating lens, and 710 denotes a holder member. In this embodiment, there is one semiconductor laser 703 as a light source, and the number of pressing members 706 corresponding to this is different from the embodiment shown in the previous figure. The same.

FIG. 7 is a diagram for explaining a problem due to the difference in the incident position of the light beam with respect to the deflecting reflection surface. FIG. 4A shows the case where the incident points are separated from each other, and FIG. 6B shows the case where the incident points coincide.
It is desirable that all light beams emitted from the semiconductor laser intersect in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 108. Reference numeral D ₁ represents the reflection surface of the polygon mirror 108 when the light beam emitted from the semiconductor laser 101 reaches a certain image height on the scanned surface 114, and D ₂ represents the light beam emitted from the semiconductor laser 104. The reflection surface of the polygon mirror 108 when reaching the same image height on the surface 114 is shown. Each light beam is separated by a relative angle difference Δα when entering the polygon mirror 403. Therefore, a time delay corresponding to the angle difference between D ₁ and D ₂ is generated on the reflecting surface for reaching the same image height by the time difference.

In the case of FIG. 5A, the two light beams are deflected and reflected at mutually different positions on the deflecting reflection surface 108 through considerably different optical paths, and in the case of FIG. After being deflected and reflected, the light passes through exactly the same optical path. When the light beam passes through different positions of each optical element, it naturally undergoes different optical action, so the optical characteristics such as aberration of the two light beams that reach the same image height in the main scanning direction on the scanned surface are different. In particular, the influence of the scanning line pitch on the image height variation is very large.
Therefore, as shown in FIG. 5B, when the two light beams intersect each other in the vicinity of the reflection surface of the polygon mirror 108, when the same image height in the main scanning direction on the surface to be scanned is reached, the main scanning of the optical element is performed. Thus, the optical paths pass in substantially the same direction, and the scanning line bending can be effectively reduced. In addition, fluctuations in the writing position in the main scanning direction between the light beams due to variations in the parts on the image plane side from the polygon mirror are substantially the same for all the light beams, and the deviation in the writing position in the main scanning direction between the beams can be suppressed. . Furthermore, by passing all the light beams that are formed at the same image height through substantially the same position in the main scanning direction of the scanning optical system, the influence of the aberration of the lenses constituting the scanning optical system can be suppressed and the main scanning can be performed. The imaging position in the direction can be accurately matched to each beam, and even if a delay time is set in common for all the light beams after synchronous detection, position deviation in the main scanning direction at the image height at the beginning of writing is suppressed. Is possible. Further, by configuring as shown in FIG. 5B, the inscribed circle radius of the polygon mirror 403 can be minimized. A multi-beam light source device that uses one semiconductor laser array is not within the scope of this description.
However, the effect of the present invention can be obtained even if a multi-beam light source device using one semiconductor laser array is used.

  In the above, an example has been described regarding multi-beams. In the case where light beams traveling toward different scanning surfaces are deflected by reflection surfaces having the same phase of the polygon mirror, the light beams intersect in the main scanning direction in the vicinity of the deflection reflection surface of the polygon mirror 108 (substantially the same reflection point in the main scanning direction). (It may be the same or separated in the sub-scanning direction). By doing so, the same effect as described above can be obtained.

FIG. 8 is a diagram for explaining a configuration in which the optical scanning device of the present invention is applied to an image forming apparatus.
In this figure, the scanning optical systems 5K, 5C, 5M, and 5Y in the configuration of FIG. 9 described as the prior art are replaced with the scanning optical system of the present invention.
With this configuration, it is possible to realize an image forming apparatus that can effectively correct scanning line bending and deterioration of wavefront aberration, and can ensure high-quality image reproducibility without color misregistration.

It is a figure which shows embodiment of this invention. It is a figure which shows the difference in the height of the polygon by the difference in a system. It is a figure for demonstrating the problem in the case of making a light beam enter obliquely. It is a figure which shows an example of the state from which the amount of tilts of subscanning cross-sectional shape changes to the main scanning direction. It is a figure which shows the example of the light source unit which comprises a multi-beam light source device. It is a figure which shows the other example of the light source unit which comprises a multi-beam light source device. It is a figure for demonstrating the problem by the difference in the incident position of the light beam with respect to a deflection | deviation reflective surface. 1 is a diagram for explaining a configuration in which an optical scanning device of the present invention is applied to an image forming apparatus. FIG. It is a figure for demonstrating the outline | summary of the optical system of an optical scanning device. It is a figure for demonstrating an example of the image forming apparatus using an optical scanning device.

Explanation of symbols

101-104 Light source 108 Optical deflector 109, 110-113 Scan lens 114-117 Surface to be scanned (photosensitive member)

Claims (9)

  A plurality of light source devices, an optical deflector composed of a rotating polygon mirror, a scanning optical system composed of lenses and the like, and a plurality of scanned surfaces, and deflects light beams from the respective light source devices by the optical deflector. Then, in the optical scanning device that condenses on the surface to be scanned corresponding to each of the plurality of light beams through the scanning optical system, the light beam from at least one light source device and at least one other light beam are the deflection reflection surface In the plane direction drawn by rotation of the normal line (this direction is referred to as the main scanning direction, and the direction perpendicular to the plane is referred to as the sub-scanning direction), the incident angles in the main scanning direction on the deflection reflecting surface are different from each other. An optical scanning device characterized by the above.   2. The optical scanning device according to claim 1, wherein at least one lens of the scanning optical system is shared by light beams from a plurality of light source devices.   3. The optical scanning device according to claim 1, wherein the optical deflector includes a plurality of deflecting reflecting surfaces having the same phase, and light beams having different incident angles on the deflecting reflecting surface in the main scanning direction are deflected and reflected differently. An optical scanning device characterized by being incident on a surface.   4. The optical scanning device according to claim 1, further comprising: a plurality of light beams incident on the deflection reflection surface at a same angle in a main scanning direction, wherein the plurality of light beams are the deflection reflection surface. An optical scanning device comprising: a light beam parallel to a plane drawn by rotation of the normal line; and a light beam having a predetermined angle with respect to the plane.   5. The optical scanning device according to claim 4, wherein a light beam parallel to the plane enters the deflection reflection surface after passing through a folding mirror.   6. The optical scanning device according to claim 5, wherein an angle formed between a light beam incident on the folding mirror and a reflected light beam is an acute angle.   7. The optical scanning device according to claim 1, wherein the lens surface of at least one scanning lens of the scanning optical system has different incident angles in the main scanning direction with respect to the deflection reflection surface. An optical scanning device characterized by having different shapes.   8. The optical scanning device according to claim 1, wherein a multi-beam light source device that emits a plurality of light beams is used as the plurality of light source devices.   An image forming apparatus using the optical scanning device according to claim 1.

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