JP2007316207A - Optical scanner and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that an optical deflector used for an image forming apparatus adopts a method by which a plurality of light beams are made incident on one and the same reflection face of one optical deflector for downsizing, the respective incident beams are made incident with different angles so that the beams after reflectance can be easily separated, but bending is caused in scanning lines when a diagonal incident angle is large, by an optical system which condenses the deflected light beams, and though this bending can be corrected by changing the form of the optical system, it does not cope with temperature changes. <P>SOLUTION: The plurality of light beams are made diagonally incident on one and the same deflecting reflection face 4a, separated by turning back mirrors 6 to vertical scanning directions after passing through a common scanning lens 5a, and guided onto corresponding faces to be scanned 7. The beam emitted to a region A and the beam emitted to a region B have bending of scanning lines which are in reversed directions to each other. The direction of bending is reversed every time when the light beam passes through one mirror. When different number of mirrors are given, the large bending of the beams L1 and L4 are set in the same direction and a color slippage is minimized. <P>COPYRIGHT: (C)2008,JPO&INPIT

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.

In general, an optical scanning device widely known in relation to a laser printer or the like generally deflects a light beam from a light source side by an optical deflector and collects the light beam toward a surface to be scanned by a scanning imaging optical system such as an fθ lens. Thus, a light spot is formed on the surface to be scanned, 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 formed by one deflecting unit. A deflection scan is performed, and a plurality of scanning imaging optical systems corresponding to the respective photosensitive members are simultaneously exposed to the respective photosensitive members to form latent images, and these latent images are developed in different colors such as yellow, magenta, cyan, and black. There is a configuration in which a color image can be obtained by making a visible image by a developing unit using an agent and then transferring these visible images to the same recording paper in order to transfer and fix them.

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 type image forming apparatus, there have been disclosed several systems in which a plurality of photosensitive media share a single optical deflector.
A plurality of light beams that are substantially parallel and separated in the sub-scanning direction are incident on the deflector, and a plurality of scanning optical elements corresponding to the plurality of light beams are arranged and scanned in the sub-scanning direction (see, for example, Patent Document 1).
A light beam is incident from one side of the deflector and is a three-lens (L1-L3) scanning optical system. L1 and L2 pass a plurality of light beams directed to different scanning surfaces, and L3 is provided for each scanning surface. (For example, refer to Patent Document 2).

As described above, when the optical deflectors are shared by a plurality of scanned surfaces, the number of the optical deflectors can be reduced, so that the image forming apparatus can be made compact.
However, for example, as an optical scanning device of a full-color image forming apparatus having four different scanned surfaces (photosensitive members) of cyan, magenta, yellow, and black, the number of optical deflectors can be reduced. There is a problem that the polygon mirror is increased in size in the sub-scanning direction because light beams directed to a plurality of photoconductors in the scanning direction are arranged substantially in parallel and enter the optical deflector. In general, the cost of the polygon mirror portion is high due to the optical elements in the optical scanning device, which is a harmful effect when the cost of the entire device is reduced and the size is reduced.

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, a light beam is incident on the deflection reflecting surface of the optical deflector at an angle in the sub-scanning direction. An oblique incidence optical system is known (for example, refer to Patent Document 3). 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, the distance between adjacent light beams in the sub-scanning direction, where each light beam can be separated by the mirror, can be increased in size (the number of polygon mirrors in the sub-scanning direction is increased, the thickness is increased). It can be realized without fleshing.

However, the oblique incidence method has a problem that “scanning line bending” is large. The amount of bending of the scanning line varies depending on the oblique incident angle of each light beam in the sub-scanning direction, and color misregistration occurs when the latent images drawn by the respective light beams are superimposed and visualized with the respective color toners. Appears.
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.
As a method of correcting the “large scanning line bending” inherent to the oblique incidence method, the scanning imaging optical system “changes the inherent inclination of the lens surface in the sub-scan 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 4), or a scanning imaging optical system in which “the intrinsic inclination of the reflecting surface in the sub-scanning 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 5) has been proposed.

There has been proposed a method of aligning scanning lines using a surface that passes obliquely incident light beams off the axis of the scanning lens and changes the aspherical amount of the scanning lens child line along the main scanning direction (for example, , See Patent Document 6). In this document, an example is given in which correction is performed by a single scanning lens, and correction of the scanning line bending is possible, but the deterioration of the beam spot diameter due to an increase in wavefront aberration described below is described. Not.
Another problem with the oblique incidence method is that a large wavefront aberration is likely to occur 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 document, a large scanning line curve peculiar to the oblique incidence method is corrected extremely well, but the correction of the wavefront aberration is not sufficient.

A scanning imaging optical system includes a plurality of rotationally asymmetric lenses as an optical scanning device that can satisfactorily correct the above-mentioned “scanning line bending and wavefront aberration degradation”, which can be said to be a problem with the oblique incidence method, and the lens surfaces of these rotationally asymmetric lenses In addition, there has been proposed one that uses a surface that has no curvature in the sub-scanning direction and changes the tilt eccentricity in the sub-scanning direction in the main scanning direction. By using at least two such special surfaces, wavefront aberration correction and scanning line curve correction are favorably performed (see, for example, Patent Document 7).
However, in the oblique incidence optical system, scanning line bending occurs when temperature fluctuations occur. Since the light beam is incident on the scanning lens while being curved in the sub-scanning direction, it is caused by a change in the radius of curvature of the scanning lens due to a temperature change, a change in thickness, or a change in the incident height of the light beam incident on the scanning lens. The scanning line is greatly bent. In the conventional scanning optical system, the light beam is incident on the optical axis almost horizontally without being curved with respect to the scanning lens, so that the scanning line is not generated or extremely small, and this problem is unique to the oblique incident optical system. It has become a problem.

  In an oblique incidence optical system, by setting a small oblique incidence angle, the curvature of the light beam incident on the scanning lens can be reduced, reducing the occurrence of scanning line bending and scanning line bending during temperature fluctuations. Although it is possible, in order to secure the interval in the sub-scanning direction necessary for separating the light beams toward the corresponding scanned surfaces, the sub-beams of the light beams are deflected on the deflecting reflecting surface of the optical deflector. It becomes necessary to increase the interval in the scanning direction, and it is necessary to increase the size of the optical polarizer (increasing the number of polygon mirrors in the sub-scanning direction and increasing the thickness). Patent Document 7 discloses an example in which a light beam having an angle with a horizontal light beam is used on a deflecting reflection surface of an optical deflector, and an oblique incident angle in the one-side scanning method is set to be the smallest. However, as described above, it is necessary to increase the size of the optical polarizer (multiple polygon mirrors in the sub-scanning direction and increase the thickness), and there are problems in reducing the size, cost and power consumption of the optical scanning device. was there.

In the opposed scanning method, since the light beams are distributed across the optical deflector, in the case of a color image forming apparatus having four surfaces to be scanned, the light beam is usually separated at one side.
On the other hand, in the one-side scanning type optical scanning device, it is necessary to separate and guide all the light beams to the corresponding scanned surfaces as compared with the counter scanning type optical scanning device. It is necessary to set a long optical path length to the photosensitive member as a scanning surface. Further, the arrangement of the folding mirrors for guiding all the light beams to the corresponding scanned surfaces is complicated.
Therefore, in the one-side scanning method, it is possible to obtain a good optical performance without reducing the degree of freedom of arrangement of the scanning lens, and to reduce the size without interfering with the scanning lens constituting the scanning optical system. There is a problem that it is difficult compared to.

JP-A-9-54263 JP 2001-4948 A JP 2003-5114 A Japanese Patent Laid-Open No. 11-14932 Japanese Patent Laid-Open No. 11-38348 JP 2004-70109 A JP 2006-072288 A

Inclined-incidence optical scanning devices that make all light beams have an angle with respect to the normal of the deflecting reflection surface of the optical deflector. Realization of a new optical scanning device that is low in cost, low in power consumption, and small in size. Let it be an issue.
An object of the present invention is to realize a novel optical scanning device that effectively corrects color misregistration caused by scanning line bending due to temperature fluctuation in an oblique incidence type optical scanning device.
Inclined-incidence optical scanning devices suitable for low cost, low power consumption, and downsizing. New image formation that effectively compensates for scan line bending and wavefront aberration degradation and produces less color drift even during temperature fluctuations. The realization of the device is an issue.

According to the first aspect of the present invention, a plurality of light source devices each emitting a light beam, a light deflector for deflecting and scanning each light beam, a scanning optical system having at least one scanning lens, and a plurality of objects to be scanned In the optical scanning device, each of the light beams is deflected by the same deflecting and reflecting surface of the optical deflector and then condensed on the different scanned surfaces by the scanning optical system. All the light beams have an angle with respect to the normal of the reflecting surface of the optical deflector with respect to the sub-scanning direction, and at least the scanning lens closest to the optical deflector of the scanning optical system is shared by all the light beams. After being deflected by the optical deflector, the light beam closest to the scanned surface in the sub-scanning direction is directed to the corresponding scanned surface at the position closest to the optical deflector, and the corresponding scanned Separated in the direction approaching the surface And wherein the Rukoto.
According to a second aspect of the present invention, in the optical scanning device according to the first aspect, a surface to be scanned corresponding to a light beam directed to the surface to be scanned farthest from the optical deflector among the plurality of light beams. The number of folding mirrors in the sub-scanning direction for guiding the light to the scanning surface is equal to or less than the number of folding mirrors arranged in the optical path of the light beam toward the other scanned surface.

According to a third aspect of the present invention, in the optical scanning device according to the second aspect, the light beam directed to the scanning surface farthest from the optical deflector is deflected by the optical deflector and then in the sub-scanning direction. The light beam that is deflected to the opposite side in the sub-scanning direction with respect to the normal line of the deflection reflection surface of the optical deflector with respect to the light beam closest to the surface to be scanned.
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 light beam directed to the surface to be scanned farthest from the optical deflector is at a position farthest from the optical deflector. It is characterized by being folded in a direction approaching the corresponding scanned surface.

According to a fifth aspect of the present invention, in the optical scanning device according to any one of the first to fourth aspects, among the light beams directed to different scanned surfaces, at least the light closest to the scanned surface from the scanned surface. The difference in the number of folding mirrors for guiding the light beam and the farthest light beam to the surface to be scanned is an odd number.
According to a sixth aspect of the present invention, in the optical scanning device according to any one of the first to fifth aspects, the deflection scanning is performed in one region in the sub-scanning direction across the normal line of the deflection reflection surface of the optical deflector. The number of folding mirrors corresponding to the light beam to be deflected and the light beam deflected and scanned in the other region is an odd number.

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 folding mirror in the sub-scanning direction is disposed between the deflection reflection surface and the corresponding scanned surface. At least the folding mirror arranged so that the light beam directed to the different scanning surface passes on the opposite side with respect to the reflection direction of the light beam deflected and reflected and the sub-scanning direction is at least the different scanning target The side through which the light beam toward the surface passes is chamfered.
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 light source device.

According to a ninth aspect of the present invention, there is provided an image forming apparatus including the optical scanning device according to any one of the first to eighth aspects as means for performing an exposure process of an electrophotographic process.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, at least four photoconductors are provided as the scanned surfaces, and color image formation is possible.

According to the present invention, a plurality of light source devices are provided, and all light beams from the respective light source devices are incident at an angle in the sub-scanning direction with respect to the normal line of the same deflecting reflection surface of the common optical deflector. In a one-side scanning oblique incidence optical system that focuses light onto different scanning surfaces using a scanning optical system with a scanning lens shared by the light beam, the optical scanning device is downsized and scanning line bending occurs due to temperature fluctuations. Thus, a novel optical scanning device that effectively corrects color misregistration caused by the above can be realized.
Furthermore, the realization of the optical scanning device considering the environment, such as the miniaturization of the optical deflector and the reduction of the power consumption due to the decrease in the rotational speed of the rotary polygon mirror, which is an optical deflector by multi-beams, and the purpose of the above description are achieved. An image forming apparatus can be realized.

1 and 2 are diagrams for explaining one embodiment of the present invention.
In both figures, reference numeral 1 is a semiconductor laser as a light source, 2 is a coupling lens, 3 is a cylindrical lens, 4 is an optical deflector, 5 is a scanning lens, 6 is a folding mirror, 7 is a photoreceptor as a surface to be scanned, L1 L4 denotes a light beam, and ST1 to ST4 denote image forming stages.
The divergent light beam emitted from the semiconductor laser 1 is converted into a light beam shape suitable for the subsequent optical system by the coupling lens 2. The form of the light beam converted by the coupling lens 2 may be a parallel light beam, or may be a light beam with weak divergence or weak convergence. The light beam from the coupling lens 2 is condensed in the sub-scanning direction by the cylindrical lens 3 and enters the deflecting / reflecting surface 4a of the rotary polygon mirror (optical deflector) 4 that rotates the polygon mirror. As shown in FIG. 2, the plurality of light beams L from the light source side are incident on the plane perpendicular to the rotation axis of the deflection reflection surface 4a of the polygon mirror. Therefore, the light beams L1 to L4 reflected by the deflecting / reflecting surface 4a are also inclined with respect to the same plane. Each light beam having an angle with respect to a plane orthogonal to the rotation axis of the rotary polygon mirror may be arranged by tilting the light source device, the coupling optical system, and the first optical system at a desired angle, or using a folding mirror. You can also make an angle. Further, the light beam directed toward the deflecting / reflecting surface 4a may be angled by shifting the optical axis of the first optical system in the sub-scanning direction. The light beam reflected by the deflecting / reflecting surface 4a is deflected at a constant angular velocity along with the constant speed rotation of the polygon mirror, passes through the scanning optical system, and is condensed on the scanned surface 7. As a result, the deflected light beam forms a light spot on the surface to be scanned 7 and performs optical scanning of the surface to be scanned 7. Of the planes, a plane including the movement locus of the normal line of the deflecting reflecting surface 4a is referred to as a plane H.

In the present invention, two light beams (light beams emitted to the region B above the plane H) that are emitted farther than the scanned surface 7 after being reflected by the deflecting reflection surface 4a are further distant. Let L1 and L2 be from the light beam exiting on the side. The two light beams emitted to the area A below the plane H are denoted as L3 and L4 in order from the side far from the scanned surface 7.
The stage ST indicates a unit unit for image formation. For example, ST1 indicates a unit unit for forming a black image. Depending on the configuration, ST4 may be for black. In the present invention, ST1 is the stage closest to the optical deflector 4, and ST4 is the stage farthest from the optical deflector 4.
In FIG. 2, the direction perpendicular to the paper surface represents the main scanning direction in optical scanning, and the direction parallel to the paper surface represents the sub-scanning direction. Strictly speaking, the sub-scanning direction is a direction perpendicular to the main scanning direction on the surface to be scanned 7, but the light beam L reaches the surface to be scanned 7 while changing its direction by the folding mirror 6. At the intermediate position, the direction substantially perpendicular to the traveling direction of the light beam is the sub-scanning direction at that position.

  Light beams from a plurality of light source devices (not shown) are obliquely incident on the same deflecting / reflecting surface 4a of the same light deflector 4. Each light beam is incident from both sides in the sub-scanning direction (region A and region B in the figure) across the normal line of the deflecting reflection surface 4a. All the light beams pass through the common scanning lens 5a, are separated by the folding mirror 6 (or 6a) in the sub-scanning direction, and are guided to the corresponding photoreceptor 7 as the scanning surface. In this embodiment, the scanning lens has a two-lens configuration (or a two-group configuration) of a first scanning lens 5a and a second scanning lens 5b, and a second optical lens is provided for each light beam directed to the corresponding scanned surface 7. A system 5b is arranged.

FIG. 3 is a diagram for explaining the difference between vertical incidence and oblique incidence of a light beam on the deflection surface. FIG. 4A shows the case of normal incidence, and FIG. 4B shows the case of oblique incidence.
In the figure, reference sign Δd indicates the interval between the light beams.
In FIG. 6A, as a one-side scanning method that does not use oblique incidence, the conventional optical scanning device in which all the light beams are horizontal with respect to the normal of the deflecting reflecting surface of the polygon mirror has good optical performance. Although it is easy to obtain, the distance between the light beams from each light source device 1, that is, the light beams guided to different scanning surfaces, is an interval necessary for separating each light beam (Δd in the figure), usually from 3 mm. It is necessary to have an interval of 5 mm. For this reason, the height (height in the sub-scanning direction) h of the deflecting means (polygon mirror) 4 is increased, the contact area with air is increased, power consumption is increased due to the influence of windage loss, noise is increased, and cost is increased. There was a problem such as. In particular, the cost ratio occupied by the deflecting means 4 in the components of the optical scanning device is high, and the cost is a major problem.

  In that regard, in FIG. 5B, according to the above-described embodiment of the optical scanning device according to the present invention, the light from the plurality of light source devices 1 reflected by the deflection reflection surface 4a of the polygon mirror as the deflection means 4 is reflected. The light beam is incident on the scanning lens 5a as a light beam having an angle (with an angle in the sub-scanning direction) with respect to the normal line of the deflecting / reflecting surface 4a of the polygon mirror, thereby greatly increasing the height h of the polygon mirror 4. It is possible to reduce the number of polyhedrons forming the deflecting / reflecting surface 4a of the polygon mirror 4 and the thickness in the sub-scanning direction, the inertia as a rotating body can be reduced, and the startup time can be shortened. An optical scanning device with low power consumption and low cost can be realized.

  However, in the optical scanning device of the present invention in which all the light beams are angled in the sub-scanning direction with respect to the normal line of the deflecting / reflecting surface 4a of the optical deflector 4, the oblique incident angle in the sub-scanning direction is set large. Need arises. As described above, in order to secure the light beam spacing in the sub-scanning direction for separating the respective light beams toward the scanned surfaces 7 corresponding to the respective light beams, the light beams directed toward different scanned surfaces. Among them, at least the light beam (L4) closest to the scanning surface 7 in the sub-scanning direction and the light beam (L1) far from the scanning surface 7 have a large oblique incident angle. That is, the occurrence of scanning line bending is increased.

The scanning line bending in the oblique incidence optical system will be described.
For example, the shape of the scanning surface 5 constituting the scanning optical system, particularly the scanning lens having a strong refractive power in the sub-scanning direction (second lens 5b in FIG. 1) in the main scanning direction is the shape of the light beam on the deflection reflecting surface. Unless the arc shape is centered on the reflection point, the distance from the deflecting / reflecting surface 4a of the optical deflector 4 to the incident surface of the scanning lens varies depending on the lens height in the main scanning direction. Usually, it is difficult to make the scanning lens in the above shape in order to maintain optical performance. That is, as shown in FIG. 1, a normal light beam is deflected and scanned by an optical deflector and does not enter the lens surface perpendicularly at each image height in the main scanning section, but has an incident angle in the main scanning direction. Have incident.

FIG. 4 is a diagram for explaining the relationship between the second scanning lens and the scanning light beam. FIG. 4A is a perspective view of a scanning lens, and FIG.
By having an angle in the sub-scanning direction (because it is obliquely incident), the light beam deflected and reflected by the optical deflector 4 is incident on the scanning lens 5b from the deflecting / reflecting surface 4a of the optical deflector 4 depending on the image height. The distance to the surface is different, and as shown in the figure, the incident height in the sub-scanning direction to the scanning lens 5b is higher or lower than the center (the angle of the light beam in the sub-scanning direction is closer to the periphery). Depending on the direction). As a result, when passing through a surface having refracting power in the sub-scanning direction, the refracting power received in the sub-scanning direction differs and scanning line bending occurs. In the case of normal horizontal incidence, even if the distance from the deflecting / reflecting surface to the scanning lens incidence surface is different, the light beam travels horizontally with respect to the scanning lens, so the incident position in the sub-scanning direction on the scanning lens is different. There is no occurrence of bending of the scanning line.
A description will be given of fluctuations in the scanning line curve when the temperature changes. In recent years, plastics are commonly used as the material for scanning lenses because of the degree of freedom in lens shape (such as aspherical shape) at the time of design for cost and high image quality. The lens shape change is larger than that of the glass lens.

As described above, in the oblique incidence optical system, the light beam is incident on the scanning lens while being curved in the sub-scanning direction. Accordingly, the ambient light is incident on the scanning lens 5b at a position off the axis. For this reason, if the curvature radius and thickness of the scanning lens, the incident angle of the light beam incident on the scanning lens, and the position in the sub-scanning direction change due to temperature changes, different refractive changes occur in the main scanning direction, and the destination of the ambient light Cannot be sufficiently guaranteed, and scanning line bending occurs.
As described above, in the case of normal horizontal incidence, the light beam travels horizontally with respect to the scanning lens even if the distance from the deflecting / reflecting surface to the scanning lens incidence surface is different, and therefore the sub-scanning direction on the scanning lens. The incident position of the scanning line does not differ at substantially the same height as the optical axis, and the occurrence of scanning line bending is extremely small. In other words, a normal lens passes a light beam on the axis, so even if the radius of curvature changes due to temperature changes, the imaging position (defocus direction) changes, but the refraction of light rays in the sub-scanning direction occurs. Since there is no (or slight) change in the scanning line bending (the position of the scanning line in the sub-scanning direction on the surface to be scanned) is extremely small.

As described above, the occurrence of a large scanning line bend is a problem peculiar to an oblique incidence optical system, and the direction of the occurrence differs on both sides of the sub-scanning direction across the normal line of the deflecting reflection surface. That is, the generation direction is reversed between the light beam incident from the region A in FIG. 2 and the light beam incident from the region B in FIG. This is because the curvature of the scanning line incident on the scanning lens is the direction of the incident angle in the sub-scanning direction of the light beam incident on the scanning lens, that is, the oblique incident direction (incident from the A side or from the B side in the figure). This is because the direction is reversed depending on whether it is incident. In particular, the curvature of the scanning line incident on the scanning lens having a strong refractive power in the sub-scanning direction causes the scanning line to be bent for the reason described above.
Similarly, even when a temperature change occurs, the change in the scanning line curve is reversed on both sides in the sub-scanning direction across the normal line of the deflection reflection surface. As described above, when the direction of the scanning line curve is reversed on different scanning surfaces 7, when the respective colors are overlapped, color misregistration is caused, and the quality of the color image is remarkably deteriorated. As the oblique incident angle increases, the curvature of the scanning line incident on the scanning lens increases and the amount of generation of the scanning line bending increases. That is, in the present embodiment, the amount of scan line bending of the two outer light beams is larger than the two inner light beams (the side closer to the normal line of the deflecting / reflecting surface). Further, the amount of scan line bending when the temperature fluctuates also increases with the outer light beam.

The occurrence of scanning line bending and wavefront aberration degradation due to oblique incidence can be corrected by using a surface that does not have refractive power in the sub-scanning direction and the tilt eccentricity in the sub-scanning direction changes in the main scanning direction. It is known. However, the correction of the scanning line bending due to the temperature variation described above cannot be performed, and color misregistration occurs in the color image.
In the optical scanning device described in Patent Document 7, a light beam having an angle with respect to the normal line of the deflecting / reflecting surface 4a of the optical deflector 4 is used and the oblique incident angle is set small. While the occurrence of scanning line bending is suppressed to a small level, the optical scanning apparatus of the present invention in which all light beams are angled in the sub-scanning direction with respect to the normal line of the deflecting reflection surface 4a of the optical deflector 4 is described above. It is necessary to increase the size of the light polarizer 4 (multiple polygon mirrors in the sub-scanning direction and increase the thickness), and the height (height in the sub-scanning direction) h of the deflecting means (polygon mirror) increases. The contact area with air increases, causing problems such as increased power consumption, increased noise, increased costs, and increased size of the optical scanning device due to the effects of windage loss.

Therefore, in the optical scanning device of the present invention, as shown in FIG. 2, among the light beams directed to different scanned surfaces, at least the light beam (L4) closest to the scanned surface in the sub-scanning direction and the far light beam (L1) are The difference in the number of folding mirrors 6 for guiding to the surface to be scanned is an odd number. Specifically, in the configuration example of the figure, the number of mirrors used for the uppermost light beam L1 and the lowermost light beam L4 of the obliquely incident light beams is not the same. The difference is an odd number. That is, if one is an even number, the other is an odd number. Since the scanning line folded by the folding mirror 6 in the sub-scanning direction is reversed in the sub-scanning direction every time it is folded, as described above, the scanning line is bent on both sides of the sub-scanning direction across the normal line of the deflecting reflection surface 4a. Even when the generation directions are different, the directions can be matched to the same direction. In color superposition in a color machine, the light beam L4 closest to the scanning surface 7 in the sub-scanning direction and the light beam L1 far away, that is, the scanning beam bending direction of the light beam having the largest oblique incident angle are matched. The occurrence of color misregistration can be reduced, and a good color image can be achieved.
Furthermore, in the optical scanning device of the present invention, the light beam L4 on the side closest to the scanned surface 7 in the sub-scanning direction (lowermost in the figure) after being deflected and scanned by the deflecting / reflecting surface 4a of the optical deflector 4 is The laser beam is separated by the folding mirror 6a toward the corresponding scanned surface 7 at the position closest to the optical deflector 4 (left end: ST1 in the figure) in the direction approaching the corresponding scanned surface 7 (downward in the figure).

FIG. 5 is a diagram for explaining a known example relating to the arrangement of the folding mirror.
The light beam L1 farthest from the scanned surface 7 in the sub-scanning direction after being deflected and scanned by the deflecting / reflecting surface 4a of the optical deflector 4 is moved from the scanned surface 7 at a position on the ST1 side closest to the optical deflector. Separated away. According to this configuration, in order to guide the light beam to the scanned surface 7, it is necessary to pass between the optical deflector 4 and the scanning lens 5a. At this time, in order to guide the light beam to the scanning lens 5 a and the photoconductor 7 as the surface to be scanned so as not to interfere with the optical deflector 4, the light beam passing between the scanning lens 5 a and the optical deflector 4 is used. Since it is difficult to set the angle large with respect to a plane orthogonal to the normal line of the deflecting / reflecting surface 4a of the optical deflector 4 (that is, it is greatly folded back to the optical deflector 4 side), the optical deflector 4 is ST1 in the figure. The arrangement needs to be shifted to the arrow C side with respect to the photosensitive member, and the optical scanning device is increased in size.

  That is, it is difficult to dispose the optical scanning device between the four photoconductors arranged, and a problem arises in downsizing the optical scanning device. Although it is possible to cope with an increase in the number of the folding mirrors 6, the cost of the folding mirror is increased, the layout of the optical scanning device is complicated, and the optical path length from the optical scanning device deflection reflection surface 4 a to the scanned surface 7 becomes long. Therefore, it is not realistic that the optical scanning device becomes larger and it becomes difficult to maintain stable optical performance due to an increase in optical elements. Further, in order to cope without increasing the number of the folding mirrors, it is necessary to increase the distance from the folding mirror 6 for passing between the scanning lens 5a and the optical deflector 4 to the photosensitive member 7 as the scanned surface. Occurs. At this time, since the optical path length of the light beam directed to the photosensitive member 7 as the other surface to be scanned becomes longer, the optical scanning device is also increased in size, making it difficult to reduce the size of the mounted image forming apparatus. . Also in known materials, since the optical path length becomes long, in the light beam toward the photoconductor 7 of ST4 farthest from the optical deflector 4, a large number of folding mirrors are used, which increases the cost of the optical scanning device. And it has a configuration that leads to an increase in size.

FIG. 6 is a diagram for explaining another known example.
After being deflected and scanned by the deflecting / reflecting surface 4a of the optical deflector 4, the light beam L1 farthest from the scanned surface 7 in the sub-scanning direction is positioned closest to the optical deflector 4 (toward ST1). It is separated to the photoconductor 7 side as a scanning surface. In this configuration, in order to avoid interference between the scanning lens 5a shared and the light beam L1 separated at the position closest to the optical deflector 4, the optical deflector 4 of the optical scanning device is shown as ST1 in the drawing. The arrangement is shifted to the C side in the figure with respect to the photosensitive member 7, and the optical scanning device is increased in size. Similar to the example of FIG. 5, it is difficult to dispose the optical deflector 4 between the four photoconductors 7 arranged, which causes a problem in miniaturization of the optical scanning device. In the optical scanning device of this configuration, by increasing the optical path length from the deflecting / reflecting surface 4a of the optical deflector 4 to the scanned surface 7, the photoconductor 7 and the optical deflector of ST1 closest to the optical deflector 4 are provided. 6 can be brought closer to the direction C in FIG. 6, but the optical path length of the light beam toward the photoconductor 7 of the ST 4 farthest from the optical deflector 4 becomes too long. It is necessary to increase the number of sheets and to fold back, and it becomes difficult to increase the cost of the fold mirror, to complicate the layout of the optical scanning device, and to maintain stable optical performance by increasing the number of optical elements. Further, although it is conceivable to reduce the distance between the folding mirror 6b at the left end of the figure and the optical deflector 4, interference with the optical element 5a in the figure occurs, so that the light beam is deflected and reflected by the optical deflector 4. It is necessary to reduce the angle with respect to the surface H including the normal locus of the surface 4a, and the arrangement positions of the photoconductor 7 and the optical deflector 4 as the scanned surface are arranged without shifting in the C direction. It becomes difficult. In addition, as the oblique incident angle increases, the occurrence of scanning line bending also increases.

That is, in the optical layout of the known optical scanning device, when an oblique incident optical system is used to reduce the size of the optical deflector 4 or to reduce power consumption and to reduce the cost of the optical scanning device, optical scanning is performed. It is difficult to reduce the size of the apparatus, which results in an optical scanning device that is not suitable for downsizing the mounted image forming apparatus. Miniaturization is a big problem in low-cost image forming apparatuses, and it is also a big problem in an optical scanning device to be mounted.
According to the form of the optical scanning device of the present invention, the light beam L4 closest to the scanned surface 7 in the sub-scanning direction after being deflected and scanned by the deflecting / reflecting surface 4a of the optical deflector 4 is the optical deflector 4 closest. Since it is separated by the folding mirror 6 in the direction approaching the corresponding scanned surface 7 toward the corresponding scanned surface 7 of ST1 at a position close to, it is possible to realize a small optical scanning device that solves the above problems.

FIG. 7 is a view for explaining another embodiment of the present invention.
The light beam L4 closest to the photosensitive member 7 as the surface to be scanned in the sub-scanning direction is first separated to the photosensitive member side with respect to the other light beams after passing through the shared scanning lens 5a, to the scanning lens 5a. Thus, it is possible to largely fold back to the optical deflector 4 side. Compared to the conventional optical scanning device, the optical deflector 4 can be laid out without increasing the number of folding mirrors 6 without shifting the deflector 4 to the C side in FIG. The optical scanning device can be downsized. The optical path length from the optical scanning device to the surface to be scanned 7 can be set as appropriate depending on the distance between the photoconductors. However, the optical path is obtained by folding the light beam L toward the surface to be scanned 7 with respect to the conventional optical scanning device. The problem that length becomes long does not arise.

As described above, according to the present invention, an optical scanning device that makes all the light beams L have an angle in the sub-scanning direction with respect to the normal line of the deflection reflection surface 4a of the optical deflector 4 is used as the optical layout. Thus, cost reduction and power consumption can be realized, and the optical scanning device can be miniaturized. In addition, the “scanning line bending direction” generated by the oblique incidence optical system is matched with at least the light beams (L1 and L4) having a large oblique incident angle (large occurrence of scanning line bending), thereby reducing color misregistration. It becomes possible.
In order to further reduce the color misregistration, in all the light beams, two light beams (for example, L1 and L2) that are deflected and scanned in one of the sub-scanning directions with the normal line of the deflecting reflection surface of the optical deflector interposed therebetween. ) And the difference in the number of folding mirrors corresponding to two light beams deflected and scanned on the other side (for example, L3 and L4) are set to odd numbers, so that the scanning line bending directions coincide with each other on all scanned surfaces. be able to. The following figure shows an example.

FIG. 8 is a diagram showing an optical system that aligns all investigation line bends in the same direction.
In the drawing, the folding mirror for the light beam emitted to the region B side is set to an odd number, and the folding mirror for the light beam emitted to the region A side is set to an even number.
The number of folding mirrors 6 corresponding to the light beam incident on the deflecting / reflecting surface 4a from one side in the sub-scanning direction with respect to the normal line of the deflecting / reflecting surface 4a, for example, from the region A in FIG. The number corresponding to the light beams incident from the region side B in the figure is arranged as an even number. The light beams L1 to L4 in the figure are light beams after being deflected by the optical deflector, and the incident light to the deflecting reflection surface 4a is incident from a region opposite to the sub-scanning direction of the light beam in the figure. It becomes. By arranging the folding mirrors 6 in this way, the number of the folding mirrors 6 slightly increases, but the scanning line bending direction on the scanned surface can be made to coincide in all the light beams. As a result, good color misregistration correction is possible even when scanning line bending occurs due to temperature fluctuations.

FIG. 9 is a diagram for explaining another embodiment.
In the figure, the folding positions of the light beams L1 and L2 are different from the previous embodiment.
Of each light beam directed to the corresponding scanned surface 7, the light beam directed to the scanned surface 7 of ST 4 farthest from the optical deflector 4 is turned back in the sub-scanning direction to be guided to the corresponding scanned surface 7. It is desirable that the number of mirrors 6 be equal to or less than the number of folding mirrors 6 arranged in the optical path of the light beam directed to the other scanned surface 7.
As described in the previous embodiment, after being deflected by the optical deflector 4, the light beam L 4 closest to the scanned surface 7 in the sub-scanning direction is directed toward the corresponding scanned surface 7, and the optical deflector 4. The optical scanning device 4 can be miniaturized by folding back in a direction approaching the corresponding scanned surface 7 at the closest position (position corresponding to ST1). Further, among the respective light beams directed to the corresponding scanned surface 7, the light beam directed to the scanned surface 7 of ST 4 farthest from the optical deflector 4 is directed in the sub-scanning direction to be guided to the corresponding scanned surface 7. The number of the folding mirrors 6 is equal to or less than the number of the folding mirrors 6 arranged in the optical path of the light beam toward the other scanning surface 7 (one in the example in the figure, and two for each of the other beams). This makes it possible to set the optical path length from the optical deflector 4 to the deflecting / reflecting surface 7 to be the shortest.

When the number of folding mirrors 6 of the light beam guided to the photoconductor 7 as the scanning surface of ST4 farthest from the optical deflector 4 increases, the optical path lengths of the deflection reflecting surface 4a of the optical deflector 4 and the scanned surface 7 are increased. It becomes long and the optical scanning device becomes large. The other light beams directed toward the scanned surface 7 can be guided to the corresponding scanned surface 7 by being sequentially folded by the folding mirror 6. However, if the optical path length is long, it is necessary to increase the number of the folding mirrors 6. For example, the optical scanning device is not only enlarged, but it is difficult to provide a low-cost optical scanning device. As in the present invention, the above problem can be solved by minimizing the number of folding mirrors 6 of the light beam directed to the photoconductor 7 of ST4 farthest from the optical deflector 4 and shortening the optical path length.
Further, among the respective light beams traveling toward the scanned surface 7, the light beam L traveling toward the scanned surface 7 of ST 4 farthest from the optical deflector 4 is deflected by the optical deflector 4 and then sub-beamed. Since the light beam L4 closest to the surface to be scanned 7 in the scanning direction is a light beam deflected to the opposite side in the sub-scanning direction with respect to the normal line of the deflection reflection surface 4a of the optical deflector 4, the color shift It is possible to achieve downsizing of the optical scanning device while achieving reduction.

  As described above, in order to align the scanning line bending direction, it is necessary to optimally set the number of folding mirrors to be an even number and an odd number. It is difficult to reduce the number of turns of the light beam L heading toward the scanning surface 7 of ST1 that is physically close to the optical deflector 4 without changing the optical path length. That is, as in the present embodiment, the number of the folding mirrors 6 corresponding to the light beam L directed to the photoconductor 7 of ST4 farthest from the optical deflector 4 is minimized, that is, an odd number (one in this embodiment). And the light beam L4 closest to the scanned surface 7 in the sub-scanning direction after being deflected by the optical deflector 4, the sub-scanning direction with respect to the normal line of the deflection reflection surface 4a of the optical deflector 4 By using the light beam deflected to the opposite side, it is possible to provide a downsized optical scanning device while matching the direction of the scanning line bending. At this time, it goes without saying that the light beam L4 closest to the surface to be scanned 7 in the sub-scanning direction needs to be in the above embodiment.

  Further, as in the present embodiment, the light beam L guided to the photosensitive member ST4 farthest from the light deflector 4 is the light beam L1 farthest from the scanned surface 7 after being deflected by the light deflector 4, and The direction of folding is on the scanning surface 7 side, and the number of folding mirrors 6 is one, so that the optical scanning device can be further miniaturized, and the light beam L1 having a large incidence of scanning lines and a large oblique incident angle. And the scanning line bending direction of L4 can be made to coincide with each other, so that it is possible to provide a small optical scanning device with reduced color misregistration.

FIG. 10 is a diagram showing a structure of a folding mirror applicable to the present invention. FIG. 4A is a main part optical path diagram, and FIG. 4B is a partially enlarged view.
Among the folding mirrors 6 in the sub-scanning direction arranged between the deflecting / reflecting surface 4a and the corresponding scanned surface 7, at least opposite to the reflection direction of the deflected and reflected light beam L and the sub-scanning direction. The folding mirror 6 arranged so that the adjacent light beam L ′ toward the scanned surface 7 passes is chamfered at least on the side through which the light beam L ′ passes.
When the angle of oblique incidence on the deflecting / reflecting surface 4a increases, various aberrations deteriorate and optical performance deteriorates. Specifically, beam spot diameter deterioration due to wavefront aberration deterioration, scanning line bending increase, and the like can be mentioned. From the viewpoint of optical performance and downsizing of the optical scanning device, it is desirable to set the oblique incident angle as small as possible.

  When the oblique incident angle is reduced, it becomes difficult to separate the light beams L on the corresponding scanned surfaces 7. In particular, as shown in the figure, a folding mirror that separates light beams traveling toward different scanning surfaces, that is, at least oppositely reflected in the sub-scanning direction with respect to the reflection direction of the light beam (for example, L2) that is deflected and reflected. The folding mirror (for example, 6-2) arranged so that the light beam (for example, L1) toward the scanning plane 7 passes needs to widen the interval between the light beams L by the thickness of the mirror. Increasing the interval between the light beams L is not preferable because it increases the oblique incident angle. Therefore, in the present embodiment, at least the hatched portion in the figure is chamfered. As a result, the problem is solved, and the oblique incident angle can be set small. Of course, in other folding mirrors 6 (for example, 6-3 and 6-4), if the relationship with the other light beams L is the same, the chamfering is performed in the same manner. By chamfering in this way, the oblique incident angle can be set smaller, the occurrence of scanning line bending can be reduced, and an optical scanning device with good color misregistration correction can be provided.

FIG. 11 is a diagram showing an example of a light source unit constituting a multi-beam light source apparatus applicable to the present invention.
In the drawing, 403 and 404 are semiconductor lasers as light sources, 405 is a base member, 406 and 407 are pressing members, 408 and 409 are collimating lenses, 410 is a holder member, 411 is a mounting wall of an optical housing, 412 is a screw, 413 414 is a screw, 415 is an aperture, 611 is a spring, 612 is a stopper member, and 613 is an adjusting screw.
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 sources. The beam may be scanned on the surface of the photoconductor at the same time. 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.

  The semiconductor lasers 403 and 404 are individually fitted into fitting holes 405-1 and 405-2 (not shown) formed on the back side of the base member 405, respectively. The fitting holes 405-1 and 405-2 are inclined at a predetermined angle in the main scanning direction, in the embodiment, about 1.5 °, and the semiconductor lasers 403 and 404 fitted in the fitting holes are also main. It is inclined about 1.5 ° in the scanning direction. The semiconductor lasers 403 and 404 have notches formed in the cylindrical heat sink portions 403a and 404a, and the projections 406a and 407a formed in the central round holes of the holding members 406 and 407 are formed in the notches of the heat sink portion. 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. The collimating lenses 408 and 409 are adjusted in the direction of the optical axis along the outer circumferences of the semicircular mounting guide surfaces 405b and 405c 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 example, since the light beams from the respective semiconductor lasers are set to intersect within the main scanning plane, the fitting holes 405a and 405b and the semicircular mounting guide surfaces 405c and 405d are formed along the light beam direction. Tilt to form. By engaging the cylindrical engaging portion 405c of the base member 405 with the holder member 410 and passing the screws 413 and 414 through the through holes 410b and 410c and screwing into the screw holes 405e and 405f, the base member 405 becomes the holder member. It is fixed to 410 and constitutes a light source unit.

The holder 410 of the light source unit has a cylindrical portion 410 a fitted in a reference hole 411 a 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 to insert the stopper member 612 into the cylindrical projection 410. Is held in close contact with the back side of the mounting wall 411, thereby holding the light source unit. 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 around the center of the cylindrical portion of the light source unit. An adjustment screw 613 provided to lock the rotational force of the light source unit is provided, and the adjustment unit 613 advances and retracts to rotate the entire unit in the θ direction around the optical axis to adjust the pitch. It is configured to be able to. An aperture 415 is disposed in front of the light source unit, and the aperture 415 is provided with a slit 415a corresponding to each semiconductor laser, and is configured to be attached to an optical housing to define an emission diameter of the light beam.
As the semiconductor laser, a semiconductor laser array having a plurality of light emitting points may be used. Needless to say, a plurality of semiconductor laser arrays may not be provided and a multi-beam may be formed independently. By using a multi-beam light source device that emits multiple light beams as the light source device for an optical scanning device, high-density writing or high speed can be achieved without increasing the rotational speed of the optical deflector, resulting in low power consumption. An optical scanning device that can realize high image quality and high speed can be realized.

FIG. 12 shows an image forming apparatus to which the present invention is applied.
In the figure, reference numeral 8 denotes a charging charger, 9 denotes an optical scanning optical system, 10 denotes a developing device, 11 denotes a transfer charger, 12 denotes a cleaning device, 13 denotes a paper feeding cassette, 14 denotes a paper feeding roller, 15 denotes a transporting roller, 16 denotes Registration roller, 17 is a conveyance belt, 18 and 19 are belt support rollers, 20 is a belt charger, 21 is a belt separation charger, 22 is a static elimination charger, 23 is a belt cleaning device, 24 is a fixing device, 25 is a discharge roller, Reference numeral 26 denotes a paper discharge tray.
An embodiment of an image forming apparatus using an optical scanning device according to the present invention will be described with reference to FIG.
The present embodiment is an example in which the optical scanning device according to the present invention is applied to a tandem type full-color laser printer. In the drawing, a conveying belt 17 for conveying a transfer sheet S fed from a sheet feeding cassette 13 arranged in a horizontal direction is provided on the lower side in the apparatus. On the conveying belt 17, a photosensitive member 7Y for yellow Y, a photosensitive member 7M for magenta M, a photosensitive member 7C for cyan C, and a photosensitive member 7K for black K are provided from the upstream side in the conveying direction of the transfer paper S. They are arranged at regular intervals in order. Hereinafter, subscripts Y, M, C, and K are appropriately added to the reference numerals for distinction. These photoreceptors 7Y, 7M, 7C, and 7K are all formed to have the same diameter, and process members that perform each process in accordance with the electrophotographic process are sequentially disposed around the photoreceptors.

  Taking the photoconductor 7K as an example, a charging charger 8K, an optical scanning optical system 9K, a developing device 10K, a transfer charger 11K, a cleaning device 12K, and the like are sequentially arranged. The same applies to the other photoconductors 7Y, 7M, and 7C. That is, in the present embodiment, the surfaces of the photoconductors 7Y, 7M, 7C, and 7K are used as the scan surfaces or the irradiated surfaces set for the respective colors, and the optical scanning optical system is applied to each photoconductor. 9Y, 9M, 9C, and 9K are provided in a one-to-one correspondence. However, the scanning lens 5a is commonly used for M, Y, K, and C. In addition, a registration roller 16 and a belt charging charger 20 are provided around the transport belt 17 on the upstream side of the photoconductor 7Y, and are positioned on the downstream side in the rotation direction of the belt 17 with respect to the photoconductor 7K. A belt separation charger 21, a charge removal charger 22, a belt cleaning device 23, and the like are provided in this order. Further, a fixing device 24 is provided downstream of the belt separation charger 21 in the transfer paper conveyance direction, and is connected to a paper discharge tray 26 by a paper discharge roller 25.

In such a schematic configuration, for example, in the full color mode (multiple color mode), each of the photoreceptors 7Y, 7M, 7C, and 7K is based on image signals of colors Y, M, C, and K, respectively. By the optical scanning of the light beam by the optical scanning devices 9Y, 9M, 9C, and 9K, electrostatic latent images corresponding to the respective color signals are formed on the respective photosensitive member surfaces. These electrostatic latent images are developed with color toners by the corresponding developing devices to become toner images, and are sequentially transferred onto the transfer paper S that is electrostatically attracted onto the transport belt 17 and transported. A full color image is formed on the transfer paper S by being superimposed. This full-color image is fixed by the fixing device 24 and then discharged to a discharge tray 26 by a discharge roller 25.
This figure is a schematic diagram for explanation, and an optimal layout for miniaturization is not taken. However, by using the optical scanning device according to the embodiment of the present invention, a low-power consumption, low-cost, small-sized image forming apparatus and full-color image forming apparatus that can ensure high-quality image reproducibility without color misregistration are realized. be able to.

It is a figure for demonstrating one Embodiment of this invention. It is a figure for demonstrating one Embodiment of this invention. It is a figure for demonstrating the difference of the perpendicular incidence of a light beam with respect to a deflection surface, and oblique incidence. It is a figure for demonstrating the relationship between a 2nd scanning lens and a scanning light beam. It is a figure for demonstrating the well-known example regarding arrangement | positioning of a folding mirror. It is a figure for demonstrating another well-known example. It is a figure for demonstrating other embodiment of this invention. It is a figure which shows the optical system which arranges all the investigation line bends in the same direction. It is a figure for demonstrating other embodiment. It is a figure which shows the structure of the folding mirror which can be applied to this invention. It is a figure which shows the example of the light source unit which comprises the multi-beam light source device which can be applied to this invention. 1 is a diagram illustrating an image forming apparatus to which the present invention is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 4 Optical deflector 5 Scan lens 6 Folding mirror 7 Photosensitive body as scanning surface

Claims (10)

  A plurality of light source devices each emitting a light beam, a light deflector for deflecting and scanning each light beam, a scanning optical system having at least one scanning lens, and a plurality of scanned surfaces, In the optical scanning device in which each light beam is deflected by the same deflecting reflection surface of the optical deflector and then condensed on different scanned surfaces by the scanning optical system, all the light beams are the optical deflection. The scanning lens having an angle with respect to the normal of the reflecting surface of the detector in the sub-scanning direction and at least closest to the optical deflector of the scanning optical system is shared by all the light beams and is deflected by the optical deflector. After that, the light beam closest to the scanned surface in the sub-scanning direction is separated toward the corresponding scanned surface at a position closest to the optical deflector in a direction approaching the corresponding scanned surface. Optical scanning characterized by Location.   2. The optical scanning device according to claim 1, wherein, among the plurality of light beams, a light beam directed to a surface to be scanned farthest from the optical deflector is guided in a sub-scanning direction for guiding the light beam to the corresponding surface to be scanned. An optical scanning device characterized in that the number of folding mirrors is equal to or less than the number of folding mirrors arranged in the optical path of a light beam directed to another surface to be scanned.   3. The optical scanning device according to claim 2, wherein the light beam directed to the scanning surface farthest from the optical deflector is deflected by the optical deflector and is then closest to the scanning surface in the sub-scanning direction. An optical scanning device characterized in that the optical beam is deflected to the opposite side in the sub-scanning direction with respect to the normal line of the deflecting reflection surface of the optical deflector.   4. The optical scanning device according to claim 1, wherein the light beam traveling toward the scanning surface farthest from the optical deflector is in a direction approaching the corresponding scanning surface at a position farthest from the optical deflector. An optical scanning device which is folded.   5. The optical scanning device according to claim 1, wherein among light beams directed to different scanned surfaces, at least a light beam closest to the scanned surface and a farthest light beam in the sub-scanning direction are An optical scanning device characterized in that the difference in the number of folding mirrors for guiding to the surface to be scanned is an odd number.   6. The optical scanning device according to claim 1, wherein a light beam deflected and scanned in one region in the sub-scanning direction across the normal line of the deflection reflection surface of the optical deflector, and the other region An optical scanning device characterized in that the difference in the number of folding mirrors corresponding to the light beam deflected and scanned is an odd number.   7. The optical scanning device according to claim 1, wherein at least one of the folding mirrors in the sub-scanning direction arranged between the deflection reflection surface and the corresponding scanned surface is deflected and reflected. The folding mirror arranged so that the light beam directed to the different scanning surface passes on the opposite side with respect to the reflection direction of the light beam and the sub-scanning direction has at least the side on which the light beam directed to the different scanning surface passes. An optical scanning device which is chamfered.   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 light source device.   An image forming apparatus comprising the optical scanning device according to claim 1 as means for performing an exposure process of an electrophotographic process.   The image forming apparatus according to claim 9, wherein the surface to be scanned has at least four photoconductors and can form a color image.

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