JP2006030492A - Optical scanning device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus and an optical scanning device in which a plurality of faces to be scanned are irradiated with light beams and a color slurring due to a bend of scanning line is efficiently corrected. <P>SOLUTION: The optical scanning device 4 radiates light beams L1 and L2 toward a plurality of faces to be scanned, respectively. Adjustment means 50A and 50B are provided so as to adjust the variation in the bend of scanning lines of the plurality of light beams L1 and L2 on the plurality of faces to be scanned. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, or a complex machine thereof, and an optical scanning device installed therein, and more particularly to a plurality of images for forming images of two or more colors. The present invention relates to an optical scanning device and an image forming apparatus provided with a light source.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a parallel plate (transparent member) is installed in the optical path of an optical scanning device in order to correct scanning line bending in a latent image formed on an image carrier. A technique is known (for example, refer to Patent Document 1).

The optical scanning device is a device that performs an exposure process in the image forming apparatus.
Specifically, in an optical scanning device, a light beam emitted from a light source is deflected by a rotating polygon mirror (optical deflector) and then directed to a surface to be scanned on a photosensitive drum (image carrier) by an imaging optical system. And a light spot is formed on the surface to be scanned. Further, the light spot on the surface to be scanned is scanned in the scanning direction by the optical scanning device, and the photosensitive drum is rotated in the sub-scanning direction (a direction orthogonal to the scanning direction), so that the photosensitive drum is placed on the photosensitive drum. A desired electrostatic latent image is formed.

  Here, a scanning line (a latent image formed by scanning a light beam in the scanning direction) formed on the surface to be scanned is in the sub-scanning direction due to an optical element mounting error or component error in the optical scanning device. It is known that a phenomenon (hereinafter referred to as “scan line bending”) occurs. When the degree of scanning line bending is poor, unacceptable bending occurs in the scanning direction even in the toner image that is visualized in the development process after the exposure process, and the image quality of the output image is degraded.

  In Patent Document 1, etc., a scanning line on a scanned surface is provided by providing a parallel plate that can rotate in the sub-scanning direction with the scanning direction as a rotation axis in the optical path of the light beam from the optical deflector to the scanned surface. A technique for correcting the bending is disclosed. In other words, by tilting a parallel plate installed perpendicular to the optical axis by a predetermined angle with respect to the optical axis, the scanning line of the scanning line formed on the surface to be scanned by the light beam after passing through the parallel plate is deformed. Change. Therefore, the scanning line bending is corrected by adjusting the rotation angle of the parallel plate when the scanning line bending occurs.

  Patent Document 2 discloses a technique for limiting the position and characteristics (transmittance) of parallel plates installed in the optical path of an optical scanning device for the purpose of efficiently correcting scanning line bending. ing.

Japanese Patent No. 2713625 JP 2003-121773 A

  In the conventional optical scanning device described above, it is difficult to efficiently correct “color misregistration” due to scanning line bending in an image forming apparatus that forms an image of two or more colors.

Details are as follows.
In a color image forming apparatus such as a color copying machine or a color printer, toner images of a plurality of colors (four colors Y, M, C, and BK in the case of full color) are formed on a transfer material (or an image carrier). Overlaid. At this time, the exposure process in the optical scanning device is performed for each image formation of a plurality of colors. That is, when four color images are formed, light beams are respectively emitted from four light sources, and each light beam is irradiated onto each of the four scanned surfaces through respective optical paths. Thus, latent images corresponding to the respective colors are formed on the four scanned surfaces.

  Therefore, when the degree of scanning line bending (the amount of scanning line bending) differs for each of a plurality of colors, “color shift” occurs in a color image obtained by superimposing toner images of respective colors visualized in the development process. Will occur. That is, a phenomenon in which the scanning lines of a plurality of colors do not overlap cleanly occurs.

  In order to solve the color misregistration in such a color image forming apparatus, when the techniques of the above-mentioned Patent Document 1 and Patent Document 2 are used, rotatable parallel plates are respectively installed in a plurality of optical paths in the optical scanning device. Thus, each parallel plate is operated so that the scanning line bending amount on each scanned surface becomes zero.

As a result of repeated research, the inventor of the present application has come to know that there are three demerits in color misregistration correction using a conventional parallel plate.
One of them is that there is a limit to the amount of scanning line bending corrected by the rotation adjustment of the parallel plates. Specifically, the amount of correction for scanning line bending varies depending on the magnification of the imaging optical system, the thickness of the parallel plate, the refractive index, and the like. However, there is a limit to the amount of correction. Specifically, when a parallel plate having a thickness (thickness in the optical axis direction) of 3 mm and a refractive index of about 1.5 is used, the state perpendicular to the optical axis of the light beam is used as a reference. As a result, the scanning line bending amount that can be corrected within a range of ± 45 ° reaches the limit. Therefore, it is difficult to make the scanning line bending amount zero for all the corrections by the plurality of parallel plates.

The second disadvantage is that the position of the scanning line is shifted in the sub-scanning direction by adjusting the rotation of the parallel plate. The amount of positional deviation in the sub-scanning direction is very sensitive to the rotation angle of the parallel plate. Specifically, when the above-described parallel flat plate (thickness 3 mm, refractive index 1.5) is rotated within a range of ± 45 °, a positional deviation amount of ± several mm is generated. When the amount of positional deviation is large, the light beam may be “scratched”. When “deletion” occurs, the light amount of the light spot on the surface to be scanned decreases and the spot diameter increases, resulting in image quality degradation in the output image.
When operating each parallel plate so that the amount of bending of the scanning line on each scanned surface becomes 0, an operation that increases the rotation angle is likely to occur, which increases the possibility that the amount of positional deviation increases. There is also a high possibility that image quality deterioration will occur due to “reb”.

The third disadvantage is that the image formation position of the light spot is shifted in the optical axis direction by adjusting the rotation of the parallel plate. Such a shift in the imaging position of the light spot means an optimal shift in the focal position, and the light spot becomes thick and causes image quality degradation. The amount of image formation position shift depends on the thickness of the parallel plate. When the image formation position shift amount increases, the light spot particularly becomes noticeably thick in the sub-scanning direction. The amount of image formation position shift accompanying the rotation adjustment of the parallel plate needs to be suppressed to ± 1.5 mm at the maximum in consideration of factors due to the mounting error of the optical element and the component error. In order to suppress the image formation position shift amount in such a range, it is necessary to suppress the thickness of the parallel plate to 5 mm or less.
In the case where each parallel plate is operated so that the amount of scanning line bending on each scanned surface becomes 0, the thickness of each parallel plate is increased in order to avoid an operation that increases the rotation angle. When set, there is a high possibility that the image formation position shift amount described above becomes large and the image quality is deteriorated.

In addition, as a technique for correcting the scanning line bending without using the parallel plate described above, an optical element (imaging optical system) installed in the optical path is decentered or deformed, or a folding mirror installed in the optical path is used. A method of bending is disclosed (for example, refer to JP-A-7-230051, JP-A-9-33846, etc.).
However, when the imaging optical system composed of one lens is decentered and deformed, there is a high possibility that other optical performances will deteriorate even if the scanning line bending is corrected. In addition, even when the folding mirror installed in the optical path is bent, it is difficult to select a target folding mirror, and there is a high possibility that deterioration in optical performance other than scanning line bending will increase.

  The present invention has been made to solve the above-described problems, and is an apparatus that irradiates a light beam toward a plurality of scanned surfaces, and efficiently corrects “color misregistration” due to scanning line bending. It is an object of the present invention to provide an optical scanning device and an image forming apparatus that can be used.

As a result of repeated researches to solve the above problems, the present inventor has come to know the following matters.
That is, in a color image forming apparatus provided with an optical scanning device that irradiates light beams toward a plurality of scanned surfaces, correction is made so that the amount of scanning line bending on the scanned surfaces is uniformly close to zero. It is more important to adjust so that the deviation of the amount of bending of the scanning line in a plurality of scanned surfaces becomes smaller. If a plurality of scanning line bends match, no color shift will occur on the color image obtained by superimposing them. At this time, a curve in the scanning direction corresponding to the scanning line curve occurs on the color image. However, if the scanning line curve amount is not zero, the curve amount may be a color image. It will be a level that is sensually no problem for users who deal with.

  The present invention is based on the matters described above. That is, the optical scanning device according to the first aspect of the present invention is an optical scanning device that respectively irradiates a plurality of scanned surfaces with light beams. And adjusting means for adjusting the deviation of the scanning line bending amounts of the plurality of light beams on the plurality of scanned surfaces.

  According to a second aspect of the present invention, there is provided the optical scanning device according to the first aspect, wherein the adjusting means is arranged such that the scanning line bending amount of the plurality of light beams approximates a scanning line bending amount. As a means to adjust as described above.

  An optical scanning device according to a third aspect of the present invention is the optical scanning device according to the second aspect, wherein the reference scanning line bending amount is one of the scanning line bending amounts of the plurality of light beams. It is a thing.

  According to a fourth aspect of the present invention, there is provided the optical scanning device according to the second aspect, wherein the reference scanning line bending amount is an average of scanning line bending amounts of the plurality of light beams. is there.

  According to a fifth aspect of the present invention, there is provided the optical scanning device according to the second aspect, wherein the reference scanning line bending amount is approximated among the scanning line bending amounts of the plurality of light beams. The above scanning line bending amount is used.

  An optical scanner according to a sixth aspect of the present invention is the optical scanner according to any one of the first to fifth aspects, wherein the plurality of light sources respectively emit the plurality of light beams, and the plurality of light sources. An optical deflector to which the plurality of light beams emitted from the light beam are incident, and a plurality of imaging optical systems that respectively image the plurality of light beams deflected by the optical deflector on the plurality of scanned surfaces And a parallel plate that is rotatably disposed in the at least one optical path among the plurality of optical paths from the optical deflector to the plurality of scanned surfaces, with the scanning direction as a rotation axis. The means for adjusting the rotation of one or a plurality of the parallel plates is used.

  According to a seventh aspect of the present invention, in the optical scanning device according to the sixth aspect of the present invention, the parallel plate is formed so that the thickness in the optical axis direction is 5 mm or less.

  An optical scanning device according to an eighth aspect of the present invention is the optical scanning device according to the sixth or seventh aspect, wherein the parallel plate moves the rotating shaft from a state of being installed perpendicular to the optical axis. The rotation is adjusted in the range of ± 45 ° to the center.

  An optical scanner according to a ninth aspect of the present invention is the optical scanner according to any of the sixth to eighth aspects, wherein each of the plurality of imaging optical systems is a single lens. is there.

  An image forming apparatus according to a tenth aspect of the present invention includes the optical scanning device according to any one of the first to ninth aspects.

  An image forming apparatus according to an eleventh aspect of the present invention is the image forming apparatus according to the tenth aspect, wherein the plurality of scanned surfaces are formed on a single image carrier.

  An image forming apparatus according to a twelfth aspect of the present invention is the image forming apparatus according to the tenth aspect, wherein the plurality of scanned surfaces are respectively formed on a plurality of image carriers.

  In the present invention, the deviation of the scanning line bending amounts of the plurality of light beams on the plurality of scanned surfaces is adjusted to be small. Accordingly, it is possible to provide an optical scanning apparatus and an image forming apparatus that can efficiently correct “color misregistration” due to scanning line bending.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
First, the configuration and operation of the image forming apparatus and the optical scanning apparatus installed therein will be described with reference to FIGS.
FIG. 1 is an overall configuration diagram showing an image forming apparatus 1. FIG. 2 is a perspective view showing a part of the optical scanning device 4 installed in the image forming apparatus 1 of FIG. In FIG. 1, illustration of optical elements arranged in the optical path to the polygon mirror 45 is omitted. In FIG. 2, the optical elements arranged in the optical paths after the lenses 46A and 46B are not shown.

  In FIG. 1, 1 is an apparatus main body (image forming apparatus main body) of a two-color printer, 2 is a photosensitive drum as an image carrier, 3 is a first charging unit for charging the photosensitive drum 2, and 4 is image information. The optical scanning device for emitting two light beams (exposure light) L1 and L2 based on the above, 5 is a first developing unit of a two-component developing system corresponding to the first developing process, and 6 is a second developing unit corresponding to the second developing process. A charging unit, 8 is a second developing unit of a one-component developing system corresponding to the second developing step, 10 is a transferring unit that transfers a toner image formed on the photosensitive drum 2 to a transfer material P, and 11 is a photosensitive member. A cleaning unit that collects untransferred toner on the drum 2, 12 a neutralization unit that resets the surface potential on the photosensitive drum 2, 26 a registration roller pair that conveys the transfer material P toward the transfer unit 10, and 27 Transfer that guides the transfer material P after the transfer process to the fixing unit 28 Belt, 28 denotes a fixing portion, which fixes the toner image on the transfer material P after the transferring process.

  1 and 2, the optical scanning device 4 includes two light sources 41A and 41B, two coupling lenses 42A and 42B, two apertures 43A and 43B, a half mirror 48, a cylindrical lens 44, A polygon mirror 45 as an optical deflector, an imaging optical system in which two lenses 46A and 46B are integrated, a plurality of mirrors 47a to 47e, parallel flat plates 50A and 50B that are rotatably supported, and the like.

  Here, one parallel flat plate 50A is installed on the optical path of the light beam L1 emitted from the first light source 41A, and is rotated and adjusted with the scanning direction (perpendicular to the plane of FIG. 1) as the rotation axis. It is comprised so that it can do (it is adjustment of the double arrow direction of FIG. 1). The other parallel flat plate 50B is installed on the optical path of the light beam L2 emitted from the second light source 41B, and is configured to be rotationally adjustable with the scanning direction as the rotation axis (the direction of the double arrow in FIG. 1). Adjustment). When these parallel flat plates 50A and 50B are rotationally adjusted, the scanning line bending on the surface to be scanned changes.

The parallel flat plates 50A and 50B according to the first embodiment are made of a transparent material having a thickness of 5 mm or less and a high transmittance that transmits a light beam. Thereby, it is possible to reduce the image formation position shift amount on the surface to be scanned and suppress the deterioration of the image quality.
Further, the parallel flat plates 50A and 50B according to the first embodiment are rotationally adjusted so that the rotation angle is within a range of ± 45 ° from a state in which the parallel flat plates 50A and 50B are installed perpendicular to the optical axis. This will be described in detail later.

Hereinafter, an operation during image formation in the image forming apparatus will be described.
The photosensitive drum 2 is driven by a drive motor (not shown) and rotates clockwise in the drawing. First, the surface of the photosensitive drum 2 is uniformly charged at a position facing the first charging unit 3 of the scorotron charge method. Then, the surface of the photosensitive drum 2 charged by the first charging unit 3 reaches the irradiation position (the first scanned surface) of the first light beam L1. Then, an electrostatic latent image corresponding to image information of the first color (for example, black) is formed at this position. The operation of the optical scanning device 4 that forms a latent image on the photosensitive drum 2 will be described in detail later.

  Thereafter, the surface of the photosensitive drum 2 on which the latent image is formed reaches a portion (developing region) facing the first developing portion 5. Then, the toner in the two-component developer carried on the two developing rollers of the first developing unit 5 adheres to the latent image on the photosensitive drum 2 to form a first color toner image (first color). Development process.)

  Thereafter, the surface of the photosensitive drum 2 on which the first color toner image is formed is charged again at a position facing the second charging unit 6. Then, the surface of the photosensitive drum 2 charged by the second charging unit 6 reaches the irradiation position (second scanning surface) of the second light beam L2. Then, an electrostatic latent image corresponding to image information of the second color (for example, red) is formed at this position.

  Thereafter, the surface of the photosensitive drum 2 on which the second latent image is formed reaches a portion (development region) facing the second developing unit 8. Then, the toner (one-component nonmagnetic developer) carried on the developing roller of the second developing unit 8 adheres to the second latent image on the photosensitive drum 2 to form a second color toner image. (Second development step).

Thereafter, the surface of the photosensitive drum 2 on which the first color toner image and the second color toner image are formed reaches a portion facing the transfer portion 10. At this position, the two-color toner images on the photosensitive drum 2 are transferred onto the transfer material P conveyed by the registration roller pair 26.
At this time, a small amount of untransferred toner that is not transferred onto the transfer material P remains on the photosensitive drum 2.

Thereafter, the surface of the photosensitive drum 2 having untransferred toner that has passed through the transfer unit 10 reaches a portion facing the cleaning unit 11. In the cleaning unit 11, untransferred toner adhering to the drum surface is collected by the cleaning blade 11 a that contacts the photosensitive drum 2 and the cleaning roller.
Thereafter, the surface of the photosensitive drum 2 that has passed through the cleaning unit 11 reaches the static elimination unit 12. Then, the residual potential on the surface of the photosensitive drum 2 is removed here, and a series of image forming processes is completed.

  Here, the transfer material P is fed from a paper feed unit (not shown) in which a plurality of transfer materials are accommodated. The transfer material P that has reached the position of the registration roller pair 26 from the paper feeding unit is conveyed to the transfer unit 10 by the registration roller pair 26 in synchronization with the toner image on the photosensitive drum 2. As described above, the transfer unit 10 transfers the toner image onto the transfer material P.

Then, the transfer material P after the transfer process is conveyed to the position of the fixing unit 28 by the transfer belt 27 running in the direction of the arrow in FIG. The fixing unit 28 fixes the unfixed toner image on the transfer material P. Here, the transfer belt 27 traveling in the direction of the arrow is cleaned at the position of the belt cleaning unit 30 provided with a blade 30 a that contacts the transfer belt 27.
Thereafter, the transfer material P after the fixing process is discharged out of the image forming apparatus main body 1 as an output image.
Thus, a series of image forming processes is completed.

Next, the operation of the optical scanning device 4 that forms a latent image on the surface to be scanned of the photosensitive drum 2 will be described in detail. The optical scanning device 4 according to the first embodiment is of a single beam type related to image formation of two colors.
Referring to FIG. 2, when two light sources 41A and 41B (semiconductor lasers) are driven based on image data input to an image data input unit (not shown), light beams are emitted from the respective light sources 41A and 41B. L1 and L2 are injected. Here, the position of the optical axis of the first light beam L1 is set to be higher than the position of the optical axis of the second light beam L2. The light beams L1 and L2 emitted from the light sources 41A and 41B are divergent light beams. The desired light beam (weak divergent light beam, weakly converging light beam is obtained depending on the optical characteristics of the optical element installed in the optical path. A luminous flux or a parallel luminous flux).

  The light beams L1 and L2 emitted from the light sources 41A and 41B reach the positions of the apertures 43A and 43B after passing through the coupling lenses 42A and 42B, respectively. The light beams L1 and L2 reach the position of the half mirror 48 after being shaped by the apertures 43A and 43B functioning as aperture stops. Then, the first light beam L1 passes through the half mirror 48 and reaches the position of the cylindrical lens 44, and the second light beam L2 is reflected by the half mirror 48 and reaches the position of the cylindrical lens 44.

Here, the cylindrical lens 44 is a common line image forming optical system for the two light beams L1 and L2, and is formed so as to give positive power only in the sub-scanning direction without giving power in the scanning direction. Arranged.
The two light beams L1 and L2 that are transmitted through the cylindrical lens 44 and focused by receiving positive power are respectively incident on the first deflection unit 45a and the second deflection unit 45b of the polygon mirror 45 as an optical deflector. . Then, the light beams L1 and L2 reflected by the deflecting reflecting surfaces of the first deflecting unit 45a and the second deflecting unit 45b are respectively deflected at an equal angular velocity accompanying the constant speed rotation of the polygon mirror 45, and the imaging optical system. Are incident on the lenses 46A and 46B. Here, the two lenses 46A and 46B are integrated by adhesion using an ultraviolet curable resin or the like.

Thereafter, the two light beams L1 and L2 transmitted through the lenses 46A and 46B reach the photosensitive drum 2 through the respective optical paths.
Specifically, referring to FIG. 1, after passing through the lens 46A, the first light beam L1 is reflected by the first mirror 47a and the second mirror 47b, passes through the parallel plate 50A, and passes through the first plate 47A. 3 is reflected on the first scanning surface of the photosensitive drum 2 as a light spot and scanned in the scanning direction.
On the other hand, the second light beam L2 passes through the lens 46B, is then reflected by the fourth mirror 47d and the fifth mirror 47e, passes through the parallel plate 50B, and passes through the second plate 47B of the photosensitive drum 2. The light is condensed as a light spot on the surface to be scanned 2 and scanned in the scanning direction.

  In this way, the light beams L1 and L2 emitted from the two light sources 41A and 41B are simultaneously shaken in the main scanning direction by the polygon mirror 45, and the surface of the photosensitive drum 2 rotating in the sub-scanning direction is irradiated with the light beam L1. , L <b> 2, electrostatic latent images are formed at different positions on the surface of the photosensitive drum 2.

Next, characteristic adjustment means for “color misregistration” caused by scanning line bending, which is characteristic in the first embodiment, will be described.
As described above, the parallel plates 50A and 50B installed in the optical paths of the two light beams L1 and L2, respectively, change the posture with respect to the optical axis (the rotation angle with the scanning direction as the rotation axis). Thus, the scanning line bending amount of the scanning line on each scanning surface can be varied.

  In the first embodiment, when the scanning line bends occur on the two scanned surfaces of the photosensitive drum 2, the adjusting means in the first embodiment sets both the scanning line bend amounts on the two scanned surfaces so that both are close to zero. Rather than adjusting the rotation of the parallel plates 50A and 50B, adjustment is made so as to reduce the deviation of the scanning line bending amount between the two scanned surfaces. Therefore, as an adjustment case, there are a case where both the two parallel flat plates 50A and 50B are rotationally adjusted, and a case where only one of the two parallel flat plates 50A and 50B is rotationally adjusted. These are preferably selected so that the total rotation angle of the two parallel flat plates 50A and 50B becomes small and the scanning line bending amount itself becomes small.

FIG. 3 is a graph showing an example of the state before and after the deviation of the scanning line bending amount is adjusted by the adjusting means described above.
FIG. 3A is a graph showing a state before adjustment, and FIG. 3B is a graph showing a state after adjustment. In the figure, the horizontal axis indicates the image height (the position in the scanning direction, the position “0” indicates the center position), and the vertical axis indicates the position of the light spot in the sub-scanning direction. Therefore, the more the shape of the graph spreads in the vertical axis direction, the greater the amount of scan line bending.

Also, the solid line SA in FIG. 3 (A) and the solid line SA ′ in FIG. 3 (B) are graphs showing the scanning line bending by the first light beam L1, and are shown in FIGS. 3 (A) and 3 (B). The solid line SB in () is a graph showing the curve of the scanning line by the second light beam L2.
Thus, when the two scanning line bends SA and SB are relatively approximate, the two parallel flat plates 50A and 50B are rotationally adjusted (about 95 μm so that both of the scanning line bend amounts approach zero. (Adjustment is about 80 μm) and one parallel plate 50A, 50B is adjusted (about 15 μm) so that the two scanning line bends SA, SB overlap (so that the deviation becomes small). The total rotation adjustment amount of the parallel flat plates 50A and 50B is drastically reduced.

  In this example, as shown in FIG. 3B, the scanning line bend SB of the second light beam L2 is fixed and the scanning line bend SA of the first light beam L1 is adjusted (scanning line bending SA ′). ). That is, only the parallel plate 50A installed in the optical path of the first light beam L1 is rotationally adjusted.

  As described above, according to the first embodiment, the adjustment using the parallel plates 50A and 50B can be suppressed to the minimum necessary, so that the color misregistration correction due to the optical scanning curve can be efficiently performed. it can.

  When the two color toner images are black and red as in the first embodiment, both toner images are layered on the photosensitive drum 2 (or the transfer material P). There are few things. However, even in such a combination of colors, when the stripe pattern is formed in two colors in the sub-scanning direction, the color of the two color toner images is mixed due to the difference in the amount of bending of both scanning lines. . According to the configuration of the first embodiment, the scanning line bends of the two colors almost coincide with each other, and thus such color mixing can be suppressed. In the present application, a phenomenon in which color mixing occurs in a region where color mixing of toner images is not planned is defined as “color shift”.

In the first embodiment, as described above, the rotation adjustment range of the parallel plates 50A and 50B is set to a range of ± 45 °. The reason for this will be described with reference to FIG.
FIG. 4 is a graph showing the relationship between the rotation adjustment amount (rotation angle) of the parallel plates 50A and 50B and the scan line bending amount on the surface to be scanned corrected by the rotation adjustment. In FIG. 4, the horizontal axis indicates the rotation angle of the parallel plates 50A and 50B, and the vertical axis indicates the scanning line bending amount. “0” on the horizontal axis means that the incident surface of the parallel plate is in a state perpendicular to the optical axis.

  As can be seen from FIG. 4, the scanning line bending amount increases as the inclination (rotation angle) of the parallel plate with respect to the optical axis increases, but the amount is limited. Specifically, when the rotation angle of the parallel plate exceeds the range of ± 55 °, the effect of correcting the scanning line bending is lost, and the correction amount of the scanning line bending is reduced instead. Further, the scan line bending amount that can be corrected is in a range of about ± 80 μm.

If this is applied to the example of FIG. 3 described above, even if the scanning line bend SB of about 100 μm is to be corrected, the scan line bend of about 20 μm remains due to the limit of the amount of correction of the scan line bend. On the other hand, according to the deviation adjustment from FIG. 3 (A) to FIG. 3 (B) by the adjusting means of the first embodiment, the correction width is 15 μm, so the limit of the scanning line bending correction amount is limited. A sufficient effect can be obtained.
Here, the limit of the scanning line bending correction amount shown in FIG. 4 varies depending on the material and thickness of the parallel plate and the magnification of the imaging optical system. Therefore, the margin is considered in a practical range. The range of ± 45 ° was set as the rotation adjustment range of the parallel flat plates 50A and 50B.

  In the first embodiment, the rotation adjustment range of the parallel plates 50A and 50B is set to a range of ± 45 °. However, when the positional deviation of the scanning lines in the sub-scanning direction due to the rotation adjustment of the parallel plates is taken into consideration. The rotation adjustment range of the parallel flat plates 50A and 50B is preferably set to a range of ± 25 °. The reason will be described with reference to FIG.

  FIG. 5 shows the relationship between the rotation adjustment amount (rotation angle) of the parallel plates 50A and 50B and the amount by which the scanning line on the surface to be scanned is displaced in the sub-scanning direction due to the rotation adjustment (scanning line position displacement amount). It is a graph. In FIG. 5, the horizontal axis indicates the rotation angle of the parallel plates 50A and 50B, and the vertical axis indicates the scanning line position deviation amount. “0” on the horizontal axis means that the incident surface of the parallel plate is in a state perpendicular to the optical axis.

From FIG. 5, it can be seen that the scanning line positional deviation amount is very sensitive to the rotation angle of the parallel plate, and the positional deviation amount is about 1.4 mm when the rotational angle is 55 °, for example. In general, in order to surely suppress the “damage” of the light beam, the scanning line positional deviation allowable in the layout of the optical scanning device 4 is set to about ± 0.5 mm. Therefore, there is a possibility that “skipping” may occur in the positional deviation amount when the rotation angle is 55 °. From FIG. 5, since the rotation angle that satisfies the positional deviation amount of ± 0.5 mm is in the range of ± 25 °, it is preferable that the rotation adjustment range of the parallel plates 50A and 50B is in the range of ± 25 °. Recognize.
If this is applied to the example of FIG. 3 described above, the correction of 15 μm can be sufficiently performed within the adjustment range of ± 25 °, so that the amount of positional deviation of the scanning line is better than ± 0.5 mm. Can be obtained.

  In the first embodiment, the rotatable parallel plates 50A and 50B are installed in the two optical paths of the optical scanning device 4, respectively, but the parallel plate is installed only in one of the two optical paths. You can also. Such a configuration is particularly effective when the deviation of the two optical scanning curves is not so large due to the configuration of the optical scanning device 4. Even in such a case, by adjusting the rotation of one parallel plate, the deviation of the scanning line bending amount can be brought close to 0, and the same effect as in the first embodiment can be obtained.

Embodiment 2. FIG.
6 and 7, the second embodiment of the present invention will be described in detail.
FIG. 6 is a perspective view showing a main part of the image forming apparatus according to the second embodiment. The image forming apparatus of the second embodiment is different from that of the first embodiment in that it is a tandem type color image forming apparatus.

The image forming apparatus according to the second embodiment is a tandem full-color image forming apparatus. As shown in FIG. 6, four photosensitive drums 2BK, 2Y, 2M, and 2C are arranged in parallel on the intermediate transfer belt 28 in the image forming unit. Although not shown, a charging unit, a developing unit, a cleaning unit, and a charge eliminating unit are disposed on the outer periphery of the four photosensitive drums 2BK, 2Y, 2M, and 2C.
Light beams L1 to L4 emitted from four light sources (not shown) of the optical scanning device are respectively applied to the scanned surfaces (irradiation positions) of the four photosensitive drums 2BK, 2Y, 2M, and 2C. To form a latent image.
Then, a toner image of each color (black, yellow, magenta, cyan) is formed on each photosensitive drum 2BK, 2Y, 2M, 2C.

  The intermediate transfer belt 28 runs in the direction of the arrow in the drawing. Then, the toner images of the respective colors formed on the respective photosensitive drums 2BK, 2Y, 2M, and 2C are sequentially superimposed and transferred onto the intermediate transfer belt 28. Thus, a full color toner image is formed on the intermediate transfer belt 28. Thereafter, the full-color toner image formed on the intermediate transfer belt 28 is transferred onto the transfer material at the position of the second transfer portion (not shown). Thereafter, the transfer material onto which the full-color toner image has been transferred passes through a fixing process and is discharged out of the image forming apparatus as an output image.

Hereinafter, the optical scanning device according to the second embodiment will be described in detail.
The first light beam L1 emitted from the first light source sequentially passes through a coupling lens, an aperture, a half mirror, and a cylindrical lens (not shown) and enters the first deflecting unit 45a of the polygon mirror 45. The light beam L1 reflected by the first deflecting unit 45a sequentially passes through the first lens 46A, the first mirror 47a, and the second mirror 47b, and then passes through the first parallel plate 50A. Irradiated onto the surface to be scanned of the photosensitive drum 2BK for black.

  The second light beam L2 emitted from the second light source sequentially passes through a coupling lens, an aperture, a half mirror, and a cylindrical lens (not shown) and enters the second deflection unit 45b of the polygon mirror 45. Then, the light beam L2 reflected by the second deflecting unit 45b sequentially passes through the second lens 46B, the third mirror 47c, and the fourth mirror 47d, and then passes through the second parallel plate 50B. Irradiated onto the scanned surface of the photosensitive drum 2Y for yellow.

  The third light beam L3 emitted from the third light source sequentially passes through a coupling lens, an aperture, a half mirror, and a cylindrical lens (not shown) and enters the second deflecting unit 45b of the polygon mirror 45. Then, the light beam L3 reflected by the second deflecting unit 45b sequentially passes through the third lens 46C, the fifth mirror 47e, and the sixth mirror 47f, and then passes through the third parallel plate 50C. Irradiated onto the surface to be scanned of the photosensitive drum 2M for magenta.

  The fourth light beam L4 emitted from the fourth light source sequentially passes through a coupling lens, an aperture, a half mirror, and a cylindrical lens (not shown) and enters the first deflection unit 45a of the polygon mirror 45. The light beam L4 reflected by the first deflecting unit 45a sequentially passes through the fourth lens 46D, the seventh mirror 47g, and the eighth mirror 47h, and then passes through the fourth parallel plate 50D. Irradiated onto the scanned surface of the cyan photosensitive drum 2C.

Next, the “color misregistration” adjusting means in the second embodiment will be described.
Also in the second embodiment, parallel plates 50A to 50D are rotatably installed in the optical paths of the four light beams L1 to L4, respectively, with the scanning direction as a rotation axis.
When the scanning line bends occur on the scanned surfaces of the four photosensitive drums 2BK, 2Y, 2M, and 2C, the parallel flat plates 50A to 50A to reduce the deviation of the scanning line bending amount on the four scanned surfaces. Rotate and adjust 50D. At this time, the scanning line bending amount deviation is adjusted so that the scanning line bending amount is within the allowable range and the total rotation angle of the four parallel flat plates 50A to 50D becomes small.

That is, the rotation angles of the four parallel plates 50A to 50A are adjusted so that the scanning line bending amount of the four light beams L1 to L4 approaches the reference scanning line bending amount (target). The rotation is not always adjusted.)
Here, the reference scanning line bending amount may be one of the four scanning line bending amounts. In this case, one parallel plate is fixed, and the other three parallel plates are rotationally adjusted.
Further, the reference scanning line bending amount may be an average of the four scanning line bending amounts. In this case, four parallel flat plates are rotationally adjusted.
Further, the reference scanning line bending amount may be two scanning line bending amounts that are approximated among the four scanning line bending amounts. In this case, two parallel flat plates are fixed, and the other two parallel flat plates are rotationally adjusted.

FIG. 7 is a graph showing an example of a state before and after the deviation of the scanning line bending amount is adjusted by the adjusting means described above, and is a graph corresponding to FIG. 3 in the first embodiment.
A solid line SA in FIG. 7 (A) and a solid line SA ′ in FIG. 7 (B) are graphs showing the bending of the scanning line by the first light beam L1, and are in FIG. 7 (A) and FIG. 7 (B). The solid line SB is a graph showing the scanning line bending due to the second light beam L2. Further, a solid line SC in FIG. 7A and a solid line SC ′ in FIG. 7B are graphs showing the scanning line bending by the third light beam L3, and are shown in FIGS. 7A and 7B. The solid line SD in () is a graph showing the curve of the scanning line by the fourth light beam L4.

  In this example, as shown in FIG. 7B, since the scanning line curve SB of the second light beam L2 and the scanning line curve SD of the fourth light beam L4 are approximated, these are fixed and the first light beam The scanning line curve SA of the beam L1 and the scanning line curve SC of the third light beam L3 are adjusted (the scanning line curve SA ′ and the scanning line curve SC ′). That is, the parallel plate 50A installed in the optical path of the first light beam L1 and the parallel plate 50C installed in the optical path of the third light beam L3 are rotationally adjusted.

  In this way, when the four scanning line bends SA to SD are relatively approximate, rather than rotationally adjusting the four parallel plates 50A to 50D so that the four scanning line bends are all close to zero. Adjustment of the parallel plates 50A and 50C related to the other two scanning line bends SA and SC so as to overlap the two closest scanning line bends SB and SD greatly improves the efficiency of the adjustment work, and scanning. The color misregistration can be reduced within the limit of the scanning line bending correction amount with little line misregistration.

  As described above, according to the second embodiment, since the adjustment using the parallel plates 50A to 50D can be suppressed to the minimum necessary, the color misregistration correction due to the optical scanning curve can be efficiently performed. it can.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the above-described embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. Is clear. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like suitable for implementing the present invention can be achieved.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a perspective view illustrating a part of an optical scanning device installed in the image forming apparatus of FIG. 1. 3 is a graph showing a state before and after adjusting a deviation of a scanning line bending amount in the optical scanning device of FIG. 2. It is a graph which shows the relationship between the rotation angle of a parallel plate, and scanning line bending amount. It is a graph which shows the relationship between the rotation angle of a parallel plate, and scanning line position shift amount. It is a perspective view which shows the principal part of the image forming apparatus in Embodiment 2 of this invention. 7 is a graph showing a state before and after adjusting a deviation of a scanning line bending amount in the image forming apparatus of FIG. 6.

Explanation of symbols

1 image forming apparatus body (apparatus body),
2, 2BK, 2Y, 2M, 2C photosensitive drum (image carrier),
4 optical scanning device, 5 first developing section, 8 second developing section,
10 transfer section, 28 intermediate transfer belt,
41A-41D light source, 42A, 42B coupling lens,
43A, 43B aperture, 44 cylindrical lens,
45 Polygon mirror (light deflector),
45a first deflection unit, 45b second deflection unit,
46A-46D lens (imaging optical system),
47a-47h mirror, 48 half mirror,
50A-50D Parallel plate, L1-L4 Light beam.

Claims (12)

An optical scanning device that respectively irradiates a plurality of scanned surfaces with light beams,
An optical scanning apparatus comprising: an adjusting unit configured to adjust a deviation of scanning line bending amounts of a plurality of light beams on the plurality of scanned surfaces. The optical scanning apparatus according to claim 1, wherein the adjusting unit is a unit that adjusts the scanning line bending amount of the plurality of light beams so as to approach a reference scanning line bending amount. The optical scanning device according to claim 2, wherein the reference scanning line bending amount is one of the scanning line bending amounts of the plurality of light beams. 3. The optical scanning device according to claim 2, wherein the reference scanning line bending amount is an average of scanning line bending amounts of the plurality of light beams. 3. The optical scanning device according to claim 2, wherein the reference scanning line bending amount is two or more scanning line bending amounts approximated among the scanning line bending amounts of the plurality of light beams. A plurality of light sources that respectively emit the plurality of light beams;
An optical deflector on which the plurality of light beams emitted from the plurality of light sources are incident;
A plurality of imaging optical systems that respectively image the plurality of light beams deflected by the optical deflector onto the plurality of scanned surfaces;
A parallel plate that is rotatably installed with a scanning direction as a rotation axis in at least one of the plurality of optical paths from the optical deflector to the plurality of scanned surfaces;
The optical scanning device according to claim 1, wherein the adjusting unit is a unit that rotates and adjusts one or a plurality of the parallel plates. The optical scanning device according to claim 6, wherein the parallel plate is formed so that a thickness in an optical axis direction is 5 mm or less. 8. The optical scanning according to claim 6, wherein the parallel plate is rotationally adjusted in a range of ± 45 ° about the rotation axis from a state in which the parallel plate is installed perpendicularly to the optical axis. apparatus. 9. The optical scanning apparatus according to claim 6, wherein each of the plurality of imaging optical systems is a single lens. An image forming apparatus comprising the optical scanning device according to claim 1. The image forming apparatus according to claim 10, wherein the plurality of scanned surfaces are formed on a single image carrier. The image forming apparatus according to claim 10, wherein each of the plurality of scanned surfaces is formed on a plurality of image carriers.

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