JP2010256576A - Optical scanner and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical scanner in which reflection light produced on a scanning lens caused by incidence of a light beam distributed to a face to be scanned is prevented from reaching other faces to be scanned, thus the occurrence of an image failure due to the reflection light is prevented, and to provide an image forming apparatus. <P>SOLUTION: A second scanning lens 46c is tilted in the direction denoted by an arrow X centering with a rotary axis 53 provided along a scanning direction as an axis so that flare light B2 is tilted with respect to incident light of beam light D3 which is deflected and scanned with a polygon mirror 44 and passed through a first scanning lens 45b, and does not reach a photoreceptor drum 1b, and so that the scanning curvature of the light beam D3 is set within a predetermined region, thus the flare light B2 is prevented from reaching the photoreceptor drum 1b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical scanning device used for image forming apparatuses such as a printer, a copying machine, and a facsimile machine, which scans a beam of light and writes and forms an image. The present invention relates to an optical scanning device suitably used for a color image forming apparatus, and an image forming apparatus including the same.

  2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system such as a copying machine or a printer, an optical scanning that scans a surface of a photosensitive drum uniformly charged by a charging unit with a light beam modulated based on input image data. An electrostatic latent image formed by the optical scanning device is developed into a toner image by a developing unit, and image formation is performed by transferring the toner image onto a recording sheet or the like. Yes.

  By the way, with the speeding up of the color image forming apparatus, for example, four photosensitive drums are arranged in the conveyance direction of the recording paper, and a plurality of optical scanning devices corresponding to the respective photosensitive drums are simultaneously exposed to electrostatically. After creating latent images and developing these electrostatic latent images with developing means using different color developers such as yellow, magenta, cyan and black, these toner images are sequentially superimposed on the same recording paper Tandem digital copiers and laser printers that transfer and transfer color images have been put to practical use.

  Such a 4-drum tandem system is advantageous for high-speed printing because both color and monochrome can be output at the same speed. However, when four optical scanning devices corresponding to four photosensitive drums are provided, the apparatus becomes large. There was a problem. Therefore, in recent years, a plurality of light beams emitted from light sources provided for each color are deflected by a single rotating polygonal mirror (polygon mirror) in response to a request for downsizing of an image forming apparatus, and each light beam is passed through a scanning lens. There has been proposed an optical scanning device that conducts exposure scanning by being guided to different photoreceptors.

  However, in the optical scanning device as described above, when a plurality of deflected light beams pass through the scanning lens before reaching each photosensitive drum, the light beam is reflected on the surface of the scanning lens. The reflected light, that is, flare light, arrives at the other photosensitive drums and causes image defects. Further, in order to cope with the above-described miniaturization, when a plurality of light beams are deflected by one polygon mirror, the configuration of the optical scanning device becomes more complicated, and image defects due to the influence of flare light are particularly likely to occur.

  Therefore, in Patent Document 1, in an optical scanning device (optical scanning device) that deflects a plurality of light beams (beam light) by different deflection surfaces of the same deflector (polygon mirror), the lens surface of one scanning lens system is used. Proposed a method that cuts off flare light and enables high-quality image formation with simple parts such as plastic lenses by providing a light blocking member that prevents the reflected flare light from entering the other scanning lens system. Has been.

JP 2003-202512 A

  However, in the method of Patent Document 1, only a method for suppressing the influence of flare light generated by the scanning lens on the polygon mirror side among the scanning lenses arranged between the polygon mirror and the photosensitive drum is disclosed. Not too much. Since the scanning lens on the polygon mirror side has a smaller radius of curvature than the scanning lens on the photosensitive drum side, the flare light generated by the scanning lens is more divergent than the flare light generated by the scanning lens on the photosensitive drum side. It is easy to become.

  For this reason, the flare light generated by the scanning lens on the photosensitive drum side having a large radius of curvature is more likely to reach other photosensitive drums than the flare light generated by the scanning lens on the polygon mirror side, resulting in poor image quality. May have a major impact. However, there is no description in Patent Document 1 regarding preventing flare light generated by the scanning lens on the photoconductor side having a large curvature radius from reaching another photoconductor drum. Thus, conventionally, a method for preventing the influence of flare light on image defects has not been sufficient.

  In view of the above problems, the present invention prevents the reflected light generated by the scanning lens from reaching the other scanned surface due to the incidence of the light beam distributed on the scanned surface, and prevents image defects caused by the reflected light. An object of the present invention is to provide an optical scanning apparatus and an image forming apparatus capable of preventing the occurrence.

  In order to achieve the above object, the present invention provides a plurality of light source units, a polygon mirror that deflects and scans a plurality of light beams emitted from the plurality of light source units, and each of the light beams that are deflected and scanned by the polygon mirrors. A plurality of scanning lenses arranged in an optical path, and an optical scanning device that scans the surface to be scanned by imaging the beam light deflected and scanned by the polygon mirror by the plurality of scanning lenses. At least one scanning lens among the scanning lenses is such that the reflected light is inclined with respect to the incident light of the beam light deflected and scanned by the polygon mirror so that the reflected light does not reach the surface to be scanned and does not reach the surface to be scanned. It is characterized in that it is tilted about the main scanning direction so that the scanning curve of the distributed light beam is set within a predetermined range.

  Further, the present invention is characterized in that the predetermined range is within 2 pixels.

  In the invention, it is preferable that the at least one scanning lens is a scanning lens disposed on the scanned surface side.

  In the invention, it is preferable that the curvature of the first lens surface on the polygon mirror side in the at least one scanning lens is larger than the curvature of the second lens surface on the scanned surface side.

  In the invention, it is preferable that the first lens surface is a flat surface.

  According to the present invention, at least one of the first and second lens surfaces is a diffraction grating surface.

  In the present invention, the plurality of scanning lenses may include a first scanning lens on which the beam light deflected and scanned by the polygon mirror is incident, and a first beam on which the beam light separated after passing through the first scanning lens is incident. And the at least one scanning lens is the second scanning lens.

  The present invention also provides an image forming apparatus on which the optical scanning device having the above-described configuration is mounted.

  According to the first configuration of the present invention, at least one scanning lens among a plurality of scanning lenses arranged in each optical path of the beam light deflected and scanned by the polygon mirror is used for the beam light deflected and scanned by the polygon mirror. The main scanning direction is set so that the reflected light is inclined with respect to the incident light, does not reach the surface to be scanned, and the scanning curve of the beam light distributed to the surface to be scanned is set within a predetermined range. By tilting as an axis, it is possible to prevent the reflected light generated by the scanning lens due to the incidence of the beam light from reaching another surface to be scanned. Thereby, it is possible to prevent the occurrence of image defects due to the influence of reflected light.

  Further, according to the second configuration of the present invention, in the optical scanning device of the first configuration, the predetermined range is set to 2 pixels or less, so that the color shift and the color change of the image are more effectively performed. Can be prevented.

  According to the third configuration of the present invention, in the optical scanning device of the first or second configuration, the at least one scanning lens is a scanning lens disposed on the scanning surface side. Even if the reflected light is arranged at a position where it can easily reach another surface to be scanned, such arrival can be prevented, so that it is possible to more effectively prevent the occurrence of image defects due to the influence of the reflected light.

  According to the fourth configuration of the present invention, in the optical scanning device of any one of the first to third configurations, the curvature of the first lens surface on the polygon mirror side in the at least one scanning lens is By making the curvature larger than the curvature of the second lens surface on the scanned surface side, even if the reflected light easily reaches the other scanned surface, it can be prevented from reaching, so the influence of the reflected light. It is possible to more effectively prevent the occurrence of image defects due to.

  Further, according to the fifth configuration of the present invention, in the optical scanning device having the fourth configuration described above, the first lens surface is a flat surface, so that the reflected light can easily reach another surface to be scanned. Even with the lens surface configuration, such arrival can be prevented, and image defects due to the influence of reflected light can be further effectively prevented.

  According to the sixth configuration of the present invention, in the optical scanning device having the fourth or fifth configuration, at least one of the first and second lens surfaces is a diffraction grating surface. Thus, the light beam can be split into a desired wavelength and distributed to the surface to be scanned.

  Further, according to the seventh configuration of the present invention, in the optical scanning device having the first to sixth configurations, the first scanning lens on which the light beams deflected and scanned by the polygon mirror are incident on the plurality of scanning lenses. And a second scanning lens on which the beam light separated after passing through the first scanning lens is incident, and the second scanning lens is used as the second scanning lens, thereby providing the second scanning lens. The incident path of the beam light to the scanning lens is limited, and even if the reflected light easily reaches the other surface to be scanned, such an arrival can be prevented, so that the image defect due to the influence of the reflected light is more effective. Can be prevented.

  Further, according to the eighth configuration of the present invention, a high-quality image formation in which image defects are prevented can be achieved by employing the image forming apparatus including the optical scanning device having any one of the first to seventh configurations. Is possible.

1 is a schematic diagram showing an overall configuration of a tandem color image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention. The top view which shows the internal structure of the optical scanner which concerns on this embodiment Side surface sectional view showing the internal structure of the optical scanning device according to the present embodiment FIG. 4 is a schematic diagram linearly showing an optical path from a polygon mirror to a photosensitive drum, and showing an optical path of flare light when the second scanning lens is not tilted. FIG. 4 is a schematic diagram linearly showing an optical path from a polygon mirror to a photosensitive drum, and showing an optical path of flare light when the second scanning lens is tilted downward. FIG. 4 is a schematic diagram linearly showing an optical path from a polygon mirror to a photosensitive drum, and showing an optical path of flare light when the second scanning lens is tilted upward.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus equipped with an optical scanning device according to an embodiment of the present invention. Here, a tandem color image forming apparatus is shown. In the main body of the color image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  The image forming portions Pa to Pd are provided with photosensitive drums (scanned surfaces) 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and further drive means (not shown). 1), an intermediate transfer belt 8 that rotates clockwise in FIG. 1 is provided adjacent to each of the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1 a to 1 d are sequentially transferred onto the intermediate transfer belt 8 that moves while contacting the photosensitive drums 1 a to 1 d, and then transferred onto the transfer paper P by the transfer roller 9. The toner image is transferred onto the transfer paper P at the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the transfer roller 9 via the paper supply roller 12a and the registration roller 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used.

  Next, the image forming units Pa to Pd will be described. Around the photosensitive drums 1a to 1d arranged rotatably, there are chargers 2a, 2b, 2c and 2d for charging the photosensitive drums 1a to 1d, and photosensitive drums 1a, 1b and 1c, respectively. An optical scanning device 4 that exposes image information to 1d; developing units 3a, 3b, 3c, and 3d that form toner images on the photosensitive drums 1a to 1d; and a developer that remains on the photosensitive drums 1a to 1d ( Cleaning portions 5a, 5b, 5c and 5d for removing toner are provided.

  When the start of image formation is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then the laser beam is irradiated by the optical scanning device 4 to each photosensitive drum. Electrostatic latent images corresponding to image signals are formed on 1a to 1d. Each of the developing units 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1 a to 1 d by the developing units 3 a to 3 d and electrostatically attached to the toner image corresponding to the electrostatic latent image formed by exposure from the optical scanning device 4. Is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the intermediate transfer rollers 6a to 6d. Transcribed above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller 12b to a transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are to be formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 7 is distributed to the paper transport path 18 by the branching unit 14, and is transferred again to the transfer roller 9 with the image surface reversed. Be transported. Then, the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image, and then discharged. It is discharged to the tray 17.

  FIG. 2 is a plan view showing an internal configuration around the optical scanning device according to the present embodiment, and FIG. 3 is a side cross-sectional view (cross section AA ′ in FIG. 2) showing the internal configuration. In FIG. 2, the description of the plane mirrors 47a to 47c is omitted. As shown in FIGS. 2 and 3, the optical scanning device 4 has a housing 48, and a polygon mirror 44 is disposed at a substantially central portion of the bottom surface 48 a of the housing 48. In this embodiment, the polygon mirror 44 is composed of a regular hexagonal rotary polygon mirror having six deflection surfaces (reflection surfaces) 44 a on the side surface, and is rotated by the polygon motor 51 at a predetermined speed.

  Moreover, four light source parts 40a-40d are arrange | positioned along the left-right direction of a figure in the front side (lower side of FIG. 2) edge part vicinity of the housing 48. As shown in FIG. Although illustrated as one in FIG. 2, the light source units 40a and 40b and 40c and 40d overlap in the sub-scanning direction (paper surface direction). The light source units 40a to 40d are configured by LDs (laser diodes), and emit light beams (laser beams) D1 to D4 that are optically modulated based on image signals.

  Between the light source units 40a to 40d and the polygon mirror 44, four collimator lenses 41 provided corresponding to the respective light source units 40a to 40d, and the beam lights D1 to D4 that have passed through the collimator lens 41 have a predetermined optical path. A width of the aperture 60, two cylindrical lenses 42 through which the beam lights D 1 and D 2, D 3 and D 4 pass after passing through the aperture 60, and beam lights D 1 to D 4 which have passed through the cylindrical lens 42 are converted into the polygon mirror 44. Two folding mirrors 43 led to the deflection surface 44a are arranged. Although shown as one in FIG. 2, the collimator lens 41 and the aperture 60 corresponding to the light source units 40a and 40b and 40c and 40d overlap each other in the sub-scanning direction.

  The collimator lens 41 converts the light beams D1 to D4 emitted from the light source sections 40a to 40d into substantially parallel light beams, and the cylindrical lens 42 has a predetermined refractive power only in the sub-scanning direction (vertical direction in FIG. 3). It is. In the housing 48, first scanning lenses (first scanning lenses) 45 a and 45 b and second scanning lenses (second scanning lenses) 46 a to 46 d are arranged to face each other with the polygon mirror 44 interposed therebetween. The first scanning lenses 45a and 45b and the second scanning lenses 46a to 46d have fθ characteristics, and the beam lights D1 to D4 deflected and reflected by the polygon mirror 44 are applied to the photosensitive drums 1a to 1d (see FIG. 1). Make an image. Further, plane mirrors 47a to 47c are arranged on the optical paths of the beam lights D1 to D4 from the polygon mirror 44 to the photosensitive drums 1a to 1d.

  The scanning operation of the light beams D1 and D2 by the optical scanning device 4 configured as described above will be described. First, the light beams D1 and D2 emitted from the light source units 40a and 40b are made into a substantially parallel light beam by the collimator lens 41 and have a predetermined optical path width by the aperture 60. Next, the light beams D 1 and D 2 that have become substantially parallel light beams are incident on the cylindrical lens 42. The light beams D1 and D2 incident on the cylindrical lens 42 are in the state of parallel light beams in the main scanning section as they are, converged and emitted in the sub-scanning direction, and formed as a line image on the deflection surface 44a of the polygon mirror 44. . At this time, in order to easily separate the optical paths of the two light beams D1 and D2 deflected by the polygon mirror 44, the light beams D1 and D2 are incident on the deflecting surface 44a at different angles in the sub-scanning direction. Is configured to do.

  The light beams D1 and D2 incident on the polygon mirror 44 are deflected at a constant angular velocity by the polygon mirror 44 and then deflected at a constant velocity by the first scanning lens 45a. The beam lights D1 and D2 that have passed through the first scanning lens 45 are folded back a predetermined number of times by the plane mirrors 47a and 47b arranged in the respective optical paths and separated from each other, and then the beam light D1 is sent to the second scanning lens 46a. The beam light D2 is incident on the second scanning lens 46b, and is deflected at a constant speed by the second scanning lenses 46a and 46b. The light beams D1 and D2 deflected at the same speed are folded back by the final plane mirror 47c arranged in the respective optical paths, and pass through the window portions 49a and 49b formed on the upper surface 48b of the housing 48, so that the photoconductors. Light is distributed to the drums 1a and 1b.

  Similarly, the light beams D3 and D4 emitted from the light source units 40c and 40d pass through the collimator lens 41 and the cylindrical lens 42, are deflected at an equal angle by the polygon mirror 44, and are deflected at a constant velocity by the first scanning lens 45b. The Then, after being folded and separated from each other by the plane mirrors 47a and 47b, the beam light D3 is deflected at a constant speed by the second scanning lens 46c, and the beam light D4 is deflected at a constant speed by the second scanning lens 46d. Further, the light is returned by the final plane mirror 47c and distributed to the photosensitive drums 1c and 1d from the windows 49c and 49d formed on the upper surface 48b.

  Next, a method for preventing the flare light generated by the second scanning lenses 46a to 46d from reaching the other photosensitive drums 1a to 1d by the incidence of the beam lights D1 to D4 will be described. Hereinafter, a method for preventing the flare light generated by the second scanning lens 46c from reaching the photosensitive drum 1b by the incidence of the beam light D3 distributed on the photosensitive drum 1c will be described as an example. The same applies to the relationship between the light beam D1 and the photosensitive drum 1a, the relationship between the beam light D1 and the photosensitive drum 1d, and the relationship between the beam light D4 and the photosensitive drum 1a.

  FIG. 4 is a schematic diagram linearly showing the optical path from the polygon mirror to the photosensitive drum, showing the optical path of flare light when the second scanning lens is not tilted, and FIG. FIG. 6 is a diagram illustrating an optical path of flare light when the scanning lens is tilted downward, and FIG. 6 is a diagram illustrating an optical path of flare light when the second scanning lens is tilted upward. Portions common to FIGS. 2 and 3 are denoted by common reference numerals, and description thereof is omitted. 5 and 6, the light beam D2 is omitted.

  An outer (second lens surface) lens surface (second lens surface) 46ca of the second scanning lens 46c is formed of a curved surface having a predetermined curvature larger than the lens surface of the first scanning lens 45b, and the inner surface (right side of the drawing). The lens surface (first lens surface) 46cb is formed from a flat surface. The beam light D3 deflected by the polygon mirror 44 and passed through the first scanning lens 45b is separated from the beam light D4 as described above, and then enters the second scanning lens 46c. When the light beam D3 is incident, the light is reflected by the inner lens surface 46cb to generate reflected light (flare light).

  As shown in FIG. 4, when the second scanning lens 46c is arranged at a predetermined position where the scanning curvature does not occur, the flare light B1 generated by the second scanning lens 46c is the first scanning lens 45b and further the polygon mirror 44. Is incident on the first scanning lens 45a and the second scanning lens 46b arranged on the opposite side of the lens, and reaches the photosensitive drum 1b. As a result, the formation of an electrostatic latent image by the light beam D2 on the photosensitive drum 1b is affected, and an image defect may occur. Here, the scanning curve means that the scanning lines of the light beams D1 to D4 scanned on the photosensitive drums 1a to 1d are curved in the sub-scanning direction.

  In addition, the second scanning lens 46c is disposed closer to the photosensitive drum 1c than the first scanning lens 45b, and the distance from the polygon mirror 44 is large. Therefore, the flare light B1 is not easily shielded by the polygon mirror 44. Further, since the inner lens surface 46cb of the second scanning lens 46c has a larger curvature than the lens surface of the first scanning lens 45b, the incident angle of the beam light D3 and the reflection angle of the flare light B1 are also small.

  Therefore, with this lens arrangement and lens surface configuration, the flare light B1 is likely to enter the first scanning lens 45a and the second scanning lens 46b, and reaches the photosensitive drum 1b, and image defects are likely to occur. In particular, since the inner lens surface 46cb of the second scanning lens 46c is a flat surface, the incident angle of the beam light D3 and the reflection angle of the flare light B1 are further reduced, and the flare light B1 is more likely to reach the photosensitive drum 1b.

  Therefore, the second scanning is performed so that the flare light B1 is inclined with respect to the incident light of the light beam D3 on the inner lens surface 46cb of the second scanning lens 46c, and the scanning curve of the light beam D3 is set within a predetermined range. By tilting the lens 46c about the rotation shaft 53 disposed along the scanning direction, the flare light B1 is prevented from reaching the photosensitive drum 1b, thereby preventing the occurrence of image defects.

  Here, the rotation shaft 53 is disposed on the inner side of the inner lens surface 46cb in the second scanning lens 46c, but may be disposed on the same plane as the inner lens surface 46cb or on the outer lens surface 46ca side. The arrangement is not particularly limited. However, depending on the arrangement of the rotating shaft 53, the optical path length between the beam light D3 and the polygon mirror 44, the scanning curve of the beam light D3, and the inclination of the flare light may be affected. May be appropriately set in consideration of these factors, for example.

  As shown in FIG. 5, the second scanning lens 46c is tilted in the arrow X direction (downward in FIG. 5) with the rotation shaft 53 as an axis. Accordingly, when the beam light D3 separated from the beam light D4 enters the second scanning lens 46c in the same manner as in FIG. 4, the flare light B2 generated on the inner lens surface 46cb is compared with the incident light of the beam light D3. In the direction of arrow X, the light is reflected downward and to the right at a larger angle than the flare light B1 shown in FIG. As a result, the flare light B2 diverges to the inner wall of the housing 48 and disappears due to absorption or the like, and therefore does not enter the first scanning lens 45a and the second scanning lens 46b and does not reach the photosensitive drum 1b.

  Next, the case where the second scanning lens 46c is tilted in the opposite direction to FIG. 5 will be described. As shown in FIG. 6, the second scanning lens 46 c is tilted in the arrow Y direction (upward in FIG. 5, opposite to the arrow X direction) about the rotation shaft 53. Thereby, when the beam light D3 separated from the beam light D4 enters the second scanning lens 46c in the same manner as in FIG. 4, the flare light B3 generated on the inner lens surface 46cb is compared with the incident light of the beam light D3. The light is reflected rightward at a smaller angle than the flare light B1 shown in FIG. 4 in the direction opposite to the arrow Y direction (arrow X direction, see FIG. 5).

  As a result, the flare light B3 passes through the first scanning lens 45b, passes through the right bottom portion of the polygon mirror 44, and enters the first scanning lens 45a. However, the incident angle of the flare light B3 with respect to the first scanning lens 45a is greatly different from the incident angle of the beam light D2 (see FIG. 4), and is refracted by the first scanning lens 45a having a small curvature. As a result, the flare light B3 that has passed through the first scanning lens 45a diverges upward without entering the second scanning lens 46b, and the flare light B3 reaches the inner wall of the housing 48 and disappears due to absorption or the like. Therefore, it does not reach the photosensitive drum 1b.

  Further, when the second scanning lens 46c is tilted in the arrow Y direction to a greater extent than in FIG. 5, the flare light B3 is reflected by the bottom surface of the polygon mirror 44 or the deflection surface 44a (see FIG. 3), or the polygon mirror. Since the optical path of the beam D2 is greatly different from that of the beam D2, it does not reach the photosensitive drum 1b. Similarly, since the optical path of the beam D1 is also significantly different, it does not reach the photosensitive drum 1a (see FIG. 3).

  On the other hand, even when the flare light B3 is reflected by the deflecting surface 44a of the polygon mirror 44 and enters the first scanning lens 45b, the beam light D3 and the beam light D4 (see FIG. 3) Since the incident angle with respect to 45b is greatly different, it does not enter the second scanning lenses 46c and 46d (see FIG. 3) and does not reach the photosensitive drums 1c and 1d (see FIG. 3).

  Note that the greater the inclination of the second scanning lens 46c, the more the flare light B2 and B3 can be prevented from entering the first scanning lens 45a and the second scanning lens 46c and reaching the photosensitive drum 1b. Accordingly, the emission angle of the light beam D3 from the second scanning lens 46c to the photosensitive drum 1c changes. In such a case, the change in the scanning curve of the light beam D3 becomes large, which affects the formation of the electrostatic latent image on the photosensitive drum 1c by the light beam D3, and the image between the photosensitive drums 1a, 1b and 1d. Color misregistration or the like may occur and the color may change.

  Therefore, the second scanning lens 46c is tilted about the rotation shaft 53 so that the scanning curve is in a predetermined range, and the influence of the flare light B2 and B3 on the electrostatic latent image formed on the photosensitive drum 1b is affected. It is necessary to prevent the influence on the electrostatic latent image formed on the photosensitive drum 1c due to the change in the scanning curve of the light beam D3.

  The range of the scanning curve can be appropriately set according to the degree of color misregistration and the degree of color change of the image, and is not particularly limited. For example, it is within 2 pixels with respect to the resolution of the image. It is preferable that By setting the number of pixels within two pixels, it is possible to reduce image color shift and color change.

  For example, the change in scanning curve when the second scanning lens 46c is tilted in the arrow X direction (see FIG. 5) is defined as + side, and the change in scanning curve when tilted in the arrow Y direction (see FIG. 6) is defined as-side. When expressed, the scanning curve can be within ± 1 pixel. Specifically, the scanning curve is set within ± 0.84 μm when the resolution is 300 dpi, within ± 0.42 μm when the resolution is 600 dpi, and within ± 0.21 μm when the resolution is 1200 dpi. It is preferable to tilt the two-scanning lens 46c.

  Here, since the curvature of the inner lens surface 46cb of the second scanning lens 46c is larger than the curvature of the outer lens surface 46ca, the flare light easily reaches the other photosensitive drums 1a to 1d. However, since such arrival can be prevented, image defects due to the influence of reflected light can be more effectively prevented. In particular, the inner lens surface 46cb is a flat surface, which is more effective.

  However, the curvatures of the inner lens surface 46cb and the outer lens surface 46ca can be the same. In addition, at least one of the outer lens surface 46ca and the inner lens surface 46cb may be a diffraction grating surface. As a result, the light beams D1 to D4 can be split into desired wavelengths and distributed to the photosensitive drums 1a to 1d.

  When the optical scanning device 4 is assembled, the rotation shaft 53 is pivoted so that the flare light is inclined with respect to the incident light beams D1 to D4 and the scanning curve is set within a predetermined range as described above. As described above, the second scanning lenses 46a to 46d are bonded using an adhesive or the like with the inclination of the second scanning lenses 46a to 46d adjusted.

  According to this method, by tilting the second scanning lenses 46a to 46d, flare light generated by the beam lights D1 to D4 is prevented from reaching the other photosensitive drums 1a to 1d, and image defects are prevented. Therefore, the highly accurate optical scanning device 4 can be manufactured easily and at low cost. Further, by mounting the optical scanning device 4 of the present invention on the image forming apparatus 100, it is possible to form a high-quality image in which image defects are prevented.

  In the present embodiment, since the second scanning lenses 46a to 46d arranged on the photosensitive drums 1a to 1d are inclined, even if the lens arrangement is such that flare light easily reaches the other photosensitive drums 1a to 1d. Since such arrival can be prevented, image defects due to the influence of flare light can be further prevented, which is more effective. However, in other cases, such as when it is necessary to prevent the flare light of the light beams D1 to D4 generated by the first scanning lenses 45a and 45b from reaching the photosensitive drums 1a to 1d, the first scanning lenses 45a and 45b. You can also tilt.

  In the present embodiment, since the second scanning lenses 46a to 46d on which the light beams D1 to D4 separated after passing through the first scanning lenses 45a and 45b are tilted, the beam light D1 to the second scanning lenses 46a to 46d. Even if the incident path of .about.D4 is limited and flare light can easily reach the other photosensitive drums 1a to 1d, such arrival can be prevented, so that image defects due to the influence of flare light can be further prevented. Can be more effective.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the first scanning lenses 45a and 45b and the second scanning lenses 46a to 46d are arranged in each optical path between the polygon mirror 44 and the photosensitive drums 1a to 1d. A scanning lens can also be provided. In such a case, at least one of the three or more scanning lenses may be tilted as described above. Further, the quantity and arrangement of the mirrors 47a to 47c and the like can be appropriately set according to the optical path configuration and the like.

  Further, in the present embodiment, the optical scanning device 4 has the polygon mirror 44 disposed substantially at the center of the housing 48, deflects the light beams D1 and D2, D3 and D4 in opposite directions and deflects them in the same direction. The four-beam method is adopted in which the beam light D1 and the beam light D2, and the beam light D3 and the beam light D4 are separated and distributed to the photosensitive drums 1a to 1d. However, the optical scanning device of the present invention is not limited to such a four-beam optical scanning device, but can be applied to other multi-beam optical scanning devices.

  For example, the optical scanning device 4 is a two-beam system that deflects the light beams D1 and D2 (or D3 and D4) in the opposite directions and distributes them to the photosensitive drums 1a and 1b (or 1c and 1d). You can also. In such a case, the two optical scanning devices 4 may be disposed in the image forming apparatus 100.

  INDUSTRIAL APPLICABILITY The present invention can be used for an optical scanning device used for image forming apparatuses such as a printer, a copying machine, and a facsimile machine, which scans a beam of light and writes and forms an image.

Pa to Pd Image forming portions 1a to 1d Photosensitive drum (scanned surface)
4 Optical scanning device 40a-40d Light source part 41 Collimator lens 42 Cylindrical lens 44 Polygon mirror 45a, 45b 1st scanning lens (1st scanning lens)
46a to 46d Second scanning lens (second scanning lens)
47a to 47c Flat mirror 48 Housing 53 Rotation axis (axis in scanning direction)
100 Image forming apparatus D1 to D4 Beam light B1 to B3 Flare light

Claims (8)

A plurality of light source units;
A polygon mirror that deflects and scans a plurality of light beams emitted from the plurality of light source units;
A plurality of scanning lenses arranged in each optical path of the beam light deflected and scanned by the polygon mirror, and the beam light deflected and scanned by the polygon mirror is imaged by the plurality of scanning lenses and scanned surface In an optical scanning device that scans above,
The reflected light is inclined with respect to the incident light of the beam light deflected and scanned by the polygon mirror so that at least one of the plurality of scanning lenses does not reach the surface to be scanned, and An optical scanning device characterized by being tilted with the main scanning direction as an axis so that the scanning curve of the light beam distributed on the scanning surface is set within a predetermined range.   The optical scanning device according to claim 1, wherein the predetermined range is within two pixels.   The optical scanning device according to claim 1, wherein the at least one scanning lens is a scanning lens disposed on the scanned surface side.   The curvature of the first lens surface on the polygon mirror side in the at least one scanning lens is larger than the curvature of the second lens surface on the scanned surface side. The optical scanning device according to 1.   The optical scanning device according to claim 4, wherein the first lens surface is a flat surface.   6. The optical scanning device according to claim 4, wherein at least one of the first lens surface and the second lens surface is a diffraction grating surface. The plurality of scanning lenses include a first scanning lens on which beam light deflected and scanned by the polygon mirror is incident, and a second scanning lens on which beam light separated after passing through the first scanning lens is incident Consists of
The optical scanning device according to claim 1, wherein the at least one scanning lens is the second scanning lens.   An image forming apparatus on which the optical scanning device according to claim 1 is mounted.

Images