JP4933970B2 - Scanning optical apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a scanning optical apparatus that is mounted on an image forming apparatus such as a copying machine, a printer, or a facsimile machine, and exposes and scans the surface of an image carrier with a light beam (for example, laser light).

  A scanning optical device used in a copying machine, a printer, or the like is generally exposed while scanning the surface of an image carrier represented by a photosensitive drum, that is, a surface to be scanned, and a predetermined static on the surface of the photosensitive drum. An electrostatic latent image is formed. In a scanning optical device, a light beam, such as laser light, emitted from a light source is deflected in the main scanning direction by an optical deflector and emitted toward a surface to be scanned by an optical system.

  In recent years, image forming apparatuses capable of forming color images have been remarkably widespread. As this image forming apparatus, there is a so-called tandem type apparatus including a plurality of color photosensitive drums. A tandem type image forming apparatus generally has four photosensitive drums corresponding to each of four colors of yellow, magenta, cyan, and black, along the paper transport direction or the movement (rotation) direction of the intermediate transfer member. They are arranged in a line in order. In this tandem type apparatus, an electrostatic latent image corresponding to each color is formed on each photoconductive drum by the laser light emitted from the scanning optical device, developed to a toner image of each color, and then these toner images are superimposed. In this way, the image is transferred onto a sheet to form a color image.

An example of a scanning optical device mounted on such a tandem type image forming apparatus can be seen in Patent Document 1. The scanning optical device (light beam scanning device) described in Patent Document 1 includes light sources corresponding to four colors of yellow, magenta, cyan, and black. Laser light emitted from these light sources is incident on a polygon mirror as an optical deflector at different angles. The polygon mirror reflects each laser beam on its reflecting surface and deflects it in the main scanning direction. Each deflected laser beam is subsequently deflected at a constant speed parallel to the axial direction of the photosensitive drum by an fθ lens, and is emitted toward the surface of the photosensitive drum through a reflection mirror to form an image.
JP 2006-91346 A (page 9, FIG. 2-3)

  A scanning optical device (light beam scanning device) mounted on a tandem type image forming apparatus as disclosed in Patent Document 1 uses a polygon mirror to measure the scanning timing of laser light corresponding to each of four colors. An optical sensor is provided for receiving the reflected laser light outside the effective exposure area of the scanned surface. Here, in Patent Document 1, in order to perform highly accurate detection, among the laser beams that have passed through the fθ lens, a laser beam having the smallest scanning curve (curved distortion of the scanning line) is used.

  However, some scanning optical devices may have a structure in which the laser beam reflected by the polygon mirror is directly incident on the optical sensor without passing through the fθ lens due to the configuration of the optical path inside the scanning optical device. In this case, there is a possibility that an adverse effect on scanning that should be corrected by the fθ lens (this adverse effect is caused by the incident angle of the laser beam on the polygon mirror or the tilting of the polygon mirror) cannot be avoided. . Alternatively, there is a case where laser light at a stage where correction is not sufficiently performed is incident on the optical sensor when the scanning curvature is corrected by a plurality of fθ lenses due to the arrangement of the optical system. In these cases, the laser light enters the optical sensor while having a scanning curve, and there is a high possibility that the scanning timing of the laser light corresponding to each of a plurality of colors will shift. As a result, color misregistration occurs in the color image, causing a problem that the image quality is degraded.

  The present invention has been made in view of the above points, and even when the optical sensor for measuring the scanning timing receives a light beam having an inclination with respect to the main scanning direction such as a scanning curve, scanning is performed. It is an object of the present invention to provide a scanning optical device that can suppress a timing shift.

A scanning optical device according to one aspect of the present invention that achieves the above object includes a light source that irradiates a light beam, an optical deflector that deflects the light beam from the light source in the main scanning direction, and light from the optical deflector. An optical system that guides the beam onto the surface to be scanned, and a light receiving unit. The light beam from the optical deflector that is outside the effective exposure area of the surface to be scanned is received by the light receiving unit, and scanning timing is set. An optical sensor for measuring and holding the optical sensor in a state where the light receiving unit is inclined so as to follow the angle of the scanning curve at a height position along the scanning curve of the light beam from the optical deflector. a holding member which, you comprising: a.

According to this configuration, the optical sensor is held in a state where the light receiving unit is inclined so as to follow the angle of the scanning curve at a height position along the scanning curve of the light beam from the optical deflector. Since the holding member is provided, when laser light passing through a locus in which the irradiation position is inclined in the height direction with respect to the main scanning direction due to scanning curvature is received, the laser light can be received at an angle according to the inclination. Thereby, it is possible to suppress a decrease in detection accuracy of the optical sensor due to the inclination of the light beam.

In addition , it is possible to reliably match the light receiving angle of the optical sensor with the angle of scanning curvature caused by the incident angle of the light beam to the optical deflector and the surface tilt of the optical deflector. This further improves the detection accuracy of the optical sensor. Therefore, it is possible to provide a scanning optical device that can measure a suitable scanning timing and can further improve the image quality.

An image forming apparatus according to another aspect of the present invention forms an electrostatic latent image by emitting a beam onto the surface of an image carrier that carries a toner image corresponding to the electrostatic latent image, and the image carrier. An image forming apparatus including a scanning optical device, wherein the scanning optical device includes a light source that emits a light beam, an optical deflector that deflects the light beam from the light source in a main scanning direction, and the optical deflector. An optical system for guiding the light beam onto the surface to be scanned and a light receiving unit, and the light beam from the optical deflector outside the effective exposure area of the surface to be scanned is received by the light receiving unit and scanned. An optical sensor for measuring timing, and a state in which the optical sensor is inclined at the height position along the scanning curve of the light beam from the optical deflector so as to follow the angle of the scanning curve And a holding member held by That.

  According to the present invention, it is possible to provide a scanning optical device capable of suppressing a shift in scanning timing and obtaining a high-quality image in which a color shift is prevented, and an image forming apparatus using the scanning optical device. it can.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 7 is a schematic cross-sectional view of a printer 7 on which the scanning optical apparatus of the present invention is mounted. Here, a tandem color printer 7 is shown. In the main body of the color printer 7, four image forming units 7Y, 7M, 7C, and 7B are sequentially arranged from the upstream side in the transfer paper conveyance direction (the right side in FIG. 7). These image forming units 7Y, 7M, 7C, and 7B sequentially form yellow, magenta, cyan, and black images through charging, exposure, development, and transfer processes, respectively.

In these image forming units 7Y, 7M, 7C and 7B, photosensitive drums 100Y, 100M, 100C and 100B carrying visible images (toner images) of the respective colors are arranged. The toner images formed on these photosensitive drums are rotated clockwise in FIG. 7 by a drive mechanism (not shown), and sequentially transferred onto an intermediate transfer belt 75 that moves adjacent to each image forming unit. The This toner image is transferred onto the transfer paper P at one time by the transfer roller 76 and fixed onto the transfer paper P at the fixing unit 77. Thereafter, the transfer paper P is discharged from the apparatus main body. While the photosensitive drums 100Y, 100M, 100C, and 100B are rotated counterclockwise in FIG. 7, an image forming process for each photosensitive drum is executed.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 78 at the lower part of the apparatus, and is conveyed to the transfer roller 76 via a paper feed roller 79a and a registration roller 79b. A sheet made of a dielectric resin is used for the intermediate transfer belt 75, and a belt in which both ends thereof are overlapped and joined to each other to form an endless shape, or a belt without a seam (seamless) is used.

  Next, the image forming units 7Y, 7M, 7C, and 7B will be described by taking up one image forming unit 7Y. Around and below the rotatable photoconductor drum 100Y, there are a charger 71 for charging the photoconductor drum 100Y, the scanning optical device 1 for exposing image information to the photoconductor drum 100Y, and the photoconductor drum 100Y. A developing unit 72 for forming a toner image thereon and a cleaning unit 73 for removing the developer (toner) remaining on the photosensitive drum 100Y are provided. The same applies to the other image forming units 7M, 7C, and 7B. The scanning optical device 1 will be described in detail later with reference to FIGS.

  When an image forming start operation is input by the user, first, the surface of the photosensitive drum 100Y is uniformly charged by the charger 71. Next, the scanning optical device 1 irradiates the photosensitive drum 100Y with laser light, and an electrostatic latent image corresponding to the image signal is formed on the photosensitive drum 100Y. The developing unit 72 is filled with a predetermined amount of yellow toner by a replenishing device (not shown). This toner is supplied onto the photosensitive drum 100Y by the developing unit 72 and electrostatically attached thereto, whereby a yellow toner image corresponding to the electrostatic latent image formed by exposure from the scanning optical device 1 is formed. The The same applies to the other photoconductive drums 100M, 100C, and 100B, and magenta, cyan, and black toner images are formed, respectively.

  After an electric field is applied to the intermediate transfer belt 75 at a predetermined transfer voltage, the yellow toner image on the photosensitive drum 100 </ b> Y is transferred onto the intermediate transfer belt 75 by the intermediate transfer roller 74. The same applies to the other photoconductive drums 100M, 100C, and 100B. Finally, yellow, magenta, cyan, and black toner images are overprinted and transferred onto the intermediate transfer belt 75. 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 surface of the photosensitive drum 100Y is removed by the cleaning unit 73 in preparation for the subsequent formation of a new electrostatic latent image.

  The intermediate transfer belt 75 is stretched between an upstream conveying roller 751 and a downstream driving roller 752. When the intermediate transfer belt 75 starts to rotate clockwise in accordance with the rotation of the drive roller 752 by a drive motor (not shown), the transfer paper P is provided adjacent to the intermediate transfer belt 75 from the registration roller 79b at a predetermined timing. The full color image is transferred to the transfer paper P. The transfer paper P on which the toner image is transferred is conveyed to the fixing unit 77.

  The transfer paper P conveyed to the fixing unit 77 is heated and pressed by the fixing roller pair 771 to fix the toner image on the surface of the transfer paper P, thereby forming a predetermined full color image. The transfer paper P on which a full-color image is formed is distributed in the transport direction by a branching portion 80 that branches in a plurality of directions. When an image is formed on only one side of the transfer paper P, it is discharged as it is onto the discharge tray 82 by the discharge roller 81.

  On the other hand, when images are formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 77 is distributed to the paper transport path 83 by the branching unit 80, and is transferred again to the transfer roller 76 with the image surface reversed. Be transported. Then, the next image formed on the intermediate transfer belt 75 is transferred to the surface of the transfer paper P on which the image is not formed by the transfer roller 76, conveyed to the fixing unit 77, and the toner image is fixed, and then discharged. It is discharged to the tray 82.

  Next, a detailed configuration of the scanning optical device 1 will be described with reference to FIGS. First, the outline of the structure will be described with reference to FIGS. 1 and 2. FIG. 1 is a schematic vertical cross-sectional view of the scanning optical device 1, and FIG. 2 is a schematic top view of the scanning optical device 1. As described above, the scanning optical apparatus 1 includes the tandem type printer 7 provided with the four photosensitive drums 100Y, 100M, 100C, and 100B corresponding to the four colors of yellow, magenta, cyan, and black, respectively. It is designed as a scanning optical device mounted on (image forming apparatus).

  The scanning optical device 1 includes a light source 3, an optical deflector 10, an optical system 20, and an optical sensor 4 inside a housing 2.

  As shown in FIG. 2, the light source 3 is provided at one end in the housing 2. The scanning optical device 1 corresponds to four colors of yellow, magenta, cyan, and black, and four independent light sources 3 are provided. The light source 3 is composed of a laser diode having a specification for irradiating a visible region light beam, for example, a laser beam of about 670 nm.

  An optical deflector 10 is provided in the vicinity of the light source 3. The optical deflector 10 includes a polygon mirror 11 and a motor 12. The motor 12 rotates the polygon mirror 11 having a regular polygonal plane shape about the axis in the vertical direction in FIG. A reflection surface for reflecting light is provided around the polygon mirror 11 that rotates about the axis.

  The laser beams LY, LM, LC, and LB emitted from the four light sources 3 are incident on the reflecting surface around the polygon mirror 11 while being shifted by a minute angle in the sub-scanning direction (vertical direction in FIG. 1). To do. The polygon mirror 11 guides each laser beam toward the other end in the housing 2 while rotating and reflecting each laser beam on its reflection surface and deflecting it in the main scanning direction (left and right direction in FIG. 2).

  The optical system 20 is provided in a region in the housing 2 where the laser light reflected by the optical deflector 10 travels. The optical system 20 includes a first fθ lens 21, a second fθ lens 22, and a reflection mirror 23.

  The first fθ lens 21 is disposed at a position just ahead of which the laser beams LY, LM, LC, and LB reflected by the optical deflector 10 travel. The first fθ lens 21 is shared for the laser beams LY, LM, LC, and LB, and one first fθ lens 21 is provided. The first fθ lens 21 deflects the laser beams LY, LM, LC, and LB at a constant speed in the main scanning direction. Further, the first fθ lens 21 corrects the scanning light effects such as the incident angles of the laser beams LY, LM, LC, and LB to the polygon mirror 11 and the surface tilt of the polygon mirror 11 to some extent while correcting the laser beams LY and LM. , LC, LB in the sub-scanning direction is slightly widened.

  The yellow laser light LY that has passed through the first fθ lens 21 is reflected by the reflection mirror 23Ya in the vicinity of the inner bottom surface of the housing 2 and is folded back toward the first fθ lens 21. Thereafter, the laser beam LY passes through the second fθ lens 22Y, is reflected by the reflecting mirror 23Yb near the upper end of the housing 2, and reaches the surface of the yellow photosensitive drum 100Y that is the surface to be scanned and forms an image. The second fθ lens 22Y also has a function of correcting the adverse effects on scanning. In the present embodiment, the scanning curvature is corrected by the cooperation of the first fθ lens 21 and the second fθ lens 22Y (22C, 22M).

  Similarly to the yellow laser light LY, the magenta laser light LM that has passed through the first fθ lens 21 is reflected by the reflection mirror 23Ma in the vicinity of the inner bottom surface of the housing 2 and folded back toward the first fθ lens 21. Thereafter, the laser beam LM passes through the second fθ lens 22M, is reflected by the reflection mirror 23Mb near the upper end of the housing 2, reaches the surface of the magenta photosensitive drum 100M, which is the surface to be scanned, and forms an image.

  The cyan laser light LC that has passed through the first fθ lens 21 is reflected substantially vertically upward by the reflecting mirror 23Ca in the vicinity of the inner bottom surface of the housing 2, and then in the substantially horizontal direction by the reflecting mirror 23Cb in the vicinity of the upper end of the housing 2. Then, it is folded in the direction of the first fθ lens 21. Thereafter, the laser beam LC passes through the second fθ lens 22C, is reflected by the reflection mirror 23Cc, and reaches the surface of the cyan photosensitive drum 100C, which is the surface to be scanned, to form an image.

  The black laser beam LB that has passed through the first fθ lens 21 passes through the second fθ lens 22B directly without passing through the reflection mirror. Thereafter, the laser beam LB is reflected by the reflection mirror 23B, reaches the surface of the black photosensitive drum 100B, which is the scanning surface, and forms an image.

  As shown in FIG. 2, the optical sensor 4 is disposed in the vicinity of the reflection mirror 23Ya and the second fθ lens 22M and closer to the outside in the main scanning direction. The optical sensor 4 receives the laser light reflected by the polygon mirror 11 of the optical deflector 10 outside the effective exposure area of the surface to be scanned. Specifically, of the laser light that has passed through the first fθ lens 21, the laser light reflected by the reflection mirror 5 provided in the vicinity of the second fθ lens 22 </ b> B is incident on the optical sensor 4. That is, the optical sensor 4 is configured to receive the laser light at a stage where the scanning curve has not been sufficiently corrected just passing through the first fθ lens 21.

  The optical sensor 4 is a synchronous detection sensor for measuring the scanning timing of the laser beams LY, LM, LC, and LB corresponding to the four colors. As the optical sensor 4, various optical sensors such as a photodiode, a phototransistor, and a photo IC can be used. Particularly, a BD (beam detector) sensor having a two-dimensional light receiving surface with a size of several millimeters is preferably used. it can.

  Next, the mounting configuration of the optical sensor 4 will be described in detail with reference to FIGS. 3 to 5 in addition to FIG. 3 is a perspective view of the optical sensor and its surroundings as viewed from above, FIG. 4 is a perspective view of the optical sensor as viewed from the front, and FIG. 5 is a partially enlarged front view of the optical sensor.

  As described above, the optical sensor 4 is disposed in the vicinity of the reflection mirror 23Ya and the second fθ lens 22M illustrated in FIGS. 2 and 3 and attached to the base member 6 (holding member). The base member 6 holds the photosensor 4 so that the laser beam reflected by the reflecting mirror 5 (see FIG. 2) is incident perpendicularly to the light receiving portion 4a of the photosensor 4 with respect to its traveling direction. ing.

  Then, as shown in FIGS. 4 and 5, the optical sensor 4 inclines the light receiving portion 4a by a predetermined angle α with respect to the main scanning direction of the laser light (two-dot chain line E in FIGS. 4 and 5). It is held in the state. The inclination angle α is set to 0.8 ° in accordance with the scanning curve angle of the laser beam reflected by the polygon mirror 11 of the optical deflector 10. This scanning curve is caused by the incident angle of the laser beam to the polygon mirror 11 or the surface tilt of the polygon mirror 11.

  Next, the inclination angle α of the light receiving portion 4a of the optical sensor 4 will be described with reference to FIG. FIG. 6 is a graph showing the trajectory in the main scanning direction of laser light having a scanning curve. In the graph shown in FIG. 6, the horizontal axis represents the image height (distance from the center in the main scanning direction), and the vertical axis represents the height in the vertical direction from the reference position of the laser beam.

  As shown in FIG. 6, the laser beam having a scanning curve is closer to the outside (on both ends in the main scanning direction where the image height is higher) with respect to the position where the image height is 0 mm (center in the main scanning direction). Curves vertically upward. Here, the position of the optical sensor 4 is a position (arrow F) where the image height is minus 157 mm in FIG. Therefore, when the angle of the laser beam at the position where the image height is minus 157 mm with respect to the main scanning direction from the reference position is calculated from FIG. 6, the inclination angle α is 0.8 °.

  FIG. 8 is a schematic diagram for explaining the effect of installing the optical sensor 4 according to the inclination angle α. In the case of laser light with no scanning curvature, the laser light passes through a certain height position in the scanning in the main scanning direction (scanning locus of S1). On the other hand, in the case of a laser beam having a scanning curve, as described with reference to FIG. 6, the height position changes and proceeds in the main scanning direction (scanning locus of S2; actually, it is a curved locus).

  The optical sensor 4 is disposed at a predetermined position on the scanning locus. When the scanning timing is to be measured at the scanning point P2 that is separated from the scanning start point P1 by a certain scanning distance d1 on the scanning locus S1, the optical sensor 4 is aligned with the scanning point P2 as indicated by a two-dot chain line in the figure. The light receiving part 4a is arranged. However, the scanning timing cannot be accurately detected if the light receiving portion 4a is disposed at the scanning point P2 despite the occurrence of scanning curvature.

  That is, on the scanning locus S2, the position of the scanning point P02 that is separated from the scanning start point P01 by a certain scanning distance d1 is shifted by Δd in the main scanning direction. For this reason, if the light receiving portion 4a is arranged at a point corresponding to the scanning point P2, the scanning timing is shifted by an amount corresponding to Δd. Therefore, the light receiving unit 4a is inclined by the inclination angle α with respect to the main scanning direction of the laser light so as to be close to the scanning start point P01, and the light receiving unit 4a is arranged at a point corresponding to the scanning point P02. Detection deviation can be prevented.

  As described above, the scanning optical device 1 of the present embodiment includes the light source 3 that irradiates the laser beam that is a light beam, the optical deflector 10 that deflects the laser beam from the light source 3 in the main scanning direction, and the light. An optical system 20 that guides the laser light from the deflector 10 onto the surface to be scanned, and the laser light from the optical deflector 10 that receives laser light outside the effective exposure area of the surface to be scanned and measures the scanning timing. And an optical sensor 4. In such a configuration, the optical sensor 4 is held in a state where the light receiving portion 4a is inclined at a predetermined angle with respect to the main scanning direction of the laser light.

  For this reason, when the optical sensor 4 receives laser light passing through a trajectory whose irradiation position is inclined in the height direction with respect to the main scanning direction due to scanning curvature, the optical sensor 4 can receive the light at an angle according to the inclination. Thereby, it is possible to suppress a decrease in detection accuracy of the optical sensor 4 due to the inclination of the laser light. Therefore, it is possible to provide the scanning optical device 1 that can suppress the detection deviation of the scanning timing and obtain a high-quality image in which the color deviation is prevented.

  The optical sensor 4 is held in a state where the light receiving portion 4a is inclined along the scanning curve angle α of the laser light from the optical deflector 10. For this reason, it is possible to reliably match the light receiving angle of the optical sensor 4 with the scanning curve angle α caused by the incident angle of the laser beam to the optical deflector 10 or the surface tilt of the optical deflector 10. Thereby, the detection accuracy of the optical sensor 4 is further improved. Therefore, it is possible to provide the scanning optical device 1 that can measure a suitable scanning timing and can further improve the image quality.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these embodiments, and various modifications can be made without departing from the spirit of the invention.

  For example, in the above embodiment, the light receiving unit 4a of the optical sensor 4 is inclined at the angle α, assuming that the scanning curve of the laser beam (the curve distortion of the scanning line) is 0.8 °. This inclination angle α is not limited to 0.8 °, but depends on the incident angle of the laser beam to the polygon mirror 11 and the surface tilt of the polygon mirror 11. It doesn't matter.

  The present invention can be used in a scanning optical apparatus including an optical sensor for receiving a light beam and measuring a scanning timing.

1 is a schematic vertical sectional view of a scanning optical device according to an embodiment of the present invention. It is a model top view of the scanning optical apparatus shown in FIG. It is the perspective view which looked at the optical sensor shown in FIG. 2 and its periphery from upper direction. It is the perspective view which looked at the optical sensor shown in FIG. 3 from the front direction. FIG. 4 is a partially enlarged front view of the photosensor shown in FIG. 3. It is a graph which shows the track | orbit of the main scanning direction of the laser beam which has a scanning curve. 1 is a schematic vertical sectional view showing an image forming apparatus to which a scanning optical device according to the present invention is applied. It is a schematic diagram for demonstrating the effect which installs the optical sensor 4 according to inclination-angle (alpha).

DESCRIPTION OF SYMBOLS 1 Scan optical device 2 Housing 3 Light source 4 Optical sensor 4a Light-receiving part 5 Reflection mirror 10 Optical deflector 11 Polygon mirror 20 Optical system 21 1st f (theta) lens 22 2nd f (theta) lens 23 Reflection mirror

Claims (2)

A light source that emits a light beam;
An optical deflector for deflecting the light beam from the light source in the main scanning direction;
An optical system for guiding the light beam from the optical deflector onto the surface to be scanned;
An optical sensor for receiving a light beam outside the effective exposure area of the scanned surface of the light beam from the optical deflector and measuring the scanning timing;
A holding member that holds the optical sensor in a state where the light receiving unit is inclined so as to follow the angle of the scanning curve at a height position along the scanning curve of the light beam from the optical deflector. A scanning optical device. An image forming apparatus comprising: an image carrier that carries a toner image corresponding to an electrostatic latent image; and a scanning optical device that emits a beam to the surface of the image carrier to form the electrostatic latent image.
The scanning optical device includes:
A light source that emits a light beam;
An optical deflector for deflecting the light beam from the light source in the main scanning direction;
An optical system for guiding the light beam from the optical deflector onto the surface to be scanned;
An optical sensor for receiving a light beam outside the effective exposure area of the scanned surface of the light beam from the optical deflector and measuring the scanning timing;
A holding member that holds the light sensor in a state where the light receiving unit is inclined so as to follow the angle of the scanning curve at a height position along the scanning curve of the light beam from the optical deflector. An image forming apparatus.

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