JP2016065997A - Optical scanning device and image formation device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform separation of a light beam by a separation mirror with high accuracy.SOLUTION: A cyan laser beam LC is reflected by a cyan separation mirror 441 provided between a yellow separation mirror 431 and a magenta separation mirror 451 toward a peripheral surface of a yellow photoreceptor drum. A diaphragm 8C for cyan includes an upper shielding piece 81 and a lower shielding piece 82 that shield at different positions in a vertical direction (sub-scanning direction) of the laser beam LC and are disposed at different positions on an optical path. The upper shielding piece 81 is disposed at a position such that a first scanning lens 6 forms a diaphragm image 81I of the upper shielding piece 81 in the vicinity of an arrangement position of the yellow separation mirror 431. The lower shielding piece 82 is disposed at a position such that the first scanning lens 6 forms a diaphragm image 82I of the lower shielding piece 82 in the vicinity of an arrangement position of the cyan separation mirror 441.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an optical scanning device including a plurality of light sources that emit light rays and a separation mirror that reflects each light beam toward a surface to be scanned, and an image forming apparatus using the same.

  For example, an optical scanning device used in a color laser printer includes a plurality of light sources that emit laser beams for cyan, magenta, yellow, and black colors, and a peripheral surface (covered surface) of a photosensitive drum for each color by deflecting the laser beams. A deflecting body that scans the scanning surface, and an imaging lens that focuses the deflected laser beam on each of the peripheral surfaces. The deflecting body may be shared by a plurality of laser beams. In this case, a separation mirror is disposed between the deflecting body and the drum circumferential surface in order to selectively reflect one laser beam from a plurality of laser beams and direct it toward one drum circumferential surface. In addition, a diaphragm for restricting the light beam traveling toward the deflecting body is disposed between the light source and the deflecting body.

  The separation mirror is desired to satisfactorily separate one laser beam to be reflected from other laser beams. Patent Document 1 discloses a technique in which a separation mirror is arranged in the vicinity of a position where an image of a diaphragm is formed by the imaging lens in a multi-beam type optical scanning device. According to this technique, since the separation mirror is arranged at the position where the principal beam interval of the multi-beam is most narrowed down, it is said that beam separation becomes easy.

JP 2009-003124 A

  When an optical system that shares one deflector with four color laser beams is employed, there are cases where four separation mirrors are arranged side by side on the optical path. These separation mirrors are arranged vertically when the sub-scanning direction is the vertical direction. In this arrangement, the middle two of the four separation mirrors must separate one laser beam from both the upper and lower passing laser beams. In this case, as in Patent Document 1, in the method in which the separation mirror is arranged at the image position of one stop, the optical arrangement capable of satisfactorily separating the upper and lower laser beams while satisfying the demand for compactness of the optical scanning device. Is difficult to set.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device capable of satisfactorily separating light beams by a separation mirror, and an image forming apparatus using the same.

  An optical scanning device according to one aspect of the present invention includes a first light source that emits a first light beam, a second light source that is disposed at a different position in the sub-scanning direction from the first light source, and A light source unit including a third light source disposed between the first light source and the second light source in the sub-scanning direction and emitting a third light beam; and deflecting the first light beam, the second light beam, and the third light beam. And a deflector for scanning the first scanned surface with the first light beam, the second scanned surface with the second light beam, and the third scanned surface with the third light beam, and the deflection on the optical path. A diaphragm group disposed between the body and the first, second, and third light sources, and including first, second, and third diaphragms that restrict the first, second, and third light beams, respectively, and an optical path The first, second, and third light beams are disposed between the deflecting body and the first, second, and third scanned surfaces in FIG. An imaging lens that forms an image on each of the first, second, and third scanned surfaces and an optical path disposed between the deflecting body and the first scanned surface, and the first light beam is disposed on the first scanned surface. A first separation mirror that reflects the surface to be scanned, and a second separation mirror that is disposed on the optical path between the deflector and the second surface to be scanned and reflects the second light beam to the second surface to be scanned. And between the first separation mirror and the second separation mirror between the deflecting body and the third scanned surface on the optical path, and on the optical path and in the sub-scanning direction. A mirror group including a third separation mirror that reflects light rays to the third surface to be scanned, wherein the third diaphragm blocks light at different positions in the sub-scanning direction of the third light rays. And the second light shielding piece, the first light shielding piece is lighter than the second light shielding piece. The first light-shielding piece is disposed at the upstream position above, and the second light-shielding piece is located at a position where the imaging lens makes an image of the first light-shielding piece in the vicinity of the arrangement position of the first separation mirror. The imaging lens is disposed at a position where an image of the second light shielding piece is formed in the vicinity of the position where the third separation mirror is disposed.

  According to this optical scanning device, the third diaphragm for restricting the third light beam directed to the third mirror disposed between the first separation mirror and the second separation mirror is disposed upstream and downstream on the optical path, respectively. In addition, since the first light shielding piece and the second light shielding piece are included, the third light beam can be prevented from entering the first separation mirror and the second separation mirror. That is, since the first light shielding piece is arranged at a position where the image of the first light shielding piece is formed in the vicinity of the arrangement position of the first separation mirror, it is difficult for the third light beam to enter the first separation mirror. Can do. Similarly, since the second light-shielding piece is arranged at a position where the image of the second light-shielding piece is formed in the vicinity of the arrangement position of the third separation mirror, the third light beam is out of the range of the third separation mirror. It is possible to easily prevent the light from entering the second separation mirror. Even if the incident optical system including the third light source is decentered, the images of the first and second light shielding pieces are formed in the vicinity of the positions where the first and third separation mirrors are arranged. Therefore, it is possible to realize a scanning optical system that is not easily affected by installation tolerances.

  In the above optical scanning device, when the sub-scanning direction is the vertical direction, the light source unit is arranged so that the first, third, and second light sources are arranged in order from top to bottom in the sub-scanning cross section. The mirror group is arranged so that the first, third, and second separation mirrors are arranged in order from the bottom in the sub-scan section, and the first light shielding piece shields the upper side of the third light beam, The two light shielding pieces desirably shield the lower side of the third light beam.

  According to this optical scanning device, the upper side and the lower side of the third light beam in the sub-scanning direction are regulated. For this reason, it is possible to reliably direct the third light beam only to the third separation mirror in the mirror group arranged in the order of the first, third, and second separation mirrors in the sub-scanning direction.

  In the above optical scanning device, the first light shielding piece and the second light shielding piece form one opening when viewed on the optical path, and the first light shielding piece is located above the third light beam. And a pair of vertical portions extending downward from both ends of the first horizontal portion, and the second light shielding piece includes a second horizontal portion that shields the lower side of the third light beam. Preferably, the lower surface of the pair of vertical portions and the lower surface of the second horizontal portion are in contact with the same seating surface.

  According to this optical scanning device, since the first light shielding piece and the second light shielding piece can be installed on the same seating surface, the structure of the optical scanning device is simplified and the assemblability is improved. Can do.

  In the above optical scanning device, it is preferable that the deflecting body includes a deflecting surface on which the first, second, and third light beams are simultaneously incident. According to this configuration, the optical scanning device can be made compact and the number of parts can be reduced.

  In the optical scanning device, the light source unit further includes a fourth light source that emits a fourth light beam, the deflector further scans a fourth surface to be scanned with the fourth light beam, The image forming lens further includes a fourth diaphragm for restricting a fourth light beam, the imaging lens further images the fourth light beam on a fourth surface to be scanned, and the mirror group includes the deflector and the fourth light beam on an optical path. A fourth separation mirror disposed between the third separation mirror and the second separation mirror; and a fourth separation mirror disposed between the second separation mirror and the second separation mirror. A separation mirror is disposed between the first separation mirror and the fourth separation mirror in the sub-scanning direction, and the second diaphragm blocks the different positions of the second light beam in the sub-scanning direction. Three light-shielding pieces and a fourth light-shielding piece, The light piece is arranged at a position upstream of the fourth light shielding piece on the optical path, and the third light shielding piece is arranged in the vicinity of the arrangement position of the third separation mirror by the imaging lens. The fourth light shielding piece may be arranged at a position where the imaging lens creates an image of the fourth light shielding piece in the vicinity of the arrangement position of the second separation mirror. .

  According to this optical scanning device, the first to fourth scanned surfaces can be scanned with the first to fourth light beams. Therefore, the above optical scanning device can be applied to a general image forming apparatus that forms a full-color toner image using a four-color image forming engine.

  An image forming apparatus according to another aspect of the present invention includes the above optical scanning device, a first photosensitive drum provided with the first scanned surface, a second photosensitive drum provided with the second scanned surface, An image forming unit including a third photosensitive drum having three scanned surfaces and a fourth photosensitive drum having the fourth scanned surface.

  According to the present invention, in an optical scanning device including a plurality of light sources that emit light rays and separation mirrors that reflect the respective light rays toward the respective scanned surfaces, the light separation by the separation mirrors is favorably performed. be able to. Therefore, it is possible to provide an optical scanning device and an image forming apparatus that are excellent in image quality.

1 is a cross-sectional view illustrating a schematic configuration of a color printer according to an embodiment of the present invention. It is sectional drawing which shows the internal structure of the optical scanning device which concerns on embodiment of this invention. FIG. 2 is a schematic optical path diagram of an optical system provided in the optical scanning device. It is a typical optical path figure of the subscanning cross section of the optical scanning device concerning a comparative example. FIG. 3 is a schematic optical path diagram of a sub-scanning section of the optical scanning device according to the embodiment. It is a figure which shows an example of a division | segmentation type aperture_diaphragm | restriction. It is a schematic diagram for demonstrating the effect | action of a division | segmentation type aperture_diaphragm | restriction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic sectional view showing an internal structure of an image forming apparatus 1 according to an embodiment of the present invention. The image forming apparatus 1 is a tandem color printer, and includes a main body housing 10 formed of a substantially rectangular parallelepiped housing. Note that the image forming apparatus may be a full-color copying machine or a multifunction machine.

  The main body housing 10 accommodates therein a plurality of processing units that perform image forming processing on sheets. In the present embodiment, the image forming units 2Y, 2C, 2M, and 2Bk, the optical scanning device 23, the intermediate transfer unit 28, and the fixing device 30 are included as processing units. A paper discharge tray 11 is provided on the upper surface of the main body housing 10. A sheet discharge port 12 is opened to face the discharge tray 11. A manual paper feed tray 13 is attached to the side wall of the main body housing 10 so as to be freely opened and closed. A sheet feeding cassette 14 that accommodates a sheet to be subjected to image forming processing is detachably attached to the lower portion of the main body housing 10.

  The image forming units 2Y, 2C, 2M, and 2Bk form toner images of colors of yellow, cyan, magenta, and black based on image information transmitted from an external device such as a computer. In tandem. Each of the image forming units 2Y, 2C, 2M, and 2Bk includes a photosensitive drum 21 that carries an electrostatic latent image and a toner image, a charger 22 that charges a peripheral surface of the photosensitive drum 21, and a developer on the electrostatic latent image. Is formed on the photosensitive drum 21. The developing unit 24 forms a toner image by attaching the toner, and the toner containers 25Y, 25C, 25M, 25Bk for yellow, cyan, magenta, and black that supply toner of each color to the developing unit 24 are formed. A primary transfer roller 26 for primary transfer of the toner image, and a cleaning device 27 for removing residual toner on the peripheral surface of the photosensitive drum 21.

  The optical scanning device 23 forms an electrostatic latent image on the peripheral surface of the photosensitive drum 21 for each color. The optical scanning device 23 of the present embodiment forms a plurality of light sources prepared for each color in a single housing and images and scans the light beams emitted from these light sources on the peripheral surface of the photosensitive drum 21 of each color. An image optical system. The imaging optical systems for the respective colors are not optical systems independent from each other, but some optical systems are shared. The optical scanning device 23 will be described in detail later.

  The intermediate transfer unit 28 primarily transfers the toner image formed on the photosensitive drum 21. The intermediate transfer unit 28 includes a transfer belt 281 that rotates while contacting the peripheral surface of each photoconductive drum 21, and a driving roller 282 and a driven roller 283 that span the transfer belt 281. The transfer belt 281 is pressed against the peripheral surface of each photosensitive drum 21 by the primary transfer roller 26. The toner images on the photosensitive drums 21 for the respective colors are primarily transferred while being superimposed on the same location on the transfer belt 281. As a result, a full-color toner image is formed on the transfer belt 281.

  A secondary transfer roller 29 that forms a secondary transfer nip T across the transfer belt 281 is disposed opposite to the driving roller 282. The full color toner image on the transfer belt 281 is secondarily transferred onto the sheet at the secondary transfer nip T. The toner that is not transferred onto the sheet but remains on the peripheral surface of the transfer belt 281 is collected by a belt cleaning device 284 that is disposed to face the driven roller 283.

  The fixing device 30 includes a fixing roller 31 having a built-in heat source, and a pressure roller 32 that forms a fixing nip portion N together with the fixing roller 31. The fixing device 30 heats and pressurizes the sheet on which the toner image is transferred at the secondary transfer nip portion T at the fixing nip portion N, thereby performing a fixing process for fusing the toner to the sheet. The sheet subjected to the fixing process is discharged from the sheet discharge port 12 toward the discharge tray 11. The fixing device 30 will be described in detail later.

  A sheet conveyance path for conveying a sheet is provided inside the main body housing 10. The sheet conveyance path includes a main conveyance path P <b> 1 that extends in the vertical direction from the vicinity of the lower portion of the main body housing 10 to the vicinity of the upper portion via the secondary transfer nip T and the fixing device 30. The downstream end of the main conveyance path P1 is connected to the sheet discharge port 12. A reverse conveyance path P2 for reversing and conveying the sheet during duplex printing extends from the most downstream end to the vicinity of the upstream end of the main conveyance path P1. Further, a manual sheet conveyance path P3 extending from the manual feed tray 13 to the main conveyance path P1 is disposed above the paper feed cassette 14.

  The paper feed cassette 14 includes a sheet storage unit that stores a bundle of sheets. In the vicinity of the upper right of the sheet feeding cassette 14, a pickup roller 151 that feeds the uppermost sheet of the sheet bundle one by one and a sheet feeding roller pair 152 that feeds the sheet to the upstream end of the main transport path P1 are provided. . The sheet placed on the manual feed tray 13 is also sent out to the upstream end of the main conveyance path P1 through the manual sheet conveyance path P3. A registration roller pair 153 that feeds the sheet to the transfer nip portion at a predetermined timing is disposed on the upstream side of the secondary transfer nip portion T in the main conveyance path P1.

  When single-sided printing (image formation) processing is performed on a sheet, the sheet is sent out from the paper feed cassette 14 or the manual feed tray 13 to the main conveyance path P1, and toner image transfer processing is performed on the sheet at the secondary transfer nip T. A fixing process for fixing the toner transferred by the fixing device 30 to the sheet is performed. Thereafter, the sheet is discharged from the sheet discharge port 12 onto the discharge tray 11. On the other hand, when a double-sided printing process is performed on a sheet, a part of the sheet is discharged from a sheet discharge port 12 onto a discharge tray 11 after a transfer process and a fixing process are performed on one side of the sheet. The Thereafter, the sheet is conveyed in a switchback, and returned to the vicinity of the upstream end of the main conveyance path P1 through the reverse conveyance path P2. Thereafter, a transfer process and a fixing process are performed on the other side of the sheet, and the sheet is discharged from the sheet discharge port 12 onto the discharge tray 11.

  Next, details of the optical scanning device 23 will be described. 2 is a cross-sectional view showing the internal structure of the optical scanning device 23, and FIG. 3 is a schematic optical path diagram of an optical system provided in the optical scanning device 23. As shown in FIG. In FIG. 3, symbol AX indicates an optical axis (optical path). The optical scanning device 23 includes a housing 231, a light source unit 4 (4Y, 4C, 4M, 4Bk; light source unit) for each color housed in the housing 231, one deflector 5, and an imaging optical system. including. The imaging optical system includes a collimator lens 41 (41Y, 41C, 41M, 41Bk), a cylindrical lens 42, a first scanning lens 6 (imaging lens), and a second scanning lens 7 (7Y, 7C, 7M, 7Bk) for each color. ), A stop 8 (8Y, 8C, 8M, 8Bk; stop group) for each color and a plurality of reflecting mirrors (mirror group).

  Each light source unit 4 includes a laser unit 40 (40Y, 40C, 40M, and 40Bk) for each color having one semiconductor laser that emits a laser beam having a single wavelength. Specifically, the yellow light source unit 4Y is a yellow laser unit 40Y (first light source) that emits a laser beam LY (first light beam), and the cyan light source unit 4C is a cyan laser unit 40C that emits a laser beam LC (third light beam). The magenta light source unit 4M emits a laser beam LM (second light beam), the magenta laser unit 40M (second light source) emits a laser beam LM (second light source), and the black light source unit 4Bk emits a laser beam LBk (fourth light beam). Each unit 40Bk (fourth light source) is provided. As the laser unit 40, a multi-beam type laser unit in which 2 to 4 semiconductor lasers are modularized or a monolithic type laser unit may be used.

  FIG. 2 shows a yellow photosensitive drum 21Y (first photosensitive drum), a cyan photosensitive drum 21C (third photosensitive drum), and a magenta photosensitive member provided in each of the image forming units 2Y, 2C, 2M, and 2Bk. A drum 21M (second photosensitive drum) and a black photosensitive drum 21Bk are depicted. The laser beams LY, LC, LM, and LBk described above are applied to each drum with respect to the peripheral surfaces (first, third, second, and fourth scanned surfaces) of the photosensitive drums 21Y, 21C, 21M, and 21Bk of the respective colors. Irradiation is performed through windows 232, 233, 234, and 235 provided in the housing 231 so as to face each other.

  The collimator lens 41, the cylindrical lens 42, and the diaphragm 8 are disposed between the laser unit 40 and the deflecting body 5 on the optical path. The collimator lens 41 converts the laser beam emitted from the laser unit 40 and diffusing into parallel light. The cylindrical lens 42 converts the parallel light into linear light that is long in the main scanning direction, and forms an image on the deflecting body 5. The diaphragm 8 regulates the laser beam emitted from the laser unit 40.

  Referring to FIG. 3, the yellow light source unit 4Y includes a yellow collimator lens 41Y, an aperture 8Y (first aperture), and a light source mirror 404 on the downstream side of the optical axis AX of the yellow laser unit 40Y. Similarly, the cyan light source unit 4C includes a collimator lens 41C for cyan, an aperture 8C (third aperture), and a light source mirror 403 on the downstream side of the cyan laser unit 40C. The magenta light source unit 4M includes a magenta collimator lens 41M, an aperture 8M (second aperture), and a light source mirror 402 on the downstream side of the magenta laser unit 40M. The black light source unit 4Bk includes a black collimator lens 41Bk, a stop 8Bk (fourth stop), and a light source mirror 401 on the downstream side of the black laser unit 40Bk.

  3 and 4, the light source unit 4 is arranged such that the cyan light source unit 4C and the magenta light source unit 4M are sandwiched between the yellow light source unit 4Y and the black light source unit 4Bk in the main scanning section and the sub-scanning section. Is provided. The apertures 8Y and 8Bk of the yellow light source unit 4Y and the black light source unit 4Bk located at both ends in the arrangement of the light source units 4 are single type apertures. On the other hand, the apertures 8C and 8M of the cyan light source unit 4C and the magenta light source unit 4M located in the middle in the arrangement are divided type apertures. The stop 8C includes an upper light shielding piece 81 (first light shielding piece) and a lower light shielding piece 82 (second light shielding piece) arranged at different positions on the optical path. Similarly, the stop 8M includes an upper light-shielding piece 83 (third light-shielding piece) and a lower light-shielding piece 84 (fourth light-shielding piece) arranged at different positions on the optical path. The significance of the divided diaphragms 8C and 8M will be described in detail later.

  The deflecting body 5 deflects the laser beams LY, LC, LM, and LBk (first, third, second, and fourth beams) emitted from the laser units 40 for the respective colors, and the photosensitive drums 21Y and 21C for the respective colors. , 21M, and 21Bk are scanned from one end to the other end of a preset scanning range on the circumferential surfaces (first, third, second, and fourth scanned surfaces). The deflecting body 5 includes a polygon mirror 51 and a polygon motor 52 that rotates the polygon mirror 51. The polygon mirror 51 is a polygon mirror in which a deflection surface is formed along each side of a regular hexagon, for example. A rotation shaft of a polygon motor 52 is connected to the center position of the polygon mirror 51.

  The polygon mirror 51 deflects each laser beam LY, LC, LM, LBk emitted from the laser unit 4 while rotating around the rotation axis when the polygon motor 52 is driven to rotate, and each drum is rotated by these laser beams. Each of the peripheral surfaces is scanned. In the optical scanning device 23 of the present embodiment, a four-color shared type optical system in which the deflection of four color laser beams is covered by one polygon mirror 51 is employed. The laser beams LY, LC, LM, and LBk emitted from the light source units are reflected by the light source mirrors 404, 403, 402, and 401, respectively, and then obliquely enter one deflection surface. According to this configuration, the optical scanning device 23 can be made compact, and the number of parts can be reduced because only one deflector 5 is required. In other embodiments, a MEMS mirror may be used as the deflecting body 5.

  The first scanning lens 6 and the second scanning lens 7 are arranged between the deflecting body 5 and the photosensitive drums 21Y, 21C, 21M, and 21Bk on the optical path, and each laser beam LY, LC, LM, and LBk is transmitted to each drum. An image is formed on the peripheral surface. The first scanning lens 6 and the second scanning lens 7 are lenses having distortion aberration (fθ characteristics) in which the angle of incident light and the image height are proportional to each other, and are long lenses in the main scanning direction. These scanning lenses 6 and 7 are manufactured by mold molding using a translucent resin material. Note that the number of scanning lenses is not limited to two and may be any number.

  The first scanning lens 6 is a scanning lens close to the deflecting body 5 on the optical path, and is a common scanning lens through which all the laser beams LY, LC, LM, and LBk pass. The incident surface and the exit surface of the light beam in the first scanning lens 6 have lens power, and have a positive refractive power in both the main scanning direction and the sub-scanning direction. The second scanning lens 7 (7Y, 7C, 7M, 7Bk) is a scanning lens disposed at a position close to each of the photosensitive drums 21Y, 21C, 21M, 21Bk on the optical path. The second scanning lens 7 is not common, and the laser beams LY, LC, LM, and LBk of the respective colors individually pass through the second scanning lenses 7Y, 7C, 7M, and 7Bk.

  The plurality of reflecting mirrors included in the imaging optical system reflects the laser beams LY, LC, LM, and LBk of the respective colors so as to be directed toward the peripheral surfaces of the respective photosensitive drums 21Y, 21C, 21M, and 21Bk. The optical scanning device 23 includes a yellow separation mirror 431 (first separation mirror) and a reflection mirror 432 arranged between the deflecting body 5 and the photosensitive drum 21Y on the optical path in order to reflect the yellow laser beam LY. . Similarly, in order to reflect the cyan laser beam LC, a cyan separation mirror 441 (third separation mirror) and a reflection mirror 442 arranged between the deflecting body 5 and the photosensitive drum 21C on the optical path include a magenta laser beam. For the reflection of LM, a magenta separation mirror 451 (second separation mirror) and reflection mirrors 452 and 453 arranged between the deflecting body 5 and the photosensitive drum 21M on the optical path are used to reflect the black laser beam LBk. For this purpose, a black separation mirror 46 (fourth separation mirror) is provided between the deflecting body 5 and the photosensitive drum 21Bk on the optical path.

  Each separation mirror 431, 441, 451, 46 selectively reflects each color laser beam toward the peripheral surface of the corresponding photosensitive drum 21. Specifically, the yellow laser beam LY passes through the first scanning lens 6, is then reflected back by the yellow separation mirror 431, further passes through the second scanning lens 7 Y, and then is reflected upward by the reflection mirror 432. Then, an image is formed on the peripheral surface of the yellow photosensitive drum 21 </ b> Y through the window 232 of the housing 231.

  The cyan laser beam LC is reflected by the cyan separation mirror 441 after passing through the first scanning lens 6, further passes through the second scanning lens 7 </ b> C, is reflected by the reflection mirror 442, and passes through the window portion 233, thereby the cyan photosensitive drum 21 </ b> C. The image is formed on the peripheral surface. The magenta laser beam LM is reflected by the magenta separation mirror 451 and the reflection mirror 452 after passing through the first scanning lens 6, further reflected by the reflection mirror 453 after passing through the second scanning lens 7 M, and through the window 234. The image is formed on the peripheral surface of the photosensitive drum 21M. On the other hand, the black laser beam LBk passes through the first scanning lens 6 and then passes through the second scanning lens 7Bk, is reflected upward by the black separation mirror 46, and passes through the window 235 to the black photosensitive drum 21Bk. An image is formed on the peripheral surface.

  FIG. 2 shows a sub-scanning section of the optical scanning device 23. As apparent from FIG. 2, the cyan separation mirror 441 is disposed between the yellow separation mirror 431 and the magenta separation mirror 451 in the optical path and in the sub-scanning direction. The magenta separation mirror 451 is disposed between the cyan separation mirror 441 and the black separation mirror 46 in the optical path and in the sub-scanning direction.

  It is necessary that only the laser beams LY, LC, LM, and LBk of the respective colors are incident on the separation mirrors 431, 441, 451, and 46, respectively. However, in the configuration in which one deflector (deflection surface) is shared by four color laser beams as in the present embodiment, the laser beam can be separated with high accuracy while satisfying the demand for compactness of the optical scanning device 23. It is difficult to make it happen. In particular, with respect to the cyan separation mirror 441 and the magenta separation mirror 451 located on the optical path and in the middle of the sub-scanning direction in the arrangement of the separation mirrors, the separation of the laser beam is performed because the separation mirror is sandwiched between the optical paths of the two laser beams. More difficult.

  This point will be described with reference to FIG. FIG. 4 is a schematic optical path diagram of the sub-scan section of the optical scanning device according to the comparative example of the present invention. Here, the sub-scanning direction is the vertical direction. The comparative example and the later-described embodiment have the same optical arrangement except for the arrangement of the diaphragm 80 (8). The apertures 80 (80Y, 80C, 80M, 80Bk) for each color are all single-type apertures. The single-type stop referred to here is a general stop composed of one plate member having a square, rectangular, circular, or elliptical opening, and the stop is disposed at a specific point on the optical path. Arrows Ay, Ac, Am, and Abk in FIG. 4 indicate areas where the apertures 80Y, 80C, 80M, and 80Bk of the respective colors can be arranged on the optical path, respectively.

  The light source unit 4 is arranged in order of the yellow light source unit 4Y, the cyan light source unit 4C, the magenta light source unit 4M, and the black light source unit 4Bk from the top. That is, the light source units 4Y, 4C, 4M, and 4Bk are arranged at different positions in the sub-scanning direction, and the cyan light source unit 4C and the magenta light source unit 4M are located between the yellow light source unit 4Y and the black light source unit 4Bk in the sub-scanning direction. Is arranged. Therefore, each laser beam is emitted from the light source unit 4 in a state where the laser beams LY, LC, LM, and LBk (first, third, second, and fourth beams) are arranged in order from the top to the bottom. The laser beams LY, LC, LM, and LBk pass through the collimator lenses 41 (41Y, 41C, 41M, and 41Bk) of the respective light source units and are converted into parallel lights, and are respectively single-type diaphragms 80Y, 80C, 80M, and 80Bk. Pass through.

  Thereafter, the laser beams LY, LC, LM, and LBk are condensed and deflected by the cylindrical lens 42 on the deflecting surface of the deflecting body 5, pass through the first scanning lens 6, and are separated from the respective separation mirrors 431, 441, 451 (black separation). The mirror goes to (not shown). The separation mirrors are arranged so that the separation mirrors 431, 441, 451, and 46 (first, third, second, and fourth separation mirrors) are arranged from bottom to top. In FIG. 4, the black separation mirror 46 is not shown. The arrangement positions of the diaphragms 80Y, 80C, and 80M on the optical path are determined so that the diaphragm images 80YI, 80CI, and 80MI for the respective color diaphragms 80Y, 80C, and 80M are formed at the arrangement positions of the separation mirrors 431, 441, and 451. The The arrows By, Bc, and Bm in FIG. 4 indicate the real images of the aperture images 80YI, 80CI, and 80MI when the apertures 80Y, 80C, and 80M are disposed in any of the areas Ay, Ac, Am, and Abk. Indicates the range that can be made.

  In such a configuration, for example, it is difficult to accurately make only the cyan laser beam LC incident on the cyan separation mirror 441 disposed between the yellow separation mirror 431 and the magenta separation mirror 451 in the optical path and in the sub-scanning direction. . In other words, it is difficult to separate the laser beam LC from the laser beam LY and the laser beam LC adjacent to the laser beam LC on the optical path with high accuracy. In determining the position of the aperture image 80CI of one aperture 80C (positioning position of the cyan separation mirror 441), the lower part of the laser beam LC is the yellow separation mirror 431 and the upper part is the magenta separation mirror 451. This is because it is difficult to detect the position to prevent the incidence within the area Ac (range Bc). This is also true for the magenta separation mirror 451 arranged between the cyan separation mirror 441 and the black separation mirror 46 in the optical path and in the sub-scanning direction.

  On the other hand, in the optical scanning device 23 according to the embodiment of the present invention, the adjacent laser beams can be separated with high accuracy. FIG. 5 is a schematic optical path diagram of a sub-scan section of the optical scanning device 23. Since the configuration of the optical scanning device 23 is the same as that shown in FIG. 4 except for the diaphragm 8, the description of the other parts is omitted. The diaphragm 8 according to the present embodiment includes a yellow diaphragm 8Y and a black diaphragm 8Bk, which are the above-described single-type diaphragm, and a divided cyan diaphragm 8C and a magenta diaphragm arranged between the diaphragms 8Y and 8Bk. 8M.

  The divided type cyan diaphragm 8C shields different positions in the vertical direction (sub-scanning direction) of the laser beam LC, and the upper light shielding piece 81 (first light shielding piece) and the lower light shielding light arranged at different positions on the optical path. A piece 82 (second light shielding piece) is provided. The upper light shielding piece 81 is arranged at a position upstream of the lower light shielding piece 82 on the optical path. Similarly, the magenta diaphragm 8M shields different positions in the vertical direction of the laser beam LM, and the upper light-shielding piece 83 (third light-shielding piece) and the lower light-shielding piece 84 (fourth light-shielding piece) arranged at different positions on the optical path. Piece). The upper light shielding piece 81 is arranged at a position upstream of the lower light shielding piece 82 on the optical path. The upper light shielding piece 81 is close to the yellow diaphragm 8Y. The lower light shielding piece 82 of the diaphragm 8C and the upper light shielding piece 83 of the diaphragm 8M are close to each other. The lower light-shielding piece 84 is close to the black diaphragm 8Bk.

  The upper light shielding piece 81 of the stop 8C shields the upper part of the laser beam LC, and the lower light shielding piece 82 shields the lower part of the laser beam LC. Since the diaphragm 8C is a split type, the diaphragm image 8CI is also created separately. The aperture image 8CI includes an aperture image 81I of the upper light shielding piece 81 and an aperture image 82I of the lower light shielding piece 82. The upper light shielding piece 81 is arranged at a position where the first scanning lens 6 creates the aperture image 81I of the upper light shielding piece 81 near the arrangement position of the yellow separation mirror 431 (near the upper edge of the separation mirror 431). The lower light shielding piece 82 is disposed at a position where the first scanning lens 6 creates the aperture image 82I of the lower light shielding piece 82 in the vicinity of the arrangement position of the cyan separation mirror 441 (near the upper end of the reflection surface of the separation mirror 441). Yes.

  The upper light shielding piece 83 of the stop 8M shields the upper part of the laser beam LM, and the lower light shielding piece 84 shields the lower part of the laser beam LM. A diaphragm image 8MI of the diaphragm 8M is also created separately. The aperture image 8MI includes an aperture image 83I of the upper light shielding piece 83 and an aperture image 84I of the lower light shielding piece 84. The upper light shielding piece 83 is arranged at a position where the first scanning lens 6 creates the aperture image 83I of the upper light shielding piece 83 in the vicinity of the arrangement position of the cyan separation mirror 441 (near the upper edge of the separation mirror 441). The lower light-shielding piece 84 is arranged at a position where the first scanning lens 6 creates the aperture image 84I of the lower light-shielding piece 84 in the vicinity of the arrangement position of the magenta separation mirror 451 (near the upper end of the reflection surface of the separation mirror 451). Yes.

  FIG. 6 is a diagram showing a specific example of the split type diaphragm 8C. 6A shows the upper light shielding piece 81, FIG. 6B shows the lower light shielding piece 82 as viewed from the optical path (optical axis) direction, and FIG. 6C shows the upper light shielding piece 81 and the lower side. It is the figure which looked at the state combined with the light-shielding piece 82 from the optical path direction. As shown in FIG. 6C, the upper light-shielding piece 81 and the lower light-shielding piece 82 form one rectangular opening 8MH when viewed on the optical path.

  The upper light shielding piece 81 has an inverted U-shape having an opening 81H on the inner side. The upper light shielding piece 81 includes a first horizontal portion 811 that shields the upper portion of the laser beam LC, and a pair of first vertical portions 812 that extend downward from both left and right ends of the first horizontal portion 811. The first vertical portion 812 shields the left and right portions of the laser beam LC. Each of the first horizontal portion 811 and the first vertical portion 812 includes a straight belt-like portion, and the three sides of the opening 81H are partitioned by these belt-like portions.

  The lower light-shielding piece 82 has a U-shape having an opening 82H on the inner side. The lower light shielding piece 82 includes a second horizontal portion 821 that shields the lower portion of the laser beam LC, and a pair of second vertical portions 822 that extend upward from the left and right ends of the second horizontal portion 821. The second vertical portion 822 shields the left and right portions near the lower side of the laser beam LC. Each of the second horizontal portion 821 and the second vertical portion 822 includes a straight belt-like portion, and three sides of the opening 82H are partitioned by these belt-like portions. The size of the second horizontal portion 821 in the left-right direction is the same as that of the first horizontal portion 811. On the other hand, the vertical size of the second vertical portion 822 is shorter than that of the first vertical portion 812.

  When the upper light shielding piece 81 and the lower light shielding piece 82 are combined, the first vertical portion 812 and the second vertical portion 822 overlap with each other when viewed in the optical axis direction. Then, the second horizontal portion 821 closes the lower end opening portion of the opening 81H, and the first horizontal portion 811 closes the upper end opening portion of the opening 82H, thereby forming one closed opening 8MH. At this time, the lower surface 813 of the first vertical portion 812 and the lower surface 823 of the second horizontal portion 821 are in contact with the same seating surface G (surface of the same height) provided in the housing 231 (FIG. 2). Yes. Thus, according to the present embodiment, the diaphragm 8C can be formed simply by installing the upper light shielding piece 81 and the lower light shielding piece 82 on the same seating surface G. Therefore, even when the divided diaphragm 8C is employed, The structure can be simplified and the assemblability can be improved. Note that the upper light-shielding piece 83 and the lower light-shielding piece 84 of the stop 8M have the same configuration as described above.

  FIG. 7 is a schematic diagram for explaining the operation of the split-type diaphragm 8C. The laser beam LC emitted from the cyan laser unit 40C passes through the cyan collimator lens 41C, is converted into parallel light, and travels toward the split type aperture 8C. The upper light shielding piece 81 restricts the light beam L01 in the upper part of the laser beam LC, and the lower light shielding piece 82 restricts the light beam L02 in the lower part. The laser beam LC that has passed through the stop 8C passes through the cylindrical lens 42, is converted into linear light, and travels toward the cyan separation mirror 441 that is deflected by the deflector 5.

  Here, attention is focused on the light beam L1 that forms the aperture image 81I of the upper light shielding piece 81 and the light beam L2 that forms the aperture image 82I of the lower light shielding piece 82. The light beam L1 passes through the upper light shielding piece 81 and then forms an image in the vicinity of the arrangement position of the yellow separation mirror 431 (near the upper end edge) by the first scanning lens 6 via the cylindrical lens 42 and the deflecting body 5. In other words, the upper light-shielding piece 81 is arranged at a position where the aperture image 81I of the upper light-shielding piece 81 is created near the upper edge of the yellow separation mirror 431. For this reason, the light beam L1 can be prevented from entering the yellow separation mirror 431. If the aperture image 81I is formed on the cyan separation mirror 441, a part of the light beam L1 is yellow unless the yellow separation mirror 431 and the cyan separation mirror 441 are arranged at a wide interval in the sub-scanning direction. The light enters the separation mirror 431.

  After passing through the lower light-shielding piece 82, the light beam L2 passes through the cylindrical lens 42 and the deflecting body 5 and is imaged near the arrangement position of the cyan separation mirror 441 (near the upper end of the reflection surface) by the first scanning lens 6. The In other words, the lower light-shielding piece 82 is disposed at a position where the aperture image 82I of the lower light-shielding piece 82 is formed near the upper end of the reflection surface of the cyan separation mirror 441. For this reason, it is possible to prevent the laser beam LC from deviating from the range of the cyan separation mirror 441 and entering the magenta separation mirror 451 disposed in the subsequent stage. Therefore, the laser beam LC can be separated from other laser beams with high accuracy and taken out by the cyan separation mirror 441.

  Further, even if the installation tolerance of the cyan light source unit 4C, for example, the eccentricity of the cyan laser unit 40C or the collimator lens in the sub-scanning direction occurs, there is an advantage that the laser beam LC does not enter the other separation mirrors 431 and 451. This is because even if the eccentricity occurs, the light beams L1 and L2 passing through the upper light shielding piece 81 and the lower light shielding piece 82 form aperture images 81I and 82I at the positions shown in FIG. The above points are the same for the diaphragm 8M. Therefore, it is possible to realize a scanning optical system that is not easily affected by installation tolerances. In addition, as a result of the high-precision separation of the laser beams LC and LM by the diaphragms 8C and 8M, there is an advantage that in the design of the optical scanning device 23, it is easy to achieve downsizing (lower height) in the vertical direction (sub-scanning direction). is there.

  Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments. For example, in the above-described embodiment, an example in which the split diaphragm 8C (8M) is configured by only the upper light shielding piece 81 and the lower light shielding piece 82 has been described. As long as the diaphragm 8C has the first horizontal portion 811 and the second horizontal portion 821, that is, as long as the upper side and the lower side of the laser beam LC can be regulated at the respective positions, the diaphragm 8C is configured by three or more light shielding pieces. May be. Moreover, the opening shape by the combination of the upper light-shielding piece 81 and the lower light-shielding piece 82 is not limited to a rectangle. For example, the first and second vertical portions 812 and 822 may be convex toward the outside and may be substantially elliptical openings.

1 Image forming apparatus 2Y, 2C, 2M, 2Bk Image forming unit 21 (21Y, 21C, 21M, 21Bk) Photosensitive drum (first, third, second, fourth photosensitive drum)
23 Optical scanning device 4 (4Y, 4C, 4M, 4Bk) Light source unit (light source unit)
40 (40Y, 40C, 40M, 40Bk) Laser unit (first, third, second and fourth light sources)
431 Yellow separation mirror (first separation mirror)
441 Cyan separation mirror (third separation mirror)
451 Magenta separation mirror (second separation mirror)
46 Black separation mirror (4th separation mirror)
5 Deflector 6 First scanning lens (imaging lens)
8 (8Y, 8C, 8M, 8Bk) stop (first, third, second, fourth stop; stop group)
81 Upper shading piece (first shading piece)
82 Lower light-shielding piece (second light-shielding piece)
83 Upper shading piece (third shading piece)
84 Lower shading piece (fourth shading piece)
LY, LC, LM, LBk laser beams (first, third, second and fourth beams)

Claims (6)

A first light source that emits a first light beam, and the first light source are arranged at different positions in the sub-scanning direction, a second light source that emits a second light beam, and the first light source and the second light source in the sub-scanning direction A light source unit including a third light source that is disposed between and emits a third light beam;
The first light beam, the second light beam, and the third light beam are deflected, and the first light beam forms the first scanned surface, the second light beam forms the second scanned surface, and the third light beam uses the third light beam. A deflector that scans each surface to be scanned;
A diaphragm which is disposed between the deflecting body and the first, second and third light sources on the optical path, and includes first, second and third diaphragms for regulating the first, second and third light beams, respectively. Group,
It is disposed between the deflecting body and the first, second, and third scanned surfaces on the optical path, and the first, second, and third light beams are applied to the first, second, and third scanned surfaces. An imaging lens for imaging each;
A first separation mirror disposed between the deflecting body and the first scanned surface on the optical path and reflecting the first light beam to the first scanned surface; and the deflecting body and the second on the optical path. A second separation mirror disposed between the scanning surface and reflecting the second light beam to the second scanning surface; and between the deflector and the third scanning surface on the optical path, A mirror group including a third separation mirror disposed on the optical path and between the first separation mirror and the second separation mirror in the sub-scanning direction and reflecting the third light beam to the third scanned surface; With
The third diaphragm includes a first light shielding piece and a second light shielding piece for shielding light at different positions in the sub-scanning direction of the third light beam, and the first light shielding piece is on an optical path more than the second light shielding piece. Placed upstream,
The first light-shielding piece is located at a position where the imaging lens creates an image of the first light-shielding piece in the vicinity of the position where the first separation mirror is disposed. An optical scanning device disposed at a position where an image of a piece is formed in the vicinity of the position where the third separation mirror is disposed. The optical scanning device according to claim 1,
When the sub-scanning direction is the vertical direction,
The light source unit is arranged so that the first, third, and second light sources are arranged in order from top to bottom in the sub-scan section.
The mirror group is arranged so that the first, third, and second separation mirrors are arranged in order from the bottom to the top in the sub-scan section.
The optical scanning device, wherein the first light shielding piece shields an upper side of the third light beam, and the second light shielding piece shields a lower side of the third light beam. The optical scanning device according to claim 2,
The first light-shielding piece and the second light-shielding piece form one opening when viewed on the optical path,
The first light shielding piece includes a first horizontal portion that shields an upper side of the third light beam, and a pair of vertical portions extending downward from both ends of the first horizontal portion,
The second light shielding piece includes a second horizontal portion that shields a lower side of the third light beam,
The lower surface of the pair of vertical portions and the lower surface of the second horizontal portion are in contact with the same seating surface. The optical scanning device according to any one of claims 1 to 3,
The optical scanning device, wherein the deflector includes a deflecting surface on which the first, second, and third light beams are simultaneously incident. In the optical scanning device according to any one of claims 1 to 4,
The light source unit further includes a fourth light source that emits a fourth light beam,
The deflecting body further scans a fourth surface to be scanned with the fourth light beam,
The aperture group further includes a fourth aperture that regulates the fourth light beam,
The imaging lens further images the fourth light beam on a fourth scanned surface,
The mirror group further includes a fourth separation mirror disposed on the optical path between the deflector and the fourth scanned surface,
The fourth separation mirror is disposed on the downstream side of the second separation mirror on the optical path,
The third separation mirror and the second separation mirror are disposed between the first separation mirror and the fourth separation mirror in the sub-scanning direction;
The second diaphragm includes a third light-shielding piece and a fourth light-shielding piece that respectively shield different positions in the sub-scanning direction of the second light beam, and the third light-shielding piece is on the optical path more than the fourth light-shielding piece. Placed upstream,
The third light-shielding piece is located at a position where the imaging lens creates an image of the third light-shielding piece in the vicinity of the arrangement position of the third separation mirror, and the fourth light-shielding piece is located at the fourth light-shielding piece. An optical scanning device arranged at a position where an image of a piece is formed in the vicinity of the arrangement position of the second separation mirror. An optical scanning device according to claim 5;
A first photosensitive drum having the first scanned surface; a second photosensitive drum having the second scanned surface; a third photosensitive drum having the third scanned surface; and a fourth scanned surface. An image forming unit including a fourth photosensitive drum;
An image forming apparatus comprising: