US20160223935A1 - Optical scanning device and image forming apparatus using the same - Google Patents
Optical scanning device and image forming apparatus using the same Download PDFInfo
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- US20160223935A1 US20160223935A1 US15/008,795 US201615008795A US2016223935A1 US 20160223935 A1 US20160223935 A1 US 20160223935A1 US 201615008795 A US201615008795 A US 201615008795A US 2016223935 A1 US2016223935 A1 US 2016223935A1
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- light beam
- optical scanning
- reflection mirror
- scanned surface
- mirror
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- 230000003287 optical effect Effects 0.000 title claims abstract description 123
- 238000012546 transfer Methods 0.000 description 28
- 238000000034 method Methods 0.000 description 13
- 239000003086 colorant Substances 0.000 description 9
- 238000011144 upstream manufacturing Methods 0.000 description 5
- 238000013459 approach Methods 0.000 description 3
- 230000015572 biosynthetic process Effects 0.000 description 3
- 230000001154 acute effect Effects 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 239000000428 dust Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 238000010348 incorporation Methods 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000002093 peripheral effect Effects 0.000 description 1
- 239000004065 semiconductor Substances 0.000 description 1
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Classifications
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
- G03G15/00—Apparatus for electrographic processes using a charge pattern
- G03G15/04—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material
- G03G15/041—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with variable magnification
- G03G15/0415—Apparatus for electrographic processes using a charge pattern for exposing, i.e. imagewise exposure by optically projecting the original image on a photoconductive recording material with variable magnification and means for controlling illumination or exposure
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/024—Details of scanning heads ; Means for illuminating the original
- H04N1/028—Details of scanning heads ; Means for illuminating the original for picture information pick-up
- H04N1/02815—Means for illuminating the original, not specific to a particular type of pick-up head
- H04N1/0282—Using a single or a few point light sources, e.g. a laser diode
- H04N1/0283—Using a single or a few point light sources, e.g. a laser diode in combination with a light deflecting element, e.g. a rotating mirror
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
- H04N1/06—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using cylindrical picture-bearing surfaces, i.e. scanning a main-scanning line substantially perpendicular to the axis and lying in a curved cylindrical surface
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
- H04N1/04—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa
- H04N1/113—Scanning arrangements, i.e. arrangements for the displacement of active reading or reproducing elements relative to the original or reproducing medium, or vice versa using oscillating or rotating mirrors
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
- H04N2201/04—Scanning arrangements
- H04N2201/047—Detection, control or error compensation of scanning velocity or position
- H04N2201/04753—Control or error compensation of scanning position or velocity
- H04N2201/04755—Control or error compensation of scanning position or velocity by controlling the position or movement of a scanning element or carriage, e.g. of a polygonal mirror, of a drive motor
Definitions
- the present disclosure relates to an optical scanning device that includes a plurality of light sources for emitting light beams and a deflector for reflecting the light beams toward corresponding scanned surfaces, and to an image forming apparatus that uses the optical scanning device.
- An optical scanning device for use in a color laser printer includes, for example: a plurality of light sources for emitting laser beams respectively for colors of cyan, magenta, yellow and black; a deflector (polygon mirror) for deflecting the laser beams such that the laser beams scan the circumferential surfaces (scanned surfaces) of the photoconductor drums for respective colors; and focus lenses for focusing the deflected laser beams on the circumferential surfaces.
- the deflector may be used in common by a plurality of laser beams.
- Each of the optical scanning devices includes two light sources and a deflector.
- a laser beam emitted from a light source is deflected at a first position on the circumference of the deflector
- a laser beam emitted from the other light source is deflected at a second position that is on the opposite side to the first position.
- An optical scanning device includes a housing, a light source portion, a deflector, a first focus lens, a second focus lens, a first mirror group, and a second mirror group.
- the light source portion includes a first light source and a second light source, the first light source emitting a first light beam, the second light source emitting a second light beam.
- the rotation axis of the deflector is inclined with respect to a first direction and a second direction, the first direction being opposite to the second direction.
- the deflector is configured to reflect the first light beam diagonally on a side of a third direction that is perpendicular to the first direction and the second direction, and on a side of the first direction, and is configured to reflect the second light beam diagonally on a side of a fourth direction that is opposite to the third direction, and on a side of the second direction, such that the first light beam scans a first scanned surface and the second light beam scans a second scanned surface.
- the first focus lens is disposed between the deflector and the first scanned surface and configured to focus the first light beam on the first scanned surface.
- the second focus lens is disposed between the deflector and the second scanned surface and configured to focus the second light beam on the second scanned surface.
- the first mirror group is disposed between the first focus lens and the first scanned surface and configured to reflect the first light beam to the first scanned surface.
- the second mirror group is disposed between the second focus lens and the second scanned surface and configured to reflect the second light beam to the second scanned surface.
- the first mirror group includes a first reflection mirror and a second reflection mirror. The first light beam that has transmitted through the first focus lens is incident on the first reflection mirror.
- the first reflection mirror is configured to reflect the first light beam in the second direction of separating away from the first scanned surface.
- the second reflection mirror is configured to reflect the first light beam reflected by the first reflection mirror, toward the first scanned surface.
- the second mirror group includes a third reflection mirror and a fourth reflection mirror.
- the second light beam that has transmitted through the second focus lens is incident on the third reflection mirror.
- the third reflection mirror is configured to reflect the second light beam in the first direction of approaching the second scanned surface.
- the fourth reflection mirror is configured to reflect the second light beam reflected by the third reflection mirror, toward the second scanned surface.
- FIG. 1 is a cross-sectional view showing the configuration of a color printer according to an embodiment of the present disclosure.
- FIG. 2 is a cross-sectional view showing the internal configuration of an optical scanning device according to an embodiment of the present disclosure.
- FIG. 3 is a plan view showing a part of an optical path of the optical scanning device according to an embodiment of the present disclosure.
- FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus 1 according to an embodiment of the present disclosure.
- the image forming apparatus 1 is a tandem color printer.
- the image forming apparatus 1 includes a main body housing 10 that is formed approximately in the shape of a rectangular parallelepiped. It is noted that the image forming apparatus may be a full-color copier or multifunction peripheral.
- the main body housing 10 includes therein a plurality of processing units for performing an image formation process to a sheet.
- the main body housing 10 includes, as the processing units, image forming units 2 Y, 2 C, 2 M and 2 Bk, color containers 25 Y, 25 C, 25 M and 25 Bk for respective colors, an optical scanning device 23 , an intermediate transfer unit 28 , and a fixing device 30 .
- a sheet discharge tray 11 is provided on the upper surface of the main body housing 10 .
- a sheet discharge port 12 is opened opposite to the sheet discharge tray 11 .
- a manual feed tray 13 is attached to a side wall of the main body housing 10 in a freely openable/closable manner.
- a sheet feed cassette 14 is attached to a lower part of the main body housing 10 in a freely attachable/detachable manner, wherein sheets on which images are to be formed by the image formation process are stored in the sheet feed cassette 14 .
- the image forming units 2 Y, 2 C, 2 M and 2 Bk are configured to form toner images of yellow, cyan, magenta and black respectively based on image information transmitted from an external apparatus such as a computer, and are aligned at predetermined intervals in tandem in the horizontal direction.
- Each of the image forming units 2 Y, 2 C, 2 M and 2 Bk includes: a cylindrical photoconductor drum 21 for carrying an electrostatic latent image and a toner image; a charger 22 ; a developing device 24 ; a primary transfer roller 26 ; and a cleaning device 27 .
- the optical scanning device 23 forms electrostatic latent images on the circumferential surfaces of the photoconductor drums 21 of respective colors.
- the optical scanning device 23 of the present embodiment includes a plurality of light sources and focusing optical systems, wherein the plurality of light sources are prepared for the respective colors, and the focusing optical systems focus and scan the light beams emitted from the light sources on the circumferential surfaces of the photoconductor drums 21 of the respective colors.
- the focusing optical systems are not independent optical systems, but a part thereof is used in common.
- the optical scanning device 23 is described below.
- the intermediate transfer unit 28 performs a primary transfer of transferring toner images formed on the photoconductor drums 21 .
- the intermediate transfer unit 28 includes a transfer belt 281 , a driving roller 282 and a driven roller 283 , wherein the transfer belt 281 circumferentially rotates while contacting the circumferential surfaces of the photoconductor drums 21 , and the transfer belt 281 is suspended between the driving roller 282 and the driven roller 283 .
- the transfer belt 281 is pressed against the circumferential surfaces of the photoconductor drums 21 by the primary transfer rollers 26 .
- the toner images are transferred from the photoconductor drums 21 so as to be overlaid at a same position on the transfer belt 281 . This allows a full-color toner image to be formed on the transfer belt 281 .
- a secondary transfer roller 29 is disposed opposite to the driving roller 282 across the transfer belt 281 so as to form a secondary transfer nip portion T.
- the full-color toner image is transferred from the transfer belt 281 to a sheet by the secondary transfer nip portion T.
- the fixing device 30 includes a fixing roller 31 and a pressure roller 32 , wherein a heat source is embedded in the fixing roller 31 , and the fixing roller 31 and the pressure roller 32 form a fixing nip portion N.
- the fixing device 30 performs a fixing process in which the sheet to which the toner image has been transferred by the secondary transfer nip portion T is heated and pressed by the fixing nip portion N so that the toner is fused and fixed to the sheet.
- the sheet subjected to the fixing process is discharged from the sheet discharge port 12 toward the sheet discharge tray 11 .
- a sheet conveyance path for conveying sheets is provided in the main body housing 10 .
- the sheet conveyance path includes a main conveyance path P 1 that vertically extends from near a lower part of the main body housing 10 to near an upper part via the secondary transfer nip portion T and the fixing device 30 .
- the downstream end of the main conveyance path P 1 is connected to the sheet discharge port 12 .
- a reverse conveyance path P 2 for conveying a reversed sheet in the double-side printing is provided to extend from the most downstream end in the main conveyance path P 1 to near the upstream end.
- a manually fed sheet conveyance path P 3 extending from the manual feed tray 13 to the main conveyance path P 1 is disposed above the sheet feed cassette 14 .
- the sheet feed cassette 14 includes a sheet storage portion for storing a stack of sheets.
- a pick-up roller 151 and a pair of sheet feed rollers 152 are disposed in the vicinity of an upper-right part of the sheet feed cassette 14 , wherein the pick-up roller 151 picks up, one by one, the top sheets of the stack of sheets, and the pair of sheet feed rollers 152 feed the picked-up sheet toward the upstream end of the main conveyance path P 1 .
- a sheet placed on the manual feed tray 13 is also conveyed to the upstream end of the main conveyance path P 1 via the manually fed sheet conveyance path P 3 .
- a pair of registration rollers 15 are disposed more on the upstream side than the secondary transfer nip portion T in the main conveyance path P 1 , wherein the pair of registration rollers 15 feed a sheet to the transfer nip portion at a predetermined timing.
- a single-side printing process image formation process
- the sheet is fed from the sheet feed cassette 14 or the manual feed tray 13 to the main conveyance path P 1 .
- a transfer process of transferring a toner image to the sheet is performed in the secondary transfer nip portion T, and the fixing process of fixing the transferred toner to the sheet is performed in the fixing device 30 .
- the sheet is discharged from the sheet discharge port 12 onto the sheet discharge tray 11 .
- the transfer process and the fixing process are performed to one surface of the sheet, then the sheet is partially projected outward on the sheet discharge tray 11 from the sheet discharge port 12 .
- the sheet is switchback-conveyed to be returned to near the upstream end of the main conveyance path P 1 via the reverse conveyance path P 2 .
- the transfer process and the fixing process are then performed to the other surface of the sheet, then the sheet is discharged on the sheet discharge tray 11 from the sheet discharge port 12 .
- FIG. 2 is a cross-sectional view showing the internal configuration of the optical scanning device 23 of the present embodiment.
- FIG. 3 is a plan view showing a part of an optical path of the optical scanning device 23 .
- the optical scanning device 23 includes a first optical scanning unit 23 A and a second optical scanning unit 23 B.
- the first optical scanning unit 23 A and the second optical scanning unit 23 B are disposed adjacent to each other in the horizontal direction.
- the first optical scanning unit 23 A is disposed below a yellow photoconductor drum 21 Y (the first scanned surface, the first photoconductor drum) and a magenta photoconductor drum 21 M (the second scanned surface, the second photoconductor drum), and scans the circumferential surfaces of the two photoconductor drums 21 .
- the second optical scanning unit 23 B is disposed below a cyan photoconductor drum 21 C (the first scanned surface, the third photoconductor drum) and a black photoconductor drum 21 BK (the second scanned surface, the fourth photoconductor drum), and scans the circumferential surfaces of the two photoconductor drums 21 .
- the main scanning direction of the first optical scanning unit 23 A and the second optical scanning unit 23 B is a left-right direction perpendicular to the plane of FIG. 2
- the sub scanning direction is a front-rear direction, namely a tangent direction at the lower-end part of each photoconductor drum 21 .
- the photoconductor drums 21 of four colors are disposed such that the rotation shaft centers are disposed adjacent to each other at intervals on a predetermined straight line (a first reference line DL) in a cross section taken along a plane including the sub scanning direction of the optical scanning device 23 , and the photoconductor drums 21 are rotated by a driving portion (not shown).
- a second reference line DR is defined as a straight line that is perpendicular to the first reference line DL.
- the second reference line DR extends along the up-down direction.
- a pair of conveyance screws 241 and a developing housing lower end portion 242 of the developing device 24 are seen between: the photoconductor drums 21 ; and the first optical scanning unit 23 A and the second optical scanning unit 23 B.
- the pair of conveyance screws 241 have a function to stir the developer in the developing device 24 .
- the developing housing lower end portion 242 is an imaginary straight line that extends along the lower end portion of the housing of the developing device 24 .
- the first optical scanning unit 23 A includes a first housing 230 A, a light source unit 80 (the light source portion), a polygon motor 51 , a polygon mirror 52 (deflector), and a focusing optical system, wherein the light source unit 80 includes light sources 81 and 82 respectively for yellow and magenta that are stored in the first housing 230 A.
- the second optical scanning unit 23 B has the same internal configuration as the first optical scanning unit 23 A, and includes a second housing 230 B, a light source unit 80 (the light source portion), a polygon motor 51 , a polygon mirror 52 (deflector), and a focusing optical system, wherein the light source unit 80 includes light sources 81 and 82 respectively for cyan and black that are stored in the second housing 230 B.
- the light source unit 80 includes light sources 81 and 82 respectively for cyan and black that are stored in the second housing 230 B.
- FIG. 2 components of the same type included in the first optical scanning unit 23 A and the second optical scanning unit 23 B are assigned a same reference number, for the sake of explanation.
- the light sources 81 and 82 of the light source unit 80 stored in the first housing 230 A each include a semiconductor laser that emits a laser beam of a single wavelength.
- a light source 81 for yellow (the first light source) is positioned more on the front side in the plane of the figure than the polygon mirror 52 , and emits a first light beam L 1 that is irradiated on the photoconductor drum 21 Y.
- a light source 82 for magenta (the second light source) is disposed at a different position from the light source 81 for yellow in the sub scanning direction (front-rear direction), more specifically, is positioned more on the front side than the light source 81 for yellow.
- the light source 82 for magenta is positioned more on the rear side in the plane of the figure than the polygon mirror 52 , and emits a second light beam L 2 that is irradiated on the photoconductor drum 21 M.
- a collemator lens (not shown), a cylindrical lens (not shown), and a diaphragm (not shown) are disposed respectively between the polygon mirror 52 and the light source 81 , and between the polygon mirror 52 and the light source 82 .
- the collemator lens converts a laser beam to parallel light beams, wherein the laser beam is emitted from the light source 81 , 82 and diffused.
- the cylindrical lens converts the parallel light beams to line-like light beams that are elongated in the main scanning direction and focuses the light beams on the polygon mirror 52 .
- the diaphragm regulates the laser beam emitted from the light source 81 , 82 .
- the polygon mirror 52 deflects laser beams L 1 and L 2 (the first light beam and the second light beam) emitted from the light sources 81 and 82 for respective colors, respectively such that the light beams scan the circumferential surfaces of the photoconductor drums 21 Y and 21 M (the first scanned surface and the second scanned surface), from one end to the other end of a predetermined scanning range.
- the polygon mirror 52 is a polygon mirror having deflection surfaces formed along the sides of a hexagon.
- the rotation shaft of the polygon motor 51 is connected to the center of the polygon mirror 52 . That is, the polygon motor 51 is coaxially fixed to the polygon mirror 52 and rotates the polygon mirror 52 .
- the rotation shaft is inclined at an acute angle with respect to the up direction (the first direction) and the down direction (the second direction that is opposite to the first direction).
- a single polygon mirror 52 is used in common to scan the photoconductor drums 21 for two colors.
- the polygon mirror 52 deflects the first light beam L 1 and the second light beam L 2 in opposite directions. More specifically, the polygon mirror 52 reflects the first light beam L 1 on the side of the rear direction (the third direction) perpendicular to the up-down direction, and in the diagonally upward direction (the rear diagonally upward direction).
- the polygon mirror 52 reflects the second light beam L 2 on the side of the front direction (the fourth direction), which is opposite to the rear direction, and in the diagonally downward direction (the front diagonally downward direction).
- the focusing optical system includes a scanning lens 53 (first focus lens), a scanning lens 54 (second focus lens), a reflection mirror 56 (first reflection mirror), a reflection mirror 57 (third reflection mirror), a reflection mirror 58 (second reflection mirror), and a reflection mirror 59 (fourth reflection mirror).
- the scanning lens 53 is disposed on the optical path of the first light beam L 1 between the polygon mirror 52 and the circumferential surface of the photoconductor drum 21 Y, and focuses the first light beam L 1 on the circumferential surface.
- the scanning lens 54 is disposed on the optical path of the second light beam L 2 between the polygon mirror 52 and the circumferential surface of the photoconductor drum 21 M, and focuses the second light beam L 2 on the circumferential surface.
- the scanning lens 53 and the scanning lens 54 are each a single lens.
- the scanning lens 53 and the scanning lens 54 have the same shape and are arranged so as to be in point symmetry with respect to the rotation center of the polygon mirror 52 , as shown in the cross section of FIG. 2 . This makes it possible to commonalize the scanning lens 53 and the scanning lens 54 , thereby the cost of the optical scanning device 23 is reduced.
- the reflection mirror 56 and the reflection mirror 58 constitute the first mirror group of the present disclosure.
- the first mirror group is disposed on the optical path of the first light beam L 1 between the scanning lens 53 and the circumferential surface of the photoconductor drum 21 Y, and reflects the first light beam L 1 to the circumferential surface.
- the reflection mirror 57 and the reflection mirror 59 constitute the second mirror group of the present disclosure.
- the second mirror group is disposed on the optical path of the second light beam L 2 between the scanning lens 54 and the circumferential surface of the photoconductor drum 21 M, and reflects the second light beam L 2 to the circumferential surface.
- the reflection mirror 56 is disposed, among the first mirror group, closest to the scanning lens 53 on the optical path of the first light beam L 1 .
- the first light beam L 1 having transmitted through the scanning lens 53 is incident on the reflection mirror 56 .
- the reflection mirror 56 reflects the first light beam L 1 downward away from the circumferential surface of the photoconductor drum 21 Y.
- the reflection mirror 58 is disposed in the downstream of the reflection mirror 56 on the optical path of the first light beam L 1 .
- the reflection mirror 58 reflects the first light beam L 1 reflected by the reflection mirror 56 , to the circumferential surface of the photoconductor drum 21 Y.
- the reflection mirror 57 is disposed, among the second mirror group, closest to the scanning lens 54 on the optical path of the second light beam L 2 .
- the second light beam L 2 having transmitted through the scanning lens 54 is incident on the reflection mirror 57 .
- the reflection mirror 57 reflects the second light beam L 2 upward in a direction of approaching the circumferential surface of the photoconductor drum 21 M.
- the reflection mirror 59 is disposed in the downstream of the reflection mirror 57 on the optical path of the second light beam L 2 .
- the reflection mirror 59 reflects the second light beam L 2 reflected by the reflection mirror 57 , to the circumferential surface of the photoconductor drum 21 M.
- dustproof glasses are provided at the portions from which the first light beam L 1 and the second light beam L 2 are emitted.
- the dustproof glasses prevent foreign materials such as dust from entering the first housing 230 A.
- the scanning lens 53 and the scanning lens 54 ( FIG. 3 ) of the present embodiment both have a free curved surface that is defined by the equation (1).
- “z” represents a surface shape of the scanning lens 53 and the scanning lens 54 in the main scanning direction.
- Table 1 shows values of coefficients that can be substituted into the equation (1), for each of the incident surface and the emission surface. It is noted that although coefficients for the surface shape in the sub scanning direction are omitted, the sub scanning magnification between the polygon mirror 52 and the photoconductor drum 21 Y (the photoconductor drum 21 M) is set to three times or less.
- the length of the optical path from the polygon mirror 52 to the scanning lens 53 and the scanning lens 54 is set to be relatively long, and the length of the optical path from the scanning lens 53 and the scanning lens 54 to circumferential surfaces of the photoconductor drums 21 Y and 21 M is set to be relatively short.
- the scanning lens 53 and the scanning lens 54 each being a single lens, the sub scanning magnification is set to a small value.
- R denotes a main scanning curvature radius
- Ci denotes a coefficient of the surface shape
- r denotes a height in a direction perpendicular to the optical axis direction.
- the scanning lens 53 and the scanning lens 54 allow an excellent focus performance to be obtained when the distances from the emission surfaces of the lenses to the circumferential surfaces (scanned surfaces) of the photoconductor drums 21 Y and 21 M are each less than 110 mm.
- the lens thickness (center thickness) of the scanning lens 53 and the scanning lens 54 is 9.0 mm.
- the distance from the deflection surface of the polygon mirror 52 to the incident surface of each lens is set to 23.7 mm.
- the polygon mirror 52 is arranged such that the rotation shaft thereof is inclined at a predetermined angle with respect to the first reference line DL that connects the rotation shafts centers of a pair of photoconductor drums 21 (photoconductor drums 21 Y and 21 M).
- the trajectory of the light beam deflected by the polygon mirror 52 is inclined at an acute angle ⁇ X with respect to the horizontal line (a straight line parallel to the first reference line DL).
- An optical path of the first light beam L 1 is formed in rear of the polygon mirror 52
- an optical path of the second light beam L 2 is formed in front of the polygon mirror 52 .
- the first mirror group and the second mirror group are arranged such that the optical path of the first light beam L 1 and the optical path of the second light beam L 2 do not intersect with each other.
- the rotation shaft of the polygon mirror 52 is inclined with respect to the up-down direction such that the front of the rotation shaft is located above, and the rear of the rotation shaft is located below.
- the first light beam L 1 emitted from the light source 81 for yellow is deflected by the polygon mirror 52 in the rear diagonally upward direction toward the scanning lens 53 in a direction of approaching the first reference line DL.
- the first light beam L 1 having transmitted through the scanning lens 53 is reflected by the reflection mirror 56 downward opposite to the first reference line DL.
- the reflection mirror 58 in the cross section shown in FIG. 2 , reflects the first light beam L 1 upward such that it passes through between the polygon mirror 52 and the scanning lens 53 .
- the first light beam L 1 is irradiated on the circumferential surface of the photoconductor drum 21 Y.
- the optical path length of the first light beam L 1 can easily be set to be the same as the optical path length of the second light beam L 2 .
- an optical path of the first light beam L 1 that travels from the polygon motor 51 to the scanning lens 53 is arranged to be shifted, in the left-right direction (a direction perpendicular to the plane of FIG. 2 ), from an optical path of the first light beam L 1 that travels from the reflection mirror 58 to the circumferential surface of the photoconductor drum 21 Y.
- the rotation shaft of the polygon mirror 52 is inclined with respect to the up-down direction such that the front of the rotation shaft is located above, and the rear of the rotation shaft is located below.
- the second light beam L 2 emitted from the light source 82 for magenta is deflected by the polygon mirror 52 in the front diagonally downward direction toward the scanning lens 54 , away from the first reference line DL.
- the second light beam L 2 having transmitted through the scanning lens 54 is reflected by the reflection mirror 57 upward in a direction of approaching the first reference line DL.
- the second light beam L 2 is reflected upward by the reflection mirror 59 and irradiated on the circumferential surface of the photoconductor drum 21 M.
- the optical path lengths of the first light beam L 1 and the second light beam L 2 in particular, the distance from the scanning lens 53 to the photoconductor drum 21 Y and the distance from the scanning lens 54 to the photoconductor drum 21 M, need to set to the same distance (length).
- two laser beams deflected by the polygon mirror 52 are reflected by different mirrors and irradiated on the photoconductor drums.
- the trajectories of the two laser beams reflected by the mirrors are arranged to intersect with each other above the polygon mirror 52 when viewed in a cross section taken along a plane including the sub scanning direction. This causes a problem that the height of the optical scanning device 23 is increased.
- the light beams that have transmitted through the scanning lens 53 and the scanning lens 54 are reflected to be opposite to each other in the up-down direction.
- the optical path lengths of the first light beam L 1 and the second light beam L 2 can easily be set to the same length. In other words, it is possible to ensure that each of the first light beam L 1 and the second light beam L 2 has a predetermined optical path length or more, while restricting the height of the first housing 230 A in the up-down direction to be low.
- the optical paths of the first light beam L 1 and the second light beam L 2 are arranged to intersect with each other above the polygon mirror 52 in the cross section shown in FIG. 2 , it is possible to reduce the height of the first optical scanning unit 23 A in a direction (up-down direction) in which the light beam is irradiated on the scanned surfaces (the photoconductor drums 21 Y and 21 M), while setting the optical path lengths of the first light beam L 1 and the second light beam L 2 to be the same.
- the optical path length of the first light beam L 1 is short.
- the optical path of the first light beam L 1 reflected by the reflection mirror 58 is arranged by using the space between the polygon mirror 52 and the scanning lens 53 . This makes it possible for the first light beam L 1 to proceed to below the scanning lens 53 , thereby the optical path length of the first light beam L 1 is ensured.
- the optical path length of the first light beam L 1 is set to be the same as that of the second light beam L 2 that is deflected by the polygon mirror 52 in a direction of separating away from the first reference line DL.
- the second optical scanning unit 23 B which has the same configuration as the first optical scanning unit 23 A, produces the same act and effect as those described above.
- the reflection mirror 58 and the reflection mirror 59 cause the first light beam L 1 and the second light beam L 2 to be irradiated on the photoconductor drum 21 Y and the photoconductor drum 21 M along directions that intersect with each other at a predetermined angle with respect to the second reference line DR, respectively.
- the incident angle ⁇ Y of the first light beam L 1 with respect to the second reference line DR is set to 10 degrees.
- the reflection light from the photoconductor drum 21 Y is restricted. It is noted that this also applies to the incident angle of the second light beam L 2 .
- the scanning lens 53 and the scanning lens 54 are each a single lens, the sub scanning magnification between them tends to be small. Even in such a case, with the above-described configuration where a part of the first light beam L 1 is reflected in a direction opposite to the photoconductor drum 21 Y, the optical path length of the first light beam L 1 is ensured. As a result, it is possible to focus the first light beam L 1 on the circumferential surface of the photoconductor drum 21 Y with a high accuracy.
- the outer appearances of the first housing 230 A of the first optical scanning unit 23 A and the second housing 230 B of the second optical scanning unit 23 B are each a parallelogram in a cross section.
- the housings of the first optical scanning unit 23 A and the second optical scanning unit 23 B can be commonalized.
- the first housing 230 A and the second housing 230 B are disposed so as to overlap with each other in a direction perpendicular to the first reference line DL (a direction in which the second reference line DR extends, the up-down direction) when viewed in a cross section taken along a plane including the sub scanning direction.
- first reference line DL a direction in which the second reference line DR extends, the up-down direction
- a second housing rear wall 230 B 1 of the second housing 230 B is disposed above a first housing front wall 230 A 1 of the first housing 230 A with a gap therebetween.
- the first mirror group and the second mirror group are disposed such that the reflection mirror 57 of the first optical scanning unit 23 A and the reflection mirror 56 of the second optical scanning unit 23 B overlap with each other in the direction perpendicular to the first reference line DL.
- the inter-axial distance between a plurality of photoconductor drums 21 that are disposed in alignment at predetermined intervals can be set to be small.
- the two housings can be arranged to overlap with each other as described above.
- the optical path of the first light beam L 1 is arranged such that it once approaches, then separates away from, and then approaches again the circumferential surface of the photoconductor drum 21 Y. This makes it possible to ensure the optical path length of the first light beam L 1 .
- the optical path of the second light beam L 2 is arranged such that it once separates away from, and then approaches the circumferential surface of the photoconductor drum 21 M.
- the first mirror group and the second mirror group may be arranged such that, when viewed in a cross section taken along a plane including the sub scanning direction, the optical path of the second light beam L 2 in the first optical scanning unit 23 A overlaps with the optical path of the first light beam L 1 in the second optical scanning unit 23 B in a direction perpendicular to the first reference line DL.
- the two optical scanning units 23 A and 23 B installed in the image forming apparatus 1 are arranged to overlap with each other partially, thereby making it possible to reduce the height and the width in the sub scanning direction, of the image forming apparatus 1 .
- the inter-axial distance between a plurality of photoconductor drums 21 can be set to be small.
- a plurality of photoconductor drums 21 are arranged above the optical scanning device 23 .
- the present disclosure is not limited to this configuration.
- the members shown in FIG. 2 may be reversed in the up-down direction such that the optical scanning device 23 is disposed above the plurality of photoconductor drums 21 , and the exposure light is irradiated downward.
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Abstract
Description
- This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2015-016337 filed on Jan. 30, 2015, the entire contents of which are incorporated herein by reference.
- The present disclosure relates to an optical scanning device that includes a plurality of light sources for emitting light beams and a deflector for reflecting the light beams toward corresponding scanned surfaces, and to an image forming apparatus that uses the optical scanning device.
- An optical scanning device for use in a color laser printer includes, for example: a plurality of light sources for emitting laser beams respectively for colors of cyan, magenta, yellow and black; a deflector (polygon mirror) for deflecting the laser beams such that the laser beams scan the circumferential surfaces (scanned surfaces) of the photoconductor drums for respective colors; and focus lenses for focusing the deflected laser beams on the circumferential surfaces. The deflector may be used in common by a plurality of laser beams.
- There has been disclosed a technology in which two optical scanning devices are used to scan four photoconductor drums disposed adjacent to each other. Each of the optical scanning devices includes two light sources and a deflector. In this case, a laser beam emitted from a light source is deflected at a first position on the circumference of the deflector, a laser beam emitted from the other light source is deflected at a second position that is on the opposite side to the first position.
- An optical scanning device according to an aspect of the present disclosure includes a housing, a light source portion, a deflector, a first focus lens, a second focus lens, a first mirror group, and a second mirror group. The light source portion includes a first light source and a second light source, the first light source emitting a first light beam, the second light source emitting a second light beam. The rotation axis of the deflector is inclined with respect to a first direction and a second direction, the first direction being opposite to the second direction. The deflector is configured to reflect the first light beam diagonally on a side of a third direction that is perpendicular to the first direction and the second direction, and on a side of the first direction, and is configured to reflect the second light beam diagonally on a side of a fourth direction that is opposite to the third direction, and on a side of the second direction, such that the first light beam scans a first scanned surface and the second light beam scans a second scanned surface. The first focus lens is disposed between the deflector and the first scanned surface and configured to focus the first light beam on the first scanned surface. The second focus lens is disposed between the deflector and the second scanned surface and configured to focus the second light beam on the second scanned surface. The first mirror group is disposed between the first focus lens and the first scanned surface and configured to reflect the first light beam to the first scanned surface. The second mirror group is disposed between the second focus lens and the second scanned surface and configured to reflect the second light beam to the second scanned surface. The first mirror group includes a first reflection mirror and a second reflection mirror. The first light beam that has transmitted through the first focus lens is incident on the first reflection mirror. The first reflection mirror is configured to reflect the first light beam in the second direction of separating away from the first scanned surface. The second reflection mirror is configured to reflect the first light beam reflected by the first reflection mirror, toward the first scanned surface. The second mirror group includes a third reflection mirror and a fourth reflection mirror. The second light beam that has transmitted through the second focus lens is incident on the third reflection mirror. The third reflection mirror is configured to reflect the second light beam in the first direction of approaching the second scanned surface. The fourth reflection mirror is configured to reflect the second light beam reflected by the third reflection mirror, toward the second scanned surface.
- This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.
-
FIG. 1 is a cross-sectional view showing the configuration of a color printer according to an embodiment of the present disclosure. -
FIG. 2 is a cross-sectional view showing the internal configuration of an optical scanning device according to an embodiment of the present disclosure. -
FIG. 3 is a plan view showing a part of an optical path of the optical scanning device according to an embodiment of the present disclosure. - The following describes an embodiment of the present disclosure with reference to the drawings.
FIG. 1 is a cross-sectional view showing the configuration of the image forming apparatus 1 according to an embodiment of the present disclosure. The image forming apparatus 1 is a tandem color printer. The image forming apparatus 1 includes amain body housing 10 that is formed approximately in the shape of a rectangular parallelepiped. It is noted that the image forming apparatus may be a full-color copier or multifunction peripheral. - The
main body housing 10 includes therein a plurality of processing units for performing an image formation process to a sheet. In the present embodiment, themain body housing 10 includes, as the processing units,image forming units color containers optical scanning device 23, anintermediate transfer unit 28, and afixing device 30. Asheet discharge tray 11 is provided on the upper surface of themain body housing 10. Asheet discharge port 12 is opened opposite to thesheet discharge tray 11. Amanual feed tray 13 is attached to a side wall of themain body housing 10 in a freely openable/closable manner. Asheet feed cassette 14 is attached to a lower part of themain body housing 10 in a freely attachable/detachable manner, wherein sheets on which images are to be formed by the image formation process are stored in thesheet feed cassette 14. - The
image forming units image forming units cylindrical photoconductor drum 21 for carrying an electrostatic latent image and a toner image; acharger 22; a developingdevice 24; aprimary transfer roller 26; and acleaning device 27. - The
optical scanning device 23 forms electrostatic latent images on the circumferential surfaces of thephotoconductor drums 21 of respective colors. Theoptical scanning device 23 of the present embodiment includes a plurality of light sources and focusing optical systems, wherein the plurality of light sources are prepared for the respective colors, and the focusing optical systems focus and scan the light beams emitted from the light sources on the circumferential surfaces of thephotoconductor drums 21 of the respective colors. The focusing optical systems are not independent optical systems, but a part thereof is used in common. Theoptical scanning device 23 is described below. - The
intermediate transfer unit 28 performs a primary transfer of transferring toner images formed on thephotoconductor drums 21. Theintermediate transfer unit 28 includes atransfer belt 281, adriving roller 282 and a drivenroller 283, wherein thetransfer belt 281 circumferentially rotates while contacting the circumferential surfaces of thephotoconductor drums 21, and thetransfer belt 281 is suspended between thedriving roller 282 and the drivenroller 283. Thetransfer belt 281 is pressed against the circumferential surfaces of thephotoconductor drums 21 by theprimary transfer rollers 26. In the primary transfer, the toner images are transferred from thephotoconductor drums 21 so as to be overlaid at a same position on thetransfer belt 281. This allows a full-color toner image to be formed on thetransfer belt 281. - A
secondary transfer roller 29 is disposed opposite to thedriving roller 282 across thetransfer belt 281 so as to form a secondary transfer nip portion T. In the secondary transfer, the full-color toner image is transferred from thetransfer belt 281 to a sheet by the secondary transfer nip portion T. Toner that has remained on the circumferential surface of thetransfer belt 281 without being transferred to the sheet, is collected by abelt cleaning device 284 disposed opposite to the drivenroller 283. - The
fixing device 30 includes afixing roller 31 and apressure roller 32, wherein a heat source is embedded in thefixing roller 31, and thefixing roller 31 and thepressure roller 32 form a fixing nip portion N. Thefixing device 30 performs a fixing process in which the sheet to which the toner image has been transferred by the secondary transfer nip portion T is heated and pressed by the fixing nip portion N so that the toner is fused and fixed to the sheet. The sheet subjected to the fixing process is discharged from thesheet discharge port 12 toward thesheet discharge tray 11. - A sheet conveyance path for conveying sheets is provided in the
main body housing 10. The sheet conveyance path includes a main conveyance path P1 that vertically extends from near a lower part of themain body housing 10 to near an upper part via the secondary transfer nip portion T and thefixing device 30. The downstream end of the main conveyance path P1 is connected to thesheet discharge port 12. A reverse conveyance path P2 for conveying a reversed sheet in the double-side printing is provided to extend from the most downstream end in the main conveyance path P1 to near the upstream end. In addition, a manually fed sheet conveyance path P3 extending from themanual feed tray 13 to the main conveyance path P1 is disposed above thesheet feed cassette 14. - The
sheet feed cassette 14 includes a sheet storage portion for storing a stack of sheets. A pick-uproller 151 and a pair ofsheet feed rollers 152 are disposed in the vicinity of an upper-right part of thesheet feed cassette 14, wherein the pick-uproller 151 picks up, one by one, the top sheets of the stack of sheets, and the pair ofsheet feed rollers 152 feed the picked-up sheet toward the upstream end of the main conveyance path P1. A sheet placed on themanual feed tray 13 is also conveyed to the upstream end of the main conveyance path P1 via the manually fed sheet conveyance path P3. A pair of registration rollers 15 are disposed more on the upstream side than the secondary transfer nip portion T in the main conveyance path P1, wherein the pair of registration rollers 15 feed a sheet to the transfer nip portion at a predetermined timing. - When a single-side printing process (image formation process) is performed to a sheet, the sheet is fed from the
sheet feed cassette 14 or themanual feed tray 13 to the main conveyance path P1. A transfer process of transferring a toner image to the sheet is performed in the secondary transfer nip portion T, and the fixing process of fixing the transferred toner to the sheet is performed in the fixingdevice 30. Subsequently, the sheet is discharged from thesheet discharge port 12 onto thesheet discharge tray 11. On the other hand, during a double-side printing process, the transfer process and the fixing process are performed to one surface of the sheet, then the sheet is partially projected outward on thesheet discharge tray 11 from thesheet discharge port 12. Subsequently, the sheet is switchback-conveyed to be returned to near the upstream end of the main conveyance path P1 via the reverse conveyance path P2. The transfer process and the fixing process are then performed to the other surface of the sheet, then the sheet is discharged on thesheet discharge tray 11 from thesheet discharge port 12. - The
optical scanning device 23 of the present embodiment is further described.FIG. 2 is a cross-sectional view showing the internal configuration of theoptical scanning device 23 of the present embodiment.FIG. 3 is a plan view showing a part of an optical path of theoptical scanning device 23. Theoptical scanning device 23 includes a firstoptical scanning unit 23A and a secondoptical scanning unit 23B. The firstoptical scanning unit 23A and the secondoptical scanning unit 23B are disposed adjacent to each other in the horizontal direction. The firstoptical scanning unit 23A is disposed below ayellow photoconductor drum 21Y (the first scanned surface, the first photoconductor drum) and amagenta photoconductor drum 21M (the second scanned surface, the second photoconductor drum), and scans the circumferential surfaces of the two photoconductor drums 21. The secondoptical scanning unit 23B is disposed below acyan photoconductor drum 21C (the first scanned surface, the third photoconductor drum) and a black photoconductor drum 21BK (the second scanned surface, the fourth photoconductor drum), and scans the circumferential surfaces of the two photoconductor drums 21. - It is noted that the main scanning direction of the first
optical scanning unit 23A and the secondoptical scanning unit 23B is a left-right direction perpendicular to the plane ofFIG. 2 , and the sub scanning direction is a front-rear direction, namely a tangent direction at the lower-end part of eachphotoconductor drum 21. In addition, as shown inFIG. 2 , the photoconductor drums 21 of four colors are disposed such that the rotation shaft centers are disposed adjacent to each other at intervals on a predetermined straight line (a first reference line DL) in a cross section taken along a plane including the sub scanning direction of theoptical scanning device 23, and the photoconductor drums 21 are rotated by a driving portion (not shown). In addition, a second reference line DR is defined as a straight line that is perpendicular to the first reference line DL. In the present embodiment, the second reference line DR extends along the up-down direction. Furthermore, inFIG. 2 , a pair ofconveyance screws 241 and a developing housinglower end portion 242 of the developingdevice 24 are seen between: the photoconductor drums 21; and the firstoptical scanning unit 23A and the secondoptical scanning unit 23B. The pair ofconveyance screws 241 have a function to stir the developer in the developingdevice 24. The developing housinglower end portion 242 is an imaginary straight line that extends along the lower end portion of the housing of the developingdevice 24. - Next, the internal configuration of the first
optical scanning unit 23A is described. The firstoptical scanning unit 23A includes afirst housing 230A, a light source unit 80 (the light source portion), apolygon motor 51, a polygon mirror 52 (deflector), and a focusing optical system, wherein the light source unit 80 includes light sources 81 and 82 respectively for yellow and magenta that are stored in thefirst housing 230A. It is noted that the secondoptical scanning unit 23B has the same internal configuration as the firstoptical scanning unit 23A, and includes asecond housing 230B, a light source unit 80 (the light source portion), apolygon motor 51, a polygon mirror 52 (deflector), and a focusing optical system, wherein the light source unit 80 includes light sources 81 and 82 respectively for cyan and black that are stored in thesecond housing 230B. As a result, in the following, detailed description of the components of the secondoptical scanning unit 23B is omitted. In addition, inFIG. 2 , components of the same type included in the firstoptical scanning unit 23A and the secondoptical scanning unit 23B are assigned a same reference number, for the sake of explanation. - The light sources 81 and 82 of the light source unit 80 stored in the
first housing 230A each include a semiconductor laser that emits a laser beam of a single wavelength. A light source 81 for yellow (the first light source) is positioned more on the front side in the plane of the figure than thepolygon mirror 52, and emits a first light beam L1 that is irradiated on thephotoconductor drum 21Y. On the other hand, a light source 82 for magenta (the second light source) is disposed at a different position from the light source 81 for yellow in the sub scanning direction (front-rear direction), more specifically, is positioned more on the front side than the light source 81 for yellow. In addition, the light source 82 for magenta is positioned more on the rear side in the plane of the figure than thepolygon mirror 52, and emits a second light beam L2 that is irradiated on thephotoconductor drum 21M. In addition, a collemator lens (not shown), a cylindrical lens (not shown), and a diaphragm (not shown) are disposed respectively between thepolygon mirror 52 and the light source 81, and between thepolygon mirror 52 and the light source 82. The collemator lens converts a laser beam to parallel light beams, wherein the laser beam is emitted from the light source 81, 82 and diffused. The cylindrical lens converts the parallel light beams to line-like light beams that are elongated in the main scanning direction and focuses the light beams on thepolygon mirror 52. The diaphragm regulates the laser beam emitted from the light source 81, 82. - The
polygon mirror 52 deflects laser beams L1 and L2 (the first light beam and the second light beam) emitted from the light sources 81 and 82 for respective colors, respectively such that the light beams scan the circumferential surfaces of thephotoconductor drums polygon mirror 52 is a polygon mirror having deflection surfaces formed along the sides of a hexagon. The rotation shaft of thepolygon motor 51 is connected to the center of thepolygon mirror 52. That is, thepolygon motor 51 is coaxially fixed to thepolygon mirror 52 and rotates thepolygon mirror 52. The rotation shaft is inclined at an acute angle with respect to the up direction (the first direction) and the down direction (the second direction that is opposite to the first direction). In this way, in the present embodiment, asingle polygon mirror 52 is used in common to scan the photoconductor drums 21 for two colors. As shown inFIG. 2 , in a cross section taken along a plane including the sub scanning direction, thepolygon mirror 52 deflects the first light beam L1 and the second light beam L2 in opposite directions. More specifically, thepolygon mirror 52 reflects the first light beam L1 on the side of the rear direction (the third direction) perpendicular to the up-down direction, and in the diagonally upward direction (the rear diagonally upward direction). In addition, thepolygon mirror 52 reflects the second light beam L2 on the side of the front direction (the fourth direction), which is opposite to the rear direction, and in the diagonally downward direction (the front diagonally downward direction). - The focusing optical system includes a scanning lens 53 (first focus lens), a scanning lens 54 (second focus lens), a reflection mirror 56 (first reflection mirror), a reflection mirror 57 (third reflection mirror), a reflection mirror 58 (second reflection mirror), and a reflection mirror 59 (fourth reflection mirror).
- The
scanning lens 53 is disposed on the optical path of the first light beam L1 between thepolygon mirror 52 and the circumferential surface of thephotoconductor drum 21Y, and focuses the first light beam L1 on the circumferential surface. In addition, thescanning lens 54 is disposed on the optical path of the second light beam L2 between thepolygon mirror 52 and the circumferential surface of thephotoconductor drum 21M, and focuses the second light beam L2 on the circumferential surface. In the present embodiment, thescanning lens 53 and thescanning lens 54 are each a single lens. In addition, thescanning lens 53 and thescanning lens 54 have the same shape and are arranged so as to be in point symmetry with respect to the rotation center of thepolygon mirror 52, as shown in the cross section ofFIG. 2 . This makes it possible to commonalize thescanning lens 53 and thescanning lens 54, thereby the cost of theoptical scanning device 23 is reduced. - In the present embodiment, the
reflection mirror 56 and thereflection mirror 58 constitute the first mirror group of the present disclosure. The first mirror group is disposed on the optical path of the first light beam L1 between the scanninglens 53 and the circumferential surface of thephotoconductor drum 21Y, and reflects the first light beam L1 to the circumferential surface. Similarly, thereflection mirror 57 and thereflection mirror 59 constitute the second mirror group of the present disclosure. The second mirror group is disposed on the optical path of the second light beam L2 between the scanninglens 54 and the circumferential surface of thephotoconductor drum 21M, and reflects the second light beam L2 to the circumferential surface. - The
reflection mirror 56 is disposed, among the first mirror group, closest to thescanning lens 53 on the optical path of the first light beam L1. The first light beam L1 having transmitted through thescanning lens 53 is incident on thereflection mirror 56. As shown in the cross section ofFIG. 2 , thereflection mirror 56 reflects the first light beam L1 downward away from the circumferential surface of thephotoconductor drum 21Y. Thereflection mirror 58 is disposed in the downstream of thereflection mirror 56 on the optical path of the first light beam L1. Thereflection mirror 58 reflects the first light beam L1 reflected by thereflection mirror 56, to the circumferential surface of thephotoconductor drum 21Y. - The
reflection mirror 57 is disposed, among the second mirror group, closest to thescanning lens 54 on the optical path of the second light beam L2. The second light beam L2 having transmitted through thescanning lens 54 is incident on thereflection mirror 57. As shown in the cross section ofFIG. 2 , thereflection mirror 57 reflects the second light beam L2 upward in a direction of approaching the circumferential surface of thephotoconductor drum 21M. Thereflection mirror 59 is disposed in the downstream of thereflection mirror 57 on the optical path of the second light beam L2. Thereflection mirror 59 reflects the second light beam L2 reflected by thereflection mirror 57, to the circumferential surface of thephotoconductor drum 21M. - It is noted that, in the
first housing 230A, dustproof glasses (not shown) are provided at the portions from which the first light beam L1 and the second light beam L2 are emitted. The dustproof glasses prevent foreign materials such as dust from entering thefirst housing 230A. - The
scanning lens 53 and the scanning lens 54 (FIG. 3 ) of the present embodiment both have a free curved surface that is defined by the equation (1). In the equation (1), “z” represents a surface shape of thescanning lens 53 and thescanning lens 54 in the main scanning direction. Table 1 shows values of coefficients that can be substituted into the equation (1), for each of the incident surface and the emission surface. It is noted that although coefficients for the surface shape in the sub scanning direction are omitted, the sub scanning magnification between thepolygon mirror 52 and thephotoconductor drum 21Y (thephotoconductor drum 21M) is set to three times or less. In particular, in the present embodiment, the length of the optical path from thepolygon mirror 52 to thescanning lens 53 and thescanning lens 54 is set to be relatively long, and the length of the optical path from thescanning lens 53 and thescanning lens 54 to circumferential surfaces of thephotoconductor drums scanning lens 53 and thescanning lens 54 each being a single lens, the sub scanning magnification is set to a small value. -
- In the equation (1),
- “R” denotes a main scanning curvature radius,
- “k” denotes a main scanning conic coefficient,
- “Ci” denotes a coefficient of the surface shape, and
- “r” denotes a height in a direction perpendicular to the optical axis direction.
-
TABLE 1 Incident surface Emission surface R 22.114 21.537 k −7.265 −6.818 C1 0 2.809E−03 C2 −1.949E−03 −3.945E−03 C3 0 −2.384E−06 C4 −2.015E−06 −1.660E−06 C5 0 4.639E−10 C6 4.123E−10 9.578E−11 C7 0 0 C8 −3.186E−14 −4.537E−14 - The
scanning lens 53 and thescanning lens 54 allow an excellent focus performance to be obtained when the distances from the emission surfaces of the lenses to the circumferential surfaces (scanned surfaces) of thephotoconductor drums FIG. 3 , the lens thickness (center thickness) of thescanning lens 53 and thescanning lens 54 is 9.0 mm. Furthermore, the distance from the deflection surface of thepolygon mirror 52 to the incident surface of each lens is set to 23.7 mm. - As shown in
FIG. 2 , in the present embodiment, thepolygon mirror 52 is arranged such that the rotation shaft thereof is inclined at a predetermined angle with respect to the first reference line DL that connects the rotation shafts centers of a pair of photoconductor drums 21 (photoconductor drums polygon mirror 52 is inclined at an acute angle θX with respect to the horizontal line (a straight line parallel to the first reference line DL). An optical path of the first light beam L1 is formed in rear of thepolygon mirror 52, and an optical path of the second light beam L2 is formed in front of thepolygon mirror 52. In this way, the first mirror group and the second mirror group are arranged such that the optical path of the first light beam L1 and the optical path of the second light beam L2 do not intersect with each other. - The rotation shaft of the
polygon mirror 52 is inclined with respect to the up-down direction such that the front of the rotation shaft is located above, and the rear of the rotation shaft is located below. As a result, the first light beam L1 emitted from the light source 81 for yellow is deflected by thepolygon mirror 52 in the rear diagonally upward direction toward thescanning lens 53 in a direction of approaching the first reference line DL. The first light beam L1 having transmitted through thescanning lens 53 is reflected by thereflection mirror 56 downward opposite to the first reference line DL. Thereflection mirror 58, in the cross section shown inFIG. 2 , reflects the first light beam L1 upward such that it passes through between thepolygon mirror 52 and thescanning lens 53. Subsequently, the first light beam L1 is irradiated on the circumferential surface of thephotoconductor drum 21Y. With such a configuration, even if a part of the first light beam L1 is reflected in a direction of separating away from the circumferential surface of thephotoconductor drum 21Y, the optical path length of the first light beam L1 can easily be set to be the same as the optical path length of the second light beam L2. It is noted that an optical path of the first light beam L1 that travels from thepolygon motor 51 to thescanning lens 53 is arranged to be shifted, in the left-right direction (a direction perpendicular to the plane ofFIG. 2 ), from an optical path of the first light beam L1 that travels from thereflection mirror 58 to the circumferential surface of thephotoconductor drum 21Y. - Similarly, the rotation shaft of the
polygon mirror 52 is inclined with respect to the up-down direction such that the front of the rotation shaft is located above, and the rear of the rotation shaft is located below. As a result, the second light beam L2 emitted from the light source 82 for magenta is deflected by thepolygon mirror 52 in the front diagonally downward direction toward thescanning lens 54, away from the first reference line DL. The second light beam L2 having transmitted through thescanning lens 54 is reflected by thereflection mirror 57 upward in a direction of approaching the first reference line DL. Subsequently, the second light beam L2 is reflected upward by thereflection mirror 59 and irradiated on the circumferential surface of thephotoconductor drum 21M. - In order to obtain good focusing on the
photoconductor drums scanning lens 53 to thephotoconductor drum 21Y and the distance from thescanning lens 54 to thephotoconductor drum 21M, need to set to the same distance (length). - In conventional technologies, two laser beams deflected by the
polygon mirror 52 are reflected by different mirrors and irradiated on the photoconductor drums. In order to ensure that each of the laser beams has a predetermined optical path length or more, the trajectories of the two laser beams reflected by the mirrors are arranged to intersect with each other above thepolygon mirror 52 when viewed in a cross section taken along a plane including the sub scanning direction. This causes a problem that the height of theoptical scanning device 23 is increased. - In the present embodiment, the light beams that have transmitted through the
scanning lens 53 and thescanning lens 54 are reflected to be opposite to each other in the up-down direction. In addition, due to the configuration where the rotation shaft center of thepolygon mirror 52 is inclined, even if the height of thefirst housing 230A is set to be low in the up-down direction, the optical path lengths of the first light beam L1 and the second light beam L2 can easily be set to the same length. In other words, it is possible to ensure that each of the first light beam L1 and the second light beam L2 has a predetermined optical path length or more, while restricting the height of thefirst housing 230A in the up-down direction to be low. In particular, compared to the other configuration where the optical paths of the first light beam L1 and the second light beam L2 are arranged to intersect with each other above thepolygon mirror 52 in the cross section shown inFIG. 2 , it is possible to reduce the height of the firstoptical scanning unit 23A in a direction (up-down direction) in which the light beam is irradiated on the scanned surfaces (thephotoconductor drums - Suppose that the first light beam L1 reflected by the
reflection mirror 56 passes through between the scanninglens 53 and thereflection mirror 56 and is irradiated on thephotoconductor drum 21Y inFIG. 2 , then the optical path length of the first light beam L1 is short. In the present embodiment, as described above, the optical path of the first light beam L1 reflected by thereflection mirror 58 is arranged by using the space between thepolygon mirror 52 and thescanning lens 53. This makes it possible for the first light beam L1 to proceed to below thescanning lens 53, thereby the optical path length of the first light beam L1 is ensured. As a result, it is possible to set the optical path length of the first light beam L1 to be the same as that of the second light beam L2 that is deflected by thepolygon mirror 52 in a direction of separating away from the first reference line DL. It is noted that the secondoptical scanning unit 23B, which has the same configuration as the firstoptical scanning unit 23A, produces the same act and effect as those described above. - Furthermore, in the cross section of
FIG. 2 , thereflection mirror 58 and thereflection mirror 59 cause the first light beam L1 and the second light beam L2 to be irradiated on thephotoconductor drum 21Y and thephotoconductor drum 21M along directions that intersect with each other at a predetermined angle with respect to the second reference line DR, respectively. With reference toFIG. 2 , the incident angle θY of the first light beam L1 with respect to the second reference line DR is set to 10 degrees. As a result, compared to the case where the first light beam L1 is incident along the second reference line DR, the reflection light from thephotoconductor drum 21Y is restricted. It is noted that this also applies to the incident angle of the second light beam L2. - In addition, as described above, when the
scanning lens 53 and thescanning lens 54 are each a single lens, the sub scanning magnification between them tends to be small. Even in such a case, with the above-described configuration where a part of the first light beam L1 is reflected in a direction opposite to thephotoconductor drum 21Y, the optical path length of the first light beam L1 is ensured. As a result, it is possible to focus the first light beam L1 on the circumferential surface of thephotoconductor drum 21Y with a high accuracy. - Furthermore, in the present embodiment, as shown in
FIG. 2 , the outer appearances of thefirst housing 230A of the firstoptical scanning unit 23A and thesecond housing 230B of the secondoptical scanning unit 23B are each a parallelogram in a cross section. As a result, the housings of the firstoptical scanning unit 23A and the secondoptical scanning unit 23B can be commonalized. As shown inFIG. 2 , thefirst housing 230A and thesecond housing 230B are disposed so as to overlap with each other in a direction perpendicular to the first reference line DL (a direction in which the second reference line DR extends, the up-down direction) when viewed in a cross section taken along a plane including the sub scanning direction. InFIG. 2 , a second housing rear wall 230B1 of thesecond housing 230B is disposed above a first housing front wall 230A1 of thefirst housing 230A with a gap therebetween. In particular, in the present embodiment, the first mirror group and the second mirror group are disposed such that thereflection mirror 57 of the firstoptical scanning unit 23A and thereflection mirror 56 of the secondoptical scanning unit 23B overlap with each other in the direction perpendicular to the first reference line DL. With such a configuration where parts of adjacent housings are set to overlap with each other, the width of theoptical scanning device 23 in the horizontal direction (the front-rear direction) can be reduced. As a result, the inter-axial distance between a plurality ofphotoconductor drums 21 that are disposed in alignment at predetermined intervals can be set to be small. In the present embodiment, by using the arrangement of the optical path of the second light beam L2 in the firstoptical scanning unit 23A and the optical path of the first light beam L1 in the secondoptical scanning unit 23B, the two housings can be arranged to overlap with each other as described above. - Up to now, an embodiment of the present disclosure has been described. With such a configuration, spaces in front and rear of the
polygon mirror 52 can be used to form the optical paths of the first light beam L1 and the second light beam L2. The optical path of the first light beam L1 is arranged such that it once approaches, then separates away from, and then approaches again the circumferential surface of thephotoconductor drum 21Y. This makes it possible to ensure the optical path length of the first light beam L1. On the other hand, the optical path of the second light beam L2 is arranged such that it once separates away from, and then approaches the circumferential surface of thephotoconductor drum 21M. This makes it possible to reduce the height of theoptical scanning device 23 in a direction in which the light beams are irradiated on the photoconductor drums 21, while setting the optical path lengths of the first light beam L1 and the second light beam L2 to be the same. It is noted that the present disclosure is not limited to the above-described configuration, but can be modified, for example, as follows. - (1) In the above-described embodiment, two housings are arranged to overlap with each other partially such that the
reflection mirror 56 of the secondoptical scanning unit 23B is disposed above thereflection mirror 57 of the firstoptical scanning unit 23A. However, the present disclosure is not limited to this configuration. In a modified embodiment, the first mirror group and the second mirror group may be arranged such that, when viewed in a cross section taken along a plane including the sub scanning direction, the optical path of the second light beam L2 in the firstoptical scanning unit 23A overlaps with the optical path of the first light beam L1 in the secondoptical scanning unit 23B in a direction perpendicular to the first reference line DL. With this configuration, too, the twooptical scanning units photoconductor drums 21 can be set to be small. - (2) In the above-described embodiment, a plurality of
photoconductor drums 21 are arranged above theoptical scanning device 23. However, the present disclosure is not limited to this configuration. In another modified embodiment, the members shown inFIG. 2 may be reversed in the up-down direction such that theoptical scanning device 23 is disposed above the plurality of photoconductor drums 21, and the exposure light is irradiated downward. - It is to be understood that the embodiments herein are illustrative and not restrictive, since the scope of the disclosure is defined by the appended claims rather than by the description preceding them, and all changes that fall within metes and bounds of the claims, or equivalence of such metes and bounds thereof are therefore intended to be embraced by the claims.
Claims (8)
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JP2015016337A JP6140740B2 (en) | 2015-01-30 | 2015-01-30 | Optical scanning device and image forming apparatus using the same |
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JP3288873B2 (en) * | 1994-10-27 | 2002-06-04 | 旭光学工業株式会社 | Mirror fixing structure of scanning optical device |
JP2004279655A (en) * | 2003-03-14 | 2004-10-07 | Seiko Epson Corp | Image forming device |
JP4469231B2 (en) * | 2004-06-30 | 2010-05-26 | 株式会社リコー | Optical scanning apparatus and image forming apparatus |
JP4557825B2 (en) * | 2004-07-21 | 2010-10-06 | キヤノン株式会社 | Image forming apparatus |
JP4609062B2 (en) * | 2004-12-16 | 2011-01-12 | 富士ゼロックス株式会社 | Image forming apparatus |
JP4963399B2 (en) * | 2006-10-23 | 2012-06-27 | キヤノン株式会社 | Image forming apparatus |
JP5121388B2 (en) | 2007-10-17 | 2013-01-16 | キヤノン株式会社 | Optical scanning device |
JP5531857B2 (en) * | 2010-08-23 | 2014-06-25 | 株式会社リコー | Optical scanning apparatus and image forming apparatus |
JP5641426B2 (en) * | 2011-01-11 | 2014-12-17 | 株式会社リコー | Optical scanning apparatus and image forming apparatus |
JP2012163868A (en) * | 2011-02-09 | 2012-08-30 | Ricoh Co Ltd | Optical scanner, and image forming apparatus |
JP5899964B2 (en) * | 2012-01-26 | 2016-04-06 | 株式会社リコー | Optical writing apparatus and image forming apparatus |
JP2015052727A (en) * | 2013-09-09 | 2015-03-19 | キヤノン株式会社 | Optical scanning device and image forming device having the same |
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JP2016142792A (en) | 2016-08-08 |
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