U.S. patent application number 15/008795 was filed with the patent office on 2016-08-04 for optical scanning device and image forming apparatus using the same.
The applicant listed for this patent is KYOCERA Document Solutions Inc.. Invention is credited to Hideji Mizutani.
Application Number | 20160223935 15/008795 |
Document ID | / |
Family ID | 56553079 |
Filed Date | 2016-08-04 |
United States Patent
Application |
20160223935 |
Kind Code |
A1 |
Mizutani; Hideji |
August 4, 2016 |
OPTICAL SCANNING DEVICE AND IMAGE FORMING APPARATUS USING THE
SAME
Abstract
An optical scanning device includes a light source portion, a
deflector, a first focus lens, a second focus lens, a first mirror
group, and a second mirror group. The first mirror group includes:
a first reflection mirror on which a first light beam having
transmitted through a first focus lens is incident, the first
reflection mirror reflecting the first light beam in a second
direction away from a first scanned surface; and a second
reflection mirror that reflects the reflected first light beam
toward the first scanned surface. The second mirror group includes:
a third reflection mirror on which a second light beam having
transmitted through a second focus lens is incident, the third
reflection mirror reflecting the second light beam in the first
direction of approaching the second scanned surface; and a fourth
reflection mirror that reflects the reflected second light beam
toward the second scanned surface.
Inventors: |
Mizutani; Hideji; (Osaka,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KYOCERA Document Solutions Inc. |
Osaka |
|
JP |
|
|
Family ID: |
56553079 |
Appl. No.: |
15/008795 |
Filed: |
January 28, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 1/0283 20130101;
G03G 15/0415 20130101; H04N 2201/04755 20130101; H04N 1/113
20130101; H04N 1/06 20130101 |
International
Class: |
B41J 2/385 20060101
B41J002/385 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2015 |
JP |
2015-016337 |
Claims
1. An optical scanning device comprising: a housing; a light source
portion including 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; a deflector whose
rotation axis is inclined with respect to a first direction and a
second direction, the first direction being opposite to the second
direction, the deflector being 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, the deflector being 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; a first focus lens disposed between the deflector and the
first scanned surface and configured to focus the first light beam
on the first scanned surface; a second focus lens disposed between
the deflector and the second scanned surface and configured to
focus the second light beam on the second scanned surface; a first
mirror group disposed between the first focus lens and the first
scanned surface and configured to reflect the first light beam to
the first scanned surface; and a second mirror group disposed
between the second focus lens and the second scanned surface and
configured to reflect the second light beam to the second scanned
surface, wherein the first mirror group includes: a first
reflection mirror on which the first light beam that has
transmitted through the first focus lens is incident, the first
reflection mirror being configured to reflect the first light beam
in the second direction of separating away from the first scanned
surface; and a second reflection mirror configured to reflect the
first light beam reflected by the first reflection mirror, toward
the first scanned surface, and the second mirror group includes: a
third reflection mirror on which the second light beam that has
transmitted through the second focus lens is incident, the third
reflection mirror being configured to reflect the second light beam
in the first direction of approaching the second scanned surface;
and a fourth reflection mirror configured to reflect the second
light beam reflected by the third reflection mirror, toward the
second scanned surface.
2. The optical scanning device according to claim 1, wherein the
second reflection mirror reflects the first light beam such that
the first light beam passes through between the deflector and the
first focus lens.
3. The optical scanning device according to claim 1, wherein the
first focus lens and the second focus lens have a same shape and
are arranged so as to be in point symmetry with respect to a
rotation center of the deflector.
4. An image forming apparatus comprising: a first photoconductor
drum, a second photoconductor drum, a third photoconductor drum and
a fourth photoconductor drum that are disposed in alignment at
predetermined intervals; and the optical scanning device according
to claim 1, wherein the optical scanning device includes: a first
optical scanning unit configured to scan circumferential surfaces
of the first photoconductor drum and the second photoconductor
drum; and a second optical scanning unit configured to scan
circumferential surfaces of the third photoconductor drum and the
fourth photoconductor drum.
5. The image forming apparatus according to claim 4, wherein a
first housing included in the first optical scanning unit and a
second housing included in the second optical scanning unit are
disposed so as to overlap with each other in the first direction
and the second direction when viewed in a cross section taken along
a plane including a sub scanning direction.
6. The image forming apparatus according to claim 4, wherein the
first mirror group and the second mirror group are disposed such
that, when viewed in a cross section taken along a plane including
a sub scanning direction, the third reflection mirror in a first
housing included in the first optical scanning unit and the second
reflection mirror in a second housing included in the second
optical scanning unit overlap with each other in the first
direction and the second direction.
7. The image forming apparatus according to claim 4, wherein the
first mirror group and the second mirror group are disposed such
that, when viewed in a cross section taken along a plane including
a sub scanning direction, an optical path of the second light beam
in a first housing included in the first optical scanning unit and
an optical path of the first light beam in a second housing
included in the second optical scanning unit overlap with each
other in the first direction and the second direction.
8. The image forming apparatus according to claim 4, wherein outer
appearances of a first housing included in the first optical
scanning unit and a second housing included in the second optical
scanning unit are each a parallelogram when viewed in a cross
section taken along a plane including a sub scanning direction.
Description
INCORPORATION BY REFERENCE
[0001] 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.
BACKGROUND
[0002] 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.
[0003] 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.
[0004] 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.
SUMMARY
[0005] 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.
[0006] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a cross-sectional view showing the configuration
of a color printer according to an embodiment of the present
disclosure.
[0008] FIG. 2 is a cross-sectional view showing the internal
configuration of an optical scanning device according to an
embodiment of the present disclosure.
[0009] 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.
DETAILED DESCRIPTION
[0010] 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 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.
[0011] 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, the main body housing 10
includes, as the processing units, image forming units 2Y, 2C, 2M
and 2Bk, color containers 25Y, 25C, 25M and 25Bk 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.
[0012] The image forming units 2Y, 2C, 2M and 2Bk 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
2Y, 2C, 2M and 2Bk 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.
[0013] 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.
[0014] 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. In the primary transfer, 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.
[0015] 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. In the secondary transfer, the
full-color toner image is transferred from the transfer belt 281 to
a sheet by the secondary transfer nip portion T. Toner that has
remained on the circumferential surface of the transfer belt 281
without being transferred to the sheet, is collected by a belt
cleaning device 284 disposed opposite to the driven roller 283.
[0016] 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.
[0017] 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 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 P1 is connected to the sheet 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 the manual feed tray 13 to the main conveyance path
P1 is disposed above the sheet feed cassette 14.
[0018] 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 P1. A
sheet placed on the manual 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.
[0019] 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 the manual 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 fixing device 30. Subsequently, the sheet is
discharged from the sheet discharge port 12 onto the sheet
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 the sheet discharge tray 11 from the sheet 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 the sheet discharge tray 11
from the sheet discharge port 12.
[0020] The optical scanning device 23 of the present embodiment is
further described. 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 23A and a
second optical scanning unit 23B. The first optical scanning unit
23A and the second optical scanning unit 23B are disposed adjacent
to each other in the horizontal direction. The first optical
scanning unit 23A is disposed below a yellow photoconductor drum
21Y (the first scanned surface, the first photoconductor drum) and
a magenta photoconductor drum 21M (the second scanned surface, the
second photoconductor drum), and scans the circumferential surfaces
of the two photoconductor drums 21. The second optical scanning
unit 23B is disposed below a cyan 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.
[0021] It is noted that the main scanning direction of the first
optical scanning unit 23A and the second optical scanning unit 23B
is a left-right direction perpendicular to the plane of FIG. 2, and
the sub scanning direction is a front-rear direction, namely a
tangent direction at the lower-end part of each photoconductor drum
21. In addition, as shown in FIG. 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 the optical
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, in FIG.
2, 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 23A
and the second optical scanning unit 23B. 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.
[0022] Next, the internal configuration of the first optical
scanning unit 23A is described. The first optical scanning unit 23A
includes a first housing 230A, 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 230A. It is
noted that the second optical scanning unit 23B has the same
internal configuration as the first optical scanning unit 23A, and
includes a second housing 230B, 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 230B. As a
result, in the following, detailed description of the components of
the second optical scanning unit 23B is omitted. In addition, in
FIG. 2, components of the same type included in the first optical
scanning unit 23A and the second optical scanning unit 23B are
assigned a same reference number, for the sake of explanation.
[0023] 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 the polygon mirror 52, and
emits a first light beam L1 that is irradiated on the
photoconductor 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 the polygon mirror 52,
and emits a second light beam L2 that is irradiated on the
photoconductor drum 21M. In addition, 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.
[0024] 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 the photoconductor
drums 21Y and 21M (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). In this way, in
the present embodiment, a single polygon mirror 52 is used in
common to scan the photoconductor drums 21 for two colors. As shown
in FIG. 2, in a cross section taken along a plane including the sub
scanning direction, the polygon mirror 52 deflects the first light
beam L1 and the second light beam L2 in opposite directions. More
specifically, the polygon 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, the polygon 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).
[0025] 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).
[0026] The scanning lens 53 is disposed on the optical path of the
first light beam L1 between the polygon mirror 52 and the
circumferential surface of the photoconductor drum 21Y, and focuses
the first light beam L1 on the circumferential surface. In
addition, the scanning lens 54 is disposed on the optical path of
the second light beam L2 between the polygon mirror 52 and the
circumferential surface of the photoconductor drum 21M, and focuses
the second light beam L2 on the circumferential surface. In the
present embodiment, the scanning lens 53 and the scanning lens 54
are each a single lens. In addition, 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.
[0027] In the present embodiment, 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 L1 between the scanning lens
53 and the circumferential surface of the photoconductor drum 21Y,
and reflects the first light beam L1 to the circumferential
surface. Similarly, 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 L2 between the scanning lens 54 and the
circumferential surface of the photoconductor drum 21M, and
reflects the second light beam L2 to the circumferential
surface.
[0028] 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 L1. The first light beam L1 having transmitted
through the scanning lens 53 is incident on the reflection mirror
56. As shown in the cross section of FIG. 2, the reflection mirror
56 reflects the first light beam L1 downward away from the
circumferential surface of the photoconductor drum 21Y. The
reflection mirror 58 is disposed in the downstream of the
reflection mirror 56 on the optical path of the first light beam
L1. The reflection mirror 58 reflects the first light beam L1
reflected by the reflection mirror 56, to the circumferential
surface of the photoconductor drum 21Y.
[0029] 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 L2. The second light beam L2 having
transmitted through the scanning lens 54 is incident on the
reflection mirror 57. As shown in the cross section of FIG. 2, the
reflection mirror 57 reflects the second light beam L2 upward in a
direction of approaching the circumferential surface of the
photoconductor drum 21M. The reflection mirror 59 is disposed in
the downstream of the reflection mirror 57 on the optical path of
the second light beam L2. The reflection mirror 59 reflects the
second light beam L2 reflected by the reflection mirror 57, to the
circumferential surface of the photoconductor drum 21M.
[0030] 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 the first housing 230A.
[0031] 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 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 21Y (the
photoconductor drum 21M) is set to three times or less. In
particular, in the present embodiment, 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 21Y and 21M
is set to be relatively short. As a result, due to the scanning
lens 53 and the scanning lens 54 each being a single lens, the sub
scanning magnification is set to a small value.
[ Math . 1 ] ##EQU00001## z = r 2 / R 1 + 1 - ( 1 + k ) ( r / R ) 2
+ i = 1 C i r i ( 1 ) ##EQU00001.2##
[0032] In the equation (1),
[0033] "R" denotes a main scanning curvature radius,
[0034] "k" denotes a main scanning conic coefficient,
[0035] "Ci" denotes a coefficient of the surface shape, and
[0036] "r" denotes a height in a direction perpendicular to the
optical axis direction.
TABLE-US-00001 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
[0037] 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 21Y and 21M are each
less than 110 mm. In addition, as shown in FIG. 3, the lens
thickness (center thickness) of the scanning lens 53 and the
scanning lens 54 is 9.0 mm. Furthermore, the distance from the
deflection surface of the polygon mirror 52 to the incident surface
of each lens is set to 23.7 mm.
[0038] As shown in FIG. 2, in the present embodiment, 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 21Y and 21M).
The trajectory of the light beam deflected by the polygon mirror 52
is inclined at an acute angle .theta.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 L1 is formed in
rear of the polygon mirror 52, and an optical path of the second
light beam L2 is formed in front of the polygon 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.
[0039] 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 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 L1 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 L1 upward
such that it passes through between the polygon mirror 52 and the
scanning lens 53. Subsequently, the first light beam L1 is
irradiated on the circumferential surface of the photoconductor
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 the photoconductor 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 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 L1 that travels from the reflection mirror 58 to
the circumferential surface of the photoconductor drum 21Y.
[0040] 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 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 L2 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. Subsequently, the
second light beam L2 is reflected upward by the reflection mirror
59 and irradiated on the circumferential surface of the
photoconductor drum 21M.
[0041] In order to obtain good focusing on the photoconductor drums
21Y and 21M, the optical path lengths of the first light beam L1
and the second light beam L2, in particular, the distance from the
scanning lens 53 to the photoconductor drum 21Y and the distance
from the scanning lens 54 to the photoconductor drum 21M, need to
set to the same distance (length).
[0042] 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 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.
[0043] In the present embodiment, 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. In addition, due to the configuration where the rotation
shaft center of the polygon mirror 52 is inclined, even if the
height of the first 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 the first
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 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 23A in a direction (up-down direction)
in which the light beam is irradiated on the scanned surfaces (the
photoconductor drums 21Y and 21M), while setting the optical path
lengths of the first light beam L1 and the second light beam L2 to
be the same.
[0044] Suppose that the first light beam L1 reflected by the
reflection mirror 56 passes through between the scanning lens 53
and the reflection mirror 56 and is irradiated on the
photoconductor drum 21Y in FIG. 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 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 L1 to proceed to below
the scanning 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 the polygon
mirror 52 in a direction of separating away from the first
reference line DL. It is noted that the second optical scanning
unit 23B, which has the same configuration as the first optical
scanning unit 23A, produces the same act and effect as those
described above.
[0045] Furthermore, in the cross section of FIG. 2, the reflection
mirror 58 and the reflection mirror 59 cause the first light beam
L1 and the second light beam L2 to be irradiated on the
photoconductor drum 21Y and the photoconductor drum 21M along
directions that intersect with each other at a predetermined angle
with respect to the second reference line DR, respectively. With
reference to FIG. 2, the incident angle .theta.Y 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 the photoconductor drum 21Y is restricted. It
is noted that this also applies to the incident angle of the second
light beam L2.
[0046] In addition, as described above, when 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 L1 is reflected in a direction opposite to the
photoconductor 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 the photoconductor
drum 21Y with a high accuracy.
[0047] Furthermore, in the present embodiment, as shown in FIG. 2,
the outer appearances of the first housing 230A of the first
optical scanning unit 23A and the second housing 230B of the second
optical scanning unit 23B are each a parallelogram in a cross
section. As a result, the housings of the first optical scanning
unit 23A and the second optical scanning unit 23B can be
commonalized. As shown in FIG. 2, the first housing 230A and the
second 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. In FIG. 2, a second
housing rear wall 230B1 of the second housing 230B is disposed
above a first housing front wall 230A1 of the first 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 the reflection mirror 57 of the first optical scanning
unit 23A and the reflection mirror 56 of the second optical
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 the optical scanning device 23 in the
horizontal direction (the front-rear direction) can be reduced. As
a result, 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. In the present
embodiment, by using the arrangement of the optical path of the
second light beam L2 in the first optical scanning unit 23A and the
optical path of the first light beam L1 in the second optical
scanning unit 23B, the two housings can be arranged to overlap with
each other as described above.
[0048] 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 the photoconductor 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 the photoconductor drum
21M. This makes it possible to reduce the height of the optical
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.
[0049] (1) In the above-described embodiment, two housings are
arranged to overlap with each other partially such that the
reflection mirror 56 of the second optical scanning unit 23B is
disposed above the reflection mirror 57 of the first optical
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 first optical scanning unit 23A overlaps with the optical path
of the first light beam L1 in the second optical scanning unit 23B
in a direction perpendicular to the first reference line DL. With
this configuration, too, the two optical scanning units 23A and 23B
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. As a result, the inter-axial distance between
a plurality of photoconductor drums 21 can be set to be small.
[0050] (2) In the above-described embodiment, a plurality of
photoconductor drums 21 are arranged above the optical scanning
device 23. However, the present disclosure is not limited to this
configuration. In another modified embodiment, 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.
[0051] 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.
* * * * *