Incremental printing of symbolic information – Electric marking apparatus or processes – Electrostatic
Reexamination Certificate
2000-03-02
2002-02-12
Pendegrass, Joan (Department: 2852)
Incremental printing of symbolic information
Electric marking apparatus or processes
Electrostatic
C347S134000, C347S232000, C347S241000, C359S204200
Reexamination Certificate
active
06346957
ABSTRACT:
FIELD OF THE INVENTION
1. Field of the Invention
This invention relates to an optical scanning device used in a color image forming apparatus such as an electrophotographic color copying machine and a color printer and an image forming apparatus for forming an image by the optical scanning device.
2. Description of the Related Art
As a color image forming apparatus such as a color copying machine and a color printer, widely known is the so-called tandem color image forming apparatus in which plural photoreceptors are arranged side by side in a designated direction, toner images of different colors are respectively formed on the plural photoreceptors, and the toner images are sequentially transferred on a transfer medium such as recording paper and an intermediate transfer belt to form a color image.
FIG. 9
is a schematic diagram of the conventional tandem color image forming apparatus.
As shown in
FIG. 9
, the color image forming apparatus includes photoreceptor drums
101
a,
101
b,
101
c,
101
d
which are arranged in parallel in the transport direction B of recording paper
106
and on the surfaces of which electrostatic latent images of Y (yellow), M (magenta), C (cyan) and BK (black) colors are respectively formed, corotron chargers
102
a,
102
b,
102
c,
102
d
for uniformly charging the respective photoreceptor drum surfaces, optical scanning devices
103
a,
103
b,
103
c,
103
d
for emitting a laser beam modulated according to each image piece of Y, M, C, BK obtained by conducting designated processing for the color data of R (red), G (green), B (blue) to the respective photoreceptor drum surfaces, cylindrical mirrors
104
a,
104
b,
104
c,
104
d
for respectively changing laser beams emitted from the optical scanning devices to an optical path heading toward the corresponding photoreceptor drum, developing devices
105
a,
105
b,
105
c,
105
d
for developing the electrostatic latent images formed on the respective photoreceptor drum surfaces by irradiation of a laser beam with toner of Y, M, C, BK to form toner images, a transport belt
107
for transporting the recording paper
106
in the transport direction B along the tangential line common to the photoreceptor drums to transfer the toner images of the respective colors formed on the photoreceptors onto the recording paper
106
, cleaners
108
a,
108
b,
108
c
108
d
for removing toner remaining on the photoreceptor drums, and a fixing roll
109
for fixing the transferred images on the recording paper
106
transferred from the photoreceptors.
FIG. 10
is a schematic diagram of an optical scanning device used in the conventional color image forming apparatus.
FIG. 10
illustrates the optical scanning device
103
a
for Y color among four optical scanning devices used in the color image forming apparatus shown in FIG.
9
. The other three optical scanning devices
103
b,
103
c,
103
d
have the substantially same constitution as the optical scanning device
103
a,
so the description will be omitted.
The optical scanning device
103
a
includes a light emission time control circuit
110
for controlling the light emission time of a laser beam according to the image data of Y color, a laser diode
111
controlled by the light emission time control circuit
110
to emit a modulated laser beam, a collimator lens
112
for converging a laser beam emitted from the laser diode
111
, a cylindrical lens
113
for converging a laser beam converged by the collimator lens
112
to diffuse from a focal point, a polygon mirror
114
for deflecting a laser beam passed through the cylindrical lens
113
, an f&thgr; lens
115
for focusing a light beam deflected by the polygon mirror
114
in the fast-scanning direction to scan on the exposure line of the photoreceptor drum
101
a
at uniform speed, and a cylindrical mirror
104
a
for finally imaging a laser beam on the photoreceptor drum
101
a.
The cylindrical mirror
104
a
used is so constructed that one face of a glass member like a rectangular parallelepiped is polished to be recessed like a cylindrical surface, and metal having high reflectance such as aluminum is deposited, and in some case, coating for further heightening the reflectance is conducted.
The operation of the color image forming apparatus shown in
FIG. 9
will now be described. The surfaces of the photoreceptor drums
101
a,
101
b,
101
c,
101
d
rotated in the direction of an arrow A are previously uniformly charged by the chargers
102
a,
102
b,
102
c,
102
d,
and laser beams modulated according to the respective image data of Y, M, C, BK are emitted from the optical scanning devices
103
a,
103
b,
103
c,
103
d
to the charged surfaces to form the electrostatic latent images on the surfaces of the photoreceptor drums. The electrostatic latent images are developed with toner of the respective colors by the developing devices
105
a,
105
b,
105
c,
105
d
to form toner images on the photoreceptor drum surfaces. The toner images are supported on the photoreceptor drums to be transported to a transfer position where the photoreceptor drums come into contact with the recording paper
106
. On the other hand, the recording paper
106
placed on the transport belt
107
is supported on the transport belt
107
to be fed to the transfer position of each photoreceptor drum in the same timing, whereby toner images of the respective colors on the photoreceptor drums are sequentially transferred onto the recording paper
106
. The recording paper
106
to which the toner images are transferred is transported to the fixing roll
109
, and the transferred images are fixed to obtain a color image.
The conventional tandem color image forming apparatus, however, has the problem that as the plural photoreceptor drums are exposed by the plural optical scanning devices corresponding thereto, the apparatus is increased in size leading to a cost increase. Further, a problem exists that as the optical elements constituting each optical scanning device are independently varied due to thermal deformation of an enclosure, the image formation position on the scanned surface of the photoreceptor drum is varied so that the image forming positions of the respective colors on the recording paper are shifted to remarkably lower the image quality.
Recently, as disclosed in Japanese Published Unexamined Patent Application No. Hei 10-20608, an optical scanning device has been proposed to reduce color aberration while reducing the size and the cost by making the optical parts related to plural laser beams for exposing the plural photoreceptor drums in common.
FIG. 11
is a schematic diagram of the conventional optical scanning device in which the optical parts are made in common.
As shown in
FIG. 11
, the optical scanning device is formed by a semiconductor laser array
125
or emitting four laser beams modulated according to each image data of Y (yellow), M (magenta), C (cyan) and BK (black), a polygon mirror
129
for commonly deflecting four laser beams emitted from the semiconductor laser array
125
, an f&thgr; lens
130
for focusing four light beams deflected by the polygon mirror
129
in the fast-scanning direction to scan on the exposure lines of the photoreceptor drums
124
a,
124
b,
124
c,
124
d
at uniform speed, a separating polygon mirror
131
which is formed by combination of four mirror surfaces having four planes of incidence different in angle for the four laser beams passed through the f&thgr; lens
130
and adapted to separate four laser beams from each other in the directions corresponding to the array positions of the photoreceptor drums, and cylindrical mirrors
132
a,
132
b,
132
c,
132
d
for focusing for laser beams separated by the separating polygon mirror
131
in the slow-scanning direction to be imaged on the corresponding photoreceptor drums.
In the optical scanning device thus constructed, four laser beams modulated according to the image data of Y, M, C, BK are emitted from the semiconductor laser array
125
, commonly deflected by the polygon mirror
129
to enter the se
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
Pendegrass Joan
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