Color printing device

Details Color printing device Color printing device

2000-10-03

2002-06-18

Pendegrass, Joan (Department: 2852)

Electrophotography

Image formation

Transfer

C399S302000

Reexamination Certificate

active

06408155

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a color image forming apparatus that is useful, for example, as a color printer, a color copying machine, a color facsimile, and the like, and in particular, to a color image forming apparatus capable of forming a color image by overlapping toner images of many colors by using electrophotography.
BACKGROUND OF THE INVENTION
As a conventional color image forming apparatus, for example, one disclosed in JP 9-304996A is well known.
The following is a description of a conventional color image forming apparatus, with reference to
FIGS. 19 and 20
.
FIG. 19
is a cross-sectional view showing an overall structure of a conventional color image forming apparatus; and
FIG. 20
is a time chart showing an image forming operation of the conventional color image forming apparatus.
As shown in
FIG. 19
, an intermediate transfer belt unit
201
includes an intermediate transfer belt
202
, a primary transfer roller
203
, a secondary transfer roller
204
, a cleaner roller
205
, a waste toner reservoir
206
, and the like, and toner image of each color can be overlapped on the intermediate transfer belt
202
. In the center part of this color image forming apparatus, a group of developing units
208
are provided. Four developing units
207
Y,
207
M,
207
C and
207
Bk for yellow, magenta, cyan and black, each unit being of sector shape in cross section, are arranged circularly to form the group of developing units
208
. These developing units
207
Y,
207
M,
207
C and
207
Bk are installed properly in the color image forming apparatus. The mechanical driving systems and electrical circuit systems are coupled between the developing units
207
Y,
207
M,
207
C and
207
Bk and other portions of the color image forming apparatus via mutual coupling members, so that both sides are mechanically and electrically connected. The developing units
207
Y,
207
M,
207
C and
207
Bk are supported by a supporting member and collectively rotated by a driving motor, so that they can rotate around a non-rotatable cylindrical drum
209
. Furthermore, at the time of image formation, the developing units
207
Y,
207
M,
207
C and
207
Bk are moved successively by rotation to an image forming position
210
, which opposes the primary transfer roller
203
that supports the intermediate transfer belt
202
. The image forming position
210
is also an exposure position for exposing a photosensitive member
218
with a laser signal beam
211
.
Inside this color image forming apparatus, a laser exposure device
212
is arranged horizontally below the group of developing units
208
. The laser signal beam
211
passes through an optical path
213
provided between the developing unit
207
M for magenta and the developing unit
207
C for cyan, and through an opening provided in a part of the cylindrical drum
209
, and is incident onto a mirror
214
, which is arranged inside the cylindrical drum
209
and fixed to the apparatus main body.
In the standing state, usually, the developing unit
207
Bk for black is located at the image forming position
210
. Therefore, first, the group of developing units
208
is rotated 90° so as to move the developing unit
207
Y for yellow to the image forming position
210
. The laser signal beam
211
, which is incident onto the mirror
214
, is reflected from the mirror
214
and enters the developing unit
207
Y for yellow, which is positioned at the image forming position
210
, by way of an exposure window
215
of the developing unit
207
Y for yellow. In this case, the laser signal beam
211
passes through an optical path between a developing device
216
and a cleaner
217
, arranged on the upper and lower sides in the developing unit
207
Y, is incident into an exposure portion on the left side face of the photosensitive member
218
, so as to scan the photosensitive member
218
in the direction of the main line. Thereby, the photosensitive member
218
is exposed, so that an electrostatic latent image is formed. Then, the electrostatic latent image is developed by the developing device
216
, and thus a toner image is formed on the surface of the photosensitive member
218
.
The toner image formed on the photosensitive member
218
is transferred onto the intermediate transfer belt
202
. Then, the group of developing units
208
is rotated 90°, so that the developing unit
207
M for magenta moves into the image forming position
210
. An operation similar to the above-mentioned formation of the yellow toner image is performed and a magenta toner image is overlapped on the yellow toner image previously formed on the intermediate transfer belt
202
. Similar operations as mentioned above are performed using developing units
207
C for cyan and
207
Bk for black to compose a full color image on the intermediate transfer belt
202
. The transfer in which the toner image of each color is transferred onto the intermediate transfer belt
202
is referred to as “primary transfer.”
When the top of the image on the intermediate transfer belt
202
on which the last black toner image is transferred reaches a secondary transfer position, a tertiary transfer roller
219
pushes the recording paper onto the intermediate transfer belt
202
. Thus, the secondary transfer of the toner image to the recording paper starts. The toner images of four colors are transferred onto the recording paper together. At the time the secondary transfer starts, the image forming process on the photosensitive member
218
is continued. The primary transfer from the photosensitive member
218
to the intermediate transfer belt
202
and the secondary transfer from the intermediate transfer belt
202
to the recording paper simultaneously proceed.
When the primary transfer of the black toner image from the photosensitive member
218
onto the intermediate transfer belt
202
is completed, the top of the toner images of four colors, which is transferred onto the recording paper, starts to pass through a fixing device
220
. Thereby, the recording paper on which toner images of four colors are transferred is fixed and ejected out of the apparatus. Even if the primary transfer of the black toner image from the photosensitive member
218
to the intermediate transfer belt
202
is completed, the secondary transfer from the intermediate transfer belt
202
to the recording paper is continued. Therefore, the photosensitive member
218
and the intermediate transfer belt
202
continue to be rotated. At this time, the photosensitive member
218
is not irradiated with the laser signal beam
211
and the photosensitive member
218
and the developing device are in a so-called idling state.
When the intermediate transfer belt
202
makes 4.5 rotations in total, the secondary transfer of the toner image from the intermediate transfer belt
202
onto the recording paper is completed and the photosensitive member
218
and the intermediate transfer belt
202
stop.
Thereafter, the group of developing units
208
is rotated 90°, so that the image formation starts sequentially from the yellow again.
By repeating the above-mentioned operations, a plurality of color images are output successively.
Any toner remaining on the intermediate transfer belt
202
is scraped off by the cleaner roller
205
that is in contact with the intermediate transfer belt
202
. The scraped-off toner is collected in the waste toner case
206
.
In general, in the conventional color image forming apparatus, as shown in
FIG. 20
, the developing speed and the primary transfer speed were the same in four colors. Also, the developing speed and the primary transfer speed were the same as the secondary transfer speed and the fixing speed.
Therefore, for example, when the time required for the operation of switching the developing unit
207
by rotating 90° the carriage
2
and coupling of the photosensitive member
218
, etc., is 1.0 second, the developing speed by each toner-of yellow (Y), magenta (M), cyan (C) and black (Bk) and the primary transfer speed is 100 mm/second, and the

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