Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-02-29
2001-03-13
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S302000
Reexamination Certificate
active
06201943
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus applicable to a color printer, a color copier and a color facsimile, etc., and more particularly, to a color image forming apparatus for forming color images by superimposing toner images of a plurality of colors by use of electrophotography, a belt unit and image forming unit of the color image forming apparatus.
As a conventional color image forming apparatus, the one is known which is described in Japanese Laid-open Patent Application No. Hei 8-152812. The structure of relevant parts thereof is shown in
FIG. 19
here as an example of conventional image forming apparatuses.
In
FIG. 19
, a photoconductor
201
is disposed in contact with an intermediate transfer belt
202
and a developer unit
203
containing toner of different colors (yellow, magenta, cyan and black). An exposure device
204
is disposed in a lower part of the figure. The toner image of each color is formed on the photoconductor
201
by a charger
205
, signal light
206
from the exposure device
204
and the developer unit
203
of the four colors, and the toner images are transferred color by color onto the intermediate transfer belt
202
. The toner remaining on the photoconductor
201
after the transfer is scraped by a photoconductor cleaner
207
which is always pressed against the photoconductor.
The intermediate transfer belt
202
rotates by being supported between a drive shaft
208
and a driven shaft
209
which are rotating. The toner image of each color on the photoconductor
201
is transferred so as to be aligned every time the intermediate transfer belt
202
rotates once, so that a color image in which the toner images of the four colors are superimposed is obtained on the intermediate transfer belt
202
. Then, the color image is secondary-transferred onto recording paper
210
by a secondary transfer roller
211
, and the toner image is fused by a fuser unit
212
, so that a full color image is obtained.
A cleaning blade
214
of a cleaning unit
213
is pressed against the surface of the intermediate transfer belt
202
with the drive shaft
208
as a backup member. After the color image has been transferred onto the recording paper
210
, residual toner which remains on the surface of the intermediate transfer belt
202
is scraped by the cleaning blade
124
. Thereby, the intermediate transfer belt
202
is cleaned in order to prepare the next image transfer. The cleaning blade
214
of the cleaning unit
213
is structured so as to be separated from the intermediate transfer belt
202
during the above-described color image formation onto the intermediate transfer belt
202
.
In the arrangement described in the Japanese Laid-open Patent Application No. Hei 8-152812, in order to prevent a slip on the contact surfaces between the intermediate transfer belt
202
and the drive shaft
208
during the primary transfer when the cleaning blade
214
is not pressed, a resin having high friction factor is applied onto a part or the whole of the contact surfaces.
As a second conventional color image forming apparatus, an arrangement shown in Japanese Laid-open Patent Application No. Hei 7-36246 will be described.
FIG. 20
is a side cross-sectional view showing the general structure of the second conventional color image forming apparatus.
In
FIG. 20
, an intermediate transfer belt unit
301
includes an intermediate transfer belt
302
, a first transfer shaft
303
, a second transfer shaft
304
, a cleaning roller
305
, and a waste toner reservoir
306
. Color images are superimposed on the transfer belt
302
. Image forming units
307
Bk,
307
Y,
307
M and
307
C for black, yellow, magenta and cyan, respectively, constitute an image forming unit group
308
, and are angularly disposed at the left portion in the body of the apparatus.
The image forming units
307
Bk,
307
Y,
307
M and
307
C are mechanically and electrically integrated with the body of the apparatus by being coupled therewith through a non-illustrated inter-coupling member at an image formation position
310
which is opposed to the transfer belt
302
. The image forming unit group
308
is structured so as to be rotatable about a generally cylindrical shaft
309
by a drive force of a frame motor. By this rotation, the image forming units
307
Bk,
307
Y,
307
M and
307
C are successively placed in the image formation position
310
.
A laser exposure device
312
is disposed in a lower part of the body of the apparatus. A laser signal beam
311
is, as shown in the figure, reflected by a mirror
314
in a shaft
309
, scans and exposes a photoconductor drum
318
in the image forming unit
307
Bk situated at the image formation position
310
, and forms an electrostatic latent image. A developer unit
316
forms a black toner image by developing the electrostatic latent image. The toner image is transferred onto the intermediate transfer belt
302
. Then, an image forming unit group
308
rotates 90 degrees, so that the yellow image forming unit
307
Y is situated at the image formation position
310
.
Then, an operation the same as the black image formation process is performed and the yellow toner image is superimposed on the black toner image on the intermediate transfer belt
302
. Then, similar operations are performed by use of the magenta and cyan image forming units
307
M and
307
C, so that the images of the four colors are completed on the intermediate transfer belt
302
. Then, the color image is transferred onto recording paper
330
by a transfer roller
319
, and lastly, the image is fixed by a fixing unit
320
.
In order to obtain highly accurate full color images in a color image forming apparatus, high accuracy is required for the positioning of the images of the four colors. No problem is caused in practical use in the case where the accuracy of positioning of the images of the four colors is not more than 100 &mgr;m. An important point for the positioning is that the periodic speed variations of the photoconductor and the intermediate transfer belt are the same among the images of the colors. Reduction of speed variation of the intermediate transfer belt due to separation and contact of the cleaning blade is also important.
Moreover, since toner images of the four colors are successively formed and superimposed, it takes considerable time to form one sheet of image. It is required to improve the throughput of the color image by reducing the time.
In the arrangement shown in
FIG. 19
, the cleaning blade is pressed after competition of the primary transfer to the intermediate transfer belt. For this reason, it is necessary that the distance from the primary transfer position to the cleaning position be greater than the image length. Consequently, the peripheral length of the intermediate transfer belt increases, and therefore the time required for one rotation increases. For this reason, the throughput of the image is lowered and it is difficult to reduce the overall size of the apparatus.
Moreover, in the Japanese Laid-open Patent Application No. Hei 7-36246 of the second prior art, no mention is made as to an optimum relationship among the following three: the diameter of the photoconductor which is important for positioning and improvement of the throughput; the peripheral length of the intermediate transfer belt serving as a transfer member; and the image length.
Generally, in order to equalize the speed variations due to eccentricity of rotary members such as the photoconductor and the drive shaft among the colors, the phases of eccentricity of the rotary members are made identical with each other for each color by rotating the rotary members an integral number of times every forming of the image of one color. Thereby, a relationship is obtained that the peripheral length of the intermediate transfer belt is an integral multiple of the peripheral length of the photoconductor.
The diameter of the photoconductor has a low degree of freedom of selection compared with the peripheral length of the interme
Asakura Kenji
Katakabe Noboru
Yoshikawa Masanori
Akin Gump Strauss Hauer & Feld L.L.P.
Grimley Arthur T.
Matsushita Electric - Industrial Co., Ltd.
Tran Hoan
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