Electrophotography – Image formation – Development
Reexamination Certificate
1999-06-10
2001-12-04
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Development
C399S228000
Reexamination Certificate
active
06327449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and the like, and more particularly, it relates to an image forming apparatus having a shiftable developing means.
2. Related Background Art
In the past, a color image forming apparatus in which a plurality of different color toner images are successively transferred onto a single transfer material in a superimposed fashion by using a plurality of developing devices containing different color toners and the color images are fixed to the transfer material to obtain a full-color image has widely been used.
FIG. 6
shows a conventional color image forming apparatus. Now, such a color image forming apparatus will be described.
FIG. 6
is a view showing an entire construction of a color laser printer as an example of a color image forming apparatus.
An image forming portion of the color laser printer is constituted by a photosensitive drum (image bearing member)
45
rotated at a constant speed, a fixed black developing device
49
B, and three rotatable color developing devices (yellow developing device
48
Y, magenta developing device
48
M and cyan developing device
48
C).
Below the image forming portion, there is disposed an intermediate transfer member
43
for holding the developed color toner images in a superimposed fashion and for transferring the color toner images onto a transfer material
42
fed from a feeding portion.
The transfer material
42
to which the color images were transferred is sent to a fixing portion
52
, where the color images are fixed to the transfer material
42
. Thereafter, the transfer material is discharged onto a discharge portion
61
provided on an upper surface of the printer via pairs of discharge rollers
58
,
59
,
60
.
The photosensitive drum
45
is constituted by coating an organic photo-conductor layer on an outer surface of an aluminium cylinder having a diameter of about 62 mm, and a cleaner blade
46
and a primary charging means
47
are disposed around the photosensitive drum.
The photosensitive drum
45
is rotated in a counter clockwise direction in
FIG. 6
in synchronous with an image forming operation by transmitting a driving force of a drive motor (not shown) provided at a rear side in
FIG. 6
to the photosensitive drum.
Exposure to the photosensitive drum
45
is effected by a scanner portion
57
. That is to say, when an image signal is sent to a laser diode, the laser diode illuminates light onto a polygon mirror at a timing corresponding to the image signal. The polygon mirror is rotated at a high speed by a scanner motor so that the light reflected from the polygon mirror can selectively expose the surface of the photosensitive drum
45
through a focusing lens and a reflection mirror, thereby forming an electrostatic image on the photosensitive drum
45
.
The electrostatic image is visualized by three rotatable developing devices
48
Y,
48
M,
48
C and a black developing device
49
B which perform yellow color development, magenta color development, cyan color development and black color development.
The black developing device
49
B is fixed at a developing position, except that this developing device is mounted to a main body of the printer. The black developing device serves to form a visualized image with black toner.
A toner containing capacity of the black developing device
49
B is selected to be greater than toner containing capacities of the other developing devices
48
Y,
48
M,
48
C by about two times or more to permit printing of 15,000 sheets (A4 size sheet, printing percentage=5%) in consideration of kinds of documents handled by an operator, image patterns and the amount of toner consumed.
By increasing the toner containing capacity of the black developing device in this way, frequency for exchanging the black developing device is reduced, and running cost for each print can also be reduced.
As shown in
FIG. 6
, the black developing device is disposed between the laser scanner and the three rotatable developing devices
48
Y,
48
M,
48
C. With this arrangement, the toners leaking when the developing devices
48
Y,
48
M,
48
C are rotated are prevented from scattering onto the optical parts such as the laser scanner. In this manner, the toner is prevented from adhering to the polygon mirror, lens and mirror to worsen electrostatic image formation, thereby obtaining a sharp output image.
Each of the three rotatable developing devices
48
Y,
48
M,
48
C contains the toner for permitting printing of 6,000 sheets (A4 size sheet, printing percentage=5%). The three rotatable developing devices are held detachably attachable to a developing rotary
51
rotated around a shaft
50
.
In the image formation, the developing devices are rotatingly shifted around the shaft
50
in the condition that they are held on the developing rotary
51
so that the pre-selected developing device is stopped at a position opposed to the photosensitive drum
45
. In this case, the visualized image corresponding to the electrostatic image on the photosensitive drum
45
is formed.
In the color image formation, whenever the intermediate transfer member
43
is rotated by one revolution, the developing rotary
51
is rotated so that developing processes of the yellow developing device
48
Y, magenta developing device
48
M, cyan developing device
48
C and black developing device
49
B are successively effected in order.
For example, when the rotatable yellow developing device
48
Y is positioned and stopped at the position opposed to the photosensitive drum
45
, the rotatable yellow developing device
48
Y effects development on the photosensitive drum
45
with yellow toner to form an yellow toner image. Similarly, regarding the magenta developing device
48
M and the cyan developing device
48
C, the color toner development is effected in the same mechanism. Application of bias and transmission of driving force to developing rollers of the rotatable developing devices
48
Y,
48
M,
48
C are performed when each of the developing devices is rotatingly shifted to the developing position.
The intermediate transfer member
43
serves to receive the toner images on the photosensitive drum
45
visualized by the developing devices during the color image formation by four times (yellow, magenta, cyan and black color images) in a superimposed fashion. The intermediate transfer member
43
is rotated in a clockwise direction in
FIG. 6
in synchronous with the outer peripheral speed of the photosensitive drum
45
.
The intermediate transfer member
43
to which the toner images were transferred in the superimposed fashion cooperates with a transfer roller
44
(to which voltage is applied) to pinch and convey the transfer material
42
therebetween, with the result that the color toner images on the intermediate transfer member
42
are collectively transferred onto the transfer material
42
.
In this example, the intermediate transfer member
43
is constituted by coating an elastic layer made of middle resistance sponge or middle resistance rubber on an aluminium cylinder having a diameter of 186 mm.
A cleaning means serves to remove residual toner remaining on the photosensitive drum
45
after the toner image on the photosensitive drum
45
visualized by the developing means were transferred to the intermediate transfer member
43
.
While the four color toner images are being formed on the intermediate transfer member
43
, i.e., while the intermediate transfer member
43
is being rotated by several revolutions, as shown by the solid line in
FIG. 6
, the transfer roller
44
is located at a lower position so that the roller is spaced apart from the intermediate transfer member
43
not to distort the images.
After the four color toner images were formed on the intermediate transfer member
43
, as shown by the two dots and chain line in
FIG. 6
, the transfer roller
44
is shifted to an upper position where the roller is urged against the intermediate transfer
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Grainger Quana M.
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