Electrophotography – Image formation – Combined or plural functions by single component
Reexamination Certificate
2000-12-29
2002-09-10
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Combined or plural functions by single component
C399S100000, C399S101000
Reexamination Certificate
active
06449448
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus which uses electrophotography or electrostatic recording, such as a copying machine or a printer.
2. Related Background Art
Various image forming apparatuses, so-called tandem type color image forming apparatuses, have been proposed which superpose toner images in different colors formed by a plurality of image forming units (image forming stations) on recording material to form a color image.
FIG. 20
is a partially schematic view of such a color image forming apparatus. In the figure, the symbols SY, SM, SC, and SB represent first through fourth image forming stations disposed from right to left. The first through fourth image forming stations form a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, respectively.
The first through fourth image forming stations SY, SM, SC, and SB are electrophotography mechanisms. The stations have electrophotographic photosensitive members
1
Y,
1
M,
1
C, and
1
B as image bearers; charging units
2
Y,
2
M,
2
C, and
2
B; developing units
4
Y,
4
M,
4
C, and
4
B; cleaning units
6
Y,
6
M,
6
C, and
6
B; and so on. The electrophotographic photosensitive members
1
Y,
1
M,
1
C, and
1
B are rotated clockwise as indicated by an arrow at a predetermined process speed (circumferential speed) to form a toner image on their surfaces by charging; exposing LY, LM, LC, and LB; and developing.
The exposing units, not shown, are laser beam scanners, for example. The laser beam scanners comprise a semiconductor laser, a polygon mirror, an F-&thgr; lens, and so on. To expose the uniformly charged surface of rotating photosensitive drum to a laser beam by scanning, the scanners emit the laser beam. This beam is modulated according to a time-series electric digital image signal carrying intended image information fed from a host apparatus (not shown) including manuscript reader having photoelectric conversion elements, such as CCD, a computer, a word processor, etc. Exposure by laser beam scanning forms on the surface of the rotating photosensitive drum an electrostatic latent image according to the intended image information.
The exposure LY in the first image forming station SY corresponds to the cyan component of a full-colored image. The developing unit
4
Y uses a developer containing a cyan toner.
The exposure LM in the second image forming station SM corresponds to the magenta component of a full-colored image. The developing unit
4
M uses a developer containing a magenta toner.
The exposure LC in the third image forming station SC corresponds to the yellow component of a full-colored image. The developing unit
4
C uses a developer containing a yellow toner.
The exposure LB in the fourth image forming station SB corresponds to the black component of a full-colored image. The developing unit
4
B uses a developer containing a black toner.
Reference numeral
51
denotes an endless belt type recording medium carrier (hereinafter called a transfer belt). The transfer belt
51
is almost horizontally tensioned under the image forming stations SY, SM, SC, and SB, across the image forming stations, and between a drive roller
52
and a turn roller
53
. A drive motor
54
drives the drive roller
52
, so that the transfer belt
51
turns counterclockwise as indicated by an arrow at a predetermined process speed.
The transfer belt
51
is made of a sheet of dielectric resin, such as polyethylene telephthalate (PET), polyvinylidene fluoride, or polyurethane. The belt is endless, that is, its original ends are connected together, or it is seamless.
Reference numerals
55
Y,
55
M,
55
C, and
55
B are transfer charging blades. The blades are disposed inside the transfer belt
51
, with the upper half of the transfer belt
51
pressed against the underside of the photosensitive members
1
Y,
1
M,
1
C, and
1
B in the image forming stations SY, SM, SC, and SB. In the image forming stations, SY, SM, SC, and SB, the contacts between the underside of the photosensitive members
1
Y,
1
M,
1
C, and
1
B and the transfer belt
51
provides first through fourth transfer units (transfer nips) TY, TM, TC, and TB.
Reference numeral
56
is a cleaning unit for the transfer belt
51
(transfer belt cleaner). The transfer belt cleaner presses a cleaning web (non-woven fabric)
57
against the transfer belt
51
to remove residual toner and other foreign material from the transfer belt.
A sheet feeding apparatus, not shown, feeds recording material P (material onto which an image is transferred), and a registration roller
8
places the material P on the upper half of the transfer belt
51
from the side of the first image forming station SY at a predetermined control timing.
The recording material P on the transfer belt
51
is electrostatically attracted to the belt
51
. As the transfer belt
51
turns, the material is conveyed from the first transfer unit TY to the second transfer unit TM, to the third transfer unit TC, to the fourth transfer unit TB. Images are transferred onto the material P as follows:
1) The first transfer unit TY transfers a cyan toner image formed on the surface of the photosensitive member
1
Y in the first image forming station SY.
2) The second transfer unit TM transfers a magenta toner image formed on the surface of the photosensitive member
1
M in the second image forming station SM.
3) The third transfer unit TC transfers a yellow toner image formed on the surface of the photosensitive member
1
C in the third image forming station SC.
4) The fourth transfer unit TB transfers a black toner image formed on the surface of the photosensitive member
1
B in the fourth image forming station SB.
By transferring and superposing these four toner images, a toner image corresponding to an intended full-colored image is composited on the material P.
Toner images start to be formed in synchronism with each other at the first through fourth image forming stations SY, SM, SC, and SB. Thus the toner images formed at the image forming stations are transferred onto recording material P, which is conveyed on the transfer belt
51
, so that the images are positioned and superposed as predetermined.
After the recording material P is conveyed on the belt through the fourth transfer unit TB, electricity is discharged from the recording material P by the electricity discharging apparatus
9
. Then the material is separated from the transfer belt
51
and introduced into a thermal fixing apparatus, not shown. The apparatus fixes an unfixed toner image on the recording material as a permanent image by melting and color mixing. Finally, the material, which bears a fixed image, is discharged.
After image transfer, residual toner on the photosensitive members
1
Y,
1
M,
1
C, and
1
B in the image forming stations SY, SM, SC, and SB is removed by the cleaning units
6
Y,
6
M,
6
C, and
6
B.
Toner and other foreign material deposited on the transfer belt
5
is removed by the cleaning unit
56
.
Besides color image forming apparatuses which have a plurality of image bearers
1
Y,
1
M,
1
C, and
1
B as described above, a color image forming apparatus is available which repeats a process consisting of charging, latent-image formation, development, and cleaning, using one image bearer to form a color image. Some of these color image forming apparatuses are of a type which attracts recording material to a transfer belt or a transfer drum to superpose toner images one after another on the same recording material and of an intermediate transfer type which superposes a plurality of toner images on an intermediate transfer member and transfers the all superposed images onto the recording material.
For such an electrophotographic apparatus, a cleanerless type, in which the cleaner for cleaning the residual toner on the photosensitive member after image transfer is eliminated and a developing device collects and reuses the residual toner, is contemplated.
When an image forming apparatus of a simultaneous deve
Bessho Yuji
Ito Yoshikuni
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