Electrophotography – Control of electrophotography process – Of plural processes
Reexamination Certificate
2002-09-03
2004-05-04
Ngo, Hoang (Department: 2852)
Electrophotography
Control of electrophotography process
Of plural processes
Reexamination Certificate
active
06731889
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a printer or the like that uses an electrophotography scheme or an electrostatic storage scheme or the like. Specifically, the present invention relates to improvements of such an apparatus in the density, tone reproduction and color tint of its toner images.
2. Description of the Related Art
FIG. 13A
schematically shows an example of a sensor utilizing a photodiode for detecting light reflected from toner.
FIG. 13B
shows an example of a circuit that converts an output current of the photodiode into a voltage. In
FIGS. 13A and 13B
, reference numeral
201
denotes a photodiode, and reference numeral
102
denotes an LED serving as a light source. Reference numeral
104
denotes a toner image (which will be referred to as a “toner patch” hereinafter) to be detected that has been formed on a transferring material. Reflected light
206
from the toner patch is incident on the photodiode
201
, so that a photocurrent is generated. The photocurrent is converted into a voltage V
203
by a resistance
202
. The voltage V
203
reflects the quantity of reflected light in real time.
FIG. 14
is a block diagram showing a structure of a conventional accumulation type line sensor. In
FIG. 14
, reference numerals
204
,
205
and
206
denote a sensor array, a readout circuit and a reset circuit respectively. Pixels
207
to
209
and
220
are dark pixels surfaces of which are shielded from light. Pixels
210
to
219
are sensitive to light. Pixels
207
and
220
also serve as dummy pixel that are disposed at the ends of the sensor array to absorb variations in characteristics of the sensor due to their locations at the ends. For the sake of simplicity, an example that includes ten light sensitive pixels is shown in
FIG. 14
, but it should be noted that the number of effective pixels is determined in accordance with various requirements. In this example, the dark pixels comprise three bits located at the front end and one bit located at the rear end, but it should also be noted that the number of bits would be increased or decreased in accordance with the extent of light leakage between pixels or with requirements posed on the system to be used.
FIG. 15
is a timing chart showing an operation of the accumulation type line sensor shown in FIG.
14
. The accumulation is started upon releasing a reset status after the sensors are reset with a reset pulse
221
. During the accumulation, accumulation capacities (not shown) of the sensors are charged by photocurrents corresponding to the incident light quantities. However, in those bits which are shielded from the light, the accumulation capacities are charged by dark currents generated in the sensors. After a predetermined time ta of the accumulation, the outputs of the sensors are transferred with a transfer pulse
222
to the readout circuit
205
at one time. Then they are output, pixel by pixel, in a serial manner as an output signal
224
, based on shift pulses
223
generated by a shift register in the readout circuit. In this process, the output corresponding to the dark pixel
208
is taken as a representative dark output, so that that output is subtracted from each of the outputs of the subsequent effective pixels to obtain a corrected signal that compensates for an error due to the dark current of the sensor.
A description will be made of the outline of an overall structure of a color laser printer as a multi-color image forming apparatus. The color laser printer forms an electrostatic latent image in an image forming unit in accordance with an image light generated based on an image signal, and then develops the electrostatic latent image so as to form a color visible image, and further transfers the color visible image onto a transfer material as a recording medium, and fixes the color visible image. The image forming unit includes, for stations arranged in parallel corresponding to respective developing colors, photosensitive drums
5
Y,
5
M,
5
C and
5
K, injection charging means
7
Y,
7
M,
7
C and
7
K as primary charging means, developing means
8
Y,
8
M,
8
C and
8
K, and toner cartridges
11
Y,
11
M,
11
C and
11
K. The image forming unit also includes an intermediate transfer member
12
, a sheet feeding unit, a transferring unit and a fixing unit
13
.
The photosensitive drums
5
Y,
5
M,
5
C and
5
K are comprised of aluminum cylinders coated with an organic photoconductive layer on their peripheral surfaces. These photosensitive drums are rotated by a driving force transmitted from a driving motor (not shown), which causes the photosensitive drums
5
Y,
5
M,
5
C and
5
K to rotate counterclockwise in accordance with image forming operations. Exposing lights for the photosensitive drums
5
Y,
5
M,
5
C and
5
K are transferred from scanner units
10
Y,
10
M,
10
C and
10
K so as to selectively expose the photosensitive drums
5
Y,
5
M,
5
C and
5
K, so that electrostatic latent images are sequentially formed.
As primary charging means for charging the yellow (Y), magenta (M), cyan (C) and black (K) photosensitive drums, four injection charging means
7
Y,
7
M,
7
C and
7
K are provided for the respective stations. The injection charging means
7
Y,
7
M,
7
C and
7
K are equipped with sleeves
7
YS,
7
MS,
7
CS and
7
KS respectively.
As developing means for making the electrostatic latent image visible, four developing devices
8
Y,
8
M,
8
C and
8
K that perform developments in yellow (Y), magenta (M), cyan (C) and black (K) are provided for the respective stations. The developing devices
8
Y,
8
M,
8
C and
8
K are equipped with sleeves
8
YS,
8
MS,
8
CS and
8
KS respectively. Each of the developing devices is detachably mounted on the body of the apparatus.
The intermediate transfer member
12
is composed of an endless belt looping around a driving roller
18
a
and driven rollers
18
b
and
18
c
, which is in contact with photosensitive drums
5
Y,
5
M,
5
C and
5
K. At the time of color image formation, the intermediate transfer member
12
is rotated clockwise so as to be sequentially transferred with images by means of primary transferring rollers
6
Y,
6
M,
6
C and
6
K of respective colors.
A sheet feeding cassette
2
or a sheet feeding tray
3
, which serves as sheet feeding means (or a sheet feeding opening), accommodates transfer materials
1
. The transfer materials
1
are transported through a transporting path
25
defined by feed rollers
4
, transporting rollers
24
etc. so as to be delivered to registration rollers
23
. The arrival of the transfer material
1
at the registration roller
23
is detected by a sensor
19
positioned before the registration roller
23
.
During the formation of the image, the transportation of the transfer material
1
is suspended for a predetermined time in synchronization with the time, which is determined based on the detection by the sensor
19
before the registration roller, at which a color visible image on the intermediate transfer material
12
would arrive at a transferring area. The transfer material
1
is fed to the transferring area at which a secondary transferring roller
9
is in contact with the intermediate transfer member
12
to receive and transport the transfer material
1
therebetween, whereby color visible images on the intermediate transfer member
12
are transferred onto the transfer material
1
at one time in a superposed manner.
While the color visible images are transferred in a superposed manner, the secondary transferring roller
9
assumes a position shown by a solid line in
FIG. 16
, at which the secondary transferring roller
9
keeps the transfer material
1
in contact with the intermediate transfer member
12
. However, after completion of the printing process, the secondary transferring roller
9
is shifted apart from the intermediate transfer member
12
to a position shown by a broken line in FIG.
16
.
The fixing unit
13
functions to fix the
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Ngo Hoang
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