Electrophotography – Image formation – Development
Reexamination Certificate
2002-07-11
2004-04-13
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Development
C399S284000
Reexamination Certificate
active
06721527
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, using an electrophotographic or electrostatic recording system and to a developing apparatus to be used in the image forming apparatus.
2. Related Art
Nowadays, an increase in speed, a reduction in size, an improvement in image quality, and an increase in service life are required of image forming apparatuses. In addition, with the development of the information technology, there is an increasing demand for color image output.
An example of a technique for meeting the demand for an increase in speed is a tandem type image forming apparatus in which developing apparatuses for four colors are arranged laterally or longitudinally. Despite the fact that a plurality of developing apparatuses are arranged, no increase in apparatus size is involved since each developing unit is thin.
FIG. 13
shows an example of such an image forming apparatus.
FIG. 13
is a side sectional view showing the inner construction of a tandem type printer. As shown in the drawing, a sheet conveying belt
111
is arranged substantially at the center of the interior of the apparatus. The belt
111
, whose end portions are held by a driving roller
112
and a driven roller
113
, circulates counterclockwise as indicated by an arrow A. On top of the belt
111
, there are arranged four photosensitive drums
114
(
114
a
,
114
b
,
114
c
, and
114
d
) in a sheet conveying direction (from the right to the left in the drawing).
On the upstream side of the belt
111
with respect to the sheet conveying direction, there is provided a registration roller pair
124
for correcting skew feeding of a sheet being fed. On the upstream side thereof, a sheet guiding path
125
is provided, and on the upstream side thereof, a sheet feeding roller
126
is provided. A sheet cassette
104
is arranged on the upstream side of the sheet feeding roller
126
.
(Description of a Process Cartridge in an Image Forming Apparatus)
FIG. 14
is an enlarged sectional view of a process cartridge
134
to be mounted in the printer of FIG.
13
. The process cartridge
134
is obtained by forming two sub units: a drum unit
135
and a developing unit
136
into an integral unit. The drum unit
135
is equipped with the photosensitive drum
114
mentioned above, a cleaner
115
arranged on the left-hand side thereof, and a charging roller
116
arranged above and on the left-hand side of the photosensitive drum
114
. Light in accordance with image information emitted from a scanner
117
mounted in the printer main body impinges upon the photosensitive drum
114
at a position indicated by reference numeral
137
.
The photosensitive drum
114
consists of a conductive metal roller whose surface is uniformly coated with a photoconductive material; the metal roller portion is grounded, and rotates clockwise as indicated by an arrow C.
The charging roller
116
is connected to a high-voltage power source and applies a blank-state charged potential (initialization potential applied uniformly; in a system it is applied in positive polarity, in another in negative polarity) to the photosensitive drum
114
, whereby the photosensitive layer on the peripheral surface of the photosensitive drum
114
is uniformly charged, for example, in negative high potential and initialized.
The scanner
117
is equipped with a laser light source or an LED light source, and performs selective exposure in accordance with image information on the peripheral surface of the photosensitive drum
114
charged in negative high potential. As a result of this exposure, there is formed on the surface of the photosensitive drum
114
a negative low potential portion with attenuated potential, and there is formed an electrostatic latent image consisting of the low potential portion and the high potential portion obtained through the initialization.
In the developing unit
136
, a non-magnetic toner is stored so as to substantially fill a developing container
118
, and a toner agitating member
144
is arranged so as to be buried under the toner; in the lowermost portion, a toner supply roller
145
formed of a sponge material is held in press contact with a developing roller
143
. A developing blade
146
in the form of a plate spring is held in press contact with the upper right portion of the developing roller
143
.
(Description of the Operation of the Image Forming Apparatus)
The operation of the above-described image forming apparatus will be briefly described with reference to
FIGS. 13 and 14
. First, when a power source is turned on and instructions on the property and number of the sheets to be used, printing mode and the like are input through keys or as signals from a host apparatus connected to the image forming apparatus, one of the sheets accommodated in the sheet cassette
104
is supplied to the registration roller pair
124
by way of the sheet feeding roller
126
. The rotation of the registration roller pair
124
is temporarily stopped, and the conveyance of the sheet is on standby with the leading end of the sheet abutting the nip portion defined by the registration roller pair
124
.
Subsequently, the driving roller
112
rotates counterclockwise, and the driven roller
113
also rotates counterclockwise, whereby the entire belt
111
circulates counterclockwise, with its upper portion in contact with the four photosensitive drums
114
.
At the same time, the developing containers
118
and the photosensitive drums
114
are successively driven in synchronism with printing. The photosensitive drums
114
rotate clockwise, and the charging rollers
116
impart a uniform high negative charge to the peripheral surfaces of the photosensitive drums
114
; the scanner
117
performs exposure on the peripheral surfaces of the photosensitive drums
114
in accordance with an image signal to form low potential portions, whereby electrostatic latent images are formed which consist of high negative potential portions due to initialization and low negative potential portions due to exposure. The developing rollers
143
of the developing containers
118
transfers toner to the low potential portions of the electrostatic latent images to thereby form toner images on the peripheral surfaces of the photosensitive drums
114
(reversal development).
As the forward end of the toner image on the peripheral surface of the upstream-end photosensitive drum
114
a
approaches an opposite portion of the belt
111
, the registration roller pair
124
starts rotation such that the printing start position of the sheet is matched with the opposite portion, and the sheet is fed to the sheet inlet portion.
The driven roller
113
and an attraction roller (not shown) convey the sheet while holding it with the belt
111
. The sheet is attracted by the belt
111
and conveyed to a first transfer portion formed by the photosensitive drum
114
a
and a transfer roller
119
a.
The transfer rollers
119
(
119
a
,
119
b
,
119
c
, and
119
d
) apply transfer current output from a transfer bias power source (not shown) to the sheet through the belt
111
. By the transfer current applied from the transfer rollers
119
, the toner images on the photosensitive drums
114
are transferred to the sheet.
The sheet to which the toner images in four colors have been transferred is separated from the belt
111
and is conveyed to a fixing apparatus
128
. The fixing apparatus
128
fixes the toner images to the sheet by heat and pressure. After the image fixation, the sheet is discharged onto a discharge tray
106
by a discharge roller pair
132
with the toner image facing downwards.
However, as shown in
FIG. 14
, in the process cartridge
134
, the toner supply roller
145
is provided in the lowermost portion of the developing unit
136
, so that the toner is carried and supplied downward from above, and the stress on the developing unit
136
is rather large, which makes the toner subject to deterioration.
In the developing unit
136
Kanari Kenji
Kawamura Takeshi
Nakagawa Ken
Tsurumi Yuzuru
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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