Electrophotography – Image formation – Development
Reexamination Certificate
2000-01-27
2001-03-06
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06198894
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a liquid electrophotographic printer, and more particularly, to a squeegee roller driving apparatus for squeegeeing excess developer liquid from a transfer surface of a photosensitive medium.
2. Description of the Related Art
As shown in
FIG. 1
, a liquid electrophotographic printer such as a color laser printer includes a development device
20
for supplying a developer liquid to an electrostatic latent image formed on a transfer surface
10
a
of a photoreceptor belt
10
as a photosensitive medium to develop the electrostatic latent image.
In the development device
20
, a developer liquid spray nozzle
21
, a development roller
22
and a squeegee roller
23
are sequentially installed. The development roller
22
transfers a developer liquid to the transfer surface
10
a
of the photoreceptor belt
10
. The squeegee roller
23
squeezes the developer liquid transferred on the transfer surface
10
a
of the photoreceptor belt
10
. Reference numerals
12
and
13
denote backup rollers opposite to the development roller
22
and the squeegee roller
23
to apply tension to the photoreceptor belt
10
.
The development roller
22
and the squeegee roller
23
, as shown in
FIG. 2
, are installed in separate elevation apparatuses
32
and
33
, respectively to be controlled to elevate according to the operating mode of the printer. Although not shown in detail, generally the elevation apparatuses
32
and
33
each includes a spring (not shown) configured to adjust its elastic force by a cam mechanism (not shown). In response to the adjusted elastic force of the spring, the development roller
22
and the squeegee roller
23
are lifted or lowered to be engaged in proximity of or disengaged away from to the photoreceptor belt
10
.
In the case where the printer is in a printing mode, the development roller
22
and the squeegee roller
23
remain in a lifted state by the driving of the elevation apparatuses
32
and
33
. Here, the development roller
22
is lifted up to a location at which a gap of about 0.1 to 0.2 mm is formed between the photoreceptor belt
10
and the development roller
22
. The squeegee roller
22
is lifted up to a location at which it presses the photoreceptor belt
10
with a force of approximately 20 kilograms even after it contacts the photoreceptor belt
10
. In the case where the printer is in a stop mode, the development roller
22
and the squeegee roller
23
are lowered to be completely disengaged from the photoreceptor belt
10
.
As the printing operation is carried out, the developer liquid may accumulate and remain on a contact portion of the squeegee roller
23
and the photoreceptor belt
10
. The excess developer liquid remaining on the photoreceptor belt
10
is referred to as a drip line (D). In order to obtain a clean-quality printed image, it is necessary to remove the drip line D at regular time intervals during the printing operation.
FIG. 2
illustrates the positional relationship between the photoreceptor belt
10
, the development roller
22
and the squeegee roller
23
in a drip line removal mode, in which the development roller
22
is completely disengaged from the photoreceptor belt
10
, as in the stop mode. Also, the squeegee roller
23
is controlled to rotate in reverse with respect to the rotating direction of the photoreceptor belt
10
in the printing mode, while the photoreceptor
10
remains pressed with a loading force of approximately 2 kilograms by adjusting the elastic force of the spring provided in the elevation apparatus
23
.
As shown in
FIG. 3
, a conventional driving apparatus for rotating the squeegee roller
23
in reverse with respect to the traveling direction of the photoreceptor belt
10
includes a squeegee gear
24
installed at a shaft end of the squeegee roller
23
, and a driving gear
25
installed at an output end of a driving source (M) positioned above the squeegee gear
24
to be engaged therewith.
In general, the squeegee roller
23
is configured to be capable of rotating in a forward or reverse direction, by installing a one-way bearing or clutch (not shown) on the driving shaft of the driving gear
25
. In other words, the squeegee roller
23
contacts the photoreceptor belt
10
in the printing mode to rotate in the same direction as that of the photoreceptor belt
10
(in a forward direction) due to a frictional force therebetween. In a drip line removal mode, the squeegee gear
24
is subjected to the driving force applied from the driving gear
25
to rotate reversely.
According to the above-described conventional squeegee roller driving apparatus, in the course of switching from a drip line removal mode, as shown in
FIG. 4A
, to a stop mode, as shown in
FIG. 4B
, the squeegee roller
23
is lowered so that the driving gear
25
and the squeegee gear
24
are spaced apart from each other, thereby stopping rotation. In this case, since the squeegee roller
23
stops temporarily on the transfer surface of the photoreceptor belt
10
, the drip line D is not completely removed due to the rolling trace of the squeegee roller
23
, leaving a small amount of carrier (approximately 0.005 gram) on the transfer surface of the photoreceptor belt
10
. As shown in
FIG. 5
, the remaining carrier is transferred to an image (D′) on printing paper
1
, degrading the print quality of the printed image.
SUMMARY OF THE INVENTION
To solve the above problem, it is an object of the present invention to provide an apparatus for driving a squeegee roller of a liquid electrophotographic printer, which can enhance the accuracy in removing a drip line, by improving a driving mechanism such that the squeegee roller keeps rotating reversely for a while even when the squeegee roller is lowered in the course of switching from a drip line removal mode to a stop mode.
Accordingly, to achieve the above object, there is provided an apparatus for driving a squeegee roller of a liquid electrophotographic printer, comprising a squeegee roller installed to be of operative to rotate in contact with a photoreceptor belt circulating along a track and to be lifted to and lowered from the photoreceptor belt, a squeegee gear coaxially installed at one shaft end of a rotation shaft of the squeegee roller, a driving gear installed such that in a state where the squeegee roller contacts the photoreceptor belt, the center of the rotation shaft thereof is positioned on a plane perpendicular to an elevating direction of the squeegee roller and passing through a center of the rotation shaft of the squeegee roller, to be engaged with the squeegee roller, and a driving source having an output shaft for rotating the driving gear to drive the squeegee roller to rotate in a reverse direction to with respect to circulating direction of the photoreceptor belt.
Preferably, the driving gear is positioned in the upstream of the squeegee gear with respect to the circulating direction of the photoreceptor belt to be engaged therewith.
REFERENCES:
patent: 3907423 (1975-09-01), Hayashi et al.
patent: 4056315 (1977-11-01), Ariyama et al.
Pendegrass Joan
Samsung Electronics Co,. Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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