Electrophotography – Image formation – Charging
Reexamination Certificate
2000-11-03
2002-04-16
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Charging
C361S225000, C399S168000, C399S313000
Reexamination Certificate
active
06374071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a charging unit and a manufacturing method thereof. Further, the present invention relates to a charging device and a transfer device utilized in a copying machine, a printer and so forth of an electrophotographic system.
Electrophotography means electrostatic copying, electrostatic recording and so forth. In the field of the electrophotography, a device for applying an electric charge to a surface of a photosensitive material is called as a charging device. Meanwhile, a device for applying a voltage to a recording medium is called as a transfer device. This transfer device applies the voltage in order to transfer a toner image, which is formed on a photosensitive material, to the recording medium (a paper, a film and so forth). The charging unit and the charging device according to the present invention are not exclusive to the field of the electrophotography, but are applicable to any cases in that the electric charge is applied to a surface to be charged. The material to be charged may be any one of a drum shape, a belt shape, a sheet shape and so forth.
2. Description of the Related Art
Both of the charging device and the transfer device comprise the charging unit, and charge the material in a same principle. Their uses are merely different. For this reason, the charging unit and the charging device are mainly described hereinafter. As to a charging method in the field of electrophotography, is widely used a contact charging system (roller, tube, blade, blush and so forth) in which ozone is hardly generated, instead of a corona discharging system accompanying generation of ozone. A roller charging system is widely used as one of the contact charging system. This system uses a charging roller comprising shaft, a conductive elastic layer provided around the shaft, and a charging layer provided around them. Although the roller charging system represents the contact charging systems, there arise problems in that it costs to manufacture the charging roller, and in that it costs to peel the conductive elastic layer from the shaft when discarding or recycling, and in that the discarded material is not good for environment. In order to solve above problems, it has recently been proposed to use a seamless charging tube.
The charging roller and the charging device using the seamless charging tube is described in Japanese Laid-Open Publication No. 5-273844, for example.
FIG. 9
shows a first embodiment of the charging roller described in the above Publication, and
FIG. 10
shows a second embodiment thereof.
In
FIG. 9
, the charging roller
30
comprises a conductive shaft
2
a
, a conductive foam layer
2
b
integrally formed on an outer surface of the shaft
2
a
, and a seamless charging tube
2
c
loosely encasing the foam layer
2
b
without adhering to a peripheral surface thereof. In other words, an inner diameter of the charging tube
2
c
is larger than an outer diameter of the conductive foam layer
2
b
. Both ends of the shaft
2
a
of the charging roller
30
are held by a bearing member, and the charging roller
30
is pressed against an outer surface of a photosensitive drum
1
by means of a spring
23
provided both ends of the shaft
2
a
under a predetermined pressing force (1 Kg).
The whole of the charging roller
30
including the seamless charging tube
2
c
is driven to rotate in association with a rotation of the photosensitive drum
1
. A power supply
4
applies, to the charging roller
30
, a superposed oscillating voltage (Vac+Vdc) with an alternating voltage Vac (2 kVpp, 600 Hz) and a DC voltage Vdc(−700 V) corresponding to a desired surface voltage. The voltage is applied via a slide electrode
24
contacted to the shaft
2
a
. Owing to this, the voltage is applied to the charging tube
2
c
via the shaft
2
a
and the conductive foam layer
2
b
. Thus, charges are interchanged at a pressure nip portion between the charging roller
30
and the photosensitive drum
1
so that the outer surface of the photosensitive drum
1
is charged up to the desired surface voltage. Incidentally, the photosensitive drum
1
and the power supply are identical with those denoted by reference numerals
1
and
4
in FIG.
1
. The spring
23
and the bearing member are identical with those denoted by reference numerals
3
and
11
in FIG.
2
.
A charging roller
31
shown in
FIG. 10
comprises a conductive elastic cylinder
2
d
formed in a thick cylindrical shape, the charging tube
2
c
integrally covering the conductive elastic cylinder
2
d
, and the shaft
2
a
loosely inserted into a hollow of the elastic cylinder
2
d
. The elastic cylinder
2
d
loosely encases the shaft
2
a
, and the inner diameter of the elastic cylinder
2
d
is larger than the outer diameter of the shaft
2
a
. The charging roller
31
is supported similarly to the embodiment
1
shown in
FIG. 9
so as to be pressed against the outer surface of the photosensitive drum
1
. The charging tube
2
c
closely contacts with the outer surface of the photosensitive drum
1
, by the pressing force of the spring
23
, at the pressure nip portion between the charging roller
31
and the photosensitive drum
1
. Meanwhile, a state that the shaft
2
a
closely contacts with the surface of the hollow of the elastic cylinder
2
d
is kept. The charging roller
31
including the elastic cylinder
2
d
, the charging tube
2
c
and the shaft
2
a
is driven to rotate in association with the rotation of the photosensitive drum
1
. Similarly to the foregoing embodiment
1
, the superposed oscillating voltage is applied. The voltage is applied to the charging tube
2
c
via the shaft
2
a
and the conductive elastic layer
2
d
so that the outer surface of the photosensitive drum
1
is charged up to the desired surface voltage.
The inventor of the present application has confirmed the following problems of the charging roller shown in FIG.
9
and the charging device using thereof. The first problem relates to the cost. As methods for integrally forming the foam layer
2
b
on the surface of the shaft
2
a
, two methods are known. In the first method, a foam material of conductive rubber is formed encasing the shaft
2
a
and then ground in a predetermined thickness. In the second method, a foam material of conductive rubber is formed in a cylindrical shape by an extruding machine such that its inner diameter is smaller than the outer diameter of the shaft
2
a
, and then, the air is blown into the cylindrical body to enlarge the inner diameter of the foam material rather than the outer diameter of the shaft
2
a
. In this state, the shaft is inserted into the cylindrical body. The cost of the second method is lower than that of the first method, however, a considerable cost is spent in both methods. The latter method needs the cost for inserting the shaft into the hollow of the cylindrical body, besides the cost for merely forming the cylindrical body.
The second problem relates to a shift of the charging tube
2
c
during the rotation. Since the charging tube
2
c
loosely encases the outer surface of the foam layer
2
b
, the charging tube
2
c
moves little by little in an axial direction in accordance with the rotation of the photosensitive drum
1
. Manufacturing accuracy of the respective parts has a limit so that combination of ideal dimensions can not be obtained relative to the respective parts. Thus, in practice, it is impossible to prevent the charging tube
2
c
from moving in the axial direction. Owing to this movement, an end portion of the charging tube
2
c
abuts on the bearing member of the shaft
2
a
. In case the pressing force is about 1 Kg, a frictional force between the charging tube
2
c
and the foam layer
2
b
becomes large so that the charging tube
2
c
can not be pushed back by the bearing member. Hence, the force for pressing the bearing member becomes large more and more. Eventually, the edge of the charging tube
2
c
is turned over or deformed. Due to this, it becomes impossibl
Brase Sandra
Keytech Co., Ltd.
Young & Thompson
LandOfFree
Charging unit, a manufacturing method thereof, a charging... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Charging unit, a manufacturing method thereof, a charging..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Charging unit, a manufacturing method thereof, a charging... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2920464