Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
1999-04-08
2001-01-09
Chen, Sophia S. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
C399S227000, C399S285000
Reexamination Certificate
active
06173138
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to a developing apparatus which uses developer to develop an electrostatic latent image formed on an image bearing member. It also relates to an image forming apparatus which comprises such a developing apparatus.
In an image forming operation, an electrostatic latent image is formed and borne on a latent image bearing member, and is developed into a visible image by a developing apparatus which uses developer. As for such a developing apparatus, a developing apparatus
103
illustrated in
FIG. 7
is well known. In the developing apparatus
103
, a developer bearing member
100
is rotated, bearing developer on its peripheral surface. In order to develop the latent image borne on the latent image bearing member, a compound voltage is applied to the developer bearing member
100
from an electrical power supply source
101
through contact terminals
102
and
102
. As the compound voltage is applied to the developer bearing member
100
, an alternating electric field is generated between the latent image bearing member (unillustrated) and the developer bearing member
100
. As a result, the developer borne on the peripheral surface of the developer bearing member
100
is transferred onto the latent image borne on the latent image bearing member, developing the latent image into a visible image.
FIG. 7
is a schematic sectional view of the developing apparatus
103
, and depicts the general structure of the developing apparatus
103
.
In the developing apparatus
103
in operation, the contact terminals
102
and
102
are placed in contact with each other to allow the compound voltage composed of AC and DC voltages, to be applied to the developer bearing member
100
from the electrical power supply source
101
. As a result, the latent image formed and borne on the latent image bearing member is turned into a visible image. After the development of the electrostatic latent image, the contact terminals
102
and
102
are separated from each other, preventing the compound voltage from being applied to the developer bearing member from the electrical power supply source
101
.
In recent years, a great number of innovative image formation technologies have been developed in terms of detail or resolution. Consequently, developer particle size has been made smaller and smaller, and also, developer particle shape has been made more and more sphere-like. This, however, created a problem called “developer blowout,” that is, a problem that developer leaks from the developing apparatus. This problem occurs for the following reason. That is, developer particles with an extremely small size are difficult to triboelectrically charge. As a result, triboelectrically insufficiently charged developer particles tend to leak through the gap between the surface of the developer bearing member and the frame of the developing apparatus, at the longitudinal ends of the developer bearing member. Thus, prevention of the so-called “developer blowout” has long been desired.
Thus, in recent years, developing apparatuses such as a developing apparatus
203
, illustrated in
FIG. 8
, which are designed to prevent the “developer blowout,” have been proposed, and some of them have been put to practical usage. In these developing apparatuses, a leak prevention member
200
in the form of a roller is placed in contact with, or extremely close to, the developer bearing member, at each longitudinal end portion of the developer bearing member. More specifically, the peripheral surface of the leak prevention member
200
is placed in contact with, or extremely close to, the peripheral surface of the developer bearing member, to prevent the “developer blowout.” In addition, a voltage with the same polarity as the polarity of the triboelectrically charged developer is applied to each leak prevention member
200
with the use of a condenser
201
as a voltage application member, and also, a voltage with the same polarity as the normal polarity to which the developer is charged is applied to the developer bearing member
100
through a diode
202
to prevent the developer from being adhered to the leak prevention members
200
and
200
.
FIG. 8
is a schematic drawing which depicts the general structure of the developing apparatus
203
.
Generally, the developing apparatus
203
is designed to take two distinctive positions, that is, a developmental position at which it develops a latent image and a nondevelopmental position to which it is retracted when it does not develop a latent image. As the developing apparatus is moved from the developmental position to the nondevelopmental position at the end of each latent image developing process, the contact terminals
102
and
102
, which are in contact with each other when the developing apparatus
203
is at the developmental position, become separated from each other, and therefore, the contact terminal
102
on the developing apparatus main assembly side (position Y in the drawing) becomes a floating terminal. As a result, the potential level of this contact terminal becomes the same as that of the condenser
202
. Therefore, if the electrical charge remaining in the condenser
202
does not sufficiently attenuate by the time the contact terminals
102
and
102
become separated from each other, sparks are created between the contact terminal
102
on the developing apparatus main assembly side (position Y in
FIG. 8
) and the contact terminal
102
on the image forming apparatus main assembly side, by the electrical charge remaining in the contact terminal
102
on the Y side immediately before the two contact terminals
102
come in contact with each other as the developing apparatus
203
is moved from the nondevelopmental position to the developmental position for the following latent image developing process. These sparks carbonize the contact terminal
102
on the image forming apparatus main assembly side, causing the image forming apparatus to malfunction. This has been one of the essential problems from which the developing apparatus
203
suffers.
SUMMARY OF THE INVENTION
The primary object of the present invention is to prevent developer from leaking from a developing apparatus, adjacent to the longitudinal end portions of the developer bearing member of the developing apparatus, and also to remove the residual electrical charge from the leak prevention member of the developing apparatus after each developing operation, so that it becomes possible to provide a leak free developing apparatus and a leak free image forming apparatus.
Another object of the present invention is to provide a developing apparatus and an image forming apparatus which reduce the residual electrical charge in the developing apparatus when voltage is not applied to the developing apparatus by an electrical power source.
Another object of the present invention is to provide a developing apparatus and an image forming apparatus which do not generate sparks by electrical discharge when the developing apparatus is moved back to the developmental position after it is moved from the developmental position to the nondevelopmental position.
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4697914 (1987-10-01), Hauser
patent: 4947211 (1990-08-01), Ono et al.
patent: 5172165 (1992-12-01), Hatakeyama et al.
patent: 5592265 (1997-01-01), Sakuraba et al.
patent: 5761576 (1998-06-01), Sugihara et al.
patent: 3-194582 (1991-08-01), None
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
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