Electrophotography – Having particular structure – Modular or displaceable
Reexamination Certificate
2003-03-17
2004-11-23
Grainger, Quana (Department: 2852)
Electrophotography
Having particular structure
Modular or displaceable
Reexamination Certificate
active
06823156
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a developing device using toner as a developer, an image formation apparatus having the developing device, and a computer system including the image formation apparatus.
Also, this invention relates to a developing device used with an electrophotographic image formation apparatus such as a laser printer, a copier, or a facsimile for storing toner and developing a latent image formed on a photoconductor drum in the toner, in particularly, to a structure to fix a roller support frame of the developing device to a housing and to a structure to put a roller support frame, a developing roller, and a regulation blade of the developing device into a unit.
As the image formation apparatus, for example, an image formation apparatus having a developing device for developing a latent image formed on a photoconductor with toner as a developer or the like is known. The image formation apparatus has the developing device placed at a developing position opposed to the photoconductor for developing a latent image formed on the photoconductor to form a toner image in response to an image signal transmitted from an external apparatus such as a host computer.
FIG. 8
shows an example of the developing device. It is a schematic drawing to describe main components of the developing device. The developing device
200
shown in
FIG. 8
has a casing
204
for forming a toner storage section
202
storing toner T, a developing roller
206
as a toner supporter supported in the casing
204
for rotation, a toner supply roller
208
as a toner supply member pressed against the developing roller
206
for supplying toner T to the developing roller
206
, and a regulation blade
210
as a thickness regulation member for regulating the thickness of the toner T supplied to the developing roller
206
.
The developing roller
206
is formed of metal and has a gap with a photoconductor
212
. The developing device
200
forms an alternating electric field between the developing roller
206
and the photoconductor
212
and develops a latent image formed on the photoconductor
212
in a noncontact state.
The toner supply roller
208
has an elastic layer of polyurethane foam, etc., placed on the outer peripheral portion of a metal shaft, and is pressed against the developing roller
206
as it is elastically deformed.
The regulation blade
210
has a rubber part
210
a
and a rubber support part
210
b
. The rubber support part
210
b
is attached to the casing
204
via a blade support metal sheet
214
. The rubber support part
210
b
is a thin plate of phosphor bronze, stainless steel, etc., having a spring property and serves as urging member for pressing the rubber part
210
a
into contact with the developing roller
206
.
In the developing device
200
, the toner T stored in the toner storage section
202
is supplied by the toner supply roller
208
to the developing roller
206
. The supplied toner T has thickness regulated by the regulation blade
210
pressed against the developing roller
206
and is charged by friction and is transported to a developing position opposed to the photoconductor
212
. The toner is moved by an alternating electric field formed between the developing roller
206
and the photoconductor
212
, whereby a latent image on the photoconductor
212
is developed.
In the developing device
200
, to provide a good image, the regulation blade
210
needs to be properly pressed against the developing roller
206
for making uniform the thickness of a toner layer formed on the developing roller
206
, and the toner T needs to be charged evenly.
However, to reliably supply the toner T on the developing roller
206
, the toner supply roller
208
made of urethane is pressed against the developing roller
206
made of metal. Both end parts of each of the rollers
206
and
208
are regulated by the casing
204
supporting the rollers
206
and
208
and the rollers
206
and
208
are pressed in a direction in which the rollers
206
and
208
approach each other. At this time, in the developing roller
206
and the toner supply roller
208
, a force acting in a direction in which the centers are brought away from each other occurs because both ends are regulated. The toner supply roller
208
absorbs the force as urethane is elastically deformed, but the developing roller
206
is a rigid body and thus deflection in a direction in which the center is brought away from the toner supply roller
208
occurs.
When deflection occurs in the developing roller
206
, the abutment position of the regulation blade
210
against the developing roller
206
shifts and the regulation blade
210
is not properly against the developing roller
206
, making the thickness of the toner layer uneven and also making uneven the charge state by friction of the regulation blade
210
, and good developing cannot be conducted.
Also, in a laser printer as an example of the image formation apparatus including a rotary developing unit, a plurality of developing devices storing toners of different colors are set in the rotary developing unit. At the printing time, while the rotary developing unit is rotated, the developing device of the necessary color is brought adjacent to a photoconductor drum. The toner is supplied on a latent image formed on the photoconductor drum and is transferred from the photoconductor drum through a transfer belt to a sheet of print paper, etc., for fixing.
Generally, the developing device has a housing made of a synthetic resin for storing toner and a roller support frame made of metal being fixed to the housing with screws for supporting a developing roller for rotation.
The roller support frame supports the developing roller, and a regulation blade is pressed against the peripheral surface of the developing roller uniformly in the length direction of the regulation blade so as to even toner on the peripheral surface of the developing roller.
However, in the related developing device, the synthetic resin of which the housing is formed has a larger thermal expansion coefficient than the metal of which the roller support frame is formed. When heat generated during the operation of the rotary developing unit conducts to the developing device, the housing is expanded larger than the roller support frame. The roller support frame may become deformed because of the expansion difference between the housing and the roller support frame.
Further, when the roller support frame becomes deformed as mentioned above, the distribution of the press pressure of the regulation blade against the peripheral surface of the developing roller changes in the length direction of the regulation blade. Thus the action of evening the toner by the regulation blade becomes insufficient and a high toner-density portion and a low toner-density portion are produced, causing low-quality print matter to be formed partially with a large density difference.
In the related developing device, the roller support frame is constituted by a frame member extending in parallel with the developing roller and side frame members bent in the same direction at 90 degrees from both ends of the frame member, and is shaped like a character U in cross section. Thus, a force is exerted to the developing roller when the developing roller is placed or removed, the roller support frame may become deformed. Accordingly, although a regulation blade was in contact with the peripheral surface of the developing roller in the length direction thereof at uniform pressure at the beginning, a local point on which pressure is exerted may occur or pressure may be exerted in a varied manner from side to side.
Thus, if the regulation blade cannot be maintained in a state in which it is in contact with the peripheral surface of the developing roller in the length direction thereof at uniform pressure, the evening effect of the regulation blade on the peripheral surface of the developing roller is not demonstrated and therefore the distribution of toner on the developing roller is made uneven, adver
Grainger Quana
Seiko Epson Corporation
Sughrue & Mion, PLLC
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