Electrophotography – Image formation – Development
Reexamination Certificate
2000-04-10
2001-07-10
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Image formation
Development
Reexamination Certificate
active
06259878
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a one-component developing device used for an electrophotographic apparatus, such as a copier or a printer, and relates in particular to a one-component developing device which uses a one-component developer.
2. Related Arts
Currently, electrophotographic apparatuses are employed as copiers or printers. Such an electrophotographic apparatus forms an electrostatic latent image on a photosensitive drum, and then develops the latent image, a task for which a developing device is required. In general, two types of devices are employed for this purpose: a two-component developing device and a one-component developing device, which respectively use a two-component developer and a one-component developer. Of the two devices, the one-component developing device is the least complicated to make and the one can be constructed the most compactly. But when a one-component developing device is used, the layer of developer with which a developing roller is coated must have a uniform thickness.
FIG. 11
is a diagram showing a conventional developing device.
As is shown in
FIG. 11
, an electrostatic latent image is formed on a latent image bearing member
90
, such as a photosensitive drum, and the latent image on the latent image bearing member
90
is then developed using a one-component developing device
91
. The components comprising a one-component developing device
91
include a developing roller (developer carrier)
92
, a feed roller (developer feeding member)
94
, and a regulating blade (developer regulating member)
93
.
In the development process, a one-component developer
95
is used to uniformly coat the developing roller
92
, which then transports the developer
95
to a developing area, facing the photosensitive drum
90
, where in response to the application to the developing roller
92
of a bias voltage (a DC or an AC voltage), developer
95
is transferred to the photosensitive drum
90
. For this process, the feed roller
94
supplies the developer
95
to the developing roller
92
, and the regulating blade
93
, which is formed of a stainless steel leaf-spring, smooths and levels the developer
95
on the developing roller
92
.
In a conventional developing device, a uniform thickness is maintained for the coating of the developer
95
, which is supplied to the developing roller
92
by the feed roller
94
, by the regulating blade
93
. And the developing roller
92
is rotated so that it transports the developer
95
to the developing area for the photosensitive drum
90
.
The arrangement of a one-component developing device can be simplified. In such a device, the regulating blade
93
is formed of a leaf-spring, which at one end is fixed to the frame of the developing device and at the other end is free. With this arrangement, based on the support provided by its fixed end, the regulation blade
93
is pressed against the developing roller
92
by the force developed by the leaf-spring and maintains on the developing roller
92
a developer
95
layer having a constant thickness. Accordingly, the blade
93
linearly contacts the developing roller
92
.
However, the conventional developing device has the following problems.
First, in order to increase the quantity of available developer
95
, the amount supplied must be sufficient to fill the space behind the regulating blade
93
. For especially when a developing unit is supplied as an exchangeable cartridge, if a large quantity of developer
95
is loaded into the cartridge the replacement period can be extended, and running costs can be reduced. However, because under the circumstances the developer
95
is stored to the rear of the leaf spring regulating blade
93
, the pressing force exerted by the blade will vary in accordance with the amount of developer
95
remaining in the cartridge. In other words, when there is a large amount of developer
95
available to the rear of the regulating blade
93
, the force with which the regulating blade
93
presses against the developing roller
92
is comparatively strong; but as the supply of developer
95
is depleted, there is a corresponding reduction in the pressing force exerted by the regulating blade
93
.
Therefore, the thickness of the developer layer on the developing roller
92
varies, and image density is accordingly changed. To prevent this, the maximum volume of the developer must be reduced so that undue pressure is not applied to the regulating blade
93
; however, when the maximum volume for the developer is reduced, the replacement period is shortened. And although the size of the developer unit may be increased so it contains more developer, such an increase will result in a like increase in the size of a printer itself.
Second, when a large amount of developer
95
is supplied, in addition to influencing the pressing force exerted by the regulating blade
93
, the developer
95
tends to compact and to form solid masses which thereafter are attached to the regulating blade
93
. As a result, the thickness of the developer
95
applied to the developing roller
92
is not uniform, and lines and stripes appear on a developed image.
SUMMARY OF THE INVENTION
It is, therefore, one objective of the present invention to provide a one-component developing device which reduces changes in image densities.
It is another objective of the present invention to provide a one-component developing device wherefor image density is not affected by the amount of developer.
It is an additional objective of the present invention to provide a one-component developing device which prevents image failures, such as the printing of lines and stripes.
To achieve these objectives, according to one aspect of the present invention, a one-component developing device comprises: a developer carrier for feeding a one-component developer to an image bearing member; and a developer regulating member for regulating a thickness of a developer layer on the developer carrier. The developer regulating member includes a blade, for regulating the thickness of the developer layer on the developer carrier, and a blade table, for supporting both ends of the blade and for achieving face-contact between the blade and the developer carrier.
Since the blade table supports the blade at either end, the blade is bent when it is pushed against the developer carrier and face-contact with the developer carrier is achieved. Therefore, the force with which the blade contacts the developer carrier is dispersed. As a result, the developer is not contacted and attached as solid masses to the blade or the developer carrier, and the generation of lines and stripes can be prevented.
Further, the developer contained in a developing unit does not contact the blade table and thereby apply no pressure to the blade. Thus, the pressure applied to the blade is not changed, and accordingly, the image density is not varied.
According to one more aspect of the present invention, the blade and the blade table do not contact each other in an area whereat the blade contacts the developer carrier.
In this case, the blade table can be formed so that a gap is defined between the blade and the blade table in that area whereat the blade contacts the developer carrier.
According to another aspect of the present invention, one end of the blade is fixed to the blade table, and a projection on the blade table supports the other end of the blade.
The end of the blade farthest from the developer carrier is fixed to the blade table, while the other end of the blade, which is closest to the developer carrier, is supported by the blade table.
The end of the blade closest to the developer carrier is not fixed to the blade table.
According to an additional aspect of the present invention, the portion of the blade table which supports the other end of the blade is formed of a flexible member.
According to a further aspect of the present invention, the blade table supports the other end of the blade, and has a projection formed of a flexible member.
Ac
Kimura Masatoshi
Sato Kunihiko
Armstrong Westerman Hattori McLeland & Naughton LLP
Fujitsu Limited
Lee Susan S. Y.
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