Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2000-02-14
2002-06-18
Royer, William J. (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
Reexamination Certificate
active
06408150
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing apparatus for developing an electrostatic latent image formed on an image bearing member with developer.
2. Related Background Art
In the past, it is already known to provide image forming apparatuses in which, after a latent image bearing member is uniformly charged, image exposure is effected by analogue exposure or a semiconductor laser or an LED, and, after an electrostatic latent image formed on the latent image bearing member, the electrostatic latent image is visualized by a developing apparatus as a toner image. After the developer image is transferred to a transfer material as a recording material, the transfer material is separated from the latent image bearing member and is subjected to fixing treatment in a fixing device to obtain a fixed image.
Now, an operation of such a conventional image forming apparatus will be described with reference to FIG.
10
.
Such an image forming apparatus includes a photosensitive drum
101
having a photoconductive layer such as OPC or, as a latent image bearing member, a-Si and is rotated in a direction shown by the arrow B.
In such an image forming apparatus, first of all, a surface of the photosensitive drum
101
is uniformly charged by a primary charger
103
to −700 Volts, for example.
Then, the surface potential of the exposed portion on the photosensitive drum
101
is reduced, by image exposure
112
corresponding to image signal information, to −200 Volts, for example, thereby forming a latent image corresponding to the image signal on the photosensitive drum
101
. For example, a semiconductor laser or an LED array is used for the image exposure
112
.
Then, the latent image is developed by a developing device
102
as a developing apparatus using dry one-component developer to visualize the latent image as a toner image. The developing apparatus using the dry one-component developer has a long endurance life because it is simple and exchange of carrier is not required, and, for example, jumping developing using magnetic one-component toner can be effected. Incidentally, the developing device
102
utilizes negatively charged black toner. Further, upon development, a DC bias of about −500 Volts is applied to a developing sleeve (developer bearing member) of the developing device
102
as a developing bias, thereby reversal-developing the latent image.
Thereafter, if desired, pre-transfer treatment is effected by using a charger
110
(normally, application of corona by DC or AC or photoelectricity removal or combination thereof), and then, the toner image is transferred, by a transfer charger
104
, onto a transfer material supplied to the photosensitive drum
101
.
Thereafter, the transfer material to which the toner image was transferred is sent to a fixing device (fixing apparatus)
107
, where the toner image is fixed to the transfer material as an image. On the other hand, transfer residual toner which was not used in the development and remains on the photosensitive drum
101
is removed by a cleaning device
106
, thereby preparing for next image formation.
On the other hand, in order to obtain a high speed image forming apparatus, in the conventional developing apparatus, as disclosed in Japanese Patent Application Laid-Open No. 3-204084 (1991), a plurality of developing sleeves are provided in a developing apparatus using a two-component magnet brush, or, as disclosed in Japanese Patent Laid-Open No. 2-188778 (1990), a replenishing amount of toner from developing sleeves (developer bearing members) to a photosensitive member (latent image bearing member) is made uniform by arranging the developing sleeves and the photosensitive member so the that distance between the developing sleeves and the photosensitive member is gradually decreased toward a downstream side in a rotational direction of the photosensitive member.
Next, a method for sealing developer at an axial end of the rotatable developer bearing member of the conventional developing apparatus will be described with reference to
FIGS. 11
to
13
.
As shown in
FIG. 11
, such a developing apparatus has a developer container
102
a
containing the developer, and agitating means
102
B are provided in the developer container
102
a
so that the developer in the developer container
102
a
is agitated and conveyed in a predetermined direction by the agitating means
102
B.
Further, the developing apparatus has a developing sleeve (developer (magnetic powder) bearing member)
120
for developing the electrostatic latent image formed on the photosensitive drum
101
and for carrying the developer in the developer container
102
a
toward the photosensitive drum
101
.
Normally, the developing sleeve
120
includes non-magnetic metal at its outer periphery and also has a magnet roller (magnetic field generating means)
120
a
fixed therewithin and having a plurality of circumferential magnetic poles N
1
, N
2
, N
3
, S
1
, S
2
, as shown in FIG.
11
.
Further, as shown in
FIG. 13
, a shaft
120
c
of the developing sleeve
120
is supported by side walls
102
e
of the developer container
102
a
via bearings
120
b.
Incidentally,
FIG. 13
shows only one side wall
120
e.
With the above-mentioned arrangement, by the rotation of the developing sleeve
120
, the developer is carried from the magnetic pole S
3
to the magnetic pole N
1
while being borne by the developing sleeve
120
, and an amount of developer on the developing sleeve
120
is regulated by a developing blade
102
g
supported by a support plate
102
f
to form a thin developer layer on the developing sleeve
120
. Incidentally, the magnetic pole N
2
is a main developing pole where the electrostatic latent image on the photosensitive drum
101
is developed by the developer. Thereafter, the developer is returned into the developer container
102
a
by the rotation of the developing sleeve
120
.
In the past, in a method for mechanically scraping the developer on the developing sleeve by felt in order to seal the developer at the ends of the developing sleeve, torque for driving the developing sleeve might become great and a great load may act on a motor to shorten endurance life of the motor and the toner may be firmly fixed to the end of the sleeve due to an increase in temperature at the sleeve ends.
Further, the developer circulated within the developer container
102
a
in the above-mentioned manner is shifted toward the bearings
120
b
along the surface of the developing sleeve
120
and leaks through the axial ends of the developing sleeve
120
to be scattered in a main body of the image forming apparatus, thereby causing various inconveniences.
In order to prevent the developer from leaking through the sleeve ends, as disclosed in Japanese Patent Application Laid-Open No. 2-262171 (1990), magnet brushes of developer are formed at both axial ends of the developing sleeve
120
along at least a part of the peripheral surface of the developing sleeve
120
with predetermined gaps with respect to the surface of the developing sleeve
120
, so that the developer is sealed by the magnet brushes not to leak through the axial ends of the developing sleeve
120
(FIG.
12
).
Further, as an improvement, as disclosed in Japanese Patent Laid-Open No. 8-137259 (1996), there has been proposed a method in which sawteeth are provided radially of the developing sleeve to concentrate the magnetic force, thereby sealing the developer not to leak through the axial ends of the developing sleeve.
However, as is in the above-mentioned conventional developing apparatus, in a developing apparatus having a plurality of developer bearing members for high speed operation, although there is an advantage that the developing ability is enhanced, the developer may leak through the axial ends of the developing sleeves (developer bearing members) due to high speed rotations of the developer bearing members.
Further, in the developing apparatus having the plural developing sleeves, the toner scattered
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Royer William J.
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