Developing device with timing control

Details Developing device with timing control Developing device with timing control

1998-02-26

2001-05-22

Grainger, Quana M. (Department: 2852)

Electrophotography

Control of electrophotography process

Control of developing

C399S285000

Reexamination Certificate

active

06236818

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a developing device for use in an image forming apparatus such as a laser printer for performing an image formation by supplying toner to an electrostatic latent image formed on a circumferential surface of a photosensitive drum, developing the image, and transferring the developed image onto a paper sheet. In particular, the present invention relates to a developing device capable of applying bias voltage to a supply roller for supplying toner onto a developing roller, whereby charged toner is transferred to the developing roller.
The present invention also relates to a developing device for an image forming apparatus capable of easily controlling a direct-current (DC) power device for a constant-current, the DC power device being connected to a toner supply roller, regardless of variation of a resistance value between a developing roller and the supply roller, to prevent breakage of the DC power device even when it stops, thereby to form a visual image with a good image quality.
Furthermore, the present invention relates to a developing device for an image forming apparatus capable of effectively preventing poorly charged toner which is produced in a toner storing unit after toner supply from adhering to the developing roller even when a surface deterioration of the developing roller caused due to aging and an increase of deteriorated toner remaining in a developing chamber, thereby to form a visual image with a good image quality.
2. Description of Related Art
Heretofore, there have been proposed various types of developing device for an image forming apparatus, e.g., a laser printer and the like. The developing device is generally constituted of a toner storing unit including a toner cartridge, an auger member for dispersing the toner supplied from the toner storing unit into a developing chamber, a toner supply roller for supplying the dispersed toner, a developing roller for performing toner development by providing the toner supplied by the toner supply roller onto an electrostatic latent image formed on a circumferential surface of a photosensitive drum. One example of a toner supply device as the developing device is shown in FIG.
11
.
FIG. 11
is an explanatory view showing a schematic sectional view of a main part of the developing device for an image forming apparatus in the prior art.
In
FIG. 11
, the toner supply device has a toner cartridge
100
which accommodates therein toner. The toner cartridge
100
is provided with a toner exhaust port at an axial center portion of the cartridge
100
. In the toner cartridge
100
, disposed is an agitator
103
for agitating toner to supply it through the toner exhaust port to a developing chamber
102
side. In a frame F, a toner introduction port is formed corresponding to the toner exhaust port of the toner cartridge
100
, both ports constituting a toner supply port
101
. The frame F includes an upper frame F
1
and a lower frame F
2
which form a closed developing chamber
102
. In this developing chamber
102
, two auger members
109
and
110
are rotatably disposed near the toner supply port
101
(at a right side in FIG.
5
), to uniformly spread the toner supplied through the toner supply port
101
in the developing chamber
102
.
At a lower side in the developing chamber
102
, a toner supply roller
104
is rotatably disposed and a developing roller
105
is rotatably arranged facing the supply roller
104
. This toner supply roller
104
serves to supply the toner transported through the toner supply port
101
to the developing roller
105
. Here, the toner supply roller
104
comprises a roller shaft
104
A made of metal (steel materials of various kinds) and a conductive sponge member
104
B for surrounding a periphery of the roller shaft
104
A. The developing roller
105
comprises a roller shaft
105
A made of metal (steel materials of various kinds) and a conductive rubber member
105
B which is generally harder than the conductive rubber member
104
B and is provided surrounding the roller shaft
105
A. At the time of toner supply from the toner supply roller
104
to the developing roller
105
, the toner supply roller
104
is in contact with the developing roller
105
such that the conductive sponge member
104
B is somewhat compressed to the conductive rubber member
105
B.
To the roller shaft
105
A of the developing roller
105
, a constant bias voltage is applied from a constant voltage DC power device
112
. To the roller shaft
104
A of the toner supply roller
104
, similarly, a constant bias voltage is applied from a constant voltage DC power device
111
so that the charged toner in the toner cartridge
100
is made to move from the toner supply roller
104
to the developing roller
105
.
Such the application of bias voltage to the supply roller
104
can cause active transfer of the toner having a good electrification property onto the developing roller
105
. Even when a larger amount of fresh toner which is not charged satisfactorily is supplied to the developing chamber
102
. Accordingly, it is possible to prevent selective collection and supply of only the insufficiently charged toner with respect to the developing roller
105
, and the occurrence of fogging which may be caused by the toner supply of a large amount of the insufficiently charged toner to the developing roller
105
.
A blade
107
is secured on an inner wall of the upper frame F
1
, above the developing roller
105
, by a fixing member
106
. This blade
107
serves to regulate the thickness of a toner layer formed on a circumferential outer surface of the developing roller
105
. The developing roller
105
is disposed so as to be in contact with a photosensitive drum
108
. An electrostatic latent image can be formed on a circumferential outer surface of the photosensitive drum
108
by a light exposure unit (not shown) which scans the surface of the drum
108
with laser light in accordance with image data. The developing roller
105
then performs toner development by supplying toner on the electrostatic latent image formed on the surface of the photosensitive drum
108
. The developed image is transferred onto a paper sheet fed from a paper supply unit (not shown) to print an image thereon.
However, in the conventional developing device for an image forming apparatus, as an operation time thereof becomes longer, insulating materials, e.g., silica, etc. covering toner particles tend to adhere to respective surfaces of the conductive sponge member
104
B of the toner supply roller
104
and the conductive rubber member
105
of the developing roller
105
, thus forming an insulating film on the surfaces of the members
104
and
105
. The bias voltage are to be applied from the constant voltage DC power device
111
and
112
to the toner supply roller
104
and the developing roller
105
respectively, so that a difference between those bias voltages is constant. The insulating film causes the current passing between the toner supply roller
104
and the developing roller
105
to become minute (for instance, 0.1 &mgr;A or less) or zero, thus resulting in a problem of preventing the transfer of the toner positively charged by an electrical field from the supply roller
104
to the developing roller
105
.
If a sufficient amount of toner is not carried on the conductive sponge member
104
B, the resistance between the supply roller
104
and the developing roller
105
decreases (for instance, 2 M&OHgr; or less), allowing an overcurrent (e.g., 50 &mgr;A or more) to flow therebetween. This can result in overcharging of toner carried on the sponge member
104
B or local accumulation of toner negatively charged.
Even when the constant voltage DC power device
111
for applying bias voltage to the toner supply roller
104
is exchanged to a DC power device for a constant-current control, there is a problem that the output voltage becomes less than the voltage that the DC device can control if the resistance (for instance, 2 M&

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