Electrophotography – Control of electrophotography process – Control of charging
Reexamination Certificate
2000-01-04
2001-10-30
Braun, Fred L (Department: 2852)
Electrophotography
Control of electrophotography process
Control of charging
C361S235000, C399S171000
Reexamination Certificate
active
06311027
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image-forming apparatuses such as, for example, optical printers such as laser printers and LED printers, electrophotographic copying machines and facsimile machines, which form images on a copying material by using developer.
BACKGROUND OF THE INVENTION
A conventional image-forming apparatus, such as a laser printer and an electro copying machine, has a construction, for example, as shown in FIG.
29
. In this image-forming apparatus, the formation of an electrostatic latent image is carried out on a photoreceptor drum
101
by uniformly charging the surface of a photoreceptor drum
101
by a charger
102
and then partially reducing the electric potential of the surface by exposure carried out by an exposure device
103
. In this case, an aluminum element cylinder (not shown in the Figure) forming a base body of the photoreceptor drum
101
is connected to ground through the drum flange and the drum shaft; thus, it is possible to partially reduce the electric potential at the exposed portions on the photoreceptor drum
101
.
Moreover, the above-mentioned electrostatic latent image is developed by applying a developing bias to a developing device
104
so as to allow developer to adhere to the electrostatic latent image in the developing device
104
.
Normally, a scorotron charger is used as the above-mentioned charger
102
. As illustrated in the same Figure, this charger is provided with a control grid
102
b
which can control the quantity of corona ions that reaches the surface of the photo receptor drum
101
from the discharge wire
102
a.
The image-forming apparatus is further provided with a transfer device
105
, a separation device
106
, cleaning device
107
and a static eliminating lamp
108
.
In the conventional image-forming apparatus, when no electric potential is applied thereto by the charger
102
, the surface electric potential of the photoreceptor drum
101
is maintained at 0 V. For this reason, in an image-forming apparatus using a reversal developing system, during non-image-forming periods such as the initial setting time, a warming up period, a printing start time or a printing end time, if the developing device
104
or the photoreceptor drum
101
is rotated, developer tends to adhere to the photoreceptor drum
101
, thereby causing the developer to be unnecessarily consumed. In order to prevent such a problem, electric potentials are applied to both of the photoreceptor drum
101
and the developing device
104
even during the above-mentioned non-image-forming periods.
For example, Japanese Laid-Open Patent Application No. 282126/1994 (Tokukaihei 6-282126), published on Oct. 7, 1994) has proposed a construction in which, during an unstable rotation period at the time of starting the main motor, an electric potential having the same polarity as the developer is applied to an area of the photoreceptor on which the developing device acts. For example, in the apparatus shown in
FIG. 29
, a high-voltage transformer power supply
109
is connected as the power source for the control grid
102
b
. In this construction, during the non-image-forming period, the respective sections are operated in synchronized timing as shown in FIG.
30
. Here, the drum motor is a driving motor for the photoreceptor drum
101
, and the laser light emission is a releasing operation of a laser beam from the laser device installed in the exposure device
103
.
Here, in the high-voltage transformer power source
109
, at the time of a rise in voltage, an unstable area appears, which is an area in which the voltage becomes uncontrollable at the leading-edge on the low voltage side. As shown in
FIG. 31
, because of this unstable area, the surface electric potential of the photoreceptor is not allowed to rise linearly, and has a distortion including so-called rounding
111
. For this reason, during the rising process of the surface electric potential of the photoreceptor to a predetermined electric potential, the electric potential difference (fog electric potential) between the surface electric potential of the photoreceptor and the developing bias becomes excessively greater. As a result, scattering of the carrier (carrier rise) from the developing device
104
occurs, resulting in problems such as short service life of the photoreceptor in the photoreceptor drum
101
, formation of toner aggregation with scattered carrier serving as cores at the time of recycling the toner, and the subsequent degradation in copied images.
SUMMARY OF THE INVENTION
The present invention has been devised so as to solve the above-mentioned problems, and its objective is to provide an image-forming apparatus which can prevent degradation in images due to the short service life of the photoreceptor caused by toner scattering and the formation of toner aggregation with scatted carrier serving as cores at the time of recycling the toner, during non-image-forming periods such as the initial setting time, a warming up period, a printing start time or a printing end time.
In order to achieve the above-mentioned objective, the image-forming apparatus of the present invention is provided with: a rotatable photoreceptor; a charging device for charging the surface of the photoreceptor to a predetermined electric potential by means of corona discharging, the charging device being provided with a control electrode for controlling the quantity of corona ions that are allowed to reach the photoreceptor from a discharging electrode; a latent image forming device for forming an electrostatic latent image on the photoreceptor that has been charged by the charging device by means of light irradiation; a developing device for developing the electrostatic latent image by using a developer; and a control voltage supply device for supplying a control voltage to the control electrode and for switching the control voltage to a plurality of stages from a low-voltage side to a high-voltage side until the surface electric potential of the photoreceptor has risen to a predetermined electric potential.
With the above-mentioned arrangement, the rotating photoreceptor is charged to a predetermined electric potential by the charging device, an electrostatic latent image is formed on the surface of the photoreceptor by the latent image forming device, and this electrostatic latent image is developed by the developing device.
When the photoreceptor is charged to the predetermined electric potential by the charging device, the control voltage, supplied from the control voltage supply device to the control electrode of the charging device, is switched to a plurality of stages from the low-voltage side to the high-voltage side until the surface electric potential of the photoreceptor has risen to the predetermined electric potential.
Thus, it is possible to prevent the generation of the unstable portion of the electric potential at the time of a rise of the surface electric potential of the photoreceptor, and consequently to allow the surface electric potential of the photoreceptor to rise linearly to the predetermined electric potential. As a result, it is possible to prevent degradation in the photoreceptor due to scattering of carrier, degradation in the image quality due to aggregation of toner with scattering carrier serving cores at the time of recycling toner, and adhesion of reversely charged toner to the photoreceptor and an increase of the consumption of toner; consequently, it becomes possible to obtain image having stable image quality.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 4335420 (1982-06-01), Mitsuo et al.
patent: 4638397 (1987-01-01), Foley
patent: 4811045 (1989-03-01), Matsushita et al.
patent: 4868907 (1989-09-01), Folkins
patent: 5173734 (1992-12-01), Shimizu et al.
patent: 5181070 (1993-01-01), Masuda
patent: 5581221 (1996-12-01), Kawai et al.
patent: 5659839 (1997-08-01), Mizude et al.
Fujita Syouichi
Nakamura Masatsugu
Naoi Hiroo
Saiko Hideji
Sakita Hirofumi
Braun Fred L
Sharp Kabushiki Kaisha
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