Electrophotography – Diagnostics – Document handling
Reexamination Certificate
2000-03-17
2001-04-03
Pendegrass, Joan (Department: 2852)
Electrophotography
Diagnostics
Document handling
C399S128000
Reexamination Certificate
active
06212339
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image forming apparatus adopting a photoelectronic technique for forming images, characters, etc. on a transfer material, and particularly relates to an image forming apparatus capable of obviating damage to a photosensitive body upon occurrence of a trouble.
BACKGROUND OF THE INVENTION
An image forming apparatus adopting a conventional photoelectronic technique is designed so that, as shown in
FIG. 14
, a charger
102
, an exposing device
103
, a developing device
104
, a transfer charger
105
, a cleaning device
106
, and a discharger lamp
107
are provided around a photosensitive drum
101
disposed at center.
In such an image forming apparatus, the photosensitive drum
101
is first charged to a predetermined potential and a predetermined polarity by the charger
102
(charging step), then a surface of the photosensitive drum
101
is exposed by a laser light or the like projected thereto by the exposing device
103
. Here, the surface of the photosensitive drum
101
comes to have areas which are exposed thereby undergoing lowering of potentials, and areas which are not exposed thereby not undergoing lowering of potentials. With such potential differences in areas, an electrostatic latent image is formed on the surface of the photosensitive drum
101
(exposing step).
The electrostatic latent image, developed by the developing device
104
, becomes a toner image (developing step). The toner image is transferred by the transfer charger
105
onto a transfer material (paper)
110
supplied from a paper feed section, not shown (transferring step).
Thereafter, the transfer material
110
on which the toner image has been transferred is subjected to a fixing step conducted by a fixing section, now shown, and discharged to outside the apparatus.
On the other hand, toner remaining on a surface of the photosensitive drum
101
after the transferring step is removed from the surface of the photosensitive drum
101
by the cleaning device
106
(cleaning step). Further, remaining charges on the surface of the photosensitive drum
101
are removed by the discharger lamp
107
(discharging step), and the operation immediately shifts to the next image forming step.
The removal of remaining charges in the photosensitive drum
101
by the discharger lamp
107
, conducted after completion of the transferring step, is an indispensable step. Without this discharging step, uniformness of a charged state is degraded, and this causes exposure memory, or a phenomenon of lowering of surface potentials at only specific portions.
Particularly, in the case where a charger of a contact type is used as the charger
102
, a discharging step is not conducted while recharging by the charger
102
is repeatedly carried out, thereby causing the potential of the photosensitive drum
101
to rise. In some cases, this may cause insulation breakdown of the photosensitive drum
101
. In the case where a charger of a non-contact type such as scorotron is used as the charger
102
, it much less likely causes insulation breakdown of the photosensitive drum
101
, but the surface potential of the photosensitive drum
101
gradually rises as the recharging is repeatedly carried out, and this is not desirable for the photosensitive drum
101
.
Provision of discharging means to be used exclusively for discharge, such as the discharging lamp
107
, however, hinders efforts for further reduction of the size and costs of the image forming apparatus. Therefore, techniques for discharge without discharging means used exclusively for discharging has conventionally been developed.
The Japanese Publication for Laid-Open Patent Application No. 3883/1994 (Tokukaihei 6-3883 [Publication Date: Jan. 14, 1994]) discloses a technique (technique {circle around (1)} in which after a part of a photosensitive drum is discharged by a laser light emitted from an exposing device, a laser light with a normal image forming exposure power is further projected thereon so that a potential on the photosensitive drum is lowered.
In this technique, after a normal image forming step, a voltage is once applied to a main charger to raise the surface potential of the photosensitive drum, then, the surface of the photosensitive drum is reversely charged by a transfer charger so that the surface potential becomes low, and thereafter, a development bias voltage is turned off. After this turning-off of the development bias voltage, a laser light is projected from an exposing device while its power is controlled, and a laser light with a normal image forming exposure power for image exposure is projected thereon so that the surface potential of the photosensitive drum is lowered to such a potential that no fog occurs (about 100V to 300V as a potential difference between the potential of the photosensitive drum and the development bias voltage). Thus the photosensitive drum surface is electrically cleaned.
Furthermore, the Japanese Publication for Laid-Open Patent Application No. 80870/1997 (Tokukaihei 9-80870 [Issue Date: Mar. 28, 1997]) discloses a technique (technique {circle around (2)}) in which a discharging operation is started in response to a detection signal of detecting means.
In this technique, in an image forming apparatus using a contact-type charger, after an AC voltage applied to a charging member is turned off upon completion of the image forming operation, a transfer material discharge sensor as detecting means detects a front edge or a rear edge of a transfer material and outputs a detection signal for discharge of the photosensitive drum before power-off of the apparatus. Based on the detection signal, an AC voltage is applied to the charging member again, and memory of the photosensitive drum is removed.
In this technique, particularly, it is implied that lamp-use exposing means for uniformly exposing the photosensitive drum can be used in the place of the charging means.
The foregoing techniques {circle around (1)} and {circle around (2)} provide only schemes applicable during normal operations, and do not provide measures to cope with irregular events. For example, in the case where a trouble during an image forming operation interrupts the image forming process before the discharge of the photosensitive drum is completed, the photosensitive drum is consequently left having a high surface potential. Therefore, this causes the following problem to arise: during an attempt to correct the trouble until finally the next image forming operation starts, the apparatus is left in a state in which toner adhesion or carrier adhesion tends to occur.
Furthermore, in the discharging step, irrespective of cases, the case where the discharge lamp
107
is used, or the case where light used for writing such as laser emitted by the exposing device
103
is used without provision of the discharge lamp
107
, the surface potential of the photosensitive drum
101
is made to sharply drop either by keeping the discharge lamp
107
turned on always or by projecting light always. Therefore, a problem arises in that the photosensitive drum
101
is excessively exposed, thereby causing the operational efficiency of the apparatus to lower.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an image forming apparatus superior in the operational efficiency, by arranging the same so that toner adhesion or carrier adhesion to a photosensitive drum, which tends to be caused upon occurrence of a trouble except an operational trouble of an exposure-use light source or upon restarting after such a trouble is corrected, is avoided for preventing damage to the photosensitive drum and ensuring safety of the photosensitive drum.
To achieve the foregoing object, the image forming apparatus of the present invention is characterized by comprising (i) a photosensitive drum for holding an electrostatic latent image on its surface, the photosensitive drum being driven to rotate by a motor, (ii) charging means for charging the surface of the photosensitive drum so that t
Hasegawa Mitsuhiro
Inoue Katsushi
Kitamura Keizo
Mamemoto Tomoko
Pendegrass Joan
Sharp Kabushiki Kaisha
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