Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2000-05-02
2001-06-05
Lee, Susan S. Y. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S101000, C399S313000, C399S314000
Reexamination Certificate
active
06243544
ABSTRACT:
BACKGROUND OF THE INVENTION
There are several methods for a transfer device used in an electrophotographic image forming apparatus. A widely known example among these methods is a transfer roller method using a conductive elastic member.
According to the transfer roller method, a transfer roller is disposed and rotated in press contact with a photosensitive member. A transfer bias of opposite polarity to that of toner on the photosensitive member is applied to the transfer roller to electrostatically attract the toner on a transfer medium.
As a method of controlling the transfer bias voltage applied to the transfer roller, Japanese Patent Laid-Open No. 4-335383 discloses a method of detecting the toner amount on a photosensitive member before transfer, and controlling the transfer bias in accordance with the detected toner amount such that if the toner amount is large, the transfer bias is decreased, and if the toner amount is small, the toner bias is increased.
However, this method does not detect the transfer efficiency during actual operation, and thus uses a table representing the relationship between the toner amount and the transfer bias that is prepared in advance by tests. Therefore, an optimal transfer bias cannot always be selected owing to environmental variations, changes in the resistance and thickness of the transfer medium in addition to the difference between the transfer roller used as a transfer means and the photosensitive drum. The method cannot satisfactorily prevent a transfer error and the like.
Japanese Patent Laid-Open No. 10-31375 discloses the following method. A toner image is transferred to a region at the end of a transfer roller where a transfer medium does not pass, and the density is detected and fed back to an image formation process control means to optimize image formation. Further, the reverse transfer bias is applied to the toner image adhering to the end of the transfer roller to reattach the toner image on a photosensitive drum, thereby cleaning the transfer roller.
However, the method disclosed in this reference suffers the following problems.
(1) Detecting toner adhering to the transfer roller is suitable for sensing variations in toner adhesion amount in developing operation under fixed transfer bias conditions. However, the toner adhesion amount after transfer is unknown, so the transfer efficiency cannot be detected.
Hence, an optimal transfer bias to be applied to the transfer roller cannot be obtained.
(2) The surface material (or the physical characteristics of the surface) is different between the image region and non-image region of the transfer roller. Optimal transfer bias conditions change depending on the surface material and surface characteristics. Thus, an optimal transfer bias actually necessary in the image region cannot be obtained.
When the transfer roller is used, the roller itself becomes dirty after repetitive printing operations. To solve this, a bias (cleaning bias) of opposite polarity to that of the transfer roller applied to the transfer roller in transferring an image to a transfer medium must be applied to the transfer roller when no printing is done, so as to reattach the toner on the photosensitive member. However, since the surface material of the transfer roller changes depending on the region, as described above, no optimal cleaning bias in the image region can be obtained.
As described above, it is difficult for the conventional methods to attain optimal transfer conditions for transferring a toner image from a photosensitive member to a transfer roller or transfer belt.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for forming an image that can attain optimal transfer conditions in transferring a toner image from a photosensitive member to a transfer means, regardless of the characteristics of the transfer means, environmental variations, and life variations.
According to the present invention, there is provided an apparatus for forming an image, comprising a developing unit for forming a visible image on a photosensitive member with a developer mix, transfer means for transferring the visible image to a transfer medium, a developer mix adhesion amount sensor which faces the photosensitive member and detects an adhesion amount of developer mix adhered on the photosensitive member, transfer bias application means for applying, to the transfer means, a first transfer bias for transferring the visible image on the photosensitive member to the transfer means, and a second transfer bias for reversely transferring the visible image on the transfer means to the photosensitive member, and transfer bias change means for, when the visible image is transferred to the transfer means by the first transfer bias and an adhesion amount of residual transfer developer mix which is not transferred and is left on the photosensitive member is detected by the developer mix adhesion amount sensor, changing the first transfer bias using the detected adhesion amount of residual transfer developer mix, and when an adhesion amount of reverse transfer developer mix upon reversely transferring the visible image on the transfer means to the photosensitive member by the second transfer bias is detected by the developer mix adhesion amount sensor, changing the second transfer bias using the detected adhesion amount of reverse transfer developer mix.
The transfer bias change means can change the first transfer bias on the basis of a deviation between the adhesion amount of residual transfer developer mix detected by the developer mix adhesion amount sensor and a predetermined transfer reference value, and can change the second transfer bias on the basis of a deviation between the adhesion amount of reverse transfer developer mix detected by the developer mix adhesion amount sensor and a predetermined reverse transfer reference value.
The transfer bias change means can be given in advance a count for correcting the first transfer bias until a deviation between the adhesion amount of residual transfer developer mix detected by the developer mix adhesion amount sensor and a predetermined transfer reference value falls within a first allowable value range, and when the deviation does not fall within the first allowable value range even after the first transfer bias is corrected by the count, can change the first transfer bias to a final correction value, and the transfer bias change means can be given in advance a count for correcting the second transfer bias until a deviation between the adhesion amount of reverse transfer developer mix detected by the developer mix adhesion amount sensor and a predetermined reverse transfer reference value falls within a second allowable value range, and when the deviation does not fall within the second allowable value range even after the second transfer bias is corrected by the count, can change the second transfer bias to a final correction value.
Before the transfer bias change means changes the transfer bias, an adhesion amount of developer mix of the visible image formed on the photosensitive member may be detected by the developer mix adhesion amount sensor, and at least one of a charging voltage for charging the photosensitive member and a developing bias for developing the image on the photosensitive member with the developer mix may be set on the basis of a deviation between the detected value and a predetermined developing reference value.
The transfer means may include a transfer roller, and the developer mix adhesion amount sensor may include an optical sensor.
REFERENCES:
patent: 6049681 (2000-04-01), Shiozawa et al.
patent: 8-190286 (1996-07-01), None
patent: 10-186877 (1998-07-01), None
Foley & Lardner
Lee Susan S. Y.
Toshiba Tec Kabushiki Kaisha
LandOfFree
Method and apparatus for forming image does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for forming image, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for forming image will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2510738