Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2003-02-21
2004-10-19
Chen, Sophia S. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S071000, C399S101000, C399S302000
Reexamination Certificate
active
06807385
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an electrophotographic image forming apparatus, such as a copying machine, a printer, a facsimile, or a multifunction apparatus formed by combining them, and in particular, to an improvement in a cleaning technique for an image forming apparatus.
Up to now, electrophotographic (electrostatic transfer type) image forming apparatuses, such as copying machines and printers, have been widely known. In such image forming apparatuses, a toner image is transferred to a recording sheet by a final transfer member, and then the toner image is fixed to thereby realize on the recording sheet the toner image as a permanent image. The portion of the toner remaining on the transfer member without being transferred to the recording sheet has to be removed by a cleaning device in the image forming apparatus. As a method for removing such residual toner, there has been proposed a technique according to which a metal cleaning roll is caused to abut the transfer member, thereby making the residual toner to adhere to the cleaning roll by electrostatic force (See, for example, JP 6-59586 A and JP 6-35340 A). Further, there has also been proposed a technique according to which a metal cleaning blade is caused to abut against a metal cleaning roll to prevent the cleaning blade from being turned up (See, for example, JP 2000-142310).
However, these conventional techniques have the following problem.
The metal cleaning roll exhibits a relatively low electrical resistance value, so that the surface potential thereof is quickly changed in response to a variation in the bias to be applied thereto. Whereas, an intermediate transfer member which is in contact with the cleaning roll exhibits a relatively high electrical resistance value, so that even if the bias to be applied varies, the surface potential thereof is only changed transitionally. Thus, an excessive difference in potential can be instantaneously generated between the cleaning roll and the intermediate transfer member. As a result, a discharge stress is imparted to the intermediate transfer member, thereby deteriorating or damaging the surface of the intermediate transfer member.
OBJECT AND SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned technical problem, and provides an image forming apparatus capable of preventing generation of an excessive difference in potential between a cleaning member and an intermediate transfer member, thereby making it possible to elongate the service life of the intermediate transfer member.
According to an aspect of the present invention, an image forming apparatus includes: an image bearing member; an image forming unit which forms a toner image on the surface of the image bearing member; an intermediate transfer device formed by at least one intermediate transfer member, and which is in contact with the image bearing member; a final transfer member which is in contact with the intermediate transfer member; a cleaning member which is in contact with the intermediate transfer member; and a control unit which applies an intermediate-transfer-member-bias to the intermediate transfer member and applies a cleaning-member-bias to the cleaning member which is in contact with the intermediate transfer member to thereby control a potential gradient between the cleaning member and the intermediate transfer member, in which when switching the intermediate-transfer-member-bias to be applied to the intermediate transfer member from a first intermediate-transfer-member-bias to a second intermediate-transfer-member-bias and switching the cleaning-member-bias to be applied to the cleaning member from a first cleaning-member-bias to a second cleaning-member-bias, respectively (substantially at the same time), the control unit makes the switching start timing for the intermediate-transfer-member-bias earlier than the switching start timing for the cleaning-member-bias.
More specifically, the control unit can be constructed such that during the transition of the intermediate-transfer-member-bias from the first intermediate-transfer-member-bias to the second intermediate-transfer-member-bias, the switching of the cleaning-member-bias is started. Further, the control unit can also be constructed such that after the transition of the intermediate-transfer-member-bias to the second intermediate-transfer-member-bias, the switching of the cleaning-member-bias is started.
According to another aspect of the present invention, the image forming apparatus includes: an image bearing member; an image forming unit which forms a toner image on the surface of the image bearing member; an intermediate transfer device formed by at least one intermediate transfer member, and which is in contact with the image bearing member; a final transfer member which is in contact with the intermediate transfer member; a cleaning member which is in contact with the intermediate transfer member; and a control unit which applies an intermediate-transfer-member-bias to the intermediate transfer member and applies a cleaning-member-bias to the cleaning member which is in contact with the intermediate transfer member to thereby control the potential gradient between the cleaning member and the intermediate transfer member, in which when switching the intermediate-transfer-member-bias to be applied to the intermediate transfer member from a first intermediate-transfer-member-bias to a second intermediate-transfer-member-bias and switching the cleaning-member-bias to be applied to the cleaning member from a first cleaning-member-bias to a second cleaning-member-bias, respectively (substantially at the same time), the control unit effects the switching of the cleaning-member-bias stepwise.
More specifically, the stepwise switching of the cleaning-member-bias may be effected in two stages; it is possible to effect switching from a first cleaning-member-bias to a transition cleaning-member-bias and then effect switching from an intermediate cleaning-member-bias to a second cleaning-member-bias. The stepwise switching of the cleaning-member-bias may be effected in three stages; it is possible to effect switching from a first cleaning-member-bias to a first transition cleaning-member-bias and then effect switching from the first transition cleaning-member-bias to a second transition cleaning-member-bias and then effect switching from the second transition cleaning-member-bias to a second cleaning-member-bias.
Further, it is possible to set the transition cleaning-member-biases (the first transition cleaning-member-bias and the second transition cleaning-member-bias) to be smaller than the second intermediate-transfer-member-bias.
Further, the stepwise switching of the cleaning-member-bias is effected such that the variation in the cleaning-member-bias increases gradually. For example, it is possible to effect setting such that the following inequality holds good: |(transition cleaning-member-bias)−(first cleaning-member-bias)|<|(second cleaning-member-bias)−(transition cleaning-member-bias)|, and that the following inequality holds good: |(first transition cleaning-member-bias)−(first cleaning-member-bias)|<|(second transition cleaning-member-bias)−(first transition cleaning-member-bias)|<|(second cleaning-member-bias)−(second transition cleaning-member-bias)|.
Further, it is also possible to combine the first and second aspects of the invention. That is, according to another aspect of the present invention, the image forming apparatus includes: an image bearing member; an image forming unit which forms a toner image on the surface of the image bearing member; an intermediate transfer device formed by at least one intermediate transfer member, and which is in contact with the image bearing member; a final transfer member which is in contact with the intermediate transfer member; a cleaning member which is in contact with the intermediate transf
Mitsu Hiroyuki
Miyake Koji
Suto Masaki
Chen Sophia S.
Fuji 'Xerox Co., Ltd.
Oliff & Berridg,e PLC
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