Electrophotography – Control of electrophotography process
Reexamination Certificate
2003-02-21
2004-02-24
Ngo, Hoang (Department: 2852)
Electrophotography
Control of electrophotography process
C399S071000, C399S101000, C399S003000
Reexamination Certificate
active
06697581
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, image forming apparatuses utilizing the electrophotographic system (the electrostatic transfer system), such as copying machines and printers, are 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 obtain a toner image as a permanent image on the recording sheet. Here, it is necessary to remove the toner which has not been transferred to the recording sheet by means of a cleaning device in the image forming apparatus. Apart from this ordinary image formation, a so-called process control is also performed, in which reference marks are formed on the image bearing member, the intermediate transfer member, and the final transfer member, and in which registration control and toner image density control are effected on the basis of the positions, density, etc. of the reference marks (patches). Here, in the process control, the reference marks (patches) are not usually transferred to the recording sheet, so that the marks have to be removed by the cleaning device in the image forming apparatus.
Regarding the cleaning inside the image forming apparatus, the following techniques have been proposed. JP 2001-75448 A discloses a technique in which the residual toner on the intermediate transfer member and the final transfer member is collected on the final transfer member, and collectively removed by a cleaning device which is in contact with the final transfer member. Further, there might be a technique according to which the final transfer member is spaced apart from the intermediate transfer member during the process control so that the reference marks may not adhere to the final transfer member.
However, in many cases, the final transfer member is arranged at an end portion inside the image forming apparatus, and the construction in which there is further provided a cleaning device, which is in contact with the final transfer member, is likely to lead to an increase in the size of the image forming apparatus. Further, when the final transfer member is constructed so as to allow contact and separation to and from the intermediate transfer member, the apparatus is rather complicated, resulting in an increase in cost.
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 which is compact and inexpensive, and which allows cleaning of the final transfer member.
Thus, according to an aspect of the present invention, an image forming apparatus includes: an image bearing member; an image forming unit that forms a toner image on the surface of the image bearing member; an intermediate transfer device which is 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 that controls the potential gradient between the image bearing member, the intermediate transfer member, the final transfer member, and the cleaning member, in which the control unit forms in an image formation mode a potential gradient for image formation which causes reverse-polarity toner on the final transfer member to adhere to the cleaning member by way of the intermediate transfer member.
Here, the image forming units include a charging unit that uniformly charges the surface of the image bearing member, a latent image forming unit (exposure unit) that forms an electrostatic latent image corresponding to the output image on the surface of the image bearing member, and a developing unit that selectively imparts toner to the electrostatic latent image formed on the surface of the image bearing member. A variation of the charging unit is a contact type charging unit which is in contact with the image bearing member and is adapted to uniformly charge the surface thereof. In this case, the control unit is capable of controlling the potential gradient not only between the image bearing member, the intermediate transfer member, the final transfer member, and the cleaning member, but also between them and the contact type charging unit.
By thus constructing the image forming apparatus, the reverse-polarity toner on the final transfer member adheres to the cleaning member by way of the intermediate transfer member in the image formation mode, so that, firstly, there is no need to provide the final transfer member with a cleaning device. That is, it is possible to construct the image forming apparatus such that the cleaning member does not come into contact with (or is held in a non-contact state with respect to) the final transfer member. Secondly, there is no need to frequently perform the cleaning mode operation. The image forming potential gradient is a potential gradient which allows the toner image as the output image on the image bearing member to be transferred to the recording sheet transported between the intermediate transfer member and the final transfer member by way of the intermediate transfer member.
According to another aspect of the present invention, the image forming apparatus includes a detecting unit that detects the density of the toner image on the intermediate transfer member, in which the control unit forms in a process control mode a potential gradient for process control which causes the toner image as a detection image on the image bearing member to adhere to the cleaning member by way of the intermediate transfer member (without adhering to the final transfer member). In this case, the process control mode performs registration control and toner image density control.
By thus constructing the image forming apparatus, it is possible to prevent the toner image as the detection image from adhering to the final transfer member, without providing a retracting mechanism for making the final transfer member abut against and space apart from the intermediate transfer member. As a result, no problem is involved even if the final transfer member is constantly held in contact with the intermediate transfer member (constantly held in contact therewith also in the process control mode, the image formation mode, and the cleaning mode except when the image forming unit is replaced).
Here, the difference in potential between the final transfer member and the intermediate transfer member which is in contact with the final transfer member when forming the potential gradient for the process control may range from 0 to 1500 [V]. When this difference in potential is ensured, there is little variation in the surface potential of the intermediate transfer member, and it is possible to detect the density of the toner image on the intermediate transfer member in a stable manner.
Further, comparison of the potential gradient for image formation and the potential gradient for process control shows that the potential relationship (potential gradient) between the intermediate transfer member and the final transfer member is reversed between the potential gradient for image formation and the potential gradient for process control. Further, the potential relationship (potential gradient) between the intermediate transfer member and the cleaning member is reversed between the potential gradient for image formation and the potential gradient for process control.
Further, the control unit effects transition of the state of the image forming apparatus from the process control mode to the image formation mode. More specifically, the control unit effects transition of the state of the image forming apparatus from the process control mode directly t
Ohtani Hideyuki
Suganuma Toshihiro
Fuji 'Xerox Co., Ltd.
Ngo Hoang
Oliff & Berridg,e PLC
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