Electrophotography – Internal machine environment – Particle or contaminant control
Reexamination Certificate
2000-06-22
2001-10-16
Pendegrass, Joan (Department: 2852)
Electrophotography
Internal machine environment
Particle or contaminant control
C399S354000
Reexamination Certificate
active
06304735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present. invention relates to an image forming apparatus such as a laser printer.
2. Description of Related Art
Laser printers and other image forming apparatuses mainly include: a photosensitive drum, a developing roller, and a transfer roller. The photosensitive drum is formed with an electrostatic latent image on its outer peripheral surface. The developing roller is disposed in confrontation with the photosensitive drum. The developing roller supplies developing agent, such as toner, to the photosensitive drum, thereby developing the electrostatic latent image into a visible image. The transfer roller is disposed also in confrontation with the photosensitive drum. The transfer roller is applied with a transfer bias voltage with a polarity opposite to that of the photosensitive drum.
Especially In non-contact type printers, a charger uniformly charges the outer peripheral surface of the photosensitive drum. A laser generating unit modulates a laser beam based on image data, and scans the laser beam across the outer peripheral surface of the photosensitive drum. As a result, a corresponding electrostatic latent image is formed on the surface of the photosensitive drum. The developing roller conveys, on its surf ace, toner that is electrically charged to the same polarity as that of the photosensitive drum. The electrostatic latent image on the photosensitive drum is developed into a visible toner image with the toner supplied from the developer roller according to a well-known reversal development process. The thus developed visible image is then transferred from the photosensitive drum onto a sheet of paper that is passing between the photosensitive drum and the transfer roller. The visible image is pulled onto the sheet of paper by an electrostatic field that is generated by the transfer blabs applied to the transfer roller. Thus, one image forming cycle is completed.
According to the above-described image forming cycle, some toner remains on the surface of the photosensitive drum after the toner image has been transferred from the photosensitive drum onto the sheet of paper. According to a well-known cleanerless method, this residual toner is collected during the next image forming cycle. Thus, in each image forming cycle, development and cleaning are performed simultaneously by the developing roller according to reversal development process.
According to this cleanerless method, there is no need to provide a blade or other type of cleaner device in the image forming apparatus. There is also no need to provide a vessel to accumulate waste toner. Accordingly, configuration of the entire image forming apparatus can be simplified and made compact. The image forming apparatus can be produced less expensively.
It is noted that when the sheet of paper passes between the photosensitive drum and the transfer roller, paper dust clings to the surface of the photosensitive drum. This paper dust will be possibly collected together with the residual toner. When the toner is reused during a later development process, the paper dust can degrade the resultant visible image. When an acid type sheet is used as the sheet of paper, the paper dust includes filler material such as talc. The filler material can cause filming and so magnify the problem of the defective visible images.
In view of the above-described problems, there has been proposed that the cleanerless-type image forming apparatus be provided with a paper-dust removing device such as a brush. The paper-dust removing device is positioned In contact with the photosensitive drum in order to remove the paper dust that clings to the photosensitive drum.
However, because the paper-dust removing device is in contact with the photosensitive drum, the residual toner also clings to the paper-dust removing device together with the paper dust. This will reduce the ability of the paper-dust removing device to remove the paper dust. The toner clinging to the paper-dust removing device can be smashed into the surface of the photosensitive drum, thereby generating filming of toner on the surface of the photosensitive drum.
SUMMARY OF THE INVENTION
A configuration is conceivable to overcome the above-described problems. In this conceivable configuration, the brush is subjected to a conductivity-enhancing processes, such as processes for dispersing conductive particles throughout the brush. The brush is applied with an electric voltage to catch only paper dust using power of the electrical field.
Paper dust normally has a negative charge. Additionally, the transfer bias potential, applied at the transfer roller, charges the sheet of paper to an electric polarity opposite to that of toner. Therefore, if positively-charging toner is used, paper dust will be strongly charged to a negative polarity at the stage between the transfer stage and the charge stage. By applying the conductivity-enhanced brush with a voltage having the same polarity as the toner, the brush will pick up only paper dust without picking up the toner much better compared to when no voltage is applied.
When a high electric voltage is applied to the conductivity-enhanced brush, however, the resistance value of the brush will decrease exponentially with respect to the applied voltage. When an excessively high voltage is applied, the brush might break down so that the resistance value suddenly lowers.
The surface potential of the photosensitive drum fluctuates, after the transfer stage, depending on the type of paper used and the ambient environment. It is difficult to adjust the voltage applied to the brush by using a fixed voltage control to control ON and OFF of a voltage of a fixed amount. Several problems occur. For example, when the surface potential of the photosensitive drum drops, for some reasons, below a certain normal value, the difference between the surface potential of the photosensitive drum and the voltage applied to the brush can become so large. In this case, electric currents may directly flow from the brush to the photosensitive body, thereby causing non-uniform charges on the photosensitive body. When this non-uniformity is too large, the non-uniformity cannot be corrected even by the charge operations by the charger. This problem is especially striking when a charge removing lamp, such as an erase lamp, is dispensed with to reduce the number of components in the entire image forming apparatus.
It is therefore an objective of the present invention to provide an improved image forming apparatus which is capable of properly removing paper dust only, without generating non-uniform charges on the photosensitive body, even when the difference between the surface potential of the photosensitive body and the voltage applied to the brush increases.
In order to attain the above and other objects, the present invention provides an image forming apparatus, comprising; an image bearing body having a surface that bears thereon a visible image, which is formed through development of an electrostatic latent image by developing agent, and that conveys the visible image to a predetermined transfer position; a transfer member, located on the transfer position, transferring the visible image from the image bearing body onto a sheet of paper: a paper dust removing member that removes paper dust clinging to the surface of the image bearing body after the visible image is transferred from the image bearing body onto the sheet of paper, the paper dust removing member including a brush member that contacts the image bearing body and that is made of fiber material whose resistance has a value preventing discharges from occurring from the brush member toward the surface of the image bearing body; and a bias voltage applying member that applies an electric bias voltage to the paper dust removing member.
The brush member may be made of fiber material which has not been subjected to a conductivity-enhancing process. The brush member may be made of fiber material whose resistance value is in a range of 10
8
to 10
10
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The bi
Fuwazaki Takeshi
Nishimura Soichiro
Brother Kogyo Kabushiki Kaisha
Oliff & Berridg,e PLC
Pendegrass Joan
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