Patent Application
20090016751
1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus able to clean surface attachments on a transfer roller and a method thereof.
2. Description of the Prior Art
The image forming process of an electrophotographic image forming device includes charging, exposing, developing, transferring, fusing, cleaning and erasing. During the developing, toner is attached on a photoconductor to form a toner image, and then in the transferring step, the toner image developed on the photoconductor is transferred onto paper. In the transferring step, the paper is delivered by utilizing a transfer roller. Because the paper will contact with the transfer roller during transferring, fibers and impurities on the paper will adhere to the surface of the transfer roller. Moreover, when an abnormal printing situation occurs such as a paper jam occurs, the surface of the transfer roller will be dirtied by toner. These situations all result in an increase of surface impedance of the transfer roller, which decreases the transferring efficiency and causes problems such as pollutions on a backside of the paper. Therefore, the transfer roller must be cleaned to maintain the printing quality of the printing device.
A conventional method of cleaning the transfer roller is to add an extra brush by the side of the transfer roller, and utilize the brush to clean the surface attachments on the transfer roller. Since the toner on the transfer roller is usually charged, the brush is provided with a voltage in some embodiments to enhance the cleaning effect. Hence, the present invention provides a method different from the conventional method for cleaning the transfer roller, and provides an image forming apparatus applying the new method.
One objective of the present invention is to provide a method of transferring surface attachments on a transfer roller of an image forming apparatus and an image forming apparatus applying the method.
According to an embodiment of the present invention, a method of transferring surface attachments on a transfer roller of an image forming apparatus is disclosed. The method comprises making the transfer roller contact with a photoconductor, and providing a voltage signal on the transfer roller to transfer the surface attachments on the transfer roller to the photoconductor.
According to another embodiment of the present invention, a method of transferring surface attachments on a transfer roller of an image forming apparatus is disclosed. The method comprises providing a voltage signal switching between a negative voltage level and a positive voltage level, and providing the voltage signal on the transfer roller to transfer the surface attachments on the transfer roller to a photoconductor.
According to another embodiment of the present invention, an image forming apparatus is disclosed. The image forming apparatus comprises a photoconductor, a transfer roller, and a power supply connected to the transfer roller, for providing a voltage signal on the transfer roller to transfer the surface attachments on the transfer roller to the photoconductor.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.
In one embodiment, the current polarity of the power supply switches between positive and negative in order to cause the voltage signal to switch between a negative voltage level and a positive voltage level, as shown in
Please refer to
In the above embodiment, when the transfer roller 110 is in contact with the photoconductor 130, the voltage/current provided on the transfer roller 110 will induce an influence on the surface voltage level of the photoconductor 130, causing damages to the photoconductor 130, and shortening usage life and changing physical properties of the photoconductor 130. This is because the photoconductor 130 has a safe charging range usually being 0˜−1000V but depending on the thickness of transport layer in dielectric layer of the photoconductor 130. When a voltage higher than 0V or lower than −1000V is applied on the surface of the photoconductor 130, the voltage will result in a dielectric breakdown through pin-holes on the surface of the photoconductor 130. This will damage the photoconductor 130 or influence the physical properties (e.g. photo sensitization and charging characteristic) of the photoconductor 130. Note that the surface voltage level variation of the photoconductor 130 caused by the voltage signal provided on the transfer roller 110 may be up to about ±400V. Therefore, if the surface voltage level of the photoconductor 130 is 0V (the photoconductor 130 is not charged in advance) or is charged to a working voltage level (such as −800V), the surface voltage level will exceed the safe charging range during the transfer process (note that the working voltage level means a desired voltage level of the photoconductor when developing an image). In order to protect the photoconductor 130, the surface voltage level of the photoconductor 130 can be adjusted according to the voltage signal before the voltage signal is applied. The adjustment is to make the surface voltage level fall in a specific (definable) voltage range, wherein the specific voltage range is determined based on a condition that the surface voltage level of the photoconductor 130 will not go beyond the safe charging range even if it is influenced by the voltage signal. The usage life of the photoconductor 130 is therefore under protection and extended.
In one embodiment, the center of the specific voltage range is a half of the working voltage (−800V) of the photoconductor 130. For example, the specific voltage range is −400±200V. When adjusting the surface voltage level of the photoconductor 130, a charger 160 in the image forming apparatus 100 can be utilized to control the surface voltage level of the photoconductor 130 within the specific voltage range. For example, adjusting the working voltage of the charger 160 to −400V, and then charging the surface of the photoconductor 130 by the charger 160. In another embodiment, the surface voltage level of the photoconductor 130 can first be charged to a specific voltage level (such as the working voltage level) by the charger 160, and then be adjusted to be within the specific voltage range by a light-emitting element 170 (i.e. an LED) or an eraser 180 in the printing device 100. Since the charger 160, the light-emitting element 170, and the eraser 180 are available elements for changing the surface voltage level of the photoconductor 130 in a common image forming apparatus, a person skilled in the art shall easily appreciate the operations and design of those elements after reading the above disclosure. Detailed description is therefore omitted for brevity.
Please note that, in the above embodiments, the transferring process on the surface attachments of the transfer roller can achieve the goal of cleaning the transfer roller. However, the present invention is not limited to only being utilized to clean the transfer roller. That is, the transferring process disclosed above can be implemented in other purposes. Printing devices applying the above transferring process should all fall within the scope of the present invention.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.
