This application claims the benefit of Korean Application No. 2005-26505, filed on Mar. 30, 2005, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
Aspects of the present invention relate to a method of and an apparatus for controlling a transfer voltage in an image forming apparatus, and more particularly, to a method of and an apparatus for controlling a transfer voltage in an electrophotographic image forming apparatus in which a type of paper is determined using a transfer roller resistance and a paper resistance, and a proper transfer voltage is applied according to a transfer table for the determined type of paper.
2. Description of the Related Art
In general, an image forming apparatus forms an image by charging a surface of a photosensitive medium using a charging device, and radiating light onto the photosensitive medium using a laser scanning unit according to a print signal to form an electrostatic latent image thereon, forming a toner image using toners supplied from developing units, and transferring the toner image onto paper.
The image forming apparatus uses a method of contacting the photosensitive medium with the charging device to charge the surface of the photosensitive medium to a predetermined potential. Using a potential difference between the devices, a toner is attached to the electrostatic latent image formed on the photosensitive medium or the toner image is transferred from the photosensitive medium onto a transfer device or from the transfer device onto paper.
In order to obtain a good quality image, an appropriate transfer voltage must be applied to a transfer roller to transfer the toner image formed on the photosensitive medium onto the paper.
U.S. Pat. No. 5,682,575, entitled “Electrophotographic Recording Apparatus Having Transfer Voltage Control Device,” discloses a method of measuring a resistance of a transfer roller when a top end of paper passes through a transfer roller and supplying a transfer voltage to the transfer roller so that an appropriate voltage is supplied to the transfer roller according to the type of paper. In the method disclosed in U.S. Pat. No. 5,682,575, the resistance of the transfer roller is detected while the paper does not pass between the photosensitive medium and the transfer roller, a high voltage is applied to the transfer roller while a leading end of the paper passes between the photosensitive medium and the transfer roller to detect a combined resistance of the paper, the photosensitive medium, and the transfer roller, the resistance of the transfer roller is compared with the combined resistance, and an appropriate transfer voltage is applied to the transfer roller, thereby controlling the transfer voltage.
However, since this method does not consider environmental changes of the transfer roller resulting from the application of a transfer voltage that varies according to the resistance of paper and any change caused by long term usage, a transfer failure may occur due to the application of an improper transfer voltage or an image may distort due to the application of an overvoltage.
Aspects of the present invention provide a method of and an apparatus for controlling a transfer voltage by detecting a transfer roller resistance and a paper resistance, determining the type of a paper using a relationship between a variation in transfer roller resistance and a variation in paper resistance, and applying an appropriate transfer voltage to a transfer roller with reference to a transfer table for each type of paper.
According to an aspect of the present invention, there is provided an apparatus for controlling a transfer voltage in an electrophotographic image forming apparatus using an electric transfer roller, the apparatus comprising: a transfer roller resistance detecting unit detecting a transfer roller resistance between a transfer roller and a photosensitive drum when a constant voltage is applied to the transfer roller in a state where the photosensitive drum and the transfer roller form a transfer nip; a paper resistance detecting unit detecting a paper resistance among the transfer roller, a paper, and the photosensitive drum when the constant voltage is applied to the transfer roller while the paper approaches the transfer nip of the transfer roller; a memory storing a paper resistance recognition table and a transfer table for each type of paper; and a transfer voltage controlling unit determining the type of the paper based on the transfer roller resistance and the paper resistance and outputting a transfer voltage with reference to the transfer table.
The transfer voltage controlling unit may comprise: a paper type determining unit determining the type of the paper using the transfer roller resistance and the paper resistance with reference to the paper resistance recognition table; and a transfer voltage outputting unit outputting the transfer voltage with reference to the transfer table for the determined type of the paper if the type of the paper have been determined, and outputting the transfer voltage with reference to a general transfer table if the type of the paper have not been determined.
According to another aspect of the present invention, there is provided a method of controlling a transfer voltage in an image forming apparatus, the method comprising: applying a constant voltage to a transfer roller in a state where a photosensitive drum and the transfer roller form a transfer nip and detecting a transfer roller resistance between the transfer roller and the photosensitive drum; applying the constant voltage to the transfer roller when paper approaches the transfer nip of the transfer roller and detecting a paper resistance among the transfer roller, the paper, and the photosensitive drum; determining a type of paper from a paper resistance recognition table based on the transfer roller resistance and the paper resistance; and applying the transfer voltage to the transfer roller with reference to the determined type paper and a transfer table to perform a transferring operation.
Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
These and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:
Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.
The HVPS 160 is controlled by the controlling unit 150 and applies a high voltage to the transfer roller 120, the charging roller 130, and the developing unit 140. The charging roller 130, which receives a high negative voltage, charges the photosensitive drum 110 to a constant negative potential. The LSU 170 radiates a laser beam onto a surface of the photosensitive drum 110, causing a potential difference. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 110. A toner charged with a negative potential is adhered to the electrostatic latent image by the developing roller 140. At a transfer nip N formed as the photosensitive drum 110 and the transfer roller 120 contact, the toner image on the photosensitive drum 110 is transferred to a paper P by the transfer roller 120 which receives a high positive voltage from the HVPS 170. In the image forming apparatus 100, the transfer roller 120 is an electric conductivity type ethylene propylene dimonomer (EPDM) sponge having a resistance between 60 MΩ and 260 MΩ.
Referring to
When printing paper is fed and approaches the transfer nip N, the paper resistance detecting unit 220 receives a signal IN2 representing the amount of current flowing in the transfer roller 120 and detects a combined resistance of the transfer roller 120, the paper P, and the photosensitive drum 110 (hereinafter, referred to as a paper resistance). At this time, the high voltage applied to the transfer roller 120 is adjusted to be equal to the voltage applied to the transfer roller 120 when detecting the transfer roller resistance. This is for reducing a deviation caused by overshoot, etc., which would occur when the voltage applied to obtain a paper resistance and the voltage applied to obtain a transfer roller resistance are different.
The transfer voltage controlling unit 230 determines the type of paper using a relationship between the transfer roller resistance and the paper resistance and outputs a transfer voltage OUT corresponding to the transfer roller resistance with reference to a transfer table for the determined type of paper. The transfer voltage controlling unit 230 includes a paper type determining unit 231 and a transfer voltage outputting unit 232.
A paper resistance recognition table 241 which is used to determine the type of paper and a transfer table 242 which provides a transfer voltage corresponding to the transfer roller resistance are stored in the memory 240.
The paper determining unit 231 determines the type of paper from the paper resistance recognition table 241 based on the transfer roller resistance and the paper resistance.
The transfer voltage outputting unit 232 outputs the transfer voltage with reference to the transfer table 242. If the type of paper is determined in the paper type determining unit 231, the transfer voltage outputting unit 232 outputs a transfer voltage corresponding to the transfer roller resistance with reference to the transfer table for the determined type of paper. If the type of the paper is not determined by the paper type determining unit 231, the transfer voltage outputting unit 232 outputs a transfer voltage with reference to a general transfer table.
The paper resistance recognition table 241 is calculated using a variation in transfer roller resistance due to environment conditions and a life span of the transfer roller and the variation in paper resistance
The result of calculating a paper resistance recognition table for A-sized paper based on the results in
The relationship between the type of paper and the paper resistance recognition table 241 may be expressed by equation (1):
Yi=eX+ƒ±α (1)
where Yi denotes the paper resistance (current), X denotes the transfer roller resistance (current), α denotes an error range, and e and f denote constants obtained from the variation in transfer roller resistance and the variation in paper resistance.
When the paper type determining unit 231 determines the type of paper using the transfer roller resistance and the paper resistance, the transfer roller resistance and the paper resistance may not accurately match values in the sheet resistance recognition table 241. However, if the transfer roller resistance and the paper resistance fall within a range α of an entry in the paper resistance recognition table for a type of paper, the paper is regarded as the type of paper corresponding to the entry. If the transfer roller resistance and the paper resistance do not lie in a range α of an entry in the paper resistance recognition table 241 for a type of paper, the paper type determining unit 231 does not determine the type of paper.
A transfer voltage representing a good printing state for each type of paper is experimentally obtained and stored in the transfer table 242.
Referring to
In operation S410, the HVPS 160 applies a voltage to the transfer roller 160 that is equal to the voltage applied when detecting the transfer roller resistance while a paper P approaches the transfer nip N, and the paper resistance detecting unit 220 detects the paper resistance as the combined resistance of the transfer roller 120, the paper P, and the photosensitive drum 110.
In operation S420, the transfer roller resistance and the paper resistance are applied to the paper resistance recognition table 241 to determine a type of the paper P.
In operation S430, it is determined whether the type of paper can be determined. If the type of paper can be determined, a transfer voltage corresponding to the transfer roller resistance is applied to the transfer roller 120 with reference to the transfer table 242 for the determined type of paper, in operation S440. Otherwise, another transfer voltage corresponding to the transfer roller resistance is applied to the transfer roller 120 with reference to a general transfer table.
According to aspects of the present invention, a proper transfer voltage is applied in consideration of environmental changes of the transfer roller and any change caused by long term usage, so that it is possible to prevent a transfer failure caused by the application of an improper transfer voltage or an image distortion caused by the application of an overvoltage.
Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.
Number | Date | Country | Kind |
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2005-26505 | Mar 2005 | KR | national |