Image forming apparatus and a method of cleaning photosensitive drum surface

An image forming apparatus is configured to execute the steps including: a step of controlling a photosensitive drum and a developing roller such that the developing roller rotates in a predetermined direction and the photosensitive drum rotates in a reverse direction; and a step of controlling the photosensitive drum and the developing roller such that the developing roller stops and the photosensitive drum rotates in the reverse direction, so as to reduce toner filming.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese Patent Application No. 2009-294599, filed on Dec. 25, 2009, the entire subject matter of which is incorporated herein by reference.

FIELD

Aspects of the disclosure relate to an electrophotographic image forming apparatus including a photosensitive drum and a method of cleaning a peripheral surface of the photosensitive drum.

BACKGROUND

A known electrophotographic image forming apparatus includes a photosensitive drum and a developing roller. Along with the rotation of the photosensitive drum, an electrostatic latent image is formed on a peripheral surface of the photosensitive drum, and toner is supplied from the developing roller to the surface of the photosensitive drum.

This develops the electrostatic latent image to a toner image, and the toner image is carried on the surface of the photosensitive drum. The toner image is transferred from the surface of the photosensitive drum to a recording medium, e.g. a recording sheet, thereby the toner image is formed or printed on the recording medium.

In such an image forming apparatus, toner may remain on the photosensitive drum after toner image has been transferred to the recording sheet, and fixedly adhere to the surface of the photosensitive drum. This is a phenomenon called toner filming. Especially in a structure where the surface of the developing roller contacts the surface of the photosensitive drum, toner filming is likely to occur because toner carried on the surface of the developing roller slides on photosensitive drum. Toner filming may result in deterioration of image quality and short lifetime of the photosensitive drum.

SUMMARY

Aspects of the disclosure provide an image forming apparatus which reduces the toner filming and a method of cleaning the surface of the photosensitive drum.

The image forming apparatus is configured to execute the steps including: a step of controlling a photosensitive drum and a developing roller such that the developing roller rotates in a predetermined direction and the photosensitive drum rotates in a reverse direction; and a step of controlling the photosensitive drum and the developing roller such that the developing roller stops and the photosensitive drum rotates in the reverse direction, so as to reduce toner filming.

DETAILED DESCRIPTION

An illustrative embodiment will be described in detail with reference to the accompanying drawings.

The general structure of an illustrative printer1as an example of an image forming apparatus according to illustrative aspects of the disclosure will be described with reference toFIG. 1.

For ease of discussion, in the following description, the top or upper side, the bottom or lower side, the left or left side, the right or right side, the front or front side, and the rear or rear side are used to define the various parts when the image forming apparatus1is disposed in an orientation in which it is intended to be used. InFIG. 1, the left side is referred to as the front or front side, the right side is referred to as the rear or the rear side, the up side is referred to as the top or upper side, and the down side is referred to as the bottom or lower side.

As shown inFIG. 1, the printer1includes a body casing2, a process unit3and an exposure unit4including a laser emitting unit, for example. The process unit3is disposed in a central portion of the body casing2. The exposure unit4is disposed above the process unit3.

The process unit3includes a photosensitive drum5, a charger6, a developing unit7, and a transfer roller8.

The photosensitive drum5is disposed rotatably on an axis extending in a direction perpendicular to a sheet ofFIG. 1.

The charger6is of a scorotron type, and is spaced apart from and opposite to a peripheral surface of the photosensitive drum5.

The developing unit7includes a developer casing9storing toner and a developing roller10rotatably supported in the developer casing9. The developing roller10is partially exposed from the developer casing9. The developing unit7is disposed such that a peripheral surface of the developing roller10contacts the surface of the photosensitive drum5.

The transfer roller8is disposed rotatably on an axis parallel to the axis of the photosensitive drum5and arranged such that a peripheral surface of the transfer roller8contacts the surface of the photosensitive drum5from below.

During image formation, the photosensitive drum5is controlled to rotate at a constant speed in a clockwise direction inFIG. 1. Along with rotation of the photosensitive drum5, the surface of the photosensitive drum5is charged uniformly at a constant positive potential, e.g., +800V, due to an electrostatic discharge from the charger6. Based on image data received from a personal computer (not shown) connected to the printer1, the exposure device4emits a laser beam onto the surface of the photosensitive drum5, which is disposed between the charger6and the developing unit7and positively and uniformly charged. In this manner, the surface of the photosensitive drum5is selectively exposed, electrical charge is selectively removed from the exposed area, and an electrostatic latent image is formed on the surface of the photosensitive drum5.

The developing roller10is subjected to the application of a positive bias for developing, e.g. +300V. When the photosensitive drum5rotates such that the electrostatic latent image is facing the developing roller10, toner positively charged is supplied from the developing roller10to the electrostatic latent image due to a difference in potential between the electrostatic latent image (from which electrical charge has been removed due to exposure) and the developing roller10. As a result, a toner image is formed on the surface of the photosensitive drum5.

A sheet supply cassette11is disposed in a bottom portion of the body casing2. The sheet supply cassette11is configured to store a stack of sheets. A pickup roller12is disposed above the sheet supply cassette11. The pickup roller12is configured to pickup a sheet from the sheet supply cassette11.

A conveyance path14having an S shape in side view is formed in the body casing2. The conveyance path14is formed from the sheet supply cassette11to an output tray13formed on the top surface of the body casing2. The conveyance path14passes between the photosensitive drum5and the transfer roller8. On the conveyance path14, a separation roller15and a separation pad16, a pair of sheet supply rollers17, a pair of registration rollers18, and a pair of ejection rollers19are provided opposite each other.

A few sheets P fed from the sheet supply cassette11are singly separated when passing between the separation roller15and the separation pad16. The sheet P separated by the separation roller15and the separation pad16is fed to the registration rollers18where skew of the sheet P is corrected. The sheet P of which skew is corrected is fed between the photosensitive drum5and the transfer roller8.

The transfer roller8is subjected to the application of a minus negative bias, e.g. −1000V. When facing the sheet P, which passes between the photosensitive drum5and the transfer roller8along with rotation of the photosensitive drum5, toner image on the surface of the photosensitive drum5is electrically attracted by the transfer roller8and transferred onto the sheet P.

On the conveyance path14, a fixing unit20is disposed downstream from the transfer roller8in a direction in which the sheet P is fed. The sheet P with the toner image is fed through the conveyance path14and passes through the fixing unit20. In the fixing unit20, the toner image is fixed, as an image, onto the sheet P through the application of heat and pressure.

The printer1has a single-sided printing mode where an image is formed on a single side of the sheet P and a double-sided printing mode where an image is formed on both sides of the sheet P.

In the single-sided mode, the sheet P having an image on one side is ejected to the output tray13by the ejection rollers19.

As a structure to realize the double-sided mode, a reverse conveyance path21is formed in the body casing2. The reverse conveyance path21starts from the proximity of the ejection rollers19, extends between the conveyance path14and the sheet supply cassette11, and joins the conveyance path14between the sheet supply rollers17and the registration rollers18. On the reverse conveyance path21, a pair of first bidirectional rollers22and a pair of second bidirectional rollers23are provided.

In the double-sided mode, after an image is formed on one side of the sheet P, the sheet P is fed into the reverse conveyance path21without being fed to the output tray13. The sheet P is fed through the reverse conveyance path21by the first and second bidirectional rollers21and22such that it is flipped over, and fed to the conveyance path14with the other side of the sheet P facing the surface of the photosensitive drum5. An image is formed on the other side of the sheet P thereby image formation onto both sides of the sheet P is completed.

An electrical structure of the printer1will be described.

As shown inFIG. 2, the printer1includes an operation panel33which is operated by a user to input instructions. The operation panel33is disposed on the top surface of the body casing2.

The printer1includes a rotation controller100. The rotation controller100includes a microcomputer34, a drum motor31, and a developing motor32. The rotation controller100is configured to control the photosensitive drum5and the developing roller5. Instructions input from the operation panel33are given to the microcomputer34. In addition, image data and various settings set on a personal computer (not shown) connected to the printer1are input from the personal computer to the microcomputer34.

The microcomputer34includes CPU and a memory as hardware structure. As a structure realized by software such as programs processed by the CPU, the microcomputer34includes a first rotation control unit35, a second rotation control unit36, a third rotation control unit37, and a fourth rotation control unit38.

The first rotation control unit35, the second rotation control unit36, the third rotation control unit37, and the fourth rotation control unit38are configured to control the drum motor31and the developing motor32for executing a cleaning process for the photosensitive drum5.

The drum motor31is configured to rotate in both forward and reverse directions. Based on the output of the drum motor31that rotates in the forward direction, the photosensitive drum5rotates in the forward direction (clockwise direction inFIG. 1) which is a rotation direction during development of the electrostatic latent image. On the other hand, based on the output of the drum motor31that rotates in the reverse direction, the photosensitive drum5rotates in the reverse direction (counterclockwise direction inFIG. 1), which is opposite to the forward direction.

The developing motor32is configured to rotate in one direction. Based on the output of the developing motor32, the developing roller10rotates in one direction only, e.g. a forward direction only. In other words, the developing roller10is not rotated in a reverse direction. The forward direction of the developing roller10is a direction in which the developing roller10moves in the same direction as the photosensitive drum5at a contact position where the peripheral surface of the developing roller10contacts the peripheral surface of the photosensitive drum5(refer toFIG. 4, first rotation process, which will be later described). As the developing roller10rotates in one direction only, hereinafter the rotation direction of the developing roller10is not described unless otherwise specified.

The cleaning process will be described.

In the cleaning process, paper dust and toner adhering to the photosensitive drum5are removed from the surface of the photosensitive drum5. The cleaning process is performed during which image formation is not performed onto a sheet P. The cleaning process may be started when image formation is carried out for a fixed number of times (or a fixed number of sheets P are printed) or when the user inputs the start of the cleaning process on the operation panel33or from the personal computer.

Prior to the start of the cleaning process in the printer1, the first rotation control unit35performs a first rotation process (first step). In the first rotation process, the first rotation control unit35controls the drum motor31and the developing motor32such that the drum motor31is driven to rotate in the forward direction, and the developing motor32is driven to rotate. Based on the output of the drum motor31, the photosensitive drum5rotates in the forward direction as shown inFIGS. 3 and 4. Based on the output of the developing motor32, the developing roller10rotates as shown inFIGS. 3 and 4. That is, in the first rotation process, the rotation directions of the photosensitive drum5and the developing roller10are the same as those when a toner image is formed on the surface of the photosensitive drum5. Thus, the first rotation process is the same as a process in which the toner image is formed on the surface of the photosensitive drum5. Thus, for the cleaning process, there is no need to add the first rotation process to the process in which the toner image is formed on the surface of the photosensitive drum5.

In the cleaning process, the second rotation control unit36performs a second rotation process (second step). In the second rotation process, the second rotation control unit36controls the drum motor31and the developing motor32such that the drum motor31is driven to rotate in the reverse direction, and the developing motor32is driven to rotate. Based on the output of the drum motor31, the photosensitive drum5rotates in the reverse direction as shown inFIGS. 3 and 4. Based on the output of the driving motor32, the developing roller10continues to rotate as shown inFIGS. 3 and 4.

At this time, the photosensitive drum5and the developing roller10move in opposite directions at the contact position where the peripheral surface of the photosensitive drum5and the peripheral surface of the developing roller10contact each other, and the peripheral surface of the photosensitive drum5and the peripheral surface of the developing roller10strongly rub against each other. Thus, the peripheral surface of the developing roller10rubs against paper dust adhering to the peripheral surface of the photosensitive drum5, which weakens the adhesion of paper dust to the peripheral surface of the photosensitive drum5. If there is a filming layer on the peripheral surface of the photosensitive drum5, the filming layer is scraped when rubbed against by the peripheral surface of the developing roller10.

The second rotation control unit36continues to perform the second rotation process until the photosensitive drum5rotates at least one turn in the reverse direction. With this turn, the adhesion of paper dust can be reduced across the entire surface of the photosensitive drum5and the filming layer can be scraped.

Then, the third rotation control unit37performs a third rotation process (third step). In the third rotation process, the third rotation control unit37controls the drum motor31and the developing motor32such that the developing motor32is stopped while the drum motor31remains rotated in the reverse direction. Thus, as shown inFIGS. 3 and 4, the photosensitive drum5continues to rotate in the reversed direction, and the developing roller10stops.

At this time, paper dust whose adhesion to the peripheral surface of the photosensitive drum5has been weakened and residues of toner scraped from the filming layer are collected at a position adjacent to the contact position where the peripheral surface of the photosensitive drum5and the peripheral surface of the developing roller10contact each other, on a upstream side in the reverse rotation direction of the photosensitive drum5.

The third rotation control unit37continues to perform the third rotation process until the photosensitive drum5rotates at least one turn in the reversed direction. With this turn, the paper dust and toner on the photosensitive drum5can be collected, across the entire surface of the photosensitive drum5, at the position adjacent to the contact position where the peripheral surface of the photosensitive drum5and the peripheral surface of the developing roller10contact each other.

Then, the fourth rotation control unit38performs a fourth rotation process (fourth step). In the fourth rotation process, the fourth rotation control unit38controls the drum motor31and the developing motor32such that the drum motor31is driven to rotate in the forward direction and the developing motor32is driven to restart to rotate. Based on the output of the drum motor31, as shown inFIGS. 3 and 4, the photosensitive drum5rotates in the forward direction. Based on the output of the developing motor32, as shown inFIGS. 3 and 4, the developing roller10restarts to rotate. That is, the operations of the photosensitive drum5and the developing roller10in the fourth rotation process are the same as those in the first rotation process. Thus, the fourth rotation process is identical to the process in which a toner image is formed on the peripheral surface of the photosensitive drum5. Thus, for the cleaning process, there is no need to add the fourth rotation process to the rotation process in which the toner image is formed on the peripheral surface of the photosensitive drum5. As an image is formed on the sheet P after the third rotation process, the performance of the fourth rotation process is automatically accomplished.

By rotation of the developing roller10in the fourth rotation process, the paper dust and the residues of toner, which are collected at the position adjacent to the contact position where the peripheral surface of the photosensitive drum5and the peripheral surface of the developing roller10contact each other, are carried onto the peripheral surface of the developing roller10, and brought to a downstream side of the developing roller10in its rotation direction. The paper dust and the residues of toner are collected in the developer casing9.

When a filming layer is present on the peripheral surface of the photosensitive drum5, not only the filming layer is scraped, but also the residues of toner generated after scraping can be effectively removed from the peripheral surface of the photosensitive drum5. In addition, paper dust can be effectively removed from the peripheral surface of the photosensitive drum5.

The fourth rotation process may be different from the process in which the toner image is formed on the peripheral surface of the photosensitive drum5. In the fourth rotation process, for example, the fourth rotation control unit38may control such that the drum motor31may be stopped, while the developing motor32may be driven to rotate. Thereby, as shown inFIG. 5, the photosensitive drum5may stop and the developing roller10may restart to rotate.

Alternatively, in the fourth rotation process, the fourth rotation control unit38may control such that the drum motor31may be driven to rotate in the reverse direction and the developing motor32may be driven to rotate. Thereby, as shown inFIG. 6, the photosensitive drum5may rotate in the reverse direction and the developing roller10may restart to rotate.

The illustrative embodiment shows, but the disclosure is not limited to, a monochrome printer. Instead, a color printer may be used.

While the features herein have been described in connection with various example structures and illustrative aspects, it will be understood by those skilled in the art that other variations and modifications of the structures and aspects described above may be made without departing from the scope of the disclosure described herein. Other structures and aspects will be apparent to those skilled in the art from a consideration of the specification or practice of the features disclosed herein. It is intended that the specification and the described examples only are illustrative with the scope of the inventions being defined by the following claims.