Paper conveyance apparatus for an image forming apparatus and a method thereof

Abstract

A paper conveyance apparatus and method for an image forming apparatus are disclosed. The paper conveyance apparatus and method provide an improved structure in which when the distance between the conveyance roller shaft and the reversible roller shaft is shortened due to the abrasion of the reversible roller, the center of a gear train which transmits a driving force to the reversible roller is swung to move as much as the shortened distance so that the reversible roller can be continuously in contact with the conveyance roller. The paper conveyance apparatus and method comprise a conveyance roller for conveying a paper sheet to an image forming section, a reversible roller for contacting the conveyance roller, a driving motor having a driving gear for supplying a driving force to the reversible roller, and an idle gear for transmitting a driving force from the driving motor to the reversible roller. The center of rotation of the idle gear is movable according to the degree of abrasion of the reversible roller in order to transmit a driving force from the driving motor to the reversible roller.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(a) of Korean Application No. 2003-93183, filed Dec. 18, 2003, in the Korean Intellectual Property Office, the entire contents of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus. More particularly, the present invention relates to a paper feeder and method for an image forming apparatus, for reducing the malfunction caused by abrasion of a reversible roller that rotates forwards and backwards in contact with a conveyance roller so that paper sheets are picked up one by one.

2. Description of the Related Art

FIG. 1 is a diagram illustrating a conventional electrophotographic image forming apparatus 1 which feeds a paper P using a knock-up plate type of a feeding device 2. As shown in FIG. 1, a paper P is picked up by a pickup roller. A conveyance apparatus 10 having a plurality of rollers is provided to prevent the simultaneous feeding of two or more paper sheets.

As shown in FIG. 2, the conveyance apparatus 10 consists of a conveyance roller 11 and a reversible roller 12. A torque limiter 13 is mounted on the same axis of the reversible roller 12. Also, a reversible motor (not shown) for reversely rotating the reversible roller 12 is provided independently from a driving device for rotating the conveyance roller 11.

The reversible roller 12 rotates in an opposite direction to the conveyance roller 11. When two or more paper sheets are fed at once, the reversible roller 12 separates the top paper sheet from the underlying paper sheets using a difference in the coefficient of friction between the reversible roller 12 and the conveyance roller 11. When a single paper sheet is fed, the friction force between the conveyance roller 11 and the reversible roller 12 becomes greater than a predetermined torque of the coaxial torque limiter 13, thereby making the reversible roller 12 rotate in the same direction of the rotation of the conveyance roller 11. A reversible gear 14 is also mounted on the same axis of the reversible roller 12 to receive a driving force from the reversible motor. The reversible gear 14 rotates in a direction opposite to the direction of rotation of the torque limiter 13, and operates independently from the rotation of the conveyance roller 11.

The conveyance roller 11 and the reversible roller 12 comprise a rubber having a predetermined solidity, friction coefficient and durability, such as a Natural Rubber (NR), an Acrylonitrile Butadiene Rubber (NBR), an Ethylene-Proplyene-Diene (EPDM), a urethane or a silicon.

Since the reversible roller 12 rotates in the opposite direction to a paper feeding direction, the surface of the reversible roller 12 contacting the conveyance roller 11 is apt to be easily abraded. As the surface of the reversible roller 12 becomes abraded, a conveyance roller shaft S1 and a reversible roller shaft S2 are not maintained in parallel with each other but form an incline, as shown in FIG. 2. This problem results from the fixed position of the reversible gear 14. When the conveyance roller shaft S1 and the reversible roller shaft S2 are not in parallel with each other, the conveyance roller 11 and the reversible roller 12 do not contact sufficiently to separate two or more paper sheets fed together and smoothly feed the paper sheets sequentially. Accordingly, the abrasion of the reversible roller 12 may cause errors in the operation of the image forming apparatus.

SUMMARY OF THE INVENTION

An aspect of the present invention is to solve at least the above problems and to provide at least the advantages described below. Accordingly, an aspect of the present invention is to provide a paper feeder and method for an image forming apparatus, having an improved structure to reduce the malfunction caused by abrasion of a reversible roller that rotates forwards and backwards in contact with a conveyance roller so that paper sheets are picked up sequentially.

In order to achieve the above-described aspects of the present invention, there is provided a paper feeder and method for an image forming apparatus. The paper feeder and method comprise a conveyance roller, a reversible roller, a driving motor and an idle gear. The conveyance roller and the reversible roller, being in contact with each other, rotate in the same direction as or the opposite direction to a direction of paper feed to convey paper sheets to an image forming section, separating paper sheets which are fed together. The reversible roller is transmitted with a driving force by the driving motor which is separate from the conveyance roller. In order to transmit the driving force, a gear train including an idle gear is used. The center of rotation of the idle gear is movable so that a contacting force between the conveyance roller and the reversible roller can be kept over a predetermined level even when the reversible roller is abraded.

The idle gear is preferable movable along a track which is a part of the circumference of a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear.

The central shaft of the idle gear may move along a swing slot formed on one sidewall of the image forming apparatus to correspond to the swing track of the idle gear.

According to a first embodiment of the present invention, the swing slot has an inner periphery with a curvature corresponding to the curved swing track of the idle gear.

According to a second embodiment of the present invention, the swing slot is formed in a direction of a tangent to a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear. The swing slot may include an elastic member for elastically supporting the central shaft of the idle gear.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the present invention will become more apparent from the following detailed description taken with the accompanying drawings in which:

FIG. 1 is a diagram illustrating a conventional image forming apparatus;

FIG. 2 is a diagram illustrating a state in which a conveyance roller and a reversible roller of the conventional image forming apparatus are inclined due to abrasion of the reversible roller;

FIG. 3 is a diagram illustrating a state in which rotation shafts of a conveyance roller and a reversible roller according to an embodiment of the present invention move in response to the abrasion of a reversible roller;

FIG. 4 is a diagram illustrating a sectional view of an arrangement of gears, motors and shafts according to an embodiment of the present invention;

FIG. 5 is a diagram illustrating a gear train of a reversible roller according to a first embodiment of the present invention; and

FIG. 6 is a diagram illustrating a gear train of a reversible roller according to a second embodiment of the present invention.

Throughout the drawings, it should be noted that the same or similar elements are denoted by like reference numerals.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a few embodiments of a paper conveyance apparatus and method for an image forming apparatus according to embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 3 is a diagram illustrating a paper feeder according to an embodiment of the present invention.

As shown in FIG. 3, the conveyance apparatus 100 includes a conveyance roller 110, and a reversible roller 120 pressed against the conveyance roller 110 at a predetermined pressure. In order to rotate the conveyance roller 110 and the reversible roller 120, a conveyance gear 112 and a reversible gear 122 are provided to receive a driving force from respective driving sources (not shown).

A load regulator having a torque limiter T coaxial to the reversible roller 120 is mounted on a reversible roller shaft 121. The torque limiter T detects whether the friction force between the conveyance roller 110 and the reversible roller 120 is reduced by a paper sheet fed between the two rollers 110 and 120 to a level below a predetermined friction coefficient. When a single paper sheet is fed, the reversible roller 120 rotates in the same direction as the conveyance roller 110 to convey the paper. When two or more paper sheets are fed at once, the reversible roller 120 rotates in an opposite direction to the conveyance roller 110 according to a detection signal from the torque limiter T in order to separate the fed paper sheets so that only the top paper sheet is conveyed to an image forming section.

More specifically, a paper picked up by a pickup roller is fed between the conveyance roller 110 and the reversible roller 120, and conveyed to the image forming section. If the friction between the conveyance roller 110 and the reversible roller 120 is greater than a predetermined coefficient of friction, the reversible roller 120 rotates in the same direction of the rotation of the conveyance roller 110. In contrast, if the friction is smaller than the predetermined coefficient of friction, the reversible roller 120 rotates in the opposite direction. The longer the reversible roller 120 is used, the more it becomes abraded due to friction with the conveyance roller 110. With the increase of the abrasion of the reversible roller 120, the reversible roller shaft 121 moves parallel by a distance ‘d’ toward the conveyance roller shaft 110 as shown in FIGS. 3 and 4. Therefore, in order to continuously transmit a driving force to the reversible roller 120 from a driving motor 130 (FIG. 4), an idle gear 140 is required, which flexibly moves to be kept in mesh with the reversible gear 122 even when the position of the reversible roller shaft 121 is changed. As shown in FIG. 4, the central shaft Ci of the idle gear 140 is designed to be movable.

The central shaft Ci of the idle gear 140 moves along a swing track A as shown in FIG. 4 to maintain the idle gear 140 and the reversible gear 122 in mesh. The central shaft Ci of the idle gear 140 is slidably mounted on one sidewall W (FIGS. 5 and 6) of the image forming apparatus. When the reversible roller shaft 121 moves parallel toward the conveyance roller shaft 111, the central shaft Ci also moves along the swing track A to maintain the idle gear 140 and the reversible gear 120 in mesh. The swing track A may be a part of the circumference of a virtual circle having a radius corresponding to the distance between the central shaft Cm of the driving gear 131 and the central shaft Ci of the idle gear 140.

FIGS. 5 and 6 are diagrams illustrating the idle gear 140 with the central shaft Ci movable along the swing track A according to first and second embodiments of the present invention.

In accordance with the first embodiment of the present invention, the central shaft Ci of the idle gear 140 is slidably mounted on one sidewall W of the image forming apparatus. For this, the sidewall W has a curved swing slot 141 having a curvature corresponding to the swing track A and a width corresponding to the diameter of the central shaft Ci. Accordingly, when the position of the reversible roller shaft 121 is changed due to the abrasion of the reversible roller 120, the central shaft Ci slides along the swing slot 141 to maintain the idle gear 140 and the reversible gear 122 in mesh.

As shown in FIG. 5, the curved swing slot 141 has a width corresponding to the diameter of the central shaft Ci of the idle gear 140. Also, the swing slot 141 has a curvature corresponding to the curved swing track A.

According to the second embodiment of the present invention, the central shaft Ci of the idle gear 140 is slidably mounted on one sidewall W of the image forming apparatus. In this connection, the sidewall W has a straight swing slot 142 formed in a direction of a tangent to the swing track A, and having a width corresponding to the diameter of the central shaft Ci. An elastic member 143 such as a compression spring is mounted within the swing slot 142. The elastic member 143 exerts an elastic restoring force so that the idle gear 140 can be maintained in mesh with the reversible gear 122.

In the paper conveyance apparatus 100 for an image forming apparatus according to the first and second embodiments of the present invention, when the reversible roller 120 is abraded, the reversible roller shaft 121 moves parallel toward the conveyance roller 110 by a distance corresponding the abraded thickness of the reversible roller 120, thereby preventing a biased abrasion of the reversible roller 120 and any error of feeding plural paper sheets at once.

When the distance between the conveyance roller shaft 111 and the reversible roller shaft 121 is shortened due to the abrasion of the reversible roller 120, the idle gear 140 for transmitting the driving force to the reversible roller 120 is swung to move upward as much as the shortened distance so that the reversible roller 120 can be constantly in contact with the conveyance roller 110. Accordingly, by eliminating any causes of biased abrasion of the reversible roller 120, reliability of the image forming apparatus is ensured.

While the invention has been shown and described with reference to certain embodiments thereof, it should be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. A paper conveyance apparatus for an image forming apparatus, comprising: a conveyance roller for conveying a paper sheet to an image forming section; a reversible roller for contacting the conveyance roller; a driving motor having a driving gear for supplying a driving force to the reversible roller; and an idle gear for transmitting a driving force from the driving motor to the reversible roller, wherein the center of rotation of the idle gear is movable according to the degree of abrasion of the reversible roller in order to transmit a driving force from the driving motor to the reversible roller.

2. The paper conveyance apparatus according to claim 2, wherein the idle gear is movable along a track which is a part of the circumference of a virtual circle having a radius corresponding to a distance between the center of the driving gear and the center of the idle gear.

3. The paper conveyance apparatus according to claim 2, wherein a central shaft of the idle gear is movable along a swing slot formed on one sidewall of the image forming apparatus to correspond to the swing track of the idle gear.

4. The paper conveyance apparatus according to claim 3, wherein the swing slot has an inner periphery with a curvature corresponding to the swing track of the idle gear.

5. The paper conveyance apparatus according to claim 3, wherein the swing slot is formed in a direction of a tangent to a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear.

6. The paper conveyance apparatus according to claim 5, wherein the swing slot comprises an elastic member for elastically supporting the central shaft of the idle gear.

7. A method of feeding paper in an image forming apparatus, comprising: conveying a paper sheet to an image forming section via a conveyance roller; contacting the conveyance roller via a reversible roller; supplying a driving force to the reversible roller via a driving motor having a driving gear; and transmitting a driving force from the driving motor to the reversible roller via an idle gear, wherein the center of rotation of the idle gear is movable according to the degree of abrasion of the reversible roller in order to transmit a driving force from the driving motor to the reversible roller.

8. The method according to claim 7, wherein the idle gear is movable along a track which is a part of the circumference of a virtual circle having a radius corresponding to a distance between the center of the driving gear and the center of the idle gear.

9. The method according to claim 8, further comprising: providing a central shaft of the idle gear which is movable along a swing slot formed on one sidewall of the image forming apparatus to correspond to the swing track of the idle gear.

10. The method according to claim 9, wherein the swing slot has an inner periphery with a curvature corresponding to the swing track of the idle gear.

11. The method according to claim 9, wherein the swing slot is formed in a direction of a tangent to a virtual circle having a radius corresponding to the distance between the center of the driving gear and the center of the idle gear.

12. The method according to claim 11, wherein the swing slot comprises an elastic member for elastically supporting the central shaft of the idle gear.