Pickup roller, image forming apparatus including the same, and method

Abstract

A pickup roller increasing a force adhering a top sheet contacting the pickup roller, an image forming apparatus with the same, and a method. A plurality of holes are formed on a surface of the pickup roller contacting the paper, and an internal diameter of part of the holes is expanded by compression between the paper and the pickup roller.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit from Korean Patent Application No. 10-2004-0063760, filed on Aug. 13, 2004, in the Korean Intellectual Property Office, the disclosure of which is hereby incorporated by reference

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image forming apparatus, and more particularly, to an improved pickup roller for increasing a force adhering to a top sheet contacting the pickup roller, and an image forming apparatus with the same.

2. Description of the Related Art

In general, image forming apparatuses, such as printers or copiers, include a paper pickup unit accommodating plural sheets of paper and picking up an uppermost paper sheet of a paper pile to feed it into a main body of the image forming apparatus. FIG. 1 shows one example of a conventional paper pickup unit 10.

Referring to FIG. 1, a paper pickup unit 10 includes a knock-up plate 12 connected to a paper cassette (not shown) and detachably mounted to a body (not shown) of an image pickup apparatus. Sheetsets of paper P are stacked on a knock-up plate 12. A spring 18 elastically biases in an upward direction a knock-up plate 12. A pickup roller 20 is provided in the body of the image pickup apparatus and positioned on the knock-up plate 12.

The pickup roller 20 is rotatably engaged with a shaft 28 transferring a rotational force, and has a surface generally made of rubber to pick up the paper P. The pickup roller 20 may be constructed such that an inside portion coupled to the shaft 28 is detachably coupleable and with a surface portion contacting the paper P, or such that the inside portion and the surface portion are integrally formed of a rubber material.

The shaft 28 has a pair of cams 30 with the pickup roller 20 interposed therebetween. The cams 30 press down both sides of the knock-up plate 12 in a printing standby state to cause a front end of the paper P to be separated from the pickup roller 20.

If a printing command is inputted into the image forming apparatus (not shown), the pickup roller 20 and the cams 30 are rotated, in direction shown by the arrow, by rotation of the shaft 28. The cam 30 pressing down the knock-up plate 12 is lifted, and the knock-up plate 12 is rotated around a hinge 14 by a biasing force of the spring 18, so that a front end of the knock-up plate 12, spaced apart from the hinge 14, moves in an upward direction. The front end of the paper P stacked on the knock-up plate 12 contacts the rotating pickup roller 20, and is picked up by a frictional force between the paper and the outer portion of the pickup roller 20 so as to feed the paper into the body (not shown) of the image forming apparatus.

The surface portion of the pickup roller 20 is surface-treated by various techniques so as to increase the frictional force between the paper and the surface portion of the pickup roller. FIGS. 2 through 4 show examples of a surface pattern of a conventional pickup roller that is formed by a surface treatment.

FIG. 2 shows a wave-type surface pattern formed by polishing a surface of a pickup roller. The wave-type surface pattern is easily abraded, and a foreign substance (e.g., dust) is likely to adhere to the wave pattern. Therefore, a problem exists in that since a frictional force of the surface will rapidly decrease, paper pickup performance is rapidly deteriorated.

FIG. 3 shows another wave-type surface pattern in which a wave is inclined with respect to a traveling direction of the paper. The wave pattern shown in FIG. 3 can reduce abrasion of a surface relative to that of the wave pattern shown in FIG. 2, but foreign substances are still likely to adhere to the surface. Therefore, the wave pattern also has a problem in that a frictional force still rapidly decreases.

SUMMARY OF THE INVENTION

Additional aspects and/or advantages of the invention will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.

The present invention provides a pickup roller in which paper pickup performance is maintained for a long time relative to that of a conventional pickup roller, and an image forming apparatus including the pickup roller.

According to one aspect of the present invention, a pickup roller that rotates and contacts a sheet of paper to pick up the paper is provided including a plurality of holes on a surface of the pickup roller that contacts the paper, and an internal diameter of a hole is expanded by a compressive force between the paper and the pickup roller.

According to another aspect of the present invention, an image forming apparatus is provided including a print unit printing an image on a sheet of paper and a paper pickup unit picking up the paper to be transferred to the print unit, in which the paper pickup unit rotates and contacts the paper so as to pick up the paper. A plurality of holes are on a surface of the pickup roller contacting the paper, and an internal diameter of a hole is expanded by compression between the paper and the pickup roller. According to an aspect of the present invention, a topology of holes for a pickup roller include a pattern of holes extending from a surface of the pickup roller.

According to an aspect of the present invention, the hole may be extend toward a rotating center of the pickup roller.

According to an aspect of the present invention, a surface of the pickup roller contacting the paper may be made of material having Poisson's ratio of 0.1 to 0.49.

According to an aspect of the present invention, a surface of the pickup roller contacting the paper may be made of EPDM material.

According to an aspect of the present invention, a plurality of holes may be distributed in a regular pattern on the surface contacting the paper. According to an aspect of the present invention, a printing medium moving member includes a surface including a plurality of holes a part of which are expandable.

BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a perspective view of a conventional paper pickup unit;

FIGS. 2 through 4 are plan views depicting examples of surface patterns of a conventional pickup roller;

FIG. 5 is a cross-sectional view of an image forming apparatus according to an example embodiment of the present invention;

FIGS. 6 and 7 are plan views depicting embodiments of surface patterns of a pickup roller in the FIG. 5; and

FIGS. 8 and 9 are partially enlarged cross-sectional views of a pickup roller in FIG. 5, in which FIG. 8 shows a state before the pickup roller contacts a paper, and FIG. 9 shows a state where the pickup roller contacted the paper.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the 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 to explain the present invention by referring to the figures.

Reference will now be made in detail to a pickup roller according to an embodiment of the present invention, and an image forming apparatus including the pickup roller.

FIG. 5 is a cross-sectional view of an image forming apparatus 100 according to an example embodiment of the present invention.

Referring to FIG. 5, the image forming apparatus 100 is a electrophotograph-type that supplies a toner as a developer onto an electrostatic latent image formed on an outer surface of a photosensitive medium by light emission to develop the electrostatic latent image into a visible image and transfers and fuses the image onto a sheet of paper to print a desired image. The image forming apparatus 100 includes a case 101, a developing unit 110, a transferring unit 125, a light scanning unit 127, and a fixing unit 130 Units 110, 125, 127 and 130 are a print unit. The image forming apparatus further includes a paper pickup unit 150 picking up a sheet of paper P to be printed.

The developing unit 110 includes a housing 111 accommodating a toner as a developer, and a photosensitive medium 115 forming an electrostatic latent image therein by a light scanning. The developing unit also includes charging roller 113 charging the photosensitive medium 115, a wasted toner cleaner 114 removing a wasted toner remained on the photosensitive medium 115, and a developing roller 117 supplying a toner onto the electrostatic latent image formed on the outer surface of the photosensitive medium 115 to develop the image onto the outer surface. The developing unit also includes a doctor blade 118 regulating a thickness of the toner adhered to the surface of the developing roller 117, and a supply roller 119 supplying the toner to the developing roller 117. Also, the developing unit 110 includes an agitator 121 agitating the toner in the housing 111 to prevent solidification of the toner. The developing unit 110 a cartridge-type, and thus is replaceable with a new cartridge if the developer is completely exhausted.

The transferring roller 125 is located opposite to the photosensitive medium 115, and in contact with the photosensitive medium 115. The transferring roller 125 presses the paper P against the photosensitive medium 115 so that the visible image developed on the outer surface of the photosensitive medium 115 is transferred onto the paper P passing through the transferring roller 125 and the photosensitive medium 115.

The fixing unit 130 includes a heat roller 131 and a pressing roller 133 opposite the heat roller. When the paper P with the visible image transferred thereon passes between the heat roller 131 and the pressing roller 133, the visible image is fixed onto the paper P by thermal compression.

The paper pickup unit 150 includes a knock-up plate 153 that is hingedly coupled to a paper feeding cassette 151 and on which paper to be printed on is stacked. A shaft 165 is positioned above a front end of the knock-up plate 153 when the paper feeding cassette 151 is mounted on the image forming apparatus 100 and rotated by a rotation of a drive motor (not shown). A pickup roller 170 is rotatably coupled to the shaft 165. The paper pickup unit 150 includes a lifting means for lifting the knock-up plate 153 in connection with the rotation of the pickup roller 170 so that a front end of paper P stacked on the knock-up plate 153 selectively contacts the pickup roller 170.

The lifting means has a spring 157 for elastically biasing the knock-up plate 153 in an upward direction, and a cam (not shown) coupled to the shaft 165 and rotated with the pickup roller 170. The cam is rotated together with the pickup roller 170, and periodically pushes a front-end of the knock-up plate 170 in a downward direction. Accordingly, paper P stacked on the knock-up plate 153 is periodically spaced apart from the pickup roller 170 so that the paper P does not contact the pickup roller 170. A friction pad 160 is provided in a front portion of the front end of the knock-up plate 153. Even though plural sheets of the paper P are picked up by the pickup roller 170, a movement of other sheets of paper is impeded by the friction pad 160, and only an uppermost sheet of paper P stacked on the knock-up plate 153 is advanced toward the print unit 110.

The image forming apparatus 100 also includes a paper arranging unit 140 providing a transferring force to the paper P picked up by the paper pickup unit 150 and arranging the paper P to transfer the visible image onto a desired part of the paper P before the paper P reaches the photosensitive medium 115. In addition, the image forming apparatus 100 includes a delivery roller 135 delivering the paper P with a desired image printed thereon to a delivery tray 102 disposed at an external position of the case 101.

An example operation of the image forming apparatus 100 will now be described. The photosensitive medium 115 is charged at a certain potential by the charging roller 113, and an electrostatic latent image corresponding to the image to be printed is formed on the outer surface of the photosensitive medium 115 by a light L scanned from the light scanning unit 127. The toner in the housing 111 is supplied through the supply roller 119 and the developing roller 117 to the photosensitive medium 115, with the electrostatic latent image formed thereon, to develop the visible image on the outer surface of the photosensitive medium 115. The paper P is picked up by the paper feeding unit 150, and passes between the photosensitive medium 115 and the transferring roller 125, being fed and arranged by the paper arranging unit 140. At this time, the visible image developed on the outer surface of the photosensitive medium 115 is transferred to a surface of the paper P that is opposite to the photosensitive medium 115. When the paper P passes through the fixing unit 130, the image transferred to the paper P is fixed onto the paper P by thermal compression. The paper P is delivered to the delivery tray 102 by the delivery roller 135.

An example pickup roller 170 is formed of EPDM material so as to increase a frictional force between the paper P and the pickup roller 170. The pickup roller 170 may be made of natural rubber (NR), nitrile rubber (NBR), urethane base rubber, or silicon base rubber.

The pickup roller 170 contacts the paper P with a plurality of holes 172 for improving paper pickup performance. The respective holes 172 extend in a direction toward the shaft 165 which is a rotating center of the pickup roller 170. The holes 172 may be regularly distributed over the surface of the pickup roller 170 as shown in FIGS. 6 and 7. More specifically, FIG. 6 shows rows of holes 172 arranged parallel with a feeding direction of the paper P indicated by an arrow. FIG. 7 shows rows of holes 172 arranged in a zigzag pattern with respect to the feeding direction of the paper P indicated by an arrow. Alternatively, the holes 165 may be irregularly distributed over the surface of the pickup roller 170. The pickup roller 170 may also include a wave-type surface pattern so as to improve the frictional force between the pickup roller and the paper.

As shown in FIG. 8, where the paper P stacked on the knock-up plate 153 (see FIG. 5) is not in contact with the pickup roller 170, the pickup roller 170 and the holes 172 on the surface of the pickup roller are maintained in original shapes. An internal pressure P_in of the hole 172 is maintained so as to be equal to an external pressure P_atm of the hole 172. As a printing process starts, the knock-up plate 153 is lifted and the paper P contacts a lower end of the pickup roller 170. A lower end of the pickup roller is pressed by the paper P and deformed, as shown in FIG. 9, so that an internal diameter of a part of the hole 172 closer to an opening of the hole is expanded from D1 to D2.

Assuming the variation is an adiabatic process, since the variation of the internal diameter instantaneously occurs, the expansion of the internal diameter of part of the hole 172 results in a cubic expansion inside the hole 172. Accordingly, as understood in thermodynamic law, the internal pressure P_in of the hole 172 will be less than the external pressure P_atm of the hole 172. Thus, it would be understood that paper P adheres to the lower end of the pickup roller 170 due to the pressure difference.

According to an aspect of the present invention, the pickup roller 170 is made of material having a Poisson's ratio of 0.1 to 0.49. The Poisson's ratio is defined as a ratio of transverse contraction strain to longitudinal extension strain of a material when a stress is applied to the material. If the Poisson's ratio is less then 0.1, the pickup roller 170 is rigid so that the variation of the internal diameter of the hole 172 is slight. If the Poisson's ratio is greater than 0.49, the pickup roller 170 is so soft that the pickup roller 170 may be deformed in a direction other hat an internal diameter of the hole 172.

The pickup roller according to aspects of the present invention and the image forming apparatus with the pickup roller include the following advantages.

Since the pickup roller pulls the paper by use of the suction force resulting from the deformation of the holes, in addition to the frictional force, the paper pickup performance is improved compared to that of a conventional pickup roller.

The paper pickup performance is not affected by reducing the frictional force due to the increased suction force resulting from the deformation of the holes. Therefore, abrasion of the pickup roller is reduced by adjusting the frictional strength between the paper and the pickup roller, thereby improving the durability of the pickup roller.

A frictional force between the sheets of paper is capable of being reduced by adjusting the frictional force between the pickup roller and the paper, thus preventing overlapping delivery of paper.

Foreign adhered to the surface of the pickup roller are easily detached from the surface of the pickup roller in a process where an inner diameter of the hole is repeatedly expanded and restored.

According to another aspect of the present invention, a pickup roller may include a plastic bracket coupled to the shaft and a rubber band wound around the bracket, and the holes may be formed in the rubber band.

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 these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

Claims

1. A rotatable pickup roller for contacting a sheet of paper to pick up the paper, comprising: a surface contacting the paper and having a plurality of holes, wherein an internal diameter of part of at least of one of the holes is expandable by a compression between the paper and the pickup roller.

2. The pickup roller of claim 1, wherein the holes extend toward a rotatable center of the pickup roller.

3. The pickup roller of claim 1, wherein the surface contacting the paper is made of material having a Poisson's ratio of substantially 0.1 to 0.49.

4. The pickup roller of claim 1, wherein the surface contacting the paper is made of EPDM material.

5. The pickup roller of claim 1, wherein the plurality of holes are distributed in a substantially regular pattern on the surface contacting the paper.

6. An image forming apparatus, comprising: a print unit printing an image on a sheet of paper; and a paper pickup unit picking up the paper to be transferred to the print unit, in which the paper pickup unit comprising: a rotatable pickup roller contacting a sheet of paper so as to pick up the paper in which a surface contacting the paper includes a plurality of holes, wherein an internal diameter of part of at least one of the holes is expandable by compression between the paper and the pickup roller.

7. The image forming apparatus of claim 6, wherein the holes extend toward a rotating center of the pickup roller.

8. The image forming apparatus of claim 6, wherein the surface contacting the paper is made of material having a Poisson's ratio of substantially 0.1 to 0.49.

9. The image forming apparatus of claim 6, wherein the surface contacting the paper is made of EPDM material.

10. The image forming apparatus of claim 6, wherein the plurality of holes are distributed in a substantially regular pattern on the surface contacting the paper.

11. A printing medium moving member comprising: a surface comprising a plurality of holes a part of which are expandable.

12. The printing medium moving member according to claim 11, wherein the holes extend toward a rotating portion of the pickup roller.

13. The printing medium moving member according to claim 11, wherein the surface is made of material having a Poisson's ratio greater than 0.1.

14. The printing medium moving member according to claim 11, wherein the surface is made of material having a Poisson's ratio less that 0.49.

15. The printing medium moving member according to claim 11, wherein at least part of the plurality of holes are distributed in a regular pattern.

16. A method of feeding paper in an image forming apparatus, comprising: creating a pressure differential between a paper mover contacting the paper and atmospheric pressure.

17. The method according to claim 16, wherein the creating a pressure differential comprises: varying a size of holes in a surface of the paper mover contacting the paper.

18. A method of reducing abrasion for a paper roller comprising: increasing an adhesion of paper moved by the paper roller in a manner other than by friction.

19. The method according to claim 18, wherein the increasing an adhesion of paper is by creating a pressure differential between a surface of the paper roller and atmospheric pressure.

20. A topology of holes for a pickup roller comprising: a pattern of holes extending from a surface of the pickup roller in which part of the holes are expandable during operation of the pickup roller.

21. The topology of holes according to claim 20, wherein the pattern is substantially regular on the surface.

22. A paper pickup roller comprising: a bracket coupled to a shaft of the paper pickup roller; and a band positioned around the bracket and having holes on a surface that contacts paper.

23. The paper pickup roller according to claim 22, wherein the band is a rubber band.