CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Application No. 2002-10261, filed Feb. 26, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a photosensitive drum structure for an image forming apparatus using a photosensitive belt, and more particularly, to a photosensitive drum structure for an image forming apparatus used in an electrophotographic printer.

2. Description of the Related Art

In general, an electrophotographic printer such as a laser printer forms a latent electrostatic image on a photosensitive medium, develops the latent electrostatic image with a toner having a predetermined color, and transfers the developed toner image to a printing paper in order to obtain a desired image. The photosensitive medium is typically a photosensitive belt or a photosensitive drum.

FIG. 1

is a view of a portion of an image forming apparatus using a known photosensitive belt as a photosensitive medium. Referring to

FIG. 1

, the rotation path of a photosensitive belt

10

that travels a continuous path due to rollers

10

a

,

10

b

, and

10

c

includes an eraser

12

, a charger

14

, a laser scanning unit (LSU)

16

, and a plurality of developing units

18

a

,

18

b

,

18

c

, and

18

d

. The eraser

12

erases charges on the photosensitive belt

10

. The charger

14

charges the photosensitive belt

10

with a predetermined electric potential. The LSU

16

radiates light onto the photosensitive belt

10

to form a latent electrostatic image. The plurality of developing units

18

a

,

18

b

,

18

c

, and

18

d

are disposed in series along the travel direction of the photosensitive belt

10

and each develops the latent electrostatic image as a toner image with a different color. The developed toner image is transferred to a transfer belt

20

that circulates in contact with the photosensitive belt

10

.

However, in the above-described transfer method, the photosensitive belt

10

may move laterally outside of a transfer range of the image. Thus, a steering unit (not shown) is needed to adjust the photosensitive belt

10

.

FIG. 2

is a view of a portion of an image forming apparatus using a photosensitive drum as a photosensitive medium to solve the problems caused by the use of a photosensitive belt. Elements that are the same as those in

FIG. 1

are described with the same numerals, and thus their detailed descriptions are omitted.

Referring to

FIG. 2

, instead of the photosensitive belt

10

of

FIG. 1

, a large-sized photosensitive drum

30

is used. A plurality of developing units

28

to develop a latent electrostatic image on the photosensitive drum

30

are disposed along the circumferential surface of the photosensitive drum

30

. Developer rollers

28

a

,

28

b

,

28

c

, and

28

d

are positioned at the tip of each developing unit

28

. The developer rollers

28

a

,

28

b

,

28

c

, and

28

d

contact the photosensitive drum

30

and develop the latent electrostatic image with a toner in the developing units

28

with a developing nip N, having a predetermined width.

However, a different problem occurs in the manufacture of the photosensitive drum

30

. That is, if a small-sized photosensitive drum

30

having a diameter of 25-32 mm is manufactured, a small-sized rotary drum having a diameter of 25-32 mm is dipped in a container containing a photosensitive solution to form a photosensitive layer on the surface of the rotary drum. In this case, a plurality of small-sized rotary drums are manufactured at the same time, and thus manufacturing costs are low. However, since the photosensitive drum

30

uses a large-sized rotary drum having a diameter of about 150 mm, it is difficult to dip multiple rotary drums in the container containing the photosensitive solution. Also, it is expensive to manufacture the photosensitive drum

30

. Further, since the photosensitive drum

30

is rigid, the developing N must be narrow, and the developing units

28

do not develop the image well.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a photosensitive drum structure for an image forming apparatus in which a gap to provide a cushion between a rotary drum and a photosensitive belt is formed by adhering the photosensitive belt on steps having a predetermined height that are formed at both ends of the circumferential surface of the rotary drum.

Additional objects and 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.

The foregoing and other objects of the present invention are achieved by providing a photosensitive drum for an image forming apparatus, the drum including a cylindrical rotary drum having steps at both ends of a circumferential surface thereof, and a photosensitive belt wound around the rotary drum and attached thereto with an adhesive adhered to the steps, wherein a gap is formed between the circumferential surface of the rotary drum and the photosensitive belt.

According to an aspect of the present invention, the gap is filled with air or an elastic member.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1

is a view of a portion of an image forming apparatus using a known photosensitive belt;

FIG. 2

is a view of a portion of an image forming apparatus using a known photosensitive drum;

FIG. 3

is a perspective view of a photosensitive drum structure according to a first embodiment of the present invention;

FIG. 4

is a cross-sectional view taken along line IV—IV of

FIG. 3

;

FIG. 5

is a schematic view of a printer using the photosensitive drum according to the first embodiment of the present invention;

FIG. 6

is an enlarged view of a portion of the schematic view shown in

FIG. 5

;

FIG. 7

is a perspective view of a photosensitive drum structure according to a second embodiment of the present invention; and

FIG. 8

is a cross-sectional view taken along line VIII—VIII of FIG.

7

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In the drawings, the thicknesses of layers or regions are exaggerated for clarity.

FIG. 3

is a perspective view of a photosensitive drum structure

130

according to a first embodiment of the present invention, and

FIG. 4

is a cross-sectional view taken along line IV—IV of FIG.

3

. Referring to

FIGS. 3 and 4

, steps S having a predetermined height are formed at both ends of the circumferential surface of a cylindrical rotary drum

132

made of aluminium or an aluminium alloy. Double-sided tapes (not shown) are adhered on the steps S, on which a photosensitive belt

134

is wound one turn, covering the circumferential surface of the rotary drum

132

. The steps S form an air gap g between the circumferential surface of the rotary drum

132

and the photosensitive belt

134

. The photosensitive belt

134

is formed of a sequential stack of a base layer, a conductive layer, and a photosensitive layer. When a laser is radiated onto the surface of the photosensitive belt

134

, electrons of the photosensitive layer pass through the conductive layer to the outside, thereby forming a latent electrostatic image. The thickness of the photosensitive belt

134

is generally 20-1000 &mgr;m.

A height of the steps S, which defines the length of the air gap g, may be 100 &mgr;m or more. The maximum height of the steps S is generally 2 mm or less. A width of the steps S may be at least 2 mm or more.

The operation of the drum

130

having the above-described structure will be described with reference to

FIGS. 5 and 6

.

FIG. 5

is a schematic view of a printer using the photosensitive drum

130

according to the first embodiment of the present invention, and

FIG. 6

is an enlarged view of a portion of the schematic view shown in FIG.

5

.

Referring to

FIGS. 5 and 6

, the printer includes the photosensitive drum

130

, an eraser

112

, a charger

114

, a laser scanning unit (LSU)

116

, developing units

128

, a transfer belt

140

, a first transfer roller

142

, a second transfer roller

144

, and a fixing unit

160

. The photosensitive drum

130

is a photosensitive body. The eraser

112

erases an electric potential on the photosensitive drum

130

. The charger

114

charges the photosensitive drum

130

with the electric potential. The LSU

116

radiates light onto the photosensitive drum

130

to form a predetermined latent electrostatic image. The developing units

128

develop the latent electrostatic image with toners, each having one of four colors, i.e., yellow Y, magenta M, cyan C, and black K. The first transfer roller

142

transfers the image that is developed on the photosensitive drum

130

to the transfer belt

140

. The second transfer roller

144

transfers the image having four colors that are developed on the transfer belt

140

to a paper. The fixing unit

160

hot-presses the paper to permanently fix the transferred image on the paper. The developing units

128

include four developer units

128

-Y,

128

-M,

128

-C, and

128

-K, which are spaced apart from each other from the photosensitive drum

130

, sequentially move toward the photosensitive drum

130

by a contact unit (not shown), and contact developer rollers

128

a

,

128

b

,

128

c

, and

128

d

at the tips of the developer units

128

-Y,

128

-M,

128

-C, and

128

-K with the photosensitive drum

130

. Reference numerals

150

and

170

represent a paper cassette and a transfer path to hold and discharge the papers, respectively.

A process of forming an image in the printer shown in

FIG. 5

will now be described. The charger

114

charges the photosensitive drum

130

with a predetermined potential. The LSU

116

radiates light onto the photosensitive drum

130

to form a latent electrostatic image that will be developed with a first color in a predetermined area of the photosensitive drum

130

. For example, if the first color is yellow, the yellow developer unit

128

-Y contacts the photosensitive drum

130

with a contact unit. Thus, the toner that is attached to the circumferential surface of the developer roller

128

a

is transferred to the latent electrostatic image of the photosensitive drum

130

that contacts the circumferential surface of the developer roller

128

a

. Here, the developer roller

128

a

contacts the photosensitive drum

130

so as to press the air gap g formed between the rotary drum

132

and the photosensitive belt

134

with a predetermined pressure. Then, the photosensitive belt

134

is pushed toward the rotary drum

132

and forms a nip N having a predetermined width. The yellow image is well developed by the developing nip N. The developed image is transferred to the transfer belt

140

through a first transfer nip N

1

. A latent electrostatic image for magenta is formed by charging the photosensitive drum

130

with a predetermined potential and exposing the photosensitive drum

130

to light. The developing unit

128

develops the magenta image and transfers the developed magenta image to the transfer belt

140

through the first transfer nip N

1

. Cyan and black images are developed and transferred by this method, and then a desired color image is finally formed on the transfer belt

140

. The color image on the transfer belt

140

is transferred to a paper that is supplied to a second transfer nip N

2

between the transfer belt

140

and the second transfer roller

144

. The completed color image is hot-pressed when passing through the fixing unit

160

and permanently fixed on the paper.

FIG. 7

is a perspective view of a photosensitive drum

230

according to a second embodiment of the present invention, and

FIG. 8

is a cross-sectional view taken along line VIII-VIII of FIG.

7

. The detailed description of the same elements as those in the first embodiment is omitted.

Referring to

FIGS. 7 and 8

, an elastic member

250

, which is formed of a silicon sponge, a polyester sponge, or an elastic rubber, is inserted into the gap between a photosensitive belt

234

and a rotary drum

232

.

The elastic member

250

according to the second embodiment performs a cushion operation similar to the air gap g, and thus a detailed description thereof is omitted.

As described above, in a photosensitive drum structure for an image forming apparatus according to the present invention, an inexpensive photosensitive belt is wound around a rotary drum. Thus, manufacturing costs are reduced. Also, a cushion operation is performed on the photosensitive drum so that there is contact with the developer roller, in order to obtain good development of the image.

Although a few preferred embodiments of the present invention have been shown and described, it will 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.