1. Field of the Invention
The present invention relates to an electrophotographic image forming apparatus, and more particularly, to a transfer unit of an electrophotographic image forming apparatus, which transfers an image formed on a developing unit onto paper.
2. Description of the Related Art
In general, electrophotographic image forming apparatuses are devices which form an electrostatic latent image on a photosensitive medium, such as a photosensitive drum or a photosensitive belt, and develop the electrostatic latent image with toner of a predetermined color, and transfer the developed electrostatic latent image onto paper, thereby obtaining a desired image.
FIG. 1 schematically illustrates the structure of a conventional electrophotographic image forming apparatus. The electrophotographic image forming apparatus 100 includes a plurality of developing units 110 and a transfer unit 140. Although a plurality of the developing units 110 are included, the present description refers to a single developing unit 110 for simplicity of explanation.
The developing Unit 110 develops an electrostatic latent image formed on a photosensitive drum 130 by a laser scanning unit (LSU) 120 with a predetermined color.
The transfer unit 140 transfers the image, transferred from the photosensitive drum 130 onto a transfer belt 145, onto paper. The transfer belt 145 is rotatably supported by a transfer belt steering roller 141 to maintain tension of the transfer belt 145, a plurality of transfer backup rollers 142, and a driving roller 144. The photosensitive drum 130 is supported by each of a plurality of the transfer backup rollers 142, wherein the transfer belt 145 is placed therebetween.
Reference numeral 170 denotes a cleaning blade which is installed opposite to the transfer belt steering roller 141, wherein the transfer belt 145 is placed therebetween. The cleaning blade 170 closely contacts the transfer belt 145 with a predetermined pressure, and cleans a developing agent remaining on the transfer belt 145 after the image is transferred onto the paper.
A photosensitive drum cleaning blade 132, which contacts the surface of the photosensitive drum 130 and removes the developing agent remaining on the surface of the photosensitive drum 130, is installed adjacent to the photosensitive drum 130.
Although not shown, a fusing unit which fuses the transferred image on the paper is further installed.
In the conventional electrophotographic image forming apparatus 100 having the above structure, the transfer unit 140 closely contacts the photosensitive drum 130 with a predetermined pressure so that the image is transferred from the photosensitive drum 130 onto the transfer belt 145. However, when the transfer unit 140 or the developing unit 110 is replaced, the transfer belt 145 and the photosensitive drum 130 that closely contact each other to form the image on the transfer belt 145 must be spaced apart from each other. Thus, a device which can closely contact the transfer unit 140 or be spaced apart from the photosensitive drum 130, is required.
The photosensitive drum 130 and the transfer belt 145 must uniformly contact each other and require a low pressure and a high precision. However, the conventional transfer unit 140 includes a plurality of components, and is thus large and heavy.
The number of components of the transfer unit 140 becomes even larger, and the precision of the components is accordingly lowered. Thus, costs increase, the life span of the electrophotographic image forming apparatus is reduced, and it is inconvenient to use the electrophotographic image forming apparatus.