Patent ID: 6999709

Claim:
A transfer unit of an electrophotographic image forming apparatus having a plurality of photosensitive drums, the transfer unit comprising: a transfer belt which has a closed shape, is rotated while contacting the photosensitive drums, onto which toner images formed on the photosensitive drums are transferred, and which transfers the toner images onto a paper; a plurality of main frames; a driving assembly having: a driving roller which is installed inside of the transfer belt to be supported by the plurality of main frames and rotates and drives the transfer belt, and a steering roller portion which is installed inside of the transfer belt to be supported by the plurality of main frames and to push the transfer belt from the inside thereof to tighten the transfer belt; a plurality of auxiliary frames; a transfer backup roller assembly having: a plurality of transfer backup rollers which are installed inside of the transfer belt to be opposite to the photosensitive drums, the transfer belt being between the transfer backup rollers and the photosensitive drums and supported by the plurality of auxiliary frames and to support the transfer belt so that the toner images formed on the photosensitive drums are transferred onto the transfer belt, and a plurality of guide rollers which are inside of the transfer belt to be supported by the plurality of auxiliary frames and guide the transfer belt; and a transfer backup roller ascending and descending portion which ascends and descends the transfer backup roller assembly towards and away from the driving assembly.