Patent ID: 7937031

Claim:
A transfer belt device comprising: an endless transfer belt capable of going into contact with peripheral surfaces of a monochrome photosensitive drum and a plurality of color photosensitive drums, all of the photosensitive drums being arranged generally in line; a driving roller for turning the transfer belt mounted thereon; a driven roller driven to rotate when the transfer belt also mounted on the driven roller is turned by the driving roller; a frame in which the driving roller and the driven roller are mounted; a plurality of transfer rollers so disposed in face to face relation with the corresponding photosensitive drums with the transfer belt passing in between as to force the transfer belt against the photosensitive drums; a roller support swingably mounted in the frame and supporting the transfer rollers disposed in face to face relation with the corresponding color photosensitive drums; a cam driving shaft rotatably mounted in the frame and fitted with a cam, the cam having capability of swinging the roller support to move the transfer rollers, disposed in face to face relation with the corresponding color photosensitive drums, toward and apart from the color photosensitive drums, to thereby switch the transfer belt and the color photosensitive drums between a state in which the transfer belt is in contact with the color photosensitive drums and a state in which the transfer belt is out of contact with the color photosensitive drums; a tension roller kept in contact with a surface of the transfer belt to exert predetermined tension on the transfer belt; and a pivotal axis on which the tension roller is swingably supported, the pivotal axis being common with the cam driving shaft.