US Patent 8010004 Belt transfer device

A belt transfer device according to the present invention includes an intermediate transfer belt, a transfer member, a shifter, a detector, and a controller. The transfer member primarily transfers a toner image from an image carrier to the intermediate transfer belt. The shifter reciprocates in specified opposite directions so as to shift the transfer member between a transfer position where the transfer member is in compressive contact with the inner surface of the intermediate transfer belt and a home position where the transfer member is away from the belt surface. The detector outputs a signal representing the position of the shifter. Based on the state of the signal output from the detector while the shifter is reciprocating each time in the opposite directions, the controller determines whether the tensile force of the intermediate transfer belt is proper.