Patent ID: 7657214

Claim:
An image forming apparatus comprising: a transfer belt adapted to allow a plurality of toner images of different colors to be sequentially superimposed and primarily transferred onto a surface thereof so as to form a color toner image; a plurality of image-forming units disposed along said transfer belt and each adapted to form a toner image with a corresponding one of said colors and primarily transfer said toner image onto said transfer belt; a drive roller for rotationally driving said transfer belt; a driven roller allowing said transfer belt to be laid thereacross in a tensioned condition in cooperation with said drive roller, said driven roller being followingly rotated in response to a rotation of said drive roller through said transfer belt; a tension roller having a rotating shaft and allowing said transfer belt to be laid thereacross in a tensioned condition in cooperation with said drive roller and said driven roller, said tension roller being adapted to apply a tension to said transfer belt; a bearing member for rotatably supporting said rotating shaft; a biasing member adapted to generate the tension by giving a biasing force to said tension roller so that a pressing force is applied to said transfer belt in a direction from an inner peripheral surface to an outer peripheral surface of said transfer belt by applying a biasing force to said bearing member to move said bearing member in a biased direction; a restricting member for restricting a moving direction of said bearing member substantially only in said biased direction; a secondary transfer roller being disposed in opposed relation to said drive roller so as to secondarily transfer, onto a sheet, the color toner image primarily transferred on said transfer belt; a speed detector for detecting a rotation speed of said tension roller and outputting a roller rotation speed signal; and a position adjustment mechanism for preventing occurrence of a relative displacement between said speed detector and said tension roller; wherein: said speed detector includes: a member to be detected, which is attached to a rotating shaft of said tension roller to be rotated in synchronization with said tension roller; and a detecting member for detecting a rotating condition of said member to be detected, said detecting member being fixed to said bearing member, or a member integral with said bearing member.