| 摘要 |
PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of detecting new and old exchangeable units with simple structure while reducing cost increase.SOLUTION: An image forming apparatus includes: a detachable unit; a rotary member that is rotatably provided in the unit with a first light-shielding face that blocks light from reaching optical detection means in a predetermined phase and that can continuously switch between at least two phase positions; and control means that detects a phase of the rotary member from a detection signal of the optical detection means. The rotary member includes a movable light-shielding member that is provided with a secondary light-shielding face different from the first light-shielding face in length of a light-shielding region in a rotation direction of the rotary member so that the secondary light-shielding face can move to a first position to block light from reaching the optical detection means by projecting from an outer periphery of the rotary member, as well as to a second position not to block light from reaching the optical detection means by retreating inward the rotary member. The control means detects that the unit is exchanged by allowing the optical detection means to detect the second light-shielding face.SELECTED DRAWING: Figure 1 |
