| 摘要 |
A drive motor (3) for a photoconductive belt (1) is energized for continuous rotation and connected to the belt (1) through a clutch. The clutch is disengaged and the belt (1) held stationary while an electrostatic image of an original document is formed on the belt (1). Then, the clutch is engaged and the belt (1) driven for developing the electrostatic image into a toner image and transferring and fixing the toner image to a copy sheet. The motor (3) also drives a pulse generator (18) which produces timing pulses. The timing pulses are counted by a counter. A control unit (E19) such as a microcomputer (19) controls the operation of the apparatus in accordance with predetermined counts in the counter. Marks (151), (152) are provided on the belt (1) in spaced relation. A compensation unit senses the number of timing pulses counted by the counter between sensing of the marks (151), (152). If the number of timing pulses counted is within a predetermined range which contains a predetermined value but is different from the predetermined value, the predetermined value is set into the counter, thereby compensating for slippage of the belt (1) relative to the motor (3). If the number of timing pulses counted is outside the predetermined range, an alarm is energized. Provision is also made for sensing a period of the timing pulses and energizing an alarm if the period is outside a predetermined range.
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