| 摘要 |
<p>A belt driving unit (20) includes a rotary belt (10) on which a scale (5) is formed, a sensor (6) that reads the scale (5), a normal-position control loop (R1) that detects an actual position of the rotary belt (10) based on information of the scale (5) read by the sensor (6), and corrects a position of the rotary belt (10) based on the actual belt position detected, an abnormal-condition control loop (R2) for a situation when an abnormality occurs in the normal-position control loop (R1), and a loop-switchover timing controller (70) that controls a switchover timing of a control loop between the normal-position control loop (R1) and the abnormal-condition control loop (R2). <IMAGE></p> |
