| 摘要 |
A belt system of the type having a transparent belt entrained about a pair of support rollers which includes an improved alignment apparatus having a plurality of opaque flags positioned along an edge of the belt and shaped to taper in a transverse dimension, an encoder for detecting movement of the belt about the rollers and generating a signal proportional in frequency to the speed of the belt, a fixed photodetector which senses the passage of a portion of the flag through a narrow window so that the time of passage is determined by the position of the belt and flag relative to the sensor, an adjusting roller actuated by a stepper motor which laterally positions the belt relative to the support rollers, and a microprocessor which determines the position of the belt from the number of pulses generated during a period of time in which the sensor detects the passage of a flag and actuates the stepper motor to position the tracking roller to shift the belt laterally in response to the number of pulses counted. In a preferred embodiment, a timer introduces a time delay between successive counting periods, the time delay varying in duration inversely with the amount of lateral deviation of the belt from its desired position.
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