| 摘要 |
A closed-loop system for precisely regulating the speed of an electrically driven rotating body. A tachometer rotor (53) mechanically linked to the rotating body is provided with p "teeth" (55) around its periphery. A sensor (57) produces a pulse signal upon passage of each of these teeth, to generate a cyclic tachometer signal having a frequency p times the frequency of rotation. A tachometer counter (5) counts this signal and produces a single output pulse after every n x p pulses from the sensor, such that the same one of the p teeth is responsible for triggering each of the successive output pulses, and variations in spacing between teeth do not cause variations in the period of the counter output. A high frequency clock (17) is counted by a second counter (14) which transfers its count to a storage register (23) and resets upon each pulse from the tachometer counter (5), such that the count held by the storage register is a continuously updated, highly accurate digital respresentation of the period of the rotating body. A period comparator (39) derives a speed control signal which is proportional to the inverse of the difference between the count and a digital speed command signal representative of the rotational period at the desired rotational speed. |
