Ultrasonic, powder-feeder vibrator under phase locked loop control

摘要

New equipment drives a feeder vibrator (10). An alternating voltage is applied to it, at resonant frequency. A phase locked loop (PLL) controller (11) is used to follow variations of the actual, mechanical resonance frequency. The frequency of alternating drive voltage is compared with the actual resonant frequency, in a mark-space ratio comparator. The drive unit has a feedback circuit (15, 14, 17) to detect the beat frequency from the ultrasonic transducer, caused by departure from resonance.