Self-oscillation system for driving a linear oscillatory actuator around its resonant frequency

摘要

An improved self-oscillation system for a linear oscillatory actuator composed of a stator and a reciprocator. The stator carries a winding to which an electric current is periodically supplied for making a resonant oscillation of the reciprocator. The system includes a self-oscillation circuit for continuing the resonant oscillation of the actuator by a positive feedback manner based upon a back electromotive force (Vbemf) appearing across the winding. The system further includes a PWM control for increasing the electric current in response to a decreasing oscillation amplitude due to an increasing load applied to the reciprocator. A detector circuit is included to monitor the oscillation amplitude of the reciprocator and provides a corresponding detector output in response to which the self-oscillation circuit provides a drive pulse of varying pulse width for making the PWM control. The detector circuit is connected to monitor Vbemf of the Winding in the absence of the electric current and to judge the instant oscillation amplitude of the reciprocator based upon the monitored Vbemf. Thus, the system can eliminate an external sensor, yet assuring the PMW control reliably based upon Vbemf correctly reflecting the actual oscillation of the reciprocator.