ABSTRACT
There are three general methods for actuator drive/control that are most commonly employed: DC drive, pulse drive, and AC drive. These methods are typically used for displacement transducers, pulse drive motors and ultrasonic motors, respectively. Displacement transducers are usually controlled in a closed-loop mode. Open-loop control can also be employed, but only when strain hysteresis is negligible and temperature fluctuation during operation is very small. Closed-loop control is a feedback method whereby the electric field-induced displacement of a ceramic actuator is monitored, deviation from the desired displacement is detected, and an electric signal proportional to this deviation is fed back to the ceramic actuator through an amplifier to effectively correct the deviation. Feedback is generally used for these devices to alleviate problems associated with the non-linearity and hysteresis commonly encountered in piezoelectric materials. The pulse drive motor is typically operated in the open-loop mode, but special care must be taken to suppress overshoot and mechanical ringing that can occur after the pulse voltage is applied. The AC voltage applied to ultrasonic motors is not very large, but the drive frequency must be precisely matched with the mechanical resonance frequency of the device for optimum performance. Heat generation, which is a potentially significant problem with this design, can be effectively minimized with the proper selection of operating parameters.
