Performance Modeling of a Piezo-Hydraulic Actuator

A simple quasi-static model has been developed as an engineering tool for improving the performance of a piezo-hydraulic actuator's fluid system. The model's predictions compare reasonably well with experimental data at low frequencies (<150 Hz) as trends in the dependence of actuation speed on driving frequency and applied load are captured within 30%. The model indicates that there is an optimum load and driving frequency that corresponds to maximum power output but that the operating conditions for optimum power output and efficiency are different. The efficiency of the fluid system decreases with increasing frequency at a rate that depends on the load. Viscous losses through the valves and tubing are negligible compared with the inertial losses associated with accelerating and decelerating the load. This acceleration and deceleration process occurs twice per piezo cycle because of the configuration of the fluid system used to rectify the oscillatory motion of the piezo stack. Accordingly, the inertia of the load dominates the behavior of the device at high frequencies. The performance of the fluid system is most sensitive to the stiffness of the fluid in the pumping chamber, which should be maximized for maximum power output.