A New Piezoelectric Actuator using a Feed-screw for Quasi-static Motion Accumulation — Part II: Mathematical Modeling and Design Optimization

In recent piezoelectric actuator development, a new feed-screw motion accumulation concept has demonstrated reversible, robust, and high force actuation. However, the feed-screw actuator's complicated structure and frequency-dependent operation necessitate the use of an efficient method to optimize its performance. Consequently, this study presents the formulation of a dynamic mathematical feed-screw actuator model and its integration in an optimization algorithm. To accurately model the feed-screw actuator, nonlinear contact stiffness and micro-slip is considered, as well as rate-dependent friction behavior. Results from numerical model simulations compare well with experimental data for a range of loads corresponding to the actuator's peak power output. A simulated annealing optimization algorithm is used to determine an actuator design that maximizes specific power (W/kg). For an actuation rate and load of 0.26in./s and 1220lb, a factor of 5 increase in specific power over that of the original experimental hardware is predicted. Expanding the optimization to consider a broad range of loads and speeds indicates that the feed-screw actuator could achieve a 195 W/kg specific power — a level approximately double that of similarly sized electromagnetic actuator. The most significant design improvements contributing to the large gains in specific power involve an increase in the screw pitch angle and a reduction of its diameter.