Resonant bimorph driven, high-torque piezoelectric rotary motor

A compact high-torque rotary motor was developed for use in large-displacement structural shape control applications. The main principle underlying its operation is rectification and accumulation of small resonant displacements of piezoelectric bimorphs using roller clutches as mechanical diodes. On the driving half of each cycle, the forward motion of the bimorph is converted to rotation of the shaft when the hub drive torque exceeds that of the load. On the recovery half of each cycle, a second, fixed, roller clutch prevents the load from backdriving the shaft. This approach substantially increased the output mechanical power relative to that of previous inchworm-type motor designs. Experiments to date, conducted under conditions of continuous operation at a 90 Vrms drive level, have demonstrated a stall torque of about 0.4 N-m, a no-load speed of about 750 RPM, peak power output greater than 1 W, and power density of about 5 W/kg. While not yet competitive with conventional motor technologies, this motor may also be fabricated in unusual (i.e., non-cylindrical) form factors, enabling greater geometric conformability than that of typical motors. The use of commercial roller clutches, piezoelectric bimorphs, and single frequency drive signals also results in a simple, inexpensive design.