Passive clamping produces high-torque piezo motor

Engineers at a US university have developed a low-cost, high-torque, piezoelectric-based motor which can be made as flat and thin as a CD case. A prototype, with a component cost of around $150, has achieved speeds of 760 rpm and delivered torques up to 0.4Nm.

Dr Gary Koopmann, professor of mechanical engineering at Penn State University, who is leading the development team, estimates that mass-produced versions of the motor could cost as little as $10.

The motor (shown above in another prototype) works by translating the bending of a piezoelectric material (lead zirconate titanate, or PZT) into the turning of a shaft. The material is bonded onto both sides of a tiny, flexible metallic strip. This creates an "arm" that bends to the left or right when an electric field is applied to the piezo material.

A dozen of these arms are placed around a central shaft, like the limbs of a starfish. By stimulating all of the arms simultaneously, they bend in the same direction. A passive clamping system, in the form of a ball and spring, or a one-way roller clutch, ensures that the motor turns in one direction only.

According to Koopmann, this passive clamping technique improves the performance, and lowers the cost of the flat motor compared to "inch-worm" piezo motor designs which require precision machining.

Penn State has recently patented the motor design. The developers believe that it could be used in spaces which are too small for conventional machines. For example, the machines could be incorporated into compact, portable consumer products and industrial moving and vibrating equipment. A more specialised application would be to adjust the curvature of aircraft wings and fins.