New flat motor can drive shape shifters, movers and shakers

Penn State engineers have developed a low- cost, high-torque rotary motor, based on “smart” materials, that can be configured in a wide range of formats, including one as flat and thin as a CD case.

The inventors say that, in the flat format, the motor could be used to drive changes in the camber of airplane wings or fins, essentially shape-shifting the curvature of the wing or fin surface.

In other formats, the motor could work in tightly integrated spaces where other motors can’t fit. For example, the “smart” material motor could serve as the drive element in thinner, lighter, laptop computers or other compact, portable consumer products or in manufacturing equipment that processes things by moving or shaking them.

Dr. Gary Koopmann, distinguished professor of mechanical engineering and director of Penn State’s Center for Acoustics and Vibration (CAV), led the development team. He says the flat motor has a starting torque advantage over conventional electric motors since speed is not required for high torque output.

The prototype flat motor has reached a free speed of 760 revolutions per minute and a maximum torque of 0.4 Nm.

Components for the prototype cost less than $150 off-the-shelf. Koopmann estimates that an optimized version of the flat motor might cost as little as $10 to mass produce.

The device was patented recently by Penn State. The inventors are Koopmann; Dr. Weicheng, CAV laboratory manager; Dr. George Lesieutre, professor of aerospace engineering and CAV associate director; Dr. Jeremy Frank, president, KCF Technologies; and Dr. Eric Mockensturm, assistant professor of mechanical engineering.

The new motor works by translating the bending of a “smart” material into the turning of a shaft. The “smart” material the inventors use is PZT (lead zirconate titanate), an inexpensive, commonly available piezoelectric that elongates when an electric field is applied to it. By bonding PZT to both sides of a tiny, flexible, metallic strip, they create an “arm” that can bend to the left and right in response to an electric field.

Placing 12 of the “arms” star-fish-style around a central shaft, the inventors stimulate them simultaneously and they all bend in the same direction. A passive clamping system, either a ball and spring arrangement or a commercial one-way roller clutch, acts as a kind of turnstile that only allows the motion to ratchet along in one direction, translating the bending into rotation of the central shaft.

Koopmann explains that using passive clamping significantly improves the performance and lowers the cost of the flat motor versus inch-worm type designs, which also use the small oscillatory motions of smart materials but require precision machining.

The development of the new motor was supported by grants from the Defense Advanced Research Projects Agency. The motor has been described in “Optimization of a Resonant Bimorph Actuator Drive” published in the Proceedings of DETC 01, the ASME 2001 Design Engineering Technical conference held Sept. 9-12, 2001 in Pittsburgh, Pa.