Machine Design

Flattening the motor

Researchers at Penn State have developed a motor that can be built as thin as a CD case.

It works by translating the bending movements of PZT (lead zirconate titanate) into rotational motion. PZT is a relatively inexpensive piezoelectric material that elongates when an electric field is applied. By bonding PZT onto both sides of tiny flexible metallic strips, they create bimorph arms that bend left or right in response to electric fields. Twelve arms radiate from a central shaft and an electric field makes them all bend in the same direction simultaneously. A passive clamping system acts as a turnstile, reducing the arms' motion to rotation and harnessing them to turn the shaft. Other motors use an inch-worm-type design rather than the passive clamping system, but the clamping system is less expensive and improves motor performance.

A prototype motor reached 760 rpm and generated 0.4 N-m of torque. Components for the prototype cost about $150, a figure that could be brought down to $10 for mass-produced versions. The inventors envision their motor being used in tight spaces, such as in thinner, lighter laptops and other consumer products.

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