Piezoelectric Motors

Piezoelectric motors use a piezoelectric ceramic element to produce ultrasonic vibrations of an appropriate type in a stator structure. The elliptical movements of the stator are converted into the movement of a slider pressed into frictional contact with the stator. The consequent movement may either be rotational or linear depending on the design of the structure.  Linear piezoelectric motors typically offer one degree of freedom, such as in linear stages.  However, these devices can be combined to provide more complex positioning factors.  Rotating piezoelectric motors are commonly used in sub-micrometric positioning devices. Large mechanical torque can be achieved by combining several of these rotational units.

Piezoelectric motors have a number of potential advantages over conventional electromagnetic motors. They are generally small and compact when compared with their power output, and provide greater force and torque than their dimensions would seem to indicate.  In addition to a very positive size to power ratio, piezoelectric motors have high holding torque maintained at zero input power, and they offer low inertia from their rotors providing rapid start and stop characteristics.  Additionally, they are unaffected by electromagnetic fields, which can hamper some other motor types.

Piezoelectric motors usually do not produce magnetic fields and they are not affected by external magnetic fields either. Because they operate at ultrasonic frequencies, these motors do not produce sound during operation. However, piezoelectric motors do have some disadvantages.  These disadvantages include the need for high voltage, high frequency power sources and the possibility of wear at the rotor / stator interface, which tends to shorten service life.

Piezoelectric motors have been in industrial use for years, but have not been popular due to what was perceived as an exorbitant cost of production and use. However, recent advances have significantly reduced the channel cost of this technology for closed-loop systems that require high positioning accuracy. With the use of a wide range of PID controllers and/or position sensors, the list of piezoelectric motor product applications is constantly growing.  Some of the common applications for piezoelectric motors includes camera focus systems, computer disk drives, material handling, robotics, and semiconductor testing and production systems.

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