Modified Hartley oscillator circuits are being developed for use in driving large piezoelectric benders in periodic motion, as in some piezoelectrically driven pumps. These circuits decrease the time-averaged consumption of power and thus increase energy efficiency by recycling large fractions of the energy stored in the capacitances of the piezoelectric benders.

This Circuit for periodically Driving a Piezoelectric Bender is a version of the classical Hartley oscillator

The amount of energy involved is significant because the capacitances of some piezoelectric benders can be large. For example, the capacitance of a system of multilayer piezoelectric benders in one pump has been estimated to be about 160 µF. If all of the energy stored in such a large capacitance during the charge phase of the operating cycle is simply dissipated during the discharge phase, then the time-averaged power consumed is correspondingly large.

An oscillator circuit of the type undergoing development (see figure) can reduce the loss of energy during the discharge phase of the operating cycle when driving a piezoelectric bender. This is because the bender capacitance is the capacitive part of the capacitive/ inductive resonant circuit that governs the frequency of oscillation, and by virtue of the fundamental nature of the oscillator circuit, much of the electromagnetic energy handled by this circuit alternates between storage in the capacitance and storage in the inductance. The overall efficiency can be increased if the frequency of mechanical resonance of the pump is matched to the frequency of oscillation.

This work was done by Frank E. Sager and William C. Robertson of Oceaneering Space Systems for Johnson Space Center.

Title to this invention has been waived under the provisions of the National Aeronautics and Space Act {42 U.S.C. 2457(f)}, to Oceaneering Space Systems. Inquiries concerning licenses for its commercial development should be addressed to

Oceaneering Space Systems
16665 Space Center Blvd.
Houston, TX 77058-2268

Refer to MSC-22556

Motion Control Tech Briefs Magazine

This article first appeared in the August, 2000 issue of Motion Control Tech Briefs Magazine.

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