Driving of a linear piezoelectric actuators

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Written by Paul Sente

The piezoelectricity

In 1880, Jacques and Pierre CURIE discovered a new property of certain crystalline minerals: when subjected to a mechanical force, the crystals became electrically polarized. Tension and compression generated voltages of opposite polarity, and in proportion to the applied force. In 1882, the converse of this relationship was confirmed by LIPPMANN: if one of these voltage-generating crystals was exposed to an electric field it lengthened or shortened according to the polarity of the field, and in proportion to the strength of the field. These behaviors were labeled the piezoelectric effect and the inverse piezoelectric effect, respectively.

Although the magnitudes of piezoelectric deformations are small (typically <0.1% of the initial length of the ceramic), piezoelectric ceramics provide high forces with low voltages. Thanks to these interesting properties piezoelectric materials have been adapted to an impressive range of applications from spatial to medical fields.

The piezoelectric ceramics are used in sensing applications, such as in force or displacement sensors or actuation applications, such as in motors and devices that precisely control positioning but as their movements are very small, they are generally amplified by a mechanical structure.

Control of a piezoelectric linear actuator used into a direct-drive servo-valve (aeronautic application)

Inside a direct-drive servo-valve, the motion of the spool controlling the direction of the hydraulic fluid flow is directly actuated by an electrical motor.

Due to the small stroke needed, it is possible to use a linear amplified piezoelectric actuator directly connected to the spool. The aim of this research is to investigate how to design the power and control electronics of a direct-drive servo-valve based on a linear amplified piezoelectric actuator in order to take full advantage of such a motor.

In particular, it has been shown that the voltage applied on the piezoelectric stacks may be successfully controlled by use of four-quadrant choppers with the benefits that the injected electrical charge stored in their capacity can be recovered. This leads to a low consumption scheme  which can be easily fed by a boost converter from the aircraft 28 VDC.