Dieter Cramer

Optical two channel elongation measurement of PZT piezoelectric multilayer stack actuators

A fast optical deflection measurement of multilayer actuators is described. This two beam method eliminates the measuring problems arising from fixing one side of clamped actuators by detecting the movements of both sides of the actuator. The frequency range of this interferometric measurement reaches from static up to 200 kHz. In this way fast mechanical response can be detected even in the case of rectangular pulses. The accuracy of the deflection measurement is better than 1%. The small and large signal effective d/sub 33/ data of PZT multilayer actuators, consisting of up to 500 single layers, are determined using this method. The dependence of these data on clamping force and pulse duration is investigated. For characterization of reliability of multilayer actuators the maximum number of cycles under hard driving conditions of rectangular pulses with rise times of 10 /spl mu/s leading to maximum loading currents of 20 A is determined.

Energy considerations of PZT multilayer actuators under dynamic driving conditions

By means of fast optical two channel elongation measurement, with a resolution of 0.05 /spl mu/m, the dynamic behavior of PZT multilayer stack actuators, consisting of some layers and with typical dimensions of 10/spl times/10/spl times/20 mm/sup 3/, driven under different clamping conditions is investigated. In addition to the deflection measurement, the electrical power consumption and the dynamic and static forces are measured simultaneously. Starting from the measurement of the working characteristics, including the determination of dynamic stiffness and blocking force, the mechanical output for different mechanical preloads and for different mechanical stiffnesses of load is evaluated. Choosing the optimum preload and stiffness of load, maximum mechanical output can be achieved. It can be shown that the mechanical load also influences the electrical power consumption of the clamped actuator. Depending on the composition of the PZT ceramic, the clamping conditions may cause depolarization. Under driving conditions additional repolarization effects induce increased deflection. This can be used to find optimum material compositions for given mechanical preloads of clamped actuators.