Modeling of piezoelectric actuators for high precision applications.

摘要

Piezoelectric actuators offer high stiffness, fast response times, high sensitivity, low wear and tear, and large force output. Unfortunately the electrical properties of lead zirconate titanate (PZT) changes significantly with an applied mechanical load disturbance and PZT suffers from hysteretic behaviour. In addition, piezoelectric actuators drift in open loop control. Therefore, in order to employ PZT actuators in high precision applications for improved regulation and control, and to achieve absolute positioning for long durations, models are required to characterize the behaviour of the material.; In this thesis first a simple resistor-capacitor (RC) model for PZT is presented. The model is used to assess the suitability of various models used throughout the literature.; An experimental test rig is developed and designed for the simultaneous application of an arbitrary input voltage and an arbitrary load to a PZT stack actuator test specimen. The test rig is used to develop and validate an electromechanical model for piezoelectric actuators, which accounts for hysteresis. The model also characterizes the coupled electromechanical effect of the sensing and actuating signals.; In addition, a dynamic electromechanical model is developed to characterize the hysteresis and drift behaviour of PZT. The presented model closely captures the absolute output displacement of the PZT actuator to a variety of applied input voltage excitations.; The electromechanical model and the dynamic electromechanical drift model were applied to an existing design of a piezoelectric driven valveless micropump, where these models can be used as design tools for the physical design of micropumps to give the optimum flow rate or performance for high precision applications, such as biomedical dispensing devices. In addition, the inverse of the electromechanical model was developed and applied to the micropump design, where such a model can be used to obtain a desired input voltage for a prescribed flow rate. This model can be used as the framework to develop controllers for output flow rate and pressure regulation and control, potentially in both open loop and closed loop control.