UBC Theses and Dissertations
Position Self-Sensing in the Presence of Creep, Hysteresis, and Self-Heating for Piezoelectric Actuators Islam, Mohammad Nouroz
Piezoelectric ceramic actuators are widely used in micro-/nano-positioning systems due to expedient characteristics such as fast response time, high stiffness, high resolution, etc. However, nonlinear effects such as hysteresis and creep affect the position accuracy of the systems if not compensated. Often, feedback position sensors are mounted to the systems to eliminate hysteresis and creep. Nonetheless, installation of feedback sensors can be prohibitive due to space constraints, reliability and cost. Alternatively, position self-sensing techniques are used to eliminate the position sensor. In this research, the objective is to develop a position self-sensing technique considering the nonlinear effects. To model the actuators for control or self-sensing, they are often considered as capacitive elements. A novel real-time impedance measurement technique is developed based on high frequency measurements to obtain clamped capacitance. Based on the real-time measurement, an improved constitutive model and parameter identification technique is presented which includes the position dependent capacitance. As a means for position self-sensing, position is linearly related to charge. However, charge measurement is prone to drift and require sophisticated hardware to implement. The new relationship between position and capacitance opens a new avenue for non-traditional position self-sensing; however, due to measurement noise, this new technique is only useful for slow operations. In this research, a novel position observer is presented that fuses the capacitance-based self-sensing with the traditional charge-based self-sensing. This allows the position estimation over a frequency band ranges from 0Hz to 125Hz where creep and rate-dependent hysteresis are observed. The estimation error is close to 3% when compared to a position sensor. Continuous operations at frequencies larger than 20Hz contribute to self-heat generation in the actuators. This elevated temperature is detrimental to the performance and life of the actuator. In this research, a self-heat generation model is presented based on power loss in the actuator to predict the temperature rise. The predicted temperature is then used to compensate the temperature related variation in the position observer. The temperature prediction error is less than 2°C which creates a position estimation error close to 4% up to a temperature variation of 55°C.
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