Sensorless Position Control For Piezoelectric Actuators Using A Hybrid Position Observer

Soft piezoelectric actuators are extensively used in micro- and nanopositioning applications. Traditional sensorless position control approaches use a hysteresis mapping between voltage and position in a voltage feedforward control scheme in order to compensate for hysteresis errors. However, several factors such as frequency, temperature, and aging influence this mapping. Recently, charge control for positioning is also attracting interest among researchers due to the linear relationship between position and charge. However, a sophisticated hardware design is required to minimize charge drift. In this study, a new sensorless position control technique is proposed which requires neither an accurate inverse mapping nor a sophisticated charge amplifier in order to compensate for hysteresis. A constitutive relationship is employed to infer position from charge measurement through current integration. To eliminate drift from the charge-based measurement, an observer is presented in this study which uses a second self-sensing position estimate that is based on the variation of effective piezoelectric capacitance with stroke. The proposed observer is tested as a position feedback sensor inside a simple integrating control loop and applied to step profiles of variable stroke and sinusoidal profiles of constant and mixed frequencies. The responses are compared with a laser interferometer and the maximum observer error between the laser and the observer is 0.89 μm ( 3% of the maximum stroke) over a frequency range of 10 to 100 Hz.