This study discusses the feasibility of contact force control without a force sensor in bimorph-type piezoelectric actuators. A feedback control system using a high-resolution force sensor is generally designed to achieve high-precision force control by suppressing the nonlinearities in the piezoelectric actuator and external disturbances. However, sensorless control is desirable to reduce the cost and space utilization of micro- and nano-control systems. In this study, the contact force is computed using the input voltage to the actuator and the voltage of a series-connected capacitor. Its estimation equation is derived based on a mechanical model and an electrical model with the capacitor. The two parameters used in the equation are calibrated based on preliminary experiments to improve the estimation accuracy. A feedback control system is designed based on the estimated force signal. The proposed force sensorless control approach has been verified by conducting experiments using a bimorph-type piezoelectric actuator and different contact objects.
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