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Self-Sensing and Feedback Control for a Twin Coil Spring-Based Flexible Ultrasonic Motor

We propose a twin coil spring-based soft actuator that can move forward and backward with extensibility and can bend left and right with flexibility. It is driven by two flexible ultrasonic motors, each consisting of a compact metallic stator and an elastic elongated coil spring. The position of the end effector is determined by the positional relationship of the two coils and can be kinetically controlled with a constant curvature model. In our design, the coil springs act not only as a flexible slider but also as a resistive positional sensor. Changes in the resistance between the stator and the coil spring end are converted to a voltage and used for position detection. Each flexible ultrasonic motor with the self-sensing is experimentally evaluated, and it has shown good response characteristics, high sensor linearity, and robustness, without losing flexibility and controllability. We build a twin coil spring-based flexible ultrasonic motor prototype and demonstrate feedback control of planar motion based on the constant curvature model.