The authors designed a bio-inspired robotic shoulder with two degrees of freedom (DoF) powered by antagonistic pairs of Peano-HASEL actuators. The key innovations of this work are:
Self-sensing capabilities: The HASEL actuators are equipped with a customized design that enables capacitive self-sensing of the actuator displacement, eliminating the need for external sensors.
Compact and compliant joint design: The ball-and-socket joint with a radius of 4 mm allows for a broad range of motion (over 80°) while maintaining a lightweight and compact system.
Tendon-based force transmission: The use of tendons for force transmission minimizes frictional losses and enables quick changes in movement while ensuring stable actuation at 3 Hz.
Closed-loop control: The authors implemented a PID controller that maps the reference and feedback signals between the task space and the tendon space, enabling precise control of the end-effector position without external sensors.
The authors conducted experiments to evaluate the performance of the self-sensing feedback control against a benchmark using a motion capture system. The results show that the self-sensing control achieved an RMSE of 4.245 mm for a lemniscate trajectory and 3.407 mm for a star-shaped trajectory, compared to the benchmark RMSEs of 2.869 mm and 2.798 mm, respectively.
The authors discuss the limitations of the current system, such as the torque limitations of the HASEL actuators, and suggest future research directions, including the integration of a third yaw axis, the use of advanced machine learning techniques for the estimation model, and the exploration of model-based control strategies.
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