Integrated proprioceptive piezoelectric actuators for miniature robots and devices

Abstract Piezoelectric motors have become a promising technology for the actuation of miniature robots. In this paper, we propose a novel integrated approach to measuring the deflection of piezoelectric actuators, by adding a thin film polyvinylidene fluoride (PVDF) as a dedicated sensor layer in a ceramic actuator laminate (PZT-5 H) to enable proprioception. We leverage our unique femtosecond laser micromachining process to pattern PVDF without altering its dielectric characteristics and validate this experimentally, including quantifying the changes with temperature and laser processing parameters, to develop a high-fidelity process for manufacturing proprioceptive actuators. The advantage of our approach lies in the requirement of minimal changes to the existing design process or fabrication workflow. To support the experimental results of actuator position tracking using the proposed approach, we derive first-principles-based theoretical expressions for modeling sensor and actuator functions and show that these predictions are in close alignment with experimental measurements. We then integrate the sensory actuators into a leg mechanism to demonstrate the use of proprioception capabilities for leg motion tracking, the detection of leg collisions with environmental obstacles and other surface interactions. Together, these experiments demonstrate the exciting potential of integrated proprioceptive sensing for robotic mechanisms by enabling servomotor-like functionality into traditional piezoelectric actuators, making them capable of closed-loop control in the near future. We conclude by examining possible limitations of this current method with potential mitigation strategies and emphasizing promising future prospects such as onboard closed-loop feedback control. We expect that the integration of PVDF sensors into actuators will enable the next generation of terrain-adaptive robots to adjust their movement to environmental changes, such as varying their gait in response to different ground surfaces.