Theoretical and experimental analyses of a legged piezoelectric bending actuator with shoe soles made of polyimide composites.

Friction materials form a critical component of piezoelectric actuators, and wear of the material affects output and service life of the actuator. This paper examines the influence of polyimide (PI) composites when used as a friction material on the performance of a legged piezoelectric bending actuator. We design and manufacture demountable shoe soles, made of a novel PI-based friction material, for an actuator. A Coulomb friction model is also established to determine the behavior resulting from contact-induced friction between the surface and the actuator. Reciprocating wear tests involving an insulation rubber pad against phosphor bronze and PI composites as friction materials yielded average friction coefficients of 0.21 and 0.28, respectively. We also found that PI composites have higher wear resistance than phosphor bronze, with a specific wear rate of 1.36 × 10 mm/N m. The results of experiments and simulations indicate that the shoe soles made of PI composites reduced the actuator's driving frequency and vibrational amplitude, but they did not affect the principle of locomotion of the actuator. Furthermore, the operational stability of the actuator improved by 46.8% by using the demountable shoe soles made of PI composites, albeit at the cost of its velocity and load capacity. This work has guiding significance for the design and selection of friction materials for piezoelectric actuators.