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 × 10-4 mm3/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.

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Micro robots, due to their light weight, small size and high mobility, can explore narrow space or hazardous locations that humans or larger robots cannot reach. Consequently, both academia and industry are concerned with the development of advanced microrobots. In this paper, we design a steerable miniature legged robot (SMLR) which possesses light weight and controllable linear/steerable motion by using two piezoelectric bending actuators. Its dimensions are 35 mm × 30 mm × 9 mm (length × width × height) and mass is 9 g. User can modulate the speed, turning radius, and load capacity of the robot by simply tuning the driving voltage. The robot exhibits a speed of 330 mm s-1 and a turning radius of 102 mm upon a driving voltage of 200 V and a frequency of 8.67 kHz. Moreover, it is capable of driving a 55 g embedded mass at a speed of 20 mm s-1 under a voltage of 200 V, and its simple design is ideal for down-sizing. Further, we establish a series of open-loop control programs in a virtual instrument through LabVIEW to accurately control the behavior of the SMLR (the location error is less than 5 mm), demonstrating its great potential in practical applications such as movement in a narrow space.@en