Design and experiment of a three-feet linear ultrasonic motor using third bending hybrid modes

A linear ultrasonic motor (USM) with two piezoelectric stators using the combination of two third bending vibration modes is proposed in this study, two orthogonal bending modes can simplify the effort of frequency degeneration. A square runner is driven by two stators through elliptical motions of their driving feet. Three driving feet in each stator are located at its middle and both ends, they vibrate with the same elliptical trajectory and push the runner together for improving the output performance. The finite element method (FEM) is adopted to optimize structural configuration of the stator, which ensures the amplitude uniformity of three driving feet. A prototype of the proposed USM is manufactured and its mechanical characteristics including velocity versus exciting voltage and velocity versus carrying load are tested in sequence. The tested results show that the maximum no-load velocity of the prototype is 117.22 mm/s at the exciting voltage of 65 V_p-p, and the maximum carrying load of the prototype is 350 g when the exciting voltage is 60 V_p-p. The tested results confirm that the developed USM has the advantages of simplified frequency degeneration in structure design and low exciting voltage.