Design, simulation, and experimental investigation on a novel multi-drive pattern three-degree-of-freedom rotary piezoelectric motor

Three-degree-of-freedom (3-DOF) rotary piezoelectric motors often suffer from low positioning accuracy, complex excitation signals, and uneven preloading, limiting their application in precision drive systems. To address these issues, this study proposes a novel multi-drive pattern 3-DOF rotary piezoelectric motor, comprising a sandwich-type hollow cylindrical stator, a spherical rotor, and a pre-tightening structure. The proposed motor can operate in both inertial and traveling wave drive patterns. In the inertial drive pattern, the first_order and the third-order bending vibration modes of the stator are simultaneously excited by a sawtooth wave signal, generating a saw-tooth displacement on its driving feet to rotate the rotor around the x or y-axis. In the traveling wave drive pattern, two mutually orthogonal first_order bending vibration modes of the stator are simultaneously stimulated by two sinusoidal signals, generating a traveling wave on its driving feet to rotate the rotor around the z-axis. Initially, finite element analysis is used to simulate the operating principle of the stator and determine its geometric dimensions. Subsequently, a prototype of the sandwich-type hollow cylindrical stator is fabricated, and its vibration characteristics are tested to confirm the validation of the proposed operating principle and the correctness of the finite element simulation. Finally, a prototype of the proposed 3-DOF rotary piezoelectric motor is assembled, and its mechanical output characteristics are experimentally evaluated. Experimental results indicate that when the excitation voltage is 200 V_pp, the no-load rotary velocities of the motor prototype in three rotation directions are 79 r min⁻¹, 76 r min⁻¹, and 101 r min⁻¹, respectively, start/stop response times are 10 ms/8.6 ms, 13.4 ms/6.2 ms, and 15.5 ms/7.7 ms, respectively, and the angular displacement resolutions are 7.4 μrad, 8 μrad, and 11.4 μrad, respectively. The proposed motor exhibits high mechanical integration, 3-DOF rotation, few excitation signals, adjustable pre-tightening force, and high positioning accuracy advantages, holding the potential applications in fields such as robotic technology and space pointing mechanisms.