A multi-degree-of-freedom spherical rotor piezoelectric actuator with flexible stator supports and adjustable preloading

Multi-degree-of-freedom spherical rotor piezoelectric actuators require multiple stators to maintain stable contact with a curved rotor, making their performance sensitive to nonuniform preload. This paper proposes a spherical rotor piezoelectric actuator comprising three symmetrically arranged traveling-wave stators, flexible stator bases, and adjustable spring preloading mechanisms. The flexible bases provide local compliance to accommodate assembly deviations and improve stator-rotor contact adaptability. Finite element analysis and vibration measurements identified the B(0,9) operating mode at approximately 29.6 and 30.0–30.3 kHz, respectively. Prototype tests demonstrated a maximum no-load speed of 42°/s at a peak driving voltage of 270 V and a nominal calculated preload of 120 N, and a maximum stall torque of 0.64 N·m at 270 V and a nominal calculated preload of 153.7 N. Under identical operating conditions, friction-material height measurements showed that the flexible-base stator exhibited a smaller circumferential height difference than the rigid-base stator, providing quantitative evidence of a more uniform wear distribution and indirect evidence of improved contact uniformity. Meanwhile, the measured three-dimensional trajectory preliminarily verified coordinated multi-axis motion within the tested workspace. These results demonstrate the feasibility of the proposed actuator and its potential for compact multi-degree-of-freedom motion applications.