Based on vibration of four side panels, a type of dual-rotor hybrid ultrasonic motor without using the torsional piezoelectric ceramics polarized along the circumferential direction is presented. The first longitudinal and the first bending vibration modes of the four side panels are used to indirectly excite the first longitudinal and the second torsional vibration modes of the stator cylinder. There are rectangle piezoelectric ceramics bonded on both sides of the four side panels, which are uniformly distributed along the circumference of the stator cylinder. One pair of panels on the opposite side is used to indirectly excite the first longitudinal vibration mode of the stator cylinder, and the other pair is used to indirectly excite the second torsional vibration mode. The simulation results, using finite element method software Workbench, reveal the operating principles, and the optimal structure is proposed. The appearance size of the prototype is 27.2 mm × 27.2 mm × 70 mm, while the outer diameter of the stator cylinder is 20 mm. The working frequency of the prototype measured in experiment is 44.7 KHz, which is consistent with the numerical results. According to the major mechanical measurement at 450 Vp−p operating voltage and 3.46 N preload, the stalling torque of the prototype is 8 mN·m and the no-load speed is 140 r/min. The experimental results indicate that the motor can operate in the first longitudinal and the second torsional coupled vibration modes transformed from the first longitudinal and the first bending vibration modes of four side panels.

A novel type of hybrid ultrasonic motor using longitudinal and torsional vibration modes is presented, which has four side panels uniformly distributed along the circumference of the stator cylinder. There is rectangle piezoelectric ceramics (PZTs) based on d31 effect bonded on both sides of each side panels, which can be used to convert the first bending vibration mode of the side panels into the second torsional vibration mode of the stator when the exciting voltage is applied. Meanwhile, there are rectangle PZTs based on d31 effect bonded on the surfaces of the stator cylinder between every two side panels, which can be used to excite the first longitudinal vibration mode of the stator. The simulation results using finite element method (FEM) software Workbench reveals the suitable polarization arrangement of PZTs and the final designed structure of the motor. The appearance size of the prototype is 28.2 mm×28.2 mm×68 mm, while the outer diameter of the stator cylinder is 20 mm. The major vibration and mechanical characteristics of the prototype have been measured. The working frequency of the prototype measured in experiment is around 43.12 kHz, which is consistent with the numerical results. When operating voltage of 350 Vp-p is applied, the no-load speed of the prototype is 103 rpm and the stalling torque is 48 mN·m.