A ring-shaped linear piezoelectric actuator with three driving teeth is proposed and designed based on an axial-radial bending coupling vibration mode. The coupling vibration mode is neither pure axial bending mode nor pure radial bending mode, but an axial-radial bending hybrid one, which is generated by only one group of PZT elements and one exciting signal under an asymmetrical fixed boundary condition. The working principle of the proposed actuator is similar to the opening and closing actions of the three-petal mouth of a rabbit, which is analyzed by the finite element method. Then, the coupling vibration mode is verified by a scanning laser Doppler vibrometer after the fabrication of a prototype. Experimental results show that the prototype can achieve a maximum velocity of 60.46 mm/s and a displacement resolution of 0.5 μ m, and the velocity of the linear actuator can be smoothly adjusted in a wide range of 0.005–60.46 mm/s. In addition, the actuator can drive a hollow cylinder mover along different slopes without other auxiliary structures. The simulated and experimental results confirm that the proposed ring-shaped actuator is feasible without any guiding structure, which has great potential to realize further miniaturization of linear piezoelectric actuators.

Inspired by a way of rowing, a new piezoelectric driving quadruped micro-robot operating in bending-bending hybrid vibration modes was proposed and tested in this work. The robot consisted of a steel base, four steel connecting pins and four similar driving legs, and all legs were bonded by four piezoelectric ceramic plates. The driving principle is discussed, which is based on the hybrid of first order vertical bending and first order horizontal bending vibrations. The bending-bending hybrid vibration modes motivated the driving foot to form an elliptical trajectory in space. The vibrations of four legs were used to provide the driving forces for robot motion. The proposed robot was fabricated and tested according to driving principle. The vibration characteristics and elliptical movements of the driving feet were simulated by FEM method. Experimental tests of vibration characteristics and mechanical output abilities were carried out. The tested resonance frequencies and vibration amplitudes agreed well with the FEM calculated results. The size of robot is 36 mm × 98 mm × 14 mm, its weight is only 49.8 g, but its maximum load capacity achieves 200 g. Furthermore, the robot can achieve a maximum speed of 33.45 mm/s.

A novel U-shaped piezoelectric ultrasonic motor that mainly focused on miniaturization and high power density was proposed, fabricated, and tested in this work. The longitudinal vibrations of the transducers were excited to form the elliptical movements on the driving feet. Finite element method (FEM) was used for design and analysis. The resonance frequencies of the selected vibration modes were tuned to be very close to each other with modal analysis and the movement trajectories of the driving feet were gained with transient simulation. The vibration modes and the mechanical output abilities were tested to evaluate the proposed motor further by a prototype. The maximum output speed was tested to be 416 mm/s, the maximum thrust force was 21 N, and the maximum output power was 5.453 W under frequency of 29.52 kHz and voltage of 100 V_rms. The maximum output power density of the prototype reached 7.59 W/kg, which was even greater than a previous similar motor under the exciting voltage of 200 V_rms. The proposed motor showed great potential for linear driving of large thrust force and high power density.