Investigation on force transmission of direct-drive thorax unit with four ultrasonic motors for a flapping microaerial vehicle

Experimental research on the evolution characteristics of a bending hybrid ultrasonic motor during long-time operation

The characteristics evolution rules of an ultrasonic motor (USM) based on the hybrid of bending modes during long-time operation are tested and analyzed in this work. The alumina and nitride silicon ceramics are used as the driving feet and rotor respectively. The variations of mechanical performances including the speed, torque, and efficiency with time are tested and evaluated in the whole life period of the USM. Meanwhile, the vibration characteristics of the stator such as the resonance frequencies, amplitudes, and quality factors are also tested and analyzed every-four hours. Moreover, the real-time test for performances is conducted to assess the effect of temperature on mechanical performances. Furthermore, the effect of wear and friction behavior of the friction pair on the mechanical performances is analyzed. The torque and efficiency have apparent decreasing trends and fluctuated widely before about 40 h, and then gradually stabilize for 32 h, and finally fall rapidly. By contrast, the resonance frequencies and amplitudes of the stator only decrease by less than 90 Hz and 2.29 μm at first, and then keep fluctuant. During the continuous operation of the USM, the amplitudes will decrease as the increase of surface temperature, and followed by long-time wear and friction of the contact surface, the decrease of contact force is incapable to support the operation of the USM at last. This work is helpful to understand the evolution characteristics of the USM and provides the guidelines for the design, optimization, and practical application of the USM.

A Multi-Point Contact Model Considering Rough Surface for Linear Ultrasonic Motors: Validation and Simulation

The performance and wear life of linear ultrasonic motors are directly determined by the stator-mover frictional contact behaviors. A complete contact model is important to clearly understand the stator-mover contact mechanism and accurately estimate the motor performance. In this paper, a multi-point frictional contact model considering the roughness of contact interfaces is presented based on a finite model of the stator and an analytical model of the mover. The static/dynamic contact behaviors and output performance of the motor can be simulated efficiently. A quantitative measuring methodology for the dynamic contact forces between the stator and mover is developed. The effectiveness of the contact model for simulating the stator-mover contact forces is first evaluated by experiment. Based on the developed model, several dynamic characteristics of a linear ultrasonic motor are discussed: (a) the static force transferred between contact interfaces under pre-pressure; (b) the transient forces and energy exchange between contact interfaces; (c) the steady-state output performance of motor under different electric excitation parameters; (d) the effects of micro-topography parameters on the output performance of the motor and the force transmission of the contact interface.

Design of a Low-Frequency Harmonic Rotary Piezoelectric Actuator

Piezoelectric actuators usually operate under a high frequency driving signal. Here we report a harmonic rotating piezoelectric actuator by coupling a harmonic wave generator and a friction rotor, in which the actuator can be actuated by a low-frequency sinusoidal signal with positive bias. The harmonic wave is generated by a two-stage magnifying mechanism consisting of a displacement amplifier and a harmonic rod. Applying piezoelectricity theory, the actuator’s output characteristic equations are deduced. What is more, the output characteristics of piezoelectric actuators are tested with the established experimental system. Results show that the generated harmonic displacements can drive the actuator to work normally at a driving voltage of larger than 90 V and the maximum total harmonic displacement of the piezoelectric actuator comes up to 427.6 μm under the driving voltage of 150 V. Meanwhile, the error between the measured and calculated values of the harmonic displacement is less than 7%. Furthermore, the rotational speed of the piezoelectric actuator reaches 5.45 rpm/min at 150 V voltage and 5 Hz driving frequency.