Ultrasonic motor operation relies on high-frequency vibration of a piezoelectric vibrator and interface friction between the stator and rotor/slider, which can cause temperature rise of the motor under continuous operation, and can affect motor parameters and performance in turn. In this paper, an integral model is developed to study the thermal–mechanical–electric coupling dynamics in a typical standing wave ultrasonic motor. Stick–slip motion at the contact interface and the temperature dependence of material parameters of the stator are taken into account in this model. The elastic, piezoelectric and dielectric material coefficients of the piezoelectric ceramic, as a function of temperature, are determined experimentally using a resonance method. The critical parameters in the model are identified via measured results. The resulting model can be used to evaluate the variation in output characteristics of the motor caused by the thermal–mechanical–electric coupling effects. Furthermore, the dynamic temperature rise of the motor can be accurately predicted under different input parameters using the developed model, which will contribute to improving the reliable life of a motor for long-term running.
A compact slider for linear ultrasonic motors (LUMs) to improve the ability of LUMs for precision positioning is proposed in this article. The compact slider can avoid the effect of variable stiffness of the traditional slider on ultra-precision positioning, which consists of two pieces of ceramic with little lubricating oil on the sliding interface. Based on contact theory and lubrication theory, the contact mechanism and the lubricating state between the slider and the support plate are analyzed. Subsequently, a dynamic model for LUMs considering the lubricating state and the ultrasonic vibration condition is obtained. Furthermore, the output speed and output force of the motor are analyzed under the influence of film lubrication. Moreover, some experiments are designed to test the feasibility and effectiveness of the compact slider for precision positioning. The results indicate that the compact slider is more effective in inhibiting the fluctuation of the output speed compared to the traditional slider, and it can improve the displacement resolution of LUMs up to 7 nm.
In this article, a favorable dynamical model for linear ultrasonic motor (LUSM) is proposed to investigate the influence of the slider movement characteristic. Linear rolling guide is the common structure as a slider in LUSM, and it also is used in this study. Based on Hertz contact theory and the coulomb’s friction law, contact mechanics and contact stiffness between the rolling balls and raceway has been analyzed. Then the dynamic model for LUSM considering the contact stiffness is obtained. In particular, the contact stiffness on the load direction will changed by the sliding of the slider during the motion of LUSM. Moreover, the output performance of LUSM has been analyzed by the suggested model. There is a speed fluctuation caused by the different internal contact stiffness of the slider periodically, affected the positioning accuracy of the LUSM. Furthermore, an experiment is designed to verify the feasibility and effectiveness of this proposed model by comparing the simulation results with the measured one. The results show that the proposed model is more accurate than the traditional model to evaluate the variation of output performance of the motor caused by the linear rolling guide movement. These discussions will be very useful for the improvement of control and the optimal design of LUSM.
In this paper, a wear model is established for a V-shaped linear ultrasonic motor. The influence of the change in the dynamic friction coefficient and the roughness parameters of the contact surface of the stator/slider on the output performance of the motor is considered in this model. The wear mechanism of the motor and the variation rules of the morphology of the contact surface during the operation of the motor are studied, as well as the relation of the wear height of the driving tip with the preload force and the relation of the preload force with the resonance frequency of the stator. The accuracy of the model is verified by numerical simulation and experimental methods. A test platform for friction and wear experiments is constructed, and the wear characteristics and the output performance of the motor are tested. The obtained results indicated that the model can accurately predict the dynamic changes during the wear process and the service life and output performance of the motor.
This paper proposes a dynamic numerical model for the bonded-type ultrasonic motor considering the load transfer in the adhesive interlayer between the piezoceramics and the host structure. The finite element method and an extended shear-lag theory are used to derive the dynamic equation. The effectiveness of this model is validated by comparing the dynamic response of the stator in frequency and time domains between simulation and experimental results, with a maximum relative error of less than 4%. The dynamic load transfer in the adhesive interlayer is analyzed when the stator is excited electrically, and the results show that the interfacial load transfer is concentrated near the bonding edges. The effects of partially bonded piezoceramics on the dynamic characteristics of the motor are investigated, where two partially bonded conditions including edge and inner debonded cases are considered. The results indicate that both the inner and edge debonded conditions could reduce the vibration amplitude of the stator and then reduce the output performance of the motor.
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