Study On Some Problems Of The Hybrid Longitudinal-Torsional Ultrasonic Motor

The developing history, basic principle, characteristics, and classification of the ultrasonic motor is stated briefly, the evolvement of the standing-wave, especially the hybrid longitudinal-torsional ultrasonic motor is introduced, the following three problems are discussed mainly: mode degeneracy and structure, contact model and noise, Thus the research content is confirmed.The basic principle and structure of the hybrid longitudinal-torsional ultrasonic motor is introduced, the resonance frequency equations of longitudinal and torsional vibrations of ultrasonic motor using the Mason equivalent circuit are deduced, the relationship between physical dimension and the resonance frequency is given, the design theory of longitudinal and torsional vibrators is founded.A-new-hollow-structure hybrid longitudinal-torsional ultrasonic motor is put forward which takes use of the first-torsional-vibration-mode and the longitudinal-vibration-mode caused by first-order-radial-vibration in designing of this kind of motor to realize mode degeneracy, which has many characteristics, such as, convenient mode degeneracy, small-axial-scale and high-torque;the frequencies and modes of longitudinal vibration and torsional vibrations as well as the relations between structure and frequency are given by FEM and experiments.The force transfer model and analytical method of the characteristics is put forward for the first time. First of all the relationships between the contact angle, preload, and physical parameters of frictional materials are given according to the impulse conservation law axially, the model of frictional force is improved on, then the equations describing output torque, amplitudes of longitudinal and torsional vibration, and parameters of the rotor is derived according to the principle that the work done by the load is equal to that by the driving force in one vibrating cycle. All factors that influence the maximum torque and no-load speed is analyzed, the formula for transfer efficiency on the stator/rotor interface is deducted, the relationship between the preload and output torque and the effect on the transfer efficiency on the stator/rotor interface of other parameters according to the above formula is given, the low-efficiency of this type motor is explained.The coupling problem of longitudinal vibration of the hybrid longitudinal- torsional ultrasonic motor is probed, the simplified coupling model of the longitudinal vibration combining the running circumstance of the motor is founded. The complex vibration of stator and rotor and the effect on the longitudinal vibration of system parameters isanalyzed, the rationality of the assumption of the force transfer model is verified. Theory basis for the design of motor is provided.The noise is analyzed by experiment and FEM, the conclusion is: there are two kinds of noise. First, nonlinearity of the system excites the fractional harmonic waves, which root in the noise. Second, the low-frequency-vibration noise of the rotor is excited by friction. The study can be useful for reducing the noise and remodeling the structure of the motor.