Design, analysis, measurement and control of a new disc-type ultrasonic motor system
In this thesis, a novel disc-type ultrasonic motor stator is investigated. The stator has an asymmetrical structure (120°-90°-150° support boundary configuration) on its surface. The advantages of this structure include a single electrical phase driving, multiple-resonant-modes driving, rotational direction changes by modulation of driving frequencies, single contact point, and simple driving electrical circuit. With the setup of a precision laser vibrometer measurement experiment, mode motions and wave propagations of the UM are analyzed. The model is further verified by using finite element simulations where a 3-dimensional mechanical element with an extra electrical degree of freedom is used and then electrical impedance response, phase response and mechanical frequency response of the UM are studied. Furthermore, a transfer function model and equivalent circuit model of the Um in terms of radial and tangential displacement components are established for control objectives and for certification of dynamic characteristic parameters. The equivalent circuit model verifies radial, tangential and couple vibration modes once more and is used in search of resonance frequencies. The PSPICE has been used to simulate the equivalent circuit components. Finally, a speed control scheme is implemented by using current modulation and commercial DSP technique, in order to keep the revolution speed constant. The proposed ultrasonic motor system has proven good dynamic behaviours with the driving frequency range of 65k-100kHz and reaches a maximum revolution speed of 600rpm.