Research And Implementation Of Compound Compensation For Regulating Characteristics Of Traveling Wave Ultrasonic Motors

By comparison with traditional electromagnetic motors,the ultrasonic motors maintain many merits,in terms of the large ratio of the output torque to the volume/mass,the compact size and the light weight,the negligible effect influenced by the external magnetic or radioactive fields,and no generation of these fields.The ultrasonic motors,therefore,are suitable for the volume/mass-sensitive applications and utilization in the high intensity of magnetic field.The ultrasonic motors have been commercialized in various areas,such as the information technology,the robotics,the biomedical engineering,the ecological engineering and the energy engineering.The dead zone and the temperature drift characteristics of the ultrasonic motors,however,seriously restrict the performance of motors especially in continuous-working applications.The research on the regulating characteristics,from the driving mechanism,the material characteristics,and the design of the driving scheme viewpoints,maintains the considerable significance.This study aims to present a compound compensation scheme of the regulating characteristics of the ultrasonic motors,which can simultaneously compensate the dead zone and the temperature drift characteristics.Subsequently,with the aid of a widely-used Shinsei ultrasonic motors excited by a generator based on the compound compensation scheme,the experiments are carried out,which indicate the that the proposed compound compensation scheme has advantages over the existing schemes in terms of tracking the preset reference velocity and maximizing the efficiency.It is important to notice that the proposed compound compensation scheme is suitable for driving the various types of the ultrasonic motors.Main contents and contributions of this study are as follows:(a)To arrive at the model of the ultrasonic motor containing the dead zone and the temperature drift characteristics,the rotating coordinate system for the ultrasonic motor is initially given.The influence factors of the dead zone and the temperature drift characteristics are then analyzed.The model is subsequently deduced with the aid of the Hamilton's principle.(b)To compensate the dead zone of the ultrasonic motor,the concept of the selfadjusting standing wave is proposed,which is generated by adjusting the amplitudes of the input voltages in the cosine and sine forms.The self-adjusting standing wave prevents the gap between the stator and the rotor from being excessively shrink.The dead zone can be then avoided.The amplitude of the self-adjusting standing wave oppositely varies with the rotating speed,which can therefore compensate the dead zone and simultaneously maximize the efficiency.There is an existing generation method of the self-adjusting standing wave,where the phase difference of the input voltages is adjusted.The amplitudes are however fixed even though the velocity approximates to zero.Then the efficiency when applying the presented compensation method is superior under same output power level.(c)The optimum frequency tracking scheme is proposed to compensate the temperature drift characteristics.The frequency of the input voltages are applied to track the newly-discovered optimum frequency,at which frequency the ultrasonic motor maintains the minimum power consumption.The proposed scheme is superior to the existing resonance and antiresonance frequency tracking approaches,in terms of maximizing the efficiency,reducing the heat generation and the temperature rise.(d)The interaction effect between the self-adjusting standing wave and the optimum frequency tracking scheme is initially analyzed.To simultaneously compensate both the dead zone and the temperature drift characteristics,the compound compensation scheme is subsequently presented.The amplitudes and the frequency are applied as the control variables to introduce the self-adjusting standing wave,seek and track the optimum frequency of the ultrasonic motor.All of the to-be-designed parameters of the compound compensation scheme have clear physical explanations.And the structure of the proposed compound compensation scheme is concise.The presented scheme is therefore easily to be realized.(e)To implement the compound compensation scheme,the quarter-phase three-level switching circuit based driving system is presented,which maintains lower consumption and subsequently higher energy transfer efficiency in comparison with the existing driving systems.Experiments are subsequently carried out to verify the merit of the proposed scheme under load over a range of working frequencies.Experimental measurements infer that the self-adjusting standing wave can efficiently compensate the dead zone and increase the speed ratio,tracking the optimum frequency can maximize the efficiency of the ultrasonic motor even under the different velocity references,the different amplitudes of the input voltages,or the different load.The presented scheme and driving system are also suitable for driving other kinds of the piezoelectric actuators which considers the compensation of the dead-zone and the temperature drift characteristics as a serious problem.