| The precision linear motion platform has become a research hotspot in recent years.The traditional electromagnetic motor usually has the disadvantages of the complex structure,poor anti-interference ability and the low resolution.Because of the advantages of the no electromagnetic interference,simple structure,high resolution,fast response speed and the self-locking ability,piezoelectric actuator has the significant application value in precision linear motion platform.Piezoelectric actuators are usually divided into inertial piezoelectric actuators,inchworm piezoelectric actuators,direct-drive piezoelectric actuators and ultrasonic motors.Because of the advantages of the fast output speed,large output load,unlimited travel and the flexible design,ultrasonic motor has attracted the attention of many domestic and international scholars in recent years.A series of key technologies related to piezoelectric ultrasonic motor are studied to meet the actual needs of precision linear motion platform in this work.Firstly,this thesis analyzes the working modes of piezoelectric ceramics,the excitation methods of ultrasonic motor’s bending vibration and the related theory of bending vibration.The basic configuration of a sandwich ultrasonic motor based on the first composite bending vibration of the cantilever beam is proposed.The working principle of the ultrasonic motor under continuous AC excitation signal and pulse AC excitation signal is analyzed.The modal analysis and transient dynamics analysis of the ultrasonic motor are carried out based on the finite element method.Then the ultrasonic motor’s specific structural parameters are determined.Finally the linear motion platform is designed according to the designed ultrasonic motor.Then,the experimental prototype of ultrasonic motor is made,and its vibration characteristics and impedance characteristics are tested to verify the results of finite element simulation analysis.The equivalent electrical parameters of ultrasonic motor are obtained,and the impedance matching is completed.In order to select the most suitable friction material combination for the linear motion platform,the mechanical output performance and long-time output speed stability of the ultrasonic motor under different common friction pairs are investigated through experiments.The test results show that the Zr O2/Si3N4 friction pair is the most suitable choice for the developed piezoelectric ultrasonic motor.Then,the linear motion platform is made,the mechanical output characteristics of it such as the speed versus frequency characteristic,the speed versus voltage characteristic,the speed versus load characteristic and the displacement resolution characteristic are studied.The test results show that the linear motion platform’s output speed can reach 426.2mm/s when the voltage peak-to-peak value is 200V and the frequency is 21.9kHz.When the peak-to-peak voltage is 200V,the maximum load mass of the platform is over 23kg.The maximum displacement resolution of linear motion platform is 85nm under the excitation of pulse AC signal.Finally,the special driving power supply is maded for the speed closed-loop control of the linear motion platform.And the speed closed-loop control system is built.The experiments of the speed step control and the speed sinusoidal tracking control are carried out for the linear motion platform at the low speed.The test results show that:when the target value of the controled speed is 3mm/s,the output of the linear motion platform is relatively stable,and the speed fluctuatio n percentage in the stable operation stage is less than 10%.When the amplitude of the tracking speed is 5mm/s and the frequency is 1Hz,the average maximum speed deviation is less than 20%.There is no obvious speed dead zone and phase lag,which indicates that the linear motion platform’s ability of tracking the low sinusoidal speed is great. |
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