Piezoelectric Motors Based On Synchronized Switching Control And Periodical Mechanical Wave Synthesis

The demand for piezoelectric motors in modern scientific and industrial fields has grown because of their simple mechanism, compact structure, ultrahigh accuracy, rapid response, availability in vacuum, and immunity from magnetic interference. Given these advantages, piezoelectric motors have become viable candidates for use inspacecrafts, medical equipments,and among others.In order to achieve a balanced performance in terms of high force, speed and efficiency, and to solve the problem of service life of the sliding friction coupling transmission type piezoelectric motors, a new working principle and prototype development for piezoelectric motors have been explored and researched.The paper proposed a new piezoelectric motor driving theory based on the synchronous clamp control and harmonic vibration synthesis firstly. Themainachievements and conclusionsof the paper are as follows:First the synchronous-clamp-controlpiezoelectricmotortheorywas proposed. Althoughtheuseoftheelectronic switchisalready quitefrequent,amachine synchronizationclampswitchapplied in the motion controlof thepiezoelectrictransduceris the first caseintheareaofthe piezoelectricmotor. Thecontrol principlewas inspired fromthetraditionalelectricaloriginalSCRand itsapplication in AC-driven DC motor. According to the resemblance of electricalsystems andmechanical systems, we abstractedthephysical modelofthesynchronized switching controlpiezoelectric motor, and built its dynamic mechanical model. Thesynchronousclamp controlprinciplecombinestwo characteristics, namelythe resonantdriveofthepiezoelectric ultrasonicmotorandthecontrol mechanism of the inchwormmotor, whileweakeningthe disadvantages of bothsliding friction existing in the work process of the piezoelectric ultrasonicmotorandthe low quasi-staticfrequency of the inchworm motor.In this paper, the physical model and the dynamics model of piezoelectric motor based on synchronized switching control are represented, and the specific operation process are discussed in detail. In a working cycle of the piezoelectric motor, the expressions of the velocity, the displacement, the clamping time pointand the step with or without load are calculated respectively. We also analyzed the relationship between performances of the motor and the parameters, such as:working frequency, vibration amplitude and clamping force. We also point out that how the phase between the drive signal and the clamp signal influence the performance of the motor.The structures of the synchronized switching controlpiezoelectric motor were designed by finite element analysis. A prototype motor was fabricated, test and analyzed. The step size was approximately5μm. The maximum load capacity of the proposed motor reachedup to5N. It reached a maximum speed of8.2mm/s with a load of0.5N. The motor achieved a net efficiency of18.5%with a load of2N.If the power that the vibrator consumeduselessly in the air is subtracted, the mechanism can drive the load with an efficiency of72.5%.The experimental results show that the synchronous switching control piezoelectric motor hasexcellent characteristics.In the theoretical study of harmonic vibration combining type of piezoelectric motor, the waveform combining method based on multiple tuning fork structure (MTFS) is proposed for the first time. The theoretical basis of waveform synthesis is analyzed systematically, and the characteristic and the application of waveform synthesis are researched, the frequency coupling process based on MTFS is described in detail. A three level tuning fork is designed and manufactured with the help of ANSYS software, and the proportion ofthe reverse resonance frequencies of first, second and third order is1:2.00:2.99which proves the frequency is well coupled. With the same drive amplitude and corresponding resonant frequency, the Q factors are5617,4883and3515separately. Four typical resonant waveforms, sawtooth wave, square wave, sine half-wave rectifier and sine wave rectifier, are synthesized approximately, which proves the correctness and feasibility of theoretical analysis.Based on the theory of harmonic synthesis, the application on harmonic vibration combining piezoelectric motor is studied. According to the mechanism of inertia impact piezoelectric motor, the structure of the harmonic sawtooth waveform driven vibrational piezoelectric actuator is found out using finite element analysis. The detailed design method is given, and prototype of piezoelectric motor is manufactured and the performance is tested. The curves of speed and displacement of piezoelectric transducer were measured, and are well matched with the theoretical analysis. The unloaded speed of piezoelectric motor is26.2mm/s, andthe maximum load capacity reached up tol N. The results of the experiments proved that the proposed piezoelectric motor had a good overall performance.