Research On Frequency Automatic Tracking Technology Of Pulse Ultrasonic Generator

Power ultrasonic machining technology is an important branch of the current ultrasonic machining technology.Because of its complex working conditions,the resonant frequency of ultrasonic transducer often drifts in the processing process,which affects the quality of ultrasonic machining.In order to solve the problem that the resonant frequency of transducer drifts with the load in the process of ultrasonic machining,an automatic frequency tracking system of ultrasonic generator is designed.Based on Mason’s equivalent circuit theory,the frequency equation of the loaded ultrasonic machining system is established,and the relationship model between the resonant frequency of the loaded transducer and the frequency modulation inductance is obtained.According to the results of theoretical analysis,the compound frequency tracking scheme is developed,and the corresponding hardware circuit and software program are designed to realize the automatic frequency tracking function of ultrasonic generator.The main research contents of this paper are as follows:1.The frequency modulation characteristics of ultrasonic transducer are analyzed theoretically.Based on the Mason equivalent circuit,the frequency characteristic equation of the transducer was established,and the series resonant points were selected as the working frequency points of the ultrasonic machining system.Combined with the resonant characteristics of the transducer,the relation expression of the load,the frequency modulation inductance and the resonant frequency of the ultrasonic transducer was obtained.Based on the results of theoretical analysis,a compound frequency tracking scheme is developed,which can effectively solve the problem of resonant frequency drift of the transducer loaded with different tool bars and ensure the working performance of the ultrasonic machining system.2.According to the parameters of the transducer to be matched,the hardware circuit of the ultrasonic generator is designed and selected and simulated.At the same time,the main program,frequency tracking subroutine and human-computer interaction program are designed and compiled.In this paper,the ultrasonic generator is divided into two parts: the main circuit system and the frequency automatic tracking system.Electrical isolation is required between the two parts of the system.The main circuit system is a large current working board,which mainly realizes the function of rectifying and filtering the 220V/50 Hz mains power into direct current first,and then inverting the direct current into supersonic alternating current.The frequency automatic tracking system is a small current working board.Its main function is to search and track the resonant frequency of the transducer based on STM32 single chip microcomputer.3.Set up the frequency automatic tracking system test platform.Based on this platform,the frequency modulation characteristic analysis test of the transducer and the frequency tracking effect test of the automatic frequency tracking system are designed.The results show that the influence of load on the resonant frequency of the transducer can be effectively compensated by adding the frequency modulation inductor into the matching loop.The frequency automatic tracking system designed in this paper has good tracking performance.