Research On Parallel Resonant Frequency Automatic Tracking System Of Ultrasonic Transducer

Ultrasonic transducers have been widely applied in power ultrasonic fields,such as ultrasonic welding,ultrasonic machining,ultrasonic cutting and so on.However,the resonant frequency of the ultrasonic transducer will be shifted with the variation of temperature,environment and other factors.Therefore,it is one the keys of making the ultrasonic transducer work efficiently and stably to realize the frequency automatic tracking function.In this paper,from the frequency automatic tracking point of view,the frequency automatic tracking system of ultrasonic transducer is designed based on the STM32 microcontroller and the DDS chip AD9833.The research contents of this paper mainly include:1.The impedance characteristics near the parallel resonant frequency is analyzed.The principles and application ranges of the minimum current method and the phase difference method are studied based on the analysis.Thus a new strategy of parallel frequency tracking combining the minimum current method and the phase difference method is proposed.2.The circuit generating symmetric PWM wave of high frequency resolution is designed.It can adjust the duty ratio of the PWM wave digitally.Thus the power inverter circuit driven by the generated symmetric PWM can achieve precise control of the frequency and power of the output signal.3.The hardware module of ultrasonic transducer frequency tracking system is designed,including a core control board based on STM32,a symmetric PWM generating circuit based DDS chip AD9833,a signal feedback circuit and a human-computer interaction circuit.4.The parallel frequency automation tracking program is designed base on the analysis of the variation characteristics of the current and phase difference when the ultrasonic transducer is loaded and unloaded,respectively.5.Some anti-jamming and reliability measures have been taken to ensure the system to run reliably and stably in terms of both hardware and software.6.An experimental platform of the parallel frequency automatic tracking system is set up,and the debugging and testing work is carried out.Experimental results show that the symmetric PWM generating circuit based on AD9833 is easy to control,and the resolutions of output waves frequency and duty ratio are high;the strategy of parallel frequency tracking combining the minimum current and phase difference method can work fast and stably.