Research And Development Of Ultrasonic Power Supply Based On Frequency Auto-Tracing And Constant Amplitude Control

ABSTRACT:In recent years, the ultrasonic technology develops very fast and is widely applied. Especially in ultrasonic machining, the application of high-power ultrasonic technology is used more and more extensively. This in reverse promoted the study on the ultrasonic power supply. In the study of ultrasonic power supply, frequency auto-tracing and constant amplitude of vibration control are two key subjects. Plenty of researchers are performing deep researches and improvements continually.In this paper, based on ARM Cortex-M3architecture embedded microprocessor STM32, a new type of intelligent high-power ultrasonic power supply has been developed. Main research contents include:Firstly, equivalent circuit characteristics of ultrasonic transducer was analyzed. Based on the equivalent theory of mechanics and electricity, the multi-peak feature and phase difference of voltage and current related characteristic were also analyzed. Thus, based on current and the phase difference of current and voltage in the transducer circuit, a frequency auto-tracing solution was proposed, which can not only make the power supply adapt to transducers with different resonant frequency by automatically searching the resonant frequency of the transducer before working, but also trace the resonant frequency drift accurately during operation. In addition, based on the relationship between RMS current of the transducer circuit and the amplitude of transducer vibration, a constant amplitude of vibration control solution have been designed to keep the amplitude constant.Secondly, the major circuit was established, including rectifier with Buck-chopper, Full-bridge inverter, matching network, feedback system and control system. A rectifier with Buck chopper accomplished adjustable power output. PWM wave generator based on DDS technique, dead time forming circuit based on RC time-delay circuit and IR2110driver chip together to drive the full-bridge inverter to realized high-power supersonic AC output with adjustable frequency. The design of the inverter made the controller be able to fast and accurately trace the resonant frequency with just simple procedures. In the feedback system, a phase difference detecting circuit designed as per feedback control plan simplified the design of software, which made the control efficient and reliable.Thirdly, according to the characteristics of ultrasonic power supply, the control system software has been programmed, including frequency auto-tracing and constant amplitude of vibration control program. Because the each part of the hardware has been optimized, the software structure thus became very simple and stable.Fourthly, the exact hardware and software of the ultrasonic power supply were made based on the theoretical design. And a large number of experiments were performed.Experiments showed that, this ultrasonic power supply could make the transducer system work at the resonant state quickly and accurately, and the vibration is stable. Both the hardware and software can achieve the expected functions.