Development Of The Driving Power For Ultrasonic Plastic Welding Instrument

During ultrasonic welding of plastic parts,the heat generated by the transducer will cause the resonance frequency to drift,causing the system to work in a non-resonant state,resulting in increased drive power loss and unstable output power,which seriously deteriorates the quality of plastic welding.Therefore,it is important to study the ultrasonic welding drive power supply that can perform fast frequency tracking and continuously adjustable output power.The thesis studies the problems of unstable output power,slow frequency tracking response,and sudden loss of load due to the traditional ultrasonic plastic welding drive power supply.A 2kW ultrasonic plastic welding drive power supply is designed.Firstly,based on the analysis of the driving power requirements of ultrasonic plastic welding,the main circuit topology analysis was carried out.Based on the design requirements,a full-bridge uncontrolled rectifier circuit was determined,and a full-bridge inverter circuit with an IGBT as the switching tube was designed.Aiming at the problems of filtering and resonance matching in the traditional matching network,an LCL type matching circuit is designed,which has the advantages of filtering and good resistance.Secondly,the overall structure of the drive power control circuit is designed.The control system uses DSP as the main control chip,and designs voltage and current sampling circuits,signal conditioning circuits,phase detection circuits,true rms conversion circuits,and drive circuits.After that,based on the integral separation PI control and digital frequency synthesis technology DDS,the automatic frequency tracking control design was performed,which solved the problem of slow frequency tracking response and volatile lockout of the traditional ultrasonic drive power supply,and the frequency resolution could reach 1Hz.Aiming at the problem of output power adjustment,phase shift control method is adopted,combined with soft switching technology to reduce switching loss.The error signal is obtained by comparing the real-time power with the given phase,and the phase-shift angle signal is output through the PI controller,and the UC3879phase-shift control IC sends out the switching tube driving signal,so that the output power is continuously adjustable and stable from 0kW to 2kW.Finally,MATLAB/Simulink was used to simulate and analyze the design of the drive power supply.The simulation verified the fast accuracy of the automatic frequency tracking and the continuously adjustable output power.An experimental platform for ultrasonic drive power was set up,and the designed ultrasonic drive power was tested and analyzed.The experimental results verify that the designed drive power can achieve rapid frequency tracking and continuously adjustable output power.