The Digitization Basis Study Of Welding Power And On-line Quality Monitoring

With the development of digital technology, industrial production sets a still higher demand on welding equipment, which is called"industrial sewing machine". Advanced welding equipment is the one of key factors to improve the welding technological property. Aiming at the technology characteristics, advanced control theories and appropriate control algorithms are used to realize the advanced welding equipment. In this paper, based on digital welding, digital welding power source, mathematical model of GMAW welding process, characteristic analysis of welding signals(current, voltage, welding speed, etc), prediction of welding quality, and on-line monitoring are studied.Based on dual processors of digital signal processor (DSP) and single chip microcomputer (MCU) a multi-function arc welding power source is made. Main circuit, digitization control circuit, driving circuit for IGBT, feedback circuits for current and voltage, circuit for man-machine interface system, circuit for wire feeding system and protection circuit are designed. In addition, system software is programmed and debugging the whole system.The study of CO2 arc welding short-circuit waveform control is done. The discussion of ideal voltage waveform and current waveform, analysis of characteristics of welding parameters, and further study of scheme of current waveform control in CO2 short circuit transition welding are taken. Three control schemes are designed and compared.For the application of advanced control methods in welding power source circuit system, arc system, forces on droplet, droplet transition and melting rate of welding wire in GMAW welding process are analyzed based on he welding parameter and its mutual relation. Mathematical model of GMAW welding process is established. By the feedback linearization method of differential geometry, Equivalent linear system is achieved by using homeomorphism mapping of models of current and arc length, which makes the complicated nonlinear control problem transformed into a simple linear control problem. Because of the decreasing of complex degree of controller design, control Effect improves. The method of sliding mode variable structure control is used in the control of welding current and arc length. And it is simulated with MATLAB. Time domain characteristics, frequency domain characteristics and time-frequency domain characteristics of the current and voltage signals are studied by using advanced signal analysis, such as correlation analysis, fourier spectrum, short-time fourier, power density spectrum, wavelet analysis and so on. The understanding of current and voltage signals is enriched.Prediction of weld line size is achieved by sample training at BP algorithm. Because of the existing problems of general BP algorithm, operation speed of BP Network is improved by using adaptive learning rate and additional item. In addition, weld size is predicted by using support vector machine(SVM),which is trained with linear kernel function, polynomial kernel function, RBF kernel function and ERBF kernel function. Real-time monitoring of welding quality and on-line control of welding process are achieved by predicting the weld appearance based on neural network model.