CMAC-based real-time calculation of the effective welding current during A.C. resistance spot welding

Real-time measurement of effective current is essential for fine control of welding process. However, conventional methods cannot simultaneously satisfy the accuracy and the real-time requirements. On the basis of the welding transformer circuit model, a new measuring method is proposed. This method measures the peak value of the welding current and then multiplies a coefficient K to obtain the root-mean-square value, which enables the processor to calculate the half-wave effective current at the moment of peak current. A Cerebellar Model Articulation Controller(CMAC) model is off-line trained and used online to compute K, which is a nonlinear function against the firing angle and the peak current angle. A DSP-based resistance spot welding monitoring system is developed to perform CMAC computation. Experimental results suggest that this measuring method is feasible.