Multi-Information Sampling System Of Resistance Spot Welding Quality Based On Dual-Microprocessor

Multi-information sampling system of resistance spot welding quality based on dual-microprocessor has been designed in this paper. The purpose of selecting a dual-microprocessor lies in conquering defects of single-microprocessor in real time measure and control, avoiding expensive problem of high performance microprocessor. The dual-microprocessor could not only sample more information, but also expand intelligence control functions in the future. AT89S51 chip computer (a kind of microprocessor) was used because it has wide-ranging application, powerful functions and cheap price.3 parameters (welding current, dynamic resistance and electrode displacement) were sampled. Type of sensors, adjustment of analog signals, A/D transform, measuring error and EMC(Electrical Magnetic Compensation) were discussed. Curves of resistance and electrode displacement were made by experiments. The regulars of curves have been analyzed in the normal and the expulsion.Control function was realized by half-period method, and control object is AC 50Hz spot welding machine. Chip computer controls welding current each 10ms by PID, corrects the current error and realizes constant current regulation.Constant and non-constant current regulation has been compared to estimate control effect. The results indicate that constant current regulation can compensate for the changes of voltage and reactance. For example, if net voltage fluctuates±5%, the current of non-constant current regulation fluctuates±15% whereas the current of constant current regulation does within±0.35%. Welding nugget sizes of constant and non-constant regulation fluctuate respectively 8% and 30% during 3-layer-board welding.However, the shunt and the electrode wear are not compensated by constant current regulation because of single-close-loop control of current. So a PI controller based on constant displacement speed was designed. It was found that the controlling of constant displacement speed can compensate the influence of shunt and electrode wear. It is fortunately that the system has the functions of multi-information sampling, the curves of the dynamic resistance and the electrode displacement have also been obtained. So multi-information fusion technology, intelligence control technology, etc., can be used to improve the level of monitoring and controlling of resistance spot welding quality.