Adaptive Synergic Pulse MIG MAG Microcomputer Control System

Literature Overview

This paper by Wang Qilong, Zhang Jiuhai, and Zhang Long, published in Welding in 1990 (Issue 9, pages 1-5), presents the development of an adaptive synergic pulse MIG/MAG welding microcomputer control system at Harbin Institute of Technology. The system employs an optical encoder for wire feed speed signal acquisition and uses pulse peak voltage as the arc voltage feedback signal. This work represents an important contribution to welding automation technology, addressing the challenge of maintaining consistent weld quality in the presence of process disturbances.

Control System Architecture

The adaptive synergic pulse control system is built upon the concept of synergic control, where multiple welding parameters (current, voltage, wire feed speed, travel speed) are coordinated to maintain a constant welding current density. Traditional synergic control assumes that welding current density is the primary determinant of weld quality and adjusts parameters proportionally to maintain it. The adaptive extension adds feedback control for arc length regulation, compensating for disturbances that affect arc length without changing wire feed speed.

The optical encoder provides a precise measurement of actual wire feed speed, eliminating errors associated with motor position feedback. The pulse peak voltage serves as a proxy for arc length, since arc voltage is directly related to arc length in pulse welding processes. This signal is used in a feedback loop to adjust the base current or pulse parameters to maintain the desired arc length.

Adaptive Control Principle

The adaptive capability of this system distinguishes it from conventional synergic control. In conventional synergic control, if a disturbance changes the arc length (for example, due to workpiece misalignment, surface contamination, or electrode wear), the system does not compensate, leading to variations in heat input and weld geometry. The adaptive system detects such disturbances through the arc voltage feedback and adjusts parameters to restore the desired arc length.

The control algorithm operates in two levels. The first level maintains synergic parameter relationships based on the commanded wire feed speed, ensuring consistent current density and metal transfer characteristics. The second level adjusts the base current or pulse frequency to compensate for arc length deviations detected by the pulse peak voltage signal. This dual-level control provides both the productivity benefits of synergic control and the robustness of adaptive control.

Process Performance Evaluation

Process trials demonstrated that the adaptive system exhibited strong anti-interference capability, stable welding process, no spatter, and aesthetically pleasing weld geometry. These results confirm the effectiveness of the adaptive control strategy for pulse MIG/MAG welding. The absence of spatter is particularly significant, as spatter is a common problem in pulse welding due to incomplete droplet detachment or arc instability.

The system hardware includes a microcomputer for control algorithm execution, a signal conditioning circuit for sensor signal processing, a power amplifier for output signal generation, and interface circuits for communication with the welding power source and wire feed motor. The main program flow includes initialization, signal acquisition, control algorithm execution, and output signal generation, operating in real-time to maintain welding stability.

Engineering Practice Considerations

For pipeline and fitting fabrication, the adaptive synergic control approach has significant implications for automated welding systems. In the production of ERW and HFW welded pipes, the welding process operates at high travel speeds with limited opportunities for manual intervention. Adaptive control systems can maintain consistent weld quality despite variations in material thickness, surface condition, and joint fit-up.

The optical encoder-based wire feed speed measurement provides a reliable reference for parameter coordination, which is essential for maintaining consistent weld metal deposition. The pulse peak voltage feedback for arc length control is particularly useful in applications where joint geometry varies, such as in the welding of pipe fittings with different wall thicknesses and diameters.

Study Insights and Outlook

This 1990 work represents an early application of microcomputer-based adaptive control to welding processes, predating the widespread adoption of such systems in industrial welding. The system design philosophy of combining synergic parameter coordination with adaptive arc length feedback remains relevant to modern welding control systems. For contemporary engineers, the key insight is that adaptive control can significantly improve process robustness without sacrificing the productivity benefits of synergic parameter management. The principles established in this work have been extended in subsequent research to multi-axis control, neural network-based adaptive systems, and data analysis-enhanced process monitoring, forming a foundation for intelligent welding systems used in modern pipeline and fitting fabrication.