Contact Information • A9 Chair Bill Rippey Telephone 301.975.3417 NIST 100 Bureau Drive, MS 8230 A SYSTEM FOR REAL-TIME CONTROL OF GAS METAL ARC WELD PROFILE D.M. Barborak, H.W. Ludewig, R. W. Richardson*, D.F. Farson, and S. Yurkovich ABSTRACT The objective of this research was to investigate the use of a unique, hybrid robotic Gas Metal Arc Welding control system for robustly controlling weld shape of single-pass fillet welds in the presence of common production perturbations and disturbances. Such a system could improve the fatigue properties of weldments, increasing service life and decreasing design requirements. A hybrid robotic control system was developed consisting of a 6-axis articulated arm welding robot, laser-based machine vision system, and weld profile controller. The control architecture consisted of integrated feedforward and feedback, multi-input/multi-output control loops that ran simultaneously to perform joint finding, joint tracking, modified fill, contact-tip-to-work (CTWD) regulation, and weld symmetry control. Complex weld profile features such as weld symmetry and weld profile were addressed as reference tracking and disturbance rejection control problems. KEYWORDS Robotic GMAW, Fillet Weld, Weld Geometry, Weld Profile, Feedback Control, Feedforward Control, Adaptive Fill, Joint Finding, Joint Tracking, Weld Symmetry Control. INTRODUCTION The surface profile of a weld deposit and presence of any discontinuities are very influential to its fatigue performance. Robotic arc welding relies on process set points derived during the development of an optimal welding procedure to produce a desired weld profile with minimal. discontinuities. Classified as open-loop control, this technique assumes all the process inputs and disturbances remain fixed and produce a repeatable output in terms of weld quality. Any error, change in plant dynamics, or disturbance to the process is likely to cause deterioration in weld quality which may require expensive rework or cause premature failure. The objective of this research has been to investigate the application of a hybrid GMAW control system for robustly controlling the weld profile of single-pass fillet welds in the presence of common production perturbations and disturbances. The purpose of this is to control fatigue properties of weldments to increase service life or decrease design requirements. It has been shown that fatigue properties are strongly affected by weld geometry and discontinuities12. For fillet-welds, this includes all geometrical surface aspects of the weld face and weld root including any discontinuities. This application of a hybrid weld profile control system requires integration of multi-input/multi-output, feedforward and feedback control loops to perform joint tracking, adaptive fill, contact-tip-to-work (CTWD) regulation, and weld symmetry control. Complex weld profile features such as weld symmetry and weld profile are addressed as reference tracking and disturbance rejection control problems. Robustness to disturbance WeldWare, Inc., Columbus, Oh. Caterpillar, Inc., Peoria, Ill. The Ohio State University, Columbus, Oh. |