Preweld Joint Tracking System For Weld Path Teaching

Precision welding of aircraft engine assemblies requires accurate tracking of the weld joint under conditions of positional uncertainty. Real-time laser based joint tracking systems are becoming available but currently cost, accuracy, field-of-view, and applicability to specific joint types, weld processes and robot controllers limit their use. When tracking prior to welding is a feasible alternative to real-time tracking, these issues can be addressed. The software and hardware for such a system is described. The system can track weld joints in two dimensions and offset weld path programs to compensate for assembly and/or fixturing errors. The technique is applicable to both plasma arc welding (PAW) and tungsten inert gas (TIG) welding as the sensor is mounted ahead of the weld torch. The weld path tracking software refines a coarsely taught weld path. To enhance tracking accuracy, reliability and speed, the joint tracking algorithm searches for the joint along a line. Search direction is calculated as the normal to the coarse path trajectory. Search direction is accomplished by rotating a window of the image. A prototype system has been implemented. The system consists of a welding robot, a custom vision system, a CCD camera and fiber optic incandescent lighting. The system has been used to successfully weld production assemblies.