INTELLIGENT SEAM TRACKING USING ULTRASONIC SENSORS FOR ROBOTIC WELDING

This paper presents a novel approach for seam tracking using ultrasoni cs. An ultrasonic seam tracking system has been developed for robotic welding which tracks a seam that curves freely on a two-dimensional su rface. The seam is detected by scanning the area ahead of the torch an d monitoring the amplitude of the waves received after reflection from the workpiece surface. Scanning is accomplished by using two ultrason ic sensors (a transmitter and a receiver) mounted on a stepper motor s uch that the transmitter angle is the same as the receiver angle. The motor is mounted on the end-effector just ahead of the welding torch a nd covers a ninety degree are in front of the torch. If there is no se am then the receiver receives most of the transmitted waves after refl ection, but if there is a seam then most of the transmitted waves are dispersed in directions other than that of the receiver. The system ha s been tested and is very robust in the harsh environments generated b y the are welding process. The robustness of the system stems from usi ng various schemes such as time windowing, a waveguide, air and metal shields, and an intelligent sensor manager. This ultrasonic system off ers some distinct advantages over traditional systems using vision and other sensing techniques. It can be used to weld very shiny surfaces, and is a very economical method in terms of cost as well as computati onal intensity. The system can be used to detect seams less than 0.5mm wide and 0.5 mm deep.