Laser Seam Finder Outperforms Mechanical Version

Ruth A. Mendonsa

Some time ago, Weibull Workshops, a Swedish manufacturer of chassis for heavy vehicles such as trucks and buses, replaced its mechanical arc welder systems with a Motoman K10 arc welding robot, but the company continued to use a mechanical means to find seams. It soon became clear that the mechanical device was not flexible enough to accommodate variations in size and position of the joints to be welded, nor did it provide the quality and consistency required. The vehicle manufacturer found the accuracy and flexibility it needed in the Selcom Laser SeamFinder, which it was able to integrate into its arc welding robotic control system.

Heavy-vehicle manufacturer Weibull Workshops chose Selcom's Laser SeamFinder to improve its welding process. To contribute to this section, contact Ruth A. Mendonsa, applications editor, at (413) 499-0514, or fax, (413) 442-3180.

The SeamFinder consists of a noncontact laser sensor and software that processes and evaluates the sensor data and then transmits the results to the Motoman controller. According to Martin Sanden, business area manager for robotic guidance systems at Selcom AB, the SeamFinder can locate a joint and define it in two dimensions in about 1 second. The system also can measure in three dimensions.

The sensor is based on laser triangulation: It projects a fixed beam of laser light to the weldment 32,000 times a second. When the laser light hits the surface, it scatters in all directions. The sensor collects part of this scattered light and focuses the image of the light spot onto the position-sensitive detector in the head. As the relative distance between the sensor and welding surface changes, the position of the image on the detector also changes.

The robot is programmed with plate-thickness and type-of-joint parameters. During the search process, one or more points along the joint are defined in two or three dimensions. All searches are accomplished without actuating the arc. SeamFinder enables the robot to position the welding tip at the exact spot for welding.

Selcom says that its system can be integrated with almost any robot arc welding system with a standard digital input/output interface. It includes an exhaust and inlet for dust protection and cooling, and is insensitive to normal welding smoke and excessive electromagnetic interference.

Weibull Workshops' project manager, Peter Skorde, said that the SeamFinder allows the company to weld seams faster and with more accuracy than before, and it accommodates the variations in size and position of the joints. The company says that since its installation, search times have been significantly reduced, fillet joints are much higher in quality and overall operating costs have decreased.