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Laser Vision Aids Robotic Welders

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Michael D. Wheeler

PARIS -- Shipbuilding plants have sought welders with top-notch skills for years. Now, thanks to photonics, a new breed of welder -- the robotic kind -- could rival humans in expertise and efficiency.
The French Welding Institute developed RoboKid, a robot with a vision system that is based on laser triangulation, a distance measurement technique involving lasers and photodetectors. A rangefinder mounted on the robot's welding torch emits laser light from several perspectives.
Depending on the vision system, Servo-Robot Inc. in Boucherville, Quebec, Canada, installs one of two types of semiconductor laser diodes: one emitting at 780 nm or another emitting in the 810- to 830-nm range. The laser light bounces off the metal part that the robot will weld. The time it takes the laser to reflect to the 3-D camera head determines the location of the part. Software interprets the measurements, which come in at a rate of 40 images per second -- enabling the robot to "see" what it welds and automatically adjust the laser torch so it remains at the center of each weld.

Servo-Robot Inc.'s 3-D laser camera has brought a new level of accuracy and adaptability to robotic are welding.
The "seeing" robots already have found a home in shipyards in Cherbourg, France; at Framatome, a manufacturer of nuclear reactors; and at several automotive assembly plants. Manufacturing Engineers at each site have fitted the robots with a PC, so they can calculate welding strategies for their particular application. The com- puter also provides camera control and image processing capabilities that aid production.

By incorporating vision in the robot, scientists have eliminated a number of constraints that have hampered its "blind" predecessors. Those robots performed along preset trajectories and required reprogramming any time a different task was required, which often led to lengthy and costly shutdowns while engineers made the necessary adjustments to the software.
Jean-Louis Bréat, a member of the French Welding Institute, said that using a vision system makes it possible for the robot to adjust to real-world conditions. He said it enables accurate calculations of volumes and pass conditions, while the quality and regularity of the molds surpass the results obtained in manual welding.

Photonics Spectra
Feb 1998
industrialResearch & TechnologySensors & DetectorsTech Pulse

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