<title>SCOUT seam follower</title>

Abstract

SCOUT a seam tracker system designed for precise machining with the capability to position the axes ofa industrial robot or gantry in space (three dimensions). This system was developed to meet the positioning accuracy of±O,05 mm (±0,0127 inch) and path above 20m/min (800 1PM) for laser welding as well as e.g. sealing or gluing. With SCOUT system it is not necessaiy to define a welding path with the very time consuming teachin process. SYSTEM COMPONENTSSCOUT is an image-processing system for three-dimensional seam following which comprises a sensor head and an eva luation unit. The opto-electronic sensor head, mounted directly on the robot's band, i.e. preceding the 1aserwelding nozzle, projects a line pattern onto the workpiece. An industrial camera generates the video image oftbis line pattern, which is digitized and then evaluated by the SCOUT real-time image-processing system. Hardware components ofthe SCOUT computer, based on VME bus, are system processor (CPU), frame grabber card (IPP) and the actual real-time signal processing unit (SPU). Hardware core are ASIC's for fast grey-scale data reduction and transfer to six DSP's in parallel architecture. The three-dimensional seam data (X Y, Z) and the orientation ofthe workpiece are transmitted to robot I gantiy control via special interface. A variety ofstandard interfaces allows control ofexternal equipment e.g. high power laser or filler rod feed. PRINCiPLE OF MEASUREMENT 1 Redundant light section methodA pattern offive parallel lines is projected at an angle onto the contour ofthe workpiece. A vertical looking CCD camera generates the video image ofthis pattern. The step at the seam is identified as offset ofpart ofthe line pattern The number offive lines was selected to eliminate ambiguities and to generate max five points along the seam vithin one video frame. Minimum three lines have to be identified to utilize this particular video frame. The density ofdata points along the seam is extremely high and data points ofone video frame overlap the preceding frame mostly, so that even the lack ofcomplete frames does not affect systems reliability and precision. Only path velocities above 40m/min (1570 1PM) will not generate overlapping video pictures. Additionally the position ofthe five lines enables the image processor to generate information of all three coordinates of the seam in space !!4bothangles ofthe surface normal in the center oftbe video picture. Grey-scale evaluationGrey-scale evaluation is applied for buttjoint or scribed line following. Contrast enhancement is achieved by homogenious illumination of sensors field of view. This way X and Y coordinates of the seam are defined. Combination of both, light section and grey-scale method allowes complex 3D seam following along butt-joint or even scbed lines. 0819413275/94/$6.O0 SP1E Vol. 2062 / 81 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/20/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx