Optical pick=up for surveying linear discontinuities - and controlling welding heads, providing more sensitivity than mechanical followers

摘要

An optical pick-up with a transverse scanning movement surveys and/or follows long narrow discontinuities. It follows the line of a joint to be welded, guiding the welding head. A thin pencil of laser light is widened and passed through a separating film, then focussed into an elliptical spot on the surface to be inspected, its major axis parallel to the discontinuity. The reflected beam is deflected by the separating film and focussed onto an optical fibre, which carries an image of the surface to an opto-electronic detector. An amplifier produces a representative voltage signal which is fed to a computer to control the welding head. For reliability, welding heads, particularly plasma units, must be guided precisely relative to the joint line. This device is more sensitive than mechanical followers, or conventional optical pick-ups. It is not sensitive to surface brilliance or to interference from heavy welding currents.