Process and apparatus for the non-contacting detection of edges of objects

TLDR: In this paper, an edge detector is used to measure scattered measured light along the main axis of the incident laser beam or at an angle which is smaller than that between the main laser light axis and the main working surface.

Abstract: In an edge detector process, a working plane (A) is scanned by a focussed light beam, e.g. a laser beam emitted by a light source (L) projected at an angle of typically 40° to 45° from the working plane. A first and a second detector (D1, D2) receive the scattered light from the working plane. The first detector (D1) is positioned behind a focussing imaging optics (0), such as an off-axis parabolic mirror, which is arranged coaxially, i.e. all round the laser beam, or is positioned below the emitted light beam relative to a main working plane (H). The second detector (D2) is positioned approximately over the light spot produced by the emitted light on the main working surface. The stray light measured by the first detector (D1) is therefore received at an angle to the main working plane, which is equal to or smaller than the angle between the emitted light and said plane. An apparatus according to the invention has imaging optics (0) and one of the detectors is positioned in such a way that it measures scattered measured light along the main axis of the incident laser beam or at an angle which is smaller than that between the main laser light axis and the main working plane.