Light scanning device for determining the condition of a surface with a light concentrator

Claim 1

A light scanning device for determining the condition of a surface comprising means for forming a scanning line on the surface of an article and an optical system for concentrating, at a point-like concentration zone, all the light beams which lie in a plane extending parallel to the scanning line and which leave the surface, depending on the surface condition, which in a specific direction corresponding to a normal reflection, or in a direction which deviates somewhat from this as a result of surface faults; wherein said point-like concentration zone is located, depending on whether the light beams have the normal direction or deviate in angle somewhat therefrom, either at a normal position on the light entry surface of a transparent light concentrator or displaced somewhat relative thereto in the direction of the light streak; wherein the light concentrator has outer mirrored side surfaces and tapers away from the concentration zone to a desired light exit surface where an areal photoconverter, in particular a photomultiplier is arranged; and wherein a dark field stop is arranged at the normal position for the light concentrator and preferably also in a small angular range about this normal position, said stop permitting only light beams which leave the surface above a predetermined angle of deviation relative to the normal direction to enter into the light concentrator, characterised in that the externally mirrored side surfaces (15) of the tapering light concentrator (11) are increasingly convexly curved in the direction away from the light entry surface in such a way that at least some (17) of the light beams which fall in the range of the dark field stop would fall, if the dark field stop were imagined to the missing, on the convexly curved side surfaces (15) at angles so steep that they would be reflected backwardly in the light concentrator without reaching the desired light exit surface (13); and in that all the light beams which enter alongside the dark field stop (14) into the light entry surface (12) of the light concentrator (11) impinge on the mirrored side surfaces (15) at such shallow angles that they all reach the desired light exit surface (13).