Hole seeking apparatus for material webs

摘要

Hole seeking apparatus for material webs is disclosed which features a light source (11) for projecting a light beam onto a mirror wheel arrangement (15) located optically in front of a concave mirror (17) so as to produce a scanning beam in the image space of the concave mirror. The scanning beam is continuously displaced parallel to itself so as to periodically scan along a scanning path on the material web (18). The mirror wheel arrangement (15) consists of two substantially identical mirror wheels (15a, 15b) which lie coaxially on one another and which are displaced by a half pitch.;The dimensions of the light bead (16) at its point of incidence on the mirror wheels (15a, 15b) and the optical geometry of the apparatus are selected to avoid light being scattered at an edge of either of the mirror wheels and passing to either side of the web. Scattered light is thus prevented from falling on a light receiving device (17) arranged behind the web and intended to detect the presence of holes therein. In this way the false recognition of a hole at the margins of web is prevented.;The invention also relates to a pair of mirror wheels for use in the hole seeking apparatus described above and in other beam scanning optical apparatus.