LIGHT CURTAIN WITH PERIODIC LIGHT TRANSMITTER ARRANGEMENT

A light curtain apparatus is described which does not require a mechanically moving light deflecting element such as a mirror wheel. Instead a number of diodes (11') are arranged in a row (11) and are sequentially energized so that light from each diode in turn passes through an objective lens (12) and an aperture diaphragm and falls on a strip-like concave mirror (14). The diode row is arranged at the focal plane of the objective (12) so that the light emerging from the objective (12) is essentially parallel light. The aperture diaphragm is located in the focal plane of the strip-like concave mirror so that the parallel light emerging from it is reflected at the strip-like concave mirror (14) in a direction parallel to the optical axis (19) and focussed in a plane corresponding to the plane of the aperture diaphragm (20) which is also the focal plane of individual lenses (16') arranged in a row within the image space of the strip-like mirror (14). Thus the light emerging from the individual lenses (16' ) of the lens row (16) is a parallel beam of light (17) which appears to be continuously displaced parallel to itself as a result of the sequential energization of the diodes. At the far end of the monitored region (18) the parallel light can either be detected by a detector (25) located there or returned by a retroreflector (24) back to a photoreceiver (27) located between the strip-like concave mirror (14) and the aperture diaphragm (20).