Light curtain generating apparatus incorporating a cycle scale.

摘要

Light curtain generating apparatus incorporating a cyclical scale features a light source (19) for directing a beam of light to a mirror wheel (22) located substantially at the focus of a strip-like concave mirror (23) and which is adapted to deflect the beam through a variety of angles into the concave mirror to generate a moving scanning beam traversing the image space of the concave mirror and forming said light curtain. A beam divider (27) is arranged to intercept the scanning beam and to divide off and direct a part of the scanning beam to a cyclical scale generator (14) which features a light conducting rod (11) with a photoelectric detector (12) at at least one end thereof and a cycle scale (14) which extends substantially parallel to the light conducting rod and which modulates the light fraction passed from the divided off part of the scanning beam to the photoelectric detector to modulate the output signal therefrom. The cycle scale can conveniently comprise a bar pattern placed in front of the light conducting rod or a series of spaced apart inclined mirrors (16) at the rear side surface of the light conducting rod. In an alternative embodiment the light conducting rod is replaced with a number of diodes.