Light grid arrangement using cyclically switched semiconductor l

Details Light grid arrangement using cyclically switched semiconductor l Light grid arrangement using cyclically switched semiconductor l

1979-11-23

1982-01-12

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

340556, G01V 904

Patent

active

043107567

ABSTRACT:
A light grid arrangement features a row of light emitting diodes 0 to 9 which are periodically switched on one after the other by a ring counter 11 and are arranged to direct their light through a monitoring region 23 towards an image forming optical means which is conveniently in the form of a concave mirror 24. The light beams are concentrated by the concave mirror 24 onto a photodetector 18 arranged behind a slot aperture 25 located at the focal point of the concave mirror. Missing pulses from the photodetector are detected by processing circuitry 26 to indicate obstruction of the light grid. The width of the slot aperture 25 restricts the width of each individual light beam so that only beams of light from the light emitting diodes that are generally parallel to the axis of the concave mirror are detected. In this way costly optical focussing elements are avoided as are the difficulties of aligning these optical elements with the other optical components of a system. The length of the monitored region can be increased as desired by placing a number of concave mirror and light emitting diode arrangements alongside one another.

REFERENCES:
patent: 1345586 (1920-07-01), Coblentz
patent: 2284289 (1942-05-01), Lindsay
patent: 2769374 (1956-11-01), Sick
patent: 3858043 (1974-12-01), Sick et al.

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