Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1987-12-07
1991-04-16
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250225, 250226, 340556, G01V 904, G08B 1318
Patent
active
050085301
ABSTRACT:
An autocollimation light curtain comprises a light source which directs a light beam onto a scanning device which scans the light beam so that it is continuously displaced parallel to itself, thus forming a light curtain which is directed through a monitoring region. A reflector is provided at the end of the monitoring region and is subdivided in the scanning direction into a plurality of fields of two types which alternate with each other. Light reflected at the reflector is directed back to a light receiving system comprising first and second photodetectors. The two types of fields of the reflector have characteristics which influence the spectral range and/or the state of polarization of the incident light. In the light receiving arrangement one photoreceiver is filtered so that it receives only light reflected from the one type of field, but not light from the other type of field, whereas the other photoreceiver responds to all the light reflected back from the reflector. Thus one photoreceiver produces a dc signal and the other an alternating signal and a free monitoring region is only signalled when both the dc signal and the alternating signal are present.
REFERENCES:
patent: 3858043 (1974-12-01), Sick et al.
patent: 4310836 (1982-01-01), Stanzani
patent: 4339660 (1982-07-01), Buehholz et al.
patent: 4546246 (1985-10-01), Bechtel
patent: 4734575 (1988-03-01), Wagli et al.
Chatmon Eric F.
Erwin Sick GmbH - Optik-Elektronik
Westin Edward P.
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