Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1981-06-12
1983-09-20
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250227, 350 9616, G01V 904
Patent
active
044058586
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a light gate with a single light source whose light beam can be successively directed by means of a light-distributing unit, energized by a control device, to several optical channels each comprising a light conductor on the transmission side, as well as with a light-receiving device which is coupled with these channels and is followed by an electronic evaluator.
Light gates have the purpose of generating, upon an undesired intrusion into the working space in a machine such as for example a press, a signal by means of which the machine is temporarily or completely arrested. They consist of a multiplicity of optical channels which encompass the working space to be monitored and which are each formed by a light transmitter and a light receiver. An electronic evaluator generates the signal upon an interruption of the light path. For light gates of this type two systems are basically known. In one system each optical channel has a light source of its own, e.g. in the form of a light-emitting diode; the light sources are simultaneously activated in cyclic succession and the signals of the light receivers are combined in an AND-circuit (German published application No. 16 16 016) or the light sources are successively cyclically activated with control of the evaluation of the output signals in the same rhythm (German Pat. No. 22 47 053), or the light signals are led by way of a common light conductor to a single photoelectric transducer (German printed specification No. 19 41 905). In the other system the optical channels are illuminated by a common light source, the distribution of the light to the channels being carried out by a lens system or with the aid of a rotary mirror and a parabolic mirror (German published application No. 14 41 426). In an arrangement operating according to this system (German published application No. 21 58 182), a control device in the form of a motor actuates a light-distributing unit which is constituted by a movable optic coacting in turn with a single light source. The swinging or rotating optic irradiates in succession, via light conductors, several optical transmitting channels with a beam emanating from the light source, and the photoelectric transducers are followed by an electronic evaluator.
The light-receiving devices can be disposed either on the side of the working space to be monitored which is opposite the light sources or on the same side as the light sources; in the latter case a reflector is disposed on the opposite side and the reflected rays are directed by semitransparent mirrors onto the corresponding light receivers.
All known incandescent or fluorescent lamps have the drawback that these light sources are of complicated structure and are highly trouble-prone (short lifespan). A pulsed mode of operation desirable for the suppression of interfering light considerably reduces the lifespan with the aforementioned light sources. The known lens systems permit only the simultaneous operation of all channels and ray distribution by means of a rotary mirror allows neither the duration of the light pulses not their sequence to be controlled. The photodiodes serving as light receivers also constitute a source of interference. With superirradiation of adjoining optical channels or with extraneous light sources they can generate error signals which must be eliminated by a complex self-supervising logical test circuit (coincidence stage).
In contradistinction thereto, the invention has the object of so designing a light gate of the generic type that the light pulses fed to the several optical channels and originating at one light source can be controlled in duration and sequence without the use of movable structural elements.
This object is realized in accordance with the invention by the features (a) to (d) of claim 1.
In the light gate designed in accordance with the invention, the directive optical couplers form electrically controllable light-switching points with whose aid the light pulses generated in a light source and transmitted through a c
REFERENCES:
patent: 3781092 (1973-12-01), Sussman et al.
patent: 4015122 (1977-03-01), Rubinstein
patent: 4310756 (1982-01-01), Sick et al.
Krohne Messtechnik GmbH & Co. KG
Nelms David C.
Ross Karl F.
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