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US 5,015,840 AGranted
Self-checking light curtain system and method of operation
AssigneeScientific Technologies Incorporated
InventorDavid Blau
Life of this patent
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AssigneeScientific Technologies Incorporated
InventorDavid Blau
Estimating the term…
A light curtain system and method of operation which detects the intrusion of objects into a protected zone. The system is characterized in having an inherent self-checking mode of operation by logic circuits which analyze data signals from both the LED light transmitters and phototransistor receiver circuits. A shutdown signal is generated if the logic circuit determines that light is not received in a selected channel at the time that the LED is strobing light exclusively for that channel. The system further provides a relatively simple and inexpensive method of selecting and amplifying the LED transmitters and PT receivers. In the circuit each PT acts as a switch which selects itself, and a single amplifier is employed for a plurality of the channels. The circuit further provides for the concatenation of groups of amplifier/PT circuits into a longer chain using a single diode.
For use in a light curtain system having a light transmitter which sequentially strobes light beams across a zone to be protected and a light receiver having a plurality of phototransistors arrayed to receive the light beams, said phototransistors each having a base, a collector and an emitter, the improvement including control circuit means for selecting the sequence in which the phototransistors are enabled to produce output signals upon receiving light beams from the light transmitter, said control circuit means including shift register means for applying a voltage to the collector of a selected phototransistor sufficient to enable the phototransistor to generate an output signal responsive to incident light, said shift register means de-selecting said phototransistor by grounding the collector at the time that the light transmitter is not strobing light in the channel of the de-selected phototransistor, said circuit means including amplifier means for receiving and amplifying output signals from the phototransistors which are selected and which receive light from the transmitter.
A light curtain system for detecting the intrusion of objects into a zone to be protected, said system comprising the combination of light transmitting means for sequentially strobing light beams in a plurality of channels projecting along predetermined paths across said zone, light receiving means for sensing the presence of the light beams in the channels, control means for controlling operation of the light receiving means in coordination with operation of the light transmitting means, said light receiving means comprises a plurality of phototransistors each of which includes a base, a collector and an emitter, said control circuit means includes shift register means for selecting a phototransistor in said given channel to enable it to generate an output signal when it receives incident light, said shift register means applying a voltage to the collector of the selected phototransistor sufficient to cause the phototransistor to generate an output signal responsive to incident light, said shift register means de-selecting said phototransistor to grounding its collector with the phototransistor thereby functioning as a pair of virtual diodes in series with no output signal being generated responsive to incident light, and relay means for generating a detection signal responsive to said light receiving means sensing a light beam in a given channel at the time said shift register means selects the phototransistor associated with the given channel.
Dependencies are inferred from the claim text.