Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1990-09-13
1992-07-14
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
340555, G01V 904
Patent
active
051305321
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a light barrier grid comprising a plurality of light sources arranged alongside one another and light receivers each associated with one light source; a light source control and also a receiver control, with the light sources and the light receivers being respectively individually activatable one after the other in time sequence to transmit and receive light pulses respectively.
The light sources of such light barrier grids transmit light beams in a time sequence which monitor a predetermined spatial region or a predetermined area. The light sources are individually activated in accordance with a predetermined time sequence. The light receivers must also be activated in a corresponding sequence and in the same rhythm, i.e. must in particular be connected to an electronic evaluation circuit. Thus, with a respectively activated light source it is only one light receiver which is activated, as a rule the light receiver fixedly associated with this light source.
The requisite synchronisation between the transmitter side and the receiver side has previously been produced by special connection lines between the light source control and the receiver control which is of disadvantage, in particular with light sources and light receivers arranged at opposite sides of the region to be monitored.
The invention is thus based on the object of providing a light barrier grid of the initially named kind which, with a simple construction and reliable operation, ensures problemfree synchronised operation of the light sources and the light receivers, in particular also when connection lines are absent between the light source unit and the light receiver unit.
This object is satisfied in accordance with the invention in that the light receivers are activated by the receiver control in dependence on the received light pulses.
As a result of this construction special connection lines between the transmitter and receiver units can be omitted, which is of decisive advantage, in particular when the light sources and the light receiver are arranged at opposite sides of the region to be monitored. As a synchronisation of the receiver unit always takes place directly starting from the received light pulses the light barrier grid of the invention requires practically no adjustment. It is suitable for the monitoring of surfaces and spatial regions of the most diverse dimensions and is characterised amongst other things by its insensitivity to vibrations and also by a low power consumption.
The receiver control is expediently capable of being switched over for the time sequential activation of the light receivers in dependence on the appearance of the received light pulses.
This switching over from one light receiver to the next can for example always take place when the expected light pulse has been timely received. The sequence of the receiver control can be preset in correspondence with the light source energisation circuit. The activation of the light receivers takes place, by way of example, cyclically, i.e. that after an activation of the last light receiver in the activation sequence the first light receiver of the sequence is again activated.
The receiver control includes, in accordance with a particularly advantageous variant, means for detecting and indicating the absence of a light pulse expected during activation of the respective receiver and the receiver control is resettable in the absence of the expected light pulse into an initial state in which a defined first light receiver is activatable. Accordingly, if at least one light path between one light source and one light receiver is disturbed by an obstacle then this leads directly to the transmission of an indication signal which signalises the intervention in the region being monitored or in the surface being monitored. The fact that the receiver control is simultaneously reset into a defined output state in the absence of a respectively expected light pulse makes it much simpler to newly synchronise the light barrier grid after the intervention.
REFERENCES:
patent: 3746863 (1973-07-01), Pronovost
patent: 4266124 (1981-05-01), Weber
Davenport T.
Erwin Sick GmbH - Optik-Elektronik
Nelms David C.
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