Patent ID: 6872932

Claim:
Light curtain comprising two elongated assemblies defining between them and lengthwise an area to be monitored, and comprising at least one light source, at least one optical receiver, and processing means able to process the signals received from the light source by the receiver, in order to output an intrusion signal, characterised by the fact that each assembly (P 1 , P 2 ) comprises, together with the other assembly a surface ( 11 ) of alternating light areas ( 13 ) and dark areas ( 12 ) distributed along the length of the assembly to form a grid, a linear (or matrix) optical receiver (R) with opto-sensitive points that are located in succession along the length of the assembly, and an optic ( 14 ) associated to the linear receiver (R) and adapted to pick up the image of at least part of the length of the opposite grid, the linear receiver (R) picks up the image of the part of the opposite grid and sends a respective grid image signal, the processing means ( 23 - 26 ) of the two assemblies (P 1 , P 2 ) process the grid image signals coming from their linear receivers to output the intrusion signal (S).