Beam Blanking with Guardscan^® Light Curtains

Beam blanking is an important function of the Guardscan Light Curtain range that allows selected areas of the sensing field to be disabled. This is particularly useful for those applications where, for example, a work-piece is obstructing the curtain or possibly moving up and down within the curtain. All Guardscan Light Curtains are capable of being blanked, with fixed and floating blanking options available for increased guarding flexibility. When in beam blanked mode, the light curtain checks for any change in the programmed condition and will initiate a stop signal to the machine if an allowable obstruction is removed.

Types of blanking
Fixed blanking-

Fixed blanking is achieved by a ‘learn’ technique. The system learns which beams are obstructed at the time of programming and the light curtain outputs will then only be operational if these beams are obstructed and all other beams are clear. If the programmed obstruction is removed, the light curtain will generate a stop signal.

Floating blanking-

Floating blanking can be selected so that either one or two beam obstructions can be ignored. Basically, an obstruction can move or ‘float’ within the detection zone without generating a stop signal provided that the obstruction does not obscure more than the specified number of beams. If ‘Floating 1’ is selected, any single beam in the curtain can be blocked (or not) without causing the outputs to be de-energised. If ‘Floating 2’ is selected, any two beam obstructions can be ignored. The beams do not have to be contiguous. Fixed and floating blanking can be used in combination. This allows the light curtain to prevent nuisance tripping, as in the situation where a fixed blanked obstruction vibrates partially in front of a beam and would otherwise make the curtain go in and out of signal.

Programming Unit

In the Guardscan range of Light Curtains, beam blanking is achieved by means of the BPU Programming Unit. Programming is simply carried out by connecting the BPU, selecting the blanking function and then removing the programming unit. This single cost-effective unit has the advantage that only one unit is needed in order to program any number of light curtains.