Machine safety was once considered by many to be a hindrance to operational productivity. But when correctly specified, applied and utilized, machine safeguards can virtually disappear from the machine
operator’s perspective, while actually increasing productivity by keeping workers safe and maximizing
machine uptime.

Safety light curtains are one method of machine safeguarding designed to protect personnel. Historically, they have been offered with a specific set of operating features such as fixed blanking,
floating blanking and muting to cover all of the potential needs a light curtain may be called to deliver.
Safety light curtains are becoming increasingly flexible and transparent, and so it is with their available feature-sets and packaging — users can now employ light curtains that have what they need, without
paying for superfluous features. Understanding these key features is vital to utilizing them to their
maximum effect. The following discussion is not exhaustive, but provides an outline for four of the more commonly used safety light curtain features today.

Users should note that safety light curtains are not the right machine safeguard for every application
and in some cases is one part of a larger machine safeguarding system. Users should conduct a thorough safeguarding risk assessment, or partner with a professional machine safety service provider to perform the risk assessment for them, before deciding on the right machine safeguard or safeguards.

Fixed Blanking
Fixed blanking allows the detection zone to have permanently blocked beams. This is valuable if tooling or other machine parts must permanently obstruct a portion of the protected zone. Should a
stationary object be moved, the safety light curtain would send a stop signal to the machine.

Floating Blanking
Floating blanking allows up to two light curtain beams anywhere in the sensing field to be disabled. This is a particularly attractive feature when process materials or other parts must transit through the detection zone. Floating blanking is sometimes used in conjunction with fixed blanking allowing
the programmed-disabled area to fluctuate in size.

Muting
Muting is another very popular safety light curtain feature. Muting is a control reliable method of temporarily bypassing the protective function of a light curtain, and is permitted only during the non-hazardous portion of the machine cycle.

Muting can deliver significant improvements in productivity; for example, enabling pallets containing parts to enter and leave a machine without stopping the machine, yet stopping the machine immediately should an operator move his or her hand or body towards a hazardous area.

New enhancements to muting functionality make it possible to program the light curtain not merely to detect the presence or absence of an object, but to perform positive identification of that object. This
technique can even profile the shape of the object to ensure that it matches, for example, the shape of the pallet used to feed parts into the machine.

Cross Talk Mitigation
Cross-talk is an issue of significance that machine builders and end-users need to keep in mind — when two or more light curtains are located in close proximity to one other, precautions should be
taken to avoid having them interfere with each other.

One simple and traditional precaution is to avoid mounting the light curtains so that their transmitters are oriented in the same direction. A superior orientation for multiple transmitters is back to back
which makes it nearly impossible for the transmitters to interfere with one another.

In cases where many light curtains are used in a small area it may be difficult to orient them in such a manner that they cannot interfere with each other. In this situation light curtains with optical scan codes can be used, as the receivers in such light curtains are sensitive only to a transmitter
that is set to the same scan code. This feature is particularly attractive to machine builder OEM’s – they can consistently build identical machines without staggering the transmitter and receiver position.

There are a number of light curtain configuration options available today to optimize safety and productivity in manymanufacturing operations. It should be noted that space limitations make it impossible to address every possible situation or to fully explain every configuration option,
so it’s important for a machine builder or end user to consult his or her light curtain vendor to obtain full details on how to properly specify, integrate and use safety light curtains for truly transparent
safeguarding for a specific application. FSM Russ Wood is application engineering
manager for Omron Scientific Technologies, Inc., Fremont, CA, 800-479-3658 www.sti.com, sales@sti.com.