Active opto-electronic protection devices, or as they are more commonly known, safety light curtain systems or light guards, provide a practical and cost effective method of protecting personnel from injury at dangerous machinery; they are generally available in two main categories: type 2 or type 4.
The selection of which category of guard should be used is directly determined by the severity of the potential damage to the operator that exists at the intended application. A full risk assessment should be applied; standards BS EN 954 and BS EN 1050 may be helpful in the risk and safety type evaluation. Basic flow chart diagrams are available.
Low Risk Hazard – A Type 2 Machine Guard
A low risk hazard, for example, is considered where the severity of damage is slight. Exposure to danger is limited by virtue of the semi automatic / automatic running of the machinery not requiring regular operator intervention. This would be considered a type 2 machine guarding product.
High Risk Hazard – A Type 4 Machine Guard
A high risk hazard is where the potential for severe damage exists and exposure to the danger area is frequent or continuous. For example, this might be the hand feeding of sheet steel into press tools every cycle. This would require a type 4 machine guarding product to be used.
The Light Curtain Length and Resolution
The active optical curtain length and the resolution of the optical curtain are factors also to be taken into consideration when sourcing your safety light curtain system.
Typically curtain lengths range from 150mm up to 1650mm and are available with resolution of 14mm / 20mm / 30mm, or body detection systems options of 300mm / 400mm / 500mm.
The active curtain length should prevent reach over and reach under into the danger area, and if necessary additional fencing or barriers should be fitted to achieve this.
The optical curtain resolution required, which is the detectable rejection distance between individual beams in the curtain, will be dependent on the distance that the guard is to be positioned away from the machine danger area.
The Machine Guarding Distance Formula
The formula “S = (K x T) + C” should be used to calculate the required separation distance and or curtain resolution (object detection capability) necessary for the application. The machine stopping performance time will also be required for this calculation.
The safety light curtain method of guarding is widely accepted throughout most industrial sectors and is becoming a more popular solution due to modern day light curtains now having more compact physical dimensions (35mm x 40mm) – coupled with ease of installation.
They also have the advantage over conventional fixed guarding by allowing easy access for the operator during production, hence reducing the possibility of repetitive strain injury, and also easier access for maintenance and tool changes.
For a full explanation of safety guard distances or information on the HSE publication “Application of electro-sensitive protective equipment using light curtains and light beam devices to machinery”, HSG180, please visit www.machineguardsolutions.com to find out more.
By Tom Andrew
Article Source: ezinearticles.com
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