Cut the cost of safety solutions
November 1st 2003

Technological development cuts cost of safety solutions - by Barry Goodwin, safety product manager, Leuze Mayser The humble safety light curtain or safety grid a familiar sight in many working environments where there is a need to provide a safety barrier between man and machine. In this instance the barrier is intangible through the use of infrared or laser light but it is always there. Widespread growth and acceptance of this safety technology began in earnest during the late 1980s after light curtain manufacturers got their act together to develop more commercially available designs. These were lighter, more compact and competitively priced, making them a real alternative to fixed guard barriers, where the application allowed. While the operating concept today remains the same, light curtain technology has advanced to keep pace with user demand. A relatively new word entering the machine guarding arena is that of MUTING, and predominantly appears when developing safety solutions for automated lines. In essence it allows production items to pass through a safety barrier without tripping and halting production, but at all times prohibits the entry of a human into the danger zone. Typical of this kind of installation is that of a car body welding assembly line or, within the warehousing industry, a palletised load passing into a shrink-wrap machine for example. Fixed guards may protect the perimeter but at the entry/exit points a hinged door would hinder the flow. To create an efficient, practical solution requires the use of a MUTING technique using a bespoke control system that is a combination of safety light grids and sensors. A typical muting system comprises a safety light grid and two or four pairs of photoelectronic sensors, positioned at the danger zone. When the entry/exit area is clear, the safety light grid provides an invisible barrier that, if broken, will signal an alert and close down all hazardous movements. As a load moves towards the exit zone it physically blocks persons access to the danger zone, however it must not trigger the safety light grid. During its approach to the safety barrier it breaks a beam path generated by the muting sensors, the electrical output from the sensors receiver is used to send an inhibit signal to the light barrier control system to prevent actuation. Once the unit load is clear of the sensors beams the safety light grid returns to its normal protection field function. The practicalities of installation may seem daunting but continuing light curtain development is making life all that much easier for the installation engineer. Convention would require all the muting sensors and light curtains to be hard-wired to a control panel streams of wire, perhaps over long distances. Not any more. Spearheading the transition of less wiring and easier installations is a new breed of safety light curtains and grids developed by Leuze that incorporate the muting controls within the main body of the safety barrier. The muting sensors connect directly to the light column, thus simplifying the wiring to achieve the muting function. Another significant benefit of the new development is its ability to provide, when requested, an inherent AS-i capability, meaning that the transceiver of the safety barrier can simply plug into a Safe AS-i bus system, easily recognised by its yellow cable. It is one of the simplest forms of connectivity, not only specific to light curtains, but also other safety and non-safety devices. The new breed of safety light curtains and barriers still offers recognised standard resolutions - 14 and 30mm for finger and hand protection. Other types are 50mm for ankle and 90mm for thigh detection and 2, 3 and 4 beam light grids specified for perimeter guarding and hence whole body protection. Ongoing technological achievements enable safety light curtain and barrier manufacturers to meet the continually changing demands of industry. The role of the light curtain or barrier remains the same as it did at its inception that of protecting man from machine. However, new innovations have brought about a reduction in size, better alignment techniques and better integration into control circuits without compromising safety. It has opened the door to other industries where there is now an appreciation of the overriding cost-benefits that light barriers can bring to safety solutions.

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