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Swiss engineers use risk analysis for safe design
by Roy OConner, European Bureau Chief, Global Design News -- Design News, January 21, 2002
Stans, Switzerland — Most engineers would surely agree that standards are particularly important when designing machine safety equipment. Complex directives and requirements, however, make some companies unsure of whether they are implementing such standards properly. To ease this situation, Sick AG has launched its Standard PLUS package for practical use. It contains 35 standards on machine safety, and supplements the company's SAFEXPERT software, which provides an efficient process for checking conformance to the European CE label.
Structured to help engineers carry out quick and simple risk analysis when designing machines, SAFEXPERT guides users through today's maze of standards and directives. There are functions to support the designer via suggestions, formulas, and safety clearances required by the relevant standards. Because stipulations on how hazards must be overcome are often buried deep in the machine directives, the package simplifies the design and equipment specification process.
Safety interlocks. Another company that has learned to live with standards is EJA Ltd., part of the Rockwell Automation Group in Wigan, England. With its brands, Guardmaster, Nelsa, and Sigma Prosafe, EJA also understands the importance of continuous product innovation to track standards and maintain competitiveness. Simon Wrigley, product manager for safety interlocks, says, "Ideally, it's important to keep one step ahead of standards where possible. New standards coming into force next year specify improved levels of safety integrity, and this has already been included in our product development."
These standards call for dual signaling channels on safety interlocks. In line with the stricter criteria, EJA has recently launched its new Guardmaster Trojan T15, a tongue-operated safety interlock switch. Designed for the required dual-channel operation, the switch incorporates two sets of safety contacts. Machine builders seeking conformance to the new standards can now save costs with the T15 switch, which avoids having to double up on switches. According to Wrigley, the degree to which standards affect the market in this field can be appreciated by the fact that, depending on the product, EJA must plan up to four years ahead in development to ensure the availability of products conforming to the latest standards.
At its plant in Leinfelden-Echterdingen in Germany, Euchner also produces safety interlock switches. The company has recently launched its TX Safety Switch, designed to meet the requirements of a guard locking device according to EN 1088, and to prevent premature access to machines and installations. One of the main features of the switch is that it can be unlocked even when high tensile forces are applied to the actuator. Euchner's product manager for Safety Engineering, Erich Wächter, explains the reason for this: "It is important to know how operators react to machine safety. With short cycle times, an operator will often pull on the guard door while waiting for it to open. This will prevent conventional switches from unlocking when the cycle is complete, but the TX Safety Switch is designed to apply extra force to ensure that opening takes place."
A special version of the TX incorporates an unlock request contact. This model handles the applications where run-on movements of the machine after switch-off present a hazard to the operator. When the operator pulls on the door, trying to open the safety guard in the locked position, the TX sends a signal to the machine controller. Once the machine has run down to a safe level, the guard is unlocked, allowing access by the operator. To interface with modern controllers, the switching element on the TX will switch very low loads in the range below 4 mA.
Light barriers. Apart from safety interlocks, light barriers also represent an important product sector in safety engineering. Although generically light barriers are not a new idea, continuous improvements in operability and increasing ranges of features provide plenty of activity in this field. Based in Tettnang, Germany, Wenglor Sensoric has recently launched a new safety light barrier for Categories 2 and 4, giving protection against medium and high risks, respectively. The barrier consists of a transmitter and a receiver unit which make use of red, rather than infrared, light. The visible light makes setting up easier.
Kristian Müller, project leader for light barriers at Wenglor, sees versatility as one of the primary considerations for a light barrier. "These days, machines and processes must be able to respond to changing production requirements. It follows that the safety system must also be flexible enough to accommodate these changes without incurring extra costs through new purchases or a lot of modification work."
The new light barrier is an example of Wenglor's strategy. Depending on machine requirements, it can be operated in five different modes. For example, in the muting mode, the light barrier differentiates between the human body and production material. Consisting of a number of sensors, the safety barrier system achieves this function by evaluating the shape of the production material and storing it. The procedure allows objects to pass through the protective field, but if a person gains access to the danger zone, the muting control detects the unknown shape and stops machine movement.
For more information about
Standard PLUS from Sick AG:
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from Guardmaster Trojan T15 from EJA Ltd.:
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from TX Safety Switch from Euchner:
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from Light barriers from Wenglor Sensoric:
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