Safe position monitoring: concepts for machine safety
Safety sensors and monitoring units should provide effective protection for personnel in accordance with international standards, but without hindering the production process. And they should also be easy to integrate into machine designs, as Rolf Brunner of Leuze explains.
Machine safety is growing in importance and is, thus, becoming an integral part of machine design. In addition to the moral obligation to protect and preserve the health of their employees, the topic of machine safety is also a matter of economic efficiency for employers and operating companies. And in addition to reliability, the fault-free integration of a solution into applications is also key.
Optoelectronic safeguards can form a key part of a machine safety concept, with ‘safe positioning’ being a good example. Typical applications in which safe positioning or safe movement monitoring is required include, among others, high-bay storage devices as they are used in, for example, intralogistics – such as for the positioning of travel and lift axes and the monitoring of the speed at the end of travel paths for collision avoidance with the end-position buffer. With a manned car on a high-bay storage device, it is – depending on the design – only possible to travel at a safely reduced speed.
Applications in the automotive industry are another typical example. With heavy-load telpher lines, the lifting device is moved up and down when the telpher line is located at a safe position. Skillet systems are not generally directly positioned, but are rather pushed through the production line in a continuous linkage with a single motor. The ‘safe position detection’ runs along in the base of the skid to then raise and lower the lifting device at predefined, safe positions.
The use of standard components (sensors, drive elements and control electronics) in safety applications is fundamentally possible in accordance with EN ISO 13849. This also applies if these components are not designated as safety components in accordance with Appendix V of Machinery Directive 2006/42/EC. When using industrial standard components that were not specifically designed for use in safety functions but which contain embedded software, further considerations must be given in accordance with the latest version of DIN EN ISO 13849-1:2016-06.
To achieve Performance Level c or d with standard components, two channels must be used. Furthermore, the components in both of these channels must be based on diverse technologies. The probability of a common cause failure (CCF) is thereby nearly completely excluded. CCF refers to the failures of redundantly designed units due to a single event with common causes, such as soiling, electromagnetic influences or pressure.
So what might such safe positioning systems look like? With the bar code positioning systems of the BPS30 and BPS300 series, Leuze Electronic meets safety applications requirements as verified by the TÜV. Indeed, the TÜV report stated: “The analysis of the software and hardware of the BPS 3xxi and BPS 3x positioning systems shows that both systems have a different structure with respect to hardware and software design, and requirement for diversity is thereby satisfied for both.”
In areas in which man-machine collaboration takes place, the requirements of the Machinery Directive with respect to safety-related aspects must be taken into account. In many applications, a position must be safely detected. But position detection always involves movement – such as high-bay storage devices and telpher lines that we have discussed, or machine components in general. In many cases, this can lead to hazards.
To avoid these hazards, the position values must be safe. This applies both for the position detection itself as well as for the subsequent position processing. To obtain a safe speed value for an axis, the position changes of the moving axis are calculated per time unit and thereby result in safe speed values.
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