24. Oktober 2011
Functional Safety for Stacker Cranes
Since the implementation of EN ISO 13849-1 "Safety of machinery – Safety-related parts of control systems" the safety functions are no longer exclusively evaluated on the basis of their hardware structure. The new standard adds a probabilistic approach (the events are determined by the probability), including a quantification of component reliability and testability and consideration of potential failures with common cause.
Furthermore, the EN 528:2009-1 as a type C standard (machinery safety standard) lays down the safety requirements for stacker cranes by establishing Performance Levels for different functions.
Both standards have been implemented successfully on all Stöcklin's stacker cranes. This requires safety-relevant components from various manufacturers in order to determine digital signals, like door contacts or key-switch positions, or to calculate the speed of different axes reliably.
Compared to conventional subassemblies, these safety components belong to a higher price segment due to their enhanced technology and quality. A logical consequence thereof would be a rise in the prices for Stöcklin products. On the other hand, these state-of-the-art components allowed for further streamlining in the control engineering area, so that the innovation of the stacker cranes in the end turned into a noticeable cost reduction. So we were able to simplify expensive, safety relevant wirings and reduce the number of contact line poles. Finally, also the fault-prone trailing cables were replaced by contact lines and data light barriers.