ABSTRACT
The Machinery Directive 2006/42/EC requires the realization of risk assessments over all life cycle phases of a machine to meet the given safety and health standards. Thereby, the safety-related reliability of a control chain is determined by using the newly introduced standard EN ISO 13849-1 whose transition period ended in December 2011. This new standard provokes a paradigm change from the classical descriptive and deterministic approach of the EN 954-1 to a new probabilistic approach. The probabilistic evaluation of the safety of machines is performed on the basis of quantitative specifications of the EN ISO 13849-1 called “Performance Level (PL)” which is a mean probability of a dangerous failure per hour and has to be proved by the manufacturer for a lifetime of twenty years. Consequently, the EN ISO 13849-1 assumes because of the constant failure rate an exponential failure behaviour of the machines and the involved components. In the area of the machine tool industry the new probabilistic approach causes huge uncertainty, in particular among Small and Medium Enterprises (SME), because there is very little experience with this kind of quantitative assessment and there are only some significant quantitative parameters known which have been detected and documented. Hence, a few general quantitative parameters were developed. These lead to the situation that the clamping functions of the existing machine tool concepts which were built for many years and have a real and high Functional Safety in the field appear to be not adequate to reach the given Performance Level, at first glance. Thus, the aim of the presented project is to determine extensive quantitative reliability parameters of machine tools on the basis of operational field data for the first time. Therewith, the given general parameters shall be checked and the assumption of the standard EN ISO 13849-1 shall be proved, if exponential failure behaviour of the machines and components really exists.
