Safety of Machinery – Risk analysis and requirements for safety of gravity loaded axes

One of the design measures adopted for the risk reduction of machinery is the deenergization of all the components of the machine for assuring a “safe stop state”. So, for gravity loaded axes, the risk of unintended gravity descent in the de-energized state has to be considered in the risk assessment. In case of power failure, the gravity loaded axes are held solely by the brake/counterweight systems, which are installed in the machine. The gravity loaded axes may drop down, if the existing brakes/ counterweights do not provide adequate protection against unintended descent due to gravity. In the paper first, a full analysis for this underestimated risk of today’s very complex machines is presented. Than a description of the problem is illustrated and the resulting requirements are presented in terms of: design measures, information to be given to the end user and testing procedures to be assured for the new machines.