ABSTRACT
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.
