Tolerance in FMS: a way to improve design

A tolerance concept is established based on the OAG operating part model. This paper studies in detail tolerance properties including the functional and structural (resources) aspects. The critical resource concept is introduced; it characterises a resource, whose failure induces the disappearance of the machining function(s) initially performed by the FMS. A sequential approach, using the OAG, is proposed to identify the criticality degree of operations and critical resources. The approach deals with the OAG from a graph structure point of view, then considers the operation nature and machining functions performed. Several quantitative criteria are defined. The paper also deals with analytic determination on several types of architectures which include the criteria evaluation, and concludes on some options that have to be taken into consideration during the FMS design