Sensitivity of freedom spaces during flexure stage design via FACT

The theoretical kinematic design of flexure stages using exact constraint methods is well known. These methods, however, do not take into account practical design considerations such as non-ideal constraint behavior. It is shown via a case study that the freedom space of a one degree-of-freedom (DOF) translation stage is extremely sensitive to both the arrangement and the elastomechanic behavior of the flexural constraints. The results of the case study show that certain combinations of constraint properties and layout yield a 1-DOF system that is more accurately modeled as a 3-DOF system. A non-dimensional constraint quality metric, CQ, is introduced in this paper to help classify the system in the case study as a 1-DOF system, a 3-DOF system, or a combination thereof. This paper is a first step in showing how practical design considerations may negatively influence the kinematics of systems that were previously assumed to have been designed “correctly” using exact constraint methods.