The use of overconstrained mechanisms is often avoided in precision mechanics. Misalignments in the mechanism can cause deteriorated system behaviour, such as buckling. Overconstrained designs do have several advantages, such as higher load bearing capacity and higher natural frequencies. However, these advantages are only present if the mechanism is aligned within certain tolerances. In this paper a method is introduced to identify the limits of these alignment tolerances. The method allows the calculation of the forces in the mechanism due to misalignment. The internal forces are compared to the buckling loads of the mechanism yielding the critical misalignments; the method is corroborated using a multibody simulations. Subsequently, both analyses are compared to an experimental setup; this setup measures the first three modal frequencies and identifies the buckling modes. The proposed method and multibody simulation match with each other and the experiment. However, the critical misalignments are about 20% larger in the experiment; this is mainly attributed to hardware imperfections. Due to misalignment and flatness limitations of the flexures, the undeflected stiffness in the experiment is lower than modelled. The deterioration of the support stiffness is smaller in the experiment. In the most serious case, it retains 80% of the modal frequency in the support directions. The proposed method can be used as a guideline to estimate the manufacturing and assembly tolerances of an overconstrained flexure-based mechanism.

Human standing balance is a complex of systems, like the muscles, nervous system and sensory systems, interacting with each other in a closed loop to maintain upright stance. With age, disease and medication use these systems deteriorate, which could result in impaired balance. In this paper, it is demonstrated that multi-input-multi-output closed loop system identification techniques (MIMO-CLSIT) can be used to assess the underlying systems involved in standing balance and guide possible therapeutic options. In this study, mechanical and sensory perturbations were combined and applied simultaneously using a Balance test Room. The results demonstrate the value of MIMO-CLSIT to assess the underlying systems involved in standing balance and therefore to improve diagnosis of impaired standing balance.