  Compliant mechanisms are alternatives to conventional mechanisms which
exploit elastic strain to produce desired deformations instead of using
moveable parts. They are designed for a kinematic task (providing desired
deformations) but do not possess a kinematics in the strict sense. This leads
to difficulties while assessing the quality of a compliant mechanism's design.
The kinematics of a compliant mechanism can be seen as a fuzzy property. There
is no unique kinematics, since every deformation need a particular force system
to act; however, certain deformations are easier to obtain than others. A
parallel can be made with measurement theory: the measured value of a quantity
is not unique, but exists as statistic distribution of measures. A
representative measure of this distribution can be chosen to evaluate how far
the measures divert from a reference value. Based on this analogy, the concept
of accuracy and precision of compliant systems are introduced and discussed in
this paper. A quantitative determination of these qualities based on the
eigenvalue analysis of the hinge's stiffness is proposed. This new approach is
capable of removing most of the ambiguities included in the state-of-the-art
assessment criteria (usually based on the concepts of path deviation and
parasitic motion).
