Constraint-based Design of Parallel Kinematic XY Flexure Mechanisms

This paper presents parallel kinematic XY flexure mechanism designs based on systematic constraint patterns that allow large ranges of motion without causing over-constraint or significant error motions. Key performance characteristics of XY mechanisms such as mobility, cross-axis coupling, parasitic errors, actuator isolation, drive stiffness, lost motion, and geometric sensitivity are discussed. The standard double parallelogram flexure module is used as a constraint building-block and its non-linear force-displacement characteristics are employed in analytically predicting the performance characteristics of two proposed XY flexure mechanism designs. Fundamental performance tradeoffs, including those resulting from the non-linear loadstiffening and elastokinematic effects, in flexure mechanisms are highlighted. Comparisons between closed-form linear and non-linear analyses are presented to emphasize the inadequacy of the former. It is shown that geometric symmetry in the constraint arrangement relaxes some of the design tradeoffs, resulting in improved performance. The non-linear analytical predictions are validated by means of computational FEA and experimental measurements.