Synthesis of contact-aided compliant mechanisms for non-smooth path generation

Topology optimization is used in this paper for the systematic synthesis of contact-aided compliant mechanisms that trace prescribed, non-smooth paths in response to a single, monotonically increasing input force. Intermittent contact interactions that enable these mechanisms to exhibit non-smooth responses also lead to algorithmic difficulties when the techniques from the synthesis of ordinary compliant mechanisms are used to design contact-aided compliant mechanisms. A sequential optimization approach based on a regularized normal contact model for large displacements is used in this work to circumvent these difficulties and to enable the use of computationally efficient, gradient-based optimization methods. We use an objective function based on Fourier shape descriptors, which allows the designer to emphasize different aspects of the design intent (such as the shape, the size and the orientation of the output path) separately. A variable-stiffness input spring is used to allow the synthesis procedure to choose the appropriate magnitude of the input force. An arc-length finite element solver and heuristic measures that guard against local and global instabilities add to the robustness of the synthesis procedure as demonstrated by the two design examples presented in this paper. Copyright q 2006 John Wiley & Sons, Ltd