Optimization of the antagonistic stiffness characteristic of afive-bar mechanism with redundant actuation

摘要

A closed-chain mechanism having redundancy in the force domain canproduce a spring effect by proper internal load distribution. Theso-called antagonistic stiffness is provided by redundant actuation inconjunction with nonlinear geometric constraints. In the paper, anoptimal structure of a five-bar mechanism that can maximize efficiencyin generation of antagonistic stiffness is evaluated and analyzed. Astiffness modulation index that represents isotropic characteristics inantagonistic stiffness generation is proposed. A gradient design indexthat shows rate of change of the isotropic index is also employed todistribute the isotropy of stiffness uniformly throughout the workspace.To deal with multi-criteria based design, a composite design index basedon the max-min principle of fuzzy theory is used as an objectivefunction. Two optimization results are obtained. One is optimizing theX-directional stiffness and the other corresponds to optimizing theY-directional stiffness. The result of the former design is foundsuitable for antagonistic stiffness generation as well as forfirst-order kinematic performances