Optimal Control for Static Stiffness and Thermal Sensitivity of a Hexapod Machine Tool

Beneath many conceptual advantages, parallel kinematic manipulators suffer some disadvantages which complicate their operation as machine tool. One of them is their inhomogeneous stiffness characteristic within the workspace, another is the high thermal sensitivity of their static accuracy due to the large strut lengths. Both properties, stiffness and thermal sensitivity, depend strongly on the configuration of the manipulator. As for machining purposes only five degrees of freedom are necessary, the 6th axis can be utilized to choose an optimal configuration with respect to stiffness or thermal sensitivity. In this contribution, an optimization method based on Jacobian matrix analysis is introduced and demonstrated for a model of the hexapod milling machine HEXACT. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)