Investigations on kinematic couplings for tool-changing interfaces in highest-precision devices

摘要

Highest precision devices are used to measure, manipulate and structure objects with a resolution down to the nanometre range. Manufacturing processes in particular are creating the demand for a highly reproducible tool changing system. The design needs to be free of overconstraints, vacuum compatible and long-term stable. Especially the demand for vacuum compatibility represents a challenge due to friction conditions, which affect the reproducibility. The tool centre point needs to be located very precisely at a defined position in the device. In case of a Cartesian device layout, the position is represented by the virtual intersection of the three linear measuring axes. Manufacturing and assembly tolerances require the adjustment of the tool centre point. Because of the limited space, the adjustment needs to be integrated into the changing system. The usage of various tools requires an individual adjustment at the side of the tool. For this purpose, new arrangements of kinematic couplings are investigated. Neither analytical nor numerical models are suficient to proof the fulfilment of the requirements. Therefore, a setup was developed to measure the reproducibility in five DOF. The metrological properties of the measuring setup were proven by means of a three-dimensional vector-based uncertainty analysis. By using this measuring setup, different arrangements of the coupling points, the influence of the geometry and the material of the coupling members as well as the influence of the adjustment on the reproducibility and long-term stability are investigated with nanometre uncertainty.