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Integral design axis for the accuracy enhancement of ultraprecision machine tools

: Brecher, C.; Utsch, P.; Wenzel, C.

Brunel University, Uxbridge; European Society for Precision Engineering and Nanotechnology -EUSPEN-:
Laser metrology and machine performance IX : 9th International Conference and Exhibition on Laser Metrology, Machine Tool, CMM & Robotic Performance, LAMDAMAP 2009. 30th June - 2nd July 2009 Hamilton Building, Brunel University, Uxbridge
Cranfield: Euspen, 2009
ISBN: 978-0-9553082-7-7
International Conference and Exhibition on Laser Metrology, Machine Tool, CMM and Robotic Performance (LAMDAMAP) <9, 2009, Uxbridge>
Conference Paper
Fraunhofer IPT ()
Bearbeitungsgenauigkeit; Dämpfung; fünf-achsiges Fräsen; Genauigkeit; hydrostatisches Lager; Mikrotechnik; Positionierungsgenauigkeit; Präzisionsteil; Radiallager; Steifigkeit; Werkzeugmaschine

The manufacturing of complex micro parts requires five-axis machining accuracy that is not covered by currently available machine systems. For this reason, the Fraunhofer IPT investigates strategies for the enhancement of positioning accuracy, stiffness and damping of five-axis machine systems. The 'Integral Design' describes one possibility to follow precision design rules by integrating several functions in one item in order to reduce error activating cantilevers andjoint patches. Hence, the volumetric positioning accuracy as well as the overall machine stiffness can be enhanced and thermal errors can be reduced, too. This work exemplifies the integration of a hydrostatic radial bearing into a torque motor in order to decrease the error influences of a rotary swivel stage by reducing the Steiner Distance (from centre of gravity to pivot axis) and the Pivot Distance. Hereby, a carbon fibre bushing with hydrostatic bearing pockets is integrated into the primary part of a torque motor while a magnet coating realises the hydrostatic counter bearing face. The principal project idea, the design and the manufacturing of the components with bearing function is described in the following. The integral design follows precision design fundamentals and focuses on the reduction of cantilevers affecting Abbe, Pivot and Thermal Errors as well as the static and dynamic machine behaviour. The described integral rotary axis is realised by the integration of a hydrostatic radial bearing into a torque drive. A fibre composite bushing with five integrated hydrostatic pockets and oil supply is manufactured and fitted into the primary part whereas the bearing counter face is made by a 2K-epoxy mass, that is cast on the rotor side, also protecting the magnets. The axial bearing is directly placed under the workpiece table for highest damping and stiffness against tilt movement. Due to a magnet restrictive measuring system only one non-contact sealing system needs to be integrated, separating the drive, bearing and measuring system towards the process. In comparison to a given partial design rotary stage, the Steiner Distance is reduced by 27%, the Steiner Inertia by more than 50% and the torque drive by 35%. This provides the potential to increase the accuracy of five-axes machines as required. Furthermore, the given integral design can be translated to conventional machine tools supporting further accuracy enhancements.