Ultra precision micro-CMM using a low force 3D touch probe

摘要

With the continued miniaturisation of mechanical and optical systems there is an increasing demand for high precision dimensional measurements on small parts. METAS combined a new probe head with a recently developed ultra precision CMM stage. The probe head with probing spheres in the diameter range of 0.1 mm to 1 mm has isotropic probing forces below 0.5 mN. Its unique parallel kinematic structure uses exclusively flexure hinges and is manufactured out of a single piece of aluminium. This structure blocks all rotational movements of the probing sphere and separates the 3D movement into three independent 1D displacements which are measured by inductive sensors. The repeatability for a single point probing is in the order of 5 nm. This probe head was combined with an ultra precision micro-CMM, which is based on a development made at Philips CFT. The micro-CMM features a 90 mm x 90 mm x 38 mm air bearing stage with interferometric position measurement at zero Abbe offset. At the reached level of precision, the shape deviation of the probing sphere becomes a major contribution to the uncertainty. Therefore a calibration method for spheres based on error separation techniques was implemented. The results of roundness measurements on 3 calibration spheres are presented.