Improvement on workpiece metrology

Facing metrology difficulties related to the high accuracy requirements for part positioning inside the machine-tools, the University of Leuven has developed a robust unidirectional measurement system based on the use of a moving measuring scale and a capacitive sensor. The design of the device has been carried out minimizing the Abbe errors and the ones coming from thermal and environmental sources. The preliminary validation of the prototype has shown a great consistency, attaining measurement uncertainties around 20 nm. Trying to provide capabilities for high precision on-machine measurements, IBS Precision Engineering has developed a full 3D ultra-precision contact probe capable of working within machine-tools on workshop environments. This probe has been tested to work on ultra-precision lathes for the measuring of calibrated artefacts and manufactured optical components, yielding measurement uncertainties below 50 nm. In order to improve probe measurements carried out off-machine, the National Physical Laboratory (NPL) has worked on the design and development of a vibrating micro-probe capable to work on non-contact mode. The stylus is placed on a MEMS structure allowing the generation of a controlled vibration of the probe tip. The performance tests carried out on an ISARA 400 ultra-precision coordinate measuring machine (CMM) have shown that the probe is capable of measurement accuracy below 60 nm. Besides probe based measurement systems, optical measuring devices have been developed within the project too. Sensofar has developed a miniaturised microscope head capable for on-machine measurements, both by confocal and interferometry techniques. This on-machine microscope has been tested to work properly within the manufacturing environment at Kaleido , probing very helpful not just for the verification of the manufactured parts, but also for the machine and tooling set-up. Concerning optical metrology, the development of an optical CMM has been carried out by IK4-Ideko, implementing a 5-axis positioning structure on a PLu Neox optical profiler from Sensofar. Thanks to this structure, it is possible to obtain detailed measurements from complex 3D parts and treat them on the same reference system. Besides, in order to make this system competitive in comparison to contact based CMMs, Sensofar has worked on the development of a focus variation measurement technique, enabling very fast measurements with a high spatial resolution. Linked to the use of optical means for the characterization of complex parts with small and even damaged features, the development software for the treatment of the obtained measurements has been undertaken during the project too. Tagueri has worked on a tool that, applying statistical data mining techniques is able to identify and disregards ‘bad’ points from the measurements, increasing the reliability of the results obtained from the optical measurements. Finally, trying to bridge the gap between contact and optical form and roughness measurements, the NPL has analysed the possibility to define traceability routes between both types of measurements. While evaluating the measurement results yielded by different optical measurement methods in order to define their application range, calibration procedures and artefacts have been defined for optical measurement equipment.