Papers by Author: Frank Härtig

Abstract: Key comparison (KC) measurements are the backbone of validating the calibration and measurement capability (CMC) of national metrology institutes (NMIs) against each other. Recommendations providing procedures for the preparation and execution of KCs as well as supplementary comparisons are given. They are justified by mathematical reasoning and by aspects of practical use. Arguments and a formal description of calculating the key comparison reference value (KCRV) by its weighted mean based on the expanded measurement uncertainty expressed by a confidence level of 95 % will be presented. Moreover, it will be explained why the calculation of the normalized error relates to the weighted mean only and why its absolute value for the expanded measurement uncertainty shall be below 1 to pass the equivalence criterion (E_n) of comparability. A deeper discussion is given on how reference values and measurement results shall be treated if few individual measurement results differ significantly from the others. Finally, it will be explained how the proposed style of the graphical presentation of measurement results allows a clear visual interpretation of the comparison. Besides the formal description, numerical examples and diagrams are presented.

Abstract: Achieving traceability is crucial for complex measurement techniques, especially for coordinate measuring machines (CMMs). For CMMs using tactile probes, traceability can for certain measurements be achieved using model-based uncertainty budgets. Up to now, uncertainty simula-tions could be used applicable only for tactile CMM measurements of regular geometries, but are available as an add-on for different CMMs. This procedure is accepted by guidelines and inter-national standards (VDI/VDE 2617-7, supplement 1 [1] to GUM). Furthermore, empirical ap-proaches to assess the measurement uncertainty by means of calibrated workpieces or prior know-ledge exist or are under development. These approaches can as a matter of principle also be used for CMMs featuring computed tomography (CT). In this paper, the empirical assessment of the mea-surement uncertainty of the upcoming measurement technology CT [2, 3] will be discussed uniting the present approaches and the current knowledge, with the focus being on the applicability of con-cepts for users in industry. For this purpose, the influences on dimensional CT measurements are analyzed and evaluated, taking the measurement data of a current industrial micro CT system as a basis.

Abstract: The reliable determination of periodic micro structures on open surfaces as they exist on involute tooth flanks gain of increasing importance. They allow conclusions from the waviness of the gear surface to the wear and running noise in gears. With the aim of determining traceable wave structures, a method has been developed at the Physikalisch-Technische Bundesanstalt (PTB) in Braunschweig by which it is possible to model, realise and, especially, reliably evaluate wave-shaped structures on the flank surfaces of involute cylindrical gears.