Areal surface topography measurement is becoming more and more widespread. In this context, increased activities in the field of standardization can be observed in order to ensure comparable measurement results. A current hot topic in the field of standardization is areal calibration, which is going to be defined in the upcoming standard ISO 25178-700. Besides, the metrological characteristics of the ISO 25178-600, representing the properties to be calibrated, as well as the corresponding material measures of the ISO 25178-70, used for imaging, are required for a comprehensive standardization of areal calibration. It can be expected that the application of the calibration guidelines is challenging as no easy-to-implement guidelines for the evaluation routines will be included. In this paper, the standards required for areal calibration are briefly presented and their metrological properties are described. A user-friendly implementation of the algorithms required for the evaluation will be discussed in detail. The basic metrological characteristics to be evaluated are the flatness deviation, measurement noise, the topography fidelity, the amplification coefficients and linearity deviations of all axes, the x/y mapping deviation and the topographic spatial resolution. With Two-Photon laser lithography, all required material measures to calibrate a measurement device according to ISO 25178 can be printed on one single calibration artefact. Based on this universal artefact, user-oriented evaluation routines to determine the aforementioned metrological characteristics are introduced and a software package implementing the algorithms and supporting the user effectively during the holistic calibration of areal surface topography measuring instruments is described.
With state-of-the-art 3D measurement systems, short-wave structures such as tool marks cannot be resolved directly inside a machine tool chamber. Up to now, measurements had to be performed outside the machine tool. We present an interferometric sensor that carries out such measurements inside the machine tool, which saves time-consuming and expensive setup procedures. Our sensor HoloCut uses digital holography as measurement principle. By the use of multiple wavelengths, we get a large unambiguous axial measurement range of up to 2 mm and achieve micron repeatability, even in the presence of laser speckles. With a lateral resolution of 7 μm across the entire 20 x 20 mm2 field of view, both macro- and microstructures (such as tool marks) are measured with an axial resolution of 1 μm. Consequently, this qualifies HoloCut for in-situ measurements and integration in a machine tool. In this paper, the boundary conditions of integrating interferometers inside a machine tool are evaluated. Occurring vibrations and limited available space are particularly challenging constraints: The optical and mechanical design of HoloCut is introduced along with numerical correction algorithms: A piezo-stage setup is used to induce known displacements. Using these algorithms, measurements even with a closed-loop control of the machine tool head activated are demonstrated on a coin measurement. The use of HoloCut is motivated on the base of the daily operation of a 5-axis machine tool: We present an evaluation of an exemplary ISO 25178 parameter Sq using HoloCut measurements and compare those with reference, yet not inline-capable systems.