Procedure and reference standard to determine the structural resolution in coordinate metrology

Abstract

A new procedure and reference standards for specifying the structural resolution in coordinate metrology traceable to the SI unit the metre are proposed. With the definition of the structural resolution, a significant gap will be closed to complete ‘acceptance and verification tests’ of the coordinate measuring systems (CMSs) which are specified in the ISO 10360 series dealing with tactile sensors, optical sensors, and x-ray computed tomography measurement systems (CTs). The proposed new procedure uses reference standards with circular rounded edges. The idea is to measure the radius of curvature on a calibrated round edge structure. From the deviation between the measured and the calibrated radius, an analogue Gaussian broadening of the measurement system is determined. This value is a well-defined and easy-to-apply measure to define the structural resolution for dimensional measurements. It is applicable to CMSs which are based on different sensing principles, e.g. tactile, optical and CT systems. On the other hand, it has a physical meaning similar to the classical optical point-spread function. It makes it possible to predict which smallest details the CMS is capable of measuring reliably for an arbitrary object shape. The theoretical background of the new procedure is given, an appropriate reference standard is described and comparative, quantitative measurement data of CMSs featuring different sensors are shown.