Improving the Quality of Measurements through the Implementation of Customised Reference Artefacts Andy ROBINSON* a , Michael MCCARTHY a , Stephen BROWN a , Anthony EVENDEN a , Lifong ZOU b a National Physical Laboratory, Teddington, Middlesex, UK; b Barts & The London School of Medicine and Dentistry, Queen Mary University of London, UK Abstract Three–dimensional (3D) optical scanning technology has made great advances over the last decade and the range of applications is continually growing. However, performance of scanning systems and the quality of measurement data can vary greatly with application. This paper discusses the need for customised reference artefacts and describes three calibrated freeform artefacts, developed at the National Physical Laboratory (NPL) – one related to generic freeform shapes, one related to body scanning, and another relating to dental scanning. The design, manufacture, calibration and implementation of these artefacts are discussed, together with examples of how they are used to add value to a measurement process. Keywords: Measurement, Standards, Reference artefact, Freeform, Metrology. 1. Introduction Significant advances have been made in 3D optical scanning technology in the last decade, and their impact is evident in the areas of aviation, automobile, medicine and dentistry. Measurements of subjects ranging from designed industrial components to human body parts, are made for a variety of purposes including inspection and reverse engineering, Flexibility, portability, speed of data capture, cost of system, and ease of use, are all reasons that make 3D scanning technology an increasingly attractive option. Currently however, very little exists in the way of documented verification standards for this technology. Standards that do exist are typically based around simple tests incorporating geometric objects. Furthermore, the performance of scanning systems is very dependent on the application. With scanning systems, many factors influence the quality of the measurements. For example, the setup of the scanning system, the object to be scanned and the measurement environment can have a profound impact on the scan quality. Whether scanning at the micrometre level or at the millimetre level, it is essential to have confidence in the quality of the measurements, in order that good decisions can be made based on the resulting data. Freeform surfaces, common in body scanning, often raise challenging problems both in terms of data capture and subsequent data analysis. This paper discusses the use of customised reference artefacts designed and developed using established metrological principles, as a way of selecting the right measurement strategy for a given application and to optimise the process to give the best possible results. The closer an artefact can replicate the intended application, in terms of surface finish, size, form and complexity, the more knowledge and confidence the user will gain with regard to the scanner’s likely performance. Three freeform artefacts and their applications are described – one related to generic freeform shapes, one related to body scanning, and one relating to dental scanning. The design, manufacture, calibration and implementation of these artefacts will be discussed, together with examples of how they are used to add value to a measurement process. 2. Challenges in Freeform measurements Freeform measurements prevalent in body scanning can present some of the most challenging and varied measurement subjects for 3D scanning systems. Fig. 1 shows a number of parts scanned at NPL. *andy.robinson@npl.co.uk 3rd International Conference on 3D Body Scanning Technologies, Lugano, Switzerland, 16-17 October 2012 235