Mobile Spatial Coordinate Measuring System: Localization and System Diagnostics

1. Introduction Accuracy specifications are becoming more and more demanding, even for large scale products or assemblies. Large scale metrology [Puttock, 1978] is a branch of metrology which is recently arousing a great interest in many production sectors (automotive, ship- building, aeronautic, etc.). Designing a large scale metrology instrument is not a trivial task. The bigger the dimensions, the harder it is to keep proper accuracy standards within the whole measuring volume. Furthermore large scale objects may cause significant prac- tical problems to the measurement process. For this reason beside accuracy, flexibility has recently become an important design factor of most of the new metrology instru- ments. 1.1 Distributed measuring systems: the new metrology paradigm Beside classical centralized metrology instruments in which a stand-alone unit works in- dependently to provide geometrical features of the object to be measured, recent ap- proaches to large scale metrology seem to turn their attention towards distributed metrol- ogy systems made of multiple components with small dimensions spread around the measuring area [Franceschini et al., 2008; Welch et al., 2001; ARC Second, 2009]. In general these components are able to form a network of sensors that allows rapid dimen- sional measurements to be performed in relation to large-size objects, with typical dimen- sions of several decametres. Distributed metrology systems introduce a new paradigm in the field of large-scale me- trology reversing the classical approach to dimensional metrology. Due to their nature, they are portable and can be easily transferred around the area where the measurand is, instead of moving the measurand to the measuring machine. Compared to centralized sys- tems, distributed systems may cover larger measuring areas, with no need for reposition- ing the instrumentation devices around the measured object [Kang et Tesar, 2004]. The portability, reconfigurability and ease of installation can make these systems attractive for many industries that manufacture large scale products. On the other hand these new sys- tems currently require appropriate testing and verification in order to understand their full potential prior to their deployment in a real manufacturing environment.