Design and development of a new large-scale metrology system: MScMS (Mobile Spatial coordinate Measuring System)

1. Introduction The field of large-scale metrology can be defined as the metrology of large machines and structures that is to say “the metrology of objects in which the linear dimensions range from tens to hundreds of meters” [Puttock, 1978]. There is an increasing trend for accu- rate measurement of length, in particular, the 3D coordinate metrology at length scales of 5m to 100m has become a routine requirement in industries such as aircraft and ship con- struction. In this direction, there have been significant advances across a broad range of technologies, including laser interferometry, absolute distance metrology, very high den- sity CCD (Charge-Coupled Device) cameras and so on. Many types of metrological equipments, utilizing different kind of technologies (opti- cal, mechanical, electromagnetic etc..), give physical representations of measured objects in a three-dimensional Cartesian coordinate system. Coordinate Measuring Machines (CMMs), theodolites/tacheometers, photogrammetry equipments, GPS (Global Position- ing Systems), Laser Trackers are typical instruments to do it. Each of these systems is more or less adequate, depending on measuring conditions, user’s experience and skill, and other factors like time, cost, size, accuracy, portability etc.. Classical CMMs, that make possible performing repeated and accurate measurements on objects which are even complexly shaped, are widespread. On the other hand, CMMs are generally bulky and not always suitable for measuring large size objects (for example, longerons of railway vehi- cles, airplane wings, fuselages etc..), because the working volume is limited [ISO 10360, part 2, 2001]. In general, for measuring medium-large size objects, portable systems can be preferred to fixed ones. Transferring the measuring system to the measured object place is often more practical than the vice-versa [Bosch, 1995]. Systems as theodolites/tacheometers, photogrammetry equipments, Laser Trackers, or GPS Ŧ rather than CMMs Ŧ can be easily installed and moved [Pozzi, 2002]. However, they can have some other drawbacks as mentioned in the remaining of this thesis (Section 2.2).