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

This thesis arises from the research activity developed at the Industrial Metrology and Quality Engineering Laboratory of DISPEA – Politecnico di Torino, on a new system prototype for dimensional measurement, called Mobile Spatial coordinate Measuring Sys-tem (MScMS) [Franceschini et al., 2008-II]. MScMS determines dimensional features of large-size objects and has been designed to overcome some limits shown by other wide-spread measuring sets used nowadays, like Coordinate Measuring Machines (CMMs), theodolites/tacheometers, photogrammetry equipments, GPS based systems, Laser Track-ers [Bosch, 1995; Pozzi, 2002].
Basing on a distributed sensor networks structure, MScMS can accomplish rapid di-mensional measurements, in a wide range of indoor operating environments. It consists of distributed wireless devices, communicating with each other through radiofrequency (RF) and ultrasound (US) transceivers. This frame makes the system easy to handle and to move, and gives the possibility of placing its components freely around the workpiece. The wireless devices − known as “Crickets” − are developed by the Massachusetts Insti-tute of Technology (MIT). Being quite small, light and potentially cheap (if mass pro-duced), they fit to obtain a wide range of different network configurations [Priyantha et al., 2000; Balakrishnan et al., 2003].
These features make the new system suitable for particular types of measurement, which can not be carried out, for example, by conventional CMMs. Typical is the case of large-size objects which are unable to be transferred to the measuring system area (be-cause of their dimensions or other logistical constraints) and thus require the measuring system to be moved to them.
In the dissertation the system is described exhaustively and characterized through prac-tical experiments. Then, the system is compared to classical CMMs and the indoor-GPS (iGPS), an innovative laser based system for large-scale metrology. Finally, future direc-tions of this research are given.

Mostra/Nascondi contenuto.
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).

Tesi di Dottorato

Dipartimento: DISPEA

Autore: Domenico Maisano Contatta »

Composta da 113 pagine.

 

Questa tesi ha raggiunto 146 click dal 25/05/2009.

 

Consultata integralmente una volta.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.