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Recent studies show that the combined use of Large-Volume Metrology (LVM) systems (e.g., laser trackers, rotary-laser automatic theodolites (R-LATs), photogrammetric cameras, etc.) can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. Unfortunately, the sensors of a specific LVM system are usually able to localize only specific targets (i.e., active/passive elements positioned in the measurement volume) and not necessarily those related to other systems (e.g., the reflective markers for photogrammetric cameras cannot be used for R-LATs or laser trackers); this represents an obstacle when using combinations of different LVM systems. This paper describes the design of a new modular probe, with different typologies of targets and integrated sensors, which allows to simplify the measurement process. The probe is versatile as the number of targets, their typology and spatial position can be customized depending on the combination of LVM systems in use. A detailed analysis of the technical and functional characteristics of the probe is followed by the presentation of a mathematical/statistical model for the real-time probe localization. Description is supported by realistic application examples.

Recent studies show that the combined use of Large-Volume Metrology (LVM) systems can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. This is actually possible using a recently developed modular probe, which is equipped with different typologies of targets and integrated inertial sensors. The goal of this paper is to present a new mathematical/statistical model for the real-time localization of this probe. This model is efficient, as it is based on a system of linearized equations, and effective, as the equations are weighed with respect to their uncertainty contribution.

The article entitled, "Multi-Target Modular probe for Large-Volume Metrology" submitted in Recent Patents on Engineering (RPENG) by Dr. Domenico A. Maisano has been withdrawn from the journal in accordance with BSP Editorial Policies.

Last decades witness an increasing interest in Large-Scale/Large-Volume Dimensional Metrology (LSDM). Many fields of application, ranging from construction to shipbuilding and aerospace, have shown more and more accurate and versatile systems for geometric control and tolerancing. Especially in the last ten years, optical technology has registered a fundamental step forward both in terms of metrological performances, versatility and convenience of use. This is further demonstrated by the current large diffusion of laser tracker and photogrammetric systems. The growth is also complemented by the development of new standards, even though a comprehensive body specific for LSDM is still lacking. The twofold aim of the present survey is to present a bibliographical and bibliometric analysis of the field and to propose a scheme of classification of the main current approaches. As an output of this paper, a “LSDM Multi-perspective Model” is introduced, according to which dominant technologies and restrictions are analyzed with the aim of individuating current lacks and defining the roadmap for future development of new instruments and systems.

Advances in the area of industrial metrology have generated new technologies that are capable of measuring components with complex geometry and large dimensions. However, no standard or best-practice guides are available for the majority of such systems. Therefore, these new systems require appropriate testing and verification in order for the users to understand their full potential prior to their deployment in a real manufacturing environment. This is a crucial stage, especially when more than one system can be used for a specific measurement task. In this paper, two relatively new large-volume measurement systems, the mobile spatial co-ordinate measuring system (MScMS) and the indoor global positioning system (iGPS), are reviewed. These two systems utilize different technologies: the MScMS is based on ultrasound and radiofrequency signal transmission and the iGPS uses laser technology. Both systems have components with small dimensions that are distributed around the measuring area to form a network of sensors allowing rapid dimensional measurements to be performed in relation to large-size objects, with typical dimensions of several decametres. The portability, reconfigurability, and ease of installation make these systems attractive for many industries that manufacture large-scale products. In this paper, the major technical aspects of the two systems are briefly described and compared. Initial results of the tests performed to establish the repeatability and reproducibility of these systems are also presented.

Distributed Large-Volume Metrology (LVM) systems are mainly used for industrial applications concerning assembly and dimensional verification of large-sized objects. These systems generally consist of a set of network devices, distributed around the measurement volume, and some targets to be localized, in contact with the measured object's surface or mounted on a hand-held probe for measuring the points of interest. Target localization is carried out through several approaches, which use angular and/or distance measurements by network devices. This paper presents a new methodology to support the design of networks of devices, for distributed LVM systems based on triangulation (i.e., systems in which network devices perform angular measurements only). It is assumed that these systems use multi-sensor networks including two typologies of devices: some are accurate but expensive and other ones are less accurate but cheaper. The goal of the methodology is establishing a link between the following parameters: (i) density of network devices, (ii) mix between the two typologies of network devices, (iii) measurement uncertainty, and (iv) cost. The methodology allows to estimate the most appropriate density and mix between the two typologies of network devices, so that the distributed LVM system is conforming with the required measurement uncertainty and cost. The methodology relies on a large number of simulated experiments, defined and implemented using a dedicated routine; feasibility and practicality is tested by preliminary experiments on a multi-sensor photogrammetric system, developed at Politecnico di Torino—DIGEP.

Large Volume Metrology (LVM) tasks can require the concurrent use of several measuring systems. These systems generally consist of set of sensors measuring the distances and/or angles with respect to a point of interest so as to determine its 3D position. When combining different measuring systems, characterized by sensors of different nature, competitive or cooperative methods can be adopted for fusing data. Competitive methods, which are by far the most diffused in LVM, basically perform a weighted mean of the 3D positions determined by the individual measuring systems. On the other hand, for cooperative methods, distance and/or angular measurements by sensors of different systems are combined together in order to determine a unique 3D position of the point of interest. This paper proposes a novel cooperative approach which takes account of the measurement uncertainty in distance and angular measurements of sensors of different nature. The proposed approach is compared with classical competitive approaches from the viewpoint of the metrological performance. The main advantages of the cooperative approach, with respect to the competitive one, are: (i) it is the only option when the individual LVM systems are not able to provide autonomous position measurements (e.g., laser interferometers or single cameras), (ii) it is the only option when only some of the sensors of autonomous systems work correctly (for instance, a laser tracker in which only distance – not angular – measurements are performed), (iii) when using systems with redundant sensors (i.e. photogrammetric systems with a large number of distributed cameras), point localization tends to be better than that using the competitive fusion approach.

Distributed systems for Large-Scale-Metrology applications generally include a set of angular and/or distance sensors, distributed around the measurement volume, and some targets to be localized, in contact with the measured object's surface. For these systems, estimating the uncertainty in target localization is far from trivial, as it may be affected by several factors: uncertainty in sensor calibration and angular/distance measurements, relative position between targets and sensors, etc. This paper proposes a novel approach based on the combined use of the Multivariate Law of Propagation of Uncertainty and Monte Carlo method. Preliminary results and experimental tests are presented and discussed.

A B S T R A C T Large Volume Metrology (LVM) tasks often require the concurrent use of several distributed systems. Competitive or cooperative methods can be adopted for fusing multiple system data. Nowadays, competitive methods are by far the most diffused in LVM; these methods basically perform a weighted mean of 3D position measurements carried out by individual systems, with respect to the relevant uncertainties. This paper proposes a cooperative approach relying on the combination of angular and distance measurements (and relevant uncertainties) yielded by the sensors of each individual system. Preliminary simulations and experimental results concerning the application of this method are presented and discussed. 2015 CIRP.

Large Scale Dimensional Metrology (LSDM) is a branch of metrology that deals with the measurement of objects with dimensions in the order of several meters. Optical systems, relying on the use of multiple cameras and photogrammetric techniques, are among the most used instruments in this field. These systems require a preliminary calibration procedure to determine some essential parameters, such as camera positions and orientations, focal length, distortion parameters, etc. A structured comparison between two different approaches to camera calibration is herein discussed.

Besides classical centralized metrology instruments in which a stand-alone unit works independently to provide geometrical features of the object to be measured, recent approaches to Large-Scale Dimensional Metrology seem to turn their attention towards distributed metrology systems made of multiple components with small dimensions spread around the measuring volume. In general this network of sensors allows rapid dimensional measurements to be performed in relation to large-sized objects, with typical dimensions of several decametres. Distributed metrology systems introduce a new paradigm in the field of Large-Scale Dimensional Metrology, reversing the classical approach to dimensional metrology. Due to their nature, they are portable and can be easily transferred around the volume where the measurand is, instead of moving the measurand to the measuring machine. Compared to centralized systems, distributed systems may cover larger measuring volumes, with no need to reposition the instrumentation devices around the measured object. Portability, reconfigurability and ease of installation make these systems attractive for many industries that manufacture large-scale products.

Measurements can be affected by errors related to many sources, such as technological features of the measuring instrument, measurement procedure and conditions, and operator’s skill. Metrological performance of an instrument can be significantly enhanced by developing a correction model, able to compensate for recognized systematic errors. After an introduction to the concept of error correction, the core of this chapter is the presentation of a methodology aimed at identifying and correcting some of the most influential systematic errors. In particular, the case of MScMS-I is analysed in detail. Finally, some general ideas about the construction of homologous models for other large-scale metrology distributed systems (i.e., the MScMS-II and the iGPS™) are given.

In order to prevent external and internal causes of error, distributed systems can implement some tests for on-line diagnostics. These tests verify the reliability of the measurements according to several acceptance criteria defined on the basis of empirical observations. After introducing the concept of “self-diagnostics” and “measurement reliability”, this chapter describes three diagnostic tests that were specifically developed for distributed metrology systems.

Indoor GPS is a recent laser-based distributed measurement system for dimensional measurements of large-size objects. The performance of iGPS™ depends both on the characteristics of the system components and their physical configuration. Hence, it is important to characterise its real capabilities and point out how they can be influenced by the system configuration and calibration. This chapter presents the system architecture, its hardware and software working principles and provides an exploratory evaluation of the system’s metrological performance, both in static and dynamic conditions.

In order to properly work, every distributed system need to know several parameters about local metrological devices. Some of these parameters may change because of environmental factors such as vibrations, thermal change or other accidental reasons. For this reason, a careful calibration activity is needed to achieve the best accuracy. During this phase, which can be automated to some extent, the system calculates information like network device positions and bearings, local temperature, humidity, pressure and so on. All this information is used during the measurement phase. Errors during the calibration phase adversely affect the accuracy of the measurements.

The Mobile Spatial coordinate Measuring System (MScMS) has been recently designed to make dimensional measurements of large-sized objects. This system, based on modular architecture, consists of three basic parts: a network of sensing devices, distributed around the working area, a portable probe to measure the coordinate points of a reference object, and a data processing unit to store measurement data and process them by means of ad hoc application software. Within the MScMS framework, two systems based on different technologies have been developed at the Industrial Metrology and Quality Engineering Laboratory of Politecnico di Torino—DISPEA. The first (MScMS-I) is based on ultrasound technology whereas the second (MSCMS-II) is based on infrared photogrammetry. In this chapter, we discuss the system architecture and working principles. Furthermore, hardware/software implementation details and metrological performance of two prototypes of these systems are presented. Next, the MScMS is compared with well-tested and widespread instruments, such as classical Coordinate Measuring Machines, and with the iGPS™, described in Chap. 2.

The Mobile Spatial coordinate Measuring System (MScMS) is a distributed wireless-sensor-network-based system used to perform dimensional measurements of large-scale objects. The system consists of a wireless mobile probe with ultrasonic (US) transceivers, the position of which is determined using a distributed constellation of US transceivers arranged around the measuring area. These US transceivers, which are known as Crickets, transmit US signals to each other and measure their time of flight (TOF) to determine the mutual distances. The MScMS is able to calculate the Cartesian coordinates of the object surface points touched by the wireless mobile probe. This paper aims to experimentally evaluate the performance of the US transducers on each of the MScMS Crickets. The experiments are designed and performed by means of a statistical factorial plan to identify the most important factors affecting the transducers' performance on TOF measurements. Particular attention is given to the error derived by the US signal attenuation and the method of US pulse detection. The results are analyzed in detail and fully interpreted. Finally, some considerations about possible actions to improve the MScMS measuring system are given.

Large scale metrology refers to dimensional measurement of objects or features of perhaps a ten of meters or more in size. Alternatively, large scale metrology could be said to apply to any dimensional measurement where the metrology instrument has to be brought to the object rather than vice versa. Recent approaches seem to turn their attention towards distributed metrology systems made of multiple components with small dimensions spread around the measuring area. In general, these components are able to form a wireless network of sensors that allows rapid dimensional measurements to be performed in relation to large-size objects, with typical dimensions of several decametres. The portability, flexibility, and ease of installation of wireless sensor networks (WSNs) make these systems attractive for many industries manufacturing large scale products. This paper proposes different WSN localization procedures designed for the mobile spatial coordinate measuring system, a distributed metrology system developed at the industrial metrology and quality laboratory of DISPEA—Politecnico di Torino.

The mobile spatial coordinate measuring system (MScMS) is a system to perform dimensional measurements of large-scale objects. It consists of a wireless measuring probe with ultrasonic (US) transceivers, the position of which is determined using a distributed constellation of analogous transceivers arranged around the measuring area. The principle is to measure the time-of-flight (TOF) of the US signals exchanged between pairs of transceivers and, consequently, to obtain an estimate of their distances. The accuracy of TOF measurements can be attributed to many factors; the most influential are those associated with US signal attenuation. The purpose of this paper is to build an experimental correction model to reduce the MScMS’ error in TOF measurements. First, a two-way block design, which is based on exploratory experiments, is created to show that transmitter—receiver distance and relative orientation between US transceivers have significant effects on TOF measurement error. Next, an empirical regressive model is constructed on the basis of additional detailed experiments. After performing an extensive experimental validation, the model is automatically implemented by MScMS, with an iterative procedure. The most important benefit of such a model is an important reduction in the dispersion and an improved accuracy associated with TOF measurements.

There is currently an increasing trend for accurate measurements of large-scale lengths; in particular, 3D coordinate metrology at length scales of 5 m to 60 m has become a routine requirement in industries such as aircraft and ship construction. This chapter focuses on the Mobile Spatial coordinate Measuring System (MScMS), a new system developed at the Industrial Metrology and Quality Engineering Laboratory of DISPEA of the Politecnico di Torino. Based on a distributed sensor network structure, MScMS is designed to perform simple and rapid indoor dimensional measurements of large-size objects. Using radiofrequency (RF) and ultrasound (US) signals, the system makes it possible to localize-in terms of spatial coordinates-the points “touched” by a wireless mobile probe. To protect the system from potential causes of error, such as US signal diffraction and reflection, external uncontrolled US sources (key jingling, neon blinking, etc.) or unacceptable software solutions, MScMS implements some statistical tests in order to perform online diagnostics. One of these tests is analyzed in depth in this chapter: the “energy model-based diagnostics test.” Although it is specifically developed for the MScMS

Mobile Spatial coordinate Measuring System (MScMS) is a wireless-sensor-network based system developed at the industrial metrology and quality engineering laboratory of DISPEA – Politecnico di Torino. It has been designed to perform simple and rapid indoor dimensional measurements of large-size volumes (large-scale metrology). It is made up of three basic parts: a “constellation” of wireless devices (Crickets), a mobile probe, and a PC to store and elaborate data. Crickets and mobile probe utilize ultrasound (US) transceivers in order to evaluate mutual distances. The system makes it possible to calculate the position – in terms of spatial coordinates – of the object points “touched” by the probe. Acquired data are then available for different types of elaboration (determination of distances, curves or surfaces of measured objects). In order to protect the system against causes of error such as, for example, US signal diffraction and reflection, external uncontrolled US sources (key jingling, neon blinking, etc.), or software non-acceptable solutions, MScMS implements some statistical tests for on-line diagnostics. Three of them are deeply analyzed in this paper: “energy model-based diagnostics”, “distance model-based diagnostics”, and “sensor physical diagnostics”. For each measurement, if all these tests are satisfied at once, the measured result may be considered acceptable with a specific confidence coefficient. Otherwise, the measurement is rejected. After a general description of the MScMS, the paper focuses on the description of these three on-line diagnostic tools. Some preliminary results achieved by the system prototype are also presented and discussed.

Indoor GPS (iGPS) is a newly developed laser based measuring system for large scale metrology. The relative portability, reconfigurability and ease of installation make the iGPS suitable for many industries manufacturing large scale products. The system performance depends on both the components characteristics and their physical configuration. Hence, an important consideration for the iGPS is to characterise its real capabilities, pointing out how they can be influenced by the system's configuration and setup. In this paper, the system is introduced and the technical aspects are briefly described. Then, an initial test is performed to establish its repeatability, reproducibility and accuracy.

Mobile Spatial coordinate Measuring System (MScMS) is a wireless-sensor-network based system developed at the Industrial Metrology and Quality Engineering Laboratory of DISPEA – Politecnico di Torino. It has been designed to perform simple and rapid indoor dimensional measurements of medium-large size objects (large scale metrology). It is made up of three basic parts: a “constellation” of wireless devices (Crickets), a mobile probe, and a PC to store and elaborate data. Crickets and mobile probe use ultrasound (US) transceivers in order to evaluate mutual distances. Each US device has a communication range limited by a cone of transmission within a nominal opening angle of about 170° and a maximum distance of no more than 8 m. The mobile probe location in the working volume is obtained by a trilateration, consequently it should communicate with at least 4 constellation devices at once. The system makes it possible to calculate the position — in terms of spatial coordinates — of the object points “touched” by the probe. Acquired data are then available for different types of elaboration (determination of distances, curves or surfaces of measured objects). During the system set-up, the constellation Crickets (beacons) are manually placed in the working volume (we define this operation as “positioning”). After that, their coordinates are determined as much precisely as possible (this operation is said “location”). The positioning of constellation devices is one of the most critical aspects in the system set-up. In principle, Crickets can be arranged without restrictions all around the measured object. However, the number and position of network devices are strongly related to the dimensions and shape of both the measuring volume and the measured object. The accuracy in the location of constellation devices is fundamental for the accuracy of the coordinates of the touched points during measurement operation. It is important to assure a full coverage of the space served by network devices by a proper alignment of US transmitters. For that reason, an ad hoc software “pre-processor” has been developed in order to help the operator in positioning and locating constellation devices in the working volume, according to the measuring space and the measured object dimensional characteristics. The aim of the paper is to introduce and describe this computer-assisted approach. Some preliminary results of experimental tests carried out on the system prototype are also presented and discussed.Copyright © 2008 by ASME