Large-scale Metrology Research Articles

Dynamic recalibration of scalable fringe-projection systems for large-scale object metrology

Three-dimensional (3D) surface shape measurement is a vital component in many industrial processes. The subject has developed significantly over recent years and a number of mainly noncontact techniques now exist for surface measurement, exhibiting varying levels of maturity. Within the larger group of 3D measurement techniques, one of the most promising approaches is provided by those methods that are based upon fringe analysis. Current techniques mainly focus on the measurement of small and medium-scale objects, while work on the measurement of larger objects is not so well developed. One potential solution for the measurement of large objects that has been proposed by various researchers is the concept of performing multipanel measurement and the system proposed here uses this basic approach, but in a flexible form of a single moveable sensor head that would be cost effective for measuring very large objects. Most practical surface measurement techniques require the inclusion of a calibration stage to ensure accurate measurements. In the case of fringe analysis techniques, phase-to-height calibration is required, which includes the use of phase-to-height models. Most existing models (both analytical and empirical) are intended to be used in a static measurement mode, which means that, typically, a single calibration is performed prior to multiple measurements being made using an unvarying system geometry. However, multipanel measurement strategies do not necessarily keep the measurement system geometry constant and thus require dynamic recalibration. To solve the problem of dynamic recalibration, we propose a class of models called hybrid models. These hybrid models inherit the basic form of analytical models, but their coefficients are obtained in an empirical manner. The paper also discusses issues associated with all phase-to-height models used in fringe analysis that have a quotient form, identifying points of uncertainty and regions of distortion as issues affecting accuracy in phase maps produced in this manner.

Optimal sensor positioning for large scale metrology applications

As it strongly affects the system performance in measuring 3D point coordinates, beacon positioning represents a challenging issue in large scale metrology applications based on wireless sensor networks. This paper presents a software-assisted procedure for efficient placement of ultrasonic beacons in a wireless distributed network-based system for medium–large sized object measurements. A regular grid-based strategy and a genetic algorithm-based approach to the deployment problem are presented. The resulting network configurations are compared in terms of overall costs, sensor availability and measurement precision. The genetic algorithm outperforms the regular deployment solution, optimizing the objective functions and providing additional capabilities to represent a realistic working environment. The novelty here is the approach to the “pre-processing” phase of a sensor network deployment, involving working environment constraints, system functional characteristics, measurand geometry, and measurement task definition in the three-dimensional network design.

The Mobile Spatial coordinate Measuring System II (MScMS-II): system description and preliminary assessment of the measurement uncertainty

According to the increasing interest in metrological systems for the dimensional measurements of large-size objects in a wide range of industrial sectors, several solutions based on different technologies, working principles, architectures, and functionalities have recently been developed. Among all, the most flexible and easily transportable solutions are those that have aroused most interest and have found greater success. In order to address the needs of Large-Scale Metrology (LSM) applications, a distributed flexible system based on a network of low-cost InfraRed (IR) sensors - the Mobile Spatial coordinate Measur- ing System II (MScMS-II) - has been developed at the Industrial Quality and Metrology Laboratory of Politecnico di Torino. This paper presents a preliminary uncertainty assessment of the system referring to the measured point coordinates in the 3D space, focusing on the sources of measurement uncertainty and the related propagation laws. A preliminary metrological characterization of MScMS-II architecture, experimentally evaluated through a system prototype, is also presented and discussed.

Ultrasound Transducers for Large-Scale Metrology: A Performance Analysis for Their Use by the MScMS

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.

Network localization procedures for experimental evaluation of mobile spatial coordinate measuring system (MScMS)

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.

Large-scale production and metrology of vertically aligned carbon nanotube films

The authors have produced carbon nanotube (CNT) films on a large scale in a commercial chemical vapor deposition (CVD) reactor. The reactor (built by Tystar, Inc) is the first of its kind and is capable of handling up to 50 150mm wafers simultaneously with industry standard process control. Electron microscopy reveals that the CNT films consist of densely packed and vertically aligned multiwalled CNTs. A variety of catalysts and reaction conditions were systematically tested. Both Fe films and Cr∕Ni∕Fe film stacks have been found favorable for the growth of aligned CNT films. While electron microscopy provides invaluable information, it is qualitative and unsuitable for process optimization and industrial quality control. A quantitative metrology standard is required for these purposes, but has to date not been explicitly defined. They report on their initial developments toward this metrology standard, considering such factors as film thickness (or CNT length), CNT wall number and diameter, amorphous carbon content, and uniformity. Various measurement techniques have been investigated and are discussed. The developed metrology will facilitate quality control and process optimization necessary for industry applications of CNT films.

An unmanned aerial vehicle-based system for large scale metrology applications

Different manufacturing environments, such as aerospace, automotive, shipbuilding, and railway, reveal their interest in large scale metrology (LSM) instruments, to provide support in assembly, alignment, inspection, and robot tracking tasks. Notwithstanding different levels of portability, the overall measurement procedure actually involves a direct interaction between the measuring equipment and the operator, as well as a strong dependence on human skills. This paper presents a novel metrological system, scaling down this interaction to a mission management task and aimed at making system performance uniform. The proposed architecture entrusts an unmanned aerial vehicle (UAV) with the task of carrying the sensor equipment and of moving the measuring probe. The design process of the proposed system is detailed and faced with a two-level approach. The first level is directed to identify the available start-up technology, its limitations and sensitivity to the design parameters, while the second level is focused on the experimental testing of a preliminary test-bed to investigate the overall system performance. An actual implementation of the proposed architecture is herein discussed, focusing on system feasibility and presenting some preliminary experimental results.

Recent developments in large-scale dimensional metrology

With ever-more demanding requirements for the accurate manufacture of large components, dimensional measuring techniques are becoming progressively more sophisticated. This review describes some of the more recently developed techniques and the state-of-the-art in the more well-known large-scale dimensional metrology methods. In some cases, the techniques are described in detail, or, where relevant specialist review papers exist, these are cited as further reading. The traceability of the measurement data collected is discussed with reference to new international standards that are emerging. In some cases, hybrid measurement techniques are finding specialized applications and these are referred to where appropriate.

On-line diagnostics in the Mobile Spatial coordinate Measuring System (MScMS)

Abstract 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.

Mobile spatial coordinate measuring system (MScMS) and CMMs: a structured comparison

In many branches of industry, most of manufacturing efforts are directed toward producing objects of specific forms and dimensions. Dimensional measurement is an important part of the production cycle, to check products compliance with specifications. For this, many substantial improvements in the existing technologies have been made, and new measuring systems have been introduced. This paper briefly introduces a recent measuring system—mobile spatial coordinate measuring system (MScMS)—which is suitable for performing dimensional measurements of large-size objects (dimension on the order of tens of meters). MScMS, thanks to its distributed wireless sensor network nature, is portable and can be easily arranged around the measured object. Furthermore, it does not require complex setup operations before being ready to perform measurements. After describing how the system works, we will compare it with well-tested and widespread instruments such as traditional coordinate measuring machines (CMMs), showing analogies and differences. The comparison is structured on the basis of different criteria, which are analyzed in detail in the first part of the paper. Although being able to perform similar measurements, CMMs and MScMS are different in technological features. CMMs are able to achieve higher level of accuracy, while MScMS is more flexible, cheap, and can be important to simplify the current measuring practices within large-scale industrial metrology. It can be concluded that these systems can easily coexist, as each system is suitable for specific applications.

Optical measurement techniques for mobile and large-scale dimensional metrology

Dimensional inspection tasks are often carried out on conventional coordinate measuring machines (CMMs). These CMMs can differ in layout and size depending on the application area. They can have measurement volumes up to 100 m 3. However, when measuring large objects it is not always possible to bring a large object to these conventional CMMs. That is why for these applications mobile measuring systems are an ideal solution. These systems often measure the dimensions through optical techniques, like interferometry and optical triangulation. After a short survey of common optical measurement techniques for mobile and large-scale measurements, this paper focuses on two industrial cases where different techniques were used to solve a measurement problem. The first case covers the measurement of a large iron casting with an optical LED-based triangulation system. It was possible to predict problems that would occur with the machining of the part, like unfinished surfaces after milling due to material shortage, and adapt the alignment of the part to prevent these problems. The second case covers the measurement of a double-decker train by means of photogrammetry, as an alternative for the currently used total station. Despite some specific drawbacks of photogrammetry systems it was possible to obtain the same accuracy and to reduce the overall inspection time significantly in comparison with the current situation.

Indoor GPS: system functionality and initial performance evaluation

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.

Key digital enterprise technology methods for large volume metrology and assembly integration

Digital enterprise technology (DET) is a theoretical framework for collaborative design and production development in the context of a product's lifecycle. The DET framework can be used to configure digital product and process development technologies which assimilate design data, at various levels of completeness, with a high degree of real-time measurement feedback from the production environment in order to validate the product's tolerance specification and the selected production and assembly processes. This paper describes research focused on the integration of two major facets of DET; process planning and large volume metrology (LMV). The challenges encountered include the representation of early designs of complex products, the definition of high risk areas in the process plan and the generation of accurate, dynamic measurement data from large-scale laser metrology in the production environment. The methods employed demonstrate how DET-based strategies for design, manufacture and integration can utilize recent technology advances in aggregate modelling and planning, tolerance analysis tools and 3D coordinate metrology. Early testing using aerospace products has been very promising and the research findings will benefit manufacturers of high-value, high-complexity products within distributed production networks.

Weighing the world’s heaviest telescope at eight points with corrections for lifting perturbations

Abstract This technical note presents a summary of internal reports [ Parker DH, Anderson R, Egan D, Fakes T, Radcliff B, Shelton J. GBT rolling weight measurements: methods, results, estimation of uncertainty, and auxiliary measurements. GBT Memo 222, The National Radio Astronomy Observatory, 2003 ; Parker DH, Anderson R, Egan D, Fakes T, Radcliff B, Shelton J. GBT rolling weight measurements: methods, results, estimation of uncertainty, and auxiliary measurements. Technical Report A0335, The National Radio Astronomy Observatory, 2003. Includes Appendices ( ≈ 250 pp.) ], on weighing The National Radio Astronomy Observatory (NRAO), Robert C. Byrd Green Bank Telescope (GBT)—the world’s largest (100 m), fully steerable, radio telescope (and involving, possibly, the most accurate large-scale metrology field measurement of weight conducted to date). The measured weight was 74 405 kN (4.448222 N/lbf), with a combined standard uncertainty (level of confidence ≈ 68%) of ± 213 kN, or a relative combined standard uncertainty of 0.3%. Two measurements of a wheel pair (mounter on a common support beam), conducted 15 days apart, reproduced within 24 kN, or 0.3%. The measured weight distribution revealed a maximum wheel pair load of 9781 ± 44 kN, or 46% greater than the original wheel and track design assumptions, and nearly 9% greater than the final symmetric load estimation. Corrections were made for perturbations in the measured forces, due to lifting approximately one-eighth of the structure at a time. The load cells were custom calibrated to more closely match the actual field conditions. Parallel measurements are also presented from the hydraulic jack pressures.

Large-Scale Metrology – An Update

Developments in large-scale engineering metrology since the 1978 report of Puttock are reviewed. Advances in optical technology and fast, low-cost computation have led to wide-spread use of laser trackers and digital photogrammetry for general-purpose coordinate metrology. Techniques for high-accuracy straightness measurement, precision leveling, and absolute distance metrology are described, together with approaches to compensation for the effects of atmospheric refraction. Methods for uncertainty evaluation are discussed and several illustrative examples are presented.

Contribution of CIRP to the Development of Metrology and Surface Quality Evaluation during the last fifty years

An overview of the contribution of the members of the C.I.R.P. community to the progress of Metrology and Surface Roughness Quality Evaluation is given. The following items are included in the part on metrology: brief overview of the existing situation before 1950, contribution to the successive definitions of the unit of length and related reference length standards, traceability, preliminary work to standardization, thermal effects, design and construction of precision machine tools and measuring machines, CMM, large scale metrology. In the field of surface quality evaluation, the following items are reviewed: reference profiles and related definitions of parameters, filtering, surface and subsurface integrity, functional meaning of parameters, instrumentation, scanning probe microscopy, 3D surface evaluation. A comprehensive list of references is provided.

Large scale metrology

Large scale metrology

Large scale metrology

Large scale metrology