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Representation of a possible measurement accident for the MScMS-II: the authentic target P (with high light intensity) is not detected by D 4 because of the interposed obstacle. On the contrary, the false target F – which is ignored by the other cameras because of the low light intensity – is erroneously detected by D 4 .
Source publication
In the field of large-scale dimensional metrology, new distributed systems based on different technologies have blossomed over the last decade. They generally include (1) some targets to be localized and (2) a network of portable devices, distributed around the object to be measured, which is often bulky and difficult to handle. The objective of th...
Context in source publication
Context 1
... us now consider a possible accident that can occur using a MScMS-II or a generic system based on IR photogrammetric technology for locating targets: false targets . Referring to the configuration in Figure 7, suppose that a generic point P inside the measurement volume has to be localized. All the network devices, with the exception of one, that is, D 4 , are able to cor- rectly measure the angles ( u M i and f M i ) subtended by P . An obstacle, for example, an operator who performs the measurement, is interposed between P and D 4 , blocking it. At the same time, the IR light reflection on a polished surface within the measurement volume produces a false target ( F ). This false target is ignored by almost all devices, thanks to a selective technique according to which – in the presence of multiple targets – only those with greater light intensity ( P in this case) are regarded as authentic, while others are excluded. On the contrary, being unable to see P since it is blocked, device D 4 wrongly considers F as a target (see the representation in Figure 9). The consequence is that the angular measurements by D 4 are wrong. See the example in Table 3(a). In this case, the algorithm will produce the following wrong localization solution: P [ ð 104 : 0, 1062 : 2, 271 : 8 Þ , (mm), characterized by a high level of error: EF ( P ) ffi 28 : 02 . 3 : 50. Owing to this result, this diagnostics suggests rejecting the measurement. After removing the obstacle, the new angles observed by D 4 are u 9 M 1 = 304 : 44 8 and f 9 M 1 = 72 : 96 8 , while those relating to the remaining devices are almost identical to the previous ones (see Table 3(b)). The new localization is P [ ð 85 : 5, 1035 : 8, 299 : 6 Þ (mm). The corresponding EF value is EF ( P ) ffi 2 : 13 4 3 : 50. Hence, the new localization can be considered reliable and the measurement is accepted. As described in Section ‘The MScMS-II’, the hand-held probe is equipped with two targets – that is, A [ ( X A , Y A , Z A ) and B [ ( X B , Y B , Z B ). The distance between the two probe devices ( d AB ) is a priori known (see Figure 5(b)). On the contrary, having localized the two targets, their Euclidean distance can be estimated ...
Citations
... Since the system in Eq. 2 is over-defined (more equations than unknown parameters), there are several possible solution approaches [22,23]. This system can be solved by applying the Generalized Least Squares (GLS) method, which gives greater weight to the contributions from equations that produce less uncertainty and vice versa [21]. ...
Large-Volume Metrology (LVM) instruments – such as laser trackers, photogrammetric systems, rotary-laser automatic theodolites, etc. – generally include several sensors, which measure the distances and/or angles subtended by some targets. This measurements, combined with the spatial position/orientation of sensors (i.e., the so-called extrinsic parameters), can be used to locate targets in the measurement volume. Extrinsic parameters of sensors are generally determined through dedicated sensor calibration methods, which are based on repeated measurements of specific artefacts.
The combined use of multiple LVM instruments enables exploitation of available equipment but may require multiple instrument-dedicated sensor calibrations, which inevitably increase set-up time/cost.
This document presents a novel calibration method – called global calibration – which allows the extrinsic parameters of all sensors to be determined in a single process. The proposed method uses a special artefact – i.e., a hand-held probe with assorted types of targets and inertial sensors – and includes a data-acquisition stage, in which the probe is repositioned in different areas of the measurement volume, followed by a data-processing stage, in which an ad hoc mathematical/statistical model is used to determine the extrinsic parameters of sensors. Additionally, the proposed method includes the formulation of a system of linearized equations, which are weighed considering the uncertainty of input variables.
... Then, the parts and fixtures are fixed by C-clamps. The dimensional variations of fixtures and parts are tested by the large-scale metrology 1 and reduced by the adjustment of the positions for the parts and fixtures. When the dimensional variations of fixtures and parts are acceptable, the parts are tightened by the solid rivets and the pins are removed. ...
... And a different AS has a different length of riveting path. Hence, 1 School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing, P.R. China 2 Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing, P.R. ...
Due to the complexities of calculations based on different representations of constituent parts in an assembly, the combined improvement of efficiency and precision for the riveting has seldom been studied by the sequence planning or dimensional engineering. This article develops an assembly sequence optimization method that simultaneously minimizes the path length and overall dimensional error for the solid riveting. The sequence is denoted by the order of classifications for the nodes around the rivet holes in the finite element model for the assembly. Ant colony algorithm is applied on the optimization by integrating two calculations, that is, the length calculation of riveting path and the calculation of the dimensional error related to rivet upsetting directions and assembly sequence. Results for three assemblies are presented which show a good degree of optimization in performance for different scales of assemblies with different numbers of rivets that share the same solid riveting process.
... The overall distortion denoted by the root mean square (RMS) of deformations of the key points on structural contour is required to be less than a value permitted. In the industrial practice of an antenna assembly, the variation of fixtures and parts inside is well dealt with by the RMS measurement using large-scale metrology 1,2 and the adjustment of layout and heights of fixtures, but the riveting-induced distortion calls for an effective prediction beforehand. The reason is that the often occurred oversize RMS after the riveting shall induce loops of reassembling and RMS measurements or cause the structure dismissal. ...
Reduction in the dimensional error of an assembly mostly focuses on the variation of fixtures and parts inside, in which the variation is mainly controlled by the methods relating to the fixture design and variation analysis. Recently, more researches concentrate on the dimensional analysis of the aluminum assembly where the distortion of rivet joints cannot be neglected, that is, the riveting-induced dimensional error. Hence, both the device design and the variation analysis for the riveting are drawing much attention to reduce the overall distortion. This article presents a dimensional reduction method, a rivet upsetting direction optimization based on a local-to-global dimensional calculation. The method is developed from a recent framework of assembly process optimization according to the discovered sensitivity between global dimensional error and rivet upsetting directions. A potential function that gathers the overall effect of every locating error is included. Simulations for three riveted assemblies are presented for comparison and results show that the method is efficient for the specific assignment of every rivet upsetting directions, and the effects of locating errors and rivet upsetting directions are highly coupled. The coupled effect yields the key questions in the improvement of this method. Detailed suggestions are then summarized.
... i represents a counterclockwise rotation around the new y i axis, which was rotated by ω i ; Ä i represents a counterclockwise rotation around the new z i axis, which was rotated by ω i and then i ; for details, see [8]. ...
... The system in Eq. (12) can be solved when P is "seen" by at least two devices (2 angles × 2devices = 4 total equations). Since this system is overdefined (more equations than unknown parameters), there are several possible solution approaches, ranging from those based on the iterative minimization of a suitable error function [8], to those based on the Least Squares method [11]. ...
... and 0 is a 2 × 2 matrix of zeros. We note that block J i depends on the coordinates of P, in the local coordinate system of the ith network device; they can be expressed as a function of the global coordinates, by applying the transformation in Eq. (8). To define the elements in J i , P has therefore to be localized, at least roughly. ...
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.
Recent studies show that the combined use of large-volume metrology (LVM) systems (e.g., laser trackers, rotary-laser automatic theodolites, photogrammetric systems, etc.) can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. The objective of this paper is to present some diagnostic tests for combinations of LVM systems that are equipped with distance and/or angular sensors. Two are the tests presented: A global test to detect the presence of potential anomalies during measurement and a local test to isolate any faulty sensor(s). This diagnostics is based on the cooperation of sensors of different nature, which merge their local measurement data, and it can be implemented in real-time, without interrupting or slowing down the measurement process. The description of the tests is supported by several experimental examples.
Recent studies show that the combined use of large-volume metrology (LVM) systems (e.g., laser trackers, rotary-laser automatic
theodolites, photogrammetric systems, etc.) can lead to a systematic reduction in measurement uncertainty and a better exploitation of the available equipment. The objective of this paper is to present some diagnostic tests for combinations of LVM systems that are equipped with distance and/or angular sensors. Two are the tests presented: a global test to detect the presence of potential anomalies during measurement and a local test to isolate any faulty sensor(s). This diagnostics is based on the cooperation of sensors of different
nature, which merge their local measurement data, and it can be implemented in real-time, without interrupting or slowing down the measurement process. The description of the tests is supported by several experimental examples.
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.
