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The impracticality of using the confirmatory factor analytic (CFA) approach in testing measurement invariance across many groups is now well known. A concertedeffort to addressing these encumbrances over the last decade has resulted in a new generation of alternative methodological procedures that allow for approximate, rather than exact measurement invariance across groups. The purpose of this article is twofold: (a) to describe and illustrate common difficulties encountered when tests for multigroup invariance are based on traditional CFA procedures and the number of groups is large, and (b) to walk readers through the maximum likelihood (ML) alignment approach in testing for approximate measurement invariance. Data for this example application derive from an earlier study of family functioning across 30 cultures that include responses to the Family Values Scale for 5,482 university students drawn from 27 of these30 countries. Analyses were based on the Mplus 7.4 program. Whereas CFA tests for invariance revealed 108 misspecified parameters that precluded tests for latent mean differences, noninvariant results were well within the acceptable range for the alignment approach thereby substantiating the trustworthiness of the latent mean estimates and their comparison across groups. The alignment approach in testing for approximate measurement invariance provides an automated procedure that can overcome important limitations of traditional CFA procedures in large-scale comparisons.

Background Due to their flexible configuration and lightweight characteristics, film structures have gained significant attention in the field of aerospace engineering. The scales of film structures typically range from several meters to over ten meters. Stereo-digital image correlation (stereo-DIC) methods offer distinct advantages for obtaining full-field measurement results. However, challenges persist in fabricating high-quality speckle patterns and addressing the problem of imaging reflections, particularly for large-scale transparent or semi-transparent film structures. Objective This paper presents an experimental measurement method for large-scale, transparent thin-film structures. The method focuses on fabricating high-quality digital speckle patterns without altering the vibration characteristics of thin film, as well as addressing the problem of imaging reflections. Methods A combined large-scale backlighting system and transmission imaging are introduced to solve the problem of reflections. To avoid altering the characteristics of the thin film, a single-particle transfer printing technique is developed. A large umbrella thin-film structure with a diameter of 6 meters is selected to validate the effectiveness of the proposed method. The structure is composed of multiple steel trusses and fan-shaped films. Results With high-quality speckle patterns and solving the problem of reflections, the full-field displacement results of the umbrella thin-film structure are measured. The first-order and second-order natural frequencies along with corresponding mode shapes are further obtained. Conclusion The effectiveness of the experimental method is demonstrated through rotational and vibration tests conducted on the large umbrella thin-film structure. This method provides a powerful means for studying the mechanical behavior and vibration characteristics of large-scale thin-film structures.

In modern manufacturing, there is an increasing demand for reliable in-process measurement methods directly on large CNC machine tools, eliminating the need to transport workpieces to metrological laboratories. This study assesses the capability and applicability of an articulated arm coordinate measuring machine and a machine tool touch-trigger probe when measuring to a specified tolerance of 0.05 mm in a production environment. Experiments were conducted using the KOBA calibration standard and included measurements with and without applying the articulated arm coordinate measuring machine leapfrog method. The results were evaluated according to ISO 22514-7:2021 and ISO 14253-1:2017, which establish criteria for measurement system capability. The findings revealed that neither measurement system met the capability requirements of ISO 22514-7:2021, particularly due to unsatisfactory QMS and CMS values. However, under ISO 14253-1:2017, both systems were deemed conditionally suitable for verifying conformity to the specifications, with the articulated arm coordinate measuring machine showing lower applicability when using the leapfrog method. This research supports the idea that unreasonable demands for compliance with current standards may lead to questioning of the systems that previously met older standards. The study contributes to the ongoing discussion on integrating advanced metrological tools into the manufacturing process and underscores the need for careful evaluation to ensure the capability and reliability of measurement systems in industrial practice.

Large-scale measurement of key feature points (KFPs) on an aircraft is essential for coordinated movement of locators, which is critical to the final assembly accuracy. Due to the large number and wide distribution of KFPs as well as line-of-sight occlusion, network measurement of laser trackers (LTs) is required. Existing approaches rely on operational experience for the configuration of stations, sequences and station transitions of LTs, which compromises both efficiency and automation capability. To tackle this challenge, this article presents an autonomous mobile measurement method for KFPs in complex scenes of aircraft assembly, incorporating path self-planning and self-positioning capabilities, thereby substantially diminishing temporal expenditure. Firstly, a simultaneous self-planning method of measurement stations and tasks is proposed to determine the minimum number of stations, optimal locations, and their specific KFPs at each station. Secondly, considering obstacles and turning time, a path planning model of mobile LTs combining coarse and fine localization is established to realize automatic station transitions. Finally, an optimal sequence of series of KFPs with a wide spatial distribution is generated to minimize total distance. Aircraft component assembly experiments validated the method, cutting measurement error by 37% and total measurement time by over 50%.

Spherical targets are widely used in coordinate unification of large-scale combined measurements. Through its central coordinates, scanned point cloud data from different locations can be converted into a unified coordinate reference system. However, point cloud sphere detection has the disadvantages of errors and slow detection time. For this reason, a novel method of spherical object detection and parameter estimation based on an improved random sample consensus (RANSAC) algorithm is proposed. The method is based on the RANSAC algorithm. Firstly, the principal curvature of point cloud data is calculated. Combined with the k-d nearest neighbor search algorithm, the principal curvature constraint of random sampling points is implemented to improve the quality of sample points selected by RANSAC and increase the detection speed. Secondly, the RANSAC method is combined with the total least squares method. The total least squares method is used to estimate the inner point set of spherical objects obtained by the RANSAC algorithm. The experimental results demonstrate that the method outperforms the conventional RANSAC algorithm in terms of accuracy and detection speed in estimating sphere parameters.

Large-scale measurement plays an increasingly important role in intelligent manufacturing. However, existing instruments have problems with immersive experiences. In this paper, an immersive positioning and measuring method based on augmented reality is introduced. An inside-out vision measurement approach using a multi-camera rig with non-overlapping views is presented for dynamic six-degree-of-freedom measurement. By using active LED markers, a flexible and robust solution is delivered to deal with complex manufacturing sites. The space resection adjustment principle is addressed and measurement errors are simulated. The improved Nearest Neighbor method is employed for feature correspondence. The proposed tracking method is verified by experiments and results with good performance are obtained.

Laser multilateration is a measurement method based on the distance intersection of multiple laser trackers which has been widely used in large-scale measurements. However, the layout of laser trackers has a great impact on the final measurement accuracy. In order to improve the overall measurement accuracy, firstly, a measurement uncertainty model based on laser multilateration is established. Secondly, a fast laser intersection detection constraint algorithm based on a k-DOPS bounding box and an adaptive target ball incident angle constraint detection algorithm are established for large-scale measurement scenes. Finally, the constrained layout optimization of the laser trackers is realized by using an improved cellular genetic algorithm. The results show that the optimized system layout can achieve the full coverage of measurement points and has higher measurement accuracy. Compared with the traditional genetic algorithm, the improved cellular genetic algorithm converges faster and obtains a better position layout.

In the application domain of large-scale high-precision measurement systems, accurately calibrating the precision of point position measurements is a pivotal issue. Traditional calibration methods rely on laser interferometers and high-precision displacement stages, which are not only costly but also challenging to implement in fixed measurement systems. Addressing this challenge, this study introduces an evaluation method for the spatial point measurement accuracy in large-scale fixed high-precision measurement systems. The models for the relationship between the limit deviation and the maximum deviation of finite measurements were established, as well as the limit deviation and point position measurement accuracy. The spatial point position accuracy of the measurement field was calculated by the measurement errors of a calibration rod. The algorithm was validated using a large-scale measurement platform based on photogrammetric technology. Experimental results demonstrate that the method achieved a point position measurement accuracy calibration better than 0.1 mm within a 20 m measurement range, effectively enhancing the measurement data’s accuracy and reliability. This research optimizes the calibration process for large-scale fixed measurement systems, improves calibration efficiency, and obviates the need for complex equipment to complete the calibration process, which is of considerable importance to the development of high-precision spatial point position measurement technology.

In advanced manufacturing, accurate and reliable 3D geometry measurement is vital for the quality control of large-sized components with multiple small key local features. To obtain both the geometric form and spatial position of these local features, a hybrid robot-assisted laser scanning strategy is introduced, combining a laser tracker, a fringe-projection 3D scanner, and a mobile robotic unit that integrates an industrial robot with an Automated Guided Vehicle. As for improving the overall measurement accuracy, we propose an accuracy-enhanced calibration method that incorporates both error control and compensation strategies. Firstly, an accurate extrinsic parameter calibration method is proposed, which integrates robust target sphere center estimation with distance-constrained-based optimization of local common point coordinates. Subsequently, to construct a high-accuracy, large-scale spatial measurement field, an improved global calibration method is proposed, incorporating coordinate optimization and a hierarchical strategy for error control. Finally, a robot-assisted laser scanning hybrid measurement system is developed, followed by calibration and validation experiments to verify its performance. Experiments verify its high precision over 14 m (maximum error: 0.117 mm; mean: 0.112 mm) and its strong applicability in large-scale scanning of key geometric features, providing reliable data for quality manufacturing of large-scale components.

In the large-scale measurement field, deployment planning usually uses the Monte Carlo method for simulation analysis, which has high algorithm complexity. At the same time, traditional station planning is inefficient and unable to calculate overall accessibility due to the occlusion of tooling. To solve this problem, in this study, we first introduced a Poisson-like randomness strategy and an enhanced randomness strategy to improve the remora optimization algorithm (ROA), i.e., the PROA. Simultaneously, its convergence speed and robustness were verified in different dimensions using the CEC benchmark function. The convergence speed of 67.5–74% of the results is better than the ROA, and the robustness results of 66.67–75% are better than those of the ROA. Second, a deployment model was established for the large-scale measurement field to obtain the maximum visible area of the target to be measured. Finally, the PROA was used as the optimizer to solve optimal deployment planning; the performance of the PROA was verified by simulation analysis. In the case of six stations, the maximum visible area of the PROA reaches 83.02%, which is 18.07% higher than that of the ROA. Compared with the traditional method, this model shortens the deployment time and calculates the overall accessibility, which is of practical significance for improving assembly efficiency in large-size measurement field environments.