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14 pages, 7666 KiB

Open AccessCommunication

Low-Cost AR-Based Dimensional Metrology for Assembly

by Rahma Nawab and Angela Davies Allen

Machines 2022, 10(4), 243; https://doi.org/10.3390/machines10040243 - 30 Mar 2022

Cited by 4 | Viewed by 2266

Abstract

The goal of this study was to create and demonstrate a system to perform fast and inexpensive quality dimensional inspection for industrial assembly line applications with submillimeter uncertainty. Our focus is on the positional errors of the assembled pieces on a larger part [...] Read more.

The goal of this study was to create and demonstrate a system to perform fast and inexpensive quality dimensional inspection for industrial assembly line applications with submillimeter uncertainty. Our focus is on the positional errors of the assembled pieces on a larger part as it is assembled. This is achieved by using an open-source photogrammetry architecture to gather a point cloud data of an assembled part and then comparing this to a computer-aided design (CAD) model. The point cloud comparison to the CAD model is used to quantify errors in position using the iterative closest point (ICP) algorithm. Augmented reality is utilized to view the errors in a live-video feed and effectively display said errors. The initial demonstration showed an assembled position error of 9 mm ± 0.4 mm for a 40-mm high post. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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15 pages, 4928 KiB

Open AccessEditor’s ChoiceArticle

3D Reconstruction of High Reflective Welding Surface Based on Binocular Structured Light Stereo Vision

by Baizhen Li, Zhijie Xu, Feng Gao, Yanlong Cao and Quancheng Dong

Machines 2022, 10(2), 159; https://doi.org/10.3390/machines10020159 - 20 Feb 2022

Cited by 24 | Viewed by 4488

Abstract

The inspection of welding surface quality is an important task for welding work. With the development of product quality inspection technology, automated and machine vision-based inspection have been applied to more industrial application fields because of its non-contact, convenience, and high efficiency. However, [...] Read more.

The inspection of welding surface quality is an important task for welding work. With the development of product quality inspection technology, automated and machine vision-based inspection have been applied to more industrial application fields because of its non-contact, convenience, and high efficiency. However, challenging material and optical phenomena such as high reflective surface areas often present on welding seams tend to produce artifacts such as holes in the reconstructed model using current visual sensors, hence leading to insufficiency or even errors in the inspection result. This paper presents a 3D reconstruction technique for highly reflective welding surfaces based on binocular style structured light stereo vision. The method starts from capturing a fully lit image for identifying highly reflective regions on a welding surface using conventional computer vision models, including gray-scale, binarization, dilation, and erosion. Then, fringe projection profilometry is used to generate point clouds on the interested area. The mapping and alignment from 2D image to 3D point cloud is then established to highlight features that are vital for eliminating “holes”—large featureless areas—caused by high reflections such as the specular mirroring effect. A two-way slicing method is proposed to operate on the refined point cloud, following the concept of dimensionality reduction to project the sliced point cloud onto different image planes before a Smoothing Spline model is applied to fit the discrete point formed by projection. The 3D coordinate values of points in the “hole” region are estimated according to the fitted curves and appended to the original point cloud using iterative algorithms. Experiment results verify that the proposed method can accurately reconstruct a wide range of welding surfaces with significantly improved precision. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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16 pages, 15903 KiB

Open AccessArticle

Precise Measurement and Visual Expression of Gear Overall Deviation

by Jianzhou Pan, Aiping Song, Jiaming Huang and Chuang Yan

Machines 2022, 10(2), 158; https://doi.org/10.3390/machines10020158 - 20 Feb 2022

Cited by 3 | Viewed by 2644

Abstract

This paper proposes a non-contact measurement, analysis, and visualization method for the overall deviation of gears based on a laser displacement sensor. We implement error compensation and coordinate transformation on the tooth profile data collected by the laser probe through an algorithm, and [...] Read more.

This paper proposes a non-contact measurement, analysis, and visualization method for the overall deviation of gears based on a laser displacement sensor. We implement error compensation and coordinate transformation on the tooth profile data collected by the laser probe through an algorithm, and fit all the data points to the gear surface using a 3 × 3 degree spline function. According to the established actual surface model of the gear, the tooth profile curve on any section of the gear and its various deviations can be obtained. To find the overall deviation on the tooth profile surface, the deviation data is refined and fitted into a curved surface by the Newton difference method. The overall deviation can be represented on the gear surface in the form of a color map, and then the color map of the overall deviation of the gear can be obtained. In addition, it can intuitively analyze the distribution of the overall deviation on the gear surface, and realize the visual expression of the deviation. Finally, through experimental verification, we prove that this method can quickly and accurately analyze the various deviations of the gears and the distribution of the deviation, and can effectively improve the detection accuracy and efficiency of the gears. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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18 pages, 59252 KiB

Open AccessArticle

A Novel Learning Based Non-Lambertian Photometric Stereo Method for Pixel-Level Normal Reconstruction of Polished Surfaces

by Yanlong Cao, Xiaoyao Wei, Wenyuan Liu, Binjie Ding, Jiangxin Yang and Yanpeng Cao

Machines 2022, 10(2), 120; https://doi.org/10.3390/machines10020120 - 8 Feb 2022

Cited by 2 | Viewed by 2914

Abstract

High-quality reconstruction of polished surfaces is a promising yet challenging task in the industrial field. Due to its extreme reflective properties, state-of-the-art methods have not achieved a satisfying trade-off between retaining texture and removing the effects of specular outliers. In this paper, we [...] Read more.

High-quality reconstruction of polished surfaces is a promising yet challenging task in the industrial field. Due to its extreme reflective properties, state-of-the-art methods have not achieved a satisfying trade-off between retaining texture and removing the effects of specular outliers. In this paper, we propose a learning based pixel-level photometric stereo method to estimate the surface normal. A feature fusion convolutional neural network is used to extract the features from the normal map solved by the least square method and from the original images respectively, and combine them to regress the normal map. The proposed network outperforms the state-of-the-art methods on the DiLiGenT benchmark dataset. Meanwhile, we use the polished rail welding surface to verify the generalization of our method. To fit the complex geometry of the rails, we design a flexible photometric stereo information collection hardware with multi-angle lights and multi-view cameras, which can collect the light and shade information of the rail surface for photometric stereo. The experimental results indicate that the proposed method is able to reconstruct the normal of the polished surface at the pixel level with abundant texture information. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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11 pages, 4561 KiB

Open AccessArticle

Carré Phase Shifting Algorithm for Wavelength Scanning Interferometry

by Hussam Muhamedsalih, Dawei Tang, Prashant Kumar and Xiangqian Jiang

Machines 2022, 10(2), 116; https://doi.org/10.3390/machines10020116 - 5 Feb 2022

Cited by 2 | Viewed by 2400

Abstract

Wavelength scanning interferometry is an interferometric technique for measuring surface topography without the well-known 2π phase ambiguity limitation. The measurement accuracy and resolution of this technique depends, among other factors, on the algorithm used to evaluate its sinusoidal interference pattern. The widely used [...] Read more.

Wavelength scanning interferometry is an interferometric technique for measuring surface topography without the well-known 2π phase ambiguity limitation. The measurement accuracy and resolution of this technique depends, among other factors, on the algorithm used to evaluate its sinusoidal interference pattern. The widely used fast Fourier transform analysis experiences problems such as waviness error across the measured surface due to spectral leakage. This paper introduces a new fringe analysis method based on the Carré phase shifting algorithm combined with a least squares fitting approach. Numerical simulation was carried out to assess the performance of the Carré algorithm in comparison to fast Fourier transform analysis, and the same was validated by presenting four experimental case study examples (a surface flat, a ceramic ball bearing, a flexible thin film, and a discontinuous step height sample). The analysis results show that the proposed Carré algorithm with least squares fitting can significantly eliminate the waviness error, especially when measuring steep surfaces. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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15 pages, 7291 KiB

Open AccessArticle

Bayesian Regularization Algorithm Based Recurrent Neural Network Method and NSGA-II for the Optimal Design of the Reflector

by Xinyong Zhang, Liwei Sun and Lingtong Qi

Machines 2022, 10(1), 63; https://doi.org/10.3390/machines10010063 - 15 Jan 2022

Cited by 6 | Viewed by 2839

Abstract

The optical-mechanical system of a space camera is composed of several complex components, and the effects of several factors (weight, gravity, modal frequency, temperature, etc.) on its system performance need to be considered during ground tests, launch, and in-orbit operation. In order to [...] Read more.

The optical-mechanical system of a space camera is composed of several complex components, and the effects of several factors (weight, gravity, modal frequency, temperature, etc.) on its system performance need to be considered during ground tests, launch, and in-orbit operation. In order to meet the system specifications of the optical camera system, the dimensional parameters of the optical camera structure need to be optimized. There is a highly nonlinear functional relationship between the dimensional parameters of the optical machine structure and the design indexes. The traditional method takes a significant amount of time for finite element calculation and is less efficient. In order to improve the optimization efficiency, a recurrent neural network prediction model based on the Bayesian regularization algorithm is proposed in this paper, and the NSGA-II is used to globally optimize multiple prediction objectives of the prediction model. The reflector of the space camera is used as an example to predict the weight, first-order modal frequency, and gravitational mirror deformation root mean square of the reflector, and to complete the lightweight design. The results show that the prediction model established by BR-RNN-NSGA-II offers high prediction accuracy for the design indexes of the reflector, which all reach over 99.6%, and BR-RNN-NSGA-II can complete the multi-objective optimization search efficiently and accurately. This paper provides a new idea of optimization of optical machine structure, which enriches the theory of complex structure design. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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16 pages, 3427 KiB

Open AccessFeature PaperArticle

Research on a Measurement Method for Middle-Infrared Radiation Characteristics of Aircraft

by Xuan Deng, Yueming Wang, Guicheng Han and Tianru Xue

Machines 2022, 10(1), 44; https://doi.org/10.3390/machines10010044 - 7 Jan 2022

Cited by 8 | Viewed by 2633

Abstract

Aiming at the problem wherein temperature inversion accuracy is unstable due to the major differences in atmospheric transmittance under various observation paths, a method for measuring radiation characteristics of an aircraft engine’s hot parts and skin using a cooled middle-wave infrared camera is [...] Read more.

Aiming at the problem wherein temperature inversion accuracy is unstable due to the major differences in atmospheric transmittance under various observation paths, a method for measuring radiation characteristics of an aircraft engine’s hot parts and skin using a cooled middle-wave infrared camera is proposed. Based on the analysis of the aircraft’s infrared radiation characteristics, the atmospheric transmission model of any observation path was revised, the absolute radiation correction model was established, and the temperature inversion equation was calculated. Then, we used the quasi-Newton method to calculate the skin temperature and discussed uncertainty sources. After the theoretical study, an outfield test was carried out. A middle-wave infrared camera with a wavelength of 3.7–4.8 μm was applied to the actual experimental observation of the turbofan civil aviation aircraft. The ground observation distance was 15 km, and the flying height was 3 km. When implementing temperature inversion with the method presented in this paper, the surface temperature of the aircraft engine hot parts was 381 K, the correction uncertainty was ±10 K, the surface temperature of the skin was 296 K, and the correction uncertainty was ±6 K. As the experiment showed, the method in this paper can effectively implement infrared target temperature inversion and provide a reference for the quantification of infrared data. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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16 pages, 11790 KiB

Open AccessArticle

Research and Experimental Verification on Topology-Optimization Design Method of Space Mirror Based on Additive-Manufacturing Technology

by Yanchao Fan, Deyi Dong, Chao Li, Yuxin Sun, Zhiyu Zhang, Fanlu Wu, Liwei Yang, Quhao Li and Yingjun Guan

Machines 2021, 9(12), 354; https://doi.org/10.3390/machines9120354 - 15 Dec 2021

Cited by 13 | Viewed by 3115

Abstract

As one of the most-critical components in space optical cameras, the performance of space mirrors directly affects the imaging quality of space optical cameras, and the lightweight form of mirror blanks is a key factor affecting the structural quality and the surface-shape accuracy [...] Read more.

As one of the most-critical components in space optical cameras, the performance of space mirrors directly affects the imaging quality of space optical cameras, and the lightweight form of mirror blanks is a key factor affecting the structural quality and the surface-shape accuracy of mirrors. For the design requirements of lightweight and high surface-shape accuracy with space mirrors, this study proposes a design and manufacturing method that integrates topology-optimization with additive-manufacturing technology. This article firstly introduced the basic process and key technologies of space-mirror design and analyzed the superiority of combining a topology-optimized configuration design and additive-manufacturing technology; secondly, the topology-optimized design method of a back-open-structure mirror was used to complete the scheme design of a

Φ

260 mm aperture mirror; finally, the laser selective-melting manufacturing technology was used to complete the

Φ

260 mm aperture mirror blank. The mirror and its support structure were assembled and tested in a modal mode; the resonant frequencies of the mirror assembly were all over 600 Hz; and the deviation from the analytical results was within 2%. The optical surface of the mirror was turned by the single-point diamond-turning (SPDT) technique. The accuracy of the optical surface was checked by a Zygo interferometer. The RMS accuracy of the mirror surface was 0.041

λ

(

λ

is the wavelength;

λ

= 632 nm). In the test of the influence of gravity on the surface-shape accuracy, the mirror was turned over, which was equivalent to twice the gravity, and the RMS of the mirror surface-shape accuracy was 0.043

λ

, which met the requirement. The verification results show that the mirror designed and fabricated by the additive-manufacturing-based mirror-topology-optimization method can be prepared by the existing process, and the machinability and mechanical properties can meet the requirements, which provides an effective development method for improving the structural design and optimizing the manufacturing of space reflectors. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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11 pages, 3270 KiB

Open AccessArticle

Measurement of Film Structure Using Time-Frequency-Domain Fitting and White-Light Scanning Interferometry

by Xinyuan Guo, Tong Guo and Lin Yuan

Machines 2021, 9(12), 336; https://doi.org/10.3390/machines9120336 - 7 Dec 2021

Viewed by 3180

Abstract

A new technique is proposed for measuring film structure based on the combination of time- and frequency-domain fitting and white-light scanning interferometry. The approach requires only single scanning and employs a fitting method to obtain the film thickness and the upper surface height [...] Read more.

A new technique is proposed for measuring film structure based on the combination of time- and frequency-domain fitting and white-light scanning interferometry. The approach requires only single scanning and employs a fitting method to obtain the film thickness and the upper surface height in the frequency and time domains, respectively. The cross-correlation function is applied to obtain the initial value of the upper surface height, thereby making the fitting process more accurate. Standard films (SiO₂) with different thicknesses were measured to verify the accuracy and reliability of the proposed method, and the three-dimensional topographies of the upper and lower surfaces of the films were reconstructed. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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13 pages, 7565 KiB

Open AccessArticle

A Comparison of the Probes with a Cantilever Beam and a Double-Sided Beam in the Tool Edge Profiler for On-Machine Measurement of a Precision Cutting Tool

by Bo Wen, Sho Sekine, Shinichi Osawa, Yuki Shimizu, Hiraku Matsukuma, Andreas Archenti and Wei Gao

Machines 2021, 9(11), 271; https://doi.org/10.3390/machines9110271 - 6 Nov 2021

Viewed by 2544

Abstract

This paper describes a comparison of the mechanical structures (a double-sided beam and a cantilever beam) of a probe in a tool edge profiler for the measurement of a micro-cutting tool. The tool edge profiler consists of a positioning unit having a pair [...] Read more.

This paper describes a comparison of the mechanical structures (a double-sided beam and a cantilever beam) of a probe in a tool edge profiler for the measurement of a micro-cutting tool. The tool edge profiler consists of a positioning unit having a pair of one-axis DC servo motor stages and a probe unit having a laser displacement sensor and a probe composed of a stylus and a mechanical beam; on-machine measurement of a tool cutting edge can be conducted with a low contact force through measuring the deformation of the probe by the laser displacement sensor while monitoring the tool position. Meanwhile, the mechanical structure of the probe could affect the performance of measurement of the edge profile of a precision cutting tool. In this paper, the measurement principle of the tool edge profile is firstly introduced; after that, slopes and a top-flat of a cutting tool sample are measured by using a cantilever-type probe and a double-sided beam-type probe, respectively. The measurement performances of the two probes are compared through experiments and theoretical measurement uncertainty analysis. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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14 pages, 6514 KiB

Open AccessArticle

A Simple Calibration Method for a Fringe Projection System Embedded within an Additive Manufacturing Machine

by Yue Liu, Liam Blunt, Feng Gao and Xiangqian Jiang

Machines 2021, 9(9), 200; https://doi.org/10.3390/machines9090200 - 17 Sep 2021

Cited by 5 | Viewed by 2996

Abstract

In additive manufacturing (AM), especially for advanced powder fusion machines, it is of high importance to develop an in situ inspection system to monitor the printed surface and pre-print powder bed as the build cycle proceeds. Consequently, high resolution, high precision and fast [...] Read more.

In additive manufacturing (AM), especially for advanced powder fusion machines, it is of high importance to develop an in situ inspection system to monitor the printed surface and pre-print powder bed as the build cycle proceeds. Consequently, high resolution, high precision and fast detection measurement systems need to be investigated, as such optically based measurement systems can provide feedback for manufacturing process optimisation. Fringe projection technology has a great advantage in the measurement of topography in such environments. The implementation of a fringe projection system requires that the system is pre-calibrated in order to obtain high measurement resolution and repeatability. This paper presents a simple calibration method for an AM-based in situ fringe projection system using a phase-depth calibration model. If a calibration plate with certificated marks is used, however, the texture of the plate will affect the measured phase accuracy. A simple calibration method to reduce the calibration plate texture effect in the process of calibration is outlined. Experimental results show that the proposed method can eliminated these effects and improve measurement resolution and repeatability. The proposed in situ/in process inspection technique has been implemented within a commercial electron beam powder bed fusion additive manufacturing machine (EBAM), to demonstrate the capability for effective feedback during the manufacturing process. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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14 pages, 6110 KiB

Open AccessEditor’s ChoiceArticle

3D Measurement of Structured Specular Surfaces Using Stereo Direct Phase Measurement Deflectometry

by Yuemin Wang, Yongjia Xu, Zonghua Zhang, Feng Gao and Xiangqian Jiang

Machines 2021, 9(8), 170; https://doi.org/10.3390/machines9080170 - 17 Aug 2021

Cited by 15 | Viewed by 3002

Abstract

With the rapid development of modern manufacturing processes, ultra-precision structured freeform surfaces are being widely explored for components with special surface functioning. Measurement of the 3D surface form of structured specular objects remains a challenge because of the complexity of the surface form. [...] Read more.

With the rapid development of modern manufacturing processes, ultra-precision structured freeform surfaces are being widely explored for components with special surface functioning. Measurement of the 3D surface form of structured specular objects remains a challenge because of the complexity of the surface form. Benefiting from a high dynamic range and large measuring area, phase measurement deflectometry (PMD) exhibits great potential in the inspection of the specular surfaces. However, the PMD is insensitive to object height, which leads to the PMD only being used for smooth specular surface measurement. Direct phase measurement deflectometry (DPMD) has been introduced to measure structured specular surfaces, but the surface form measurement resolution and accuracy are limited. This paper presents a method named stereo-DPMD for measuring structured specular objects by introducing a stereo deflectometor into DPMD, so that it combines the advantages of slope integration of the stereo deflectometry and discontinuous height measurement from DPMD. The measured object is separated into individual continuous regions, so the surface form of each region can be recovered precisely by slope integration. Then, the relative positions between different regions are evaluated by DPMD system to reconstruct the final 3D shape of the object. Experimental results show that the structured specular surfaces can be measured accurately by the proposed stereo-DPMD method. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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15 pages, 3319 KiB

Open AccessArticle

An Offset Laser Measurement Method for the Deviation Analysis of Cylindrical Gears

by Ning Mei, Aiping Song, Chenwei Yu and Jianzhou Pan

Machines 2021, 9(6), 111; https://doi.org/10.3390/machines9060111 - 28 May 2021

Cited by 2 | Viewed by 3742

Abstract

Generally, in the laser measurement of gears, the laser beam passes through the center of the gear, and the laser displacement sensor reads the spatial distance from the gear involute tooth surface to the laser displacement sensor. However, in this method, the angle [...] Read more.

Generally, in the laser measurement of gears, the laser beam passes through the center of the gear, and the laser displacement sensor reads the spatial distance from the gear involute tooth surface to the laser displacement sensor. However, in this method, the angle between the laser beam and the normal vector of the measured tooth surface is too large, which affects the accuracy of the measurement and the stability of the data. This paper proposes an offset laser measurement method. The laser beam is offset from the center of the gear by a certain distance to form a larger incident angle with the tooth surface, which can effectively address the problem and increase the measurement accuracy. Through a selection of the optimal offset distance, the range of optimal offset measurement positions was obtained and clarified by experiments. We solved the data conversion problem caused by the change in measuring position, and we measured the pitch deviation and helix angle of the gear to confirm the feasibility of this method. According to the theoretical calculation and experimental verification, it was found that this method has the advantages of better measurement accuracy and less fluctuation in measurement data. It is, thus, suitable for precision gear measurement. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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13 pages, 4072 KiB

Open AccessArticle

Design and Thermal Stability Analysis of Swing Micro-Mirror Structure for Gravitational Wave Observatory in Space

by Kunyao Zheng and Mingming Xu

Machines 2021, 9(5), 104; https://doi.org/10.3390/machines9050104 - 18 May 2021

Cited by 2 | Viewed by 2611

Abstract

A kind of swing micro-mirror structure with high stability for gravitational wave observatory in space is proposed in this paper. As the key interface instrument in the gravitational wave observatory, the swing micro-mirror structure plays a very important role. Firstly, the 3D model [...] Read more.

A kind of swing micro-mirror structure with high stability for gravitational wave observatory in space is proposed in this paper. As the key interface instrument in the gravitational wave observatory, the swing micro-mirror structure plays a very important role. Firstly, the 3D model of the mechanism is designed and established. Then, the solution method of the index of stability, pointing jitter, is researched. After that, the thermal stability and the first-order natural frequency of the mechanism are researched via finite element analysis. The first-order natural frequency of the mechanism is 247.55 Hz, which can meet the requirements of the design. It can be seen from the results of the simulation, the amplitude spectral density of the mirror angle deviation is 3.975 nrad/√Hz when the range of temperature variation is 0.1 °C, which is able to meet the requirements of the design. The thermal stability has a closed relationship with the structural stability around the X-axis. In addition, this article also studies the thermal stability of the mechanism in the case of temperature changes in different directions. It is found that the thermal stability of the mechanism around the Y-axis would be significantly affected by the temperature changes along the Y-axis. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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Review

Jump to: Research

26 pages, 22559 KiB

Open AccessReview

Advances and Prospects of Vision-Based 3D Shape Measurement Methods

by Guofeng Zhang, Shuming Yang, Pengyu Hu and Huiwen Deng

Machines 2022, 10(2), 124; https://doi.org/10.3390/machines10020124 - 10 Feb 2022

Cited by 15 | Viewed by 5651

Abstract

Vision-based three-dimensional (3D) shape measurement techniques have been widely applied over the past decades in numerous applications due to their characteristics of high precision, high efficiency and non-contact. Recently, great advances in computing devices and artificial intelligence have facilitated the development of vision-based [...] Read more.

Vision-based three-dimensional (3D) shape measurement techniques have been widely applied over the past decades in numerous applications due to their characteristics of high precision, high efficiency and non-contact. Recently, great advances in computing devices and artificial intelligence have facilitated the development of vision-based measurement technology. This paper mainly focuses on state-of-the-art vision-based methods that can perform 3D shape measurement with high precision and high resolution. Specifically, the basic principles and typical techniques of triangulation-based measurement methods as well as their advantages and limitations are elaborated, and the learning-based techniques used for 3D vision measurement are enumerated. Finally, the advances of, and the prospects for, further improvement of vision-based 3D shape measurement techniques are proposed. Full article

(This article belongs to the Special Issue Precision Measurement and Machines)

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