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14 pages, 10076 KiB

Open AccessArticle

Design of a Concentric Multi-Scale Zoom Optical System Based on Wide Object Distance and High-Precision Imaging

by Kun Zhang, Zheng Qu, Jingchen Li, Jian Wang, Si Sun and Fan Yang

Sensors 2022, 22(19), 7356; https://doi.org/10.3390/s22197356 - 28 Sep 2022

Cited by 2 | Viewed by 1985

Abstract

To effectively balance the trade-off between a large field of view (FOV) and high resolution of an optical system, as well as to solve the problem of image stitching misalignment after focusing, firstly, this paper conducts a theoretical analysis of the design principle [...] Read more.

To effectively balance the trade-off between a large field of view (FOV) and high resolution of an optical system, as well as to solve the problem of image stitching misalignment after focusing, firstly, this paper conducts a theoretical analysis of the design principle of the concentric multi-scale optical system and the causes of image stitching misalignment after focusing. Secondly, the design idea of using a combination structure of a two-layer front concentric imaging group and an image-space telecentric relay imaging array and then a joint full-motion zoom relay imaging system is proposed. Finally, an image-space telecentric two-step zoom concentric multi-scale optical system with a 7 × 7 relay imaging array is designed. The FOV of this optical system is 60° × 45°; the focal lengths are 50 mm and 100 mm for the center channel and 50 mm for the other channels. This concentric multi-scale zoom system has the advantages of both high-precision imaging stitching with a wide object distance and high-resolution imaging, which makes up for the defects of the conventional concentric multi-scale optical system, making it a promising application in the fields of aviation and security. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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12 pages, 4711 KiB

Open AccessCommunication

Design of a Multimodal Oculometric Sensor Contact Lens

by Jean-Louis de Bougrenet de la Tocnaye, Vincent Nourrit and Cyril Lahuec

Sensors 2022, 22(18), 6731; https://doi.org/10.3390/s22186731 - 6 Sep 2022

Cited by 1 | Viewed by 1835

Abstract

Oculometric data, such as gaze direction, pupil size and accommodative change, play a key role nowadays in the analysis of cognitive load and attentional activities, in particular with the development of Integrated Visual Augmentation Systems in many application domains, such as health, defense [...] Read more.

Oculometric data, such as gaze direction, pupil size and accommodative change, play a key role nowadays in the analysis of cognitive load and attentional activities, in particular with the development of Integrated Visual Augmentation Systems in many application domains, such as health, defense and industry. Such measurements are most frequently obtained by different devices, most of them requiring steady eye and body positions and controlled lighting conditions. Recent advances in smart contact lens (SCL) technology have demonstrated the ability to achieve highly reliable and accurate measurements, preserving user mobility, for instance in measuring gaze direction. In this paper, we discuss how these three key functions can be implemented and combined in the same SCL, considering the limited volume and energy consumption constraints. Some technical options are discussed and compared in terms of their ability to be implemented, taking advantage of recent developments in the field. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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12 pages, 2661 KiB

Open AccessCommunication

High-Speed Infrared Radiation Thermometer for the Investigation of Early Stage Explosive Development and Fireball Expansion

by Matthew J. Hobbs, Andrew Barr, Scott Woolford, Dain Farrimond, Sam D. Clarke, Andrew Tyas and Jon R. Willmott

Sensors 2022, 22(16), 6143; https://doi.org/10.3390/s22166143 - 17 Aug 2022

Cited by 8 | Viewed by 6506

Abstract

The understanding of blast loads is critical for the development of infrastructure that protects against explosions. However, the lack of high-quality experimental work on the characterisation of such loads prevents a better understanding of many scenarios. Blast loads are typically characterised by use [...] Read more.

The understanding of blast loads is critical for the development of infrastructure that protects against explosions. However, the lack of high-quality experimental work on the characterisation of such loads prevents a better understanding of many scenarios. Blast loads are typically characterised by use of some form of pressure gauge, from which the temperature can be inferred from a pressure measurement. However, such an approach to temperature measurement is limited; it assumes ideal gas laws apply throughout, which may not be the case for high temperature and pressure scenarios. In contrast, infrared radiation thermometers (IRTs) perform a measurement of temperature based upon the emitted radiance from the target object. The IRTs can measure fast changes in transient temperature, making them seemingly ideal for the measurement of a fireball’s temperature. In this work, we present the use of a high-speed IRT for the measurement of early-stage explosive development and fireball expansion within a confined blast, with the temperature of the explosive fireball measured from its emitted radiance. The temperature measured by the IRT was corroborated against the temperature inferred from a pressure gauge measurement; both instruments measured the same temperature from the quasi-static pressure (QSP) point onwards. Before the QSP point, it is deduced that the IRT measures the average temperature of the fireball over a wide field-of-view (FOV), as opposed to that inferred from the singular shocks detected by the pressure gauge. Therefore, use of an IRT, in tandem with a pressure gauge, provides a potential invaluable measurement technique for the characterisation the early stages of a fireball as it develops and expands. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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19 pages, 2366 KiB

Open AccessArticle

Doppler Measurement of Modulated Light for High Speed Vehicles

by Kookjin Sung and Manoranjan Majji

Sensors 2022, 22(4), 1444; https://doi.org/10.3390/s22041444 - 13 Feb 2022

Cited by 2 | Viewed by 3137

Abstract

Technical details associated with a novel relative motion sensor system are elaborated in the paper. By utilizing the Doppler effect, the optical sensor system estimates the relative motion rates between the sensor and the moving object equipped with modulating light sources and relatively [...] Read more.

Technical details associated with a novel relative motion sensor system are elaborated in the paper. By utilizing the Doppler effect, the optical sensor system estimates the relative motion rates between the sensor and the moving object equipped with modulating light sources and relatively inexpensive electrical components. A transimpedance amplifier (TIA) sensing circuit is employed to measure the Doppler shift exhibited by the amplitude modulated light sources on the moving platform. Implementation details associated with the amplitude modulation and photo-detection processes are discussed using representative hardware elements. A heterodyne mixing process with a reference signal is shown to improve the signal-to-noise ratios of the Doppler shift estimation processing pipeline. Benchtop prototype experiments are used to demonstrate the utility of the proposed technology for relative motion estimation applications. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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16 pages, 468 KiB

Open AccessArticle

Estimation and Error Analysis for Optomechanical Inertial Sensors

by Patrick Kelly, Manoranjan Majji and Felipe Guzmán

Sensors 2021, 21(18), 6101; https://doi.org/10.3390/s21186101 - 11 Sep 2021

Cited by 1 | Viewed by 2064

Abstract

A sensor model and methodology to estimate the forcing accelerations measured using a novel optomechanical inertial sensor with the inclusion of stochastic bias and measurement noise processes is presented. A Kalman filter for the estimation of instantaneous sensor bias is developed; the outputs [...] Read more.

A sensor model and methodology to estimate the forcing accelerations measured using a novel optomechanical inertial sensor with the inclusion of stochastic bias and measurement noise processes is presented. A Kalman filter for the estimation of instantaneous sensor bias is developed; the outputs from this calibration step are then employed in two different approaches for the estimation of external accelerations applied to the sensor. The performance of the system is demonstrated using simulated measurements and representative values corresponding to a bench-tested 3.76 Hz oscillator. It is shown that the developed methods produce accurate estimates of the bias over a short calibration step. This information enables precise estimates of acceleration over an extended operation period. These results establish the feasibility of reliably precise acceleration estimates using the presented methods in conjunction with state of the art optomechanical sensing technology. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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19 pages, 2204 KiB

Open AccessArticle

Feasibility of Novel Rear-Side Mirage Deflection Method for Thermal Conductivity Measurements

by Gwantaek Kim, Moojoong Kim and Hyunjung Kim

Sensors 2021, 21(17), 5971; https://doi.org/10.3390/s21175971 - 6 Sep 2021

Viewed by 2278

Abstract

Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity [...] Read more.

Among the noncontact measurement technologies used to acquire thermal property information, those that use the photothermal effect are attracting attention. However, it is difficult to perform measurements for new materials with different optical and thermal properties, owing to limitations of existing thermal conductivity measurement methods using the photothermal effect. To address this problem, this study aimed to develop a rear-side mirage deflection method capable of measuring thermal conductivity regardless of the material characteristics based on the photothermal effect. A thin copper film (of 20 µm thickness) was formed on the surfaces of the target materials so that measurements could not be affected by the characteristics of the target materials. In addition, phase delay signals were acquired from the rear sides of the target materials to exclude the influence of the pump beam, which is a problem in existing thermal conductivity measurement methods that use the photothermal effect. To verify the feasibility of the proposed measurement technique, thermal conductivity was measured for copper, aluminum, and stainless steel samples with a 250 µm thickness. The results were compared with literature values and showed good agreement with relative errors equal to or less than 0.2%. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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18 pages, 2386 KiB

Open AccessArticle

Investigation and Mitigation of Noise Contributions in a Compact Heterodyne Interferometer

by Yanqi Zhang, Adam S. Hines, Guillermo Valdes and Felipe Guzman

Sensors 2021, 21(17), 5788; https://doi.org/10.3390/s21175788 - 28 Aug 2021

Cited by 22 | Viewed by 3101

Abstract

We present a noise estimation and subtraction algorithm capable of increasing the sensitivity of heterodyne laser interferometers by one order of magnitude. The heterodyne interferometer is specially designed for dynamic measurements of a test mass in the application of sub-Hz inertial sensing. A [...] Read more.

We present a noise estimation and subtraction algorithm capable of increasing the sensitivity of heterodyne laser interferometers by one order of magnitude. The heterodyne interferometer is specially designed for dynamic measurements of a test mass in the application of sub-Hz inertial sensing. A noise floor of

3.31 \times 10^{- 11}

m

/

\sqrt{Hz}

at 100

m

Hz

is achieved after applying our noise subtraction algorithm to a benchtop prototype interferometer that showed a noise level of

2.76 \times 10^{- 10}

m

/

\sqrt{Hz}

at 100

m

Hz

when tested in vacuum at levels of

3 \times 10^{- 5}

Torr. Based on the previous results, we investigated noise estimation and subtraction techniques of non-linear optical pathlength noise, laser frequency noise, and temperature fluctuations in heterodyne laser interferometers. For each noise source, we identified its contribution and removed it from the measurement by linear fitting or a spectral analysis algorithm. The noise correction algorithm we present in this article can be generally applied to heterodyne laser interferometers. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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14 pages, 4185 KiB

Open AccessArticle

On-Board Monitoring of SO₂ Ship Emissions Using Resonant Photoacoustic Gas Detection in the UV Range

by Mahmoud El-Safoury, Miguel Dufner, Christian Weber, Katrin Schmitt, Hans-Fridtjof Pernau, Bert Willing and Jürgen Wöllenstein

Sensors 2021, 21(13), 4468; https://doi.org/10.3390/s21134468 - 29 Jun 2021

Cited by 13 | Viewed by 3753

Abstract

A photoacoustic gas detector for SO₂ was developed for ship exhaust gas emission monitoring. The basic measurement setup is based on the absorption of electromagnetic radiation of SO₂ at 285 nm wavelength. A commercially available ultraviolet (UV) light-emitting diode (LED) is [...] Read more.

A photoacoustic gas detector for SO₂ was developed for ship exhaust gas emission monitoring. The basic measurement setup is based on the absorption of electromagnetic radiation of SO₂ at 285 nm wavelength. A commercially available ultraviolet (UV) light-emitting diode (LED) is used as the light source and a micro-electro-mechanical system (MEMS) microphone as the detector. In order to achieve the required detection limits in marine applications, a measuring cell which allows an acoustically resonant amplification of the photoacoustic signal was developed and characterized. A limit of detection of 1 ppm was achieved in lab conditions during continuous gas flow. Long-term measurements on a container ship demonstrated the application relevance of the developed system. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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15 pages, 7276 KiB

Open AccessArticle

Motionless Polarizing Structured Illumination Microscopy

by Hyo Mi Park and Ki-Nam Joo

Sensors 2021, 21(8), 2837; https://doi.org/10.3390/s21082837 - 17 Apr 2021

Cited by 3 | Viewed by 4261

Abstract

In this investigation, we propose a motionless polarizing structured illumination microscopy as an axially sectioning and reflective-type device to measure the 3D surface profiles of specimens. Based on the spatial phase-shifting technique to obtain the visibility of the illumination pattern. Instead of using [...] Read more.

In this investigation, we propose a motionless polarizing structured illumination microscopy as an axially sectioning and reflective-type device to measure the 3D surface profiles of specimens. Based on the spatial phase-shifting technique to obtain the visibility of the illumination pattern. Instead of using a grid, a Wollaston prism is used to generate the light pattern by the stable interference of two beams. As the polarization states of two beams are orthogonal with each other, a polarization pixelated CMOS camera can simultaneously obtain four phase-shifted patterns with the beams after passing through a quarter wave plate based on the spatial phase-shifting technique with polarization. In addition, a focus tunable lens is used to eliminate a mechanical moving part for the axial scanning of the specimen. In the experimental result, a step height sample and a concave mirror were measured with 0.05 µm and 0.2 mm repeatabilities of step height and the radius of curvature, respectively. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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19 pages, 6144 KiB

Open AccessArticle

Development of a Compound Speckle Interferometer for Precision Three-Degree-of-Freedom Displacement Measurement

by Hung-Lin Hsieh and Bo-Yen Sun

Sensors 2021, 21(5), 1828; https://doi.org/10.3390/s21051828 - 5 Mar 2021

Cited by 1 | Viewed by 2721

Abstract

In this study, a compound speckle interferometer for measuring three-degree-of-freedom (3-DOF) displacement is proposed. The system, which combines heterodyne interferometry, speckle interferometry and beam splitting techniques, can perform precision 3-DOF displacement measurements, while still having the advantages of high resolution and a relatively [...] Read more.

In this study, a compound speckle interferometer for measuring three-degree-of-freedom (3-DOF) displacement is proposed. The system, which combines heterodyne interferometry, speckle interferometry and beam splitting techniques, can perform precision 3-DOF displacement measurements, while still having the advantages of high resolution and a relatively simple configuration. The incorporation of speckle interferometry allows for non-contact displacement measurements by detecting the phase of the speckle interference pattern formed from the convergence of laser beams on the measured rough surface. Experiments were conducted to verify the measurement capabilities of the system, and the results show that the proposed system has excellent measurement capabilities suitable for future real-world applications. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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16 pages, 1181 KiB

Open AccessArticle

Ghost Beam Suppression in Deep Frequency Modulation Interferometry for Compact On-Axis Optical Heads

by Oliver Gerberding and Katharina-Sophie Isleif

Sensors 2021, 21(5), 1708; https://doi.org/10.3390/s21051708 - 2 Mar 2021

Cited by 8 | Viewed by 3300

Abstract

We present a compact optical head design for wide-range and low noise displacement sensing using deep frequency modulation interferometry (DFMI). The on-axis beam topology is realised in a quasi-monolithic component and relies on cube beamsplitters and beam transmission through perpendicular surfaces to keep [...] Read more.

We present a compact optical head design for wide-range and low noise displacement sensing using deep frequency modulation interferometry (DFMI). The on-axis beam topology is realised in a quasi-monolithic component and relies on cube beamsplitters and beam transmission through perpendicular surfaces to keep angular alignment constant when operating in air or in a vacuum, which leads to the generation of ghost beams that can limit the phase readout linearity. We investigated the coupling of these beams into the non-linear phase readout scheme of DFMI and implemented adjustments of the phase estimation algorithm to reduce this effect. This was done through a combination of balanced detection and the inherent orthogonality of beat signals with different relative time-delays in deep frequency modulation interferometry, which is a unique feature not available for heterodyne, quadrature or homodyne interferometry. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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16 pages, 5322 KiB

Open AccessArticle

Improved Self-Calibration of a Multilateration System Based on Absolute Distance Measurement

by Quoc Khanh Nguyen, Seungman Kim, Seong-Heum Han, Seung-Kook Ro, Seung-Woo Kim, Young-Jin Kim, Wooram Kim and Jeong Seok Oh

Sensors 2020, 20(24), 7288; https://doi.org/10.3390/s20247288 - 18 Dec 2020

Cited by 7 | Viewed by 2905

Abstract

Multilateration tracking systems (MLTSs) are used in industrial three-dimensional (3D) coordinate measuring applications. For high-precision measurement, system parameters must be calibrated properly in advance. For an MLTS using absolute distance measurement (ADM), the conventional self-calibration method significantly reduces estimation efficiency because all system [...] Read more.

Multilateration tracking systems (MLTSs) are used in industrial three-dimensional (3D) coordinate measuring applications. For high-precision measurement, system parameters must be calibrated properly in advance. For an MLTS using absolute distance measurement (ADM), the conventional self-calibration method significantly reduces estimation efficiency because all system parameters are estimated simultaneously using a complicated residual function. This paper presents a novel self-calibration method that optimizes ADM to reduce the number of system parameters via highly precise and separate estimations of dead paths. Therefore, the residual function to estimate the tracking station locations can be simplified. By applying a suitable mathematical procedure and solving the initial guess problem without the aid of an external device, estimation accuracy of the system parameters is significantly improved. In three self-calibration experiments, with ADM repeatability of approximately 3.4 µm, the maximum deviation of the system parameters estimated by the proposed self-calibration method was 68.6 µm, while the maximum deviation estimated by the conventional self-calibration method was 711.9 µm. Validation of 3D coordinate measurements in a 1000 mm × 1000 mm × 1000 mm volume showed good agreement between the proposed ADM-based MLTS and a commercial laser tracker, where the maximum difference based on the standard deviation was 17.7 µm. Conversely, the maximum difference was 98.8 µm using the conventional self-calibration method. These results confirmed the efficiency and feasibility of the proposed self-calibration method. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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21 pages, 4659 KiB

Open AccessArticle

Multi-Camera-Based Universal Measurement Method for 6-DOF of Rigid Bodies in World Coordinate System

by Zuoxi Zhao, Yuchang Zhu, Yuanhong Li, Zhi Qiu, Yangfan Luo, Chaoshi Xie and Zhuangzhuang Zhang

Sensors 2020, 20(19), 5547; https://doi.org/10.3390/s20195547 - 28 Sep 2020

Cited by 10 | Viewed by 4312

Abstract

The measurement of six-degrees-of-freedom (6-DOF) of rigid bodies plays an important role in many industries, but it often requires the use of professional instruments and software, or has limitations on the shape of measured objects. In this paper, a 6-DOF measurement method based [...] Read more.

The measurement of six-degrees-of-freedom (6-DOF) of rigid bodies plays an important role in many industries, but it often requires the use of professional instruments and software, or has limitations on the shape of measured objects. In this paper, a 6-DOF measurement method based on multi-camera is proposed, which is accomplished using at least two ordinary cameras and is made available for most morphological rigid bodies. First, multi-camera calibration based on Zhang Zhengyou’s calibration method is introduced. In addition to the intrinsic and extrinsic parameters of cameras, the pose relationship between the camera coordinate system and the world coordinate system can also be obtained. Secondly, the 6-DOF calculation model of proposed method is gradually analyzed by the matrix analysis method. With the help of control points arranged on the rigid body, the 6-DOF of the rigid body can be calculated by the least square method. Finally, the Phantom 3D high-speed photogrammetry system (P3HPS) with an accuracy of 0.1 mm/m was used to evaluate this method. The experiment results show that the average error of the rotational degrees of freedom (DOF) measurement is less than 1.1 deg, and the average error of the movement DOF measurement is less than 0.007 m. In conclusion, the accuracy of the proposed method meets the requirements. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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17 pages, 1503 KiB

Open AccessArticle

Single-Element Dual-Interferometer for Precision Inertial Sensing

by Yichao Yang, Kohei Yamamoto, Victor Huarcaya, Christoph Vorndamme, Daniel Penkert, Germán Fernández Barranco, Thomas S. Schwarze, Moritz Mehmet, Juan Jose Esteban Delgado, Jianjun Jia, Gerhard Heinzel and Miguel Dovale Álvarez

Sensors 2020, 20(17), 4986; https://doi.org/10.3390/s20174986 - 3 Sep 2020

Cited by 7 | Viewed by 4277

Abstract

Tracking moving masses in several degrees of freedom with high precision and large dynamic range is a central aspect in many current and future gravitational physics experiments. Laser interferometers have been established as one of the tools of choice for such measurement schemes. [...] Read more.

Tracking moving masses in several degrees of freedom with high precision and large dynamic range is a central aspect in many current and future gravitational physics experiments. Laser interferometers have been established as one of the tools of choice for such measurement schemes. Using sinusoidal phase modulation homodyne interferometry allows a drastic reduction of the complexity of the optical setup, a key limitation of multi-channel interferometry. By shifting the complexity of the setup to the signal processing stage, these methods enable devices with a size and weight not feasible using conventional techniques. In this paper we present the design of a novel sensor topology based on deep frequency modulation interferometry: the self-referenced single-element dual-interferometer (SEDI) inertial sensor, which takes simplification one step further by accommodating two interferometers in one optic. Using a combination of computer models and analytical methods we show that an inertial sensor with sub-picometer precision for frequencies above 10 mHz, in a package of a few cubic inches, seems feasible with our approach. Moreover we show that by combining two of these devices it is possible to reach sub-picometer precision down to 2 mHz. In combination with the given compactness, this makes the SEDI sensor a promising approach for applications in high precision inertial sensing for both next-generation space-based gravity missions employing drag-free control, and ground-based experiments employing inertial isolation systems with optical readout. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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18 pages, 6167 KiB

Open AccessArticle

A Combined Measurement Method for Large-Size Aerospace Components

by Zhilong Zhou, Wei Liu, Qiong Wu, Yuxin Wang, Binchao Yu, Yi Yue and Jiabo Zhang

Sensors 2020, 20(17), 4843; https://doi.org/10.3390/s20174843 - 27 Aug 2020

Cited by 21 | Viewed by 3743

Abstract

Automated and high-accuracy three-dimensional (3D) shape measurement is required in quality control of large-size components for the aerospace industry. To eliminate the contradiction between global measurement and local precision measurement control in 3D digitalization for the key local features of the large-size components, [...] Read more.

Automated and high-accuracy three-dimensional (3D) shape measurement is required in quality control of large-size components for the aerospace industry. To eliminate the contradiction between global measurement and local precision measurement control in 3D digitalization for the key local features of the large-size components, a combined measurement method is proposed, including a 3D scanner, a laser tracker, and an industrial robot used as an orienting device, to achieve high-accuracy measurement. As for improving the overall measurement accuracy, an accurate calibration method based on coordinate optimization of common points (COCP) and coordinate optimization of global control points (COGP) is proposed to determine the coordinate systems. Firstly, a coordinate optimization method of common points (COCP) is recommended. Then, a coordinate optimization method of global control points (COGP) based on the angular constraint is proposed for minimizing the measurement errors and improving the measurement accuracy of the position and orientation of the 3D scanner. Finally, a combined measurement system is established, and validation experiments are carried out in laboratory within a distance of 4 m. The calibration experiment results demonstrate that the max and mean errors of the coordinate transformation have been reduced from 0.037 and 0.022 mm to 0.021 and 0.0122 mm. Additionally, the measurement experiment results also show that the combined measurement system features high accuracy. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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21 pages, 6571 KiB

Open AccessArticle

Multiple Optical Sensor Fusion for Mineral Mapping of Core Samples

by Behnood Rasti, Pedram Ghamisi, Peter Seidel, Sandra Lorenz and Richard Gloaguen

Sensors 2020, 20(13), 3766; https://doi.org/10.3390/s20133766 - 5 Jul 2020

Cited by 5 | Viewed by 3374

Abstract

Geological objects are characterized by a high complexity inherent to a strong compositional variability at all scales and usually unclear class boundaries. Therefore, dedicated processing schemes are required for the analysis of such data for mineralogical mapping. On the other hand, the variety [...] Read more.

Geological objects are characterized by a high complexity inherent to a strong compositional variability at all scales and usually unclear class boundaries. Therefore, dedicated processing schemes are required for the analysis of such data for mineralogical mapping. On the other hand, the variety of optical sensing technology reveals different data attributes and therefore multi-sensor approaches are adapted to solve such complicated mapping problems. In this paper, we devise an adapted multi-optical sensor fusion (MOSFus) workflow which takes the geological characteristics into account. The proposed processing chain exhaustively covers all relevant stages, including data acquisition, preprocessing, feature fusion, and mineralogical mapping. The concept includes (i) a spatial feature extraction based on morphological profiles on RGB data with high spatial resolution, (ii) a specific noise reduction applied on the hyperspectral data that assumes mixed sparse and Gaussian contamination, and (iii) a subsequent dimensionality reduction using a sparse and smooth low rank analysis. The feature extraction approach allows one to fuse heterogeneous data at variable resolutions, scales, and spectral ranges and improve classification substantially. The last step of the approach, an SVM classifier, is robust to unbalanced and sparse training sets and is particularly efficient with complex imaging data. We evaluate the performance of the procedure with two different multi-optical sensor datasets. The results demonstrate the superiority of this dedicated approach over common strategies. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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11 pages, 4171 KiB

Open AccessArticle

Anomaly Detection Neural Network with Dual Auto-Encoders GAN and Its Industrial Inspection Applications

by Ta-Wei Tang, Wei-Han Kuo, Jauh-Hsiang Lan, Chien-Fang Ding, Hakiem Hsu and Hong-Tsu Young

Sensors 2020, 20(12), 3336; https://doi.org/10.3390/s20123336 - 12 Jun 2020

Cited by 97 | Viewed by 9505

Abstract

Recently, researchers have been studying methods to introduce deep learning into automated optical inspection (AOI) systems to reduce labor costs. However, the integration of deep learning in the industry may encounter major challenges such as sample imbalance (defective products that only account for [...] Read more.

Recently, researchers have been studying methods to introduce deep learning into automated optical inspection (AOI) systems to reduce labor costs. However, the integration of deep learning in the industry may encounter major challenges such as sample imbalance (defective products that only account for a small proportion). Therefore, in this study, an anomaly detection neural network, dual auto-encoder generative adversarial network (DAGAN), was developed to solve the problem of sample imbalance. With skip-connection and dual auto-encoder architecture, the proposed method exhibited excellent image reconstruction ability and training stability. Three datasets, namely public industrial detection training set, MVTec AD, with mobile phone screen glass and wood defect detection datasets, were used to verify the inspection ability of DAGAN. In addition, training with a limited amount of data was proposed to verify its detection ability. The results demonstrated that the areas under the curve (AUCs) of DAGAN were better than previous generative adversarial network-based anomaly detection models in 13 out of 17 categories in these datasets, especially in categories with high variability or noise. The maximum AUC improvement was 0.250 (toothbrush). Moreover, the proposed method exhibited better detection ability than the U-Net auto-encoder, which indicates the function of discriminator in this application. Furthermore, the proposed method had a high level of AUCs when using only a small amount of training data. DAGAN can significantly reduce the time and cost of collecting and labeling data when it is applied to industrial detection. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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Review

Jump to: Research, Other

33 pages, 5564 KiB

Open AccessReview

Optical Fibre-Based Sensors for Oil and Gas Applications

by Jincy Johny, Solomon Amos and Radhakrishna Prabhu

Sensors 2021, 21(18), 6047; https://doi.org/10.3390/s21186047 - 9 Sep 2021

Cited by 43 | Viewed by 6752

Abstract

Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in [...] Read more.

Oil and gas (O&G) explorations moving into deeper zones for enhanced oil and gas recovery are causing serious safety concerns across the world. The sensing of critical multiple parameters like high pressure, high temperature (HPHT), chemicals, etc., are required at longer distances in real-time. Traditional electrical sensors operate less effectively under these extreme environmental conditions and are susceptible to electromagnetic interference (EMI). Hence, there is a growing demand for improved sensors with enhanced measurement capabilities and also sensors that generates reliable data for enhanced oil and gas production. In addition to enhanced oil and gas recovery, the sensing technology should also be capable of monitoring the well bore integrity and safety. The sensing requirements of the O&G industry for improved sensing in deeper zones include increased transmission length, improved spatial coverage and integration of multiple sensors with multimodal sensing capability. This imposes problems like signal attenuation, crosstalks and cross sensitivities. Optical fibre-based sensors are expected to provide superior sensing capabilities compared to electrical sensors. This review paper covers a detailed review of different fibre-optic sensing technologies to identify a feasible sensing solution for the O&G industry. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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Other

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10 pages, 1806 KiB

Open AccessLetter

High-Performance Ultra-Thin Spectrometer Optical Design Based on Coddington’s Equations

by Zhiwei Feng, Guo Xia, Rongsheng Lu, Xiaobo Cai, Hao Cui and Mingyong Hu

Sensors 2021, 21(2), 323; https://doi.org/10.3390/s21020323 - 6 Jan 2021

Cited by 13 | Viewed by 4867

Abstract

A unique method to design a high-throughput and high-resolution ultrathin Czerny–Turner (UTCT) spectrometer is proposed. This paper reveals an infrequent design process of spectrometers based on Coddington’s equations, which will lead us to develop a high-performance spectrometer from scratch. The spectrometer is composed [...] Read more.

A unique method to design a high-throughput and high-resolution ultrathin Czerny–Turner (UTCT) spectrometer is proposed. This paper reveals an infrequent design process of spectrometers based on Coddington’s equations, which will lead us to develop a high-performance spectrometer from scratch. The spectrometer is composed of cylindrical elements except a planar grating. In the simulation design, spot radius is sub-pixel size, which means that almost all of the energy is collected by the detector. The spectral resolution is 0.4 nm at central wavelength and 0.75 nm at edge wavelength when the width of slit is chosen to be 25 μm and the groove density is 900 lines/mm. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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Open AccessLetter

Applying Differential Wave-Front Sensing and Differential Power Sensing for Simultaneous Precise and Wide-Range Test-Mass Rotation Measurements

by Neda Meshksar, Moritz Mehmet, Katharina-Sophie Isleif and Gerhard Heinzel

Sensors 2021, 21(1), 164; https://doi.org/10.3390/s21010164 - 29 Dec 2020

Cited by 9 | Viewed by 3088

Abstract

We propose to combine differential wave-front sensing (DWS) and differential power sensing (DPS) in a Mach-Zehnder type interferometer for measuring the rotational dynamics of a test-mass. Using the DWS method, a high sensitive measurement of 6 nrad Hz^−1/2 in sub-Hz frequencies can [...] Read more.

We propose to combine differential wave-front sensing (DWS) and differential power sensing (DPS) in a Mach-Zehnder type interferometer for measuring the rotational dynamics of a test-mass. Using the DWS method, a high sensitive measurement of 6 nrad Hz^−1/2 in sub-Hz frequencies can be provided around the test-mass nominal position (

\pm 0.11

mrad), whereas the measurement of a wide rotation range (

\pm 5

mrad) is realized by the DPS method. The interferometer can be combined with deep frequency modulation (DFM) interferometry for measurement of the test-mass translational dynamics. The setup and the resulting interferometric signals are verified by simulations. An optimization algorithm is applied to find suitable positions of the lenses and the waist size of the input laser in order to determine the best trade of between the slope of DWS, dynamic range of DPS, and the interferometric contrast. Our simulation further allows to investigate the layout for robustness and design tolerances. We compare our device with a recent experimental realization of a DFM interferometer and find that a practical implementation of the interferometer proposed here has the potential to provide translational and rotational test-mass tracking with state-of-the-art sensitivity. The simple and compact design, and especially the capability of sensing the test-mass rotation in a wide range and simultaneously providing a high-precision measurement close to the test-mass nominal position makes the design especially suitable for example for employment in torsion pendulum setups. Full article

(This article belongs to the Special Issue Optical Sensors: Innovative Designs, Configurations, Measurements, and Applications)

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