Non-contact Displacement Research Articles

Non-contact Structural Displacement Measurement using UAV and DIC with Non-coplanar Fixed Region of Interest

The use of unmanned aerial vehicles (UAV) for displacement measurement using Digital Image Correlation (DIC) has been popular. A fixed region of interest (FROI) is often used to calibrate the UAV camera. Existing techniques require the FROI to be coplanar with the target plane, such that a corner of the FROI can be taken directly as the origin of the global coordinates. However, this condition does not exist when the target plane is in motion, and this has been a significant challenge in the correction of the UAV images. This paper proposed an algorithm to estimate the posture of the UAV camera for solving this issue. Numerical simulation shows that the proposed algorithm has high computation accuracy and stability, and it is robust to the amplitude of motion of the target image or camera. Field experiments confirm the feasibility of the proposed algorithm for images with non-coplanar conditions with a maximum error of less than 2.3 mm and a peak error below 5 %. In comparison to the traditional coplanar correction method, the CPS method demonstrates lower errors, making it better suited for cases where the FROI and the target plane are not coplanar.

Multiaxial creep deformation investigation of miniature cruciform specimen for type 304 stainless steel at 923 K using non-contact displacement-measuring method

Abstract Multiaxial creep investigations at high temperatures are required to guarantee the integrity of structural materials such as boiler pipes for power generation and turbine blades for aviation and industrial applications. The multiaxial creep testing method using a cruciform specimen has several advantages, and the authors successfully downsized the specimen. The authors also developed a technique for the in situ observation of the specimen in an electric furnace and the non-contact displacement measurement in the development of a biaxial tensile creep testing machine for the miniature cruciform specimen. By observing the specimen at a target mark during the creep testing through an observation window installed at the bottom of the furnace, it was possible to visualize the specimen surface variations and obtain the axial strain from the locus of the target marks. The Mises-type equivalent strain was calculated from the axial strains obtained in the equi-biaxial tensile multiaxial creep testing and was compared with the strains obtained in the uniaxial creep testing. The Mises-type equivalent strain can be expressed using a unified method up to approximately 5% of the initial strain in the test, even in the multiaxial stress state.

B-026 Transforming PCR protocols in pandemic response with automated non-contact liquid dispensing

Abstract Background During the COVID-19 pandemic, effective Polymerase Chain Reaction (PCR) protocols were crucial for detecting SARS-CoV-2 in clinical samples, playing a key role in rapid infection control and easing the strain on healthcare services. However, with the critical need for fast and accurate pathogen surveillance, the manual execution of PCR workflows presented numerous challenges, including limited throughput, risk of human error and variability, and risk to human health. Several automated liquid handling systems from a range of vendors were considered to prepare extraction plates for this process. Ultimately, RFL decided on dragonfly® discovery, a non-contact positive displacement dispenser. Methods The analytical sensitivity for the UltraDx SARS-CoV-2 N1/N2/RP assay was evaluated by the RFL development team using RNA extracted from a panel of virus inputs from a Qnostics Analytical Q Panel, Product Number: SCV2AQP. Samples were extracted using a modified RNA extraction procedure for Thermo MagMax reagents and consumables with dragonfly discovery. dragonfly discovery was utilized to distribute a combination of inactivation buffer and beads into a 96-well kingfisher flex plate. This process was accomplished using a peristaltic pump and a 6-way Auto Feed Reservoir (AFR) to ensure a constant buffer flow. Simultaneously, the AFR ensured that the beads were kept in constant suspension, resulting in precise dispensing across all wells. The EPCR assay, UltraDx SARS-CoV-2 N1/N2/RP assay (LGC, Biosearch Technologies), utilized two CDC-characterized amplicon primer sets alongside two additional probes using fluorescence-based (FAM dye) detection. The input RNA extracted from clinical samples was combined with RT-PCR reaction mixes, before the reaction arrays were amplified. The reactions were then measured by a single scan on a multi-channel fluorescence reader. Results The UltraDx SARS-CoV-2 N1/N2/RP assay (when performed using the manufacturer method and in the absence of dragonfly discovery) has an LoD of 80 copies per reaction for the N1 assay, and 20 copies per reaction for the N2 assay, across 20 replicates for each copy number tested. Using the same/equivalent reagents and control materials, inclusion of dragonfly discovery showed an LoD of 70 copies/mL (0.9 copies/reaction) sensitivity when compared to the LoD suggested by the manufacture. Conclusions Integrating dragonfly discovery into the UltraDx SARS-CoV-2 N1/N2/RP assay led to an 80-fold reduction in the limit of detection for the N1 assay compared to the reagent manufacturer's recommendation. Some of this improvement can be attributed to dragonfly discovery's non-contact positive displacement dispensing, coupled with the AFR pump mechanism that ensures a continuous suspension of magnetic beads, enhancing accuracy and precision. dragonfly discovery's versatility supports a robust business-as-usual (BAU) process and is easily scalable for pandemic-level testing. Its user-friendly software interface requires zero computer programming knowledge, providing end-users with the flexibility to run multiple protocols on the same instrument, making it ideal for BAU assay processing. The instrument played a pivotal role in the UltraDx SARS-CoV-2 N1/N2/RP assay conducted by UKHSA during the pandemic, and SPT Labtech will continue to support UKHSA in their mission to protect communities from the impact of health threats.

Non-contact measurement of structural dynamic displacement based on improved edge detection and video interpolation

In structural health monitoring (SHM), smartphones are increasingly used for non-contact dynamic displacement measurement using computer vision. To overcome limitations in capturing high-frame-rate data, a non-contact measurement method of structural dynamic displacement based on an improved edge detection algorithm and video frame interpolation is proposed. Initially, a smartphone is employed to capture the structure’s vibration video and then generates intermediary frames between adjacent frames that match the structure’s motion state by using a video frame interpolation algorithm to obtain a video with a high frame rate. Subsequently, the improved edge detection algorithm is applied to measure the displacement within the interpolated video. In order to address the problem that traditional edge detection may have false edges leading to the degradation of measurement accuracy, a feature point tracking technique is proposed based on the traditional edge detection technique, which effectively excludes the interference of false edges in ROI and improves the accuracy of displacement monitoring. Experimental validation on a cantilever beam and steel frame bridge demonstrates the method’s viability and precision, highlighting its effectiveness in improving displacement measurement accuracy compared to traditional methods.

Enhancing force plate design through optimization of spring constant distribution

Force plates have been widely used in various scientific fields to measure ground reaction forces experienced by animals and humans. A force plate that incorporates mechanical springs and non-contact displacement sensors offers the advantages of facilely modifying its shape and performance. However, the design protocol was limited to adjusting the plate size and spring constants of the springs supporting the plate at the four corners. Herein, we propose an optimization method for determining the spring constant distribution of a force plate. The proposed design enables the use of simulations to optimize the mechanical properties of the force plate, such as resonant frequency and error due to position. The experimental results demonstrated that the resonant frequency of the fabricated force plate was 133 Hz and the error due to position was within ±5 %. These results confirm that the proposed force plate can be effectively adjusted through optimization.

Non-contact sub-nanometer displacement sensing based on optical digital coherent detection using frequency-domain filters

Non-contact sub-nanometer displacement sensing based on optical digital coherent detection using frequency-domain filters

Flight test results for microgravity active vibration isolation system on-board Chinese Space Station

The Fluid Physics Research Rack (FPR) is a research platform employed on-board the Chinese Space Station for conducting microgravity fluid physics experiments. The research platform includes the Microgravity Active Vibration Isolation System (MAVIS) for isolating the FPR from disturbances arising from the space station itself. The MAVIS is a structural platform consisting of a stator and floater that are monitored and controlled with non-contact electromagnetic actuators, high-precision accelerometers, and displacement transducers. The stator is fixed to the FPR, while the floater serves as a vibration isolation platform supporting payloads, and is connected with the stator only with umbilicals that mainly comprise power and data cables. The controller was designed with a correction for the umbilical stiffness to minimize the effect of the umbilicals on the vibration isolation performance of the MAVIS. In-orbit test results of the FPR demonstrate that the MAVIS was able to achieve a microgravity level of 1–30 μg0 (where g0 = 9.80665 m ∙ s−2) in the frequency range of 0.01–125 Hz under the microgravity mode, and disturbances with a frequency greater than 2 Hz are attenuated by more than 10-fold. Under the vibration excitation mode, the MAVIS generated a minimum vibration acceleration of 0.4091 μg0 at a frequency of 0.00995 Hz and a maximum acceleration of 6253 μg0 at a frequency of 9.999 Hz. Therefore, the MAVIS provides a highly stable environment for conducting microgravity experiments, and promotes the development of microgravity fluid physics.

A novel magnetic actuated ultra-clean poppet valve and its dynamic characteristics analysis

The liquid delivery in the semiconductor process is highly protected against leakage and contamination. To avoid the dynamic sealing points in valves, a novel ultra-clean poppet valve driven by permanent magnets is proposed. To reduce the risk of instability due to the lack of a fixed connection structure, static and dynamic characteristic analyses of the valve poppet needs to be carried out. However, the conventional theoretical model of poppet vibration generally focuses on the vibration in axial direction, which lacks consideration of the vibration in lateral direction. Therefore, a new theoretical model for analyzing the vibration characteristics in both axial and lateral directions is proposed. The displacement of poppet and flow response of the valve are predicted. Based on the experimental system of non-contacting displacement measurement, the accuracy of the model is verified. Furthermore, the influence of parameters on the stability is revealed through theoretical calculation, which provides a reference for the design of magnetic actuated valve.

Evaluation of Desiccation Behavior in Basalt Microfiber–Reinforced Bentonite Clay for Geological Repositories of Nuclear Spent Fuel Using Digital Image Correlation

Abstract Secure storage of nuclear spent fuel (NSF) is of great concern for protecting public health and safety. The preferred long-term solution is underground containment in geological repositories, where one or more engineered barrier materials (EBM) encapsulate the NSF and separate it from the natural rock. Bentonite clay is commonly used as an EBM due to its many advantageous properties including low hydraulic conductivity, which ensures limitation of water infiltration to the system and the subsequent risk of corrosion in NSF canisters. However, bentonite clay subjected to heating from nuclear decay may form desiccation cracking. This study conducted disk-shaped free shrinkage tests and ring-shaped restrained shrinkage tests of bentonite clay samples reinforced with basalt microfibers. Digital image correlation was used as a noncontact full-field displacement measurement to track the time-evolving shrinkage and desiccation cracking phenomena and make quantified comparisons between plain bentonite and bentonite with varying contents of basalt microfibers (i.e., 0.0, 0.5, 1.0, and 1.5 % wt.). Results indicate that plain bentonite and basalt microfiber-reinforced samples showed similar free shrinkage behavior, while desiccation cracking behavior was significantly altered by adding basalt microfibers. Microfiber reinforcement effectively reduced major cracks through a “crack-bridging” effect while causing minor cracks to initiate earlier and at higher moisture contents than plain bentonite. Results infer that reinforcing plain bentonite with inorganic microfibers can potentially control desiccation cracking, leading to safer and improved nuclear waste management.

Nano-displacement sensing by phase-diversity optical digital coherent detection utilizing alternating quadrature phase-modulated reference light

We have introduced a nanometer-scale non-contact displacement sensing method that relies on phase-diversity optical digital coherent detection. In our prior work, we used a conventional setup involving a 90°optical hybrid, two balanced amplified photodetectors (BAPs), and a narrow-linewidth (NLW) laser, which is complex and costly. However, in this paper, we have streamlined the system configuration by employing alternating quadrature phase modulation (AQPM) reference light, implemented using a phase modulator and a BAP. Moreover, we’ve employed an economical distributed feedback (DFB) laser, enabling us to achieve displacement sensing at 1.6 nm with a resolution of 0.6 nm. It is notable that there is some degradation in the performance due to the phase noise compared to the NLW laser, which achieves a displacement sensing down to 0.6 nm with a 0.2 nm resolution. Nevertheless, the DFB-AQPM system holds a significant potential for cost-effective, high-resolution nanometer-scale sensing applications.

Dynamic Characterization of Optical Coherence-Based Displacement-Type Weight Sensor

Dynamic characteristics play a crucial role in evaluating the performance of weight sensors and are essential for achieving fast and accurate weight measurements. This study focuses on a weight sensor based on optical coherence displacement. Using finite element analysis, the sensor was numerically simulated. Frequency domain and time domain dynamic response characteristics were explored through harmonic response analysis and transient dynamic analysis. The superior dynamic performance and reduced conditioning time of the non-contact optical coherence-based displacement weight sensor were confirmed via a negative step response experiment that compared the proposed sensing method to strain sensing. Moreover, dynamic performance metrics for the optical coherence displacement-type weight sensor were determined. Ultimately, the sensor’s dynamic performance was enhanced using the pole-zero placement method, decreasing the overshoot to 4.72% and reducing the response time to 0.0132 s. These enhancements broaden the sensor’s operational bandwidth and amplify its dynamic response capabilities.

Applications of Computer Vision-Based Structural Monitoring on Long-Span Bridges in Turkey.

Structural displacement monitoring is one of the major tasks of structural health monitoring and it is a significant challenge for research and engineering practices relating to large-scale civil structures. While computer vision-based structural monitoring has gained traction, current practices largely focus on laboratory experiments, small-scale structures, or close-range applications. This paper demonstrates its applications on three landmark long-span suspension bridges in Turkey: the First Bosphorus Bridge, the Second Bosphorus Bridge, and the Osman Gazi Bridge, among the longest landmark bridges in the world, with main spans of 1074 m, 1090 m, and 1550 m, respectively. The presented studies achieved non-contact displacement monitoring from a distance of 600 m, 755 m, and 1350 m for the respective bridges. The presented concepts, analysis, and results provide an overview of long-span bridge monitoring using computer vision-based monitoring. The results are assessed with conventional monitoring approaches and finite element analysis based on observed traffic conditions. Both displacements and dynamic frequencies align well with these conventional techniques and finite element analyses. This study also highlights the challenges of computer vision-based structural monitoring of long-span bridges and presents considerations such as the encountered adverse environmental factors, target and algorithm selection, and potential directions of future studies.

Stereovision-based vibration measurement of stay cable using synchronized multi-camera setup and video motion magnification

This paper proposes a new framework for 3D noncontact stereovision-based displacement measurement in conjunction with Phase-based Video Motion Magnification (PVMM) to capture in-plane and out-of-plane vibrations of stay cables. In the proposed method, cable vibrations are captured by a pair of synchronized digital cameras, then PVMM method is applied to magnify micro vibrations of the cable (ambient responses) recorded by video cameras. Next, a camera calibration technique is proposed to convert the 2D image coordinates to 3D global coordinates, followed by the stereo calibration between the two cameras to synchronize the target points. Afterwards, a Centroid-based Bounding-Box Tracking (CBBT) technique is proposed and used to track the movements of the cable in each video frame. As a result, time-history displacements of the cable are extracted from the magnified videos. Finally, natural frequencies and damping ratios of the cable are extracted from the in-plane and out-of-plane displacements using Wavelet-screening Random Decrement Technique (WS-RDT). The proposed methodology has been validated through a couple of wind-tunnel tests of cable vibrations. The results have demonstrated a good agreement between the proposed method and conventional accelerometer-based measurement results.

Mechanical behavior analysis using small-size graphite disc compression testing with digital image correlation methods

The ASTM InternationalStandard Test Method for Tensile Stress-Strain of Carbon and Graphite (ASTM C749) requires dog-bone shaped specimens. Unfortunately, specimen sizes required in ASTM C749 are much too large for irradiation within a test reactor and are incompatible with irradiation capsule volumes, molten salt degradation facilities, or oxidation apparatus. The ASTM InternationalStandard Test Method for Tensile Strength Estimate by Disc Compression of Manufactured Graphite (ASTM D8289) was developed as an alternative that provides a means for testing tensile properties using smaller specimens when geometric constraints are present. However, the important stress–strain relation throughout the test loading history that could be recorded using ASTM C749 is lost by using ASTM D8289 because of the difficulties involved with using traditional strain gauges or extensometers on such a small specimen. In this work, a digital image correlation (DIC) method, which uses a full-field noncontact surface displacement measurement technique, was applied along with the ASTM D8289 splitting tensile test on eight small samples of graphite grade Mersen 2114 to track their deformation during compressive loading. Initial results showed that the DIC technique can measure the surface displacement/strain on these small (Ø6 × 3 mm) graphite specimens with high accuracy and good repeatability, indicating that the DIC technique, combined with the small-disc splitting tensile test in ASTM D8289, can capture the strain evolution in the test. Further comparison of measured strains with analytical and numerical simulation results provides additional understanding of the mechanical behaviour of this nuclear graphite material in complex stress states.

A Hybrid Strategy for Profile Measurement of Micro Gear Teeth.

A hybrid strategy is proposed to meet the challenge of obtaining the profile of micro gear teeth with a small modulus. Firstly, the contact probe segmentally obtained the falling flank profiles with an auxiliary lifting mechanism to avoid interference when it climbs on the rising slope. Then, the noncontact chromatic confocal displacement sensor efficiently acquired the gear peak positions to carry out the two-point error separation with the gear peak positions from the probe measurement. Finally, actual experiments were carried out to obtain the profile of a harmonic drive flexspline. Compared with the commercial ultraprecise profiler, the proposed method provides measurement results with a deviation of less than 20 μm. In conclusion, the hybrid strategy is feasible and accurate for drawing the micro gear teeth profile without any collision between the measuring probes and the measured workpiece.

A deformation measurement method based on surface texture information of rocks and its application

Users of the digital image correlation method are faced with the problem of poor operability, low repeatability, and lack of standardized specifications for spraying speckles. To solve the problem, the research proposed a rock deformation measurement method that obviates the need to spray speckles. A local binary model was established by using the local binary pattern (LBP) operator based on deep texture features on rock surfaces. The resulting LBP digital speckle pattern can substitute artificial speckle patterns and demonstrates high quality and strong applicability. Based on the LBP digital speckle pattern, the target tracking algorithm was employed to achieve non-contact measurement of the dynamic displacements of rocks. The feasibility and effectiveness of the algorithm in practical application were verified by conducting shear tests on granite and siltstone. Test results show that the deformation characteristics in the displacement nephograms are in line with the measured data pertaining to rock fracturing and conform to the basic characteristics of the shear failure of rocks. The deformation measurement method based on surface texture information can realize non-contact displacement measurement of rocks under conditions without speckles: this obviates the influence of the quality of sprayed speckles on the accuracy of the measurement of deformation.

Noncontact Structural Displacement Measurements Using a Low-Cost Motion Tracking System

Structural health monitoring (SHM) depends on precise displacement measurements to evaluate a structure’s condition. Current measurement systems face challenges such as contact-type restrictions, high costs, uniaxial limitations, and significant computational power requirements. A novel low-cost, non-contact displacement measurement system, called the HTC-VTS (Vive Tracking System), developed by Hongda International Electronics Co., Ltd. (New Taipei City, Taiwan), is proposed. The system setup and data acquisition of the HTC-VTS for SHM involve coordinate transformations to convert six degrees of freedom (DOFs) from raw motion data into 3-DOF structural displacement measurements. The HTC-VTS was experimentally validated using laboratory-scale free vibration tests on a cantilever beam and shaking table tests with actual bridge displacement measurements, demonstrating satisfactory performance in both scenarios. The proposed system expands the potential for cost-effective motion capture systems in both experimental and real-world structural applications.

Vision and Vibration Data Fusion-Based Structural Dynamic Displacement Measurement with Test Validation.

The dynamic measurement and identification of structural deformation are essential for structural health monitoring. Traditional contact-type displacement monitoring inevitably requires the arrangement of measurement points on physical structures and the setting of stable reference systems, which limits the application of dynamic displacement measurement of structures in practice. Computer vision-based structural displacement monitoring has the characteristics of non-contact measurement, simple installation, and relatively low cost. However, the existing displacement identification methods are still influenced by lighting conditions, image resolution, and shooting-rate, which limits engineering applications. This paper presents a data fusion method for contact acceleration monitoring and non-contact displacement recognition, utilizing the high dynamic sampling rate of traditional contact acceleration sensors. It establishes and validates an accurate estimation method for dynamic deformation states. The structural displacement is obtained by combining an improved KLT algorithm and asynchronous multi-rate Kalman filtering. The results show that the presented method can help improve the displacement sampling rate and collect high-frequency vibration information compared with only the vision measurement technique. The normalized root mean square error is less than 2% for the proposed method.

A semi-analytical dynamics method for spindle radial throw in boring process

In precision boring processing, accurate prediction of the radial throw of a boring tool spindle has critical significance for reducing machining errors. However, the classical dynamics method of radial throw based on the rigid body partition method ignores special characteristics of the boring tool spindle, resulting in additional errors regarding radial throw evaluation. Hence, a semi-analytical dynamics method considering the axial length, variable cross-section, and offset distance was proposed to decrease the computational error of the current dynamics model. The mechanism of radial throw was analyzed by the mechanics of materials and mathematical formulas. The Euler-Bernoulli beam theory and partial differential equation method were utilized to derive the dynamics model of the boring tool spindle, and an improved Galerkin variational algorithm was used to resolve the dynamics formulas for the radial throw. Then, the proposed dynamics method was compared with the non-contact displacement measurement and the traditional lumped mass parameter method. The validated results showed that the presented dynamics method had good agreement with the experimental data, and the maximum predictive error was 16.08 μm lower based on the proposed method. Furthermore, the machining precision of holes was also clearly evaluated and discussed using the proposed dynamics method under different processing conditions, and the lower uncertainty of the proposed dynamics method was also demonstrated. As a result, the proposed semi-analytical dynamics method can accurately compute the radial throw and evaluate the machining error in boring technology.

Experimental study on the galloping characteristics of single ice-coated transmission lines under oblique flows

Galloping of ice-coated transmission lines is occasionally observed under oblique wind directions. However, most current investigations on the galloping mechanisms are for flow perpendicular to the span of the transmission lines. In order to address this gap, this research studies the galloping characteristics of ice-coated transmission lines under oblique flows based on wind tunnel tests. The wind-induced displacement of an aero-elastic iced-coated transmission line model was measured with a noncontact displacement measurement equipment in a wind tunnel at different wind speeds and directions. The results show that galloping is characterized by elliptical trajectories and negative damping, which is more likely to occur under oblique flows than the direct flow (0°). At 15° wind direction, a galloping in vertical direction was observed at wind speeds above 5 m/s. At 30° wind direction, galloping was observed over the entire range of the tested wind speeds. Moreover, the galloping amplitudes under oblique flows are observed to be larger than that at the direct flows. Consequently, when the wind direction between the major winter monsoon azimuth and the lateral direction of transmission line route is between 15° and 30°, appropriate anti-galloping devices are highly recommended in practice.