Displacement Sensor Research Articles

A high-sensitivity rotatable 3D displacement sensor

Aiming at the problems of low sensitivity and low accuracy caused by the displacement transfer mechanism of three displacement sensors used simultaneously in the 3D displacement monitoring of seismic isolation bearings, the paper has proposed a high-sensitivity rotatable 3D displacement sensor. The sensor adds through holes on the surface of the equal-strength cantilever beam to form a cross beam, which increases the bending strain on the beam surface to improve the sensitivity. By adding a gyroscope and a mechanical rotation structure, a single sensor can measure the 3D displacement at the same time, reducing the adverse effects displacement transmission mechanism on the accuracy of the measurement. ANSYS software was used to simulate and optimize the parameters of the size of through-hole of the sensor beam to determine the appropriate size and location of the through-hole. Finally, the sensor was developed and its static characteristics and displacement measurement performance in static and dynamic 3D space were tested based on the simulation results. The test results have shown that the sensor has a sensitivity of 16.29 mV/mm and an accuracy of 0.9% in the range of 0–160 mm. Its static and dynamic 3D spatial displacement measurement errors are less than 2 mm, which can meet the accuracy requirements of 3D displacement measurement and sensitivity for structural health monitoring of seismic isolation bearings.

Numerical Analysis of Thorax Injury Caused by the Blunt Impact of SIR-X Sponge Grenade

To effectively assess the injury risk of the blunt impact of the SIR-X sponge grenade on the human thorax, in this paper, we used a numerical simulation technique to test the non-lethal kinetic energy projectiles that blunt impact on the Hybrid III 50th dummy model. By simulating the effect of the L5 projectile on the thorax of the Hybrid III 50th dummy model, about NATO standard AEP-99 (2021 edition), the thoracic displacement curves of the dummy model in three testing conditions were obtained in the validation corridors. The idea of replacing the finite element model of the human body with the Hybrid III 50th dummy finite element model was proposed. We considered the difficulty in obtaining data due to the large deformation of the contact position when the SIR-X sponge grenade impacts the dummy’s thorax. We proposed a mathematical model to predict the impact injury of the human thorax using the rib displacement measured by the rib displacement sensor of the Hybrid III 50th dummy. We simulated the SIR-X sponge grenade blunt impacting the dummy model’s thorax. The measured rib displacement was used to predict and analyze the injury risk of the human thorax, providing a specific data reference for practical application.

Physical Modeling and Intelligent Prediction for Instability of High Backfill Slope Moisturized under the Influence of Rainfall Disasters

The stability of high backfill slopes emerges in practice due to the expansion of transportation infrastructures. The seepage and infiltration of rainfall into the backfills brings challenges to engineers in predicting the stability of the slope, weakening the shear strength and modulus of the soil. This study carried out a series of model tests under a plane strain condition to investigate the stability of a high backfill slope moisturized by rainfalls, considering the influences of rainfall duration and intensity. The slope displacements were monitored by a laser displacement sensor and the moisture content in the backfill mass were obtained by a soil moisture sensor. The test results show that increasing the rainfall intensity and duration caused the slope near the surface to be saturated, resulting in significant influences on the lateral displacement of the slope and the reduction of stability as well as the sizes of the sliding mass. Based on the model tests, the numerical analysis was adopted to extend the analysis cases, and the backpropagation (BP) neural network model was further adopted to build a model for predicting the stability of a high backfill slope under rainfall. The trained BP model shows the average relative error of 1.02% and the goodness of fitness of 0.999, indicating a good prediction effect.

High-precision micro-displacement measurement in a modified reversal shearing interferometer using vortex beams

We propose a novel micro-displacement measurement system that employs a modified reversal shearing interference structure based on vortex beam interference. The micro-displacement in the measurement path caused a change in the light path and resulted in an optical path difference (OPD) between the reference and measurement paths. This OPD led to the rotation of the petal-like pattern obtained by the interference between two paths. The rotation angle of the petal-like pattern was proportional to the OPD caused by micro-displacement. We used the virtual phase-shifting method to extract the helical phase front, and the Radon transform to measure the angle of the helical phase front. We achieved a high-accuracy micro-displacement measurement with a measurement error of less than 0.067 nm when using a vortex beam with a topological charge of six. This system has an extremely simple structure and is easy to adjust. It is of great significance to the miniaturized design of high-precision displacement sensors.

Parasitic time-grating angular displacement sensor for precision position measurement of turntable bearing

This paper proposes a parasitic time-grating angular displacement sensor for detecting the position of the turntable bearing. The sensor is mainly composed of probe, rotor, and supporting signal circuit. The probe consists of two separated measuring units on the left and right, and each measuring unit is composed of four sensing units with iron cores, excitation windings, and induction windings arranged according to specific rules. The rotor is made of sinusoidal isometric grooves based on the bearing end cover of the original turntable bearing. The signal processing circuit is used to filter, amplify, and compare the induction signal; meantime, it can generate the excitation signal. The high-frequency clock pulse signal is used as the measurement benchmark to realize the analysis of the position information of the induction signal. The structure and working principles of the sensor are presented in detail. Through the finite element method simulation, the feasibility of sensor scheme is verified, and the theoretical resolution of the prototype sensor is estimated to be about 1.33e−5. A sensor prototype is designed for testing, and the experimental results show that its accuracy can reach −0.003611° to 0.002583° in the range of [0°, 360°] after compensating the error point-by-point through the look-up table method.

Design and Parameter Identification for a Positioning Platform with a Large Stroke and High Precision for Segmented Mirrors

An active optical system with three segmented mirrors was proposed to verify the co-focus and co-phase progress. In this system, a kind of large-stroke and high-precision parallel positioning platform was specially developed to help support the mirrors and reduce the error between them, which can move in three degrees of freedom out of plane. The positioning platform was composed of three flexible legs and three capacitive displacement sensors. For the flexible leg, a kind of forward-type amplification mechanism was specially designed to amplify the displacement of the piezoelectric actuator. The output stroke of the flexible leg was no less than 220 μm and the step resolution was up to 10 nm. Further, a linear model was established to identify the amplification ratio between the actuator and the flexible leg, which can increase the precision of the positioning platform. Moreover, three capacitive displacement sensors with a resolution of 2.5 nm were symmetrically installed in the platform to accurately measure the position and attitude of the platform. To improve the stability and precision of the platform, particle swarm optimization algorithm was applied to identify the control matrix, which can help the platform achieve ultra-high precision positioning. The results showed that the theoretical matrix parameters had a maximum deviation of 5.67% from the experimental ones. Finally, abundant experiments verified the excellent and stable performance of the platform. The results proved that while bearing the heavy mirror, which is no more than 5 kg, the platform can realize a 220 μm translation stroke and 2.0 mrad deflection stroke, with a high step resolution of 20 nm and 0.19 μrad. These indicators can perfectly cater to the requirements of the proposed segmented mirror system’s co-focus and co-phase adjustment progress.

Reliability Assessment of a Vision-Based Dynamic Displacement Measurement System Using an Unmanned Aerial Vehicle.

In recent years, many studies have been conducted on the vision-based displacement measurement system using an unmanned aerial vehicle, which has been used in actual structure measurements. In this study, the dynamic measurement reliability of a vision-based displacement measurement system using an unmanned aerial vehicle was examined by measuring various vibrations with a frequency of 0 to 3 Hz and a displacement of 0 to 100 mm. Furthermore, free vibration was applied to model structures with one and two stories, and the response was measured to examine the accuracy of identifying structural dynamic characteristics. The vibration measurement results demonstrated that the vision-based displacement measurement system using an unmanned aerial vehicle has an average root mean square percentage error of 0.662% compared with the laser distance sensor in all experiments. However, the errors were relatively large in the displacement measurement of 10 mm or less regardless of the frequency. In the structure measurements, all sensors demonstrated the same mode frequency based on the accelerometer, and the damping ratios were extremely similar, except for the laser distance sensor measurement value of the two-story structure. Mode shape estimation was obtained and compared using the modal assurance criterion value compared with the accelerometer, and the values for the vision-based displacement measurement system using an unmanned aerial vehicle were close to 1. According to these results, the vision-based displacement measurement system using an unmanned aerial vehicle demonstrated results similar to those of conventional displacement sensors and can thus replace conventional displacement sensors.

High-Precision Wearable Displacement Sensing System for Clinical Diagnosis of Anterior Cruciate Ligament Tears.

An anterior cruciate ligament (ACL) tear is a common musculoskeletal injury with a high incidence. Traditional diagnosis employs magnetic response imaging (MRI), physical testing, or other clinical examination, which relies on complex and expensive medical instruments, or individual doctoral experience. Herein, we propose a wearable displacement sensing system based on a grating-structured triboelectric stretch sensor to diagnose the ACL injuries. The stretch sensor exhibits a high resolution (0.2 mm) and outstanding robustness (over 1,000,000 continuous operation cycles). This system is employed in clinical trial to diagnose ACL injuries. It measures the displacement difference between the affected leg and the healthy leg during Lachman test. And when such a difference is greater than 3 mm, the ACL is considered to be at risk for injury or tear. Compared with the gold standard of arthroscopy, the consistency rate of this wearable diagnostic system reached about 85.7%, which is higher than that of the Kneelax3 arthrometer (78.6%) with a large volume. This shows that the wearable system possesses the feasibility to supplement and improve existing arthrometers for facile diagnosing ACL injuries. It may take a promising step for wearable healthcare.

Technique for assessing the stress state of a rock mass by a multicomponent displacement sensor using the overcoring method

Relevance. Currently, the mining industry is at the beginning of a new stage of development, which corresponds to the extraction of minerals at great depths in difficult conditions. Based on this, an uncertainty is formed in the assessment of the parameters of the stress state of the rock mass in which mining operations are carried out, which contributes to the growth of emergency situations in underground conditions. The method of overcoring is able to provide quantitative and qualitative information about the stress state. The purpose of the research – substantiation of the methodology for assessing the stress state of the rock mass by the method of overcoring, which includes two main stages: 1 – field tests; 2 – processing of field test data. Research methodology. The method of overcoring is based on measuring the displacements of the points of the walls of the measuring well with a multicomponent displacement sensor as a result of creating an annular gap (formation of complete unloading). Data processing is carried out by two main approaches: 1 – numerical modelling; 2 – analytical calculation. Results. The concept of carrying out work on the assessment of the stress state of the rock mass by the method of overcoring is described. Detailed information about the field test is provided, namely the sequence of measurements and the necessary equipment. A step-by-step algorithm for processing data obtained as a result of field tests based on numerical modelling and analytical analysis has been created. Conclusion. The technique presented in this paper was tested at the deposits of AO Apatit and PAO Norilsk Nickel and showed correct quantitative and qualitative results, according to the stress state of the rock mass.

An error compensation scheme for polar coordinate glass edging machines using the contour registration method

This paper proposes a comprehensive error compensation method for the glass edging machine using polar coordinates. An error model is established to evaluate the error source of the contour deviation from the ideal position after glass installation. According to the simulation results, it is determined that the misalignment of the linear axis and the rotary table and the inaccuracy of the fixture are the main reasons for the installation error of the work-piece. Then, a two-step contour registration method is introduced to accomplish the task of error identification. The glass contour is first measured by a laser displacement sensor after being installed on the rotary table. The coarse registration is presented to align the centroid positions of the measured and the ideal contours, and the fine registration is developed to match them precisely. After that, the installation error can be extracted from the transformation parameters by the least square method. Furthermore, a compensation model is proposed to map the original contour to the actual installation position using the transformation matrix constructed by the identified errors. Finally, a verification experiment is implemented that compares the grind edge without and with compensation to validate the efficiency and accuracy of the proposed method. After error compensation, the mean value and the variance value of the polar diameter deviation of the glass work-piece decreased by 87.5% and 83.0%, respectively. This paper provides a simple way to identify and compensate the installation errors online with high accuracy and efficiency. The proposed method can improve the machining accuracy of the polar coordinate glass edging machines and reduce glass waste.

Study on the evolution and suppression strategy of the interlayer gap in the drilling of CFRP/Al stacked materials

In aircraft assembly operations, interlayer gap formation during drilling through stacked materials positively affects interlayer burr size. Removing these burrs needs disassembly, deburring, and reassembly, and these processes are time-consuming, expensive, and non-value-added. This study visualizes the real-time variation of the interlayer gap to understand its evolution process and proposes a method of designing feed motion for reducing the interlayer gap. First, a real-time measurement method of the interlayer gap and deflection using a 2D laser displacement sensor is proposed, and the evolution of the interlayer gap in the drilling of stacked materials is described. Besides, a simplified analytical model of the stacks is built to explain the development of interlayer gaps during stack drilling. Then, a variable feed method based on the discrete sine curve is proposed to suppress the interlayer gap. Finally, the drilling experiments of the constant feed and the discretized sine curve feed are performed to compare the change of interlayer gap, and the results showed that the maximum interlayer gap (excluding the effect of chips), the maximum interlayer gap (not excluding the effect of chips), the final interlayer gap and the average interlayer gap was reduced by 25.2 %, 45.1 %, 72.7 % and 35.9 %, respectively. In addition, a small interlayer gap corresponds to a small flexural deformation, which helps reduce the material's stress. The bending deformation of the Al layer is reduced by 54 %, and its maximum stress value can be reduced by 22 %.

RJVS: A novel, compact and integrated rotating joint with variable stiffness

A variable stiffness joint is a key element for structural deformation, which is widely used in morphing mechanisms including mechanical arms, folding wings, etc. By adjusting the stiffness of the joint according to the external environment and/or system instruction, the motion response of the mechanical system can be controlled and its security and stability can be guaranteed. However, to develop a variable stiffness joint with small size and large bearing capacity is still challenging. Also, an accurate mathematical model and control method to describe the variable stiffness joint is very important. In this paper, a novel, compact and integrated rotating joint with variable stiffness is developed, whose rotational stiffness and motion can be real-time controlled. A new configuration of a stiffness-adjusting module with superior mechanical properties is proposed by changing the arm length of cantilever leaf springs. Then a universal mechanical model of stiffness which adapts to a wide range of deformation is proposed. The status of the stiffness-adjusting module is changed by rope driven in order to minize the structure. Angular displacement sensors and torque sensors are integrated to observe the static and dynamic performance of the joint. According to the established rotational stiffness model, the stiffness of the joint is adjusted by reverse calculation of the motor’s rotating angle. A nonlinear Proportion-Integral-Derivative method based on a Genetic Algorithm is proposed for motion control. The experimental results show that the proposed joint, with large bearing capacity and a wide range of stiffness adjustment, has integration functions of driving and sensing, and can achieve a good motion control performance.

On the use of Kalman filters for high-order mode rejection in PZT-based microscanners

This work discusses and compares two strategies for closed-loop control of quasi-static silicon mirrors for raster-scanning applications, actuated by thin films of lead–zirconate–titanate and with embedded piezoresistive angular displacement sensors. A first feedback control approach, based on piezoresistive readout of the device angular displacement through an integrated sensor, shows limitations related to high-order resonant modes of the mechanical structure. To overcome this issue, a feedback control scheme based on the use of a Kalman filter to estimate the angular displacement and velocity of the scanner is presented, achieving a maximum positioning error of 0.14∘ (1.75% of a 8∘ full-scale angular displacement), and a mean error within (0.74% peak-to-peak) over 80% of the scanned trace.

Shake table tests on 1:2 reduced scale masonry house with the application of horizontal seismic bands

The safety of people's lives is crucial in structures that provide shelter. Earthquakes are a major natural disaster that have claimed thousands of lives over the years, but other factors can also cause damage to these structures. Building collapses are often due to their inability to endure the seismic loading, not the earthquake itself. Most residential buildings are masonry structures. There are many strategies for enhancing structural behavior, but very little research has been done on masonry structures, which house about 1/3rd of the world's population. This study focuses on characterization of seismic response using shake table tests to assess the dynamic behavior of masonry structures when horizontal seismic bands are applied. Horizontal seismic band is one of the traditional techniques used in masonry structure. Three reduced scale models were constructed with one using a reinforced concrete band, one with a timber band, and one without a band. All models were constructed using extruded earth block and mud mortar, common building materials in developing nations. The models were tested on a shake table using the same loading signal to compare their response behavior. A high-speed camera was also used to capture images; accelerometers and displacement sensors were installed to record the response. Digital Image Correlation (DIC), which provides non-contact optical measurement, has been essential in obtaining full-field measurement. The results showed significant improvement in the seismic response of structures with horizontal seismic bands. The behaviors are compared in terms of natural frequency, damping, energy dissipation, and crack propagation patterns using two types of materials as seismic bands.

An Optimal Strain Gauge Layout Design for the Measurement of Truss Structures

Sensor measurements diagnose and evaluate the structural health state. A sensor configuration with a limited number of sensors must be designed to monitor sufficient information about the structural health state. The diagnosis of a truss structure composed of axial members can begin with a measurement by the strain gauges attached to the truss members or by the accelerometers and displacement sensors at the nodes. This study considered the layout design of the displacement sensors at the nodes for the truss structure by using the effective independence (EI) method based on the mode shapes. The validity of the optimal sensor placement (OSP) methods depending on their synthesis with the Guyan method was investigated by the mode shape's data expansion. The Guyan reduction technique rarely affected the final sensor design. A modified EI algorithm based on the strain mode shape of the truss members was presented. A numerical example was analyzed, showing that the sensor placements were affected depending on the displacement sensors and strain gauges. Numerical examples illustrated that the strain-based EI method without the Guyan reduction method has the advantage of reducing the number of sensors and providing more data related with the displacements at the nodes. The measurement sensor should be selected when considering structural behavior, as it is crucial.

FE‐based modeling of a mesoscale piezoelectric motor

AbstractThe manufacturing of systems at the mesoscale on the order of millimeters to centimeters is costly and challenging. To simplify the development process, the finite element method (FEM) can be used to compare and evaluate different design variations at an early stage. This method also allows for gaining a more precise understanding of the system's behavior. In robotic applications it is the torque that is of the greatest interest as a sufficiently high torque mitigates the need for a gearbox, which is very difficult to manufacture and integrate at small scales. Given this background, the present work aims to develop a finite element model for the numerical representation of a class of rotational piezoelectric motors based on multiple unimorph arms. The influence of different design parameters on the resulting torque is analyzed utilizing this model. The motor design consists of a planar rotor and a flat spring, a stator with three unimorph arms, as well as a shaft. With a total integrated motor thickness of 0.8 mm, the weight is approximately 200 milligrams. The rotation is mainly caused by the tip contact between the arms of the stator and the rotor itself. Experiments with prototypes have shown that bidirectional rotation is possible with the design, which is then investigated in more detail using the numerical model. There are several challenges here in the non‐linearity due to the contact between the individual components and the high‐frequency excitation of the motor in the kHz range.The modeling also requires validation experiments to determine the resulting properties for the coupled system of structural and piezoelectric components. This includes both the measurement of the unimorph arms and the measurement of the natural frequencies of the stator with the piezoelectric unimorphs by a laser scanning vibrometer and displacement sensors. The scanning vibrometer also provides the opportunity to compare the vibration modes, as an important non‐local output quantity, in order to achieve good agreement between the numerical and experimental results.In the next stage, the model is to serve as the basis for multi‐objective optimization to achieve maximum torque in the smallest possible volume. Further miniaturization possibilities will also be investigated in future studies.

Geometric part error and material property profile separation technique of the additively manufactured and post-processed rods.

This paper presents novel surface profilometry for both geometric part error and metallurgical material property distribution measurements of the additively manufactured and post-processed rods. The measurement system, the so-called fiber optic-eddy current sensor, consists of a fiber optic displacement sensor and an eddy current sensor. The electromagnetic coil was wrapped around the probe of the fiber optic displacement sensor. The fiber optic displacement sensor was used to measure the surface profile, and the eddy current sensor was used to measure the change in permeability of the rod under varying electromagnetic excitation conditions. The permeability of the material changes upon exposure to mechanical forces, such as compression or extension and high temperatures. The geometric part error and material property profiles of the rods were successfully extracted by using a reversal method that is conventionally used for spindle error separation. The fiber optic displacement sensor and the eddy current sensor developed in this study have a resolution of 0.286 µm and 0.00359μr, respectively. The proposed method was applied not only to characterize the rods but also to characterize composite rods.

Experimental Study of Influence Line–Based Damage Localization for Long-Span Cable Suspension Bridges

Influence line (IL)–based damage indices for long-span bridges are investigated in this study. Their effectiveness is experimentally validated for the first time through the scaled physical model of the Tsing Ma Bridge (TMB). First, the IL mechanism for damage detection and its corresponding damage indices are briefly introduced. Subsequently, the scaled TMB model instrumented with different types of sensors, including displacement sensors, strain gauges, and accelerometers, is introduced. The IL characteristics of different bridge components are compared. Two different damage cases with single- and double-damage locations at the bottom chord were tested. In the single-damage case, different ILs extracted from the nearby components were used for damage identification. These ILs can successfully locate damage visually. The strain IL (SIL) is more sensitive to local damage than deflection IL, but its detection performance degrades rapidly with the increasing distance between sensor and force locations. In the double-damage case, the SIL extracted from a single sensor cannot identify both damage cases because of the limited detectable range of each SIL; therefore, using multiple sensor information becomes necessary. For comparison, the modal parameters were also employed for damage detection. These experimental results validated the merits of the IL–based methods proposed for long-span bridges, indicating that IL–based damage indices are good indicators of local damage detection in long-span bridges. This finding contributes to the development of real-time techniques for damage localization in long-span bridges equipped with a structural health monitoring system.

Interaction between an Optically Levitated Nanoparticle and Its Thermal Image: Internal Thermometry via Displacement Sensing.

We propose and theoretically analyze an experiment where displacement sensing of an optically levitated nanoparticle in front of a surface can be used to measure the induced dipole-dipole interaction between the nanoparticle and its thermal image. This is achieved by using a surface that is transparent to the trapping light but reflective to infrared radiation, with a reflectivity that can be time modulated. This dipole-dipole interaction relies on the thermal radiation emitted by a silica nanoparticle having sufficient temporal coherence to correlate the reflected radiation with the thermal fluctuations of the dipole. The resulting force is orders of magnitude stronger than the thermal gradient force, and it strongly depends on the internal temperature of the nanoparticle for a particle-to-surface distance greater than two micrometers. We argue that it is experimentally feasible to use displacement sensing of a levitated nanoparticle in front of a surface as an internal thermometer in ultrahigh vacuum. Experimental access to the internal physics of a levitated nanoparticle in vacuum is crucial to understanding the limitations that decoherence poses to current efforts devoted to preparing a nanoparticle in a macroscopic quantum superposition state.

Automatic Calibration of Tool Center Point for Six Degree of Freedom Robot

The traditional tool center point (TCP) calibration method requires the operator to use their experience to set the actual position of the tool center point. To address this lengthy workflow and low accuracy, while improving accuracy and efficiency for time-saving and non-contact calibration, this paper proposes an enhanced automatic TCP calibration method based on a laser displacement sensor and implemented on a cooperative robot with six degrees of freedom. During the calibration process, the robot arm will move a certain distance along the X and Y axes and collect the information when the tool passes through the laser during the process to calculate the runout of the tool, and then continue to move a certain distance along the X and Y axes for the second height calibration. After the runout angle is calculated and calibrated by triangulation, the runout calibration is completed and the third X and Y axis displacement is performed to find out the exact position of the tool on the X and Y axes. Finally, the tool is moved to a position higher than the laser, and the laser is triggered by moving downward to obtain information to complete the whole experimental process and receive the calibrated tool center position. The whole calibration method is, firstly, verified in the virtual simulation environment and then implemented on the actual cooperative robot. The results of the proposed TCP calibration method for the case of using a pin tool can achieve a positioning deviation of 0.074 and 0.125 mm for the robot moving speeds of 20 and 40 mm/s, respectively. The orientation deviation in the x-axis are 0.089 and −0.184 degrees for the robot moving speeds of 20 and 40 mm/s, respectively. The positioning repeatability of ±0.083 mm for the moving speed of 20 mm/s is lower than ±0.101 mm for the speed of 40 mm/s. It shows that lower moving speed can obtain higher accuracy and better repeatability. This result meets the requirements of TCP calibration but also achieves the purpose of being simple, economical, and time-saving, and it takes only 60 s to complete the whole calibration process.