Linear Displacement Sensor Research Articles

Selection and experimental study of the linear displacement converter for the automated monitoring system of mine roofs

The justification of the linear displacement sensors installation in mine workings is described in this paper. The required technical characteristics of the sensors are given. The main types of primary linear displacement converters are presented. The choice of inductive solenoid-type converters and sensors based on linear differential transformers (LVDT) is justified. The advantages and disadvantages of inductive transducers, their accuracy and measurement limits are described, and measuring methods of inductance of the solenoid-type transducers and the converter output signal based on LVDT are considered. The results of sensors experimental studies based on the solenoid-type inductive transducers are presented.

Pneumatic actuator positioning with pilot controlled check valves

Abstract Tests of accuracy and repeatability of the pneumatic cylinder positioning in intermediate positions using a check valve are presented. The tests were performed under different loads and for different piston speeds and operating pressure in a pneumatic system with throttle check valves and an optical linear displacement sensor measuring the position of the actuator rod. Assessment of the effect of the cylinder performance parameters on the accuracy and repeatability of piston rod positioning was done and limitations and possible applications of the pneumatic cylinder positioning in intermediate positions with a check valve were identified.

Application of the signal speed change limiting method for increasing the indications credibility on the example of hydraulic shock absorber monitoring system

This article is devoted to the problem of unreliable indications in a system with sensors operating in harsh environmental conditions. To increase the indications credibility, an algorithm based on the signal speed change limiting method is proposed when calculating the average speed value using the simple moving average formula. The result of the algorithm obtained by modeling the algorithm in a software environment on a sample of linear displacement sensor indications obtained from the hydraulic shock absorbers monitoring system of the current NPP power unit is also presented.

Nonlinear Correction of LVDT Sensor Based on ACO-BP Neural Network

In this paper, the output signal of the linear variable differential transformer type displacement sensor (LVDT) is nonlinear, a BP neural network optimized by the ant colony algorithm is designed to fit and correct the nonlinear output of the LVDT. This scheme first uses the ant colony algorithm to search the optimal range of neural network weights and thresholds, and then uses the BP neural network to fit any non-linear function to LVDT nonlinear output fitting and correction, which overcomes the shortcomings of BP neural network easily falling into local minimum and slow convergence. Through MATLAB simulation experiments, it is concluded that the convergence speed, average error and average error percentage of the ACO-BP neural network are better than the BP neural network. This solution has certain feasibility for solving the LVDT nonlinear problem, and provides a new solution for the sensor nonlinear correction.

An Inductive Linear Displacement Sensor With Bilateral Sensing Units

This paper presents an inductive linear displacement sensor with bilateral sensing units, which consists of a stator with excitation coils, two movers with pickup coils and a mover base. Two movers have the same structure and work on two sides of the stator to realize bilateral sensing. Bilateral sensing units contribute to reducing the negative influence from the gap change between the movers and stator on the measurement performance of the sensor, because bilateral mover structure is able to maintain the sum of two side gaps constant and thus reach good magnetic coupling with the stator. Comparison experiments of the prototypes in different working gaps have been implemented and verified that the sensor with bilateral sensing units has better repeatability and accuracy than that with unilateral sensing unit. Based on the regular errors shown in the measurement results of the proposed bilateral sensing sensor in comparison experiments, this paper also presents the detailed analysis about the sources of some dominating error components. Accordingly, a sensor prototype with improved designs for reducing measurement errors was developed. Final experimental results of the improved sensor prototype show that the accuracy is better than 15μm and the repeatability is about 7μm with less than 1.2μm resolution in the range of 0mm~288mm.

A Long-Range High Applicability Length Comparator for Linear Displacement Sensor Calibration

In this article, a long-range length comparator, applicable for both static- and dynamic-index calibrations of a linear displacement sensor, is presented. The comparator consists of an air-floating linear motion generator (LMG) and an interferometric optical length calibrator (OLC). A novel design of the LMG made by multisegment splicing is introduced, in which a two-level vibration isolation arrangement, a multiple sliders' setup, and an exoskeleton framework are adopted. The resulting linear motion can be extremely ideal even with a large stroke. The angular error is within 11.89 μrad covering the -2m range. The maximum operating speed and the acceleration of the LMG are 10 m/s and 20 m/s <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively. A dual-path optical design of the OLC is displayed, resulting in high environmental tolerance and a small trigger delay of 4.75 ns. The best accuracy of the comparator can be ±(0.041+0.106L) μm with a resolution of 0.3 nm. The maximum error and operation speed of a 2-m range exposed encoder were successfully calibrated, and the grating pitch deviation was also found, by which the effectiveness of the comparator is proven. The proposed length comparator introduces a possible solution, for how a long-range linear displacement sensor, can be calibrated with high accuracy, efficiency, and applicability.

Analysis of the surface rupture process of strong earthquakes based on centrifuge tests

Surface ruptures caused by strong earthquakes are one of the most concerning issues for construction projects. In this paper, geotechnical centrifuge model tests is performed to successfully simulate the reverse faulting process. Using a linear laser displacement sensor (LLDS) and the particle image velocimetry (PIV) technique, the surface deformation process and faulting behaviours are studied in dry and wet sand with a thickness of 40 m above a bedrock surface. Based on an analysis of high-precision surface monitoring data, the soil rupture process is divided into four stages: the overall uplift period, inclination deformation period, scarp growth period, and deformation slowdown and lag period. In addition, the characteristics of the soil deformation and the propagation behaviour of the upper fault tip are obtained. This experiment and related achievements can provide references for further understanding the deformation of thick soil layers caused by reverse faulting.

A New High Precision Linear Displacement Sensor Based on Single Light Field Orthogonal Modulation

This paper present a single light field orthogonal modulation displacement measurement method which is based on time and space modulation technology. This method uses an alternating light intensity modulation in the time domain and modulation of four sinusoidal light-transmitting surfaces in the spatial domain to synthesize a traveling wave signal. The displacement was accurately reflected in the phase shift of the traveling wave signal, which could be measured by the time difference. A prototype with a measuring range of 500 mm and a pitch of 0.6 mm was fabricated to evaluate the proposed method. Combined with the measurement mechanism, the measurement errors caused by the spatial modulation were analyzed in detail. To reduce those primary periodic errors, we proposed an optimization structure of continuous cosinusoidal transmitting surfaces and demonstrated the effectiveness of this method by simulations and experiments. The experimental results indicate that the short period measurement accuracy reached ±0.29 $\mu \text{m}$ with 1 nm resolution within one period of 0.6 mm, which means that the accuracy in one period (0.6 mm) exceeded 0.1%. Furthermore, the original measurement accuracy of the full range of 500 mm was ±1.3 $\mu \text{m}$ , the error showed great regularity, and the better performance of the sensor could be obtained by digital calibration for the measurement data or improvement in the structure. Therefore, compared with the traditional measurement methods, the sensor described in this paper can achieve high-precision measurement with a low cost of manufacture.

3-D-Printed High Data-Density Electromagnetic Encoders Based on Permittivity Contrast for Motion Control and Chipless-RFID

The 3-D-printed electromagnetic encoders based on permittivity contrast are presented and discussed in this article. The encoders, implemented using exclusively dielectric materials, are based on linear chains of dielectric inclusions. Two types of encoders are considered: 1) those where the inclusions are simple apertures made on a 3-D-printed dielectric plate (or substrate) and 2) those with inclusions made of high dielectric constant material 3-D-printed on a dielectric substrate (also 3-D-printed). In both cases, encoding is achieved by varying the dielectric constant of the substrate at predefined positions by means of the inclusions. For encoder reading, a microstrip line loaded with a slot resonator (etched in the ground plane) and a series gap is proposed. Such structure is very sensitive to short range dielectric constant variations, being able to detect the presence or absence of closely spaced inclusions when the encoder is displaced on top of the sensitive part of the reader, the slot resonator. For that purpose, the reader line is fed by a harmonic signal conveniently tuned, so that an amplitude-modulated (AM) signal containing the identification (ID) code is generated at the output port of the line. The proposed reader/encoder system is useful for motion control applications (linear displacement and velocity sensors) and for near-field chipless-radio frequency ID (RFID). Lower cost and major robustness against mechanical wearing are potential advantages of these encoders over other electromagnetic encoders based on a similar principle but based on metallic inclusions.

Phase Imbalance Optimization in Interference Linear Displacement Sensor with Surface Gratings.

In interferential linear displacement sensors, accurate information about the position of the reading head is calculated out of a pair of quadrature (sine and cosine) signals. In double grating interference schemes, diffraction gratings combine the function of beam splitters and phase retardation devices. Specifically, the reference diffraction grating is located in the reading head and regulates the phase shifts in diffraction orders. Measurement diffraction grating moves along with the object and provides correspondence to the displacement coordinate. To stabilize the phase imbalance in the output quadrature signals of the sensor, we propose to calculate and optimize the parameters of these gratings, based not only on the energetic analysis, but along with phase relationships in diffraction orders. The optimization method is based on rigorous coupled-wave analysis simulation of the phase shifts of light in diffraction orders in the optical system. The phase properties of the reference diffraction grating in the interferential sensor are studied. It is confirmed that the possibility of quadrature modulation depends on parameters of static reference scale. The implemented optimization criteria are formulated in accordance with the signal generation process in the optical branch. Phase imbalance and amplification coefficients are derived from Heydemann elliptic correction and expressed through the diffraction efficiencies and phase retardations of the reference scale. The phase imbalance of the obtained quadrature signals is estimated in ellipticity correction terms depending on the uncertainties of influencing parameters.

Sensing and Decentralized Control of a Five-Axis Monolithic Nanopositioning Stage

Abstract This article describes the design and calibration of a five degree-of-freedom linear and angular displacement sensor utilizing piezoresistive strain gages. A simple decentralized controller is then implemented to follow linear and angular reference signals. The foremost difficulty with piezoresistive sensors is their high-temperature sensitivity. In addition, they are sensitive to motion in multiple degrees of freedom, which must be decoupled before use as a displacement sensor. A new sensing design is proposed which provides decoupled measurements of linear and angular displacements in multi-axis monolithic nanopositioning stages. The proposed method employs system identification and feedforward techniques to calibrate each axis and minimize cross-coupling.

一种大量程光纤弯曲损耗型线性位移传感器研究

一种大量程光纤弯曲损耗型线性位移传感器研究

Optical Sensors for Multi-Axis Angle and Displacement Measurement Using Grating Reflectors

In dimensional metrology it is necessary to carry out multi-axis angle and displacement measurement for high-precision positioning. Although the state-of-the-art linear displacement sensors have sub-nanometric measurement resolution, it is not easy to suppress the increase of measurement uncertainty when being applied for multi-axis angle and displacement measurement due to the Abbe errors and the influences of sensor misalignment. In this review article, the state-of-the-art multi-axis optical sensors, such as the three-axis autocollimator, the three-axis planar encoder, and the six-degree-of-freedom planar encoder based on a planar scale grating are introduced. With the employment of grating reflectors, measurement of multi-axis translational and angular displacement can be carried out while employing a single laser beam. Fabrication methods of a large-area planar scale grating based on a single-point diamond cutting with the fast tool servo technique and the interference lithography are also presented, followed by the description of the evaluation method of the large-area planar scale grating based on the Fizeau interferometer.

Modeling of Phase Shifts of Light in Orders of Diffraction Gratings of an Interference Linear Displacement Sensor

Phase shifts of light in orders of diffraction grating for the interference linear displacement sensor are considered. Using the phase diffraction grating with given geometric parameters of the surface relief allows one to stabilize phase relations in optical signals and in resulting signals outputted from the displacement sensor. Based on the mathematical simulation data, technically feasible parameters of the grating relief are proposed for creating the required phase shifts between diffracted beams leading to quadrature modulation. It helps reaching the required measurement accuracy with nanometric resolution.

Performance optimization of magnetostrictive guided wave sensor based on waveguide wire

In this paper, an open magnetic circuit magnetostrictive guided wave sensor that allows free regulation of the static working point is proposed for ferromagnetic material waveguide wires applied to non-destructive testing of wire bars, guided wave mechanics study, magnetostrictive linear displacement sensors and other fields. The sensor was made up of an iron-gallium alloy wire, a ring-shaped permanent magnet and a concentric coil, which was used to excited a longitudinal mode guided wave on the iron-gallium alloy wire. The structural parameters of the permanent magnet were optimized, the axial relative distance between the permanent magnet and the coil was studied and the superposition of and matching between the dynamic magnetic field and the static bias magnetic field were adjusted, allowing identifying the optimal magnetization point, so that the magnetic acoustic transduction efficiency was optimized. The sensor was analyzed, by means of finite element simulation, to produce the best system combination, which improved the sensitivity of the measurement. The improvement has been experimentally verified.

Development of a segment of a series of linear displacement sensors

Purpose. Presentation of the results of development and practical implementation of a segment of a series of inductive linear displacement sensors (linear variable differential transformer LVDT) for hydraulics systems of the aerospace industry. Methodology. Calculations of three-dimensional magnetic fields are carried out with the finite elements method. The solution of the differential equations connecting the input voltage, current, magnetic flux and EMF of the windings is performed by numerical integration. Results. As a result of calculations, the sensor configuration, embodied in the models DLP-17, DLP-30, DLP-50 and DLP-80, was obtained. Tests of the prototype models of the all sensors confirmed the principle workability of the adopted design and design solutions in its development. Originality. The use of three-dimensional field models allows to make an accurate calculation of the sensor's magnetic field, taking into account the edge effects on its characteristics. As a result of the calculations, a variants of the configurations of the secondary windings was chosen, which made it possible to increase the accuracy of the sensors. Practical value. The developed sensors DLP-17, DLP-30, DLP-50 and DLP-80 in its technical characteristics are correspond to the design specification.

Development of a novel system for linear displacement sensor calibration

This paper presents the development of semi-autonomous metrological devices, capable of calibrating variety of linear displacement sensors, like Linear Variable Differential Transformers (LVDT), string potentiometers, laser displacement sensors and other. Data acquisition equipment that could be used for measuring objects of various shapes and sizes are already available; however, devices specifically tailored for the calibration of displacement sensors are not currently offered. Advantages of this new technology, that we are investigating and developing, include reduction of time, costs and human resources required to perform calibration. In addition to that, the advantages of an affordable calibration device will allow calibrations to be carried out internally, as opposed to outsourcing to dedicated facilities. The scope of the project encompasses research into the device’s compliance with ISO/IEC 17025 to obtain NATA accreditation, research into design, and selection of material and manufacturing processes to ensure an acceptable measurement of uncertainty is achievable across all varieties of linear displacement sensors. The sensors are used to measure suspension displacement, steered angle and various other geometries on vehicles and test equipment. Outcomes of this research project offer experimental evidence that proves the feasibility of developing and manufacturing devices that produce an acceptable uncertainty that meets testing standards requirements at a fraction of the cost of comparable measuring devices.

Influence of Micro and Nanosilica on the Frost–Heave Process

Frost-heave of soils is an important problem in engineering practice. Thus, it became necessary to find an adequate method that would reduce the negative effect of this phenomenon on building structures. The paper presents the preliminary tests results of microsilica (MS) and nanosilica (NS) influence on the water freezing process in frost-susceptible soils. The selection of stabilising additives also allowed for the analysis of changes that result from their transition from micro to nanoscale. For the purposes of the experiment a test stand was constructed, that enables to analyse six samples at the same time, at inflow of water from the bottom and freezing direction from the top. The use of linear potentiometer displacement sensors allowed to measure the increase in the height of samples automatically. Additionally, the measurement stand was equipped with digital semiconductor temperature sensors, so temperature could be measured at various heights of the samples. Moreover, an array of electrodes was applied to measure the electrical conductivity of soil at various levels of samples, which enabled the analysis of changes that occur in freezing soil. The tests were conducted according to the BS 812-124:1989 standard, in three variants: soil, soil + 5% MS, soil + 5% NS. The obtained results demonstrated that the addition of microsilica reduces the occurrence of ice lenses, which in turn significantly decreases the growth in sample height. However, the addition of nanosilica completely stops the frost-heave process. Ice lens is not created, only a frost line is noticeable. Analysing the distribution of temperatures at different heights, it was noted that stabilised samples are characterised by higher temperature in comparison to the soil without additives. This means that the analysed stabilisers reduce the degree of freezing of the soil mixture. The highest temperatures were noted in samples stabilised with nanosilica. Conductivity tests also demonstrated that the smallest changes occurred in samples stabilised with nanosilica. This results from the fact that ice lenses did not occur in such samples. In order to analyse the obtained results and their interpretation thoroughly, it is necessary to perform a detailed analysis of the microstructure both of soil and of soil with stabilising additives.

A Linear Differential Inductive Displacement Sensor With Dual Planar Coils

A non-contact displacement sensor employing a couple of planar coils etched on printed circuit boards (PCBs) and an E-type soft ferromagnetic core is proposed here. The E-type soft ferromagnetic core moves over two triangular shaped spiral coils etched on a couple of PCBs. The variation in the inductances of the two coils has a cubic polynomial relationship with the displacement of the core. An appropriate signal conditioning technique operates on the inductances and provides an output that varies linearly with the displacement. The symmetrical structure of the sensor provides negligible cross axis sensitivity. Simulation studies and results obtained from a prototype sensor having a 70-mm range and a resolution of $2~\mu \text{m}$ , built and tested, establish the efficacy of the proposed technique. The worst-case nonlinearity observed from the prototype is 0.4%.

Observer-based compensation of thermal disturbances for linear displacement sensors

A compensation method is proposed that enables the correction of temperature disturbance effects on the mechanical structure of linear displacement sensors, when measuring in environments with moderately changing temperatures. Based on the surface temperature information of the sensor housing, an open loop observer estimates the thermal error, considering the clamping configuration of the sensor with respect to the target surface. Correspondingly, the indicated value is corrected by the estimated thermal error. The validity of the correction after calibration is checked by various experiments, in which setup settings are varied and different time-temperature-sequences are tested.