Precision Displacement Measurement Research Articles

On-machine multi-directional laser displacement sensor using scanning exposure method for high-precision measurement of metal-works

We propose a multi-directional triangulation optical system and scanning exposure method for precise height displacement measurement of metal-works. It is difficult to measure metal surfaces precisely with a conventional triangulation-laser displacement sensor due to machining traces. Because reflection characteristics vary by position on the workpiece, measurement errors occur even with positions of the same height. Our multi-directional triangulation optical system performs triangulation using a lens array consisting of four lenses located in a cross. Since our optical system can detect reflected light from four directions, we can achieve high-precision measurement even if the reflection characteristics vary. In addition, our scanning exposure method accumulates reflected light from many positions by scanning a projection beam onto a workpiece during the image sensor’s exposure time. Because the shape of a spot image on an image sensor is the sum of the reflected light from many positions, measurement error due to measurement position is reduced. Our proposed methods can achieve on-machine deflection measurement of metal-works with a target accuracy of ±1μm.

Ionospheric Correction of L-Band SAR Offset Measurements for the Precise Observation of Glacier Velocity Variations on Novaya Zemlya

The synthetic aperture radar (SAR) offset tracking method has been widely used for multitemporal analysis of fast glacier movements in the polar region. However, it can be severely distorted, particularly in the case of L-band SAR systems mainly due to a frequent occurrence of ionospheric effects in the polar region. In this study, we developed an efficient method to extract and correct the ionospheric contribution from SAR offset tracking measurements. The method exploits an iterative directional filtering approach, which is based on the pattern and directionality of ionospheric streaks. The measurement performance of the proposed method was evaluated by using three L-band advanced land observing satellite phased array type L-band synthetic aperture radar pairs. Our results showed that the proposed correction achieved the improved measurement accuracies from 4.68–23.88 to 1.03–1.51 m/yr. It means that the accuracies of corrected measurements were about 5–16 times better than those of the original measurements. From the results, we concluded that our correction technique is highly suitable for the precise measurement of the glacier displacements even in the presence of strong ionospheric effects. Using the proposed method, the variations of glacier velocities were measured in the Vylki, Shury, and Kropotnika glaciers on Novaya Zemlya, which is located in the Russian Arctic Ocean, and the grounding zones were detected from the measurements in the Shury and Kropotnika glaciers. It further confirmed that the proposed correction method is allowed for the precise monitoring of glacier movements. However, in cases of severe ionosphere-distorted measurements, the proposed method may be limitedly applied.

THE PLATFORM MONITORING SYSTEM FOR WISDOM SHIPYARD BASED ON THE CCD SENSOR

Usually the settlement monitoring system was mainly applied in buildings, roads and so on in the city, which cannot meet the requirements of complex environments. While the train rail vibration monitoring, wind power platform settlement monitoring，etc are facing severe environmental interference. In order to ensure that rail, power tower platform and other field facilities to long-term and stable operation, there is a set of real-time monitoring system to monitor the settlement of the platform is particularly important. This paper proposes a new kind of high precision and micro displacement measurement technology based on laser and CCD devices, with the help of FPGA and MCU, we can complete the function of high-speed data acquisition and real-time monitoring easily. Compared with some traditional methods, this technology of measurement take great advantages in high-speed data acquisition, real-time performance, high-precision measurement and strong adaptability to complex environment, etc.

Front-end design of high precision displacement sensor based on linear array CCD

In order to achieve the high-precision non-contact measurement for tiny displacement, a high-precision displacement sensor front-end module is designed based on linear array CCD. An optical lens is designed using the principle of laser triangulation, and the system uses the FPGA to generate the drive timing required for the linear array CCD. The one-dimensional video signal output by CCD is handled to obtain a stable analog signal through the front circuit, and the signal is available for digital circuitry. The system has the characteristics of simple structure, small volume, stable output signal, high resolution and high precision. Experimental tests show that the sensor front-end module outputs are stable with small interference analog signal after calculation, the maximum range is ±15 mm, and the accuracy can reach 20 μm. The system can be widely used in the precise measurement of tiny displacement.

Design and Analysis of a Mutual Inductance Coupling-Based Microdeformation Sensor

Mutual inductance coupling-based electromagnetic sensors utilize the quasi-static or dynamic magnetic excitation and sensing signals to detect the multiaxis deformation. The compact size and high sensitivity allow their application in tiny and precise measurement systems, such as space-confined minimally invasive surgery. Until now, however, there has not been any theoretical derivation of the relationship between microdeformation and obtained electromagnetic signals yet. To address this problem, this paper presents a triaxial deformation sensor with corresponding measurement electronics based on lock-in technique to pick up the sensing signals for deformation reconstruction. Simulations and experiments were carried out to explore the relationship between mutual inductance and triaxial deformation, including longitudinal compression from 3 to 4.8 mm, inclination angle from −20° to 20 °, and orientation angle from 0 ° to 360 °. The results indicate that the orientation angle $\beta $ can be expressed in terms of arctan function of the mutual inductance and longitudinal compression $\rho $ can be achieved through polynomial fitting method. The inclination angle $\alpha $ shows a linearity with the mutual inductance components along $\alpha $ direction when $\rho $ is fixed, and the linear coefficient changes with $\rho $ . Finally, the deformation was reconstructed with the average errors of 0.00037 mm, 0.9199 °, and 0.000026 ° and the corresponding root-mean-square errors of 0.0144 mm, 1.3608 °, and 0.1356 ° for $\rho $ , $\beta $ , and $\alpha $ , respectively. The reconstruction algorithms and measurement circuit will promote the application of microtriaxial deformation sensors in high precision displacement measurement and multiaxis force sensing systems.

A differential Michelson interferometer with orthogonal single frequency laser for nanometer displacement measurement

A novel differential Michelson laser interferometer is proposed to eliminate the influence of environmental fluctuations for nanometer displacement measurement. This differential interferometer consists of two homodyne interferometers in which two orthogonal single frequency beams share common reference arm and partial measurement arm. By modulating the displacement of the common reference arm with a piezoelectric transducer, the common-mode displacement drift resulting from the environmental disturbances can be well suppressed and the measured displacement as differential-mode displacement signal is achieved. In addition, a phase difference compensation method is proposed for accurately determining the phase difference between interference signals by correcting the time interval according to the average speed in one cycle of interference signal. The nanometer displacement measurement experiments were performed to demonstrate the effectiveness and feasibility of the proposed interferometer and show that precision displacement measurement with standard deviation less than 1 nm has been achieved.

Real-time phase delay compensation of PGC demodulation in sinusoidal phase-modulation interferometer for nanometer displacement measurement.

As the phase delay between the carrier component of the detected interference signal and the carrier has adverse effect for phase generated carrier (PGC) demodulation, it is essential to compensate the phase delay to improve the accuracy of precision displacement measurement in sinusoidal phase-modulation interferometer (SPMI). In this paper, a real-time phase delay compensation method is proposed by regulating a compensating phase introduced to the carrier to maximize the output of the low pass filter so as to make the carrier synchronize with the interference signal. The influence of phase delay for PGC demodulation is analyzed and the method for real-time phase delay compensation is described in detail. The simulation of the method was performed to verify the validity of the phase delay compensation algorithm. A SPMI using an EOM was constructed and several comparative experiments were carried out to demonstrate the feasibility of the proposed method. The experimental results show that the phase delay can be compensated accurately in real time, and nanometer accuracy is achieved for precision displacement measurement.

基于衍射光栅的干涉式精密位移测量系统

基于衍射光栅的干涉式精密位移测量系统

Understanding interferometry for micro-cantilever displacement detection.

Interferometric displacement detection in a cantilever-based non-contact atomic force microscope (NC-AFM) operated in ultra-high vacuum is demonstrated for the Michelson and Fabry–Pérot modes of operation. Each mode is addressed by appropriately adjusting the distance between the fiber end delivering and collecting light and a highly reflective micro-cantilever, both together forming the interferometric cavity. For a precise measurement of the cantilever displacement, the relative positioning of fiber and cantilever is of critical importance. We describe a systematic approach for accurate alignment as well as the implications of deficient fiber–cantilever configurations. In the Fabry–Pérot regime, the displacement noise spectral density strongly decreases with decreasing distance between the fiber-end and the cantilever, yielding a noise floor of 24 fm/Hz0.5 under optimum conditions.

Novel linear piezoelectric motor for precision position stage

Conventional servomotor and stepping motor face challenges in nanometer positioning stages due to the complex structure, motion transformation mechanism, and slow dynamic response, especially directly driven by linear motor. A new butterfly-shaped linear piezoelectric motor for linear motion is presented. A two-degree precision position stage driven by the proposed linear ultrasonic motor possesses a simple and compact configuration, which makes the system obtain shorter driving chain. Firstly, the working principle of the linear ultrasonic motor is analyzed. The oscillation orbits of two driving feet on the stator are produced successively by using the anti-symmetric and symmetric vibration modes of the piezoelectric composite structure, and the slider pressed on the driving feet can be propelled twice in only one vibration cycle. Then with the derivation of the dynamic equation of the piezoelectric actuator and transient response model, start-upstart-up and settling state characteristics of the proposed linear actuator is investigated theoretically and experimentally, and is applicable to evaluate step resolution of the precision platform driven by the actuator. Moreover the structure of the two-degree position stage system is described and a special precision displacement measurement system is built. Finally, the characteristics of the two-degree position stage are studied. In the closed-loop condition the positioning accuracy of plus or minus <0.5 μm is experimentally obtained for the stage propelled by the piezoelectric motor. A precision position stage based the proposed butterfly-shaped linear piezoelectric is theoretically and experimentally investigated.

Synthetic-wavelength self-mixing interferometry for displacement measurement

A simple synthetic-wavelength self-mixing interferometer is proposed for precision displacement measurement. Choosing the frequency difference of the orthogonally polarized dual frequency He–Ne laser appropriately, we introduce synthetic wavelength theory into self-mixing interference principle and demonstrate a feasible optical configuration by simply adjusting the optical design of self-mixing interferometer. The phase difference between the two orthogonally polarized feedback fringes is observed, and the tiny displacement of the object can be measured through the phase change of the synthetic signal. Since the virtual synthetic wavelength is 106 times larger than the operating wavelength, sub-nanometer displacement of the object can be obtained in millimeter criterion measurement without modulation, demodulation and complicated electrical circuits. Experimental results verifies the synthetic wavelength self-mixing interferometer's ability of measuring nanoscale displacement, which provides a potential approach for contactless precision displacement measurement in a number of scientific and industrial applications.

Audio-Band Frequency-Dependent Squeezing for Gravitational-Wave Detectors.

Quantum vacuum fluctuations impose strict limits on precision displacement measurements, those of interferometric gravitational-wave detectors among them. Introducing squeezed states into an interferometer's readout port can improve the sensitivity of the instrument, leading to richer astrophysical observations. However, optomechanical interactions dictate that the vacuum's squeezed quadrature must rotate by 90° around 50Hz. Here we use a 2-m-long, high-finesse optical resonator to produce frequency-dependent rotation around 1.2kHz. This demonstration of audio-band frequency-dependent squeezing uses technology and methods that are scalable to the required rotation frequency and validates previously developed theoretical models, heralding application of the technique in future gravitational-wave detectors.

Modulating carrier and sideband coupling strengths in a standing-wave gate beam

We control the relative coupling strength of carrier and first order motional sideband interactions of a trapped ion by placing it in a resonant optical standing wave. Our configuration uses the surface of a microfabricated chip trap as a mirror, avoiding technical challenges of in-vacuum optical cavities. Displacing the ion along the standing wave, we show a periodic suppression of the carrier and sideband transitions with the cycles for the two cases $180^\circ$ out of phase with each other. This technique allows for suppression of off-resonant carrier excitations when addressing the motional sidebands, with applications in quantum simulation and quantum control. Using the standing wave fringes, we measure the relative ion height as a function of applied electric field, allowing for a precise measurement of ion displacement and, combined with measured micromotion amplitudes, a validation of trap numerical models.

Simulation of the SuperSAR Multi-Azimuth Synthetic Aperture Radar Imaging System for Precise Measurement of Three-Dimensional Earth Surface Displacement

The SuperSAR imaging system, a novel multi-azimuth synthetic aperture radar (SAR) system capable of detecting Earth surface deformation in three dimensions from a single satellite platform, has recently been proposed. In this paper, we investigate the feasibility of detecting precise 3-D surface displacement measurements with the SuperSAR imaging system using a point target simulation. From this simulation, we establish both a relationship between the interferometric SAR phase and the across-track displacement and a relationship between the multiple-aperture interferometry phase and the along-track displacement based on the SuperSAR imaging geometry. The theoretical uncertainties of the SuperSAR measurement are analyzed in the across- and along-track directions, and the theoretical accuracy of the 3-D displacement measurement from the SuperSAR system is also investigated according to both the decorrelation and the squint and look angles. In the case that the interferometric coherence is about 0.8 and that five effective looks are employed, the theoretical 2-D measurement precision values are about 3.67 and 6.35 mm in the across- and along-track directions, respectively, and the theoretical 3-D measurement precision values for 3-D displacement are about 4.05, 4.56, and 3.45 mm in the east, north, and up directions, respectively. The result of this study demonstrates that the SuperSAR imaging system is capable of measuring the 3-D surface displacement in all directions with subcentimeter precision.

Integrated tuning fork nanocavity optomechanical transducers with high fMQM product and stress-engineered frequency tuning

Cavity optomechanical systems are being widely developed for precision force and displacement measurements. For nanomechanical transducers, there is usually a trade-off between the frequency (fM) and quality factor (QM), which limits temporal resolution and sensitivity. Here, we present a monolithic cavity optomechanical transducer supporting both high fM and high QM. By replacing the common doubly clamped, Si3N4 nanobeam with a tuning fork geometry, we demonstrate devices with the fundamental fM≈29 MHz and QM≈2.2×105, corresponding to an fMQM product of 6.35×1012 Hz, comparable to the highest values previously demonstrated for room temperature operation. This high fMQM product is partly achieved by engineering the stress of the tuning fork to be 3 times the residual film stress through clamp design, which results in an increase of fM up to 1.5 times. Simulations reveal that the tuning fork design simultaneously reduces the clamping, thermoelastic dissipation, and intrinsic material damping contributions to mechanical loss. This work may find application when both high temporal and force resolution are important, such as in compact sensors for atomic force microscopy.

Use of the digital image correlation and acoustic emission technique to study the effect of structural size on cracking of reinforced concrete

An experimental investigation is performed to study the degradation of reinforced concrete beams by employing two experimental techniques simultaneously i.e. digital image correlation and acoustic emission. The former method gives very precise measurement of surface displacements, thus crack openings and crack spacing are determined. In order to complement this method and to investigate damage mechanisms, acoustic emissions resulting from internal damage are also analysed. Beams of three different sizes but proportionally similar, are tested to study the effect of structural size. A comparison of the experimental measurements with Eurocode expressions is also presented.

Michelson Interferometer Based Displacement Measurement Using Video Processing

In this study, investigation of video processing method which is a new technique for precision displacement measurement is presented. The video processing method was integrated with an interferometric system and the thermal expansion results and linear thermal expansion coe cients of a heated sample metals were compared with theoretical results. Michelson interferometer setup was used in our study due to its advantages in precision displacement information of a visual output, called interferograms. In the experimental studies, signals of interferograms containing displacement information were obtained from the measurement system. The amount of displacement in the sample metals under the temperature variation due to thermal expansion was measured with the analysis program, written in Matlab/Simulink environment, with a micrometer precision. The measured displacement amounts were compared with the results of theoretical calculations. According to the theoretical values, the relative error of the values measured with video processing based method, was found found to be 0.3%

Quantum measurement with cavity optomechanical systems

Cavity optomechanics originated from the research of interferometric detection of gravitational waves, and later became a fast-growing area of techniques and approaches ranging from the fields of atomic, molecular, and optical physics to nano-science and condensed matter physics as well. Recently, it focused on the exploration of operating mechanical oscillators deep in the quantum regime, with an interest ranging from quantum-classical interface tests to high-precision quantum metrology. In this paper, recent theoretical work of our group in the field of quantum measurement with cavity optomechanical systems is reviewed. We explore the quantum measurement theory and its applications with several unconventional cavity optomechanical schemes working in the quantum regime. This review covers the basics of quantum noises in the cavity optomechanical setups and the resulting standard quantum limit of precision displacement and force measurement. Three novel quantum measurement proposals based on the hybrid optomechanical system are introduced. First, we describe a quantum back-action insulated weak force sensor. It is realized by forming a quantum-mechanics-free subsystem with two optomechanical oscillators of reversed effective mass. Then we introduce a role-reversed atomic optomechanical system which enables the preparation and the quantum tomography of a variety of non-classical states of atoms. In this system, the cavity field acts as a mechanical oscillator driven by the radiation pressure force from an ultracold atomic field. In the end, we recommend a multimode optomechanical transducer that can detect intensities significantly below the single-photon level via adiabatic transfer of the microwave signal to the optical frequency domain. These proposals demonstrate the possible applications of optomechanical devices in understanding of quantum-classical crossover and in achieving quantum measurement limit.

MEMS whistle-type temperature-compensated displacement sensor using resonant frequency shift

Sound from a whistle can be modulated by adjusting the length of the whistle's resonant tube. Using this principle, a whistle-type displacement sensor has been previously proposed but has not been achieved because of technological constraints. Owing to the precise flow control techniques presently available as well as the high processing accuracy, advanced miniaturization, and high-density integration capabilities offered by MEMS technology, we have developed microelectromechanical systems (MEMS) whistle-type displacement sensors that use only acoustic signals to measure displacement. The MEMS whistle-type displacement sensor was 5.0mm in length, 2.1mm in width, and 1.4mm in thickness. The sensor achieves precise displacement measurement with a possible error of a few μm. Furthermore, the range of the deviation caused by a temperature change of 10°C was reduced by approximately 90% when an additional whistle-type sensor was used as a temperature compensator, for an input displacement of 200μm.

Laser heterodyne interferometer for simultaneous measuring displacement and angle based on the Faraday effect.

A laser heterodyne interferometer for simultaneous measuring displacement and angle based on the Faraday effect is proposed. The optical configuration of the proposed interferometer is designed and the mathematic model for measuring displacement and angle is established. The influences of the translational, lateral and rotational movements of the measuring reflector on displacement and angle measurement are analyzed in detail. The experimental setup based on the proposed interferometer was constructed and a series of experiments of angle comparison and simultaneous measuring displacement and angle were performed to verify the feasibility of the proposed interferometer for precision displacement and angle measurement.