Shield tunneling machine is a kind of special engineering equipment used for underground construction, which plays an important role on city development. Automatic segment assembly can significantly improve the operation efficiency and ensure the safety of workers. In this paper we present an automatic segment assembly method of shield tunneling machine based on multiple optoelectronic sensors, which includes laser displacement sensors (LDSs) and smart cameras. The LDSs are used to get the level difference information by measuring the distance between the erector and the corresponding segments, and the gap of the segments is achieved through sense the mating surfaces of both the under assembly and previously assembled segments by the smart cameras. Experiments were conducted to confirm the performance of the proposed method. The results demonstrated the feasibility and effectiveness of the method.
In this paper, we propose and investigate a novel long period fiber grating (LPFG) refractive index (RI) sensor, which is inscribed in a two-mode fiber and coated with the zinc oxide (ZnO) thin film. According to the coupled mode theory, the resonant wavelength, which appears at approximately 1550 nm, originates from the mode coupling between the LP11 core mode and the sixth order cladding mode. As a comparison, single-mode LPFGs (LPFG-SMFs) with and without ZnO thin film are fabricated and they are formed by coupling light from the LP01 core mode into the sixth order cladding mode. The sensing performance is researched by observing the shift of resonant wavelength with the increasing of surrounding refractive index (SRI) in the range from 1.3300 to 1.4577. The experimental results demonstrate that LPFG inscribed in a two-mode fiber (LPFG-TMF) has a higher RI sensitivity than the LPFG-SMF. And the LPFGs with coated ZnO thin film can achieve a higher RI sensitivity than the bare LPFGs in the mode transition region. The highest sensitivity of LPFG-TMF coated with ZnO thin film reaches 7578.94nm/RIU in the RI region between 1.4558 and 1.4577, which is 23.90 and 38.69 times higher than the bare LPFG-TMF and LPFG-SMF coated with ZnO thin film, respectively. The proposed sensor offers a promising platform to achieve a higher sensitivity for SRI.
A fiber-optic distributed acoustic sensing method based on phase-sensitive optical time domain reflectometry combined with dual-chirped pulse and micro-reflective fiber Bragg grating (FBG) is proposed. The sensing fiber consists of a micro-reflective FBG with uniform spatial interval. The micro-reflective FBG help to gain a high signalto-noise ratio light signal, comparing with the Rayleigh backscattering (RBS) light of optical fiber itself. The dualchirped pulses are generated by a time delay, whose corresponding spatial interval approximately equal to twice the spatial interval of adjacent micro-reflective FBG. A beating signal is generated due to the interference of the two identical chirped pulses reflected by the micro-reflective FBG array. Acoustic disturbance between the microreflective fiber gratings will change the phase of the beating signal and the interference waveform will shift. Quantitative measurement can be achieved by directly demodulating the beating signal through using a crosscorrelation algorithm. By using such a method to perform the sensing for the micro-reflective FBG array, distributed quantitative measurement can be realized with only direct detection scheme and simple demodulation algorithm. Experiment are carried out with 2km fiber and PZT vibration simulation and the results verified the effectiveness of our method.
The shield method is one of subsurface excavation method in underground construction. It’s a fully mechanized construction method using shield machine. However, the process of segment assembly now mainly relies on manual work, controlling the assembly robots by experience. This work aims to aid the automation of precise movement control of the assembly robot, especially the movements of sliding, rotating, and deflecting directions. It proposes a new method using multiple imaging sensors to collect image information needed for automatic assembly of segments, and uses information extraction, size measurement and other real-time image processing to determine the spatial attitude of the three directions of the segments to be assembled. By Importing the data into an automation solution, the segments could move along the correct path. Experiments are conducted to test the performance and reliability of the proposed method in an actual underground working environment. The results are validated by successful bolting process in the actual subway construction, showing several different types of segments can move to the correct assembly position and the process is reproducible. Some disadvantages of the method are discussed, and suggestions for improvements are suggested. The proposed method has the potential to be adopted to enable the automation of segment assembly in shield method and may be applied to actual construction.
We demonstrate a method for fabricating a fiber sensor which is based on the Mach-Zehnder interference principle and used to the curvature sensing. By using of the CO2 laser fusion, a standard single-mode fiber surface forms a collapse, which is asymmetrical in the normal direction. When the core mode of the transmitted light enters the fusion region, a portion of the light will enter the cladding of the fiber and transport as cladding modes. The cladding modes are sensitive to the external environment and the deformations of the structure. When the cladding modes leave the fusion region, they are re-coupled into the core. Mach-Zehnder interference occurs between the cladding modes and the core mode. The transmission spectrum of the sensor at 1460 nm changes with the curvature. The average sensitivities of the sensor to curvature sensing on the two directions are up to 4.941nm/m-1 and -1.933nm/m-1. This characteristic of the sensor could be used to sense the degree and direction of the curvature of constructions. The curvature sensor we proposed is simple, reproducible and low-cost. It offers a promising applications in construction health monitoring.
Silicon and sapphire crystal materials have excellent thermal stability and heat transfer characteristics, making them widely used in the field of high temperature sensing. Based on the optical properties of silicon and sapphire crystals, we have fabricated two different kinds of extrinsic optical fiber Fabry-Perot high temperature sensors and matching signal transmission waveguides to investigate the effects of different temperature-sensitive materials on the response speed of the high temperature sensors. The first kind of sensor uses a C-plane double-sided polished sapphire wafer as the temperature sensing element. Heterogeneous fiber splicing between sapphire fiber and multimode silica fiber is realized for long-distance transmission of interference signals. The second kind of sensor uses a single-crystal silicon wafer as the temperature sensing element. Single-mode optical fiber of silicon dioxide is used as transmission waveguide. A series of high temperature assault experiments for heating and cooling processes from room temperature to 800°C, were performed on the two kinds of sensors to investigate their difference on the temperature response speed. In the experiment, the response time of the sapphire fiber high temperature sensor in the heating section is 38s, and the response time in the cooling section is 31.6s. The response time of the silicon-based fiber high temperature sensor in the heating section is 35.8s, and the response time in the cooling section is 28.2s. Due to the higher thermal conductivity of silicon, the silicon-based fiber sensor responded 5.78% faster than the sapphire fiber sensor in the temperature rise experiment and 10.85% faster than the sapphire fiber sensor in the temperature drop experiment
A hybrid fiber grating for refractive index (RI) measurement with temperature compensation is reported and experimentally validated. The sensor is fabricated successively by inscribing long period grating (LPG) and tilted fiber Bragg grating (TFBG) in the same region of an optical fiber in sequence. The measured RI at different temperature agreed well with the standard value. The RI sensitivities is 579.36 nm/RIU.
We propose a miniaturized fiber optic fabry-perot pressure measuring system, which consists of two parts: ultra-high pressure sensor with embedded MEMS Fabry-Perot cavity and miniaturized phase demodulation system, for marine pressure measurement. The ultra-high pressure sensor have been analyzed and proved to meet the requirements of the full ocean pressure measurement by analyzing mechanical and optical characteristics. In order to meet the application demands of marine pressure measurement, the pressure fatigue test and hydrostatic pressure test have been carried out. The test results show that the pressure measuring system has a stable response relationship between the absolute phase and pressure in the range of 2–120 MPa, and no significant changes was found neither in four consecutive months of ultra-high pressure tests. The repeated error of system is less than 0.012MPa at 60MPa. The miniaturized measuring system can be applied to the ocean profiling measurement plan named the Argo plan.
We propose a real-time monitoring method for shield tunnel boring machine cutter wear based on chirped fiber Bragg grating (CFBG). We use the chirped fiber Bragg grating as the wear detection sensor. When the wear occurs at the end face of the wear detection sensor (the end face of chirped fiber Bragg grating), the grating area of the chirped fiber Bragg grating will shorten with the occurrence of wear, which causes the bandwidth of the grating reflection spectrum to be narrowed, and the correlation theory of the fiber Bragg grating is used to calculate the wear rate. Experimental data shows that the sensor can survive in the actual operating conditions of the shield tunnel boring machine. After calibration, measurement accuracy can less than 1mm, and it can be used for real time wear detection of large machinery, such as shield tunnel boring machine.
Proc. SPIE. 10620, 2017 International Conference on Optical Instruments and Technology: Optoelectronic Imaging/Spectroscopy and Signal Processing Technology
Coherent Anti-Stokes Raman Scattering (CARS) microscopy has attracted lots of attention because of the advantages, such as noninvasive, label-free, chemical specificity, intrinsic three-dimension spatial resolution and so on. However, the temporal overlap of pump and Stokes has not been solved owing to the ultrafast optical pulse used in CARS microscopy. We combine interference spectrum of residual pump in Stokes path and nonlinear Schrodinger equation (NLSE) to realize the temporal overlap of pump pulse and Stokes pulse. At first, based on the interference spectrum of pump pulse and residual pump in Stokes path, the optical delay is defined when optical path difference between pump path and Stokes path is zero. Then the relative optical delay between Stokes pulse and residual pump in PCF can be calculated by NLSE. According to the spectrum interference and NLSE, temporal overlap of pump pulse and Stokes pulse will be realized easily and the imaging speed will be improved in CARS microscopy.
In this paper, an optical fiber Fabry–Perot (F-P) pressure sensor based on micro-electro-mechanical system (MEMS) techniques is presented. We use SOI wafer and Pyrex glass wafer with micro-circular shallow pit array to fabricate the sealed F-P cavity structure by employing Au-Au thermal-compression bonding technique which avoids the gas releasing due to chemical reaction during anodic bonding process. The loaded pressure on the silicon diaphragm is transferred to cavity length information and measured by using polarization low-coherence interference demodulator. The response range and sensitivity of this pressure sensor can be simply altered by adjusting the parameters of radius and thickness of silicon diaphragm. This batch fabrication process is helpful for keeping performance consistency of the sensors. Fabrication and experimental investigation of the sensors are described. Results show that the sensor exhibits a relatively linear response within the pressure variation range of 3-283kPa with a sensitivity of 23.63 nm/kPa and the repeatability of the sensor is about 0.119%F.S. Additionally, the temperature dependency is approximately linear with 1.7nm/°C from -20°C to 70°C.
In this paper, a double-sideband heterogeneous with suppressed carrier (DSBH-SC) pulse modulation method for fiber-optic distributed acoustic sensing is proposed. An electro-optic in-phase/quadrature (I/Q) modulator is used to realize carrier-suppressed double-sideband heterogeneous pulse modulation in which the positive and the negative optical sidebands can carry independent modulation signals. Due to the modulation curve of the electro-optic I/Q modulator irregularly, the factors that influence the performance of the DSBH-SC are analyzed from modulation amplitude and frequency. The analysis shows that the constant frequency modulation on the lower optical sideband while a stable wide band linear frequency chirping on the upper optical sideband can be obtain in appropriate modulation conditions. It presents a method of digital subcarrier modulation for distributed optical sensing.
Proc. SPIE. 10025, Advanced Sensor Systems and Applications VII
KEYWORDS: Optical amplifiers, Modulation, Polarization, Sensors, Control systems, Modulators, Lab on a chip, Sensing systems, Particle swarm optimization, Signal detection
In digital coherent optical time domain reflectometer (coherent-OTDR) system, a dual-parallel Mach-Zehnder modulator (DP-MZM) is employed to modulate the signal light and to generate frequency-shifted pulse light. However, the environment temperature strongly influent the stability of the DP-MZM. To stabilize the quality of the frequency-shifted pulse light, we proposed a bias control method to keep the modulator at the optimum bias. This bias control method search for the optimum bias by changing three bias voltages at the same time based on chaotic particle swarm optimization algorithm(PSO). The experimental results show obvious effect on locating the optimum bias voltages for the DP-MZM.
In a typical laminar optical tomography (LOT) system, the dip-angle between the incident light (or the emitting light) and the normal of the detection plane randomly changes during raster-scanning. The inconstant dip-angle causes consistency between the measurement and the light transportation model where a fixed dip-angle of the incident light is generally required. To eliminate the effect from this dip angle, methods such as keeping the angle unchangeable by moving the phantom instead of scanning the light were investigated. In this paper, a LOT system with small dip-angle over the whole detection range is developed. Simulation and experimental evaluation show that the dip-angle of the modified system is much smaller than that of the traditional system. For example, the relative angle between the two incident light at (x=0mm, y=0mm) and (x=0mm, y=2.5mm) on the image plane is about 0.7° for the traditional system while that is only about 0.02° for the modified system. The main parameters of the system are also evaluated and an image reconstruction algorithm is developed based on Monte Carlo simulation. The reconstructed images show that the spatial resolution and quantitative ratio is improved by the modified system without loss of the scanning speed.
Monitoring corrosion of steel reinforcing bars is critical for the durability and safety of reinforced concrete structures. Corrosion sensors based on fiber optic have proved to exhibit meaningful benefits compared with the conventional electric ones. In recent years, Fiber Bragg Grating (FBG) has been used as a new kind of sensing element in an attempt to directly monitor the corrosion in concrete structure due to its remarkable advantages. In this paper, we present a novel kind of FBG based rebar corrosion monitoring sensor. The rebar corrosion is detected by volume expansion of the corroded rebar by transferring it to the axial strain of FBG when concrete structure is soaked in salt water. An accelerated salt water corrosion test was performed. The experiment results showed the corrosion can be monitored effectively and the corrosion rate is obtained by volume loss rate of rebar.
We fabricated MEMS-based optical fiber pressure sensor with anodic bonding. The vacuum-sealed microcavity with
a thin silicon diaphragm is used as sensing element and its deformation characteristics determine the pressure
measurement performance. Considering residual gas inside Fabry-Perot cavity and the thermal properties of material, we
established a sensor’s temperature response mathematical model based on ideal gas equation and elastic theory.
Temperature experiment of this sensor was carried out under vacuum. This work will provide a guide of temperature
compensation process for achieving high precision pressure measurement.
We present an effective method to compensate the spatial-frequency nonlinearity for polarized low-coherence
interferometer with location-dependent dispersion element. Through the use of location-dependent dispersive
characteristics, the method establishes the exact relationship between wave number and discrete Fourier transform (DFT)
serial number. The jump errors in traditional absolute phase algorithm are also avoided with nonlinearity compensation.
We carried out experiments with an optical fiber Fabry-Perot (F-P) pressure sensing system to verify the effectiveness.
The demodulated error is less than 0.139kPa in the range of 170kPa when using our nonlinearity compensation process
in the demodulation.
Optical fiber sensor has great advantage for applications dealing with extreme environment. We developed a high
precision optical pressure sensor for aviation industry. The optical pressure sensor is based on two-beam interference of
microcavity and is fabricated with Micro-electromechanical systems (MEMS) and laser fusion technology. The cavity
length variation resulting from external pressure is demodulated with spatial polarization low coherence interference unit
and a high stable phase demodulation algorithm. The effect of light source output parameter is also investigated. We
carried out research on optical fiber strain, temperature and acoustic vibration sensor for aerospace application. The
optical fiber sensors for strain and temperature measurement are based on fiber Bragg grating(FBG).Both bare FBG and
packaged FBG performances under cryogenic temperature and high vacuum are investigated. An eight-channel parallel
FBG wavelength interrogator is developed. The optical fiber acoustic vibration sensor is based on two-beam interference
of microcavity and use intensity demodulation method for high speed response. The mutiple-parameter and multiplepoint
measurement instrument is successfully applied to status monitoring of water sublimator.
A novel demodulation algorithm, comprising of a calibration algorithm and improved linear fitting phase-shift algorithm,
is proposed for optical fiber sensing system based on low-coherence interference. The calibration algorithm is used to
identify the fringe order. Traditional phase-shift algorithm is improved to get the linear fitting curve of the relative phase
corresponding to zero-order fringe and the peak position is retrieved from its zero point. Comparing with Fourier based
algorithms, the computation of proposed algorithm is small (approximately 25 times faster) while sustains high precision
with 2nm maximum error of cavity length. Experiments were carried out to verify the performance.
Nowadays seals play an important role in China. With the development of social economy, the traditional method of
manual check seal identification can't meet the need s of banking transactions badly.
This paper focus on pre-processing and registration algorithm for check seal verification using theory of image
processing and pattern recognition. First of all, analyze the complex characteristics of check seals. To eliminate the
difference of producing conditions and the disturbance caused by background and writing in check image, many methods
are used in the pre-processing of check seal verification, such as color components transformation, linearity transform to
gray-scale image, medium value filter, Otsu, close calculations and labeling algorithm of mathematical morphology.
After the processes above, the good binary seal image can be obtained.
On the basis of traditional registration algorithm, a double-level registration method including rough and precise
registration method is proposed. The deflection angle of precise registration method can be precise to 0.1°.
This paper introduces the concepts of difference inside and difference outside and use the percent of difference inside
and difference outside to judge whether the seal is real or fake. The experimental results of a mass of check seals are
satisfied. It shows that the methods and algorithmic presented have good robustness to noise sealing conditions and
satisfactory tolerance of difference within class.
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