Real-Time Structural Health Monitoring Using a Novel Fiber-Optic Accelerometer System

This paper presents a novel fiber-optic accelerometer system to monitor civil engineering structures in real time and a successful application of the novel sensor system for damage detection of the concrete slab structure. This sensor system integrates the Moireacute fringe phenomenon with fiber optics to achieve accurate and reliable measurements. A signal processing unit implements unique algorithms to further enhance the resolution and increase the dynamic bandwidth of the sensors. The sensor system is immune to electromagnetic (EM) interference, making it suitable for difficult applications in such environments involving strong EM fields, electrical spark-induced explosion risks, and cabling problems, prohibiting the use of conventional electromagnetic accelerometers. Especially, this paper presents a unique real-time signal processing algorithm and applications to real-time damage assessment, demonstrating the uniquely high performance of the Moireacute fringe fiber-optic sensor system     

加速度计稳定性测试的补偿技术

介绍了加速度计稳定性的测量装置及方法。由于环境因素可以对稳定性测试产生影响,因此对加速度计的工作温度、基础水平倾角的影响进行了分析。通过研究加速度计温度误差模型,确定了建模方法。在稳定性试验中,使用高精度铂热电阻测量加速度计的工作温度,对加速度计的模型方程系数和输出进行温度补偿;使用地震前兆倾斜仪监测基础水平倾角变化,对加速度计零位输出进行补偿。     

Fundamental noise limit of piezoelectric accelerometer

Since significant progress is achieved in the development of piezoelectric (PE) accelerometers for small signal applications nowadays (for example, piezoelectric seismic vibration sensors), the question about the fundamental noise limit of these sensors becomes vital. The noise of the PE transducer is the fundamental noise limit of the PE accelerometer and should be taken into account if the noise of the electronics is small enough. The two noise sources of PE transducer, the mechanical-thermal noise of the damped mechanical harmonic oscillator and the electrical-thermal noise of the PE element's material, are analyzed in this paper. The equation of the total fundamental noise limit of the PE accelerometer is presented. This equation can be used for the calculation of the fundamental noise limit of PE accelerometers if their parameters are known or can be obtained by measurement.     

A Novel Threshold Accelerometer With Postbuckling Structures for Airbag Restraint Systems

Based on the postbuckling theory of large deflection beams, the nonlinear stiffness of a postbuckling beam is deduced and in agreement with the results of buckling experiments. Then, a novel post machined threshold accelerometer is designed, which consists of eight oblique post beams with an inertial mass in the middle to ensure its single moving direction and an electrical contact part fabricated on the bottom of the inertial mass. The threshold accelerometer is an integration of a threshold sensor and an inertial driven actuator used in airbag restraint systems. When the acceleration reaches the threshold, the beams buckle and close the threshold accelerometer, and when it gets down to be a certain value, the accelerometer opens quickly under the effect of the elastic force developed by the postbuckling beams. Compared with the design models of other threshold accelerometers with linear beam structures, the nonlinear postbuckling beams are introduced as threshold sensing elements. A number of design factors such as the air film damping and the contact force are taken into full consideration, thus establishing the dynamic equation of the accelerometer under coupled forces. The dynamical simulation for the strong nonlinear system with elliptic integrals indicates its good threshold characteristic and high contact reliability. The threshold accelerometer responds within 4 ms when it is triggered by a threshold acceleration ac = 20 g, and cuts off quickly when the cutoff acceleration is under ad = 5 g. Meanwhile, the unstable contact time is only 0.02 ms for the contact force to reach 50 mN, which guarantees the contact resistance to be less than 20 mOmega. With the results of the dynamic simulation, supported by previous buckling experiments, the accelerometer can provide accurate threshold sensing without false actuations under interferences outside, especially electromagnetic and vibration interferences, and hence their wide applications in safe-arming systems.     

Joint-Angle Measurement Using Accelerometers and Gyroscopes—A Survey

This paper presents an analysis of rigid-body joint-angle measurement based on microelectromechanical-system (MEMS) biaxial accelerometers and uniaxial gyroscopes. In comparison to conventional magnetic and optical joint angular sensors, this new inertial sensing principle has the advantages of flexible installation and true contactless sensing. This paper focuses on the comparison of four different inertial-sensor combination methods that are reported in reference papers and utilizes the theory of rigid-body kinematics to explain and analyze their advantages and weaknesses. Experiments have also been conducted to further verify and strengthen the arguments put forward in the analysis. All experiments in this paper took place on a custom-built rigid-body robot arm model that can be manipulated by hand. Sensor calibration and accelerometer alignment issues are also described, and their details are discussed. The experiment results presented in this paper show significant differences with reference to the achieved angular accuracy for various situations when using the four different sensor combination methods. In some cases, the angular error based on one method is more than 0.04 rad, while that from another method is within $pm$0.005 rad. The noise levels of angular readings from different methods are also experimentally compared and analyzed. The conclusion drawn serves to guide readers toward a suitable method for their particular application.      

SAW Sensor Network Fabricated on a Polyvinylidine Difluoride (PVDF) Substrate for Dynamic Surface Profile Sensing

A combination of two 2-D sensor networks is proposed as a dynamic surface profile sensor network for biomimicing applications. A surface acoustic wave device fabricated on a polyvinylidine difluoride substrate has been investigated as the elementary 1-D bending curvature sensor used in the network. The device was tested under an injected signal and it shows the variation in amplitude and phase angle of output signal with respect to the injected signal in response to the bending curvature. These dual outputs provide opportunity to make an intelligent sensor with self error limit determination capability. Finally, a network of such sensors is proposed as a dynamic surface profile sensor     

一种基于人工鱼群算法的微机电系统加速度计静态修正方法

微机电系统加速度计是惯性跟踪系统的一部分,用来获得运动的位置信息。为了对运动姿态进行精确定位,必须对它的误差进行修正。根据加速度计误差来源和产生机理建立了误差模型,通过分析误差模型,提出了一种基于人工鱼群算法修正加速度计静态误差的方法,并与六位置测试法比较。前者在一定程度上降低了误差,提高了测量角精度,使微机电系统加速度计输出能够准确反映出真实值。     

基于加速度计阵列的六自由度振动台测试方法研究

目前多自由度振动台缺乏方便有效的多自由度振动测试手段,通过探讨基于加速度传感器的六自由度振动测试方法,提出基于4只三向加速度计的加速度计阵列构型,依据六自由度运动系统方程对该构型的运动状态进行了理论推导,并设计了具体的封装方法,最后对封装的加速度计阵列构型进行了多自由度振动测试试验验证。试验结果表明:所提出的基于4只三向加速度计的加速度计阵列构型能够对角加速度进行测试与还原,简易可靠,可以作为多自由度振动的测试手段。本文提出的加速度计陈列构型有望被推广应用于现场低频振动测量或校准工作中。     

单轴摆式加速度计输出异常的故障分析

针对某型单轴摆式加速度计在使用过程中出现的电压输出异常典型故障问题进行理论分析,利用故障树综合性分析方法,层层追踪分析,表达出输出电压出现异常故障内在联系,直观指出单元故障与整体故障之间的逻辑关系,切实归纳总结了工程运用中实际遇到的单轴摆式加速度计输出电压异常故障问题。而后对故障原因进行精确细致定位,提出振荡器电路中的D4二极管正极金丝断裂为此型号加速度计故障根本原因,融入电路金丝断裂机理分析法,并通过试验测试与改进措施方式验证了此故障分析的准确性,一定程度上提升了加速度计可靠性。研究成果可以为加速度计可靠性使用提供一定参考。     

用于运动姿势捕捉的可穿戴MEMS微型化加速度计研制

在人体上穿戴加速度计能够实现对人体运动姿势捕捉,进而在体育教学和运动训练中有利于提升教学和训练效果,而加速度计的固有频率和测量灵敏度存在相互制约的关系.为此,研制一种孔缝复合八梁结构的MEMS加速度计.该加速度计质量块由四根宽大的支撑梁和四根短小的敏感梁共同支撑,在敏感梁上引入应力集中孔.采用离子注入、背腔干法刻蚀、I...     

基于椭球假设的三轴加速度计无依托校准方法

针对现有航姿测量系统三轴加速度计校准方法成本高、精度低以及现场校准能力不足的问题,本文提出了一种基于椭球假设的无依托现场校准方法.首先,根据传感器的灵敏度、偏置以及非正交耦合因素对加速度计的影响,建立了误差椭球校准模型.该模型将三轴加速度计的校准过程转化为将椭球面还原成圆球面的几何变换过程,使得校准参数由15个减少到9个,同时克服了部分非正交耦合参数难以辨识的问题.其次,构造了变权值似然目标函数,根据加速度计测量值的方差调整权值大小,从而降低了测量噪声对校准结果的影响.最后,运用粒子群优化(PSO)算法求解几何变换参数的最大似然估计值,并利用椭球校准模型对三轴加速度计进行校准.实验结果表明,采用椭球假设无依托现场校准方法不依赖外部辅助姿态信息,可在现场将航姿测量系统的倾角误差降低为校准前的1/5,满足了航姿系统的使用需求.     

Damping of compression and shear piezoelectric accelerometers byelectromechanical feedback

It is shown that the very pronounced resonance peak in the frequency entirely by a simple modification of existing accelerometers, providing them with an electrical sensor output as well as an electrical actuator input, and using a charge amplifier in a feedback path between the sensor output and the actuator input. Because a piezoelectric accelerometer is normally read out by a charge amplifier, no extra circuitry (expense) is necessary to provide this electromechanical feedback. It is shown that a maximally flat response (Butterworth) can be obtained with little peaking (approximately 2 dB) and excellent dynamic stability, which makes the acceleration usable up to its resonance frequency     

Wearable Sensing Glove With Embedded Hetero-Core Fiber-Optic Nerves for Unconstrained Hand Motion Capture

In this paper, we present a wearable sensing glove with embedded hetero-core fiber-optic nerve sensors that detect finger flexion to achieve unconstrained hand motion monitoring. The hetero-core fiber sensor is suited to the wearable sensing glove because it is capable of optical intensity-based measurements with excellent stability and repeatability using single-mode transmission fibers and is unaffected by temperature fluctuations. The hetero-core sensor elements are located on the back of the hand so that they are not affected by random wrinkles in the glove at the joints. As a result, the hetero-core flexion sensor after calibration is capable of detecting the joint angles of the fingers regardless of differences in hand size, and the hetero-core sensing technique enables the sensing glove to be constructed with a minimum number of sensor points. The optical loss performance of the hetero-core sensors reveals monotonic characteristics with respect to the flexion angle of joints. The optical loss is 1.35 dB for a flexion angle of approximately 97.2$^{circ}$ with accuracy of 0.89$^{circ}$ in the detected flexion angle. Real-time hand motion capture was demonstrated by means of the proposed sensing glove without restricting natural human behavior.      

Effect of Telemetry Channel Noise on the Output of Accelerometers

The noise in the FM telemetry channel may decrease significantly the accuracy of accelerometer readings. The noise effects in both digital and analog accelerometers are examined in this paper. A maximum-likelihood estimate of the accelerometer output is made and the mean-square error of the estimate is evaluated. It is shown that the digital accelerometer is superior to the analog accelerometer in the presence of noise. Two methods of reducing the mean-square error are suggested.     

离心机误差对陀螺加速度计K2和K3项标定精度的影响

为了准确标定陀螺加速度计的二阶非线性误差系数K2与三阶非线性误差系数K3,首先在带反转平台的离心机上建立坐标系,进而在考虑离心机误差源的基础上,推导出了陀螺加速度计上的精确比力输入和角速度输入,再根据陀螺加速度计的误差模型,给出了离心机各个误差源对K2、K3项标定误差的贡献．仿真试验给出了各误差项对于K2、K3项标定的具体影响大小,可通过误差补偿提高陀螺加速度计K2、K3项的标定精度,并且给出了不同精度加速度计在进行标定时要重点考虑的离心机误差项：同时仿真表明。采用带反转平台的离心机对陀螺加速度计进行标定时可以不进行加速度计调心：另外,主轴速率与反转平台回转轴角速度矢量大小不完全相等,方向不完全相反对标定结果几乎无影响．     

Estimation of Attitude and External Acceleration Using Inertial Sensor Measurement During Various Dynamic Conditions

This paper proposes a Kalman filter-based attitude (i.e., roll and pitch) estimation algorithm using an inertial sensor composed of a triaxial accelerometer and a triaxial gyroscope. In particular, the proposed algorithm has been developed for accurate attitude estimation during dynamic conditions, in which external acceleration is present. Although external acceleration is the main source of the attitude estimation error and despite the need for its accurate estimation in many applications, this problem that can be critical for the attitude estimation has not been addressed explicitly in the literature. Accordingly, this paper addresses the combined estimation problem of the attitude and external acceleration. Experimental tests were conducted to verify the performance of the proposed algorithm in various dynamic condition settings and to provide further insight into the variations in the estimation accuracy. Furthermore, two different approaches for dealing with the estimation problem during dynamic conditions were compared, i.e., threshold-based switching approach versus acceleration model-based approach. Based on an external acceleration model, the proposed algorithm was capable of estimating accurate attitudes and external accelerations for short accelerated periods, showing its high effectiveness during short-term fast dynamic conditions. Contrariwise, when the testing condition involved prolonged high external accelerations, the proposed algorithm exhibited gradually increasing errors. However, as soon as the condition returned to static or quasi-static conditions, the algorithm was able to stabilize the estimation error, regaining its high estimation accuracy.     

A New Flexible Optical Fiber Goniometer for Dynamic Angular Measurements: Application to Human Joint Movement Monitoring

The electronic measurement of the angle between two planes is generally performed by using the so-called electrogoniometers. The major drawback in using such devices is the presence of a fixed hinge that imposes a fixed center of rotation. This can cause problems when measuring the bending angle in some joints, such as Cardan or human joints, which have a variable rotation center. Based on an optical fiber, a sensor measuring the relative angle in a rotating joint has been developed. This joint makes use of the intensity modulation of a laser beam propagating in a single-mode optical fiber, due to the changes of its polarization status originated by the rotation of contiguous portions of the fiber, where controlled birefringence has been induced by the joint rotation. A prototype of this sensor has been developed with a range of the relative angle of 90$^{circ}$ , a resolution of less than 0.01$^{circ}$, and a standard deviation of 0.1$^{circ}$. The main advantages of this innovative sensor are lightness, flexibility, high speed of reaction, and high accuracy. This paper describes the development of the proposed sensor, with particular reference to the applications of human joint movement monitoring. Additionally, the equipment implemented for the test is illustrated, and results from laboratory tests are reported and discussed.      

Inertial sensor technology trends

This paper presents an overview of how inertial sensor technology is applied in current applications and how it is expected to be applied in nearand far-term applications. The ongoing trends in inertial sensor technology development are discussed, namely interferometric fiber-optic gyros, micro-mechanical gyros and accelerometers, and micro-optical sensors. Micromechanical sensors and improved fiber-optic gyros are expected to replace many of the current systems using ring laser gyroscopes or mechanical sensors. The successful introduction of the new technologies is primarily driven by cost and cost projections for systems using these new technologies are presented. Externally aiding the inertial navigation system (INS) with the global positioning system (GPS) has opened up the ability to navigate a wide variety of new large-volume applications, such as guided artillery shells. These new applications are driving the need for extremely low-cost, batch-producible sensors     

Drop Tower Microgravity Improvement Towards the Nano-g Level for the MICROSCOPE Payload Tests

The Bremen drop tower at the Center of Applied Space Technology and Microgravity (ZARM) provides high quality micro-g condition needed for many high precision tests. This is even more improved by the development of a free flyer technology. This new technology is used for a free fall test of the MICROSCOPE differential accelerometers which only can work with a residual acceleration disturbance level below 25 nano-g in the high resolution mode. The French MICROSCOPE space mission for testing the Weak Equivalence Principle is scheduled for 2012/2013. The free fall accelerometer test campaign at ZARM is an important part of the pre-mission test program. In this article the new free flyer technology, its performance as well as the accelerometer tests are described.     

陀螺加速度表在高精度三轴转台上的测试方法研究

本文提出了在三轴转台上标定陀螺加速度表的新方法,分离了加速度表外环轴的摩擦力矩及交叉加速度引起的交变力矩对加速度表精度的影响,通过新的加速度表输入轴不对准试验方法,减小了加速度表失调角,提高了加速度表标定精度。