Multilayer planar inductor array based angular position sensor for cryogenic application

The design, development and testing of a cryogenically operated multilayer planar inductor array based eddy current angular position/rotation transducer is claimed. An array of 4 multi-layered coils is used to divide the 360° into four sectors of 90° each. Switching between each of the inductor is done by a cold electronics based multiplexer circuit coupled to an unbuffered inverter LC oscillator. The angular displacement is a function of frequency of cold electronic LC oscillator. The pickup coil forms the inductor of the oscillator which is operated down to 4.2 K and uses thermal cycled stable components. The change in frequency as a function of angular displacement was calibrated at cryogenic temperatures. The developed sensor was found to have good thermal stability, sensitivity and repeatability over the entire cryogenic range.     

Production of 400 mirrors with high VUV reflectivity for use in the SLD Cherenkov ring imaging detector

The Stanford Large Detector for experimental particle physics detection at the SLAC Linear Collider contains a Cherenkov ring imaging detector (CRID). The barrel CRID mirrors have been successfully produced and installed. The industrial mirror production process, the quality control of the mirrors produced, and the results of the vacuum ultraviolet (VUV) reflectivity and mirror-shape accuracy are described. An average reflectivity of at least 80% for light at 160 nm and 85% for light in the 180–230 nm wavelength range has been achieved in the production of over 400 mirrors of a typical size of 30 by 30 cm. The surface roughness and optical distortion measurements imply that the light loss due to scattering is a few percent of the incident light and the angular error due to shape distortion is less than 1 mrad.     

Angular displacement fiber-optic sensor: theoretical and experimental study

An optical-fiber sensor based on twist-induced optical activity has been developed for measuring angular displacements at low temperature. The sensing part is composed of a fiber coil rotated between two points, which induces a twist of two sections of fiber. A theoretical study of the evolution of a general input state of polarization in the sensor gave us its main characteristics. Then experimental investigations permitted the construction of a sensor to take angular measurements over a 100-deg range with an accuracy of 0.2 deg. The thermal sensitivity of this kind of sensor is also briefly reported.     

Compensation of Angular Errors Using Decision Feedback Equalizer Approach

Speed and position measurements of rotating shafts are very important in the field of mechanical engineering. In automotive applications, magnetic field sensors for such measurements (camshaft, crankshaft, anti-lock braking system, windshield wiper, etc.) have the largest market share of all sensor types. Camshaft applications are challenging due to their requirements on high angular accuracy under harsh environmental conditions. Due to mounting and packaging tolerances, the magnetic field at the sensors position varies, resulting in angular measurement errors for sensor concepts in use today. Mounting and packaging tolerances cannot be avoided; however, they can be compensated by a new filter structure which is described in this paper. The decision feedback equalizer (DFE)—known from digital communication—was analyzed and modified for the use in angular measurement applications. A new filter structure, using data prediction and an adaptive algorithm based on a physical model, is proposed. This filter calculates and compensates angular errors caused by mounting and packaging tolerances.      

An overview and a contribution to the optical measurement of lineardisplacement

The present work is a contribution to the field of linear displacement measurements by optical means. For that purpose, a brief overview of some existing solutions is presented and two systems for axial linear displacement measurement based on light intensity detection are introduced. The systems have redundancy and were designed with the purpose of achieving identification and automatic correction of errors arising from inadvertent angular variations between the sensor and the light beam positions     

激光跟踪仪测角误差的位移标定法

提出了激光跟踪仪测角误差的位移标定方法,通过在跟踪仪的切向位置上引入标准位移量,根据余弦定理对跟踪仪的角度码盘的误差进行标定.在小位移的情况下,跟踪仪角度的变化量很小,由此引入的非线性误差可以忽略,测角误差可以通过位移误差直接反映出来,当给定的标准位移测量不确定度已知时,其角度标定的不确定度可以直接估算出来.     

Optical Reflectance Sensor Measures Displacement in Magnetic Suspension

In active magnetic suspension systems, electromagnetic forces are used to keep a body in stable equilibrium without mechanical contact. Basically, an active magnetic suspension is a position servomechanism. Thus, accurate measurement of the position of the levitated part is important. A variety of displacement transducers has been in use, the eddycurrent sensor being the most favored one at present. This paper describes an optical reflectance sensor used in a novel configuration to measure the position in a levitation setup. A sensitivity of 10.5 V/mm, and a linearity range of about 0.5 mm, were obtained by this method. The sensor and the measurement technique are described in detail here.     

Laser-speckle angular-displacement sensor: theoretical and experimental study

A novel, to our knowledge, method for the measurement of angular displacement for arbitrarily shaped objects is presented in which the angular displacement is perpendicular to the optical axis. The method is based on Fourier-transforming the scattered field from a single laser beam that illuminates the target. The angular distribution of the light field at the target is linearly mapped on a linear image sensor placed in the Fourier plane. Measuring this displacement facilitates the determination of the angular displacement of the target. It is demonstrated both theoretically and experimentally that the angular-displacement sensor is insensitive to object shape and target distance if the linear image sensor is placed in the Fourier plane. A straightforward procedure for positioning the image sensor in the Fourier plane is presented. Any transverse or longitudinal movement of the target will give rise to partial speckle decorrelation, but it will not affect the angular measurement. Furthermore, any change in the illuminating wavelength will not affect the angular measurements. Theoretically and experimentally it is shown that the method has a resolution of 0.3 mdeg ( approximately 5 murad) for small angular displacements, and methods for further improvement in resolution is discussed. No special surface treatment is required for surfaces giving rise to fully developed speckle. The effect of partially developed speckle is considered both theoretically and experimentally.     

A capacitance based axial position sensor for cryocoolers

The recent development of a Stirling cryocooler designed to operate with a body temperature of less than 220 K required an axial motor position sensor which could operate over this temperature range. Although linear variable differential transformers (LVDTs), have traditionally been used, these are temperature dependent and would have required development due to integrated electronics, which could not be used at these low temperatures. A sensor was therefore developed based on the principle of measuring the capacitance between static and moving concentric rings. The design is presented along with the signal conditioning circuit. Experimental results show that the sensor had suitable bandwidth with a temperature independent gain between room temperature and 220 K. Future developments are described including a similar sensor to measure the radial motion of a motor during operation.     

永磁式角加速度传感器及其标定方法的研究

介绍了一种新型永磁式角加速度传感器及其机械结构和工作原理,针对该角加速度传感器的标定问题,提出了一种基于机械扭摆机构的标定方法和标定系统。推导证明了其标定原理,并通过实验证明该标定方法和标定系统能客观反映出永磁角加速度传感器非电量输入和输出电压之间的关系,确保了角加速度传感器的标定精度,证明了永磁式角加速度传感器及其标定方法的可行性。实验结果表明传感器的灵敏度约为6.562 μV/(rad·s^-2).     

Signal Averaging for Noise Reduction in Mobile Robot 3D Measurement System

Accurate information from sensors plays an important role in precision measurement. In such measurement small component of a noise can leads to a large variation in the output of the system. For the applications like multi-sensor data integration, sequences of observations from a number of different sensors are used to integrate into a single best estimate of the state of the environment. For integration of sensory information, sensor registration is considered as an important step. This research work is focused upon reduction of a noise from the repetitive motion of the pan tilt unit. The outcome of this paper is implemented on 3D feature extraction of the mobile robot’s environment using a laser range finder. In the proposed work averaging technique is implemented on the Pan Tilt Unit (PTU) of the system where laser range finder is fixed upon the PTU to extract the 3D feature of the target objects. Registration of the angular displacement of PTU and laser range finder is an essential element of the 3D feature extraction. An experimental result of sensor registration shows a substantial improvement in signal to noise (S/N) ratio and quality of 3D feature extraction is also found improved.     

Position and displacement sensing with shack-hartmann wave-front sensors

The use of a Shack-Hartmann wave-front sensor as a position-sensing device is proposed and demonstrated. The coordinates of a pointlike object are determined from the modal Zernike coefficients of the wave fronts emitted by the object and detected by the sensor. The position of the luminous centroid of a moderately extended incoherent flat object can also be measured with this device. Experimental results with off-the-shelf CCD cameras and conventional relay optics as well as inexpensive diffractive microlens arrays show that axial positioning accuracies of 74 mum rms at 300 mm and angular accuracies of 4.3 murad rms can easily be achieved.     

Nanometer-scale displacement sensor based on phase-sensitive diffraction grating

In this paper, a nanometer-scale displacement sensor based on a phase-sensitive diffraction grating with interferometeric detection is described and experimentally demonstrated. The proposed displacement sensor consists of a coherent light source, a microstepping motor controller, an integrated grating, a mirror, and a differential circuit. Experimental results show that the displacement sensor has a sensitivity of about 6 mV/nm and a resolution of less than 1 nm. This displacement measurement is an attractive technology with high sensitivity, broad dynamic range, good reliability, and immunity to electromagnetic interference.     

An improved dynamic model for angular contact ball bearings under constant preload

High-speed spindles are typically installed with angular contact ball bearings. This research has established a dynamic model for angular contact ball bearings under constant preload. By analyzing the constant preload mechanism, and the gyroscopic and centripetal forces, a dynamic non-linear model for angular contact ball bearings was proposed using Hertz contact theory. The model was solved by numerical iteration to obtain the dynamic parameters of an angular contact ball bearing which included: the dynamic normal contact force and contact angle, the maximum compressive stress and axial displacement, the contact pattern, stiffnesses, etc. To validate the model, a test device was designed which was equipped with a constant preloaded bearing group. By measuring the relative displacement of the bearings’ inner and outer rings under different conditions, the accuracy of the model was proved. This modeling method provided a theoretical basis for calculating bearing thermal characteristics, fatigue life, and an optimized radius of curvature of the bearing ring channel.     

Analysis and design of a CMOS angular velocity- and direction-selective rotation sensor with a retinal Processing circuit

This paper implements and analyzes a CMOS angular velocity- and direction-selective rotation sensor with a retinal processing circuit. The proposed rotation sensor has a polar structure and is selective of the angular velocity and direction (clockwise and counterclockwise) of the rotation of images. The correlation-based algorithm is adopted and each pixel in the rotation sensor is correlated with the pixel that is 45/spl deg/ apart. The angular velocity selectivity is enhanced by placing more than one pixel between two correlated pixels. The angular velocity selectivity is related to both the number and the positions of the edges in an image. Detailed analysis characterizes angular velocity selectivity for different edges. An experimental chip consisting 104 pixels, which form five concentric circles, is fabricated. The single pixel has an area of 91/spl times/84/spl mu/m/sup 2/ and a fill factor of 20%, whereas the area of the chip is 1812/spl times/1825/spl mu/m/sup 2/. The experimental results concerning the fabricated chip successfully verified the analyzed characteristics of angular velocity and direction selectivity. They showed that the detectable angular velocity and range of illumination of this rotation sensor are from 2.5/spl times/10/sup -3/ /spl pi//s to 40 /spl pi//s and from 0.91 lux to 366 lux, respectively.     

2 m激光干涉测长基准装置

阐述了2 m激光干涉测长基准装置工作原理及系统组成,以线间距测量功能为基础,研究了接触式和非接触式的几何测长对准方法,实现了其测长功能拓展应用。介绍了实现纳米精度测长的技术措施。对称布局的双光电显微镜同步扫描测量接长的方式实现2 m刻线间距测量,信号处理系统具有标准间距位置脉冲发生功能,可以实现位移传感器动态触发校准和其它应用。对于高质量的线纹尺,2 m激光干涉测长基准装置单次测量刻线间距的最佳瞄准精度优于10 nm(1σ),1 m测量范围内的线纹测量不确定度U=（20+40 L） nm （k=2）。     

车台用角位移传感器自动分度校准系统设计

为实现高精度SJJF型数显手动分度头的数控化改造应用,满足某航空发动机整机性能测试中车台用角位移传感器自动校准检测的实用性需求,解决手工角度分度耗时费力的难题,提出了角度量自动分度控制系统设计方案,运用逻辑可编程器件（Programmable Logic Controller,PLC）配合专用梯形图编程指令,实现角度光栅信号自动数字化采集、角度值换算、比例微分积分闭环控制（Proportion Integration Differentiation Controller,PID）定位及光栅对零,能够有效满足车台用角位移传感器线性度、灵敏度等校准精度要求,且节约了70%的时间,提高角度分度效率的同时也降低了劳动强度。     

Optical levitation and translation of a microscopic particle by use of multiple beams generated by vertical-cavity surface-emitting laser array sources

An optical levitation and translation method for a microscopic particle by use of the resultant force induced by multiple light beams is studied. We show dependence of the radiation pressure force on the illuminating distribution by numerical calculation, and we find that the strongest axial force is obtained by a specific spacing period of illuminating beams. Extending the optical manipulation technique by means of vertical-cavity surface-emitting laser (VCSEL) array sources [Appl. Opt. 40, 5430 (2001)], we are the first, to our knowledge, to demonstrate levitation of a particle and its translation while levitated by using a VCSEL array. The vertical position of the target particle can be controlled in a range of a few tens of micrometers with an accuracy of 2 microm or less. The analytical and experimental results suggest that use of multiple beams is an effective method to levitate a particle with low total illumination power. Some issues on the manipulation method that uses multiple beams are discussed.     

标定飞机方向舵角位移的视觉测量法

飞机飞行性能试验前需标定其方向舵的角位移传感器.基于单目视觉,以三个圆心为靶面的基本标志,圆周为辅助标志;用两直线段的交点标明圆心位置.取平行于像面的直径为特征直径,借助它容易从像面椭圆图像提取靶面深度信息,并建立简单、精确的逆透视变换公式.设计了亚像素法处理照片,能精确测出圆心像点位置和特征直径的像长,用来求圆心的世界坐标,得到靶面的平面方程.舵的角位移可用靶面角位移表示.计算机仿真结果,圆心像点位置测量误差小于0.02 pixel,角位移测量误差小于0.005°.靶面与舵轴不平行导致的测量误差能及时修正,可降低对靶面安装的要求,使操作简单.能在现场标定飞机副翼、襟翼,升降舵、方向舵的角位移.     

Spatially integrated speckle intensity: maximum resistance to decorrelation caused by in-plane target displacement

Laser speckle produced from a diffuse object can be used in determining the angular position of a rotating object. When the object rotates the backscattered speckle pattern, which changes continuously but repeats exactly with every revolution, is sampled by a suitably positioned photodetector. The photodetector output signal is periodic, and one period is stored in the memory as a reference. Shaft position can then be determined by the comparison of this stored reference signal with the current photodetector output signal. When the shaft is axially displaced, for example, by vibration, the backscattered speckle pattern changes on the photodetector and the similarity between the reference signal and the current signal is reduced. We examine the cross correlation of the real-time photodetector output signal and the stored reference signal as a function of axial shaft position. Use of a rotating shaft when collecting data is shown to be an efficient means by which to make effectively several thousand independent estimates of the maximum axial displacement tolerable before decorrelation of the photodetector output. Theoretical results and experiments conducted show that the decorrelation displacement varies, according to optical configuration, to a maximum value of 0.7 of the beam diameter. This has important implications for a proposed laser torquemeter as well as additional applications in which changes to the sampled speckle pattern, including decorrelation, are either desirable or undesirable.