Development of an optical sensor for dynamic monitoring of off-round and eccentric errors of cylindrical parts

An optical angular deflection sensor has been implemented to assess the shape and axis position of rotating cylindrical parts. The deviation of the shape from the nominal circular cross-section (the off-round error) and the departure of the rotation axis from the geometric axis of the parts (the eccentric error) are determined. The technique is simple and inexpensive, with acceptable accuracy for mechanical engineering, is capable of monitoring rotating parts and has the potential to gauge parts on the production line.     

Calibration error analysis of electro-optical detection systems

We present detailed analysis of calibration process error for electro-optical detection systems, which can be simplified as the plane rotation around a non-orthogonal axis. By means of octonions it firstly proves that the plane rotation around a non-orthogonal axis can be decomposed into rotations around two perpendicular axes. The rotation is further divided into three steps, and the calibration error is hence discussed and obtained. The simulation and test results indicate that there are large calibration errors in calibration process. The pointing error can be effectively improved after separating error components, which provides a more accurate set data for further comDensation.     

Measurement of tilt of a diffuse object by double-exposure speckle photography using speckle fanning in a photorefractive BaTiO3 crystal

A technique has been proposed for the measurement of tilt of a diffuse object using speckle fanning in a photorefractive BaTiO₃ crystal. Free space geometry has been used for recording in which the axis of rotation of the object lies away in three-dimensional space. The method is based on recording of two exposures, one before- and another after the tilt, thus producing speckle correlation fringes due to overlapping of two speckle fans. We consider a generalized case of tilt, generating curved fringes with center shifted in the transverse direction. The axis of rotation lies perpendicular to the optical axis in three-dimensional space having the transverse and axial components of the shift in the center of rotation with respect to the diffuser plane. Fourier transform of the curved fringes produces correlation output. Measure of separation between the correlation peaks in transverse and axial directions provides information about the tilt angle, the direction of tilt, and the distance of rotation axis from the optical axis. Experimental results have been presented to validate the theoretical predictions.     

六方晶系Brillouin散射的旋转对称性

指出六方晶系Ｂｒｉｌｏｕｉｎ散射具有围绕晶体六次轴的任意旋转对称性,给出该晶系含体积元转动贡献的散射张量的简洁形式,讨论了压电效应对这种旋转对称性的影响。     

A new electro-optic modulated circular heterodyne interferometer for measuring the rotation angle in a chiral medium

A new optical polarimeter capable of measuring the rotation angle in a chiral medium is developed successfully, and is an extension of previously developed simultaneous or sequential measurement system of the principal axis and retardance in linearly birefringent materials. The polarimeter for measuring the rotation angle is based on an electro-optic modulated circular heterodyne interferometer and using phase-lock technique to measure the rotation angle directly and precisely. The validity of the proposed design is demonstrated by the measurement of rotation angle in a half-wave plate and the glucose sample. The average relative error in rotation angle level of 0.00284° has been obtained for a half-wave plate. A correlation coefficient value of 0.9999975 is determined; it indicates a highly linear relationship between the reference values and the measured rotation angles. Moreover, a standard deviation in rotation angle level of 0.005275° has been obtained for glucose solutions with concentrations ranging from 0 to 1.2 g/dl in 0.2 g/dl increments, with a correlation coefficient value of 0.99915 between the reference and the measured values. This setup is compact in configuration, and is easy in calibration. The linearity and resolution characteristics of this system are comparable to those previous studies adopting phase-sensitive techniques.     

Rotational motion in sensorless freehand three-dimensional ultrasound

Freehand three-dimensional ultrasound is usually acquired with a position sensor attached to the ultrasound probe. However, position sensors can be expensive, obtrusive and difficult to calibrate. For this reason, there has been much research on alternative, image-based techniques, with in-plane motion tracked using conventional image registration methods, and out-of-plane motion inferred from the decorrelation between nearby B-scans. However, since out-of-plane motion is not the only source of decorrelation, image-based positions determined in this way suffer from cumulative drift errors. In this paper, we consider the effect of probe rotation on correlation and how this affects the position estimates. We then present a novel technique to compensate for out-of-plane rotations, by making use of orientation measurements from an unobtrusive sensor. Using simulations and in vitro experiments, we demonstrate that the technique is able to reduce the drift error in elevational positioning by 57% on average.     

Optical measurements of angle and axis of rotation

A carousel interferometer is designed to find the unknown angle and axis of rotation simultaneously. A set consisting of a compensator glass plate and a right-angle prism is placed in each of the two arms of the interferometer while located at the same rotational stage. When rotation takes place individual and relative optical path differences are generated in the beams that contribute toward finding out the angle and axis of rotation. Computer simulation shows that error remains less than a nanometer for a 1 m length of unknown radius and rotation range of +/-15 degrees .     

Optimization of Selective Assembly for Shafts and Holes Based on Relative Entropy and Dynamic Programming

Selective assembly is the method of obtaining high precision assemblies from relatively low precision components. For precision instruments, the geometric error on mating surface is an important factor affecting assembly accuracy. Different from the traditional selective assembly method, this paper proposes an optimization method of selective assembly for shafts and holes based on relative entropy and dynamic programming. In this method, relative entropy is applied to evaluate the clearance uniformity between shafts and holes, and dynamic programming is used to optimize selective assembly of batches of shafts and holes. In this paper, the case studied has 8 shafts and 20 holes, which need to be assembled into 8 products. The results show that optimal combinations are selected, which provide new insights into selective assembly optimization and lay the foundation for selective assembly of multi-batch precision parts.     

Mapping misoriented fibers using X-ray dark field tomography

X-ray grating interferometers produce three distinct signals; an absorption signal, a differential phase signal and a dark field signal. Until now a method for successfully creating dark field tomograms of nonisotropic samples has not been demonstrated. In this paper we test a method for creating such tomograms on a highly nonisotropic sample, i.e. a five layer “sandwich” of oriented carbon fibers. The fibers are parallel within the individual sandwich layers, but perpendicular to the fibers in the adjacent layers. We show that by choosing a rotation axis parallel to the grating stepping direction (i.e. a horizontal rotation axis in most setup configurations) it is possible to produce a darkfield tomogram where fibers parallel to the probed scattering direction appear to have no dark field signal. The method produces a tomogram in the form of a scalar field of dark field scattering values.     

月基对地观测跟踪转台设计与分析

针对登月过程严酷的力学条件、月球表面复杂的环境特征以及严格的重量要求,设计了一种可适用于月基观测的跟踪转台.该转台主要由水平轴系及驱动机构和竖直轴系及驱动机构组成,采用霍耳元件作为位置检测元件,其综合指向准确度≤0.1°.基于有限元分析方法确定转台结构方案、优化主要支撑件结构及合理选材,并对驱动机构与轴系对转台刚度、温度适应性和指向准确度的影响做了深入分析与计算.同时进行了整机的力学模拟试验和运动机构的高低温试验,一阶谐振频率为49 Hz,在-40 ℃ ～+80 ℃温度范围内工作正常.结果表明转台各项性能指标满足工程任务要求,具有结构紧凑、可靠性高、重量轻的特点.     

General coarsened measurement references for revelation of a classical world

It has been found that for a fixed degree of fuzziness in the coarsened references of measurements,the quantum-toclassical transition can be observed independent of the macroscopicity of the quantum state.We explore a general situation that the degree of fuzziness can change with the rotation angle between two states(different rotation angles represent different references).The fuzziness of reference comes from two kinds of fuzziness:the Hamiltonian(rotation frequency)and the timing(rotation time).For the fuzziness of the Hamiltonian alone,the degree of fuzziness for the reference will change with the rotation angle between two states,and the quantum effects can still be observed with any degree of fuzziness of Hamiltonian.For the fuzziness of timing,the degree of the coarsening reference is unchanged with the rotation angle.During the rotation of the measurement axis,the decoherence environment can also help the classical-to-quantum transition due to changing the direction of the measurement axis.     

Quark mixing in the standard model and space rotations

The rotation matrix and the Cabibbo–Kobayashi–Maskawa (CKM) matrix are discussed. The CKM matrix is viewed as the rotation matrix in Euler angles with pitch–roll–yaw convention for the angles and as the angle–axis representation of the rotation matrix. A comparison of the exponential parameterisation of the CKM matrix with the matrix exponent generator of the space rotations is made. How to account for the CP violating phase in CKM and the O(3) rotation matrix in the angle–axis form is discussed in the context of such a view of the mixing matrix. The generation of the new parameterisations of the CKM matrix in an exponential form with distinguished CP violating part is demonstrated.     

Transport properties of cholesteric liquid crystals studied by molecular dynamics simulation

We have studied the transport properties of a cholesteric liquid crystal by molecular dynamics simulation. The molecules consist of six soft ellipsoids of revolution, the axes of which are perpendicular to the line connecting their centres of symmetry. The angle between the symmetry axes of two adjacent ellipsoids is 7.5°, so the molecules are twisted. At high densities they form a cholesteric phase where their twist axes are oriented around the cholesteric axis and the symmetry axes of the ellipsoids are approximately parallel to the local director. We have been particularly interested in thermomechanical coupling or the Lehmann effect, which arises when a temperature gradient parallel to the cholesteric axis induces a torque that rotates the director. The converse is also possible: rotation of the director can drive a heat current. The thermal conductivity, the twist viscosity, the cross-coupling coefficient between the temperature gradient and the torque, and the cross-coupling coefficient between the director angular velocity and the heat current have been calculated by non-equilibrium molecular dynamics simulation methods (NEMD) and by evaluation of the Green-Kubo relations from equilibrium simulations. Two ensembles have been utilized: the ordinary canonical ensemble and another ensemble where the director angular velocity is constrained to be a constant of motion. All the methods give consistent results for the twist viscosity and the thermal conductivity. The NEMD estimates of the cross-coupling coefficients agree within a relative error of 20%. This is consistent with the Onsager reciprocity relations that state that the two cross-coupling coefficients should be equal. The relative error of the Green-Kubo estimates is about 100% even though the order of magnitude is the same as that of the NEMD estimates.     

Selective rotation pulses calculated with an inverse scattering algorithm

Selective rotation pulses cause magnetization within a given frequency range (or slice) to undergo a specified rotation, about a specified axis. Magnetization outside this slice remains unaffected if it is initially along the z axis. It has previously been shown that the design of such pulses can be reduced to the design of selective "point-to-point" pulses, which rotate magnetization within the slice from the y axis. By decomposing the point-to-point pulses into two sub-pulses, it is shown that an inverse scattering algorithm for selective pulse design can be used to calculate selective rotation pulses with any desired spinor response, subject to the constraint that the second spinor component have constant phase across the slice. The design of selective refocusing pulses can be treated specially, requiring the calculation, by the same inverse scattering algorithm, of a single sub-pulse.     

Further Development of Automatic Activation Analysis System (AAAS) with Fast Neutrons

Improvement of results of activation analysis has been achieved by using a device for simultaneous rotation of the sample around tow axes: one parallel and the other perpendicular to the target during the irradiation. A change of the construction of the container resulted in the increase of its volume and a decrease in the mean sample-to-target distance. The distribution of the neutron flux along the axis of the container during the irradiation has been measured. An arrangement for automatic loading and unloading of sample is also described.     

What are the instrumentation requirements for measuring the isotopic composition of net ecosystem exchange of CO2 using eddy covariance methods?

Better quantification of isotope ratios of atmosphere-ecosystem exchange of CO2 could substantially improve our ability to probe underlying physiological and ecological mechanisms controlling ecosystem carbon exchange, but the ability to make long-term continuous measurements of isotope ratios of exchange fluxes has been limited by measurement difficulties. In particular, direct eddy covariance methods have not yet been used for measuring the isotopic composition of ecosystem fluxes. In this article, we explore the feasibility of such measurements by (a) proposing a general criterion for judging whether a sensor's performance is sufficient for making such measurements (the criterion is met when the contribution of sensor error to the flux measurement error is comparable to or less than the contribution of meteorological noise inherently associated with turbulence flux measurements); (b) using data-based numerical simulations to quantify the level of sensor precision and stability required to meet this criterion for making direct eddy covariance measurements of the 13C/12C ratio of CO2 fluxes above a specific ecosystem (a mid-latitude temperate forest in central Massachusetts, USA); (c) testing whether the performance of a new sensor-a prototype pulsed quantum cascade laser (QCL) based isotope-ratio absorption spectrometer (and plausible improvements thereon)-is sufficient for meeting the criterion in this ecosystem. We found that the error contribution from a prototype sensor (approximately 0.2 per thousand, 1 SD of 10 s integrations) to total isoflux measurement error was comparable to (1.5 to 2x) the irreducible 'meteorological' noise inherently associated with turbulent flux measurements above this ecosystem (daytime measurement error SD of approximately 60% of flux versus meteorological noise of 30-40% for instantaneous half-hour fluxes). Our analysis also shows that plausible instrument improvements (increase of sensor precision to approximately 0.1 per thousand, 1 SD of 10 s integrations, and increased sensor stability during the half-hour needed to integrate eddy covariance measurements) should decrease the contribution of sensor error to the point where it is less than the contribution from meteorological noise. This suggests that new sensors using QCL-based isotope ratio absorption spectroscopy should make continuous long-term observations of the isotopic composition of CO2 fluxes via eddy covariance methods feasible.     

GNSS天线连接器同轴度误差测量技术

为测量GNSS天线连接器同轴度误差,构建了连接器分段旋转数学模型,提出了一种水平转台和机器视觉结合的非接触式测量方法,搭建测量装置并进行了测量实验.分析连接器运动方式和同轴度误差测量方法,确定各轴线之间的偏移关系,建立同轴度误差数学模型和测量模型.搭建测量装置,相机安装在水平转台上方,光轴平行于水平转台轴线.旋转水平转台,使用相机捕捉转接螺杆端面圆心位置并拟合轨迹,完成测量装置同轴度误差自标定.将连接器安置在水平转台上,旋转水平转台,测量连接器顶部螺纹杆轴线相对水平转台轴线的偏移.旋转连接器的承载器,测量连接器顶部螺纹杆轴线相对承载器轴线的偏移.最终,综合各轴线的偏移关系得到连接器同轴度误差的最大值.实验结果表明,测量装置对GNSS天线连接器同轴度误差的测量标准差为9μm,单次测量结果的扩展不确定度U=30μm(k=2),满足GNSS天线连接器0.1 mm至1 mm量级的同轴度误差的测量需求,使用连接器同轴度误差修正GNSS超短基线测量结果,可以显著提升基线测量精度.     

Determination of aerodynamic characteristics of turbine vanes with vertical rotation axis

Presented below are the results of tests of turbine vanes with vertical rotation axis aimed at determination of their aerodynamic characteristics. Three types of vanes with the profiles in the form of semicylinder, semiellipse, and semiellipse with stabilizing plane have been tested. The last type of vane has been tested with stationary and rotary stabilizing planes.     

大尺度多光谱多光轴平行性检校系统

为对室内不拆装情况下大型或整车上的多谱段光电装备进行光轴平行性检校,设计了大尺度多光谱多光轴平行性检校系统。系统采用一个多光谱平行光管提供多个谱段的无限远目标,通过二维移动平台实现平行光管的室内大跨度移动。利用倾角传感器、双线阵CCD测量系统和姿态调整机构来恢复和保证平行光管移动前后的光轴平行性,实现室内分布在车体上不同轴距不同谱段光电装备的光轴平行性进行统一检校。系统设计方案和误差分析结果表明:该系统平行光管移动前后的光轴平行性总误差小于0.142 mrad,在提高检校精度的同时还大大减小了光轴平行性检校的工作量;各分系统中倾角传感器和姿态调整机构误差对系统总误差贡献最大,通过选用更高精度的分系统还可进一步提高系统的总体精度,满足更高精度装备的光轴平行性检校要求。     

地平式望远镜跟踪机架结构设计与分析

针对某700 mm口径地平式望远镜系统,提出了一种U型跟踪架的结构设计方案。跟踪架结构中方位轴系采用双排密珠球轴承,轴承设计为双排轴向止推钢珠及双排径向钢珠结构,滚珠的密集及均化作用可保证轴系具有高回转精度。俯仰轴系设计采用一端固定、一端游动的结构方式,以补偿机械误差及热变形对回转精度的影响。对望远镜跟踪架进行有限元建模,分析得出其一阶谐振频率可达到47.6 Hz,说明它具有良好的模态特性。使用电子水平仪及自准直仪分别对方位轴及俯仰轴进行定量检测,方位轴轴系晃动优于1.3″,俯仰轴轴系晃动优于1.8″。通过仿真分析及实验测试,证明设计的望远镜跟踪架结构具有高刚度及高回转精度,为同类跟踪架的结构设计提供了一定的参考价值。