Design considerations for the absolute testing approach of aspherics using combined diffractive optical elements

Aspheric optical surfaces are often tested using diffractive optics as null elements. For precise measurements, the errors caused by the diffractive optical element must be calibrated. Recently, we reported first experimental results of a three position quasi-absolute test for rotationally invariant aspherics by using combined-diffractive optical elements (combo-DOEs). Here we investigate the effects of the DOE substrate errors on the proposed calibration procedure and present a set of criteria for designing an optimized combo-DOE. It is demonstrated that this optimized design enhances the overall consistency of the procedure. Furthermore, the rotationally varying part of the surface deviations is compared with the rotationally varying deviations obtained by an N-position averaging procedure and is found to be in good agreement.     

Absolute calibration in grazing incidence interferometry via rotational averaging

Interferometry in grazing incidence can be used to test cylindrical mantle surfaces. The absolute accuracy of the resulting surface profiles is limited by systematic wavefront aberrations caused in the interferometer, in particular due to an inversion of the test wavefront in an interferometer using diffractive beam splitters. For cylindrical specimens, a calibration method using four positions has therefore been investigated. This test is combined with another method of optical metrology: the rotational averaging procedure. The implementation for grazing incidence is described and measurement results for hollow cylinders are presented. The gain in accuracy is demonstrated.     

Method to test rotationally asymmetric surface deviation with high accuracy

We have proposed a new absolute method to test rotationally asymmetric surface deviation. Relying on the high accuracy of Zernike polynomial fitting with least-squares algorithm for the low-frequency component and preserving the high-frequency component with the averaging method, the new method can guarantee the high accuracy of the measurement result with fewer rotational measurements compared to the traditional multiangle averaging method. It realizes a balance between the accuracy and efficiency of the measurements. It has been verified by experiments; the root mean square (rms) of residual figure between the two methods is ～0.6 nm. Meanwhile, the new method can suppress environmental noise introduced in measurement results well.     

Absolute interferometric testing based on reconstruction of rotational shear

A method, believed to be new, for the absolute interferometric testing of flat or spherical surfaces is presented. It is based on the classic three-flat test, combined with additional measurements of one test piece in different rotational positions. Full-surface absolute maps for each test piece are determined with a data-processing technique based on the rotationally sheared maps of the rotated surface. An optimized numerical reconstruction algorithm employing linear filtering and superposition of the different rotational shear spectra in the angular frequency domain is used to reconstruct the rotationally sheared data. The technique does not require any assumptions about the surfaces under test; has low error propagation, even in the case of high spatial resolution; and is computationally efficient.     

Charpy impact damage behaviour of single and multi-delaminated hybrid composite beam structures

The ply delamination which is known as a principle mode of failure of layered composites due to separation along the interfaces of the layers is one of the main concerns in designing of composite material structures. In this regard, the effect of hybrid laminate lay-up with different delamination positions in composite beam was investigated. The Charpy impact test was chosen to study the energy absorbing capability of delaminated composite beam. Hybrid composite beams were fabricated from combination of glass/epoxy and carbon/epoxy composites. It was shown that composite beams with closer position of delamination to impacted surface are able to absorb more energy in comparison with other delamination positions in hybrid and non-hybrid ones. The Charpy impact test of delaminated composite beams was also simulated by finite element software LS-DYNA and the results were verified with the relevant experimental results.     

Accessibility analysis for star probes in automatic inspection of rotational parts

This article describes a method of accessibility analysis based on the geometrical study of all possible interferences between the probe and the part to be inspected. The parts considered in the analysis are rotational parts and their recognition is automatically made from a feature-based design. The probe considered is a star type, defined by adjustable parameters that allow for the adaptation to different types and sizes. The system analyses the possible collision with the machine column, touch probe and probe stylus. Apart from determining the conditions of collision, the system also calculates any collision-free positions on each surface to be probed. These positions can be used to obtain inspection paths for communication to a CMM or to a global inspection planning system. The collision conditions calculated have been checked and validated using different rotational parts.     

面向精密制造的光学自由曲面在位偏折测量技术

复杂光学曲面的在位测量是当前精密工程领域面临的重要难题。偏折术对光学曲面的测量精度可与干涉仪相比,而且拥有更高的测量效率、稳定性及动态范围,因此具有广阔的应用前景。但是偏折测量本质上是一个标定问题,其测量精度直接取决于几何标定的可靠性。本文结合单点金刚石切削机床设计了原位偏折测量系统,采用机床中自带的气浮转台安装辅助反射镜,在两个姿态下进行光线追迹,通过数值优化计算各元件之间的相对位置,将标定精度提高一个数量级。根据反向投影偏差的统计规律,可有效分离工件的面形偏差与位姿误差。该方法有效利用了工件的名义面形信息,将传统的位置-面形单向映射转变为双向映射,显著提高了在位测量的灵活性与效率。对于复杂的自由曲面,采用子孔径拼接测量方法,对待测的局部区域发展了精准定位技术,有效保证了迭代重构过程的正确收敛。采用离轴抛物镜等光学曲面进行实验验证,所提出的偏折测量方法的精度优于150 nm RMS。     

Dynamics of anisotropic composite cantilevers weakened by multiple transverse open cracks

In this paper an exact solution methodology, based on Laplace transform technique enabling one to analyze the bending free vibration of cantilevered laminated composite beams weakened by multiple non-propagating part-through surface cracks is presented. Toward determining the local flexibility characteristics induced by the individual cracks, the concept of the massless rotational spring is applied. The governing equations of the composite beam with open cracks as used in this paper have been derived via Hamilton's variational principle in conjunction with Timoshenko's beam model. As a result, transverse shear and rotatory inertia effects are included in the model. The effects of various parameters such as the ply-angle, fiber volume fraction, crack number, position and depth on the beam free vibration are highlighted. The extensive numerical results show that the existence of multiple cracks in anisotropic composite beams affects the free vibration response in a more complex fashion than in the case of beam counterparts weakened by a single crack. It should be mentioned that to the best of the authors' knowledge, with the exception of the present study, the problem of free vibration of composite beams weakened by multiple open cracks was not yet investigated.     

The recovery of the density scale using a stochastic quasi-realization of additive conjoint measurement

This paper attempts to illuminate some of the practical limitations that the Rasch model (and by extension, Item Response Theory models) may have by focusing on the recovery of the density scale. Five simulation trials were conducted: the first four to recover the density scale with different deviations from the assumptions implicit in the use of the Rasch model and the fifth trial with an almost ideal data set. Results demonstrate that when error distributions are insufficient the results may be ordinal at best, and when error distributions are non-symmetrical, the positions of items may be biased with respect to the positions of persons. Results also confirm that errors of estimation, and test and sample information functions are sample dependent.     

A general rotation averaging method for granular materials

In order to study the rotational behavior of granular materials, rotation averaging methods are required. Most of the existing rotation averaging methods are only for 2D cases and limited by the shape, position and size of the averaging volumes. Hence, a general rotation averaging method is proposed in this paper. Our approach is simple yet works for both 2D and 3D cases with very little restriction. The performance of this method is shown by both hypothetical examples and DEM simulations of plane strain tests with different boundary conditions.     

The method of maximum likelihood applied to the statistical analysis of fatigue data

The application of the principle of maximum likelihood to the analysis of fatigue test results, including run-outs, is described. The particular method used is that developed by Edwards, called ‘Support’. The paper describes the use of this method in determining means and standard deviations for test results, the determination of ‘best-fit’ S/N curves with their associated standard deviations and the determination of the significance of differences between groups of results, different S/N curves and the determination of ‘best’ common slopes and the intercepts of such curves. A computer program developed to perform the necessary calculations is outlined. Examples are given of the types of results produced by this analysis and of certain difficulties in the interpretation.     

Test optics error removal

Wave-front or surface errors may be divided into rotationally symmetric and nonrotationally symmetric terms. It is shown that if either the test part or the reference surface in an interferometric test is rotated to N equally spaced positions about the optical axis and the resulting wave fronts are averaged, then errors in the rotated member with angular orders that are not integer multiples of the number of positions will be removed. Thus if the test piece is rotated to N equally spaced positions and the data rotated back to a common orientation in software, all nonrotationally symmetric errors of the interferometer except those of angular order kNθ are completely removed. It is also shown how this method may be applied in an absolute test, giving both rotationally symmetric and nonsymmetric components of the surface. A general proof is given that assumes only that the surface or wave-front information can be described by some arbitrary set of orthognal polynomials in a radial coordinate r and terms in sin θ and cos θ. A simulation, using Zernike polynomials, is also presented.     

Influence of friction stir processing parameters on surface modified 90Cu-10Ni composites

Friction Stir Processing (FSP) has emerged as a distinctive and pioneering solid state technique to produce surface composites. The objective of the present research is to produce reinforced 90/10 Copper–Nickel surface composites with different carbide-based ceramic particles through FSP and study the relationship of its dynamic parameters including tool rotational speed, tool traverse speed, and width of the groove over the surface behavior. Responses such as sliding wear, microhardness, and surface modified area in the friction stir processed region are modeled using polynomial, nonlinear, multiple regression based on the central composite design of experiment. Analysis of the developed models showed that the FSP parameters; traverse speed, rotational speed, and groove width have significant influence on both the sliding wear and microhardness of developed surface composite. And furthermore, tool rotational speed and tool traverse speed, simultaneously control dispersion of reinforcement in the surface. To validate the abovementioned noteworthy results and to study the microstructural aspects, selected specimens were carried over metallurgical analysis and the obtained results were put forward in detail in this paper.     

Three-flat test solutions based on simple mirror symmetry

In interferometric surface and wavefront metrology, three-flat tests are the archetypes of measurement procedures to separate errors in the interferometer reference wavefront from errors due to the test part surface, so-called absolute tests. What is believed to be a new class of solutions of the three-flat problem for circular flats is described in terms of functions that are symmetric or antisymmetric with respect to reflections at a single line passing through the center of the flat surfaces. The new solutions are simpler and easier to calculate than the known solutions based on twofold mirror symmetry or rotation symmetry. Strategies for effective azimuthal averaging and a method for determining the averaging error are also discussed.     

水平单管传热性能试验台设计与试验研究

基于测量单管换热性能的目的,设计一个以R134a为制冷剂,用于进行满液蒸发、管外冷凝与降膜蒸发试验研究的水平单管换热性能测试试验台,并介绍其系统原理和流程。通过光管蒸发、光管冷凝的验证性试验和重复性试验,进行管内和管外换热系数测试值与理论计算值的误差分析,并研究降膜蒸发工况制冷剂流量对换热系数的影响。试验结果表明:测试值与理论计算值的偏差均在要求范围内,试验台可以为试验研究提供准确、可靠的数据。     

Damage detection in beams from modal and wavelet analysis using a stationary roving mass and noise estimation

This paper uses the Continuous Wavelet Transform Analysis on mode shapes for damage identification. The wavelet analysis is applied to the difference in the mode shapes between a healthy and a damaged state. The paper also includes a novel methodology for estimating the level of noise of the experimental mode shapes based on a standard Signal to Noise Ratio (SNR). The estimated SNRs are used for identifying and making emphasis on the less noisy data. Moreover, a mass attached to the structure is considered to enhance the sensitivity of the structure to damage. Modal analysis is performed for different positions of the mass along the beam. The results obtained for all the positions of the mass are combined so an averaging process is implicitly applied. The paper presents the results from an experimental test of a cantilever steel beam with different severity levels of damage at the same location. The results show that the use of the attached mass reduces the effect of noise and increases the sensitivity to damage. Little damage can be identified with the proposed methodology even using a small number of sensors and only the first five bending modes.     

三维点云无线遥控测量台的设计与标定

使用数控测量台和双目立体视觉测量设备实现被测样件完整的三维点云测量。设计了一种具有有线和红外遥控两种控制模式、可实现二轴移动和二轴回转运动的测量台,提出了一种标定测量台旋转轴的方法。在测量台上粘贴3个以上圆形标靶点并控制测量台绕待标定轴转动,使用测量设备获取测量台两个不同转角位置的标靶点三维坐标点集,利用点集坐标计算出待标定轴在摄像机坐标系下的一个位置,由多个位置优化完成轴的标定。实验结果表明,测量台的控制方式柔性、方便;标定方法简便、成本低、稳定可靠。     

基于地面共振试验的操纵面间隙非线性颤振分析方法

以某型民机带中心对称间隙的方向舵为研究对象。按动力相似准则设计了尾翼颤振风洞模型,通过地面共振试验获得不同操纵刚度和自由间隙组合情况下方向舵旋转模态的力频曲线,根据收敛的频率值获得有限元模型作动器单元的等效刚度,经动力学特性修正后的有限元模型进行了颤振分析。风洞试验后通过比较表明,计算结果与试验结果吻合:①颤振速度一致;②颤振频率的偏差不大于6.5%;③颤振型一致。由此可见,根据试验频率得到的等效操纵刚度是准确的,用来预测弹性操纵面的极限环振荡临界速度是可行的,可以作为民机适航符合性验证的一种手段。     

A novel image analysis method for rotational motion of circular feature based on perspective projection

Abstract

Circular feature has been widely applied in recognising moving object and estimating its position and orientation. Based on the principle of perspective projection, the rotational motion of circular feature was analysed. According to whether the rotational motion occurred in the plane of circular feature, the rotational motion could be classified into two types: in-plane rotation and non-in-plane rotation. For the convenience of computation, we set the camera’s initial position and orientation. The optical axis of camera was set perpendicular to the plane of circular feature. We analysed the perspective distortion of the circular feature. Additionally, based on the geometrical reasoning, we also proposed the method of computing the rotation angles. Finally, some experiments were carried to verify correctness and feasibility of the computing method. The results showed that the measurement of rotation angle could achieve better performance though the error existed. The maximum value of errors was only 0·4°. The average errors and the standard deviations of errors were also small.     

不同海拔下涡轮增压柴油机表面辐射噪声试验研究

采用表面声压级测量法,运用大气压模拟测试系统,以4100QBZL柴油机为研究对象．测试计算涡轮增压柴油机同转速不同海拔下声功率,不同海拔不同转速下的声功率,不同转速下不同喷油提前角的声功率：分析测试结果表明：表面辐射噪声随转速增加而增大;同转速下,增压柴油机整机噪声随海拔增加而增大;以及不同转速下,喷油提前角对柴油机噪声影响规律。