Alignment measurement of two-dimensional zero-reference marks

Alignment with submicron or even nanometer scale resolution is of vital importance in precision engineering. By superimposing a pair of specially coded two-dimensional gratings, the correct alignment position of the two gratings can be obtained by detecting the maximum output of the sharp intensity peak. In this paper, design and fabrication of such two-dimensional zero-reference gratings are introduced. The arrangement of the experiment system is presented in detail. The alignment measurement of the reference marks is tested, and the results are compared with those obtained by autocorrelation method and diffraction analysis. It is found that experimental results are in good agreement with theoretical analysis.     

二维零位光栅自动纳米定位系统

搭建了能够在二维方向上实现纳米级定位的二维自动定位系统。首先,加工了栅格间距为5 μm的64×64编码的透射式二维零位光栅;然后,分析设计了光栅系统光电转换电路和数据控制电路,实现了系统数据采集、显示和运动控制等功能。在此基础上搭建了基于二维零位光栅的纳米定位系统,并利用积分法实现了二维方向的自动定位。实验结果表明,系统定位速度对透射光强分布具有很高的依赖性,系统一次定位的成功率与初始位置密切相关。若起始位置在以零位为中心,半径为2.5 μm圆形区域内,系统可实现纳米量级定位对准;当起始位置在以零位为中心,5~200 μm为半径的圆环范围内,自动定位可能存在盲点,但通过改变初始位置重新进行搜索,仍然能够准确地实现纳米定位。     

曲面小构件变形状态的全场检测问题研究

针对传统方法难以测量曲面小构件非均匀变形的问题,比如受力时发生变形失稳的镍钛形状记忆合金微管,提出了显微成像法和三维形扫描法.它们以非接触和全场的方式追踪构件在不同变形状态下表面标记点的位置,从而获取位移数据,并通过固体力学中经典的几何方程计算得到应变结果.实验证明了所提出方法的易操作性和可靠性,还得到了对于相变材料的力学问题的研究具有重要意义的结果.     

Application of a novel nonperiodic grating in scanning probe microscopy drift measurement

A technique based on two-dimensional nonperiodic grating is proposed to quantitatively measure the drift of scanning probe microscopy (SPM) instruments. Cross-correlation image analysis is adopted in determining the drift. The grating, named as zero-reference mark (ZRM), has specially designed codes and arrangement of the elements can be optimized to have maximum ratio of maximum peak to second maximum of the image correlation matrix. Design considerations of ZRM for drift measurement are discussed theoretically. Advantages of applying ZRM are analyzed by numerical simulation. Comparisons between ZRM and periodic grating show that ZRM has a sharper, less ambiguous correlation function. Adopting ZRM is much more insensitive to drift larger than one element width. Measurement sensitivity is improved by almost one order of magnitude. These characteristics of ZRM imply that it is suitable to be severed as a reference mark for SPM drift measurement.     

具备自标定功能的绝对式时栅位移传感器

时栅位移传感器的绝对式实现方法主要采用单对极+多对极和多对极差一对极组合两种形式实现。对于两层传感器结构的单对极+多对极的组合形式,由于极对数相差较多、分辨力差别较大,不利于实现高精度。对于差一对极的组合方式,由于极对数较多,在传感器原始加工精度较差时,会产生位置解算困难、甚至无法正确解算的情况。为解决上述问题,提出对极数呈互质关系的两层传感器结构的新组合模式。该模式可实现自校正,有效提高产品精度。通过试验验证了该方法的可行性,获取的传感器精度为-4.5″-3.9″。     

Accurate alignment of sets of images

Two modifications to the conventional procedure of cross-correlation are described, widely used for establishing the relative alignment of the members of a set of images from which a higher resolution or more interpretable restoration is sought. Both achieve a high and sharp peak in circumstances where the conventional peak is too ill defined to be recognizable; neither involves significant additional computation time. The more general method requires rough knowledge of the imaging conditions, but a variant applicable to images with axial resolution has no such requirement. In addition, a least-squares procedure is presented for achieving an optimum compromise between many pair-wise displacement measurements, preventing the accumulation of alignment errors across a set of images.     

视觉测量中圆形标志两种提取方法的比较

针对靶场视觉测量相机标定中圆形标志在复杂背景图像上的提取和定位问题,研究了两种不同的圆形标志提取方法,一种是基于感兴趣区域的交互式提取方法,另一种是基于图像灰度和几何形态学的提取方法。对两种方法的圆形标志提取过程进行了研究,并分别采用两种方法对视觉测量图像中的圆形标志进行提取实验,对两种方法的边缘提取效果和定位结果进行了对比,分析了两种方法的优势和不足。圆形标志的提取结果表明,第一种方法能够平滑地提取出圆形标志的边缘,但受圆形标志的成像情况影响较大,第二种方法边缘提取效果受圆形标志的成像情况影响较小,但提取出的边缘为锯齿形,部分圆形标志的像素点被误判为背景,与圆形标志的实际成像有一定误差。     

Computed three-dimensional reconstruction of median-eminence capillary modules: Image alignment and correlation

Image alignment is an absolute requirement for three-dimensional (3-D) reconstruction from serial sections, and Fourier correlation is the most powerful way to compute alignments. The rotational and translational components of misalignment can be corrected by an iterative correlation procedure, but for images having significant differences, alignment can fail with a likelihood proportional to the extent of the differences. We found that translational correction was determined much more reliably when low-pass filters were applied to the product transforms from which the correlations were calculated. Rotational corrections based on polar analyses of the auto-correlations of the images instead of on the images directly contributed to more accurate alignments. These methods were used to generate 3-D reconstructions of brain capillary modules from serial-section mosaics of digitized transmission electron micrographs.     

对准误差对半球谐振陀螺仪输出精度的影响

通过误差机理分析以及在单轴速率转台上的标定试验,分析了半球谐振陀螺仪的激励器和位移传感器对准误差对输出精度的影响.利用环形谐振子的运动方程,得出了在对准误差的情况下谐振子的径向振动方程.根据半球谐振陀螺仪闭环检测原理,计算了陀螺仪输出角速率的误差.计算结果表明,对准误差将产生与角速率平方项有关的误差,导致陀螺仪输出非线性.在单轴速率转台上进行了标定试验,验证了输出中存在与速率平方项有关的误差,并针对克服此项误差进行了一些探讨.     

Wear behavior of chromium nitride coating in dry condition at lower sliding velocity and load

Quantitative information about the contributions of individual cutting phenomena to linear roughness profiles may aid in optimizing processes with fewer expensive successive trial parts. Linear roughness profiles of metallic hard turned parts contain feed marks, each mark representing a snapshot in time of the state of the cut. This suggests that roughness measuring machines may be an attractive avenue for offline, inexpensive, non-destructive, quantitative evaluation of the time-dependent mechanisms active during the cut. Principal component analysis of feed marks reveals theoretically expected feed mark deformations without coercing the data by fitting. Novel in this paper, we show that those components of feed mark variability appear to correspond to radial and axial displacement of the cutting tool, ploughing, and side flow. Those components are sufficient to explain nearly all the variability between feed marks. The components are easily idealized in a general manner, and their influences on experimental profiles are quantified as percentage contributions to ordinary roughness parameters.     

Computational parametric analysis and experimental investigations of a compact flexure-based microgripper

This paper presents a flexure-based piezoelectric actuated microgripper for high precision grasping/releasing tasks. The design of the microgripper consists of a three-stage amplification and transmission mechanism, and the parallel grasping technique. A bridge-type mechanism and two sequential lever-type mechanisms are symmetrically connected to amplify the output displacement of the embedded piezoelectric actuator. The parallelogram mechanisms assist in linearizing the output displacement of both jaws of the microgripper. The computational analysis is conducted to investigate the effect of the dimensional parameters on the characteristics of the microgripper. A computational parametric optimization methodology is established to achieve the required attributes of the microgripper. The design optimization resulted in a compact design, a high displacement amplification ratio, and a large output displacement of the microgripper. The experimental studies are conducted to investigate the key characteristics of the microgripper such as the displacement amplification ratio, the output displacement, tracking performance. Further, the parasitic motion, input-end and output-end motion resolution of the microgripper are identified. The experimental results indicate that the compact microgripper can achieve a high displacement amplification ratio and large output displacement with a high positioning accuracy.     

Multichannel (e,2e) apparatus

We describe an apparatus for the coincident observation of both outgoing electrons in an electron impact ionization, or (e,2e), experiment. The device employs ten detectors arranged such that every pair corresponds to a different set of momenta for the outgoing electrons intercepted by that pair. By simultaneously monitoring the output from all ten detectors it is possible to perform 25 simultaneous (e,2e) experiments. The results of these experiments can be compared without considering temporal variations of source conditions.     

Characterization of nanoscale recording mark on Ge2Sb2Te5 film

We have fabricated nanoscale recording marks on Ge(2)Sb(2)Te(5) (GST) films with conductive atomic force microscope (AFM). GST films were deposited on glass or polyimide film with thickness of 150-200nm by the rf-sputtering method. Through current-voltage (I-V) spectroscopy, good cantilevers for fabrication and characterization of nanoscale marks on GST were selected. A fresh and highly conductive tip showed voltage-switching characteristic in the I-V curve, where the threshold voltage was approximately 1.6V. Nanoscale dot and wire arrays of crystalline phases were successfully obtained by varying sample bias voltage from -10 to 10V. With highly conductive tips, nanowires having full-width at half-maximum of approximately 20nm could be fabricated, whereas nanowires could not be fabricated with bias voltage below -2V. The width of the nanoscale mark was increased by repetition of AFM lithography even with same applied voltage and lithography speed. For a thicker nanowire, the width measured in current-image (C-image) was observed to be approximately 2 times of that measured in topography-image (T-image). This result supports that current sensing provides an image of phase-changed GST area with higher resolution than topography sensing.     

光学拼接镜面微位移主动调节机构的设计和实测

设计和制造了一套微位移主动调节机构和支撑系统,用以实现拼接镜面天文光学望远镜的每块平面子镜精密地调节倾斜和轴向平移,并在典型的仰角工况下对该机构进行了实测。设计技术要求子镜主动调节行程须达±1 mm,同时分辨率须达50 nm以下。选用了工作行程为6 mm和分辨率为50 nm的位移促动器,并引入杠杆机构提高位移分辨率和抑制误差;采用平衡配重和预拉弹簧机构使工作中位移促动器上保持恒定负载,以保护位移促动器和保证其输出位移精度。依据拼接镜面的工作原理,建立了子镜微位移调节系统性能测试的数学模型,并在实验室内采用分辨率为5 nm的位移传感器进行了实测。结果表明其位移分辨率可达12 nm,线性良好,与理论值相对误差为5.6%,验证了该机构设计的合理性和在不同工作位置良好的灵敏度。     

出刃高度差对金刚石有序排布工具的影响

采用单颗粒金刚石沿不同的切削路径(不同间距切痕或重叠切痕)与不同切削深度的组合形式进行了平面划擦广西白大理石的试验。分析了两种切削路径下出刃高度差对有序排布金刚石工具切削力Fz的影响,结果表明:在不同间距切痕的条件下,当ap1<20μm、L2<200μm时,第二道切痕切削力随着出刃高度差的增大而急剧增大,而当L2>600μm时,出刃高度差的增大却对第二道切痕切削力的影响较小,而当ap1>30μm时,可切削性能随着出刃高度差的增大而变差,但切痕距离越小越有利于切削加工,但影响较小;在重叠切痕条件下,当出刃高度差apx<30μm时,第二道切痕的切削力随着出刃高度差的增大而增大,而当出刃高度差apx>30μm时,却恰恰相反;在两种切削路径下,随着第一道切痕的切削深度ap1的增加,切痕重叠的可加工性能要更优于切痕间距。     

A fibre-optic 3-D microscope with high depth sensitivity

A new fibre-optic microscope with high depth resolution is proposed and experimentally realized. In this microscope, a pair of monomode optical fibre couplers are used to form a six-port all-fibre Michelson interferometer. A lock-in amplifier is used to improve the depth sensitivity and to simplify the optical and electronic circuits. The phase sensing signal is applied to a mirror at one arm of the interferometer. The optimum resolution was about 0?4 nm. The transverse resolution of this microscope is determined by the core diameter of the monomode fibre (9 μm). This 3-D microscope is quite stable to ambient mechanical disturbances, and can be applied to the 3-D microscopy of various biological objects.     

一种基于灰度向量匹配的平面绝对位移测量方法

对于平面位移的测量,传统方法需要采用特殊机构将其分解为两个线性位移和一个角位移分别测量,因而测量系统复杂。随着数字图像处理技术的不断发展,采用该技术进行位移的测量已经成为现代测量技术发展的新方向。本文提出了一种新的基于图像处理的平面位移测量方法。该方法采用事先通过标定的图像,对自然标志（特征点）的提取和基于灰度向量匹配来完成绝对位移的测量。最后经实验验证了该原理的可行性。     

CSP轧机扭振中“伪拍振”的研究

某厂CSP轧机出现了严重的扭振.扭振具有拍振的特征.为摸清轧机振动规律进而解决轧机振动问题.对栽CSP轧机拍振进行了研究.测试分析和理论研究发现这是一种"伪拍振"现象,"伪拍振"的形成是由于工作辊辊面局部区域有振纹存在.振纹区域与轧件接触时,轧机以振纹频率做强迫振动;没有振纹的辊面区域与轧件接触时,因负阻尼作用,系统表现为固有频率下的自激振动.两种振动形式交替出现,且振动强度大小不同,使扭振表现出"拍振"的形态.上述发现对轧机的振动机理及其抑制措施的研究有重要价值.试验证明,据此提出的使用高速钢轧辊等抑制振动措施有很好的效果.     

Automatic identification of feed marks in machined surface roughness profiles by correlating random variations

A new method is detailed to identify the positions of the ends of the tool marks in linear surface roughness profiles. No feed mark shape must be assumed and the process is entirely automated. The approach may find applications in automated quality control, surface texture classification, and modeling of metal cutting processes. Validation was done with 40 finish hard turning specimens. The method relies on the justified hypotheses that a feed mark profile is a superposition of a fixed and a random component, and that the random component has a spatial period equal to one feed mark length. A brief typology of tool mark particularities revealed by the method is presented as well as observations on the correlation of the random events within marks and between marks, both at short and at long range. Feed marks difficult to identify by visual inspection were easily identified with the method and evidence of overlapping tool marks and unstable regions was discovered. The limits of the method are also explored.     

A flexible method for multi-view point clouds alignment of small-size object

Alignment is a key step of the point cloud processing. We propose a flexible, easy-implemented, low-cost alignment method for multi-view point clouds of small-size objects (≦50 cm). The method is based on the idea of rotating measurement, firstly more than three pieces of point clouds of cylinder calibration pattern are used for calibrating the center axis of a single-axis turntable in the scanner’s coordinate system, so the rigid relationship of the turntable and scanner can be obtained. Then the rotation matrix can be calculated using the known angle parameter of the turntable, and finally an arbitrary view of point cloud can be easily transformed into a unified coordinate system by the rotation transformation. Our method does not require overlapping feature or co-markers constraint between point clouds, and only the rigid relationship between the scanner and the turntable and rotate angle need to be known. More importantly, the calibration of the turntable is flexible and low-cost: (1) the calibration pattern can be a common cylinder objects (such as cup, paper tube, caddy, water pipe, etc.), (2) the turntable and the alignment method can be integrated with variety 3-D scanners. The result of experiment has demonstrated the efficiency and automatic characteristic of the alignment method compared with other two convention methods.