Novel SFS-NDT in the field of defect detection

NDT plays a crucial role in everyday life and is necessary to assure safety and reliability. NDT applied to surface detection as far as possible should be a non-contacting technique operating easily with low inspection costs and a high accuracy, human beings as inspectors as well as the environment should not be harmed. A novel NDT based on Shape From Shading (SFS) is introduced in this paper. SFS is a prospecting 3D recovery method because it recovers 3D shape of work piece only from one image. We firstly use SFS in the field of 3D surface defect detection, which is an effective way to guarantee the product quality. Compared with other defect detection method, this SFS method only needs CCD, optical system, image-collection card and computer. It has the merits such as low cost, easy operation, non-contact, non-destructive, no harming to people, and it is 3D overall shape detection. SFS-NDT has been used in the online defect detection measurement of TianJin SanHuan new material Ltd in Chinese Academy of Science. The 3D shape recovery method and application in the field of defect detection are presented. The precision of 3D recovery is analyzed.     

Auto-detection of strip area in 3D measurement

3D measurement is an important task for modern manufacturing, because 2D measurement cannot meet the increasing requirements for quality control in engineering. Among all, 3D recovery methods, by using structural lighting system are the most popular methods because of its non-destructive character. The acquiring of lighting strips, which have to be projected on the object is the most important work to ensure later matching work. In the former research, the position of the stripes in the image was very difficult to locate and must be drawn manually. Therefore, the aim of our research is to find a method to auto-detect the strip area. FFT (fast Fourier transform algorithm) are used to analyze the image character by row and by column. From the FFT result, in the power spectrum the strip area and non-strip area can be distinguished clearly. So the strip area can be marked exactly on the image, and image process algorithm can be used to pick up the strips only on this area. After the matching and 3D recovery algorithm, the 3D shape of the object can be plotted. The auto-detection strip algorithm can save a lot of time for the 3D measurement, automatically complete the 3D recovery procedure, and bring convenience to operators.     

Evaluation of sphericity error from form data using computational geometric techniques

The measurement data for evaluation of sphericity error can be obtained from inspection devices such as form measuring instruments/set-ups. Due to misalignment and size-suppression inherent in these measurements, sphericity data obtained will be distorted. Hence, the sphericity error is evaluated with reference to an assessment feature, referred to as a limacoid. Appropriate methods based on the computational geometry have been developed to establish Minimum Circumscribed, Maximum Inscribed and Minimum Zone Limacoids. The present methods start with the construction of 3-D hulls. A 3-D convex outer hull is established using computational geometric concepts presently available. A heuristic method is followed in this paper to establish a 3-D inner hull. Based on a new concept of 3-D equi-angular line, 3-D farthest or nearest equi-angular diagrams are constructed for establishing the assessment limacoids. Algorithms proposed in the present work are implemented and validated with the simulated data and the data available in the literature.     

3D Fe-Rich Phases Evolution and Its Effects on the Fracture Behavior of Al-7.0Si-1.2Fe Alloys by Mn Neutralization

The evolution of the 3D Fe-rich phases of Al-7.0Si-1.2Fe alloys with different Mn contents was visualized and characterized using synchrotron X-ray computed tomography, and the effect of Fe-rich phases with typical morphologies on the fracture behavior during tensile testing was analyzed. The results showed that the Fe-rich phase changed from platelet-like β-Al₅FeSi into α-Al₁₅(FeMn)₃Si₂ with various morphologies after the addition of Mn. The Mn addition not only significantly reduced the volume fraction, equivalent diameter and interconnectivity of the Fe-rich phase but also greatly increased the sphericity, surface thickness, and distribution of the mean curvature and surface thickness. Furthermore, the equivalent diameter of α-Al₁₅(FeMn)₃Si₂ had an inverse exponential function relationship with its sphericity. The 3D morphology of α-Al₁₅(FeMn)₃Si₂ can be summarized as massive and regular polyhedrons, hollow and regular polyhedrons, and multibranched polyhedrons. The fraction of the different 3D morphologies in each alloy is related to the Mn content, where excess Mn increased the number and volume fraction of the large Fe-rich particles with a low sphericity. The ductility of each alloy was significantly improved by the addition of Mn but gradually decreased when the Mn/Fe ratio exceeded 1.2. The increase in large α-Al₁₅(MnFe)₃Si₂ with a low sphericity was the main reason for the decreased ductility of alloys with a high Mn content.     

New approach in tool wear measuring technique using CCD vision system

This paper suggests a reliable direct measuring procedure for measuring different tool wear parameters. Modern image processing techniques and machine vision systems today enable direct tool wear measurement to be accomplished in-cycle. The presented system is characterized by its measurement flexibility, high spatial resolution and good accuracy. The system consists of a light source to illuminate the tool, CCD camera, laser diod (used in conjunction with profile deepness assessment) with linear projector, grabber for capturing the picture, and a PC. The technique is specially characterized by its determination of profile deepness with the help of projected laser raster lines on a tool surface. So it has advantage comparing with other techniques, which can measure only 2D profiles. With the technique presented in this paper a 3D image of relief surface can be obtained without having need to employ a very complicated measuring system. All indirect methods like acoustic emission, force measurement, spindle current measurement, vibration sensors, etc. are very time consuming and demand very expensive subsidiary measurement equipment, compared with the method presented here.     

Error analysis and in-process compensation on cup wheel grinding of hard sphere

Grinding using cup wheel has been widely used in hard sphere machining process. In conventional sphere grinding (CSG), the linear velocity of the point with the same latitude on the sphere varies, which causes the sphericity error. The misalignment of the machine tool is another source of sphericity error. In this paper, these two types of sphericity errors are analyzed, and an adjustable depth of cut sphere grinding (ADCSG) is proposed to reduce the sphericity error. CSG and ADCSG were carried out on a home-made MD6050 NC precision sphere grinding machine, and the effectiveness of ADCSG is demonstrated with grinding tests. The results showed that ADCSG can reduce the sphericity error effectively compared with CSG. The sphericity error can reach less than 5 μm.     

A novel grating matching method for 3D reconstruction

Automatic 3D surface reconstruction has been an important research topic in digital photogrammetry for many years. Shaping from stereoscopic information is one of the widely studied topics in computer vision. Its central part is to solve the stereo matching problem automatically. Most algorithms used to solve the matching problem can be categorized as either area-base techniques or feature-based techniques. Feature-based techniques have gained more and more popularity for and it is the method that supports activities in object recognition and image understanding. But none of the former research can ensure the 100% matching exactness, thus, cannot complete high precision 3D surface measurement. In order to improve the precision of 3D measurement, we design a novel grating matching method, which can ensure 100% matching accuracy. It does not need any other assistant symbol or flag, only select one of the gratings which have to be projected to the objects. On the beginning of the measurement, the background of the object is captured by a CCD camera. Later gratings include single grating and group gratings will be projected to the object in sequence. All the images include gratings will make a subtraction with the background. The difference of the two images will be treated as 3D cues to acquire the 3D shape. Because no recognizing work is needed, the location of the single grating and each one in the group can be positioned exactly. From a lot of experiments, the proposed grating matching method is proved and it is a technique with high precision, low costs, easy operation, and an automatically matching method. Furthermore, it can be widely used in most of 3D vision recovery systems.     

Pearlite determination in plain carbon steel by eddy current method

Eddy current method has been used for the evaluation of pearlitic microstructure in low to high plain carbon steels. Plain carbon steel samples were heat treated in a furnace. Half of these were slowly cooled in the furnace and half in the air. This resulted in different pearlitic microstructures in the samples. Eddy current readings for all the samples were recorded and studied. It was found that eddy current measurement can be used for obtaining reliable and quick detection of pearlitic percentage in plain carbon steels.     

Reliable tool life measurements in turning — an application to cutting fluid efficiency evaluation

The paper proposes a method to obtain reliable measurements of tool life in turning, discussing some aspects related to experimental procedure and measurement accuracy. The method (i) allows an experimental determination of the extended Taylor's equation, with a limited set of experiments and (ii) provides a basis for the quantification of tool life measurement uncertainty. The procedure was applied to cutting fluid efficiency evaluation. Six cutting oils, five of which formulated from vegetable basestock, were evaluated in turning. Experiments were run in a range of cutting parameters, according to a 2^3–1 factorial design, machining AISI 316L stainless steel with coated carbide tools. Tool life measurements were associated to an estimation of their uncertainty, and it was found that by taking three repetitions the uncertainty calculated with a coverage factor of two was on average three times bigger than the experimental standard deviation.     

基于MCS-51单片机的微电阻测量系统

以MCS-51单片机为核心组成智能型微电阻测量系统。该系统依据四探针法原理，采用高稳定度的恒流源电路，低漂移、低噪声的直流放大器电路和自动量程转换电路构成测量回路。测量回路具有很高的输入阻抗，消除了试样接触电阻的影响，对微小电阻可进行精确的测量。     

基于双蓄能器切换的非对称泵势能回收系统

针对挖掘机动臂在下落过程中单个蓄能器回收势能效率有限的问题,提出一种高低压双蓄能器切换的能量回收策略。基于能量回收原理,利用计算机仿真软件SimulitionX,根据工作装置的三维结构模型建立3D仿真模型和液压系统仿真模型。在此基础上研究挖掘机工作装置姿态对动臂势能回收效率的影响,对不同作业模式下蓄能器不同压力时的动臂伸缩过程进行模拟分析。最后调查统计了某工地挖掘机某段时间内的作业情况,并进行了计算分析。结果表明：挖掘机在该作业情况下,使用3 MPa和5 MPa的高低压双蓄能器回收能量比使用3 MPa的低压蓄能器效率提升29.23%,比使用5 MPa的高压蓄能器效率提升9.06%。     

A practical method to determine rake angles of twist drill by measuring the cutting edge

Rake angle and its distribution on the cutting edge of a twist drill are of vital importance to its performance. This paper presents a practical method to determine the cutting edge and rake angles. Firstly, 3D coordinates of the points on the cutting edge are inspected by using 2D measurement apparatus. Secondly, the flute profile is deduced from the data measured, and the rake angles are evaluated by numerical computation. Conventionally, rake angle calculation is based on a series of plane definitions and laborious work in plane projection is inevitable. To facilitate the process, a vector based procedure is presented. As an example, cutting edge of a standard drill is measured by using tool microscope and image-based instrument. In each case, the normal rake angle distribution is determined. Numerical results exhibit that average error and mean square error of the latter deviated from the former are 0.95^o and 0.33^o, respectively. It verifies the validity of the proposed procedure and the measurement device.     

A new method to quantify radial error of a motorized end-milling cutter/spindle system at very high speed rotations

The radial error motion of a machine tool cutter/spindle system is critical to the dimensional accuracy of the parts to be machined. The spindle's radial error motions can be measured by mounting a sphere target onto the spindle as a reference. A set of sensors is used to measure displacements of the reference sphere in various directions to determine spindle error motions. This measurement technique can be reliably carried out when the spindle is at rest or at low rotational speeds. However, at very high speeds, the reference sphere must be carefully centered and balanced to avoid introducing additional error motions. In addition, the sensors must be held with very rigid mounts in order to avoid measurement errors caused by vibrations. For high-speed end milling spindles, the spindle is operated with a cutter. The cutter must be removed when mounting a reference sphere. Because the cutter itself can introduce errors due to centering and unbalancing effects, the error motions measured by the reference sphere method do not include the error caused by the cutter. This paper introduces a new and practical method to provide an indicator of the radial error of a motorized end-milling cutter/spindle system at very high speed rotations without the need of a reference sphere. This indicator of the radial error is based on the size of the cutting marks produced by the end mill, which is attached to the spindle. The cutting marks are circular, and their diameters are related to the radial error of the cutter/spindle system. Quantitative precision analysis was carried out to confirm the accuracy and repeatability of this new measurement technique. This technique has been implemented in order to determine the effects of the spindle speed, the level of unbalanced mass, and the spindle stiffness on the cutter/spindle's radial error. The results reveal that the centrifugal force generated by the unbalanced mass is the main factor causing the increase in radial error. One way to compensate for the effect of unbalanced mass is to increase the spindle stiffness. Experimental results confirm that a higher front bearing preload can render the spindle stiffer, thus reducing the radial error of the cutter/spindle system. Finally, it should be pointed out that the proposed cutting mark measurement cannot replace the sphere method because it cannot provide time-resolved or angle-resolved information as those obtained from polar charts. However, the proposed cutting mark measurement can provide the characterization of the spindle with the cutter attached. As a result, both methods can complement each other to provide a more complete picture of the behavior of the cutter/spindle system at high speeds.     

立体视觉在航空发动机无损检测中的应用

内窥检测技术在航空发动机故障诊断实际工作中有着广泛的应用。针对传统内窥技术存在的无法定量测量和检测可达性差等弱点，将主体视觉技术与内窥技术相融合，从硬件和软件两方面入手，研制开发出一套新型的基于立体视觉的航空发动机内窥图像分析系统，实现了图像显示、深度测量和三维重建等创新性功能。该系统的开发促进了面向可靠性维修(RCM)的航空发动机无损评价(NDE)技术的发展，对提高发动机故障诊断和预测水平具有显著的意义。     

空间直线基元在双目立体视觉系统中重建方法的研究

在机器视觉的工程实践的很多场合中,以直线基元为基础的三维重建,不但会提高检测系统的效率、有利于实现在线检测,而且能够解决一些特定环境下三维重建的难题。为满足如此需求,对以直线为基元的三维重建进行分析与研究,按照立体视觉的物理意义,推导了直线三维重建的模型,并据此完成了实验系统搭建。实验研究表明,所构建的系统能够实现直线基元的三维重建,并具有较高的精度,可以满足工程实际应用的精度要求。     

维氏硬度试验的测量不确定度评定

利用FW214自动维氏硬度计,通过综合评定法对经校准的459HV10标块进行试验;并对测量结果的影响因素进行了分析,进而评定了维氏硬度试验的测量不确定度。结果表明：该试验室检测方法、检验水平能够满足GB/T 4340.2要求;综合评定法在提高检验效率的同时也能满足试验准确度需求。     

基于非等径双球堆积模型和蒙特卡罗仿真模拟的纳米铜烧结互连机理分析

为了满足第三代半导体低温封装、高温服役的要求,纳米金属颗粒烧结封装互连逐渐替代传统钎料回流焊工艺,而高致密度烧结是实现高可靠性封装的必要条件之一.为了研究纳米铜颗粒烧结互连机理,首先通过非等径双球三维密集堆积模型构建理论颗粒配比与堆积孔隙率之间的关系,然后采用蒙特卡罗仿真模拟不同粒径比的双球模型颗粒烧结过程,最后通过纳...     

五轴数控机床刀座架圆度测量的不确定度评定研究

五轴数控机床刀座架孔的圆度测量具有重要意义,刀座架孔圆度对后续批量化生产起决定性影响。为了更加科学合理地评定五轴数控机床刀座架孔圆度的测量结果,应用三坐标测量机测量五轴数控机床刀座架孔圆度,研究测量结果不确定度的评定方法,提出基于不确定度分量建模和分量综合建模评定方法。对已加工的样品刀座架应用三坐标测量机进行反复测量,获取刀座架圆度测量特征数据,将测量数据结合不确定度评价模型进行计算和评定分析,最后将评定结果与现行规范和标准进行比对和匹配来验证其合理性和正确性。结果表明：该方法评定结果可靠。     

Development of in situ measurement system for welding deformation using digital cameras

Abstract

A three-dimensional (3D) deformation (in plane and out of plane deformations) measurement method is developed using digital cameras, which require no special equipment. This method is a non-contact method, and it can sequentially measure over the entire photographed image. Furthermore, since image analysis is based on the technique of image matching, the method is applicable even when the deformation to be measured is large. In addition, since it is possible to use all pixels as measuring points, the number of available measuring points at one time is the same as the number of effective pixels of the camera. In this study, the proposed method is applied to the sequential measurement of displacement under strong lighting levels in arc welding. Through the comparison of the results measured by a 3D shape measurement system (LAT-3D) using a laser displacement gauge and digital caliper, the quantitative validity of the proposed method is also verified.     

基于图像三维重建的退役零件表面失效特征表征方法

退役零件的失效程度是判断其可再制造性的关键因素之一,为克服失效程度难以快速精确量化的问题,提出一种基于图像三维重建的退役零件失效特征表征方法。针对失效特征重建精度要求高的特点,在由运动恢复形状(Shape from motion,SFM)算法的基础上提出一种自标定全局SFM三维点云重建算法,利用光束平差法优化相机焦距、径向畸变参数,实现了相机自标定,增加了全局SFM算法的鲁棒性;以重建有效三维点数量占比、点云完整度和相机位姿准确度为评价指标,构建了重建精度评价模型,实现了图像三维重建精度的量化评价;提出了退役零件表面失效特征量化方法和实施流程,并定义了失效特征信息计算公式;最后,以电梯导靴为例,对其表面磨损失效特征进行了量化表征。试验结果表明,该方法可以有效地用于毫米级及以上的退役零件表面失效特征的快速量化表征。