Reproducing aircraft structural components using laser scanning

In the past few years, laser scanning has become a popular digitising tool for rapidly manufacturing commercial products, moulds and dies, and industrial parts. This popularity can be attributed to continual improvement in the accuracy and reliability of the technology. In this study, the re-engineering and re-manufacturing capabilities of laser scanning systems in aircraft structural components manufacturing are evaluated. The study includes surveying state-of-the-art laser scanning systems; scanning, modelling, and machining a sample aircraft structural component; comparing the duplicated model/part with the original model/part; and estimating savings achieved by laser scanning. The significant findings from this study include the following:Laser scanning technologies have matured to a stage at which they can capture and reproduce volumetric features, such as pockets, slots, steps, irregular cavities, bosses, etc., typically present in aircraft structural components.Laser scanning technologies, through both re-engineering and re-manufacturing approaches, can dramatically reduce the part turnround time and skill levels required to replicate aircraft structural components.     

Path planning of multi-patched freeform surfaces for laser scanning

In this paper, a new method for scanning a complex surface model with multiple patches is proposed. In scanning of freeform-shaped models, it is difficult to generate a measuring plan by human intuition due to the complexity of the part. The developed method calculates the number of scans, scan direction, and scan path for a stripe-type laser scanner. The user can designate the surface patches that need to be scanned. In generating the scan plan, surface information is first extracted from the CAD model automatically. Other information such as, design knowledge, functionality and machine parameters are provided interactively. Based on this information, the original surface model is sampled in the u, v parameter domain and the sampled points are grouped using the view angle of the laser scanner. The scan direction is determined by calculating the global mean vector of the sampled points that belong to a group. The range of the view angle can be varied to enhance the quality of captured point data. The optical scan paths for each scan direction are calculated by projecting the sampled points onto a 2D plane. The optical constraints are also verified to guarantee the generated scan plan.     

Measurements of fillet weld by 3D laser scanning system

The external geometry of a fillet weld affects not only the quality but also the safety of a structure. Two parameters that influence the geometric quality of a fillet weld are the weld size and the weld surface profile. A 3D laser scanning measurement system integrating the techniques of reverse engineering is adopted in this study to provide a more accurate measurement of the weld profile. The section profiles of the external weld geometry along the longitudinal axis of the weld are generated by the measured data set through CAD software. A computer programme based on the AWS Structural Welding Code is used to judge the acceptability of a fillet weld based on the CAD section profile of the weld. The proposed 3D laser scanning system with integrated CAD software can provide a more accurate and efficient method to estimate the geometric quality of a fillet weld .     

Analysis of digitizing errors of a laser scanning system

The digitizing errors of a high-speed 3D laser scanning system are analyzed and characterized in this paper. As the laser scanner is an electro-optical device and based on the principle of optical triangulation, the measurement accuracy is affected by the measured part geometry and its position within the scanning window. Commercial laser scanners are often calibrated in the scanning plane to account for variation of the incident angle of the laser beam. The effects of the scan depth and the projected angle, characterizing the surface normal of the measured part external to the scanning plane, on the measurement accuracy are not considered in the standard calibration process and have been identified by experiments in the present work. Experimental results indicate that the random error of the scanned data is close to the nominal value provided by the manufacturer. The systematic error shows a bilinear relationship with the scan depth and the projected angle and has a maximum value of about 160 μm. The developed empirical model correctly predicts the systematic error with a maximum deviation of only 25 μm.     

A laser sensor with multiple detectors for freeform surface digitization

In this paper, an integrated laser scanning sensor for freeform surface digitization is presented. The sensor consists of a diode laser light source and four position-sensitive device (PSD) detectors. The stand-off distance of the sensor is 180 mm and the measurable range is 90 mm. The Lambert model is applied to calculate the displacement between the sensor and the measured point on the object surface along the optical axis, under the assumption of a diffusive surface. The inclination angle of the measured point from the vertical plane of the laser beam is calculated by mathematical inference. Those data are used in error compensation to improve the system precision. The new design of multiple detectors could increase the measurable angle and could solve the dead-space problem in the single-point laser of triangulation measurement. The computer simulation and actual measurements show that the displacement resolution is around 50 μm, and the system performs well in terms of stability and repeatability. The sensor system could be mounted on the NC machine or on the X–Y platform for freeform surface digitization.     

CR扫描仪激光扫描光学系统的设计

设计了一种适合于计算机X射线扫描仪的新型激光扫描系统,其空间分辨率为10lp/mm。针对常用扫描机构的不足,用五角棱镜和聚焦物镜组成扫描臂取代传统的Fθ镜头,利用成像板的柔韧性实现圆弧形进片,扫描臂同时作为接收器收集激发出的荧光,从而简化系统结构,提高系统性能。利用所设计的光学系统,分析了激光光点大小对分辨率的影响,结果显示光点越小,系统分辨率越高。分析了系统中影响激光光点大小的因素,在高转速条件下对扫描臂进行了有限元仿真,计算了当入射光与五角棱镜入射面不垂直及五角棱镜存在安置误差时,对激光光点大小的影响。结果显示光点直径最大相对变化量为0.07%,表明所设计的激光扫描光学系统具有一定的容差性和实用性。通过实验验证了所研制扫描仪的性能,结果表明图像具有良好的视觉效果,能够满足工业检测要求。     

激光共聚焦扫描显微镜在微机电系统中的应用

在微机电系统中,三维微结构分析是对微加工工艺进行表征的一种重要手段。随着微机电系统研究的深入和产业化的需求,其微结构分析在微机电系统中的重要性日益凸现。激光共聚焦扫描显微镜因其高分辨率、非接触、数据结构分析快等优点,在微结构分析中得到了大量的应用。本文介绍激光共聚焦扫描显微镜的成像原理,重点介绍激光共聚焦显微镜在大角度测量和形貌分析中的应用。同时,与台阶仪、扫描电子显微镜和白光干涉仪相比较,指出激光共聚焦扫描显微镜在微结构分析中的优点和局限性。     

Elasto-geometrical error modeling and compensation of a five-axis parallel machining robot

Parallel manipulators have the potentials of high efficiency and high precision in the field of machining and manufacturing. However, accuracy improvement of the parallel manipulator is still an essential and challenging issue, encountering two important problems. Firstly, the ignorance of elastic deformation caused by gravity or deviations of static stiffness model restricts further improvement of accuracy. To solve this problem, an elasto-geometrical error modeling method is proposed. The comprehensive effects of structural errors, elastic deformation under gravity and compliance parameter errors on pose deviations are disclosed. On this basis, the identification equation of actual structural errors and compliance parameter errors can be established. Secondly, the ill-conditioned identification matrix and the identification equation with anisotropic residual error can lead to inaccurate identification results. To solve this problem, a weighted regularization method is proposed. The identification equation with isotropic residual error is built, and accurate identification can be realized with the regularization method. Based on the proposed methods, the error compensation experiment is conducted on the prototype of a five-axis parallel machining robot using a laser tracker. Experiment results show that the accuracy of the machining robot is significantly improved after compensation. An M1_160 test piece and an S-shaped test piece are machined and measured to further validate the effectiveness of the proposed methods. The elasto-geometrical error modeling method and the weighted regularization method can be applied to other parallel manipulators’ accuracy improvement.     

3D modeling by means of videogrammetry and laser scanners for reverse engineering

The knowledge of the 3D geometry for reverse engineering studies is based on images and/or distances. The use of scanner laser has replaced the photogrammetry in the last decade, due to its easy handling and intensive data provided. However it requires multiple data captures, a subsequent filtering and a complex data processing, and its accuracy is highly dependent on the material. These limitations mean that many times it will not be the best option (in addition to its high cost). The videogrammetry is capable of generating a high number of images (which implies a high number of points) in a shorter time and regardless of the type of material. This paper analyses the accuracy of a new videogrammetric system respect to two scanner lasers. Results obtained certify that videogrammetry reaches similar accuracy than EScan (high resolution portable 3D scanner for reverse engineering), and higher accuracy than architectural scanner laser. In both cases the time spent in the 3D model generation by means of videogrammetry results much lower and the process is completely automatic requiring no post-processing or filtering work. Finally videogrammetry also enables real 3D object visualization through anaglyphs in all desired positions, while laser systems cannot provide that kind of information.     

基于激光测距传感器的机器人末端定位扫描装置设计

为实现变截面复杂管道内壁喷涂机器人的定位、喷涂目标模型重建和喷涂轨迹规划功能,设计了末端激光定位扫描装置,描述了该装置传感器的选型、扫描头机构设计和相应的数学模型,并着重阐述了喷涂管道内截面自动扫描的流程以及测量路径规划算法的实现。实验证明,该设计实现了一类超常规尺寸喷涂目标在喷涂机器人坐标系中的数模重建功能,解决了逐点示教无法完成复杂内表面喷涂轨迹规划的问题。     

An integrated experimental approach to link a laser digitiser, a CAD/CAM system and a rapid prototyping system for biomedical applications

This study is carried out to develop a direct link between a laser digitiser and a rapid prototyping system for biomedical applications. Two CAD/CAM systems, DUCT and Pro-Engineer, are investigated and the DUCT system is found to be more suitable for this purpose. A laser digitiser is used to capture three-dimensional surface data for the object. With the aid of the CAD/CAM system, the data can be manipulated in a number of ways for display, modification and enhancement. In addition, the object scanned by the laser digitiser can be physically produced relatively quickly and accurately using StereoLithography Apparatus (SLA), a leading rapid prototyping system. Feasible and practical solutions to the problems encountered in the CAD surface model construction are proposed and illustrated. Two case studies, a facial and a breast model, are presented. Results show that this integrated approach can be applied effectively in the biomedical field.     

基于532nm半导体激光器的远距离传输高精度准直系统设计

半导体激光器在军事、工业、医学等许多方面有着重要的应用前景,但由于半导体激光器输出光束具有较大的发散角,因而在几乎所有要求较高的应用领域中,其输出光束都必须通过特殊的光学系统进行准直。扩束镜因其结构简单、材料便宜以及加工容易而在半导体激光束准直领域获得较多的应用。     

基于激光莫尔信号精密定位装置的精度提高

为提高基于激光莫尔信号精密装置的定位精度 ,本文探讨了激光束束径与激光莫尔信号的依存关系 ,给出了与光栅衍射缝隙条数相对应的最小激光束束径的大小。其次还说明了激光源的光强度变化对精密定位装置的定位精度影响     

基于Matlab/Simulink的激光圆网雕刻调速系统的建模与仿真

介绍了调速控制系统在Matlab/Simulink中相应的子模块的功能及构造方法.针对激光圆网雕刻对定位精度要求准确和速度变换频繁快速的特点,对激光圆网雕刻机调速控制系统进行结构化和模块化处理,在Matlab/Simulink中建立该调速模型,并对其高/低速瞬时变换的进行仿真.模拟实际调速系统从低密度网点雕刻网辊高速运动变换为高密度网点雕刻网辊低速运行的工况.通过对仿真数据分析,验证了系统具有快速的启动及良好的速度转换特性,抗干扰能力强.仿真模型可以逼真地模拟实际系统,实现简单,便于修改,为激光圆网雕刻调速系统的设计和调试提供了依据.     

Modeling of binocular vision system for 3D reconstruction with improved genetic algorithms

This paper models the binocular vision system focused on 3D reconstruction and describes an improved genetic algorithm (GA) for estimating camera system parameters. The two-camera system model that takes into account camera radial distortion includes a total of 24 parameters. The proposed improved GA is used to solve this nonlinear optimization problem with high dimension. In our improved GA, the adaptive control of camera parameter search interval and the catastrophe strategy with elitist preservation are employed. The experimental results indicate that our improved GA is effective to solve the multi-peak function optimization problem and the 3D reconstruction accuracy of the binocular vision system is promising.     

Validation of terrestrial laser scanning and photogrammetry techniques for the measurement of vertical underclearance and beam geometry in structural inspection of bridges

This research shows a novel methodology based on the application of terrestrial laser scanning and photogrammetry techniques as auxiliary metric tools for bridge inspections procedures. These methodologies are validated throughout a case study where the minimum underclearance and the overall geometry of a prestressed concrete beam are obtained. Data obtained are compared with high accurate measurements provided by a total station. Results show a good agreement for beam geometry with high statistical correlation coefficients. Minimum vertical underclearance also shows a good agreement for all the systems, which appears good enough due the metric tolerances required in these inspection works.     

航空相机扫描镜系统的线性近似模型辨识

为深入认识摩擦对航空相机扫描镜系统频率响应特性的影响,获得更准确描述该系统真实动态的模型,使用随机相位多正弦信号测量了扫描镜系统的频率响应特性并进行了线性近似参数模型辨识.首先,介绍扫描镜系统辨识的实验平台与激励信号选择.然后,使用奇-奇频率随机相位多正弦信号分别测量扫描镜系统在非激励频率处和激励频率处的输出对输入信号幅值的依赖,从而定量评估摩擦非线性的影响.最后,基于信号采样均值及噪声采样方差、协方差估计辨识了扫描镜系统线性近似参数模型.实验结果表明,扫描镜系统的摩擦非线性主要出现在奇频率处,高于噪声10dB;系统的频率响应特性依输入信号幅值不同而各异,在低于20 rad/s频率区该差别尤为显著.由于摩擦非线性影响,扫描镜系统需要使用3阶模型描述;与正弦扫描方法相比,基于多正弦信号激励获得的参数模型可更好地描述扫描镜系统真实动态特性.得到的结果为控制器的设计奠定了基础.     

Closed-loop control of a 2-D mems micromirror with sidewall electrodes for a laser scanning microscope system

This article presents the development and implementation of a robust nonlinear control scheme for a 2-D micromirror-based laser scanning microscope system. The presented control scheme, built around sliding mode control approach and augmented an adaptive algorithm, is proposed to improve the tracking accuracy in presence of cross-axis effect. The closed-loop controlled imaging system is developed through integrating a 2-D micromirror with sidewall electrodes (SW), a laser source, NI field-programmable gate array (FPGA) hardware, the optics, position sensing detector (PSD) and photo detector (PD). The experimental results demonstrated that the proposed scheme is able to achieve accurate tracking of a reference triangular signal. Compared with open-loop control, the scanning performance is significantly improved, and a better 2-D image is obtained using the micromirror with the proposed scheme.     

基金会现场总线系统的验证计算与应用分析

简要概述了基金会现场总线的技术特点,重点介绍了基金会现场总线控制系统的整体结构、设计过程以及系统网段内仪表数量与电缆长度的具体验证计算方法。通过与海洋石油平台传统的集散式控制系统对比,结合在海洋石油领域的实际工程案例探讨了基金会现场总线技术的优势和应用前景。     

光机二维扫描技术在激光共聚焦生物芯片扫描仪中的应用

介绍了应用于激光共聚焦生物芯片扫描仪中的光机二维扫描技术 ,即用振镜和f- θ扫描物镜构成其中一维的光扫描系统 ,用步进电机驱动扫描工作台移动构成另一维机械扫描系统 ,并在此基础上分析研究了光机二维扫描控制系统的设计。为快速、高精度激光共聚焦生物芯片扫描仪的研制作了新的有益尝试 ,并取得了初步的实验结果