动态傅里叶变换轮廓术实现路面形变快速检测

公路表面的三维结构对于判断公路路面破损状况具有重要的意义。基于光栅投影的傅里叶变换轮廓术将物体的高度信息编码在投影到待测物面上的正弦条纹的形变信息中,可以实现对物体的垂直测量。探讨了傅里叶变换轮廓术在高速公路路面面形测量-动态实时系统中的应用,提出了利用自适应标准模版匹配,基于特征图像识别的方法,分选破损的公路路面,从而实现对高速公路路面形变的快速实时检测。     

叶片型面数控加工精度与测量误差分析

五坐标数控加工中心在航空发动机叶片生产现场的大量应用,使叶片型面误差得到有效控制,同时,也对叶片型面测量方法提出了更高要求,本文从分析、计算五坐标数控加工叶片型面误差入手,论述生产现场使用叶片样板和测具测量型面误差时存在的问题。     

基于傅里叶变换的点衍射干涉术

在相移算法的点衍射干涉术的基础上,提出了基于傅里叶变换的点衍射干涉测量术.基于傅里叶变换的点衍射干涉测量术是一种建立在点光源衍射干涉理论基础上的测量方法,它采用傅里叶条纹分析方法来求解干涉条纹的相位分布,运用基于BFGS的拟牛顿算法进行三坐标的迭代计算,确定点光源的三维空间坐标.通过计算机模拟实验,验证了该方法在有噪声干扰的情况下,可以有效降低干扰噪声对测量的影响.     

白光光学测头测量发动机叶片型面技术分析

为解决接触式三坐标测量机检测航空发动机叶片效率低下的问题,探索更加高效、准确的检测手段,采用白光光学测头对航空发动机叶片型面进行测量对比实验,对各截面的叶型轮廓度参数进行评价,得出测量结果。分析各种误差因素对测量结果的影响,对白光光学测头检测叶片叶型轮廓度的测量不确定度进行评定。与此同时,将同一叶片的白光光学测头测量结果与接触式三坐标测量机测量结果进行对比分析,验证白光光学测头应用于航空发动机叶片型面检测中的准确性。实验结果表明白光光学测头测量航空发动机叶片型面既能保证叶片型面测量精度,又能提高叶片测量工作效率。     

双频光栅用于动态过程破裂表面的三维重建

针对在冲击炮轰等快变化过程的傅里叶变换轮廓术测量中,CCD的拍摄速度低于物体的运动速度导致对动态条纹的时间采样不足,提出了采用双频正弦光栅进行测量的三维轮廓术,以傅里叶轮廓术为基础,利用低频光栅条纹图的截断相位做标记条纹,跟踪锁定高频光栅条纹图的同一级次条纹,利用高频光栅的变形条纹进行动态破裂物体的三维面形重建,有效的解决了在快变化动态过程的三维测量中因时间采样不足和条纹断裂带来的问题,正确的获得了物体的面形分布.计算机模拟实验和对瓷砖破裂过程的实际测量验证了此种方法的正确性.     

傅里叶变换轮廓术测量方法的分析研究

对传统傅里叶变换轮廓术（FTP)、π相移法以及灰度图法测量结果进行对比分析。结果证明,随着被测物体高度梯度的增加,基于灰度图和π相移技术的改进傅里叶变换轮廓术取得了很好效果,特别是在梯度大于3的情况下适合采用π相移法,能更有效地提高傅里叶变换轮廓术的测量精度。     

基于投影光栅的大型三维曲面轮廓测量技术

本文提出一种基于投影光栅的傅里叶变换轮廓法来实现大型三维曲面表面轮廓非接触测量的新方法，并讨论了滤波器的设计和傅里叶变换轮廓法的最大测量范围。最后给出了测量结果。     

傅里叶单元在航空发动机机匣强度振动分析中的应用

基于ANSYS内置的二维傅里叶轴对称单元,研究该单元在具有轴对称特征的航空发动机机匣静强度和振动分析中的应用,通过在傅里叶单元周向展开截面上设置轴向加强筋等措施,使二维傅里叶轴对称单元可以用于处理具有轴对称特征、但局部存在非轴对称属性(如存在轴向安装边)的航空发动机机匣应力、变形沿周向不均匀度和振动问题。研究结果表明:相对于三维实体机匣分析模型,二维傅里叶轴对称单元可以有效降低航空发动机机匣计算规模,并可以获得基于二维传统轴对称机匣分析模型无法得到的机匣变形沿周向的不均匀度和振动分析结果。     

航空发动机叶片加工变形因素分析及控制

航空发动机是一个国家工业实力的重要体现,同时也是科学技术的结晶。做好航空发动机的加工制造对于提升一个国家的航空实力有着极为重要的意义。在航空发动机的制造过程中,叶片是航空发动机中极为重要的一环。航空发动机叶片对于加工精度和叶片的稳定性要求极高,由于航空发动机叶片的曲面较大且对于叶片的型面轮廓精度要求较高,从而使得航空发动机叶片的制造速度和表面加工质量很难达到设计要求。为做好航空发动机叶片的加工,应当在总结分析造成航空发动机叶片加工变形因素的基础上采取相应的控制方法,确保航空发动机叶片的加工效率和加工质量。     

气球快速泄气过程动态面形测量方法

提出一种气球快速泄气过程中动态三维面形的测量方法。用正弦光栅投影到处于快速泄气 过程中的气球表面,使用高帧频CCD获取随时间变化的一系列变形条纹,再采用傅里叶变换轮廓术的方法进行处理,能再现气球快速泄气的整个变化过程。该方法为诸如爆轰、膨胀和萎缩等相关领域的动态过程的研究提供了一种新的方法。     

基于激光点云数据的叶片型面三维重构

在四坐标叶片型面检测基础上,提出基于激光点云数据的叶片型面三维重构方法。激光位移传感器对叶片型面进行多视角扫描采样,快速采集叶片型面海量点云数据。运用由点到线到面的数学建模原理,先基于端点一阶导矢连续法拟合出光顺NURBS曲线,再依据分片能量法构建辅助曲面拟合出光顺NURBS曲面,最后对分片NURBS曲面进行统一描述,构造出精确光滑的叶片型面,实现叶片型面的三维重构。实验结果表明：采用该方法实现对各类叶片复杂型面的三维重构,重构误差均<0.015 mm,能够满足精密零件的测量需求。     

基于线结构光的叶片型面特征检测方法研究

叶片是燃气轮机和航空发动机的核心部件,随着我国两机行业的高速发展,对于叶片在研发、生产和维修等方面全生命周期检测的要求不断提高。光学测量是目前叶片三维形貌高效检测的新手段,但是在测量精度等方面相比传统三坐标测量机仍存在一定局限。该文提出一种基于线结构光的叶片型面特征检测方法,设计开发一套四自由度检测平台,针对基于标定物的平台位姿校准和数据采集方法开展研究,并以某气轮机导向叶片为检测对象进行实验测试。测试数据与精密三坐标测量机实测数据的对比结果表明:型面型线轮廓度偏差在±0.02 mm以内,截面主要特征参数偏差均在±0.018 mm以内,该文面向叶片型面实际检测需求的方法可行。     

Three-dimensional profiling using the Fourier transform method with a hexagonal grating projection

We present three-dimensional profilometry based on triangulation in which a hexagonal pattern is projected on the object. To obtain an accurate result with a one-shot photographic image, the Fourier transform method and method of excess fraction are adopted. The three grating components of the hexagonal pattern are used. For compactness a new pattern projection scheme is introduced. The experimental results show that the constructed optical system works well for measuring the profile of a mannequin with a height resolution of ~ +/- 1 mm.     

Application of modulation measurement profilometry to objects with surface holes

We present a detailed discussion of how modulation measurement profilometry (MMP) is applied to measuring an object that has holes on its surface. MMP is not based on the conventional three-dimensional profilometry method with structured light triangulation but on modulation measurements; it has the advantage of measuring the surface of a test object by perpendicular projection, that is, the direction of the CCD camera is the same as that of the projecting light, and the wrapped phases need not be calculated. Thus the difficulties from shadows and spatial discontinuities in phase measurement profilometry and Fourier transform profilometry methods do not exist in MMP. Here we measure a wheellike object that is 31.5 mm thick with an outer diameter of 80 mm and an inner diameter of 20 mm. All the object seen with the CCD camera can be measured including the hole. Experimental results prove that this method is useful for three-dimensional profilometry measurement, especially for objects with discontinuous height steps and spatial isolation.     

基于条纹投影的复杂曲面测量技术

如何快速、高精度地测量复杂曲面的三维轮廓是目前的一个热点研究方向。与现有的测量方法相比,条纹投影轮廓测量技术具有非接触测量、测量速度快和重构点云密集等优点,在逆向工程等领域得到了广泛的应用。本文搭建了基于条纹投影轮廓测量技术的复杂曲面测量装置,并且对相位误差标定及补偿、投影仪精确标定、高阶系统模型简化以及有效点云快速识别等条纹投影轮廓测量的关键技术进行了深入地研究。最后使用该装置进行了叶片表面轮廓测量实验,实验结果表明,本文设计装置的测量偏差最大值不超过0.05 mm。     

Handheld pocket-size Fourier transform profilometry using projector-enabled smartphone

ABSTRACT

Surface Fourier transform profilometry (FTP) is a technique used for reconstructing three-dimensional (3-D) surface topography using light. It has been widely used in machine vision for biomedical and biometric automations, providing solutions beyond conventional 2-D imaging. This paper proposes an implementation of the handheld pocket-size FTP for 3-D surface profile imaging using a projector-enabled Samsung Galaxy Beam smartphone. In the implementation, a crossed-optical-axes geometry of the FTP is formed by using a mirror positioned over the phone’s projector via an adjustable tilt mounting bracket. Experimental proof-of-concept of the proposed profilometry is done by implementing conventional and non-phase shifting FTPs with different diffuse test objects. The experimental results obtained by using the non-phase shifting technique are in good agreement with those of the direct contact measurement. Besides having superiority of compactness, the proposed profilometry paves the way for the development of real-time 3-D profiling and printing through internet or Bluetooth interconnection.     

Nonlinear transient dynamic response of a blade subject to a pulsating load in a decaying centrifugal force field

This study is concerned with an analytical solution for the nonlinear transient dynamic response of a rotating blade in a gas turbine engine experiencing dynamic unbalance due to a blade-off scenario leading to rotor unbalance. As a consequence of rotor unbalance, the blade experiences a pulsating load at its tip due to contact with the casing and a decaying centrifugal force field due to the rotor deceleration. The governing equations of motion consider the blade as an elastic Timoshenko beam of varying thickness subject to changing rotational speeds. The analysis takes into account the variation in the thickness of the beam, the coupled axial and lateral displacements of the beam as a result of Coriolis component of acceleration, shear deformation, rotary inertia, and friction resulting from the contact between the blade and the casing. Our findings indicate that the thickness profile of the beam plays a significant role in the transient response. It further reveals that the decaying centrifugal force field leads to a dramatic change in the dynamic response and the resulting forces on the blade.     

Spatial carrier-fringe pattern analysis by means of wavelet transform: wavelet transform profilometry

We present an analysis of a spatial carrier-fringe pattern in three-dimensional (3-D) shape measurement by using the wavelet transform, a tool excelling for its multiresolution in the time- and space-frequency domains. To overcome the limitation of the Fourier transform, we introduce the Gabor wavelet to analyze the phase distributions of the spatial carrier-fringe pattern. The theory of wavelet transform profilometry, an accuracy check by means of a simulation, and an example of 3-D shape measurement are shown.