采用准正弦投影光场的三维面形测量系统

本文提出一种直接由罗奇光栅离焦产生准正弦投影光场,进而采用离散相移技术对观察光场解调,实现三维面形测量的方法。研究了准正弦光场随离焦量的变化规律,离散相移次数与测量精度的关系,建立了一个微型计算机三维面形测量系统,给出了该系统对实物模型的测量结果。     

基于光栅相位法三维重构技术研究

投影光栅相位法（PMP）是一种基于光栅投影和相位测量的光学三维轮廓测量技术,可实现物体表面三维轮廓的自动测量。提出了结合投影仪移轴技术的平行光轴系统,利用计算机编程生成具有高对比度和高亮度、有相差的正弦光栅,用数字投影仪LCD将这些条纹依次投射到被测物体表面,由CCD摄像机获取受物体表面面形调制的变形光栅像,根据数字相移算法计算出相位分布再通过相位展开恢复出连续相位分布,由相位．高度关系最终求出物体轮廓的三维数据信息。针对该原理进行了阐述,并给出了详尽的算法及实验结果。通过MATLAB实验仿真,对条纹图像进行处理和轮廓重构。模拟实验证明,这种测量方法快速高效、分辨率高,且易于实现。     

基于双频彩色光栅投影测量不连续物体三维形貌

为减少多频条纹相移法进行三维形貌测量时的投影条纹数量,提高测量速度, 提出了采用双频四步相移彩色条纹投影技术来准确测量具有台阶状不连续或孤立物体表面三维形貌的方法。利用计算机将高低两种不同频率的正弦条纹分别输入彩色图像的红色和蓝色通道合成为彩色条纹,由数字视频投影仪将四步相移彩色条纹投影到被测物体,然后利用彩色CCD或CMOS相机采集4幅彩色条纹图并存储于计算机中。基于色彩分离技术得到8幅两种不同频率的四步相移条纹图并由图像灰度算法获得1幅反映背景的灰度图像;由低频条纹确定台阶状的物体边缘,高频条纹计算物体的形貌,并通过背景图像的二值化定位阴影和不连续区域。提出的方法仅用4幅彩色图像完成了台阶状不连续或孤立物体三维形貌的准确测量。与现有的多频4步相移条纹投影形貌测量技术需要8~12幅图像相比,该方法有效地减少了条纹投影与图像采集的数量。     

单摄像机结构光扫描系统中投影仪标定技术

传统的单摄像机、单投影仪三维扫描系统,利用相位值计算被测物体的高度信息,可操作性差,且测量精度不高.将立体视觉的三维重构技术引入到单摄像机、单投影仪扫描系统,利用相位值实现投影仪与摄像机的匹配,根据双目视觉的原理进行三维重构,测量精度明显提高.该技术的关键是投影仪的定标,研究了基于相位匹配技术的投影仪标定算法,实验结果验证了该算法的可行性.     

大尺度钢板的三维测量和拼接

提出了基于投影的三维测量拼接方法,用于测量大尺度钢板表面的三维形状。首先,利用光学扫描仪、背景投影仪两种装置实现大尺度钢板的三维测量。其中,三维光学扫描仪负责测量大尺度钢板不同部分的三维数据,背景投影仪用于向被测钢板投射背景纹理;然后,利用基于随机抽样一致性算法(RANSAC)的拼接算法,将不同时刻测量的局部三维数据进行拼接,得到完整的钢板三维数据;最后,提出了一种拼接误差的评价方式来检验拼接精度。实验结果表明:所提方法的单次拼接精度为0.5mm左右;测量一个7.5m长的钢板,其累计拼接误差为2mm左右。得到的结果基本满足船舶外板加工的精度要求,具有较高的实用价值。     

基于多频外差原理的三维测量技术

提出了一种基于外差原理的三维测量技术,该技术由相位移法、外差原理和双目立体视觉3部分组成。相位移法和外差原理相结合能够自动完成相位展开,同时保持相移法原有的相位求解精度;然后根据相位展开后的相位图,使用双目立体视觉原理自动完成左、右对应点的立体匹配和被测物体的点云重构。利用基于多频外差原理的三维测量技术建立了一套三维测量系统,该系统由2个CCD摄像机和1个DLP投影仪组成。利用上述系统对人脸模型进行测量试验,测量结果表明该系统能够完成复杂自由曲面的测量,测量数据完整可靠。     

基于DLP技术的刀具刃口检测系统

硬质合金刀具刃口是影响精密加工表面质量以及表面微观几何形貌的重要因素。针对目前测量过程中出现的问题,提出利用DLP技术来测量刀具刃口的三维形貌。其原理是用计算机产生正弦投影条纹,经数字投影仪投射到物体表面,条纹经物体表面调制产生变形,用CCD摄像机将变形条纹拍摄下来。再利用计算机进行相位场提取、相位去包裹,得到绝对相位值。最后经系统标定、坐标变换可得物体表面的三维数据基于数字条纹投射的光学3D传感器,这样能够很好很快地提取刀具刃口的三维形貌。     

基于光栅投射的光学三维测量仪的研制

利用商用数字LCD投影仪和数字CCD摄像机构成一套基于光栅投射的光学三维测量系统,介绍系统的测量原理、硬件结构和软件系统,最后给出该系统的一些测量结果。     

用投影散斑法测量三维微位移

采用光学非接触法测量三维微位移,基于三角测量法投影数字散斑照射参考面和待测物体表面,利用数字散斑相关法原理,求解变形位移信息,实验结果表明,数字散斑相关技术在三维变形测量的有效性和可靠性,并且为三维物体形变的测量提供了新的研究思路。     

基于光栅投影的工件表面缺陷检测方法研究

针对工件厚度与表面缺陷检测精度不足的问题,提出一种基于双投影的光栅投影缺陷检测方法。采用CCD相机采集两个方向上投影到工件表面的云纹图像,利用相移法求解两个方向的云纹图像相位,将两个方向的重建三维轮廓进行融合,实现工件表面缺陷的检测。试验结果证明:工件的厚度测量精度为0.05mm,缺陷测量精度提高到0.1mm。     

基于彩色条纹投影术的三维形貌测量

物体表面三维形貌数据的获取在智能制造、航空航天、文物保护、医疗卫生、远程教育等领域有着广泛的应用。三维形貌数据的获取受限于系统硬件的性能,特别是现有数字投影系统的投影速度,无法快速测得物体面形的三维形貌。彩色成像和投影系统的出现,为并行多颜色通道三维成像系统提供了新的研究方向。详细综述了基于彩色条纹投影术的三维形貌数据测量研究的现状。具体包括彩色条纹投影术的基本原理、彩色条纹调制和解调相关技术、三维成像系统的标定、以及未来的研究方向。接着给出几个利用彩色条纹投影术获取物体表面三维形貌和彩色纹理的实例。为彩色条纹投影术测量物体表面三维形貌数据提供了详尽的综述,并指明了未来潜在的研究新方向。     

一种基于相移技术的物体表面三维轮廓测量方法

提出一种将阴影莫尔条纹法与相位测量技术相结合的物体表面三维轮廓测量方法 ,该方法利用电磁铁和精密机械部件对光栅进行定位控制以实现精确相移 ,并采用三步相移技术对CCD摄像机采集的物体表面形貌莫尔条纹进行相位解调 ,可有效实现物体表面三维轮廓的高速、高精度自动测量。     

Research and development of an accurate 3D shape measurement system based on fringe projection: Model analysis and performance evaluation

In this paper, the research and development of an accurate 3D shape measurement system based on fringe projection is presented. This system utilizes a sliding projection unit to project the desired encoding fringe patterns onto the object and the object shape can be obtained by analyzing the images captured with a camera for each projection. The sliding projection unit uses a high precision grating element fabricated by electron beam lithography to produce the accurate encoding fringe patterns thus to reduce the projection error. And a method based on gray-code and phase-period edge detection is developed to align the grating element with its sliding direction to guarantee the alignment between the projected patterns. The influence of the lens distortion of both the projection unit and the camera is also studied and an improved nonlinear system model is developed based on triangulation. This model gives a more accurate mathematical representation of the shape measurement system and thus improves the system measurement accuracy. The experimental results show that an overall measurement error of 0.04 mm with a variability of ±0.035 mm can be obtained for the developed system.     

基于TI DLP技术的投影机驱动电路设计和实现

DLP是由美国德州仪器公司研制的一种全数字投影技术,在投影机上已经得到广泛的应用。但是,面对LCD和LCOS投影机的竞争,如何在保持投影机的良好性能基础上尽可能地降低成本,成为每个DLP投影机生产厂商必须考虑的问题。设计了以TIDDP2230芯片为核心的DLP投影机驱动电路,利用了“极致色彩”技术实现完美的投影效果。该电路性能优良,具有设计简单、功能强大、成本低等优点;有极高的应用价值和市场前景。     

Demonstration of a tunable two-frequency projected fringe pattern with acousto-optic deflectors

We report on a fringe projector for three-dimensional shape measurement. The developed instrument is able to project a two-frequency fringe pattern, each frequency is independently controlled by electronics. Moreover, each phase of the two fringe patterns is also independently adjusted. The projection system is based on the use of a pair of custom large bandwidth (40 MHz) and high efficiency (60%) TeO2 deflectors. The developed instrument offers the combined advantages of a static two-frequency fringe projector and of a tunable single frequency fringe projector.     

A low cost 3D shape measurement method based on a strip shifting pattern

We present a simple, low cost but fast 3D shape measurement method. There is no limitation on the object's material and texture. We use a projector to project a strip shifting pattern on the object, and a digital camera to record videos of the scene. The distortion of the strip shadow on the object is used to get the object's 3D information. A novel space-time edge finding method is introduced to position the shadow edge accurately. This edge finding method overcomes the effect of inter-reflection and high light. Using this space-time information, we can calculate the pixels' 3D coordinates. To get the 3D shape of an object with black texture, we improve the black strip pattern to a 3-color strip pattern. The bad data are filtered by a post-processing 3D filter, which makes full use of the neighborhoods' geometric constraints and the view point constraint. Meanwhile, our measurement method is fast, regardless of the complexity of the shape.     

A New Method of Non-Contact Measurement for Microtopography in Semiconductor Wafer Implementing a New Optical Probe Based on the Precision Defocus Measurement

In this paper, a new method of non-contact measurement has been developed for 3D topography for a semiconductor wafer, implementing a new optical probe based on precision defocus measurement. The developed technique consists of the new optical probe, precision stages, and the measurement/control system. The basic principle of the technique is to use the reflected slit beam from the specimen surface to measure the deviation of the specimen surface. The defocusing distance can be measured by the reflected slit beam, where the defocused image is measured by the proposed optical probe, giving very high resolution. A distance measuring formula has been proposed for the developed probe, using the laws of geometric optics. A precision calibration technique has been applied, giving about 10 nm resolution and 72 nm four-sigma uncertainty. In order to quantitise the micro pattern on the specimen surface, some efficient analysis algorithms have been developed to analyse the 3D topography pattern and some parameters of the surface. The developed system has been successfully applied to measure the wafer surface, demonstrating the line scanning feature and the excellent 3D measurement capability.     

Development of a dynamic surface shape measurement for magnetic fluid

Traditional measurement techniques such as fringe and stereo projection can hardly measure the black surface shape of magnetic liquid in revolving container which has a cover to prevent the liquid spilling out. To solve this problem, a multi-step measurement method based on linear laser projection is proposed. Modulated laser by synchronous revolving chopper is introduced to obtain the steady projection light curve on the measured location of the magnetic fluid surface. In order to capture the instantaneous reflected light of the projection light curve, a camera used a long exposure time of shooting is used. Taking the advantages of multiple exposure luminance enhancement effect of long exposure time, pictures with high brightness and contrast projection light are obtained. The overall surface shape of the fluid can be reconstructed by many laser projection lines extracted from the pictures captured at different angles of revolving container. A high transparency acrylic cover is adopted to provide good sealing performance and light transmission quality in the experiment. On the base of correction of influence of refractive index of the acrylic cover, the height formula of magnetic fluid surface is derived. The camera installation angle and distance between the camera and the container are not required as the size of container are utilized to calibrate the camera. The relationship between image coordinates and world coordinates is also obtained. According to the height curves of the projection lines and their measuring angles on the container, 3-D surface shape of magnetic fluid is reconstructed. The surface shape is verified indirectly by using the imbalance of the container, and the relative unbalance errors between the measurement results and the results by Shenk dynamic balancing machine under different conditions are between 0.8% and 11%. Another performance experiment on measuring the surface shape of an rubber block indicates that the measurement range of the proposed method is that the slope of the measured surface must be less than 3.94, and the sensitivity is 0.18 mm. All performance of the proposed method is acceptable, so such a complex industrial problem is solved only by a daily digital camera.