天文定位中倾角传感器的标定

为提高天文定位系统的定位精度,减小倾角传感器安装误差对系统水平测量精度的影响,对系统中倾角传感器的安装参数标定及校正进行了研究.首先,给出基于倾角传感器的天文定位系统工作原理,分析倾角传感器安装过程中存在的误差源.然后,提出一种通过对天文定位系统进行改造,利用系统自身完成倾角传感器安装参数标定的方法,并给出了倾角测量数据的校正算法.最后,建立三视场天文定位系统仿真测试平台,对标定方法的性能进行了分析和验证.实验结果表明:该倾角传感器安装参数标定方法的标定精度与倾角传感器自身测量精度保持一致,在全量程范围内校正后的倾角测量结果最大误差为4.315 5″,基本满足天文定位系统中高精度倾角测量要求.     

三维形貌柔性测量系统标定方法及验证

为了避免机器人模型误差对三维形貌柔性测量系统手眼标定的影响,对手眼关系的标定方法进行了研究。提出了一种融合特征点拟合的手眼标定方法。将三维形貌扫描仪安装在工业机器人末端搭建三维形貌柔性测量系统。标定时,首先利用激光跟踪仪对工业机器人末端法兰盘坐标系进行测量,得到两者转换关系;然后,利用三维形貌扫描仪和激光跟踪仪对空间固定的特征点组进行测量,利用特征点约束和基于罗德里格矩阵的算法求解两者转换关系即可间接地求解出手眼关系。基于ATOS三维扫描仪、安川HP20D机器人和API公司生产的激光跟踪仪进行了手眼标定实验,并进行了精度验证。结果表明:标定后的三维形貌柔性测量系统,其重复性测量精度(3σ)不超过0.1 mm,长度测量精度的均方根误差在0.2 mm以内,点云拼接精度优于±0.7 mm。该方法有效避免了传统手眼标定过程中会引入机器人模型误差的问题,在求解手眼关系解时采用了线性的解法,并且适用于三维形貌柔性测量系统。     

基于物体特征有效提取和离散点三维重建的3D扫描系统原型研究

针对3D扫描技术的近期发展情况,以及市场关于被摄物体特征有效提取的迫切需求,通过系统的对照相机和投影仪测量的方法与计算,利用离散点三维重建算法、标准化算法详细分析了,作为3D扫描原型系统的关键技术,并深入的对三维坐标重复演算的过程,进行了实践研究与计算,论证了基于投影光编码技术的3D扫描仪原型系统,在物体特征有效提取和离散点三维重建中完全可以高效应用;同时,使用焦距标准化运算、逆向倾角变形运算、逆向扭曲变形运算三种方法,综合论述了物体特征有效提取和离散点三维重建过程的相关内容,测试了原型系统对真实文物的扫描情况,展开了该原型系统可应用于不同材料,不同种类物体的扫描,并能有效的进行数字化物体特征识别的研究结论。     

基于三线结构光的相机平面标定方法研究

相机标定技术是结构光三维视觉测量的关键技术之一,结构光系统的相机标定的精度对三维测量的精度有很大影响。首先对三线结构光系统图的相机标定方法进行了分析,简单介绍了工业相机成像的几何模型及标定的原理;其次利用Harris角点检测方法提取特征点坐标,并选用了BP神经网络来校正工业相机的畸变模型,以提高标定算法的优化速度和标定精度;最后采用张正友的平面标定法对校正后的摄像机模型进行标定实验,由实验结果知,该方法具有一定的准确性和有效性,在一定误差范围内,基于神经网络畸变校正的张正友相机标定能够有效提高视觉检测的精度。     

一种双目立体视觉系统的误差分析方法

基于摄像机透视成像的针孔模型,分析了立体视觉中摄像机标定和三维重建过程的主要误差来源。基于各主要误差源的模型分析,建立了双目视觉系统3D测量误差与摄像机参数、基线长度、测量距离等因素之间的关系式。如已知相关参数,可以估算出双目视觉系统的3D测量精度,或根据3D测量精度要求,初步确定摄像机的内部各项参数和基线长度、测量距离等参数。     

长程轮廓仪用于筒状超光滑表面测量的误差分析及校正

为了提高使用长程轮廓仪对筒状超光滑非球面进行面型测量的精度,研究并总结了测量过程中常见的误差源及校正方法.针对测量过程中对结果影响较大的转台转轴与待测筒状镜光轴之间的倾斜和偏心误差做了详细的分析,提出利用数据处理校正这部分误差的方法.编写了相应的数据处理程序,通过数值模拟实验对该程序进行了验证.实验结果表明,该程序能够...     

基于线定标光的内窥镜图像垂直倾斜校正方法

内窥镜图像测量中为了保证测量精度,理论上要求成像系统的光轴与物平面保持垂直,而实际测量过程中光轴与物平面一般存在一定程度的垂直倾斜。针对垂直倾斜对内窥镜图像测量的影响,提出了一种基于内窥镜发射的线定标光的垂直倾斜校正方法。该方法从线定标光的位置信息中提取光轴倾斜信息,并对图像进行校正。实验结果表明,所提出的图像垂直倾斜校正方法能对内窥镜图像进行准确校正。     

基于图像自标定的3D打印模型高效生成方法

为了克服三维重建高度依赖标定板,满足3D打印模型的工业需求,提出基于图像自标定的高效3D打印模型生成方法,无需借助标定板计算相机参数,直接使用单相机采集序列图像进行三维重建。为了克服基于自标定方法易受图像质量和特征点匹配精确度的影响,根据人机交互与自适应分割算法相结合的方法去除原始图像背景及过滤噪声,使图像感兴趣区域特征更为明显,采用快速稳定特征算法提取序列图像中特征点并根据特征点的匹配度进行精确的特征点匹配,再使用匹配信息自标定求解得到相机模型参数,最后根据相机模型以及特征点信息完成三维目标的稠密重建。实验结果表明,自标定及重建方法对大小各异,表面材质不同的目标均可实现重建。     

条纹投影三维测量的Gamma畸变校正方法

Gamma畸变是影响条纹投影三维测量精度的重要因素,为提高条纹投影系统的测量精度,通过分析Gamma值与谐波系数的定量关系研究了一种准确、简便的Gamma系数预标定技术。在仿真实验中,通过该方法将Gamma校正前后的相位平面与标准相位平面之间的误差降低了一个数量级,提高了测量精度。搭建了条纹投影实验系统,对人嘴雕像进行三维重建,并对Gamma畸变校正前后的测量结果进行了对比分析,验证了该方法的有效性。     

卡塞格林系统装调过程中高精度测角方法

为了能够准确测量同轴三反相机中次镜的倾斜量变化,提出一种新的角度测量方法,即用大口径干涉仪与经纬仪相结合进行测量。以主镜为测量基准,两镜相对倾角较小时,使用大口径干涉仪同时测量两镜的干涉条纹,相对倾斜角度过大时次镜无干涉条纹,加入一台经纬仪分别自准直于干涉仪和次镜,间接测量两镜相对夹角。通过模拟计算与实验验证表明,对于次镜组件倾角测量误差可以控制在0.5″以内。结果表明,该检测方法具有通用性强,测量精度高等特点,克服了传统检测方法测量精度不足的问题。     

Measurement of tilt of a diffuse object by double-exposure speckle photography using speckle fanning in a photorefractive BaTiO3 crystal

A technique has been proposed for the measurement of tilt of a diffuse object using speckle fanning in a photorefractive BaTiO₃ crystal. Free space geometry has been used for recording in which the axis of rotation of the object lies away in three-dimensional space. The method is based on recording of two exposures, one before- and another after the tilt, thus producing speckle correlation fringes due to overlapping of two speckle fans. We consider a generalized case of tilt, generating curved fringes with center shifted in the transverse direction. The axis of rotation lies perpendicular to the optical axis in three-dimensional space having the transverse and axial components of the shift in the center of rotation with respect to the diffuser plane. Fourier transform of the curved fringes produces correlation output. Measure of separation between the correlation peaks in transverse and axial directions provides information about the tilt angle, the direction of tilt, and the distance of rotation axis from the optical axis. Experimental results have been presented to validate the theoretical predictions.     

补强片自动贴片系统高精度手眼标定方法

针对补强片自动贴片系统的手眼标定问题,为了消除相机安装的垂直度偏差带来的误差,提出了一种新的手眼标定方法。使用标定板得到相机的外参数,将外参数与常规的二维标定模型相结合,从而间接计算出相机坐标系与机器人基础坐标系的齐次坐标转换矩阵,使手眼标定模型扩展为三维。三维模型的标定计算误差小于0.1 m,相比二维模型降低了1个数量级,有效提高了标定计算精度。利用厚度较小的菲林修正齐次坐标变换矩阵的Z方向分量,系统具有较高的定位精度,手眼标定的误差绝对值小于0.015 mm,有效减小了误差均值,设备性能得到大幅提高。该方法在系统可控自由度有限的情况下,能够得到手眼标定问题的唯一解,提出的三维模型中包括了相机的完整姿态信息,相比常规的标定方法没有相机安装等额外的限制条件,能有效提高系统的手眼标定精度。     

Characteristics of Friedel pairs and diffraction contrast tomography with non‐perpendicular rotation axis

The characteristics of Friedel pairs in diffraction contrast tomography (DCT) are studied in the condition that the rotation axis of the sample is not exactly perpendicular to the incident X‐ray direction. For the rotation axis approximately aligned along the vertical direction, the Friedel pairs close to the horizontal plane are insensitive to the non‐perpendicularity of the rotation axis, and can be used to refine the sample‐to‐detector distance and X‐ray energy, while the Friedel pairs close to the vertical direction are sensitive to the non‐perpendicularity of the rotation axis, and can be used to determine the rotation axis orientation. The correct matching proportion of Friedel pairs decreases with increasing non‐perpendicularity of the rotation axis. A method of data processing considering rotation axis misalignment is proposed, which significantly increases the correct matching and indexing proportions of the diffraction spots. A pure aluminium polycrystalline sample is investigated using DCT at beamline 4W1A of Beijing Synchrotron Radiation Facility. Based on the analysis of Friedel pairs, the sample‐to‐detector distance and X‐ray energy are refined to be 8.67 mm and 20.04 keV, respectively. The non‐perpendicular angle of the rotation axis is calculated to be 0.10°. With these refined geometric parameters, the matching proportion of the spatial position of diffraction spots is 90.62%. Three‐dimensional reconstruction of the sample with 13 grains is realised using the algebraic reconstruction technique. It is demonstrated that the precise correction of the orientation of the sample rotation axis is effective in DCT suffering from rotation axis misalignment, and the higher accuracy in determining the rotation axis is expected to improve the reconstruction precision of grains.     

Large depth-of-view portable three-dimensional laser scanner and its segmental calibration for robot vision

A portable 3D laser scanning system has been designed and built for robot vision. By tilting the charge coupled device (CCD) plane of portable 3D scanning system according to the Scheimpflug condition, the depth-of-view is successfully extended from less than 40 to 100 mm. Based on the tilted camera model, the traditional two-step camera calibration method is modified by introducing the angle factor. Meanwhile, a novel segmental calibration approach, i.e., dividing the whole work range into two parts and calibrating, respectively, with corresponding system parameters, is proposed to effectively improve the measurement accuracy of the large depth-of-view 3D laser scanner. In the process of 3D reconstruction, different calibration parameters are used to transform the 2D coordinates into 3D coordinates according to the different positions of the image in the CCD plane, and the measurement accuracy of is obtained experimentally. Finally, the experiment of scanning a lamina by the large depth-of-view portable 3D laser scanner used by an industrial robot IRB 4400 is also employed to demonstrate the effectiveness and high measurement accuracy of our scanning system.     

准同心广义经纬相机的成像模型及高精度标定

对于大尺度运动目标的参数测量,固定相机存在着视场与空间分辨率之间的矛盾,并且当测量空中或海上目标时相机的标定也十分困难。跟踪式相机(如光电经纬仪)能解决此问题,但存在体积大、成本高和操作复杂等缺点。结合两者特点取长补短,将相机固定在二维旋转平台上,尽可能实现同心放置,组成准同心广义经纬相机进行中远场高精度测量,测量过程中转台实时跟踪目标并为相机提供外参数。此方法并没有光电经纬仪非常严格的同心同轴的安装要求。在合理假设基础上建立了经纬相机成像模型,提出了线性求解及平差优化相机参数的方法。大量仿真与实际测量验证了模型和标定方法的正确性和高精度。广义经纬相机测量系统组合巧妙、装拆和操作简单、体积小、成本低、可全视场测量且测量精度高,有广泛且重要的应用前景。     

体布拉格光栅外腔半导体激光器的光栅旋转角度容差

采用步进电机控制光栅角度,对200 m和600 m圆柱透镜准直的体布拉格光栅（VBG）外腔单管C封装半导体激光器进行了系统研究。实验结果表明:激光二极管（LD）驱动电流越大,准直效果越好,VBG的角度调整容差越小;快轴方向的准直效果越好,慢轴方向的光栅调节角度容差越大;对于衍射效率28%、厚1.4 mm的光栅,LD快轴发散角为7.3 mrad时,快轴方向的角度容差不大于3.2 mrad,慢轴方向的角度容差较快轴大约一个数量级。     

体布拉格光栅外腔半导体激光器的光栅旋转角度容差

采用步进电机控制光栅角度,对200 m和600 m圆柱透镜准直的体布拉格光栅（VBG）外腔单管C封装半导体激光器进行了系统研究。实验结果表明:激光二极管（LD）驱动电流越大,准直效果越好,VBG的角度调整容差越小;快轴方向的准直效果越好,慢轴方向的光栅调节角度容差越大;对于衍射效率28%、厚1.4 mm的光栅,LD快轴发散角为7.3 mrad时,快轴方向的角度容差不大于3.2 mrad,慢轴方向的角度容差较快轴大约一个数量级。     

Rotation axis calibration of a turntable using constrained global optimization

For determining the rotation axis as the baseline to transform between camera and turntable coordinate frames, rotation axis calibration of a turntable using constrained global optimization is proposed. At the beginning, camera parameters are calibrated using multiple views of only one pattern positioned differently and 3D corner points are retrieved with the pattern placed onto the rotation turntable in a 360° view. Then the rotation axis direction vector is decided under the constraint of the distance between each closed circle trajectory plane and each circle with its center is determined by fitting the circle with global least squares method, respectively. Experimental results demonstrate that the proposed method is effective for estimating the parameters of rotation axis.     

All-optical steering of laser-wakefield-accelerated electron beams

We investigate the influence of a tilted laser-pulse-intensity front on laser-wakefield acceleration. Such asymmetric light pulses may be exploited to obtain control over the electron-bunch-pointing direction and in our case allowed for reproducible electron-beam steering in an all-optical way within an 8 mrad opening window with respect to the initial laser axis. We also discovered evidence of collective electron-betatron oscillations due to off-axis electron injection into the wakefield induced by a pulse-front tilt. These findings are supported by 3D particle-in-cell simulations.