Volumetric phase-measuring interferometer for three-dimensional coordinate metrology

We present a volumetric interferometer that has been specially designed to improve the measurement accuracy of the three-dimensional coordinate metrology by reducing excessive Abbe offsets. The interferometer is composed of two main parts; one is a three-dimensionally movable target and the other is a stationary two-dimensional array of photo-detectors. The target made of point diffraction sources emanates two spherical wavefronts, of which interference intensity is monitored by the photo-detectors. Applying phase shifting allows the phases of the photo-detectors to be precisely obtained, and the measured phases are fitted to a geometric model of multilateration so as to determine the xyz-location of the target by minimizing least square errors. A prototype built on a CMM demonstrates that the proposed interferometer is capable of measuring the xyz-coordinates of the probe with a volumetric uncertainty of less than 1.0 μm.     

基于虚拟立体视觉的气液两相流三维测量系统的标定

研究了基于虚拟立体视觉的气液两相流三维测量系统的标定技术。首先,基于单台高速摄像机和两组反射镜组构建虚拟立体视觉测量系统,建立高速摄像机透视投影变换模型以及虚拟立体视觉三维测量模型,对虚拟立体视觉系统中摄像机及虚拟立体视觉传感器进行标定。用靶标基准球模拟气泡在水中的分布,以其空间距离作为测量评价指标,比较了不同标定方法对三维重建精度的影响。实验结果表明,将标定参照物置于水箱内,并且分别对左、右虚拟摄像机及传感器进行标定,三维重建精度最高,测量空间距离绝对误差优于0.13 mm,相对误差优于0.49%。实验认为,对基于虚拟立体视觉的气液两相流三维测量系统进行标定时,必须充分考虑折光分光光路以及管壁折射对三维重建所带来的影响。     

A novel way of understanding for calibrating stereo vision sensor constructed by a single camera and mirrors

As a kind of binocular stereo vision system, stereo vision sensor constructed by a single camera and mirrors (SSCMs) has been paid increasing attention for three-dimensional measurement applications due to its low cost, high efficiency and synchronization. Currently, the existing model for SSCM considers the real camera as two half-Field-of-View (FOV) virtual cameras formed by reflection effects of the mirrors. The calibration methods based on this conventional model are either complicated to operate or deriving non-identical system parameters. To solve the problem, a novel model and the corresponding calibration approach are presented, which take the sensor as an integrated structure with the viewpoint that the camera captures two virtual points formed by the same object point due to the reflection effects of the mirrors. Also, the calibration and the measurement accuracy evaluation functions are discussed. Both simulated and real experiments compare the calibration and the measurement error of the proposed method with the two traditional methods. The results show that the proposed approach has higher measurement accuracy and more robust than the traditional methods, which meet high-precision requirements for low-cost three-dimensional measurement applications.     

Calibration-based thermal error model for articulated arm coordinate measuring machines

The influence of thermal changes in the accuracy of articulated arm coordinate measuring machines (AACMMs) is one of their main error sources. Usually, the effects of this problem are minimized by using low thermal-expansion materials in the arm design or by implementing an empirical error correction model based on the outputs of several temperature sensors placed inside the arm. These models, inherited from temperature correction models for robot arms, are based on the empirical arm positioning error characterization of several temperatures inside its measuring range and by posterior corrections implemented using an average error approximation. Considering this approximation as a correction valid for all the temperature range violates the AACMM calibration conditions, which are defined by a kinematic parameter identification procedure at 20 °C. This implies that, by applying these models, the AACMM will work outside of calibration conditions and will not meet the nominal accuracy values obtained from the identification procedure. In this work a new empirical correction model for thermal errors is presented. This model keeps the calibration conditions established in the parameters identification procedure unaltered. This fact makes it possible to apply other correction models for geometric and non-geometric errors obtained at the calibration temperature after having applied the temperature correction. The algorithm and objective functions used, which are based on a new approach including terms regarding measurement accuracy and repeatability and using the measurements of a ball-beam gauge artifact are shown. The empirical correction model and the arm accuracy and repeatability results before and after correction are also explained, showing an important accuracy improvement in the arm performance for typical arm operation at temperatures different from 20 °C.     

Volumetric performance evaluation of a laser scanner based on geometric error model

We discuss a geometric error model for those large volume laser scanners that have the laser source and a spinning prism mirror mounted on a platform that can rotate about the vertical axis. We describe the terms that constitute the model, address their effect on measured range and angles, and discuss the sensitivity of different two-face and volumetric length tests to each term in the model. We report on experiments performed using commercially available contrast targets to assess the validity of the proposed model. Geometric error models are important not only in improving the accuracy of laser scanners, but also in facilitating the identification of test procedures for performance evaluation of these instruments and therefore in the development of documentary Standards. The work described in this paper lays the foundation for such efforts.     

激光跟踪仪几何误差修正

本文推出了激光跟踪仪主要几何误差数学模型，给出了误差分离方法及修正方法，首次在激光跟踪仪全程35m范围内进行了比长实验和误差修正实验，得到了LTD500大范围空间测长精度，同时验证了误差修正的正确性和有效性。     

激光测量几何误差补偿算法

激光技术作为重要的测量手段,已经被广泛的应用到精密运动控制系统中。激光测量误差直接影响到运动控制系统的控制精度,其中阿贝与余弦误差等几何误差对激光测量精度影响显著,在精密运动控制中必须予以补偿与校正。以精密运动台多维激光测量模型为基础,介绍了阿贝与余弦误差产生原因。在不考虑激光干涉仪的加工和安装误差的情况下,推导了运动台存在倾斜角度下的阿贝与余弦误差计算模型,在此基础上给出了激光测量数据误差补偿模型,以实现测量数据的实时补偿与修正。算法已经成功应用在实例中,表明该算法的有效性与可靠性。     

Proposition for a Volumetric Error Model Considering Backlash in Machine Tools

This paper proposes a new scheme for evaluating the machine tool volumetric error model including the backlash error. The effects of backlash errors are assessed by experiments, conducted on a three-axis vertical-type machining centre. The assessment was taken for 18 error components out of the 21 geometric errors of a machine tool. It was shown that the backlash error of a machine tool is one of the systematic errors. Some important characteristics of the backlash error were identified; that is, the backlash error is a function of position, it decreases as the feedrate increases, and its size and shape vary according to the machine structure.     

时栅传感器直驱式误差自动标定与修正系统

针对研制时栅位移传感器过程中的误差标定环节,常规光栅传感器精度不满足要求的问题,采用激光干涉仪作为误差标定基准,自主研制了基于激光干涉仪的直驱式时栅角位移传感器误差自动标定与修正系统。利用时栅角位移传感器的多测头结构与误差曲线等间距周期性分布的特性,以一个对极的误差曲线重构传感器整周的误差曲线,采用多项式拟合算法构建了时栅角位移传感器的误差修正模型。实验结果表明,误差自动标定与修正系统可以快速、准确地对时栅角位移传感器进行自动误差标定与修正,修正后的时栅角位移传感器的整周误差达到±0.43″。     

旋转变压器的角度误差校正系统设计

针对旋转变压器输出数据存在的角度误差问题,对旋转变压器校正方法进行了研究,设计并实现了旋转变压器角度误差校正系统。该系统充分利用了旋转变压器工作原理,发挥了光电编码器优势,采用了FPGA和ARM的优点,由同一电机带动光电编码器和被测旋转变压器,以FPGA+ARM组成的控制模块读出光电编码器和被测旋转变压器的角度,并进行比较分析,测量旋转变压器的非线性误差,建立误差分析表,提出了一种根据系数进行补偿的方式,对旋转变压器的误差进行了补偿。研究结果表明,该系统能对旋转变压器的输出数据进行校正,校正前旋转变压器的角度误差最大为21.2弧分,通过该系统校正后,测角误差最大为5.3弧分,系统校正速度较快且效果明显。     

相差式测量仪表零点误差在线自动校正技术

本文提出一种能够在线自动校正相差式测量仪表测量电路系统部分的零点误差的技术方法。文中介绍了这种技术方法的工作原理及硬件设计,讨论了软件数据处理方法。     

测量误差不确定性加权的立体视觉位姿估计目标函数

针对视觉测量过程中配合目标特征点在成像时灰度模式的各向异性且非独立同分布对位姿估计求解的影响,建立了基于特征点测量误差不确定性加权的位姿估计目标函数。利用协方差矩阵描述特征点的方向不确定性,分析成像特征点的不确定性对目标函数的作用权重,并将特征点测量误差的不确定性融入到空间共线性误差函数中,进而构造了基于成像特征点测量误差不确定性加权的新目标函数。该方法适应于特征点测量误差具有不同程度的方向不确定性的情况,最后通过广义正交迭代算法对该目标函数进行迭代优化求解。实验表明,当测量空间为2 300 mm×1 400 mm×1 400mm,采用新目标函数得到靶标重投影后图像坐标的最大误差不超过0.11pixel,立体视觉系统对标准杆的相对测量精度优于0.01%。所得的结果验证了新目标函数的位姿估计精度高、稳定性强,适用于实际的工程应用。     

基于坐标测量机的轴向立体视觉测量方法研究

为了解决双目立体视觉测量过程中图像匹配计算量大、算法复杂、误匹配率高的问题,提出了一种轴向立体视觉测量方法。该方法由单个摄像机沿坐标测量机轴向先后捕捉被测物表面,利用同轴摄像机外极线相互平行的特性进行同源相点的逐个匹配,并根据视差原理反求三维坐标。着重论述了该方法的原理、同源点匹配及具体实现过程,并通过实验进行了验证,测量了一个塑料盘的边缘并进行了重建。研究结果表明该方法能提高匹配效率,减小误匹配几率,实现快速高效的非接触式测量。     

灰色关联分析方法在双目视觉测量系统误差分析中的应用

针对双目视觉测量系统存在误差因素繁多、分析困难等问题,提出了一种基于灰色关联技术的误差分析方法。考虑视觉系统的灰色属性,将灰色系统理论及其相关技术运用于视觉测量系统的误差分析。以镜头畸变、质心定位误差及双目视觉系统内、外参数等9项因素或参数为自变量,通过基于单项因素变化的实验,获取了误差分析的数据样本;采用灰色数据处理方法及灰色关联分析技术,从无明显规律的数据样本中明确了视觉系统各项误差因素对最终测量精度的影响。分析结果证明了灰色理论用于定量分析视觉系统误差的正确性和有效性;在灰色理论意义下,镜头径向畸变、切向畸变、摄像机夹角及特征点质心定位误差4项因素对测量精度的关联度均大于等于0.859,高于其余误差因素。     

Multi-Range approach of stereo vision for mobile robot navigation in uncertain environments

The detection of free spaces between obstacles in a scene is a prerequisite for navigation of a mobile robot. Especially for stereo vision-based navigation, the problem of correspondence between two images is well known to be of crucial importance. This paper describes multi-range approach of area-based stereo matching for grid mapping and visual navigation in uncertain environment. Camera calibration parameters are optimized by evolutionary algorithm for successful stereo matching. To obtain reliable disparity information from both images, stereo images are to be decomposed into three pairs of images with different resolution based on measurement of disparities. The advantage of multi-range approach is that we can get more reliable disparity in each defined range because disparities from high resolution image are used for farther object a while disparities from low resolution images are used for close objects. The reliable disparity map is combined through post-processing for rejecting incorrect disparity information from each disparity map. The real distance from a disparity image is converted into an occupancy grid representation of a mobile robot. We have investigated the possibility of multi-range approach for the detection of obstacles and visual mapping through various experiments.     

应用在拼接镜面中的电容位移传感器的结构性误差分析及校正

分析了子镜运动和电容传感器极板运动之间的理论关系并探讨了电容位移传感器读数的"结构性"误差的处理方法。基于电容位移传感器的工作原理,对极板为圆形的电容位移传感器提出了采用以位移的测量值和子镜转角为自变量的多项式拟合的校正方法。计算表明该误差处理和校正方法是简洁可行的。对于转角的拟合只需2阶,同时位移测量值只需4阶的多项式进行拟合即可使输出位移达到3 nm的精度。进一步分析表明,直接使用位移传感器读数计算极板转角,并对误差的主动校正控制非常有利于该多项式拟合,可一次性达到优于5 nm的校正误差,完全满足拼接镜面主动光学工程应用的技术要求。     

A three-dimensional triangular vision-based contouring error detection system and method for machine tools

Contouring error detection for machine tools can be used to effectively evaluate their dynamic performances. A triangular vision-based contouring error detection system and method is proposed in this paper, realizing the three-dimensional error measurement of an arbitrary trajectory in conditions of a high feed rate and wide motion range. First, a high-precision measurement fixture, which consists of high-precision circular coded markers and a highly uniform light source, is designed to accurately characterize the motion trajectory of a machine tool and realize the high-quality collection of an image sequence. Then, to improve the contouring error detection accuracy, a coded marker decoding and center location method for the automatic recognition and high-precision center positioning of the circular coded markers are applied. Using image preprocessing and matching, the markers’ three-dimensional coordinates in the camera coordinate system can be constructed. Moreover a data transformation method induced by the orthogonal motion of machine tools is proposed to obtain the three-dimensional trajectory in the machine tool coordinate frame and the contouring error can be calculated. Finally, a three-dimensional contouring error detection study of an equiangular spiral interpolation at different feed rates is performed in the laboratory. It is shown that the average contouring error for a feed rate of 1000 mm/min is about 3 µm, which verifies the vision measurement accuracy and feasibility.     

A comprehensive method for calibration of volumetric positioning accuracy of CNC-machines

A comprehensive method for measuring the systematic errors of CNC-machine tools has been studied. The method used for measurement and calibration of machine tool errors should be general and efficient. The objectives of this study include:

浅谈自动气象站的仪器差修正

自动气象站在各级气象台站使用仅几年时间,尚存在一些管理上的空档。本文从地面观测资料的准确度出发,阐述了自动气象站仪器差修正对提高地面观测资料准确度的必要性,并提出了相应的修正方法。     

旋转导向钻井工具近垂直姿态校正矩阵 误差的等角距均衡校正

旋转导向钻井工具中姿态校正方法的校正点本身包含各种系统误差,会引入校正矩阵误差,是近垂直姿态下姿态角解算精度低的原因之一.平均均衡校正方法(ABC)可补偿校正矩阵误差,但整体误差并不均匀.以等分角度间距设计校正点,建立一种等角距均衡校正(EABC)模型,推导校正矩阵误差表达式,研究其引起的姿态角误差特征.对多组近垂直姿态的测试数据分别进行传统校正、平均均衡校正和等角距均衡校正,结果表明：等角距均衡校正后,井斜角误差平均值均小于0.012°,井斜角误差峰峰值均小于0.027°;工具面角误差平均值均小于0.008°,工具面角误差的峰峰值和标准差分别降低到平均均衡校正的54%～95%和40%～63%,进一步提高垂直小井斜井段的姿态解算整体精度。