基于单目视觉的激光光束方向标定研究

在由激光位移传感器组成的测量系统中,激光光束的方向是一个关键参数.方位角和俯仰角对于一条激光光束是最为重要的两个参数.本文中提出一种基于单目视觉的激光光束方向测量方法.首先,将CCD相机放置于基础平面上方,保持相机光轴与基础平面接近于垂直状态,并利用误差为10μm的圆孔型标定板建立单目定位模型.然后将激光光束发生装置放置在基础平面上并保持位置固定,同时在基础平面上放置特制靶块,使激光光束可以投射到靶块斜面上并形成一个激光光斑.在基础平面上方放置的CCD相机可以清晰的采集到激光光斑、靶块斜面的图像,应用相关算法提取出光斑质心的二维图像坐标.沿激光光束方向以相等间距移动靶块,通过CCD相机采集每移动一次靶块在当前位置下的光斑、靶块图像.利用相关的转换公式,结合靶块本身固有参数,将光斑质心图像二维坐标转换为基础平面下的空间三维坐标.由于靶块的移动,会得到靶块不同位置下激光光斑质心的三维坐标,将这些三维坐标拟合成空间直线表征待测激光光束.拟合直线得俯仰角即为待测激光光束的俯仰角.实验中,应用高精度仪器对靶块参数进行测定,并使用高精度标定板标定相机内外参数建立相应的定位模型.测量精度主要通过单目视觉定位精度、光斑重心提取精度来保证.结果显示,待测光束的俯角最大误差达到0.02°,光束间夹角的最大误差为0.04°.     

基于单目视觉的激光光束方向标定研究（英文）

在由激光位移传感器组成的测量系统中,激光光束的方向是一个关键参数。方位角和俯仰角对于一条激光光束是最为重要的两个参数。本文中提出一种基于单目视觉的激光光束方向测量方法。首先,将CCD相机放置于基础平面上方,保持相机光轴与基础平面接近于垂直状态,并利用误差为10μm的圆孔型标定板建立单目定位模型。然后将激光光束发生装置放置在基础平面上并保持位置固定,同时在基础平面上放置特制靶块,使激光光束可以投射到靶块斜面上并形成一个激光光斑。在基础平面上方放置的CCD相机可以清晰的采集到激光光斑、靶块斜面的图像,应用相关算法提取出光斑质心的二维图像坐标。沿激光光束方向以相等间距移动靶块,通过CCD相机采集每移动一次靶块在当前位置下的光斑、靶块图像。利用相关的转换公式,结合靶块本身固有参数,将光斑质心图像二维坐标转换为基础平面下的空间三维坐标。由于靶块的移动,会得到靶块不同位置下激光光斑质心的三维坐标,将这些三维坐标拟合成空间直线表征待测激光光束。拟合直线得俯仰角即为待测激光光束的俯仰角。实验中,应用高精度仪器对靶块参数进行测定,并使用高精度标定板标定相机内外参数建立相应的定位模型。测量精度主要通过单目视觉定位精度、光斑重心提取精度来保证。结果显示,待测光束的俯角最大误差达到0.02°,光束间夹角的最大误差为0.04°。     

点激光测头激光束方向标定

为了使点激光测头能在任意方向上实现测量功能,提出一种逆向工程中标定激光束方向的方法,设计了一种标定面方向可调的标定块配合标定。标定过程中,让激光测头在标定面上分别沿X、Y、Z3个轴方向做等间距运动,根据进给步长与激光束长度变化量之间的关系确定激光束的方向。以三坐标测量机为平台,给出了以任意方向安置点激光测头时,测量值从传感器坐标系到基准坐标系的转换过程,并对标定算法及整个标定过程进行了详细描述。最后,通过与接触式测量进行对比实验,验证标定后点激光测头的测量效果。实验结果表明,用该方法标定的点激光测头在3σ范围内沿任意方向的测量误差为(0.0452±0.0168)mm,满足逆向工程的测量要求。     

基于磨齿机的螺旋锥齿轮小轮齿形误差的在机测量

为了在国产数控螺旋锥齿轮磨齿机上实现齿形误差的精密测量,对螺旋锥齿轮小轮齿形误差的在机测量技术进行了研究。根据H350G型数控磨齿机的机床结构和机床坐标系,利用标定块标定了测球球心在机床坐标系中的坐标。建立了小轮齿形误差的在机测量方法,通过将理论齿面各离散点旋转到机床坐标系XZ平面,并将小轮绕轴线相对于参考点位置旋转一定角度,同时控制机床各数控轴的运动,使测头沿理论齿面各离散点法矢方向逼近实际齿面,根据测头触发时测球球心的坐标,运用曲面拟合技术和最优化算法,计算了实际齿面相对于理论齿面的齿形误差。通过比对在机测量和齿轮测量中心的齿形误差测量结果,验证了小轮齿形误差在机测量方法的正确性。     

在机测量线激光传感器安装位姿的全局标定

针对三轴数控机床激光测头安装位姿误差造成测量误差且不易调整和校准的问题,提出了一种在机测量线激光传感器 安装位姿标定方法。 建立了线激光在机测量系统的数学模型,通过机床运动带动线激光测头对标定基准点的空间位置进行测 量,基于手眼标定原理给出了关于测头安装位姿参数的线性求解算法,完成了对测头安装误差的全局标定。 考虑了机床定位误 差对于标定结果精度的影响,采用蒙特卡洛模拟进行了误差分析。 采用半径为 35 mm 的圆孔进行测量验证,实验结果表明,标 定后圆孔测量误差为 0. 051 6 mm,测量精度提高了约 96% ,实验结果验证了该标定方法的有效性和可行性。     

三维螺纹测量机接触式测头的优化设计

为削弱接触式测头对高精度三维螺纹测量机精度的影响,设计了一种接触式测头结构尺寸优化方案,并提出了相应的标定方法。通过有限元仿真和正交试验优化测头结构参数,确定最优结构参数;利用坐标变换理论和最小二乘法原理建立测头标定模型并进行了标定试验;通过不同预压量下的螺纹塞规对比试验及螺纹环规、塞规对比试验对优化后的测头进行测试。结果表明：接触式测头测量螺纹塞规、环规参数标准偏差在1 μm左右,满足三维螺纹综合测量机接触式测头测量精度要求。该优化方案及标定方法为测头结构设计提供了重要的理论基础。     

非接触激光测头测量轴线标定系统

提出一种用于三坐标测量机的非接触激光测头的标定系统，该系统利用位置敏感探测器和特别设计的测头夹具机构对非接触激光测头测量光束的轴线进行调整，使其通过测头回转体的回转中心。文中对具体的夹具结构标定方法以及数据分析方法做了详细的论述。     

亚微米级高精度复合式坐标测量机的研制

坐标测量机(CMM)是最常用的长度测量仪器,但在面对复杂结构工件的高精度测量时,配备单一接触式测头的坐标测量机往往无法完全满足测量需求。针对这种情况,本文研制了一种亚微米级的高精度复合式坐标测量机。该仪器集成接触式测头、影像测头和光谱共焦测头,充分利用每种测头各自的优势,实现复杂工件的快速高精度测量。本文介绍了高精度复合式坐标测量机测量精度影响因素的处理方法,完成了测量机的机械结构设计,进行了几何误差和热误差补偿,对测量机3种测头进行了独立标定及融合标定。精度验证测试结果表明,所研制的复合式坐标测量机测量精度可达到亚微米级水平。     

基于误差隔离的触发式测头预行程标定方法

触发式测头是在机测量系统的主要组成部分,其预行程会计入测量结果从而影响测量精度,因此有必要对其在实际工况下的预行程进行标定并补偿.在分析预行程产生原因的基础上,提出了一种全新的预行程定量标定方法,它通过在实际工况下检测探针与工件接触状况及接触时刻与测头触发时刻之间工件相对测头位移变化而标定出预行程,有效避免了机床伺服系统误差、机床几何及运动误差、探针测球圆度误差、标定体制造误差等因素对标定结果精确性的影响.标定了某高精密测头在实际工况下的预行程,并依据标定结果,完成了触发式测头预行程补偿实验.补偿结果表明,该标定方法实施简单、可行有效,标定精度高.     

三坐标测量机驱动的摄像机标定技术

为了降低摄像机的标定费用和提高标定精度,提出了一种基于三坐标测量机平动的摄像机标定技术,对该技术的原理、数学模型、标定步骤和标定精度进行了研究。根据摄像机标定的基本原理,利用三坐标测量机沿X、Y、Z轴移动和正交精度都很高的特点,以三坐标测量机带动待标定摄像机产生和白色陶瓷标准球球心(标定特征点)在X、Y、Z轴方向上的相对平动,得到标定特征点在测头坐标系中不同位置的坐标;在每一个确定位置,摄像机拍摄标定特征点的像,经图像处理后,计算出像点在计算机帧存坐标系中的坐标。引入测头坐标系,建立了该项摄像机标定技术的数学模型,给出了标定步骤,组建了标定系统。比对标定实验结果表明,基于三坐标测量机平动的摄像机标定系统与专用标定系统的标定精度相当,数据相差在±1μm以内,满足工程实际精度要求,成本低、标定效率高。     

基于CPA方法的串联工业机器人运动学标定精度试验研究

几何参数误差是影响工业机器人定位精度的主要误差源,约占总误差的80%以上。基于圆点分析法(circle points analysis,CPA)所标定的几何参数与机器人的实际结构相关,并且能够将几何参数误差与其他误差源解耦。研究表明CPA方法的测量策略对其标定精度具有较大影响。针对基于CPA方法的串联工业机器人运动学标定技术的测量策略展开试验研究,分别对各轴测量角度范围、各轴测量步长、初始位姿构型、靶球安装位置等因素进行了分析,并得出一个优化的测量策略。实验结果表明该测量策略能够有效地提升CPA方法的标定精度,误差减少了43.99%,明显优于其他测量方案。通过与误差模型方法对比,经CPA方法标定的机器人具有更好的全局定位精度。     

平面十字磁梯度张量系统的两步线性校正

磁梯度张量系统的测量精度受限于磁传感器的零漂、灵敏度差异和三轴非正交性等系统误差以及各传感器轴系间的非对准误差。构建了平面十字磁梯度张量系统的误差参数线性模型,提出了两步线性校正法。利用两个非线性变量转换构建单磁传感器系统误差的线性方程组,对误差参数进行最小二乘估计,将传感器实际输出校正为各自理想正交输出;利用旋转矩阵构建各传感器理想正交轴间非对准误差的线性方程组并求出最小二乘解,将各传感器输出校正到参考平台框架正交坐标系上。两步校正过程均无数学简化。仿真与实验表明,相比忽略二阶及以上高阶小量的常规线性校正,提出的张量系统两步线性校正法更为精确,误差参数仿真估计准确率高于93%,实测校正后总场强度均方根误差小于13 n T,张量分量均方根误差小于90 n T/m。     

采用间接测量法对VAMT1Y型虚拟轴机床运动学标定的仿真研究

在对虚拟轴机床进行运动学标定的仿真计算过程中 ,采用间接测量法对虚拟轴机床的运动进行间接测量 ,然后通过矩阵重构的方法来解决测量噪声的干扰问题。仿真结果表明 ,虽然在虚轴机床的工作空间里无法将其可能存在的结构误差全部求出来 ,但计算结果完全可以满足机床在工作空间里的运动精度要求。因此采用此方法对虚拟轴机床进行标定是可行的     

结构光三维双视觉检测方法研究

介绍了结构光三维双视觉检测的基本原理，提出了标定点的空间坐标和图像坐标的获取方法，设计了用于获取标定点的双向光电瞄准装置，并建立了双向光电瞄准装置安装误差的补偿方法，在此基础上实现了双视觉传感器标定点数据的全局统一。最后，利用标定点样本数据建立了结构光三维双视觉RBF神经网络模型，最佳RBF模型的训练精度为0.078mm，测试精度为0.084mm。     

A general strategy for geometric error identification of multi-axis machine tools based on point measurement

Geometric error component identification is needed to realize the geometric error compensation which can significantly enhance the accuracy of multi-axis machine tools. Laser tracker has been applied to geometric error identification of machine tools increasingly due to its high capability in 3D metrology. A general method, based on point measurement using a laser tracker is developed for identifying the geometric error components of multi-axis machine tools in this study. By using this method, all the component errors and location errors of each axis (including the linear axis and rotary axis) of the multi-axis machine tools can be measured. Three pre-described targets are fixed on the stage of the under-test axis which moves step by step. The coordinates of the three targets at every step are determined by a laser tracker based on the sequential multilateration method. The volumetric errors of these three target points at each step can be obtained by comparing the measured values of the target points’ coordinates with the ideal values. Then, nine equations can be established by inversely applying the geometric error model of the axis under test, which can explicitly describe the relationship between the geometric error components and volumetric error components, and then the component errors of this axis can be obtained by solving these equations. The location errors of the axis under test can be determined through the curve fitting. In brief, all the geometric error components of a single axis of multi-axis machine tools can be measured by the proposed method. The validity of the proposed method is verified through a series of experiments, and the experimental results indicate that the proposed method is capable of identifying all the geometric error components of multi-axis machine tools of arbitrary configuration.     

Autonomous calibration method of the zero-difference without using a standard gauge for a straightness-measuring machine

An autonomous method to calibrate the zero-difference for the three-point method of measuring surface straightness is proposed. A simple cone-disc, which can be made by a CNC turning machine, is used for the calibration. The calibration method is comprised of two steps. In the first step, the cone-disc rotates around and parallel to three displacement sensors built-in to a holder. In the second step, the geometrical parameters between the sensors and the cone-disc are simultaneously acquired during each predetermined movement of the sensors, and the zero-differences are computed by the proposed algorithm within a few revolutions.The conceptual design and the algorithm to realize the proposed method are explained with theoretical analyses and numerical simulations. The results of this study are as follows:

(1)

The repeatable accuracy of the zero-difference determination using the proposed method is at the same level of quality as that of the reverse method using the three-point method.

(2)

When the zero-difference is calibrated using a cone-disc gauge of 200 mm radius and 10 μm peak height, which can be manufactured by a CNC turning machine, the shape error of the object's surface (which is analyzed for its systematic error component and its repeatability error component) becomes less than 0.5 and 2 μm at measured lengths of 100 and 200 mm, respectively.

     

Plane kinematic calibration method for industrial robot based on dynamic measurement of double ball bar

A new calibration method is proposed to improve the circular plane kinematic accuracy of industrial robot by using dynamic measurement of double ball bar (DBB). The kinematic model of robot is established by the MDH (Modified Denavit-Hartenberg) method. The error mapping relationship between the motion error of end-effector and the kinematic parameter error of each axis is calculated through the Jacobian iterative method. In order to identify the validity of the MDH parameter errors, distance errors and angle errors of each joint axis were simulated by three orders of magnitude respectively. After multiple iterations, the average value of kinematic error modulus of end-effector was reduced to nanometer range. Experiments were conducted on an industrial robot (EPSON C4 A901) in the working space of 180 mm × 490 mm. Due to the measuring radius of DBB, the working space was divided into 30 sub-planes to measure the roundness error before and after compensation. The average roundness error calibrated by the proposed method at multi-planes decreased about 21.4%, from 0.4637 mm to 0.3644 mm, while the standard deviation of roundness error was reduced from 0.0720 mm to 0.0656 mm. In addition, by comparing the results of positioning error measured by the laser interferometer before and after calibration, the range values of motion errors of end-effector were decreasing by 0.1033 mm and 0.0730 mm on the X and Y axes, respectively.     

Design of a Two-Step Calibration Method of Kinematic Parameters for Serial Robots

Serial robots are used to handle workpieces with large dimensions, and calibrating kinematic parameters is one of the most efficient ways to upgrade their accuracy. Many models are set up to investigate how many kinematic parameters can be identified to meet the minimal principle,but the base frame and the kinematic parameter are indistinctly calibrated in a one-step way. A two-step method of calibrating kinematic parameters is proposed to improve the accuracy of the robot's base frame and kinematic parameters.The forward kinematics described with respect to the measuring coordinate frame are established based on the productof-exponential(POE) formula. In the first step the robot's base coordinate frame is calibrated by the unit quaternion form. The errors of both the robot's reference configuration and the base coordinate frame's pose are equivalently transformed to the zero-position errors of the robot's joints. The simplified model of the robot's positioning error is established in second-power explicit expressions. Then the identification model is finished by the least square method, requiring measuring position coordinates only. The complete subtasks of calibrating the robot's 39 kinematic parameters are finished in the second step. It's proved by a group of calibration experiments that by the proposed two-step calibration method the average absolute accuracy of industrial robots is updated to 0.23 mm. This paper presents that the robot's base frame should be calibrated before its kinematic parameters in order to upgrade its absolute positioning accuracy.     

Spindle thermal drift measurement using the laser ball bar

Thermally induced errors are major contributors to the overall accuracy of machine tools. An important component of thermally induced errors is the error associated with spindle thermal drifts. In this paper, a novel method is developed to measure spindle thermal drifts in machine tools using a laser ball bar (LBB) as the calibration instrument. The method is implemented on a two-axis CNC turning center. The LBB is used to measure the coordinates of the spindle center and the direction cosines of the spindle axis at various thermal states. The axial, radial, and tilt thermal drifts of the spindle are then computed from the changes in these coordinates. The new method is verified by comparing the spindle drifts measured with the LBB to those measured by capacitance gauges. The results obtained by the new method show good agreement with the capacitance gauge technique. The primary advantage of the new method is the ability to measure the spatial coordinates of the spindle center and direction cosines of the spindle axis with the same instrument used for measurement of the geometric errors of the machine axes.