The kinematic parameter identification technique of robot arm is effective for enhancing the absolute positioning accuracy.For the low efficiency of the general calibration methods based on planar constraints,which data can only be captured by manual teaching method,an automatic method was proposed for the kinematic parameter identification of the robot arm with the help of a stereo vision system to locate the constraint planes.In order to remedy the limitation of the common field range of two industrial cameras,three target spots were attached to each constraint plane,so the location of each constraint plane could be equivalent to locate their target spots cor-respondingly.The binocular stereo vision system extracted the center of target spots and then matched them respectively,so that the 3D position information of each target spot in the base co-ordinate system of the robot arm was calculated.Meanwhile,a target coordinate system was built to plan the constraint points according to a certain rule.To enhance the calibration precision fur-ther,an error model based on two planes perpendicular to each other was proposed,then a set of nominal vectors of each plane were calculated by three non-collinear constraint points and the dot product of each pair of nominal vector was zero,namely,there existed an extra restraint in the error model.Then a probe fixed to the end flange of robot arm was used to touch two perpendicu-lar constraint planes automatically,and the actual values of all kinematic parameters could be i-dentified by the improved least squares.Experiments showed that the absolute positioning accura-cy of the robot arm was enhanced from 1.234 mm to 0.453 mm after modifying the kinematic pa-rameters based on the proposed error model.The proposed method realizes automatic measure-ment of data,and highly increases the efficiency of robot arm calibration,and provides a reference for mass calibration,which has great significance of engineering.%标定机器臂的运动学参数可以有效提高机械臂的绝对定位精度.针对一般平面约束标定方法往往通过手动示教获取测量数据,效率低,提出一种基于视觉辅助定位约束平面的机械臂运动学参数辨识方法.为了弥补双目视觉视场范围狭小的弊端,在约束平面上粘贴3个靶点,以此将对平面的定位等效成对靶点的定位.应用双目视觉系统提取靶点中心并进行立体匹配,得到靶点在机械臂基坐标系下的三维位置信息;同时构建靶点坐标系,以此规划出按一定规律分布的约束点;为了进一步提高标定精度,建立双平面约束误差模型,通过两垂直平面上任意非共线的3个点得到一系列法向量,每一对法向量的数量积为0,即增加了约束方程;利用机械臂对相互垂直的两约束平面自动进行接触式测量,通过改进的最小二乘法辨识出真实的运动学参数误差.实验结果表明,基于双平面约束误差模型,修正运动学参数后,机械臂绝对位置精度由1.234 mm提高到了0.453 mm.该方法实现了数据的自动化测量,大大提高了标定效率,为机械臂批量标定提供了参考,具有工程意义.
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