基于末端圆周运动的可变形臂旋量参数快速标定算法

A Fast Calibration Algorithm for Screw Parameters of a Deformable Manipulator by Using the Circular Motion of End-effector

针对家庭服务机器人工作的非结构化环境,设计了一种可以根据任务需求相应地调整连杆形状的可变形操作臂.该操作臂工作空间易于拓展、灵活度较高且成本低廉.但臂形的改变也给操作臂的建模和控制带来了困难.首先,可变形臂的运动学参数发生了巨大且无规律的变化,使得固结在连杆上的坐标系脱离连杆本体,变得不可测量.其次,为适应不同任务需求,可变形臂的连杆形状需要经常改变,而传统标定方法往往追求更高的标定精度而非标定效率,因而需要开发一种耗时较短的标定方法.最后,可变形臂的标定方法必须简便而易于在家庭环境中实施.针对上述问题,本文提出了一种基于末端圆周运动的可变形臂旋量参数快速标定算法.对于任意一个旋转关节,单独转动该关节时,操作臂末端的轨迹形成了一个圆弧,且该关节轴垂直于圆弧所在平面(旋转平面)并经过圆弧的圆心.基于该性质,利用随机抽样一致性(RANSAC)算法和最小二乘算法来拟合操作臂末端轨迹,从而获取操作臂的旋量参数初值.在获取到初值的基础上,提出了一种扩展卡尔曼滤波(EKF)算法进一步优化旋量参数,提高标定精度.仿真和实验结果验证了本文方法的有效性.

A deformable manipulator whose links can be bent according to different tasks is designed for unstructured environments in home service. The deformable manipulator can obtain relatively dexterous end-effector and extended workspace with much lower cost. However, frequent changes in link shape bring difficulties to the modeling and control of the manipulator. Firstly, the kinematic parameters of the deformable manipulator change significantly and irregularly. It is hard to measure the parameters directly due to the offset between the link coordinate and the link body. Secondly, the bending operations are frequent in order to deal with various tasks. Therefore, a less time-consuming calibration method is necessary, while the traditional calibration methods pursue high accuracy instead of efficiency. Finally, the calibration process for the deformable manipulator must be easy to be applied in home environment. To tackle above problems, a fast calibration algorithm for screw parameters of a deformable manipulator is proposed by using the circular motion of end-effector. When rotating any joint separately, the locus of end-effector is a circle in a plane, called the plane-of-rotation. The joint axis is perpendicular to the plane-of-rotation and goes through the centre of the circle. By using this property, the random sample consensus(RANSAC)and least-squares algorithms are used to fit the locus of end-effector and obtain the initial values of screw parameters. Then an extended Kalman filter(EKF) method is used to optimize the screw parameters with initial values and improve the calibration accuracy. The simulation and experimental results validate the effectiveness of the proposed method.