多目标复合可视性约束下的机械臂无模型标定位姿研究

Research on Model-Free Calibration Pose of Manipulator under Multi-target Composite Visibility Constraint

与基于模型的机械臂标定方法相比,无模型标定方法具有算法简洁和线性化误差小的优点,但这种方法需要在多个机械臂姿态下同时采集各连杆表面的靶标位姿,因此其可视性同时受视场角狭窄、靶面方向异常以及臂体遮挡的影响,增加测量位姿的构造难度。为此,提出一种基于多目标视觉的复合可视性约束下的机械臂无模型标定位姿遴选方法。依据机械臂连杆参数及轮廓尺寸,生成贴合其等效模型的有向包围盒树,并依据臂体外形特征设定各连杆靶标固连位姿。在此基础上,分别建立靶标角点被包含判据、靶面法向夹角判据以及各包围盒与靶面视锥干涉判据,将其融合为多目标复合可视性约束条件,该算法可在既定工作轨迹下遴选出全体靶标均为可视的机械臂位姿。最后,通过搭建实验台验证所提方法的有效性。实验结果表明:该方法对臂体与靶面的遮挡关系判断精准,靶标在所选位姿处可视性良好,满足机械臂实时无模型标定方法对于多靶标位姿同时采集的需求。

Compared with model-based manipulator calibration method,model-free calibration method has the advantages of simple algorithm and small linearization error,but this method requires the simultaneous acquisition of the target pose of each link surface under multiple manipulator poses,so its visibility is affected by narrow field of view angle,abnormal orientation of the target plane and the occlusion of the manipulator body at the same time,which increases the construction difficulty of measuring the pose.Therefore,a model-free calibration pose selection method based on multi-object vision was proposed.According to the parameters and contour size of the links of the manipulator,the oriented bounding box trees that fitted the equivalent model was generated,and the fixed connection position of the target was set according to the manipulator′s shape characteristics.On the basis,the criterions of the target inclusion,the angle between the target plane normal direction and the line-of-sight,and the interference between the surrounding box and the target plane cone were established respectively,which were fused into the multi-target composite visibility constraint conditions.The algorithm can be used to select the pose of the manipulator with all targets visible under the established working trajectory.Finally,an experimental bench was set up to verify the effectiveness of the proposed method.The experiment results show that the method can accurately judge the occlusion relationship between the arm and the target surface,and the target has good visibility at the selected pose,which meets the requirements of the real-time model-free calibration method for the simultaneous acquisition of multi-target poses of the manipulator.