An uncertainty analysis method for error reduction in end-effector of spatial robots with joint clearances and link dimension deviations

The position accuracy of the robot end-effector is inherently affected by uncertainties. In order to design and manufacture robots with high accuracy, it is essential to know the effects of these uncertainties on the motion of robots. Uncertainty analysis is a useful method which can estimate deviations from desired path in robots caused by uncertainties. This paper presents an applied formulation for 3D statistical error analysis of open-loop mechanisms and robotic manipulators. In order to have an accurate analysis, uncertainty effects of both the link dimension deviation and the joint clearance in performance of the spatial open-loop mechanisms and the robots are considered. The maximum normal and parallel components of the position error on the end-effector path are introduced as error bands for all over range of motion. Furthermore, the percent contributions of manufacturing variables are estimated and the corresponding tolerance that has the most significant effects on the uncertainty zone of the end-effector position is determined. The proposed method is illustrated using a spatial manipulator with three revolute joints and verified with a Monte Carlo simulation method. The results of applying this method demonstrate that estimating the position error and its reduction in mechanisms and robots can be done efficiently and precisely.