On-Line Collision-Recognition and Collision-Avoidance Control for Redundant Articulated Robots

This work 1 presents a suitable mathematical formulation of robot and obstacles such that for on-line collision recognition only robot joint positions in the workspace are required. This reduces calculation time essentially, because joint positions in workspace can be computed at every time from the joint variables through robot geometry. It is supposed that the obstacles in the workspace of the manipulator are represented by convex polygons in 2D. The recognition of collisions of the links of the manipulator with obstacles results on-line through a nonsensory method. For every link of the redundant robot and every obstacle a boundary ellipse in 2D is defined in workspace such that there is no collision if the robot joints are outside these ellipses. In addition to this, two collision avoidance methods are presented which allow the use of redundant degrees of freedom such, that a manipulator can avoid obstacles in workspace while tracking the desired end-effector trajectory. Moreover, the new methods are applied directly in workspace. This paper gives also a comparison of these two methods. The effectiveness of the porposed methods is discussed by theoretical considerations and illustrated by simulation of the motion of a planar four-link manipulator between obstacles.