Obstacle Avoidance Control for Redundant Manipulators Utilizing the Contact Forces

The paper considers the behavior of redundant manipulators which collide with an obstacle and the obstacle avoidance after the collision. Without changing the motion of the end-effector, the reconfiguration of the manipulator into a collision-free configuration can be done only by utilizing the self-motion of the manipulator. In the paper some motion controllers are analyzed which minimize the contact forces and utilize the self-motion caused by the contact forces to avoid the obstacles. A controller which ensures stiff behavior in the task space and compliant behavior in the null space is proposed as the best solution. The efficiency of the proposed control is illustrated by the simulation and experiments on a four link planar manipulator.