Obstacle avoidance of redundant robotic manipulators using safety ring concept

Obstacle avoidance is one of the basic, but computationally, costly issues of robotic science. In this paper, a safety ring around the work piece was defined, so that since the wrist of the robot is inside the ring, it is guaranteed that no collision will occur. Considering the wrist of the robot, instead of a tooltip, reduces the computational cost due to removal of the three last robot joints from calculations. The robot wrist is able to move freely inside the safety ring volume instead of a specific curve. The rotation of the end effector around its axis in some applications like welding, cutting, etc. is not important; therefore, this functional redundancy was used in inverse kinematic solution in order to search in the null space to find the optimal joint angles for moving the robot wrist inside the safety ring. In addition, inherent redundancy of the robot base movement on the rail was used to avoid joint limits. The algorithm was applied to a common industrial application i.e. intersecting pipes welding.