Coordinated motion control of multiple robotic devices for welding and redundancy coordination through constrained optimization in Cartesian space

S. Ahmad, S. Luo
1989 IEEE Transactions on Robotics and Automation  
A b stract In this paper we consider the problem of coordinating multiple motion devices for welding. We focus on the problem of coordinating a positioning table and a seven axis manipulator, given the parametric definition of a trajectory on a weld piece. The prob lem is complex as there are more than nine axis involved and a number of permutations are possible which achieve the same motions of the weld torch. The system is This work is funded by a cooperative research grant provided by the
more » ... provided by the Indiana Corporation of Science and Technology. redundant and the robot has singular configurations. As a result, manual programming of the robot system is rather complex. Our approach to the coordination problem is based on subdivision of constraints. The welding table is coordinated to ensure down-handed welding convention, while the seven axis robot (a six axis Cybotech WV15 robot and track) are coordinated to track the weld point. The coordination is achieved by keeping the robot in good maneuvera bility position, so as to avoid the robots singularity conditions and motion limits of the track. We were able to express the singularity conditions in terms of cartesian coordi nates [I]. As a result, we could obtain analytic solution to our optimization of the maneuversability and therefore avoid using known pseudoinverse techniques which are known to exhibit inaccuracies [2] . The output of our optimization process is the posi tions of the track and the robot end-effector, these positions are used to generate the joint angles of the arm by inverse kinematics. Introduction In this paper we address the problem of coordinating a two axis table and a seven axis robot, given the mathematical description of the weld seam trajectory with refer ence to the part coordinate frame. The welding is to be carried out in down-handed convention to allow the plasma to flow appropriately along the weld contour. This requires the weld piece surface normal to be aligned in the opposite direction of the gravity vector throughout the entire welding process. A seven axis robot consisting of a track and a six-axis arm is used to guide the weld torch. Redundant manipulator sys tems are quite often used in welding systems because, (i) a larger robot work envelope is obtained, (ii) singular configurations in the robot can be avoided by optimal movement of the redundant axes, i.e. the track. M ary/A hm ad/m oti.jour/M arch 29, 1988 -2 -® Shaheen Ahmad
doi:10.1109/70.88055 fatcat:kxbjp6q5fbeejlywnt5gve2koa