Online Coordinated Motion Control of a Redundant Robotic Wire Arc Additive Manufacturing System

Abstract

This paper considers the trajectory tracking control for wire arc additive manufacturing (WAAM). Some aspects of the WAAM process, such as the angles between welding torch direction, deposition surface normal and gravity are very important to ensure the quality of the manufactured parts. A task-priority based kinematic control scheme is proposed to control a manipulator and a positioning table coordinately. The manipulator and the positioning table are considered as a single robotic chain, and the primary task is defined to make the welding torch follow a desired trajectory defined in the positioning table deposition frame, while the secondary task is to align the welding torch in a desired direction defined in the inertial frame, e.g., gravity direction. A complete Lyapunov stability analysis is performed considering unmodeled dynamics in the kinematic control loop. The effectiveness of the proposed method is shown experimentally on a WAAM robotic system composed of a 6-axis industrial manipulator, a 2-axis positioning table and a Cold Metal Transfer (CMT) power source.