Macro-mini collaborative manipulator system for welding in confined environments

Welding plays an important role in a wide range of industries, including aviation, aerospace, automobile manufacturing, and nuclear and chemical plants, all of which contain critical industrial assets. However, confined spaces and complex structures in these environments severely restrict the accessibility and functionality of in-situ welding tasks. Therefore, to enable welding operations in constrained spaces, a macro-mini collaborative manipulator system with multiple Degrees of Freedom (multi-DoF) is proposed in this paper. The collaborative system consists of a 6-DoF macro robotic arm and a novel 2-DoF slim mini manipulator. The macro manipulator (i.e., the robotic arm) provides large-scale movement to position the slim mini manipulator within confined environments. The slim mini manipulator, which features a novel serial mechanism, then adjusts and controls the pose of the end-effector (welding torch) to perform welding tasks in spaces that the macro manipulator cannot access. Given the novel design of the mini manipulator, kinematic and Jacobian modelling have been developed to enable intimate and accurate control of the collaborative welding system. The collaboration between the macro and mini manipulators occurs not only for individual movements but also at the level when compensatory movements are performed on each system to enable error compensation for the end-effector (i.e., welding torch). Finally, validation experiments of the collaborative manipulator system have been conducted in confined scenarios to verify its functionality and performance.