Designing a Mobility Solution for Fully Autonomous Welding of Double-Hull Blocks

Abstract

Automating the double-hull block welding improves the shipbuilding efficiency and mitigates health risk to the welders. Due to the unique challenge posed by the internal structures, existing technologies are at most semi-autonomous. Believing that mobility is key to full autonomy, we employ mobile robot technology to transport the welding manipulator, treating the internal structures as obstacles. Though many robot designs for obstacle scaling exist, there is no selection guideline. To this end, we surveyed existing robots and came out with a taxonomy to explain the design philosophies behind them. From the survey, it is ascertained that there are two suitable philosophies: bridging and conforming. Bridging mechanisms create links between points on obstacles while conforming mechanisms have the robot’s body attuned to the surface contour of obstacles. Understanding the pros and cons, we conclude that having a hybrid mechanism with tracked arms and articulated body would be ideal for the structured environment. Subsequently, we studied the feasibility of the design in terms of configuration, geometry, kinematics, and stability. Lastly, the proposed design was tested by building a 1/3 scale prototype robot. It was made to perform the expected motions in a mock double-hull block setup. The experiment proved that the design achieves the mobility objectives of the robot. With this mobility design, we solved the most challenging issue in enabling fully autonomous welding in double-hull blocks. The taxonomy is instrumental in our design selection and could be helpful for other robot designers too.