Development of a mobile robotic system for working in the double-hulled structure of a ship

Shipbuilding processes involve highly dangerous manual welding operations. Welding ship walls inside double-hulled structures presents a particularly hazardous environment for workers. This paper describes the “Rail Runner X” (RRX), a new robotic system that can move autonomously inside the walls of a double-hulled ship and automatically execute the required welding processes. The RRX robotic system is composed of a mobile platform and a welding robot consisting of a 3P3R serial manipulator. The robot is used to weld U-shaped trajectories located between two longitudinal stiffeners. The mobile platform enables traverse movements onto neighboring longitudinal stiffeners. The entire cross section of the robotic system is small enough to be placed inside the double-hulled structure via a conventional access hole from the outside shipyard floor. The overall engineering design process that led to the final robot solution developed is presented in this paper, including kinematic analysis data and experimental results for verifying the autonomous movement and welding performance.     

Coupled linkage system optimization for minimum power consumption

This paper presents the dynamic analysis and kinematic parameter optimization of a coupled linkage system for the purpose of employing the system in construction industry. So far, the kinematic optimization of wheel loaders was approached heuristically rather than utilizing elaborate theoretical examinations due to the complexity of coupled linkage structures. The results of the theoretical analysis and kinematic parameter optimization are presented in this paper. A wheel loader with Z-bar linkage was analyzed. For a given end-effector path, the linkage system was optimized to carry out effective motion while exhibiting minimum power consumption during operation. A modified principle of reduced system was applied in order to execute the dynamics analysis of the coupled linkage system. As a result, an optimal Z-bar linkage structure and a distribution of power consumption within the given conditions were obtained.     

Development of the end-effector measurement system for a 6-axis welding robot

We develop a new measurement system which can measure position and orientation of the end-effector of a six-axis welding robot. The developed measurement system consists of five digital probes. The measurement values from the digital probes are transformed into position and orientation of the end-effector with consideration of measurement system kinematics. Calibration procedure is applied to the probe system and accuracy of the system is measured. After the calibration, the positional accuracy is observed as 0.025mm, and the orientational accuracy is 0.075°, respectively. By using the developed measurement system, we present an experimental result for controller gain tuning about a welding robot. We used Taguchi method to find optimal gain set and succeeded to suppress the fluctuation of the end-effector. The fluctuation with high frequency can be reduced by 54% after gain tuning.