Developing Metrics for Comparison of Mobile Robots Performing Welding Tasks

Abstract

Developments in mobile robotic systems are leading to new methods and techniques for manufacturing processes in fields that traditionally have not seen much automation. Some of these tasks require process validation prior to use in the manufacturing process. One such example process is welding. However, there is a lack of industry standards for mechanized or robotic welding that can impede the introduction of mobile robotic welding systems in the market place. There is also a lack of generalized fitness measures that gauge the suitability of mobile robot topologies or dimensional designs to a set of tasks and can be used in the design or verification process. This paper will propose such a metric and demonstrate its use in evaluating mobile robot designs for welding tasks. The approach will be based on the representation of a general task as a pair of n-dimensional subsets in the Euclidean n-space. Similarly, the robot capabilities are represented as n-dimensional subsets (manipulability and torque ellipse) in the Euclidean n-space. The motivation is to enable a direct geometric comparison of the capabilities of the robot to the requirements of the task yielding a quantitative measure of fitness. This method is suggested to be well suited to tasks comprised of a relatively short sequence of well-defined motions, called gaits, which are performed repeatedly or in a periodic manner. Some examples are welding, swimming, painting or inspection. The paper will demonstrate the use of this metric in the evaluation and design of mobile robots for welding tasks with a desired set of weld pattern motions. Three mobile welding platforms having different topological kinematic arrangements will be evaluated based on this design verification metric. This metric will further be shown to supplement the weld qualification process through verification of the motion control portions of the weld process based on a specific robot design. The method will contribute to the design and development of mobile robotic welding systems to become viable and accepted manufacturing processes.