Design and Control of Paired Mobile Robots Working Across a Thin Plate With Application to Aircraft Manufacturing

Abstract

A pair of mobile robots acting on opposite sides of a thin plate is developed for a class of tasks where robots have to work together, carrying a pair of end-effectors and traversing across a plate surface. Using powerful magnets, the paired robots attract each other, support themselves against gravity, and generate traction force to move across the panel.First, the design concept of paired mobile robots is presented, followed by dynamic modeling and magnetic analysis. Conditions for preventing the robot from falling as well as from slipping on the plate surface are examined. Time-optimal control of the paired robots subject to the no-fall, no-slip conditions is formulated and solved numerically. Precision positioning control using a laser beacon is designed and tested. A prototype of the paired robots using Halbach array permanent magnets and Lorentz force actuators is developed, and the control methods are implemented and tested on the prototype.Note to Practitioners-The paired robot architecture presented here was inspired by aircraft wing box assembly, where two end-effectors, (one inside and the other outside), must be coordinated to tightly clamp a skin panel and perform precision drilling and fixing operations. This paper aims to automate this process with paired mobile robots that transport and align the two end-effectors anywhere on the aircraft wing. This will eliminate the need for scaffold and fixtures to support the end-effectors, since the paired mobile robots are attached directly to the aircraft body and position the end-effectors at desired locations. This paper presents the necessary analysis to be performed when applying this dual robot concept. We show how much force is necessary to support the paired robots against gravity and perform locomotion and fine positioning. We show that a special permanent arrangement, called the Halbach array, allows us to generate sufficient forces. We further discuss the complications of eddy currents, friction, and the whole system dynamics. It is shown that a prototype paired robot system can generate 1000 N of attractive force and achieve high positioning accuracy of less than 100 um of error. Potential applications include tank or pipe inspection, ship building, or general sheet metal manufacturing processes.

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