Decentralized Kinematic Framework for Payload Transportation by a System of Mobile Manipulators

In this paper, we examine the development of a decentralized control framework for a modular system of wheeled mobile manipulators that can team up to cooperatively transport a large common object. Each individually autonomous mobile manipulator consists of a differentially-driven wheeled mobile robot (WMR) with a passive, two-degree-of-freedom, planar, revolute-jointed arm mounted in the plane parallel to the base of the WMR. The composite multi -degree-of-freedom vehicle, formed by placing a common object on the end-effector of two (or more) such mobile manipulator systems, possesses the ability to accommodate relative positioning errors of the mobile bases as well as change its relative configuration. Particular attention is paid in systematically developing a decentralized kinematic control scheme for the mobile manipulator modules, which can be implemented using only the actuated nonholonomic bases in the presence of passive joints in the manipulator system. The control scheme developed for the individual mobile manipulator is then adapted for the decentralized kinematic control of two mobile manipulators carrying a common object along a desired trajectory. Experimental evaluation of the performance of the resulting approach and the ability of the overall collaborating system to accommodate, detect and correct for relative positioning errors between the mobile platforms is also presented. Keywords—Mobile Manipulator, Formation, Nonholonomic Constraints, Twist Analysis, Decentralized Control.