Modeling and Control of Wheeled Mobile Robots

The accurate model-based servo-control of wheeled mobile robots (WMRs) relies upon the formulation of realistic kinematic and dynamic models. We* identify six special WMR characteristics (closed-chains, hig her-pair joints, unactuated and unsensed joints, friction, and pulse-width modulation) that require methodologies for modeling and control beyond those conventionally applied to stationary manipulators. Then, we develop methodologies for the kinematic and dynamic modeling of robotic mechanisms incorporating these special characteristics. We introduce instantaneously coincident coordinate systems and the wheel Jacobian to resolve WMR kinematic modeling. We introduce the concepts of force/torque propagation and frictional coupling at a joint to formulate a powerful unifying dynamic modeling framework. We compute the inverse and forward kinematic and dynamic solutions for modelbased WMR servo-control and simulation. We demonstrate the applicability of (kinematics-based) resolved motion rate and (dynamics-based) resolved acceleration servo-control methodologies to WMRs through computer simulation evaluation studies. We exemplify our modeling and servo-control methodologies through Uranus, a three degree-offreedom (DOF) WMR, and Bicsun-Bicas, a two DOF WMR. Our results show that resolved motion rate servo-control is adequate for general-purpose applications of Uranus. In contrast, the mechanically simpler Bicsun-Bicas requires the computationaly complex resolved acceleration servo-control to compensate for the significant coupling and nonlinear components in its dynamic model. We recommend Bicsun-Bicas with resolved acceleration servo-control for generalpurpose indoor applications because it is mechanically simple, capable of tracking any spatial x-y path, and if a turret is added, provides onboard manipulators, sensors, or docking instruments with three DOFs.