Development of omnidirectional wheeled mobile robots using structural properties

Abstract

This thesis lays a theoretical foundation for omnidirectional wheeled mobile robots. Omnidirectional mobile robots are those that can steer their motion in any direction in the configuration space. The requirement necessitating the reorientation of the wheels before steering gives rise to nonholonomic robots, and when the reorientation of the wheels is not necessary, holonomic robots result. Since the mechanisms depend on the wheels for mobility, typical approaches to building such systems have been designing omnidirectional wheels which have at least two DOF in motion relative to the robot body. However, since the motion of wheeled mechanisms is subject to constraints imposed by the wheels, the properties of motion constraints, rather than omnidirectional wheel requirements, must be taken into consideration in developing omnidirectional wheeled mechanisms. In this thesis, the structural conditions of the motion constraints are derived for holonomic and nonholonomic omnidirectional motion. Using the derived conditions, omnidirectional mobility can be determined without finding the robot Jacobian in a closed form. Also, the wheel configurations for omnidirectional motion can be decided. In addition to omnidirectional mobility, the derived structural conditions also imply the existence of constraints on joint motions, called joint motion constraints in this thesis, if there is actuation redundancy or the existence of constraints on robot motion, called robot motion constraints in this thesis, if the robot motion is nonholonomic. These constraints can be found using the structural conditions. The actuation redundancy results in an over-constraint problem which leads to temporal body deformation or tire slippage. To overcome such problems of conventional omnidirectional robots, the mobility augmentation method (MA) is proposed to produce omnidirectional motion with conventional wheeled bases with the degree of mobility less than three. It is shown that combined wit...