| Holonomic vehicles, having three degrees of freedom, are well suited for use in congested environments and tight spaces, and can execute complex motions with ease. Use of robots in indoor environments is facilitated by the use of holonomic vehicles as the basic building block for wheeled office-type robots. Many holonomic robot designs that use compound wheels and other complex mechanisms have been proposed.; This thesis presents the design and control of a holonomic robotic vehicle that uses ordinary wheels: the Powered-Caster Vehicle, or PCV. A powered-caster vehicle provides smooth accurate motion. The design can be used with two or more wheels, and is shown in this work in a four-wheeled incarnation: the Nomad XR4000 mobile robot; A PCV is a type of parallel mechanism for which there is no unique Jacobian relating the known joint velocities to the Cartesian velocities. To simplify the development of the kinematic and dynamic equations, however, the PCV can be viewed as a collection of cooperating serial manipulators. This dissertation presents a new approach for a modular, efficient dynamic modeling of powered-caster vehicles based on the augmented object model, which was originally developed for the study of cooperative manipulation. The proposed controller enables direct operational space position control and force control. Using the vehicle dynamic model, and actuation and measurement redundancy resolution, a control structure has been developed that allows vehicle dynamic decoupling and slip minimization. The effectiveness of this approach is experimentally demonstrated for motions involving large dynamic effects.; The integration of a manipulator and a mobile robot base places special demands on the vehicle's drive system. For smooth accurate coordination with an on-board manipulator, a holonomic vibration-free wheel system that can be dynamically controlled is needed. The PCV dynamic model and control structure have been integrated into a new mobile manipulation platform integrating the XR4000 mobile robot and a PUMA 560 arm. The experimental results illustrate the performance of this platform and demonstrate full dynamic decoupling and its significance in mobile manipulation tasks. |
