Control of a reconfigurable, redundant ball wheel drive mechanism based omnidirectional mobile platform

The Human-Assisted Nonstationary Device for Lifting (HANDL) is motivated by enhancing worker's safety for lifting and/or movement of on-site materials in highway work zones. Corresponding to this requirement, a new, robust omnidirectional wheeled mobile platform based on a unique ball wheel actuator mechanism and lifting device are being developed by the Advanced Highway Maintenance and Construction Technology (AHMCT) Research Center in collaboration with the Stevens Institute of Technology. This work has been sponsored by the California Department of Transportation (Caltrans).; The proposed ball wheel mechanism can move in all directions on the plane, instantaneously and isotropically. For accurate motion with parametric uncertainty in the dynamic model, an adaptive controller is applied to the trajectory tracking control of the single ball wheel platform. The redundant drive system of the ball wheel mechanism changes its configuration according to the heading direction by changing the contact pressure between the drive wheel and the sphere. A weighted torque optimization method is used for the resolution of redundancy and for smooth reconfiguration.; An omnidirectional platform, integrated with a manipulator, will typically involve the loading and unloading of an unknown object, and both its dynamic and kinematic parameters will change due to deformation of the ball wheels. The proposed robust adaptive tracking controller estimates both parameters and uses them in the controller, so that position errors are significantly reduced compared to those for a PD controller and an adaptive controller with dynamic parameter estimation.; Motion on uneven terrain by an omnidirectional platform is addressed. According to kinematic analysis, the contact point between the ground surface and the ball wheel plays a significant role for motion control. Euler-Rodrigues parameters and Montana's contact equations are used for tracing the contact point.