Virtual link model for redundantly actuated holonomic omnidirectional mobile robots

This paper presents a new modeling method for holonomic omnidirectional mobile robots propelled by powered-casters. A mobile robot with powered-casters is redundantly actuated since it is controlled by four or more numbers of motors while its configuration is represented by 3DOF on the ground. The redundant architecture leads inverse problems on motion planning, actuator coordination, static or dynamic control, and dead-reckoning calculations with redundant wheel information. To overcome those problems led by the redundant architecture, a new modeling method based on the virtual linkage concept is proposed. The virtual linkages are applied for representing virtual deformations of a robot frame even though an actual robot frame cannot be deformed. The virtual frame deformation provides additional DOF on the robot, which allows total robot DOF equal to the number of actuators equipped with the mobile robot. The acquired n-wheeled robot model with virtual linkages satisfies a class of 2n by 2n system, no redundancy is found in a control system where no inverse calculations of non-square matrices, nor motion planning of redundant actuators. The proposed virtual link model is generalized and a unified procedure is presented for n-wheeled mobile robots. A modeling example is shown and experiments of a three-wheeled robot prototype are performed for evaluating the proposed model and its implementation to a redundantly actuated omnidirectional mobile robot