Singularity avoidance for over-actuated, pseudo-omnidirectional, wheeled mobile robots

For mobile platforms with steerable standard wheels it is necessary to precisely coordinate rotation and steering angle of their wheels. An established approach to ensure this is to represent the current state of motion in form of the Instantaneous Centre of Motion (ICM) and to derive a trajectory within this space. However, while control in the ICM space does guarantee adherence to the system's nonholonomic constraints, it does not avoid the system's singular configurations. Within this work we address the problem of singularity avoidance within the ICM space. Singularities related to the mathematical representation of the ICM are reduced by a reformulation of this representation. Furthermore, a controller based on artificial potential fields avoiding singular configurations of the robot by representing them as obstacles in the derived ICM space is designed. The resulting controller is particularized and analyzed w.r.t. the Care-O-bot 3 demonstrator.