Kinematic analysis and singularity robust path control of a non-holonomic mobile platform with several steerable driving wheels

The use of more than one steerable (standard) driving wheel allows a robot to perform omnidirectional motions. However, the modeling and control of such robots is challenging since the system is non-holonomic, nonlinear and typically over actuated. Moreover, such platforms exhibit kinematic singularities. A well known singular configuration is the configuration where two steerable driving wheels are coaxial aligned. This is highly problematic since this configuration corresponds to pure rotations, which is crucial for narrow space navigation. In this paper a control scheme with improved robustness w.r.t. these singularities is derived. It is based on the second order (accelerations) non-holonomic constraints. The remaining singularity is tackled by a regular parametrization of the robot's motion. Thereupon a novel control concept is presented which is based on an input-output linearization in terms of a path parameter. The choice of this parametrization provides an additional parameter in the controller design. The approach is demonstrated for a prototype implementation.