Motion Discontinuity-Robust Controller for Steerable Mobile Robots

Abstract

Steerable wheeled mobile robots are able to perform arbitrary three-dimensional (3-D) planar trajectories, only after initializing the steer joint vector to the proper values. These robots employ fully steerable conventional wheels. Hence, they have higher load carrying capacity than their holonomic counterparts, and as such are preferable for industrial applications. Industrial setups nowadays are being prepared for the emerging field of human-robot collaboration/cooperation. Such field is highly dynamic, due to fast moving human workers, sharing the operation space. This imposes the need for human safe trajectory generators that can lead to frequent halts in motion, replanning, and to sudden, discontinuous changes in the position of the robot's instantaneous center of rotation (ICR). Indeed, this requires steer joint reconfiguration to the newly computed trajectory. This issue is almost ignored in the literature and motivates this work. The authors propose a new ICR-based kinematic controller, that is capable of handling discontinuity in commanded velocity while respecting the maximum joint performance limit. This is done by formulating a quadratic optimization problem with linear constraints in the 2-D ICR space. The controller is also robust against representation and kinematic singularities. It has been tested successfully on the Neobotix-MPO700 industrial mobile robot.