Unified motion control of 4WIS-4WID WMR with unlimited steering and load transfer consideration

Abstract

This paper presents a unified motion control framework for a four-wheel independent steering (4WIS) and four-wheel independent drive (4WID) wheeled mobile robot (WMR) equipped with an unlimited steering angle system. Unlike conventional methods that rely on mode-specific kinematic controllers, the proposed controller does not require prior classification of driving modes. The controller defines the necessary forces at the tire positions to track the desired velocity profile in the body-fixed frame, considering tire slip dynamics, load transfer effects, and friction constraints based on the Magic Formula. The steering angles and in-wheel motor torques are then determined to generate the required forces. Due to the difficulty of directly measuring tire forces, a disturbance observer (DOB) is used to estimate these forces in real-time. Simulation results demonstrate that the proposed controller outperforms conventional kinematics-based approaches in velocity tracking accuracy, while maintaining stable tire force distribution and vertical load limits, ensuring the robot’s stability and effective maneuverability even under highly dynamic conditions characterized by large lateral accelerations and the resulting tire slip and load transfer.