Optimal Trajectory Tracking Control of Four-Wheel Independent Driving Robots With On-Axle Steering

This article proposes an optimal trajectory tracking method for a novel robotic platform featuring four-wheel independent driving and on-axle steering (4WID-OAS). Unlike conventional mobile robots, the 4WID-OAS robotic vehicle adopts a unique coordinated differential steering system that possesses the low torque characteristics of differential steering and the high maneuverability of four-wheel independently steering (4WIS). To enable autonomous trajectory tracking, a lightweight control scheme is developed by integrating a four-wheel speed distribution strategy with an optimal tracking control law. The maneuvering model of the 4WID-OAS robot is first investigated as the foundation for the trajectory tracking system. Subsequently, an explicit nonlinear model predictive control (ENMPC) strategy is designed to solve the optimal tracking problem. With the closed-form ENMPC solution, online optimization is not required, thereby enabling high control bandwidth of advanced control strategies with reduced cost. The stability of the system is rigorously proven. Comprehensive simulations and field experiments validate the superiority of the 4WID-OAS robot and demonstrate that the proposed controller effectively balances tracking accuracy with computational efficiency, facilitating real-time deployment on embedded platforms.