Hierarchical Scheme Based Trajectory Tracking Control for 4-Wheel Skid-Steering Mobile Robots With Unknown Disturbances and Motion Constraints

The trajectory tracking problem of 4-wheel skid-steering mobile robots (SSMRs) with unknown disturbances and motion constraints is considered in this paper. A hierarchical control scheme is proposed to solve these problems. The motion constraints are considered in the kinematic layer with the model predictive control (MPC) approach, and the disturbances are estimated and compensated in the dynamics layer by a time-varying gain extended state observer (ESO). In addition, the control allocation is considered to allocate the virtual control inputs obtained by the upper layer controller to make the 4-wheel motors turn as instructed. Finally, the stability and tracking performance of the proposed control scheme are verified by theoretical analysis and comparative numerical simulations.