Adaptive Sliding Mode Control for Vehicle Platoons with State-Dependent Friction Uncertainty
Rishabh Dev Yadav
TL;DR
This work tackles robust formation control of vehicle platoons under unknown state-dependent friction by introducing an adaptive sliding mode control (ASMC) framework. The control architecture separates kinematic planning from dynamic execution, employing force and torque controllers with adaptive laws and a Lyapunov-based stability proof to achieve Uniformly Ultimately Bounded behavior. Analytically, the closed-loop system with $F(t) = - \Lambda_v s_v - \rho_v sgn(s_v)$ and $\tau(t) = - \Lambda_\omega s_\omega - \rho_\omega sgn(s_\omega)$ is shown to be stable, with $V=V_v+V_\omega$ ensuring bounded convergence despite unknown friction and disturbances. Simulations in Gazebo with a three-robot platoon demonstrate improved trajectory tracking and inter-robot gap maintenance across varying friction conditions, highlighting the method's potential for real-world autonomous fleets and decentralized platooning.
Abstract
Multi-robot formation control has various applications in domains such as vehicle troops, platoons, payload transportation, and surveillance. Maintaining formation in a vehicle platoon requires designing a suitable control scheme that can tackle external disturbances and uncertain system parameters while maintaining a predefined safe distance between the robots. A crucial challenge in this context is dealing with the unknown/uncertain friction forces between wheels and the ground, which vary with changes in road surface, wear in tires, and speed of the vehicle. Although state-of-the-art adaptive controllers can handle a priori bounded uncertainties, they struggle with accurately modeling and identifying frictional forces, which are often state-dependent and cannot be a priori bounded. This thesis proposes a new adaptive sliding mode controller for wheeled mobile robot-based vehicle platoons that can handle the unknown and complex behavior of frictional forces without prior knowledge of their parameters and structures. The controller uses the adaptive sliding mode control techniques to regulate the platoon's speed and maintain a predefined inter-robot distance, even in the presence of external disturbances and uncertain system parameters. This approach involves a two-stage process: first, the kinematic controller calculates the desired velocities based on the desired trajectory; and second, the dynamics model generates the commands to achieve the desired motion. By separating the kinematics and dynamics of the robot, this approach can simplify the control problem and allow for more efficient and robust control of the wheeled mobile robot.