Robust Control of an Off-Road Single-Wheel Module Using Sliding Mode Control and Fuzzy Logic Control

In this paper, the linear speed tracking control problem of a single-wheel module (SWM) operating in an off-road environment is discussed. The approach is an extension to the authors’ previous work for angular speed control based on sliding mode control methodology. The linear speed tracking is performed by incorporating an adjusted reference angular speed. This reference speed is constructed utilizing a proportional control method. Further, two different approaches for tire slippage suppression are proposed. Both methods provide a corrected reference angular speed such that tracking it limits the tire slippage growth. The first method utilizes a pre-defined slippage limit, while the second method bounds the slippage by considering a range of characteristic slippages corresponding to different tire-terrain attributes. The second method is based on fuzzy logic control (FLC) and specifically is designed according to Mamdani fuzzy inference system. The efficacy of the controlled system is evaluated through numerical simulations. It is shown that the closed-loop system is able to robustly track a reference linear speed while it suppresses the tire slippage. Nonetheless, only the method based on FLC is able to address varying tire-terrain conditions and possible terrain transitions without compromising the system performance.