Based on wheeled mobile robots (WMRs) with unknown longitudinal slipping parameters, an adaptive control strategy for a tracked mobile robot is presented, in which the longitudinal slipping of the left and right wheels are described by two unknown parameters. The kinematic model of mobile robot with wheels’ slipping is derived from the motion model of mobile robot without wheels’ slipping. Employing the Lyapunov direct method, an adaptive nonlinear feedback control law that compensates for the longitudinal slipping is proposed to achieve an objective of tracking a given trajectory. The orientation angle observer is designed to estimate the immeasurable orientation angle of the robot by employing the coordinate information. Asymptotic stability of the closed-loop system is ensured by choosing an appropriate Lyapunov function. Numerical and experimental results show the effectiveness of the proposed control approach.

Introduction

In the past two decades, wheeled mobile robots (WMRs) are increasingly presented in the fields of industry, agriculture, national defense and service, accordingly the problem of motion control of WMRs has attracted the interest of the researchers in view of its theoretical challenges result from the nature of the nonholonomic constraints [1], [2]. Many researchers have designed tracking and stabilization controllers for nonholonomic mobile robots using nonlinear control methods, such as sliding mode control[3]–[۶], adaptive control[7]–[۱۰], back-stepping control[11], [12], optimal control [13]–[۱۵], intelligent control based on neural network[16]–[۱۸] and fuzzy control[19], [20]. The previous papers mostly assume that the WMR satisfies nonholonomic constraints [1]–[۲۰]. The nonholo- nomic constraints are generated by the assumption that the mobile robots are subject to a ‘pure rolling without slipping’. However, since the robotic wheels’ slipping can happen in various practical environments such as the on wet or icy roads, rough terrain, or the rapid cornering, the nonholonomic constraint can be disturbed in a few literatures [21]–[۲۸]. Therefore, it is necessary to study the control method of mobile robot considering wheels’ slipping. In [21], Wang and Low presented the model of wheeled mobile robot with wheels’ longitudinal and lateral slipping, and its controllability was tested according to the maneuverability of the mobile robot. They also proposed a control method for path following and tracking of mobile robots considering slipping [22], [23].