Research On Robust Sliding Mode Control Of A Self-balancing Two-wheeled Robot

The self-balancing two-wheeled robot(SBTWR)has the advantages of simple structure,small volume and good flexibility.It can move in narrow and much limited construction space,so it will be more freely and effectively for the robot to replace the manual labor.Thus,it has extensive application foreground in military and civilian and some other fields.Meanwhile,the SBTWR,with the typical characteristics of multi-variables,under-actuated,nonlinear and coupled,has become an essential experimental platform for the research and verification of various kinds of control theory and control method.The research object of this article is the GBOT2001 self-balancing two-wheeled robot produced by GOOGOLTECH.Considering the unknown external disturbances as well as the slipping and skidding disturbances on the ground,the control methods are studied on trajectory tracking of the SBTWR.The main research contents of this article are as follows:Firstly,according to the structure and the motion characteristics of the SBTWR,the kinematic models of the SBTWR are established under two conditions: one is under the condition of pure rolling;the other is under the impact of the slipping and skidding.And the nonlinear dynamic model of the SBTWR is established based on Newton's Mechanics.Considering that the pitch angle and the yaw angle of the SBTWR are irrelevant,the dynamic model of the SBTWR is decoupled into two subsystems for the convenience of controller designing: the displacement-pitch angle subsystem and the yaw angle subsystem.After linearizing the dynamic models at the equilibrium point,the stability analysis of the linear systems is studied.Then,the LQR controller is designed to realize the self-balancing of the SBTWR based on the linearized model.And the affections of the states and control variables by the parameters change of Q and R are analyzed.Taking the external disturbances into consideration,the sliding mode controller based on the previous LQR controller is designed,so as to enhance the disturbance rejection performance of the system.Next,the fuzzy sliding mode controller is proposed to realize the trajectory tracking based on the nonlinear model of the SBTWR.It combines the fuzzy control method with the sliding mode control method.The fuzzy controller is designed to tune the gain value of the switching term in the sliding mode controller,so as to eliminate the chattering of the sliding mode control.Following,considering the external unknown disturbances with pure rolling condition,the nonlinear disturbance observer is designed to estimate the external disturbances,the kinematic controller based on the Lyapunov method is designed according to the kinematic error model.According to the nonlinear dynamic model,the sliding mode controller is developed to track the designed kinematic control law,so as to realize the trajectory tracking control of the SBTWR.Finally,considering the slipping and skidding disturbances,the second-order disturbance observer is designed to estimate the slipping and skidding perturbation.The kinematic controller based on the Lyapunov method is designed to tackle the influence of slipping and skidding,and the sliding mode controller based on double power reaching law is designed to achieve the tracking control of the SBTWR.