Study On Posture Control Algorithm Of The Unicycle Robot

As an inherently unstable wheeled mobile robot, the unicycle robot is multi-variable, non-linear, strong coupled and underactuated which make it can be an ideal testbed for many kinds of control algorithms. So it has very important value of theoretical research. Meanwhile, the unicycle robot also has a broad application prospect since it has simple mechanism, can move flexibly and work in small space.This paper mainly discusses the posture control algorithm design-related problems of the unicycle robot, laying a theoretical foundation for autonomous mobility of the unicycle robot,Firstly, the dynamics of the unicycle robot is derived using Lagrange formulation through analyzing the kinematics of the robot and solving the kinetic energy and potential energy of the system. Then, for real-time control of the robot, the complicated Lagrange dynamic equations are simplified and the whole dynamics is divided into three subdynamics, that is, lateral posture balance dynamics, longitudinal motion dynamics and dynamics of the yaw direction. Corresponedly, three state space submodels are obtained. Finally, based on the simplified model, a convenient state feedback control design with linear structure was proposed and implemented by coordination of the separated lateral posture balance control and longitudinal motion control. Considering the interactions between the yaw direction and the roll and picth direction, gain scheduling method was adopted, thus realizing the posture control of the unicycle robot in straight line movement.The asymptotical stability of the posture stabilization control system in the neighborhood of the upright posture of the robot is proved by the Lyapunov direct method, which inllustrates the reasonability of the design. Then, the effectiveness of the proposed control algorithm is also verified through simulation results in Matlab; and the good performance to impulse disturbance in roll and pitch direction respectively shows the robustness of the controller.In order to enable the underactuated unicycle robot move freely, based on the simulation, a brief discussion of control to the yaw direction of the unicycle robot is made. And it draws the conclusion that we can steer the unicycle robot to another direction by making the robot track a certain angle command in roll and pitch direction respectively. Then, a detailed analysis of impact of various parameters (velocity command of the wheel, direction, amplitude, frequency and phase difference of the roll and pitch angle commands) on the yaw direction of the robot was given.