Motion Coordination Control Of Wheeled Rover Under Large Slip

Using planetary vehicles to detect planets is one essential part of the deep space exploration mission and the safe and reliable operation of the planetary rover on the surface of the planet is the basis of all exploration missions.However,there are many craters and rocks on the planet’s surface and the star soil’s structure is loose and porous.Consequently,longitudinal and lateral slip will inevitably occur when the planetary vehicle runs on such soft and rugged terrain,which affects the safety and reliability of the planetary vehicle.Especially when the planetary vehicle faces more severe working conditions such as large curvature steering,slope steering and high-speed cruise,the planetary rover will have relatively large longitudinal and lateral slip.To improve the safety of the planetary vehicle operating in the complex alien environment,the control of the planetary vehicle under the condition of ”large slip” is necessarily to be investigated.In addition,the multi-wheel rover is independently driven and steered,whose drive system is redundant.Hence,Coordinating and optimizing the control input of each wheel are valuable to research,which can not only reduce the internal force loss,but also improve the planetary vehicle’s mobility to overcome obstacles.To aim at the soft and rugged terrain environment of the alien,a series of researches on the coordination control of the planetary vehicle under the large longitudinal and lateral wheel slip are carried out.Taking the six-wheeled rocker-bogie rover as the research object,the kinematics modeling of the planetary vehicle is derived by using the coordinate transformation method,and the two slip parameters of the slip rate and the sideslip angle are introduced in the model.Based on the Lagrange method,the vehicle dynamics model is established.Combining with the Terramechanics,the force status of the system is analyzed and the complete vehicle dynamics model is given,which includes the vehicle body suspension system dynamics and wheel-ground interaction mechanics.Due to the passive suspension structure of the planetary vehicle,some degrees of freedom are not available.Therefore,the planetary vehicle is reasonably simplified into a single-track model,which is suitable for the design of the control system.Meanwhile,aiming at the problem that the unknown noise interference during the operation of the planetary vehicle results in inaccurate parameter estimation,the adaptive Kalman filter algorithm is used to estimate the two key kinematic slip parameters: slip rate and side-slip angle.To solve the problem of coordination control under large slip conditions,A layered architecture is adopted in the vehicle control system.To solve the vehicle tracking problem The upper controller is based on the dynamics model under the condition of large slip,and the control law is designed by means of the robust control which gives the optimal turning angle of the wheel and the optimal speed of the vehicle body;the lower controller is mainly based on the kinematics model and wheel dynamics,which coordinates and allocates the optimal speed of the rover body to each wheel.Then the speed of each wheel is compensated according to the slip rate.Finally,the control law is designed by Lyapunov stability theorem,and the control torque of the six wheels is obtained.In order to verify the dynamic model,the parameter estimation algorithm and the control system,a simulation system including the dynamics module,the control module and the parameter measurement module is built with the help of Matlab Simulink platform.Firstly,the correctness of the system dynamics module is verified by comparing the open-loop result with the ADAMS dynamic model.Then the parameter measurement algorithm is verified by scaling the intensity of noise interference.At last,the effectiveness of the control system is verified by the simulation of the typical large slip conditions such as the steep slope climbing,the high-speed steering and the slope steering.The results show that the trajectory tracking control system of the rover still has good robustness under the condition of large slip.