Research On Modeling And Motion Control Of A Two-wheel Drive Mobile Robot On Deformable Terrains

As the future missions of Mars exploration become various,the requirement of motion control on two-wheel drive mobile robot on deformable terrains appears.For example,the researches on tethered rover for caldera and cave exploration starts,and the tethered child rover which is generally a two-wheel drive mobile robot need to move on the bottom of the caldera covered with deformable terrains.Due to the lack of the dynamic model of wheeled mobile robot on deformable terrains,this paper creates a two-wheel drive mobile robot which can move on deformable terrain with forces feedback,proposes the model of the robot and design the motion control system based on this model.Based on the structure of the tethered child rover,a two-wheel drive mobile robot with two drive wheel and a follower wheel is developed.Three F/T sensors are respectively installed in the centers of wheels for the real-time force/torque feedback.The robot supports for both ‘velocity mode' and ‘monent mode'.According to the experimental results of the single wheel experiment,the resistance coefficient of a wheel on soft deformable terrains is redefined as a variable.The strong linear relationship between resistance codfficient and slip ratio is found and a linear model of them is built.The model then is modified to support for wheels with lugs.Two parameter identification methods for the modified model are proposed,and then the kinematics and dynamics models of the WMR are built.By using the kinematics and dynamics models of the WMR,a velocity control system is built and its stability is proved by Lyapunov methods.In order to solve the problem of low velocity feedback frequence,the velocity control system is modified.A new velocity control system under the situation that the body velocity of the WMR is unknown,is also proposed by using the esitamtion method of s based on the RC model.A trajectory tracking system is also built based on the velocity control system,and its stability is proved by Lyapunov methods.Experiments show that the accuracies of both ‘velocity mode' and ‘monent mode' of the WMR are high,and the mobility of the WMR on soft deformable terrain is good.The parameters of the resistance coefficient model are identified by two methods,which proves the validation of these two methods.The performance of those poposed velocity control system and trajectory control system are tested experimental.