Passive Articulated Rover With Eight Wheels And Its Trajectory Planning And Motion Control

The passive articulated rover has been applied in the planetary exploring because of its simple mechanism, good motion performance in rough terrain. It has been the main research focus in the field of planetary rover design in the entire world, and its configuration has been widely studied and developed. With the startup of China moon exploration project, it becomes urgent to develop a lunar rover with independent intellectual property and good performance, and study its key techniques, which have the graveness and profound meaning in technology and politics.This paper presents a new passive articulated rover, which is based on the passive articulated suspension, with link mechanism, symmetrical structure, and torsion-bar between links as shock-absorbing device. The new rover can improve the performance of overcoming obstacle capability and terrain adaptability, and can reduce the difference of rover motion direction. Using common method for suspension design, basic rover configuration dimension is determined, design of torsion-bar and differential device analyzed in detailed, and experiments about damp performance of torsion-bar is presented. Through simulation and experiments, it is verified that new rover has good performance motion and adaptive terrain.As an important rover structure for future planetary exploration, it is critical to develop and analyze its kinematics modeling. To demonstrate kinematics modeling method, according to mechanics of passive articulated rover, this paper takes new eight-wheel rover as an example, and three different kinematics models, using Denavit-Hartenberg transform modeling method, plane geometry kinematics method and 3D geometry kinematics, are made based on rover's mechanical characterization and contact situation between terrain and rover. Then the comparative analysis on three different kinematics models was produced with their respective application conditions and scope. It gives the basic theory for motion control and simulation of the passive articulated rover.In order to study trafficability and to provide theory and kinematical estimation model for rover moving in rough terrain, the kinematical estimation method for passive articulated rover in rough terrain is presented. In this method, based on the study of passive articulated rover, the complete suspension kinematics model from wheel to inertial reference frame is presented, which uses D-H kinematics model method of manipulator and presentation with Euler angle of pitch, roll and yaw. Using this complete suspension kinematics model and numerical continuous and discrete Newton's method with iterative factor, the numerical solving method of kinematic observer estimation of articulated rovers on smooth rough and discrete terrain is constructed. But lunar soil is loose and lunar terrain is rough, the assumption that each wheel has a single point of contact with non-deformable terrain is not fit, so an improved contact model is adopted. To demonstrate this numerical solving method, an example about eight-wheel lunar rover with two torsion-bar rocker-bogie is presented. Simulation results show that this numerical solving method of kinematic observer estimation of articulated rovers on rough terrain is valid and its precision can satisfy requirement of simulation system.According to complexity of moon environment and limitation of trajectory generation based 2D terrain, an adaptive trajectory generation model for passive articulated rovers on arbitrary rough terrain which satisfies arbitrary constraints is constructed. This method adopts numerical solving method, combined with principle of parameterized control based on kinematic estimation numerical solving method. It considers the influence of rough terrain in the phase of planning, and modifies the trajectory error through pose estimation arithmetic, not through realtime feedback. Simulation results indicate this method is a new adaptive trajectory generation method for passive articulated rovers on arbitrary rough terrain.On moon, there are many obstacles impassable for rover, so the parameterized smooth trajectory generation method for wheeled planetary rover in multi-obstacle environment is presented based on method of trajectory generation, which satisfies arbitrary constraints. This method takes obstacle as model of parameterized trajectory generation in C-Space, and then takes it as a constraint, uses numerical solving method to generate trajectory. Simulation results indicate this method can be taken for trajectory generation method for wheeled rover in multi-obstacle environment in C-Space.In order to reduce power consumption among suspension for passive articulated rover moving in rough terrain, and to improve motion performance, control algorithm of multi-wheel coordination based on estimation of wheel-terrain angle is presented. This method uses the mechanics of passive articulated rover, principle of wheel speed matching and estimation method of wheel-terrain angle in rough terrain, combining kinematics model to control each wheel speed to adapt terrain topography. To improve performance of rover in soft soil better, sliding mode motion control method, based on optimum slip is adopted. This method uses dynamics modeling deduced from tire-soil interaction mechanics, adopts control modeling with slip ratio as state variable and optimum slip from simulation and experiments; and integrates sliding modecontrol method to modify rover wheel speed to improve motion performance in soft soil. Simulation and experiments show this method is valid.