Research On Six-Wheeled Rover Mobile System With Series Multi-Articulated Suspension And Its Key Technology

A lunar rover is the major equipment of lunar surface exploring and sample returning, and its kinematic and dynamic characteristics will directly affect execution of lunar surface explorationThis dissertation has put forward a six-wheeled lunar rover mobile system with series multi-articulated suspension, and systematically studied the mobile system. The research works focus on following aspects:The key technologies of overall design of the rover mobile system are studied. Based on configuration synthesis and analysis of rover chassis and suspension, a lunar rover mobile system in hybrid locomotion, which means the mobile system may be in either active locomotion or passive locomotion according to mobility demand, has been put forward in this dissertation. In the design concept,the rover mobile system has six individually motorized wheels and a multi-articulated suspension composed of two parts of series linkage frameworks connected by a differential balance linkage mechanism, and ensured with advantages of average weight and good traction on each wheel. Thereafter selected outline size minimizing as a object function and locomotion performances as constraints,the parameters of the rover mobile system are optimized. According to the optimal parameters, structure design of the rover mobile system has been performed, meanwhile lunar environment has been taking into serious account during design,and some technologies such as cylinder-conical wheel body with lugs, ceramic bearings,metal rubber vibration absorbers are applied to the rover mobile system. Furthermore, simulating models in Pro/E software and ADAMS software have been built up for making a prototype and simulation thereafter.Regarding to its performance analysis of the rover mobile system, locomotion modes have been designed to take advantage of its hybrid locomotion concept and be in favor of trafficability analysis of the rover mobile system, and therein mechanism and locomotion principle of the modes have been introduced. According to typical cases of trafficability loss, geometry limiting values of the trafficability of the rover mobile system have been defined along longitude and transverse. For analysis of obstacles trafficability of the rover mobile system, quasi-static method is applicable due to its very low locomotion velocity, so the quasi-static equilibrium equations have been derived to express critical conditions and solve limiting values of mobile system surmounting obstacles. Because it is the most difficult for two wheels simultaneously surmounting obstacles, quasi-static equilibrium equations and locomotion geometry constraints have been derived for analysis of two wheels climbing up a vertical obstacle, hurdling a ditch, and climbing on a slope in the passive locomotion mode or active locomotion modes respectively, curves of surmounted obstacle dimension versus equivalent traction ratio of wheel-soil and some limiting trafficability values have been obtained by solving equations. In addition, the corresponding simulations of mobile system to surmount above motioned obstacles in ADAMS have been accomplished, and the simulating results validate the correctness of theoretical calculating results by comparing with each other.Kinematics modeling and analysis of the rover mobile system in a 3-dimension terrain is another research aspect. The forward kinematics models involving wheel slips has been made on the basis of deriving wheel-soil interaction coordinate transform matrix and applying D-H coordinate transform matrix, velocity equations about the main body and wheels have been formed by Jacobian matrix. Then the inverse kinematics solutions have been farther derived, and a path model for mobile system kinematics has been described. The kinematics simulations of the rover mobile system moving on the rugged terrain have been carried out, and the variable curves of the main body have been obtained.With respect to its dynamics analysis of the rover mobile system, introducing and defining equivalent traction ratio, a simplified wheel-soil interaction model has been derived firstly on the basis of Soil-Vehicle Mechanics. The dynamics model of the rover system on the rugged terrain has been formed by applying the dynamic theory of multi-body system, Kane's method and the simplified wheel-soil interaction model, and then the dynamic vector equations have been derived. Both for analysis of riding quality of the rover mobile system and for evading great complexity of its theoretical vibration model and computing, riding quality simulation has been carried out in ADAMS. During simulation, simulating vibration absorbers were installed on front wheels but not on other wheels, which are composed of springs and dampers to simulate metal rubber vibration absorbers. The simulation results validate the effectiveness of metal rubber vibration absorbers by comparing riding quality of platforms on front wheels and rear wheels, when the simulating mobile system moves on hard ground or climb over an obstacle.This dissertation has developed a prototype of presented rover mobile system with series multi-articulated suspension and a multi-purpose testbed to test the cylinder-conical wheel traction characteristics of the rover mobile system prototype on soft soil, traction characteristic curves of the wheels have been obtained, and that feasible wheel slips of the prototype on soft soil have been presented. Some simulating lunar surface terrains have been constructed for the mobile system prototype testing,and its locomotion performances in these simulating terrains have been tested such as mobile velocities, controllability, obstacles trafficability in passive locomotion mode or active locomotion modes, as well as function of metal rubber vibration absorbers. These testing experiments validate the correctness of theoretical computation and simulation for above locomotion performances of the mobile system. Meanwhile,in order to provide a comparability reference for testing and analysis of locomotion performances of the rover mobile system, the uniform equivalent traction ratio for full prototype traction is defined and its measuring method has been presented. Experiments prove that the rover mobile system prototype is applicable for rugged and unstructured terrain and strong capable of terrain adaptability and obstacles trafficability.