| The complex landform and harsh environment of Mars have become one of the obstacles to the deep and extensive exploration of Mars.There are many crushed rocks on the ground of Mars,and the terrain is rugged and complex,which requires the rover to have an excellent ability of "obstacle crossing".Soft and fluid,easy to cause wheel skid and subsidence,which requires the rover to have excellent "high traction capacity." China’s Zhurong spacecraft successfully burned down on May 15,2021.It is the first time in the world to use an "active suspension" mobile system,which enables the rover to travel in a cross-sport mode.In this paper,the method of "motion mode matrix" is created,and all motion modes that can be formed by the active suspension rover are exhaustively listed.Five important "obstacle-jumping motion modes" and two "traction motion modes" were selected and implemented.The autonomous switching strategies in five "obstacle jumping motion modes" and two "traction motion modes" are also studied.Finally,Vortex simulation platform is used to verify the autonomous switching strategy.In this paper,based on the "active suspension" mobile system structure of the rover,the motion information of each joint of the active suspension is expressed in the form of matrix,and the "motion mode matrix" is constructed.The motion pattern matrix was simplified based on the motion constraint relationship between each joint.After the bit traversal,the "Basic Action Table of Active Suspend Rover" is obtained.All actions in the table can be combined freely,so that infinite "motion modes" can be constructed.According to the requirements of "obstacle-jumping ability" and "towing ability" of the Mars surface probe,five main "obstacle-jumping mode" and two "towing mode" were selected,and joint space optimization and wheel-leg coordination kinematics design were carried out to realize the parameterized realistic motion of these several motion modes.Finally,the traction performance of the two "traction" modes and the performance of the five "obstacle crossing" modes are calculated.Based on the information of the position,height and surface topography of the obstacle,the switching strategy of the obstacle mode is studied in this paper.Based on the study of the contact state of "wheel-rock" surface,an online method for calculating the surface topography of obstacles is proposed creatively,which solves the problem of selecting the motion mode of the rover facing the irregular obstacles.On this basis,aiming at solving the obstacle crossing ability of the rover’s obstacle crossing mode,the selection strategy of obstacle crossing mode is formulated.Aiming at two kinds of "traction mode",this paper studies the autonomous switching strategy of "traction mode" based on the motion state information of wheel slip rate and driving moment.In this paper,a fuzzy control switching strategy based on slip rate and slip rate change rate information is established to realize the online real-time autonomous switching from "wheel mode" to "creep mode" in traction mode.The fuzzy control switching strategy based on performance index and driving slip rate information was established,and the online real-time autonomous switching from "creep mode" to "wheel mode" was realized,as well as the online autonomous adjustment of sliding rate driven by creep mode was realized.In the Vortex simulation system,the parameterized models of the above seven motion modes are completed.In the simulation environment of abrupt mechanical properties of ground and steep slope climbing,the two traction modes can be switched to each other autonomously,and the rover can escape the trap and climb steep slope autonomously.According to the requirements of obstacle surfacing,the online calculation of obstacle surface topography is carried out.In the Vortex simulation system,the process of obstacle surfacing is simulated with five obstacle surfacing modes. |
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