The Inverted Modelling Method For Legged Mobile Lander And Gait Planning Based On Scale-distortion And Fault-toleration

Landing exploration of extraterrestrial planets such as Moon and Mars is a major strategy of deep space exploration for our country.At present,detection is mainly carried out in the form of the combination of a fixed lander and a rover.With the continuous development of deep space exploration,it is urgent to upgrade the fixed lander to the mobile lander that integrates the landing and patrolling function in order to expand the patrol area.The mobile lander has multi-task functions such as landing on different terrains and stable walking,so as to meet the needs of large-area detection and future base construction tasks.The proposal of mobile lander improves the terrain landing adaptability and stable walking ability,so as to meet the needs of large-area detection and base construction tasks in the future.Compared with the wheeled rover,the legged mobile lander has stronger terrain adaptability.The flexible leg mechanisms can span more complex terrain.The leg mechanisms also have better landing buffer capacity and acts as a return to the launch bracket.After landing,legs are uniquely deformed due to the collapse of buffers.This feature brings challenges to gait planning during the walking phase.In this paper,a walking performance modelling method based on scale distortion,the Inverted Modelling,is proposed in view of the characteristics of different leg lengths and scales of legged mobile lander.Different from the traditional performance representation method based on the ground or body coordinate system,the Inverted Modelling transforms the capability expression over the workspace from the local representation that depends on the certain terrain and pose to a global representation.The workspace of the lander on the complex ground and distorted length is generally described,and the global walking performance of the lander is analyzed by taking the two as input parameters.Secondly,based on the Inverted Modelling and scale distortion condition,the global performance indexes of the lander are established.The motion characteristics of the lander are investigated from the aspects of kinematics,mechanics and gait.The objective functions are also established from the aspects of posture adjustment,motion stability,motion continuity,foot force distribution,etc.The corresponding optimization strategies and performance indexes are designed as well.The walking performance of the lander under the condition of distorted scale is analyzed by the Inverted Modelling.The ability of stepping,obstacle-surmounting and climbing under different terrain are investigated.Finally,gait planning and fault-tolerant gait planning under scale distortion of the lander are designed in complex environments.Aiming at the characteristics of different scales and joint locking,the methods of body posture optimization,leg sequence design,step length design and foothold selection are proposed.By adjusting body posture,the optimization equation is established based on the proposed performance indexes.Taking a specific legged mobile lander as an example,digital prototype simulations are designed on flat and rough roads respectively,which verified the correctness and effectiveness of gait planning of the lander under the condition of scale distortion.