Research On Space Robotic Joint Stability With Strong Nonlinear Interference Caused By Cables

The space robot cables are responsible for the end load transportation and the power transmission of the space robot,and they are mounted on the robot body and move together with the robot body.In the extreme environment of multi-physics coupling such as high and low temperature,radiation and micro gravity,the heavy space robot cables covered by the shield layer become extremely hard due to the effects of ultra-low temperature and outer space radiation.Heavy space robotic cables can cause strong nonlinear disturbances to weak space robot joints,causing slow rotation or oscillation of space robot joints at specific locations.Studying the physical characteristics of space cables,the mechanical characteristics of space robot joints and their mutual coupling relationship is of great significance for improving the accuracy and stability of the end of space robot operations.In this paper,the improved space cable mechanics model is established,and a space robot cable modeling method based on obstacle(surface)constraint and a Levenberg-Marquardt algorithm based on trust strategy improvement are also proposed.The stability of space robot joints is studied and the space robot is obtained.The physical characteristics of the cable and its interference torque to the space robot joints provide a powerful guarantee for the development of the lunar exploration engineering robot products.The main contents of this article are as follows:(1)Research on the establishment and solution of cable mechanical model.First,the geometric characteristics of the cable are described from the perspectives of curvature,torsion and twist angle.Then the mechanical model of space robot cable is established,and it is discretized by finite difference method.An improved algorithm based on trust region strategy is proposed.Moreover,the rationality and convergence of the cable model are verified from the perspectives given by the ultra-long cable,the local distribution force in the middle of the cable,and the number of different nodes.(2)Research on cable physical properties.The mathematical model of space robot is given,and the physical characteristics of space robot cable are analyzed.At the same time,the mechanical model of the cable under the constraints of dynamic clamp or static clamp is established.Considering the surface constraint,gravity distribution force and friction distribution force of complex space,this paper proposes a modeling method of space robot cable under the constraint of surface.Moreover,the influences of different parameter changes on the solution results of the cable model under surface constraints are analyzed.(3)Robot joint stability study.The joint mechanics model of space robot was established,and the reasons for the slow rotation or oscillation of the space robot joint at a specific pose were analyzed.The pose change of the end of the space robot is analyzed,and the theoretical interference torque of the space strong cable to the orientation joint is obtained.(4)Experimental Study.Prove the correctness of the proposed theoretical model from the perspective of experimental verification.First,a space robot orientation joint interference torque measurement platform was built.Under the constraints of both ends,the theoretical and measured interference moments of the orientation joint are compared.In addition,the theoretical interference torques of the orientation joint under the constraints of both ends and surface are compared.Finally,a watershed algorithm is proposed for the extraction of the actual shape centerline of the cable,and the theoretical and practical shape of the space robot cable is compared.