Study On Design And Control Of Novel Super-flexible Joint For Tri-Co Robots

With the continuous emergence of new fields,new tasks,and new objects,traditional wheeled robots,rigid mechanical arms,foot mechanical legs and so on in outdoor non-structured natural environments can no longer meet new production and living requirements.Coexisting-Cooperative-Cognitive Robots(Tri-Co Robots),which naturally interact with other robots,autonomously adapt to complex dynamic environments,and work together,have emerged.Traditional robot joints are rigid joints,which have the disadvantages of low human-machine interaction safety,no torque self-sensing function,and unadjustable stiffness.They are not suitable for Tri-Co Robots with special performance requirements.In order to solve the problem that the existing robot joints cannot effectively achieve super-flexible force output,and effectively realize the human-machine-environment safe interaction of Tri-Co Robots,through the development of a new generation of novel bionic flexible joints,it provides important key technical support for Tri-Co Robots.The main research work of the paper includes:(1)Super-flexible theoretical criterion of Tri-Co Robot joints and a new type of SEA.Based on the analysis of the existing series elastic actuator(SEA)at home and abroad and the flexible joints of Tri-Co Robot,a "primary criterion" and four "secondary criteria" for the super-flexible theoretical criterion of the joints of Tri-Co Robot are proposed,and the basic properties of two super-flexible joint are obtained through analysis.Based on the analysis of the respective characteristics of two kinds of SEA mechanisms based on cam and lever,a flexible output mathematical model of variable stiffness lever SEA mechanism is established,and detailed output characteristics simulation analysis is performed.Finally,a new type of SEA structure with bidirectional output of super-flexible force is proposed,and the output characteristics of the mechanism are analyzed and a mathematical model is established.(2)Design,analysis and test of a novel super-flexible robot joint(NSFRJ).A novel super-flexible robot joint based on the "inverse antagonism" bilateral symmetrical flexible transmission mechanism is proposed based on super-flexible theoretical criterion of Tri-Co Robot joints and incorporating the rigid drive module of the new SEA.The motion characteristics of the joint are analyzed,and the mathematical model of the equivalent stiffness of the joint system is derived and simulated.The simulation results show that NSFRJ meet the design requirements.By making a joint prototype and setting up a test platform,a compliance characteristic output test was performed.The test results show that the compliance output torque of NSFRJ prototype is basically consistent with the simulation results.It shows that NSFRJ can not only complete the active-passive adjustment of stiffness,but also effectively achieve super-flexible force output.(3)Research on NSFRJ control method.The mathematical model of the dynamics of NSFRJ is established,and the dynamic equations of the joint are transformed into the form of state equations.The problem of controlling motion precision of NSFRJ is transformed into the problem of joint node target object tracking expected target instruction.Considering the flexible variable stiffness characteristics of NSFRJ,the joint variable stiffness factor is incorporated into the traditional backstepping controller,and an backstepping control method considering the variable stiffness factor is established.Finally,the actual motion trajectory of the joint under control is obtained through simulation analysis.The results show that the control method can effectively achieve the precise motion control of NSFRJ,and the control object error converges to zero.