| Hydraulic legged robot has excellent bearing capacity and response speed,which is suitable for transporting materials,scout and rescue in all kinds of complex terrain.The biggest effect factor of stable walking of the legged robot in complex environment is the unpredictable impact force between the foot end and the environment.To avoid bad motion performance and damage to some components,the legged robot should have certain compliance characteristics.Compliance control is divided into active compliance control and passive compliance control.At present,the active compliance control method has been widely used in the hydraulic system,which can achieve better compliance control performance,but it is inferior to the passive compliance control in some respects such as reducing the instantaneous impact force.If only the passive compliance control is used,the system performance will be affected.Therefore,it is necessary to explore the relationship between active and passive compliance control and find an effective active and passive composite compliance control method.In this paper,aiming at the leg hydraulic drive system with three degrees of freedom(3-DOFs),the goal is to reduce the impact force and improve the compliance performance for single leg hydraulic drive system.The main research tasks include:(1)In this paper,the impact force of the foot end between the ground is analyzed.The impact contact model is used to analyze the landing impact problem of the system.The active and passive compound compliance model for the driving unit with single degree of freedom(1-DOF)is established by using the state space equation to simulate the process of landing impact force.Using Cartesian space compliance control method,the active passive compound compliance control model is extended to the single leg of the legged robot;the driving unit with 1-DOF and the active and passive compound compliance control model of the legged robot are analyzed,and the active and passive compound compliance series coupling relationship is obtained,which provides the basis for the active and passive compliance parameter adjustment for the legged robot in the actual motion.(2)The mathematical model and virtual physical model of the system are built respectively,and the active and passive compound compliance effect of the driving unit with1-DOF is simulated and analyzed under multiple working conditions,and the selection rule of active and passive compliance parameters is obtained;the virtual physical model of single leg with 3-DOFs is built,and the feasibility that the Cartesian space compliance control method is used to the to the legged robot is verfied.(3)According to the single leg mechanical structure of the legged robot with passive spring,the forward and inverse kinematics solutions are solved,and the relationship between joint angle and the extension length of the hydraulic driving unit is obtained;combined with Cartesian space compliance control method,the active and passive compound compliance control model of the single leg hydraulic system is established;the model is built by using MATLAB/Simulink and Adams for simulation analysis.(4)Firstly,The accuracy of forward and inverse kinematics solutions is verified by using the single leg test platform.Secondly,four control methods,namely no compliance control,active compliance control,passive compliance control and active and passive compound compliance control,are adopted to make the single leg of foot robot fall to the ground from a certain height,which verifies that the active and passive compound compliance control method has both advantages of the active compliance control and the passive compliance control,and has good compliance for the legged robot. |
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