| Hydraulic drive legged robots have excellent adaptability and motion performance to unknown and unstructured environments,and have become a research hotspot in many countries.During the actual motion of the robot,there are constant contact,collision and impact between the foot end and the environment.To avoid the damage of the electronic equipment and mechanical structure carried by the robot,each leg of the legged robot should have certain compliance.Position-based and force-based impedance control are common compliance control methods applied to LHDS of each joint is identical.At the same time,the two kinds of impedance control methods have different dynamic compliance and opposite stability.It can be seen from above analysis that the impedance inner loop of HDU of each joint cannot give full play to their respective advantages when it only adopts one control method,therefore,it is necessary to select different inner loop methods in each leg joints,which can enhance the compliance control performance of LHDS,further improve motion performance of the legged robot.In this paper,aiming at LHDS with 3 DOFs(degrees of freedom)of the legged robot,the main research work is as follows:(1)Research on the realization method of position-based and force-based impedance control of LHDS with 3 DOFs.The kinematics and statics models of the leg mechanical structure are the basis for the impedance control of the LHDS,in this paper,the kinematics and statics models of the leg mechanical structure were first solved by using the connecting rod formula and force Jacobi matrix.Then,according to the mechanical structure size of the leg,the functional relationship between the elongation of HDU(hydraulic drive unit)and the rotation angle of each joint is solved,and the functional relationship between the force of HDU and the torque of each joint is solved.Finally,based on leg kinematics,statics,dynamics and the principle of impedance control,the realization method of LHDS positionbased and force-based impedance control is obtained.(2)Research on the kinematic correction strategy of the semi-cylindrical foot end.When the legs of legged robot with the semi-cylindrical foot end are at the supporting phase,due to the existence of the semi-cylindrical foot end,the foot end will roll,which causes the desired position of the foot end to deviate from the actual position,further causes the error of the root joint trajectory,and results in the wrong posture of the robot.To avoid root joint trajectory deviation caused by semi-cylindrical foot end,which leads to the decrease of motion control accuracy of LHDS,the causes of root joint trajectory shift caused by the semi-cylindrical foot end are firstly analyzed.Then,when the robot body and the contact surface are at different angles,the position error of the root joint trajectory caused by the semi-cylindrical foot end in the motion space is derived,and a kinematic correction strategy for the semi-cylindrical foot end is designed based on the virtual DOF.Finally,the joint simulation model established by MATLAB/Simulink and ADAMS is used to test the correction strategy proposed in this paper under multiple working conditions.(3)Research on force sensor correction method of HDU of the legged robot based on virtual model.To achieve leg impedance control of the legged robot,the contact force between the foot end and the ground need to be measured in real time.One-axis force sensor mounted on HDU has the advantages of high data stability,long service life and high reliability than multi-axis force sensor mounted on the foot end.However,The one-axis force sensor mounted on HDU is more susceptible to many factors such as preload,friction,dynamics,null drift and temperature drift than the multi-axis force sensor,which will cause the error between the calculated contact force the actual contact force.Firstly,the causes of the error are analyzed,and the performance test platform of LHDS is used for the experimental test to obtain the causes of the error.Based on the virtual model,a correction strategy is designed for the force sensor of the legged robot.At last,the correction strategy is tested under multiple working conditions.(4)Research on the basic principle of the new impedance configuration of robot leg with 3 DOFs.In this chapter,different impedance control methods are applied to different joints to form a variety of impedance configuration schemes,and the realization principle of each impedance configuration is studied.Then,the equivalent mass distribution of HDU of each joint is analyzed when LHDS is in the soaring phase and the landing phase in the motion space of the foot end,respectively.Finally,through analyzing the effect of the equivalent mass distribution of HDU of each joint,the differences between the outer disturbance characteristics and distribution of equivalent mass on the properties of joints in the soaring phase and the landing phase,the best impedance inner loop control method is selected for different joints of the leg to make it have the best compliance control performance. |
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