Research On Leg Model Modification And Force Control Of Hydraulic Quadruped Robot

In the actual motion process of the hydraulic drive legged robot,its motion performance is determined by the control performance of each leg of the robot.If the legs of the robot do not have good compliance when the foot ends of the robot contact with the environment,the impact caused by the foot ends contact with the environment will have a negative effect on the motion control performance of the robot.The contact force control is an effective control method which can not only make the legs of the robot compliant but also keep the contact force of the foot ends stable.It takes the hydraulic servo control as the core,and adds the impedance control,and finally realizes the contact force control on the outer loop.There are two commonly used inner loop core control methods,namely,position and force control.These two control methods have significant differences in mathematical model building,core controller design and parameter selection,etc.Therefore,the two core control methods have significant differences in dynamic compliance.At this point,based on the two inner loop control methods,the impedance control is introduced as the outer loop to form the position-based impedance control and the force-based impedance control.The dynamic compliance of the two impedance control methods in the actual control is quite different,and the dynamic compliance will affect the performance of the robot foot contact force control.How can play the advantages of two impedance controls,and break the traditional mode that only adopts the same kind of inner core control for each joint control,based on the principle of the new configuration impedance control,a new contact force control is put forward,this is the main innovation in the paper.To improve the motion control ability of the hydraulic drive legged robot,the following research works are carried out in this paper:(1)Static modification for single leg of the legged robot.Aiming at the phenomenon of contact point deviation caused by the semi-cylindrical foot end in the actual movement of the legged robot,the statics of the single leg is modified based on the force translation theorem.Then,Solid Works,a 3D modeling software,and Matlab,a simulation software,are combined to build the joint simulation model of the robot's single leg,and the static correction algorithm was verified through the simulation model.(2)Dynamics modeling of single leg of the legged robot.Due to the different contact states between the foot end and the ground during the movement,the dynamics models of single leg in the flight phase and the landing phase are built respectively.Firstly,based on the Lagrange dynamic equation,the dynamic equation of the flight phase in the motion of the robot is deduced.Then,combining with the Jacobian matrix of statics deduced in Chapter 2,the dynamic equation of the landing phase is obtained,and a dynamic switching method was designed to switch the dynamics according to the motion state.Finally,in order to verify the accuracy of the gravity term in the dynamics deduced in this paper,the zeroforce control is introduced to verify the gravity term in the dynamics.Based on the simulation model built in Chapter 2,the zero-force control,flight phase dynamics and landing phase dynamics are simulated and verified respectively.(3)Research on the contact force control based on new impedance configuration.Firstly,the principle of impedance control and the control principle of new impedance configuration are simply introduced.Then,based on the previous research of the author's team,the optimal control scheme of the new impedance configuration is simulated and verified.Then,the contact force error of the foot end between with the environment in the contact stability stage is analyzed,a contact force control method based on the new impedance configuration is derived.Finally,the simulation model of the proposed algorithm is built by using the MATLAB/Simulink simulation platform,and the simulation results are verified under different working conditions.The simulation results show that the contact force control based on new impedance configuration proposed in this paper can achieve the desired force following in unknown environment.(4)Experimental verification.Based on the principle of the statics correction algorithm and the dynamic equations of the two motion states,these algorithms are verified experimentally by using the single leg experimental platform of the robot under a variety of working conditions.