Research On Dynamic Walking Of The Biped Robot Based On Vitual Model And Active Impedance Control

Biped robot,one important branch of the robot technology,has always been regarded as an important participant in the future of human life owing to its anthropomorphic characteristics and the ability to move in unstructured environments.In recent years,with the advent of the latest generation of Atlas bipedal robot,the development of bipedal robot has entered a new era that biped robot can move with agility in any kind of terrain and achieve multiple tasks.In this area,there is still a big gap between China and the world advanced level.Biological studies have shown that the ability of legged animals to adapt to different types of terrain and to deal with different tasks are closely related to leg impedance parameters.Therefore,this paper will focus on the problem of insufficient adaptability of biped robot and take the high-level control algorithm as the research object,to improve the performance of the biped robot effectively based on the idea of changing the impedance characteristic of the system.In this paper,the prototype model of the biped robot is designed and established according to the biological lower limbs with the lightweight and compact requirements,and the establishment of hydraulic-driven bipedal robot prototype model lay the foundation for the follow-up research work.The kinematic relationship is the link between the movement of the connecting rod and the joint movement.In this paper,the kinematics analysis of the biped robot is carried out by the method of floating kinematics,and the mapping relationship between the connecting rod and the joint movement is established.On this basis,the parametric method is used to plan the hip and foot trajectory of the robot and is mapped to the joint space as the input signal of the biped robot controller using the inverse kinematics method.The biped robot system is a multivariable,strongly coupled,nonlinear and naturally unstable system with time-varying topological structure,and the foot-end contact force changes constantly during the motion cycle.Its system characteristics determine the difficulty of the robot control.In order to improve the performance of the controller and eliminate the nonlinearity of the system,the corresponding dynamic model is established by Lagrangian dynamics method for different topological structures,and the relationship between joint motion and joint torque is established.The influence of the collision process on the system characteristics is analyzed theoretically.Impedance control is one of the important methods to change the impedance characteristics of the robot system.The characteristics of the position-based impedance control and the force-based impedance control is ambiguously,so the features and the application environment of the two control methods are discussed with the combination of theoretical derivation and simulation,and the characteristics of the impedance control method is described by the state space method.By contrast,this paper selects the forcebased impedance control method.In order to verify the effectiveness of the active impedance control method,the Simulink-ADAMS simulation model of the monopodial robot is established,and the trajectory following in free-space,nonlinear and linear spring simulation and active hopping trials are carried out.The simulation results show that the method is effective in adjusting the system impedance.In order to illustrate the effectiveness of impedance control method in improving the performance of biped robot,this paper adopts the method of computed torque control based on the inverse dynmic model and the active impedance control method based on the virtual model control to control the robot.The computed torque control method is a part of the traditional model-based control algorithm using the feedback linearization to eliminate the nonlinearity of the system and realize the walking by reproducing the joint trajectory.The control algorithm proposed in this paper adopts the combination of virtual model control and force based impedance control.The virtual model control method is mainly used for the control of the support leg.The force based impedance control method is focused on the control of the swing leg.The cosimulation model is established and the simulations of walking on flat road,uneven road and road with different stiffness are carried out.The simulation results show that,compared to the computed torque control method,the combination of the virtual model control and the force based impedance control improves the ability of robots to adapt to different types of terrain and to deal with unknown environmental obstacles effectively.