Identification And Control Of Comprehensive Leg-ground Stiffness In The Stance Phase Of Quadruped Robots

The legged robots have become the frontier research and hotspot of intelligent mobile robots with the advantages of flexible movement and strong terrain adaptability.There are a lot of interactions between the legged robot and the terrain during moving.The unknown terrain not only affects the stability of the robot,but also makes the robot losing much energy because of the collision.Identification and control of the comprehensive leg-ground stiffness is the key point for improving energy efficiency and stability of the robot.At present,the research on the identification of terrain features is mainly based on statistical methods.The research on the leg-ground stiffness of robot is still in the exploratory stage.This thesis mainly studies the identification and control of comprehensive leg-ground stiffness in the interaction between the quadrupled robot and the unknown terrain.A simple and easy method is proposed for achieving high efficiency and stability of the quadrupled robots during moving.First,the dynamic equations of a quadruped robot in trot gait are deduced.The features of the terrain is introduced into the spring loaded inverted pendulum model and the leg-ground serial spring model is established.The stance phase of the quadruped robot is decomposed.Then,the time allocation of leg-ground stiffness identification and adjustment is studied.A classification criteria of soft terrain and hard terrain is established based on the frequency characteristics of touchdown force.The influence of comprehensive leg-ground stiffness on the stability and energy efficiency of the robot are analyzed.The dynamic model is established and the comprehensive leg-ground stiffness is identified by the frequency characteristics of touchdown force on the hard terrain.The relationship between the terrain stiffness and the terrain normal settlement is established.Then,we can identify the comprehensive leg-ground stiffness by touchdown force and the terrain normal settlement on the soft terrain.The planned leg-ground stiffness can be got from the research of human and animal walking.The conversion relationship between the leg spring stiffness and joint stiffness of the leg is established.An admittance control strategy of hydraulic servo system is proposed to realize the control of joint stiffness.Because of the nonlinear characteristics of the hydraulic servo system,a feedback linearization control strategy is proposed to improve the force control bandwidth and accuracy.For improving the control accuracy of stiffness and position,a gravity compensation strategy is proposed.A single-leg prototype platform is set up to imitate touchdown process of the robot.We can get the terrain stiffness by the two identification strategies proposed above.Comparing the two results of terrain stiffness,the stiffness identification strategies can be proved correct.We realize the control of leg spring stiffness by controlling the joint stiffness of the robot in a quadruped robot prototype platform.