Study On Galloping Stability Of Bionic Cheetah

Cheetah is the fastest mammal on land,its high running speed and strong explosive power is impressive,as a result,the physiological characteristics,body structures,and running pattern attract more and more interests of domestic and international scholar.Running cheetah with high speed is a transient instable,intermittent contact with the ground,and non-linear multi-body dynamic system,therefore,keeping body attitude stable is the precondition of cheetah's high speed running.Hence,analyzing the stability is significant for studying the high speed and strong explosive power of cheetah,and is instructive for designing and controlling high speed quadruped robot.This thesis builds the passive dynamic model with a spine joint motion by abstracting and simplifying cheetah's body skeletal structures;and presents the Poincare fixed point's searching method based on the optimization method;presents the stability criterion by analyzing the relation between kinematics symmetry and stability;on the basis of analyzing the galloping gait's stability,this thesis presents the stability control strategy for the passive dynamic model;based on the stability criterion,this thesis realizes the stable running control of the active model,verifies the correctness and practicability of the stability criterion,meanwhile,analyzes the kinematics and dynamics mechanisms of the rotary galloping gait;at last,this thesis develops bionic cheetah robot to verify the theoretical study and simulation analysis.Based on analyzing the cheetah's skeletal structures,this thesis builds the bionic dynamic model with passive spine joint and virtue spring legs.For the purpose of contrastive analyzing the effect on the kinematics,dynamics,and stability caused by the spine joint,this thesis also builds the passive dynamic model with rigid spine and virtue spring legs.By analyzing the kinematics of the real cheetah galloping gait,the rationality and applicability of system dynamic modeling have been verified.In order to search multi parameters simultaneously,the new Poincare fixed point's searching strategy is presented based on particle swarm optimization and Poincare map,and a series of stable galloping gaits are realized.This study presents the control strategy of spine joint to broaden the matching scope between spine stiffness and leg stiffness,thereby,this study can analyze the kinematics and dynamics of cheetah galloping gait.On the basis of analyzing the kinematic symmetry and stability,this study presents the stability criterion and galloping gait's instability degree,therefore,the galloping gait's stability can be analyzed quantitatively.Based on the stability criterion and galloping gait's instability degree,the galloping stability has been analyzed against all the parameters of two cheetah's dynamic models.According to the effect on the stability of the parameters,this thesis presents the stability control strategy for the passive dynamic model;the stability control strategy can adjust and control the body posture when the galloping gait is disturbed,and at last,the instable galloping gait can regain the stable state.The stability law achieved ideally under the passive dynamic model is instructive for designing the quadruped robot's structure and mechanism,and it can provide the theoretical basis for the control strategy of complex robot.This thesis develops the cheetah's multi-body dynamic model with mimicking the real cheetah.The two spine joints and four joints per leg can simulate the sharply motion of spine and leg of real cheetah.For controlling the stability of the cheetah,the active stability control strategy realized by controlling the spine and leg joints' motion is presented based on the stability criterion.The final realized bounding gait verifies the correctness and practicability of the stability criterion;furthermore,the conclusion that introducing the spine joint motion can improve the galloping kinematics and dynamics performance has been confirmed by comparing the kinematics between the rigid spine simulation and flexible spine simulation.This thesis builds the bionic cheetah robot experiment platform,focuses on the spine joint and leg joints' bionic design.It presents a three levels control system with ‘high-level,central nervous system,and low-level sub-controller' to control the quadruped robot,and realizes the bionic control system with hardware.The rigid spine and flexible spine rotary gallop gait are realized on the treadmill,and the stability criterion has been verified.Through contrasting the experimental data of two different spine's model,it is concluded that introducing spine joint motion can improve the galloping stability.In addition,the faster is the running speed,the higher is the galloping stability.