Fault-tolerance Gait And Stability Control Of Hexapod Walking Vehicle

With the rapid development of technology,the research of special vehicles is also in the ascendant.Various types of special vehicles widely appear in various fields and play a huge role,such as flexible wheeled vehicles,foot walking vehicles,etc.In this paper,combined with the current research on the foot walking vehicles,the walking gait and stability control strategy of the hexapod walking vehicles with failure legs are studied,aiming to realize the locomotion control of the hexapod walking vehicles in the failure state.In this paper,the configuration of the hexapod walking vehicle is analyzed,the coordinate system of the hexapod walking vehicle is established,and the transformation relationship between different coordinate systems is analyzed.Based on the D-H method,the forward kinematics model and the inverse kinematics model of the system are analyzed.By analyzing the velocity Jacobian matrix of the leg of a foot walking vehicle,the relationship between the joint coordinate space and the velocity of cartesian coordinate system is obtained.The center of gravity of the hexapod walking vehicle is regarded as a joint with six virtual degrees of freedom,and the kinematic constraints are analyzed.The relationship between the controllability of the body and the number of supporting legs is obtained.According to the relationship between the number of fault legs and the relat ive position of the fault legs and the body,the fault tolerance ability of the hexapod walking vehicle is analyzed.A method of tripod-quadruped mixed gait is proposed for hexapod walking vehicle with one fault leg,then the tripod gait is proposed for hexapod walking vehicle with two fault legs.Based on the stability constraints,the phase sequence of fault tolerance gait of hexapod walking vehicle is planned,and the complete sequence generation mechanism is established.In view of the problem that the stability margin is too small in the specific movement process of the hexapod walking vehicle,a stability control method of coxa joint pre-adjustment is proposed,and a numerical method for solving the relative optimal coxa adjustment angle is given.Based on the compound cycloid,the swing trajectory for swing and the moving trajectory for the center of gravity of hexapod walking vehicle are planned,and the joint angle is obtained by combining the inverse kinematics model with the trajectory.Based on the dynamic simulation software ADAMS and control software MATLAB,a simulation model of the hexapod walking vehicle is established and a simulation system is developed.The straight walking gait with one leg and two legs failure is simulated respectively,and the simulation results are analyzed.A position and attitude closed-loop control model is established to solve the problem that the hexapod walking vehicle deviates from the planning direction.The theoretical model of velocity inverse kinematics related to the attitude of vehicle body is derived.The simulation model of attitude closed-loop control system is built in ADAMS and MATLAB.The integral gain and differential gain of the model are adjusted,and the results of closed-loop control and open-loop control are compared.Combined with fault-tolerant gait planning method,stability control strategy and attitude control,the hexapod walking vehicle with one fault leg and two fault legs has good fault-tolerant ability,can achieve the desired trajectory,and realize the stable walking on the structured road.