Study On Walking Gait Of Quadruped Robots Based On Predictive Control

Quadruped robots can be stable and efficient when performing outdoor tasks,such as military transportation,scientific exploration and disaster rescue.In performing these tasks,they exhibit agile and dexterous locomotion capabilities in a compliant manner and show their strong environmental adaptability and load capacity.Quadruped robots' walking gait has great advantages in doing up and down stairs,jumping over obstacles,climbing and so on.Firstly,the mechanism of walking gait motion of quadruped robot is proposed in this paper.In the walking gait,the inertia force of the robot is an important requirement for the stability of the robot.Therefore,ZMP(Zero Moment Point)based methods can be used to calculate the stability margin and generate physically viable locomotion trajectories of the robot.Secondly,a method of on-line generation of walking gait pattern based on predictive control is proposed for quadruped robots walking under unperceived disturbances and traveling over rough terrains.The predictive control is designed to plan the CoM(Center of Mass)trajectory to realize the desired ZMP.When the robot suffers from interference of environmental disturbances,an adjusted expected ZMP is planed to suppress the change of the ZMP.In order to improve the flexibility and stability of the robot,a position control algorithm based on contact force is designed,including body's position and attitude control algorithm,force distribution algorithm,force control algorithm.The position controller uses spring damping model to control the body's position and orientation.A force distribution method is established to calculate desired contact force by minimizing the sum of the weighted torque efforts of the robot.A contact force controller is used to make the contact force track the desired force to realize the foot soft contact with the ground.Simulations were performed without four feet supporting period,the robot model successfully fast walking over rough terrain and going upstairs and downstairs.Then in the experiments,the quadruped robot achieved going upstairs with a stair of 0.15 m.Simulations and experiments demonstrate the effectiveness of the predictive control algorithm and the robot's position control algorithm.