Study On Buffering Strategy In Landing Process Of A Quadruped Robot

Quadruped robots,as a typical kind of legged robots,are widely studied by scholars due to their stability and adaptability in strong unstructured environment and a number of remarkable advanced quadruped robots are invented.However,the investigations on tumbling or falling from a high place are barely involved.In this dissertation,falling and landing process of a quadruped robot is considered,which could improve the adaptability of the robot in strong unstructured environment.In the falling process,there will be a violent interaction between the foot and the ground.This impact will react on the foot,torso or the joints of the legs,which may result in huge torques.These torques may cause great damage to the robots.Besides,the impact process lasts very short while the contact forces change rapidly,which makes it difficult for the quadruped robots to make effective reaction.These limitations undermine the adaptability of the quadruped robots.It is difficult to describe the interaction between the foot and ground precisely.,In this dissertation,the process from falling to landing is mainly studied and a buffering strategy for quadruped is proposed.Also,impedance control and PDSMC(Proportion Differential Sliding Model Control)are respectively studied With the strategy,the quadruped robot is enabled to fall from a high place and land with compliance.1.The configuration of leg joints is analyzed and a single-leg model for the quadruped robot with 3 rotational degrees of freedom is established.With this model,the kinematics equation and the dynamics equation are established,which provides the theoretical basis for the motion control.2.PDSMC approach is first applied in legged robots and a comparison is conducted between impedance control and PDSMC control.With the single-leg dynamic model of the quadruped robot,the disturbance tolerance is testified,which indicates the advantage of PDSMC method in maintaining the stability of one-leg robot system.In addition,with PDSMC control,the one-leg robot can land with compliance,which is testified in Webots and in a real robot as well.3.Focusing on the falling process of quadruped robots,buffering strategies based on impedance control and PDSMC control are testified in joint space and Cartesian space,respectively.It can be seen from the simulation results that PDSMC approach is superior in the compliance of the robot.4.A buffering strategy based on active impedance control is proposed.In this section,the previous method is further improved through active impedance control using instead of PDSMC.With this approach,the compliant control in joint space is studied.To achieve compliance,the control parameters are switched according to the motion phase of the robot.5.There is a fact that control in joint space is not sufficient to globally control the quadruped robot.To deal with this limitation,variable impedance control in Cartesian space is proposed.With this approach,the required force or torques applied on torso's CoM(center of mass)can be directly calculated.With virtual model control,the torque needed for each joint can be achieved.Finally,this approach is testified in simulation and on a small real robot,which demonstrates that this strategy is effective on stability and compliance.