Research On Locomotion Control On A Quadruped Robot With Running Trotting Gait

Quadruped robots have the integrative predominance in the terms of stability,speed,load capacity and the adaptability to complex environment when compared to other types of legged robots,and it has become one of the most active research topics in the field of mobile robotics technology.With the existence of almost perfect relative locomotion control methods and theories,Trot Gait has become the main gait of quadruped robot.In the presentation of four-leg flying phase,Running Trot Gait can be regarded as an unique mode of the general Trot Gait,not only enchancing the athletic performance,but preserving the superiority in stability and low energy-consumption of the general Trot Gait.However,there are also several resulted distinctive problems on locomotion control,such as stable-hopping control and adjustment on torso attitudes,making the locomotion control on the Running Trot Gait of quadruped robot a so challenging and valuable research work.It's generally impractical to directly implement an overall locomotion control strategy because of the native characteristics of MIMO,strongly nonlinear and coupling dynamics in the control system of quadruped robots.Based on the analysis of the motion characteristics and the demand on the solving of special locomotion control problems for the Running Trot Gait,this work generally decomposes the quadruped robot into two mutually decoupled models,one of which is the 3D seven-linkage mechanism and the other the planar inverted pendulum.Five aspects are considered in this paper on the research of the posture & pose control of the former model during the stance phase and the speed control for the latter during the flying phase oppositly,as demonstrated below:(1)We have firstly acquired the specific motion characteristics and relevant positive conclusion about the feasibility of settlement on these exceptional locomotion control problems during the stance phase of the Running Trot Gait;and then,we propose a kind of motion-decoupled control strategy switching between the support phase and the flight based on the motion decomposition,which decreases the complexity of the implementation of the Running Trot Gait greatly.(2)We have pertinently adopted a hierarchical control strategy combined with Decoupling Control on torso,Contact Forces Distribution and Single-leg control pattern following the definition of three sequencially related sub-problems which are equal to the whole posture & pose control problems of the 3D seven-linkage mechanism during the stance.And in that case,only three simple sub-problems need to be solved instead in this paper.(3)For the vertical hopping control of the quadruped robot,we have derived control method switching between the stance and the flight based on the equivalent reference two-mass model;and the planning method of the reference asymmetric state transition trajectory for the torso from the reference limit cycles,making the control on lift-off states of the torso at high stability,accuracy and timely.(4)We have proposed an event-driven-based Finite Sstate Machine for the overall locomotion control of the quadruped robot,which determines the switching between the stance-phase control mode and the flying-phase control mode for the torso control,decides the selection on single-leg control mode and applies on the strategy of segmented trajectory planning for the swing legs;and the design process of the controllers for all three types of singl-leg control mode is also discussed in details;and consequently improve the adaptability and robustness of the quadruped robot system.(5)We have implemented a speed control strategy based on foot position selection and proposed a specific functional expression of the reference trajectory for the swing legs which avoids the resulting nagetive disturbance to the flying posture of the torso in the maximum extend,aiming at the speed control of the planar inverted pendulum during the flight.