Research On Mechanism Of Double Support Phase And Gait Planning Methods For Biped Robots

Humanoid robot has similar appearance characteristics to human,can move autonomously in the environment of human life and work,has strong environmental adaptability,and can complete various tasks instead of human.Therefore,it has broad application prospects.However,stable walking is the basis for humanoid robot to achieve all functions.If humanoid robot does not have the ability to walk,it will lose the meaning of "humanoid".In addition,gait planning is the first step for stable walking of biped robots.Without generating the trajectory of each joint,the robot does not know what to do next.At present,most scholars only consider the single support phase(SSP)and ignore the double support phase(DSP)in gait planning.In fact,DSP is an important part of biped walking cycle.In the DSP,the support polygon formed by the supporting feet and the ground is much larger than that in the SSP,which makes the ground reaction force provide larger moment.Therefore,the DSP has a better adjustment effect on the robot state,which makes the robot control more robust and has stronger ability on disturbance.Several gait planning methods with DSP are studied from different aspects,and the effects of DSP on biped walking performance is analyzed.The innovations and main research contents of this paper are as follows:1.Research on the impact dynamics of biped robot with the ground.The impact between the robot's feet and the ground is inevitable and frequent.Whe the swing foot collides with the ground at the end of SSP,there may be two types of impact: single impact and double impact.Based on the assumption that the ground and the robot are rigid bodies and the collision happens instantaneously,the dynamic formulas and valid conditions of single impact and double impact are derived.An analysis method is proposed to distinguish the type type according to the reaction force of the rear foot,and the relationship between the robot motion condition and the collision type before collision is studied;The feasible regions of two kinds of impact are studied,which provides theoretical foundation for trajectory planning in the following chapters.2.Research on gait pattern based on simplified centroid model.The linear inverted pendulum model(LIPM)is an effective simplified model and has been widely used by many researchers.However,the LIPM can only plan the trajectory of center of mass(Co M)in SSP.A gait pattern composed of linear inverted pendulum model(LIPM)and linear pendulum model(LPM)is proposed to plan the trajectory of center of mass(Co M)in SSP and DSP,respectively.The stability of gait was analyzed.A flexible walking method based on this gait pattern is proposed,which can realize the stable walking in various situations and carry out simulation verification.3.Research on trajectory planning method based on workspace.Gait planning method based on workspace is to plan the trajectories of some specific parts of the robot,then obtain the joint angles by inverse kinematics.Commonly used gait planning method based on workspace is introduced.From the perspective of improving walking efficiency,the gait is improved in terms of hip height and trunk angle.The energy consumption of the gait before and after the improvement is compared,and the reasons for the energy saving of the improved gait are analyzed.4.Research on trajectory planning method based on joint space.A trajectory planning method including DSP for underactuated biped robots is proposed.It overcomes the disadvantage of weak interference suppression ability only including SSP.A five link planar underactuated biped robot model is established.The virtual constraint method is used to design the trajectories of actuated joints in SSP,and the trajectories of independent joint are designed as polynomial functions in DSP.The optimization technology is used to solve the undetermined parameters,and the results are simulated.5.Research on trajectory planning method based on optimal control.How to transform the trajectory optimization problem into a nonlinear programming problem is introduced.An improved Hermite-Simpson collocation method is proposed.The dynamic equations and cyclic walking constraints are given,and the optimal trajectory problem is transformed into a nonlinear programming.Different collocation methods are used to solve optimal trajectory problem,and the performances of these methods are compared.Finally,the error of the solution is estimated.6.Research on the effects of double support phase on improving walking performance.A gait without DSP is presented,and its convergence condition and attraction region are analyzed.A gait including DSP is given,and its convergence condition and region of attraction are also analyzed.By comparing the two kinds of gait,it is found that the addition of DSP can improve the convergence of gait and accelerate the convergence rate.