Three-Dimensional Modeling And Stability Analysis&Control Strategy Of Under-actuated Biped Robot

Traditional under-actuated biped robot can only walk down a slope along a straight line,in this circumstance its centroid trajectory is a2D planar curve, that is the reason why it iscalled2D planar movement, and the motion plane is called sagittal plane. By contrast, whenthe robot can also move in the orthogonal plane of the sagittal plane, the centroid trajectoryappears as a3D spatial curve, so we can call it3D spatial movement, and the orthogonalplane is called lateral plane.In order to improve the stability of the under-actuated biped robot, reduce thecomplexity of theoretical research and simplify the robot’s mechanical design and stabilitycontrol algorithm, the trajectory of the robot is usually restricted to its forward direction bymechanical constraints, which is a2D planar movement allowed only in the sagittal plane.But when taking the actual movement into account, lateral rolling must be added, and thismakes it a3D spatial movement.Stability, efficiency and robustness are fundamental requirements for biped walkingrobot, and stability is the basis of study. It has been confirmed that the3D spatial movementof passive biped robot without stability can generate stable3D dynamic walking by usingspecial structural design and passive energy storage components.The work in this paper is supported by the863Program (No.2006AA04Z251) andNational Nature Science Fund Project (No.60974067). It focuses on the biped walkingstructure, hybrid dynamics modeling and gait characteristics of the3D spatial motion basedon passive dynamic walking theory, and also includes research on the locomotionmechanism and stability control algorithm of3D locomotion. The main contents aredescribed as follows:1. Establishment of the3D hybrid model for biped robot. In order to achieve3D stablewalking, flexible feet are studied, and then the3D hybrid model with knees and flexible feetis established, which not only narrows the gap between the theoretical model and theprototypes, but also expands the motion space from two-dimension to three-dimension,which shortens the difference between humanoid robot gait and human gait. It provides the model basis for the further study.2. Study of the three-dimensional locomotion mechanism. The models of the sagittalmotion and lateral motion are analyzed respectively before the study of the couplingrelationship between them. Conclusions from the study of the locomotion mechanism makea new breakthrough in the passive dynamic walking theory. Model simulation and prototypeexperiment are also made to prove the correctness of our theoretical model and prototype.3. Analysis on stable characteristics of three-dimensional locomotion. Robot gaitstability is defined by the stability of periodic orbits. The local stability of the system isanalyzed by orbital stability theory based on Poincare mapping, and the global stability isanalyzed by cell mapping method based on Poincare mapping. Then the impact of structuralparameters and walking environment on the gait stability is studied, which has greatsignificance on the prototype design.4. Research on the stability control algorithm of three-dimensional locomotion.Three-dimensional stability control algorithm is studied based on the3D model we built inthis paper. By utilizing energy control algorithm and3D stability control algorithm based onthe decoupling characteristics, the robot state after disturbance can converge to the stablelimit cycle, and simulation results show that the control algorithms are both effective.