Locomotion Control Of Bipedal Robots Based On Passivity And Underactuation

Bipedal humanoid robot has a great advantage in adaptability to the environment and strong affinity in human-machine interaction. However, there is a great disparity between bipedal locomotion developed by the existing control theory and real human bipedal loco-motion. Inspired by the passivity and underactuation existing in human bipedal locomotion, this dissertation combines passivity-based control, energy shaping control, hybrid zero dy-namics and time scaling control in order to study stable, agile and efficient locomotion control methods of bipedal robots based on passivity and underactuation. The contribution of this paper can be listed as follows:Firstly, method combined time scaling control and energy shaping control is proposed for full actuated bipedal robot to construct reference trajectories with different step length and walking speed. A feedback control law is obtained via feedback linearization technique so that the trajectory of the robot converges to a desired passive walking gait. A larger basin of attraction can be obtained. Corresponding feedback control laws are updated at the beginning of each step. Then, the controller condition that the errors measuring the difference of the response trajectory and the reference one asymptotically converge to zero is given. The problem of achieving a stable walking in complex environments for full actuated bipedal robot with regulable step length and walking speed is first solved in this dissertation. The agility of bipedal locomotion is increased.Secondly, balance control problem of planar bipedal robots with underactuation dur-ing disturbed standing is investigated. Virtual holonomic constraints which specify the an-gles of actuated joints as a function of the rotation angle between the sole of stance foot and ground are introduced. Several conditions guaranteeing the balance of standing for given virtual holonomic constraints arc obtained. Moreover, for a disturbance beyond the bal-ance conditions for single-leg support, robot changes to a double support posture to avoid turnover by the virtual holonomic constraints and this reaction is very human-like. Further, for a special kind of balance:standing on toe which leads to underactuation, the design conditions of virtual holonomic constraints and estimate set of basin of attraction are first given in theory.Thirdly, a unified feedback control law for n degree-of-freedom biped robots with one degree of underactuation so as to generate periodic orbits on different slopes is first developed in this dissertation. The periodic orbits on different slopes are produced from an original periodic orbit, which is either a natural passive limit cycle on a specific slope or a stable periodic walking gait on level ground generated with active control. Necessary and sufficient conditions are investigated for the existence and stability properties of periodic orbits on different slopes with the proposed control law. The adaptability and agility of undcractuated bipedal locomotion are greatly increased.Fourthly, stable running problem of a planar underactuated biped robot which has two springy telescopic legs and one actuated joint in the hip is investigated. Based on a natural passive running limit cycle in level ground, a feedback control is proposed to stabilize the passive limit cycle and enlarge the basin of attraction. By this controller, there is no energy consumed when state vector of the robot reaches the running limit cycle under ideal impact condition. This conclusion is a great inspiration for achieving efficient human-like bipedal locomotion.This dissertation gives rigorous theoretical proof for the proposed analysis and control design methods. Several simulations are given in each chapter to illustrate the results.