Gait shape control for 2-D.O.F bipedal robots using hybrid virtual holonomic constraints

bipedal robot;hybrid;virtual constraints;gait;nonlinear control;System Design Engineering

Al Lawati, Mohamed Ali

University of Waterloo

关键词: bipedal robot;    hybrid;    virtual constraints;    gait;    nonlinear control;    System Design Engineering;   

Others  :  https://uwspace.uwaterloo.ca/bitstream/10012/8587/1/Allawati_Mohamed.pdf

瑞士|英语

来源: UWSPACE Waterloo Institutional Repository

【 摘 要 】

Motion control for bipedal robots is an active research area becausebipedal robots can perform tasks and work in terrain where wheeledrobots cannot. Researchers have developed bipedal robots that are ableto walk, run and perform predefined tasks such as stair climbing.Mimicking human motion is one of the potential benefits of bipedalrobots. In the robotics and control literature, many controllers havebeen presented that achieve dynamically stable gait motions (i.e.stable walking). This thesis studies virtual holonomicconstraint (VHC) based control laws that generate stable gaits for2-DOF bipedal robots.The planar 2-DOF robot under study is modelled as a hybrid automatonand consists of three physical components: a stance leg, a swing leg and a hipmass. The robot is actuated by a hip torque and an ankle torque.For the continuous phase, the dynamics of the robot are similarto a rigid double pendulum except that the robot has an ;;extra;; massattached to its hip position. At ground impact events, the system;;s configuration variables areredefined and the associated velocities change instantaneously. Theground is modelled as an inclined surface with no curvature. Due to the hybrid nature of 2-DOF bipedal robots, this thesis extends the notion of VHC to hybrid VHC for a generalEuler-Lagrange system with impacts and applies it to a 2-DOF bipedal robot. For any desired gait of the 2-DOF robot, the motion of the swing leg can be expressed as afunction of the stance leg. Using this function, a hybrid VHC isgenerated and the control objective becomes enforcing the hybrid VHC.A design procedure is developed that returns a feasible hybrid VHC forthe 2-DOF bipedal robot.The concept of VHC motivates the design of feedback linearizing controllers that drive thestates of the robot to a constraint manifold. Feedback linearizingcontrollers are designed that enforce the hybrid VHC. In thisframework, two possible control laws are presented. The first controllaw generates a fully actuated robot in closed-loop configuration.Sufficient conditions for stability are given and proven. The second control lawyields an under-actuated system in closed-loop configuration. Thiscontrol design is shown to consume no energy as long as the hybrid VHC thatmodels a passive gait is enforced. The stability of this controlleris studied numerically through the method of Poincaré sections.