Nonlinear Control Systems
Non-Linear Control for Underactuated Mechanical Systems
Non-Linear Control for Underactuated Mechanical Systems
Asymptotically stable walking of a five-link underactuated 3-D bipedal robot
IEEE Transactions on Robotics
Stable Bipedal Walking With Foot Rotation Through Direct Regulation of the Zero Moment Point
IEEE Transactions on Robotics
Walking and steering control for a 3D biped robot considering ground contact and stability
Robotics and Autonomous Systems
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This paper presents two walking controllers for a planar biped robot with unactuated point feet. The control is based on the tracking of reference motions expressed as a function of time. First, the reference motions are adapted at each step in order to create a hybrid zero dynamic (HZD) system. Next, the stability of the walking gait under closed-loop control is evaluated with the linearization of the restricted Poincare map of the HZD. When the controlled outputs are selected to be the actuated coordinates, most periodic walking gaits for this robot are unstable, that is, the eigenvalues of the linearized Poincare map (ELPM) is larger than one. Therefore, two control strategies are explored to produce stable walking. The first strategy uses an event-based feedback controller to modify the ELPM and the second one is based on the choice of controlled outputs. The stability analysis show that, for the same robot and for the same reference trajectory, the stability of the walking (or ELPM) can be modified by some pertinent choices of controlled outputs. Moreover, by studying some walking characteristics of many stable cases, a necessary condition for stable walking is proposed. It is that the height of swing foot is nearly zero at the desired moment of impact. Based on this condition, the duration of the step is almost constant in presence of initial error, so a method for choosing controlled outputs for the second controller is given. By using this method, two stable domains for the controlled outputs selection are obtained.