Control of a compass gait walker based on energy regulation using ankle push-off and foot placement

Abstract

In this paper, we present a theoretical study on the control of a compass gait walker using energy regulation between steps. We use a return map to relate the mid-stance robot kinetic energy between steps with two control inputs, namely, foot placement and ankle push-off. We show that by regulating robot kinetic energy between steps using the two control inputs, we are able to (1) generate a wide range of walking speeds and stride lengths, including average human walking; (2) cancel the effect of external disturbance fully in a single step (dead-beat control); and (3) switch from one periodic gait to another in a single step. We hope that insights from this control methodology can help develop robust controllers for practical bipedal robots. IntroductionCurrent research on bipedal robots has focussed on planning and control of a singe steady state (periodic) walking gait. We characterize a walking gait by a given combination of step length and step velocity. However, for bipedal robots, to be able to walk in man-made environments, they need to be able to walk at a wide range of steady state periodic gaits and be able to switch from one periodic gait to another quickly.In this paper, we show theoretical calculations on how to use energy regulation between steps to plan and control walking of a compass gait model. We first review past work on compass gait models and common control approaches, followed by a discussion on our model.

Discrete-Decision Continuous-Actuation Control: Balance of an Inverted Pendulum and Pumping a Pendulum Swing

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A Discrete Control Lyapunov Function for Exponential Orbital Stabilization of the Simplest Walker

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“…Since the point mass torso is heavy compared to the legs, the swing leg motion cannot affect the stance leg motion in the swing phase, and the system is thus decoupled. However, the swing leg (actuated degree-of-freedom) motion can influence the stance leg (unactuated degree-of-freedom) motion by appropriate foot placement (e.g., big step reduces the stance leg velocity [19]), which is exploited in the DCLF approach. Figure 2 shows a cartoon of the simplest walker [18].…”

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