On the stability of legged locomotion

Zhuohua Shen, Purdue University

Abstract

Spring-Loaded Inverted Pendulum(SLIP) is a canonical model legged locomotion, but it fails to predict dynamical stability of real world legged locomotion. Recently there are some actuated models with greater stability than SLIP developed and analyzed. But the reason behind the improved stability is still unknown. Here, we introduce a new model called Forced-Damped Spring-Loaded Inverted Pendulum(FD-SLIP) capable of achieving fully asymptotic stable Center-of-Mass (CoM) motion. FD-SLIP is quite simple in form, with only one more nondimensionalized model parameters than the simple SLIP model at fixed points. Through numerical simulation of FD-SLIP, we found that hip torque and leg damping can greatly improve CoM motion stability. A complete exploration of the parameter space of FD-SLIP showed that it has a much bigger stable parameter region than SLIP. To better understand the change of model stability during the transition from SLIP to FD-SLIP. We developed new closed form solutions of SLIP and FD-SLIP with weak hip torque and leg damping mainly by assuming gravity only acts along the leg during stance. Both analytical solutions can qualitatively capture the dynamical characteristics of each model when compared with numerical simulation results. And by a simple adjustment, we extended the analytical solution of FD-SLIP so that it is also applicable when hip torque and leg damping are reasonably large.

Degree

M.S.E.

Advisors

Seipel, Purdue University.

Subject Area

Mechanical engineering|Biomechanics

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