Analysis of walking and balancing models actuated and controlled by ankles

Abstract

Experimental data show that ankle torque is the most important actuator in normal human locomotion. I investigate the dynamics of simple models actuated by ankles alone. To assess the contribution of ankle actuation to locomotion, I first analyze the dynamics of some passive walkers without any joint torque. These passive walkers include a rimless wheel model and springy-legged models with and without a double stance phase. I analyze the stability of the period-one gait of each passive walker to compare it with the stability of the period-one gait of an ankle actuated model. Subsequently, I investigate whether balancing of a double inverted pendulum model whose shape and mass distribution are similar to a human can be achieved by control of ankle torque in a frontal plane. I study the dynamics of the model and design a controller that makes the model balance with biologically realistic ankle torque and a reasonable foot-floor friction coefficient. I conclude that an ankle-actuated model can make a stable period-one gait in a sagittal plane. Also, I deduce that the ankle torque control in a frontal plane can stabilize a double inverted pendulum model whose shape and mechanical properties are similar to those of humans.