Variable bipedal walking gait with variable leg stiffness

Abstract

The Spring-Loaded Inverted Pendulum (SLIP) model has been shown to exhibit many properties of human walking, and therefore has been the starting point for studies on robust, energy-efficient walking for robots. In this paper, the problem of gait variation during walking on the SLIP model is addressed by controlling the leg stiffness and the angle-of-attack in order to switch between gaits and thus regulate walking speeds. We show that it is possible to uniquely describe SLIP limit cycle gaits in fully normalised form. Using that description, we propose both an instantaneous switching method and an interpolation method with an optimisation step to switch between limit cycle SLIP gaits. Using simulations, we show that it is then possible to transition between them, after which the system converges back to zero-input limit cycle walking.

Bipedal walking gait with variable stiffness knees

“…The system starts in the slow gait (gait 1), is commanded to change to fast gait (gait 2) at 1.0 m, and then to switch back to the slow gait (gait 3 = gait 1) at 5.5 m. The controller references are produced using the switching method in [11].…”

“…As x was identified to be a periodic variable and required to be monotonically increasing in time, the references are reparametrised on x. The references ỹ * (x), ẋ * (x) are then sufficiently described as ỹ * (x) = ỹo (x) ẋ * (x) = ẋo (x) (11) However, as a general analytic expression for the springloaded pendulum does not exist [10], a Fourier series expansion approximation of the numerical solution is used. We extend ( 5) to obtain d dt…”