Using Parallel Joint Compliance to Reduce the Cost of Walking in a Planar Bipedal Robot

Abstract

This paper presents numerical and experimental studies of the influence of parallel knee joint compliance on the average power cost of walking in an underactuated planar bipedal robot, ERNIE. The use of parallel compliance does not increase the control design complexity, as would the addition of series compliance. Four scenarios were studied: one without springs, and three with springs of different stiffnesses and preloads. Optimal gaits in terms of average power cost for various speeds were designed for each scenario. It was found that for low-speed walking, soft springs are helpful to reduce power cost, while stiffer springs increase power cost. For high-speed walking, it was found that both soft and stiff springs reduce the average power cost of walking, but stiffer springs reduce the cost more than do softer springs.