Improving hopping stability of a biped by muscular stretch reflex

Animals have several peripheral feedback control networks such as stretch reflexes that are supposed to be contributing to stability of their behavior. In this paper, we focus on rolling stability of hopping of a biped robot, and investigate several schemes on an experimental robot for implementing the stretch reflex: no reflex, undelayed and delayed reflex, how they contribute to the stability. For eliminating effect of changing environment and initial postures, we conduct large number of hopping experiments on a real robot. From the experimental results, we can conclude (1) two reflex schemes, with delay and without delay, can both increase the frontal stability in hopping, and (2) the delay time has little influence on the stability. By these result, we can derive a stable hopping controller for a biped robot, and may be able to understand the mechanism of human adaptive hopping as well.