MHS measure for postural stability monitoring and control of biped robots

Abstract

Stability fulfilment for biped robots is drastically essential. Thus, to predict and maintain a dynamic stable status of biped robots defining an accurate stability measure is required which can represent dynamic equilibrium condition. Several postural stability metrics have been proposed so far. In this article, the Moment-Height stability (MHS) measure which has been previously proposed for wheeled mobile robots is developed for biped robot control. The responses of this criterion for stability monitoring of a biped robot is compared with the well known stability criterion Zero-Moment Point (ZMP). To this end, two common case studies of robot’s motion including standing up and walking are considered and the results of application of the MHS are compared with those of the ZMP. The obtained results reveal the merits of MHS over ZMP in terms of its higher sensitivity to walking height (overall height of the robot’s center of mass) and indicating the direction of foot rotation. The MHS metric is able not only to monitor the state of postural stability of a biped robot during the entire gait cycle, but also it does reliably indicate the severity of instability of the gait.