Gallop with speed change for quadruped robots

Abstract

This paper proposes a method to change the speed of gallop for a quadruped robot by controlling the vertical ground reaction forces. For easy and stable galloping of a quadruped robot, the basic motion of each foot with respect to its main body is expressed by an elliptic path. The elliptic footpath is simple, efficient and quite similar to that of a four-legged animal. The desired GRF is computed using the momentum equation. Since the body balance is very important in stable galloping locomotion, the body balance is determined by the measured roll and pitch angles at the moment of touch down. Based on this, the desired ground reaction force is computed, and force control is used for the ground reaction force to track it for stable gallop. For the control of roll motion, a fuzzy-logic controller is used to redistribute the ground reaction forces. For the control of pitch motion, a fixed control law based on the pitch error is used. And, in order to change the gallop speed, another fuzzy logic controller is used to change the TD position on the elliptic footpath. Computer simulations were done based on the quadruped model of HUNTER, and their results showed that the proposed generation method is effective for stable gallop.