Autonomous gait transition method for pacing four-legged robots

Abstract

This study aims to suggest a method for achieving an autonomous gait transition according to speed for a four-legged robot pacing at medium speeds. Our quadruped robot is simply designed and applies a central pattern generator (CPG) for each leg. Each leg is controlled by a PD controller based on a rhythmic output from the CPG. The four CPGs are coupled, and a hard-wired CPG network is constructed to generate a default pace pattern. In addition, we apply feedback of the body tilt to the CPG as vestibular sensory feedback. As a result, our robot safely locomotes at various speeds by autonomously changing the gait from walking to pacing to rotary galloping according to speed, despite the fact that the walk and rotary gallop are not predefined. A factor that causes the gaits' emergence is considered the body oscillation that changes according to the speed. The body oscillation exhibits a double peak per leg frequency at low speeds, no peak at medium speeds, and a single peak at high speeds. The phase differences between the four legs are adjusted according to the body oscillation by feeding the body tilt back to the CPG. The gait transition is triggered only by the body tilt angle, we expect that the suggested method can be generally used for quadruped robots.