Design of a leg system for quadruped gallop

Abstract

Ohio State (OSU) and Stanford Universities are cooperating to understand quadruped galloping through the design of a self-contained, biomimetic, galloping robot. The leg for this quadruped was first designed at Ohio State University (OSU). A second-generation leg, with the same functional geometry, has been designed and tested at Stanford University. The objective of these tests was to determine that the single leg would be capable of prolonged operation at a velocity of 5m/s, and that the control system, developed in simulation, would function under real-world conditions. The mechanical design of the quadruped is based on properties of biological quadruped animal legs. Important biomimetic design characteristics include minimal impact loss, elastic energy storage, and low inertia. The cable linkage, which works against a large spring to flex the knee, is uncoupled from the front-to-back hip actuator through a parallelogram-like cable mechanism. The controller developed for the leg is a direct adaptive fuzzy controller. The direct adaptive approach does not require system identification and can use heuristics to successfully control a complex system. With this controller we were able to successfully control a single 2dof leg constrained in yaw, pitch, roll and transverse translation. This controller was executed once each cycle at the top-of-flight. Parameters set by the controller were passed to PD controllers at each of the 2 joints: the hip and cable-actuated knee. The control of this leg required only 7 x 5 x 3 = 105 rules, each with a corresponding output for thigh and knee angle. This controller was implemented on an embedded processor attached to the leg. The leg reached a speed of 3m/s. Modifications to the leg will increase this speed. The controller successfully adapted to the leg.