Design of a Crank-and-Rocker Driven Pantograph: A Leg Mechanism for the University of Maryland's 1991 Walking Robot

Abstract

The National Aeronautics and Space Administration has been funding university research into flexible, six-legged walking machines capable of exploring alien terrain. This research has led to a progressive new look at standard four bar mechanisms.<P>Four bar mechanisms, by definition, consist of a crank link, coupler link, rocker link and fixed (ground) link. The passive role of the coupler link, in traditional four bar mechanisms, can be reversed so that the coupler becomes the transmission link. This is achieved by replacing the coupler with an oblique triangular link. The internal angles of the modified coupler can be varied to create an array of continuous, ovoid paths at the disjointed vertex of the triangle.<P>Attaching a pantograph mechanism to the modified coupler's trace point amplifiers and translates the ovoid path. The combination of these two mechanisms provides a stable, one degree of freedom walking path which emulates that of humans. This mechanism can therefore be used as a robotic leg.<P>A second degree of freedom is obtained by attaching an adjacent link to the pantograph mechanism which raises or lowers the walking path without effecting its shape or magnitude. This is used for climbing and maneuvering amidst rugged terrain.