A Gravity Compensation Technique for an N-Legged Robot

Abstract

Steady state errors resulting from gravitational loading are significant in legged robots, particularly when controller gains are set to low values to achieve the desirable property of compliant legs. This paper presents a gravity compensation scheme which not only eliminates steady state errors but which also generates foot reaction distributions that are optimal in terms of minimizing the likelihood of foot constraints being broken. This is achieved by minimizing a cost function, designed to reflect the condition of foot constraints, in conjunction with the equations of static equilibrium for the robot. A method of performing the minimization based on a combination of an analytical and a Newton—Raphson technique is presented. Results are given for hexapod and biped simulation models and for an experimental biped.