H-Infinity Control of a Six-Legged Robot in Lifting Mode

Abstract

The present work aims at elaborating an efficient robust control approach of a six-legged robot in the lifting phase movement with the presence of nonlinearities, internal and external disturbances. A dynamic model of the legged robot is derived using the Newton-Euler formalism. Furthermore, an identification method is used to determine the system’s behavior by considering the joint variables at low, medium and high velocities. The variations between the obtained models in the different velocity margins are considered as nonlinearities and dynamic uncertainties, and are represented by the multiplicative uncertainty configuration. The H-infinity mixed-sensitivity method is applied in order to achieve a good performance and robust stability against external disturbances and the internal uncertainties represented by the unmodeled dynamics, the sensor noise, and the restrictions on the actuators control weight. In order to verify the capability of this controller to achieve the system stability and performances against the different disturbances, the small gain theorem method and robust stability and performance margin plots are used. The simulation results show that the control algorithm proposed in this paper can effectively achieve the robust stability and the hexapod robot performances.