Sliding-Mode Tracking Control of a Walking Quadruped Robot with a Push Recovery Algorithm Using a Nonlinear Disturbance Observer as a Virtual Force Sensor

摘要

Abstract This paper offers a new push recovery method to stabilize the quadruped robots walking on even terrains in the presence of external disturbance forces exerted on the body and legs of the robot. To avoid force sensors, a class of nonlinear observers is usually used to estimate all the forces that are applied to the leg joints. However, such estimations involve permanent errors in the case of fast varying external forces. A new sliding-mode control method is designed to enable the robot to track a desired gait with high precision despite the persisting estimation error of the original nonlinear disturbance observer. A new push recovery method that uses the estimations of the disturbance observer is proposed to help the robot maintain its balance in the presence of sudden external forces applied to the robot legs and body. To this end, an optimization problem is proposed to calculate the optimized accelerations of the leg joints of the robot. This controller was applied to the TMUBot quadruped robot as a case study to verify the effectiveness of the design. Moreover, unlike other similar works, which use massless model of the legs, the masses of the legs of the quadruped are considered in this work. As such, the dynamic equations of the legs have also been considered throughout the proposed design method.