A Sliding Mode Force and Position Controller Synthesis for Series Elastic Actuators

TL;DR

This paper introduces a robust sliding mode control method for Series Elastic Actuators that effectively handles disturbances and does not require precise dynamic models, enabling accurate trajectory tracking and safe environmental interaction.

Contribution

A novel robust motion controller combining Disturbance Observer and Sliding Mode Control for Series Elastic Actuators, addressing both force and position control with disturbances.

Findings

Effective disturbance rejection demonstrated experimentally.

Precise trajectory tracking achieved without detailed dynamic models.

Applicable to various robotic systems like humanoids and exoskeletons.

Abstract

This paper deals with the robust force and position control problems of Series Elastic Actuators. It is shown that a Series Elastic Actuator's force control problem can be described by a second-order dynamic model which suffers from only matched disturbances. However, the position control dynamics of a Series Elastic Actuator is of fourth-order and includes matched and mismatched disturbances. In other words, a Series Elastic Actuator's position control is more complicated than its force control, particularly when disturbances are considered. A novel robust motion controller is proposed for Series Elastic Actuators by using Disturbance Observer and Sliding Mode Control. When the proposed robust motion controller is implemented, a Series Elastic Actuator can precisely track desired trajectories and safely contact with an unknown and dynamic environment. The proposed motion controller does not require precise dynamic models of the actuator and environment. Therefore, it can be applied to many different advanced robotic systems such as compliant humanoids and exoskeletons. The validity of the motion controller is experimentally verified.