Sequen-Sync Contact Force/Torque Control Using Nested Fast Terminal Sliding Mode Control Approach

Abstract

As one of the most fundamental control modes in robotics, force/torque (F/T) control plays an essential role in a wide range of applications. However, classical F/T control fails to offer effective means to regulate the convergence sequence of the controlled states, which is beneficial in many real-world tasks, e.g., unknown surface contact, where the force should preferably converge later than the alignment angles to ensure sufficient contact and avoid dangerous misalignment. In this work, a novel nested fast terminal sliding mode control approach is proposed. This approach establishes a hierarchical structure for the controlled states, such that the Lyapunov stabilities of controlled states can be achieved in both a sequential and a time-synchronized manner within finite time, which is named as ‘Sequen-Sync’. Extensive experiments are conducted for various tasks in two different environments. The experimental results show that the proposed approach successfully achieves Sequen-Sync stability, which leads to improved contact quality and enhanced safety.