Non-linear Task-Space Disturbance Observer for Position Regulation of Redundant Robot Arms against Perturbations in 3D Environments

TL;DR

This paper introduces a non-linear task-space disturbance observer for redundant robot arms, enabling accurate position regulation in complex 3D environments despite uncertainties and perturbations, demonstrated through simulations and comparisons with conventional methods.

Contribution

The paper presents a novel non-linear disturbance observer that improves position regulation of redundant robot arms under perturbations, outperforming traditional mass-damper based approaches.

Findings

Enhanced disturbance rejection in simulations

Successful human-like motion under perturbations

Better performance than conventional observers

Abstract

Many day-to-day activities require the dexterous manipulation of a redundant humanoid arm in complex 3D environments. However, position regulation of such robot arm systems becomes very difficult in presence of non-linear uncertainties in the system. Also, perturbations exist due to various unwanted interactions with obstacles for clumsy environments in which obstacle avoidance is not possible, and this makes position regulation even more difficult. This report proposes a non-linear task-space disturbance observer by virtue of which position regulation of such robotic systems can be achieved in spite of such perturbations and uncertainties. Simulations are conducted using a 7-DOF redundant robot arm system to show the effectiveness of the proposed method. These results are then compared with the case of a conventional mass-damper based task-space disturbance observer to show the enhancement in performance using the developed concept. This proposed method is then applied to a controller which exhibits human-like motion characteristics for reaching a target. Arbitrary perturbations in the form of interactions with obstacles are introduced in its path. Results show that the robot end-effector successfully continues to move in its path of a human-like quasi-straight trajectory even if the joint trajectories deviated by a considerable amount due to the perturbations. These results are also compared with that of the unperturbed motion of the robot which further prove the significance of the developed scheme.