  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.
