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Disturbance observer based dynamic load torque compensator for assistive exoskeletons
KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, perception and learning, RPL. Univ Gavle, Dept Elect Math & Sci, S-80176 Gavle, Sweden.
KTH, School of Electrical Engineering and Computer Science (EECS), Robotics, perception and learning, RPL.ORCID iD: 0000-0003-2078-8854
Univ Gavle, Dept Elect Math & Sci, S-80176 Gavle, Sweden..
2018 (English)In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 54, p. 78-93Article in journal (Refereed) Published
Abstract [en]

In assistive robotics applications, the human limb is attached intimately to the robotic exoskeleton. The coupled dynamics of the human-exoskeleton system are highly nonlinear and uncertain, and effectively appear as uncertain load-torques at the joint actuators of the exoskeleton. This uncertainty makes the application of standard computed torque techniques quite challenging. Furthermore, the need for safe human interaction severely limits the gear ratio of the actuators. With small gear ratios, the uncertain joint load-torques cannot be ignored and need to be effectively compensated. A novel disturbance observer based dynamic load-torque compensator is hereby proposed and analysed for the current controlled DC-drive actuators of the exoskeleton, to effectively compensate the said uncertain load-torques at the joint level. The feedforward dynamic load-torque compensator is proposed based on the higher order dynamic model of the current controlled DC-drive. The dynamic load-torque compensator based current controlled DC-drive is then combined with a tailored feedback disturbance observer to further improve the compensation performance in the presence of drive parametric uncertainty. The proposed compensator structure is shown both theoretically and practically to give significantly improved performance w.r.t disturbance observer compensator alone and classical static load-torque compensator, for rated load-torque frequencies up to 1.6 Hz, which is a typical joint frequency bound for normal daily activities for elderly. It is also shown theoretically that the proposed compensator achieves the improved performance with comparable reference current requirement for the current controlled DC-drive.

Place, publisher, year, edition, pages
Pergamon Press, 2018. Vol. 54, p. 78-93
Keywords [en]
Load torque compensator, Exoskeleton, Serial manipulator, Disturbance observer
National Category
Robotics
Identifiers
URN: urn:nbn:se:kth:diva-237104DOI: 10.1016/j.mechatronics.2018.07.003ISI: 000446949100007Scopus ID: 2-s2.0-85050674987OAI: oai:DiVA.org:kth-237104DiVA, id: diva2:1258261
Note

QC 20181024

Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2018-10-24Bibliographically approved

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