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Disturbance observer based dynamic load torque compensator for assistive exoskeletons
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics. Department of Robotics, Perception and Learning, Royal Institute of Technology, Stockholm, Sweden.
Department of Robotics, Perception and Learning, Royal Institute of Technology, Stockholm, Sweden.
University of Gävle, Faculty of Engineering and Sustainable Development, Department of Electronics, Mathematics and Natural Sciences, Electronics.
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
Elsevier Ltd , 2018. Vol. 54, p. 78-93
Keywords [en]
Disturbance observer, Exoskeleton, Load torque compensator, Serial manipulator, Actuators, DC motors, Dynamic loads, Electric machine control, Electric machine theory, Joints (anatomy), Manipulators, Robotics, Torque, Torque measurement, Application of standards, Compensation performance, Compensator structure, Higher-order dynamics, Load torques, Parametric uncertainties, Serial manipulators, Exoskeleton (Robotics)
National Category
Robotics
Identifiers
URN: urn:nbn:se:hig:diva-27633DOI: 10.1016/j.mechatronics.2018.07.003ISI: 000446949100007Scopus ID: 2-s2.0-85050674987OAI: oai:DiVA.org:hig-27633DiVA, id: diva2:1238608
Note

Ambient Assisted Living (AAL) Program  Grant no: AAL-2013-6-042

Available from: 2018-08-14 Created: 2018-08-14 Last updated: 2018-11-26Bibliographically approved

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Masud, NaumanIsaksson, Magnus

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