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Output feedback assistive control of single-DOF SEA powered exoskeletons

Iman Kardan (Center of Excellence on Soft Computing and Intelligent Information Processing, Mechanical Engineering Department, Ferdowsi University of Mashhad, Mashhad, Iran)
Alireza Akbarzadeh (Center of Excellence on Soft Computing and Intelligent Information Processing, Mechanical Engineering Department, Ferdowsi University of Mashhad, Mashhad, Iran)

Industrial Robot

ISSN: 0143-991x

Article publication date: 15 May 2017

Abstract

Purpose

This paper aims to overcome some of the practical difficulties in assistive control of exoskeletons by developing a new assistive algorithm, called output feedback assistive control (OFAC) method. This method does not require feedbacks from force, electromyography (EMG) or acceleration signals or even their estimated values.

Design/methodology/approach

The presented controller uses feedbacks from position and velocity of the output link of series elastic actuators (SEAs) to increase the apparent integral admittance of the assisted systems. Optimal controller coefficients are obtained by maximizing the assistance ratio subjected to constraints of stability, coupled stability and a newly defined comfort measure.

Findings

The results confirm the effectiveness of using the inherent properties of SEAs for removing the need for extra controversial sensors in assistive control of 1 degree of freedom (1-DOF) SEA powered exoskeletons. The results also clearly indicate the successful performance of the OFAC method in reducing the external forces required for moving the assisted systems.

Practical implications

As the provided experiments indicate, the proposed method can be easily applied to single DOF compliantly actuated exoskeletons to provide a more reliable assistance with lower costs. This is achieved by removing the need for extra controversial sensors.

Originality/value

This paper proposes a novel assistive controller for SEA-powered exoskeletons with a simple model-free structure and independent of any information about interaction forces and future paths of the system. It also removes the requirement for the extra sensors and transforms the assistive control of the compliantly actuated systems into a simpler problem of position control of the SEA motor.

Keywords

Citation

Kardan, I. and Akbarzadeh, A. (2017), "Output feedback assistive control of single-DOF SEA powered exoskeletons", Industrial Robot, Vol. 44 No. 3, pp. 275-287. https://doi.org/10.1108/IR-08-2016-0214

Publisher

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Emerald Publishing Limited

Copyright © 2017, Emerald Publishing Limited