Design and testing a highly backdrivable and kinematic compatible magneto-rheological knee exoskeleton

Author:

de Andrade Rafhael Milanezi12ORCID,Fabriz Ulhoa Pedro Henrique3,Fragoso Dias Eduardo Antônio1,Filho Antônio Bento1ORCID,Vimieiro Claysson Bruno Santos24ORCID

Affiliation:

1. Graduate Program in Mechanical Engineering, Universidade Federal do Espírito Santo, Vitoria, Brazil

2. Graduate Program in Mechanical Engineering, Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil

3. Department of Electrical Engineering, Universidade Federal do Espírito Santo, Vitoria, Brazil

4. Graduate Program in Mechanical Engineering, Pontifícia Universidade Católica de Minas Gerais, Minas Gerais, Brazil

Abstract

Lower limb exoskeletons (LLE) have been successfully used in robotic-assisted rehabilitation to reduce the burden of locomotor impairment of disabled people. However, the design limitations of LLE mechanisms, such as the lack of kinematic compatibility relative to the user’s joints and the use of high stiff or heavy actuators, limit the outcomes of treatment and increase the risk of injury. To address these shortcomings, in this work we present the design of the MRKneeExo, a highly backdrivable and kinematically compatible active knee exoskeleton. The powertrain of the system is composed of a BLDC 70 W motor associated with a harmonic drive gearbox and a customized magneto-rheological (MR) clutch. To improve kinematic compatibility with the user’s knee, a crossed four-bar linkage mechanism (FBLM) was optimally designed to follow the trajectory of the instant center of rotation (ICR) of the knee projected in the parasagittal plane where the joint is placed. The MR clutch is used to decouple the motor-reducer from the FBLM, thus enabling high backdrivability. The results showed a small error (<3 mm) between the FBLM and the knee ICR. Furthermore, the MR clutch allowed for low back-drive torque (1.28 N m) compared to the torque to back-drive the motor-reducer (18.51 N m). This paper is presented in a framework that can be generalized to support the design of other knee exoskeletons.

Funder

Financiadora de Estudos e Projetos

Fundação de Amparo à Pesquisa e Inovação do Espírito Santo

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Publisher

SAGE Publications

Subject

Mechanical Engineering,General Materials Science

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