Transparency enhancement for an active knee orthosis by a constraint-free mechanical design and a gait phase detection based predictive control

• Published in: Meccanica (Milan) 2017-02, Vol.52 (3), p.729-748
• Main Authors: Cai, Viet Anh Dung, Ibanez, Aurelien, Granata, Consuelo, Nguyen, Viet Thang, Nguyen, Minh Tam
• Format: Article
• Language: English
• Subjects: Advances in Biomechanics: from foundations to applications; Automotive Engineering; Civil Engineering; Classical Mechanics; Gait; Mechanical Engineering; Physics; Physics and Astronomy; Predictive control
• ISSN: 0025-6455; 1572-9648
• DOI: 10.1007/s11012-016-0575-z

This paper proposes a novel mechanical design of a lower limb exoskeleton device which prevents the residual stresses due to arthro-kinematics movements of synovial joints and by the way allows effective compensation for dynamic disturbances in osteo-kinematic movements of the wearer. Here, the exoskeleton is only actuated at the knee joints to provide assistive torques, which are required to assist the anatomical joint motion and to increase the transparency of the device. Dynamic simulations of a virtual human equipped with this exoskeleton are used to quantify the disturbances induced by the device during locomotion and to show the benefit of passive mechanisms introduced in the mechanical attaches as well. The authors also demonstrated how the device’s transparency can be improved by providing the motor torques in order to compensate the inertial and gravitational effects. This can be done rely on the knowledge of the locomotion movement phases. A robust gait phase detection method was implemented on the experimental device in order to identify specific gait phases in real time. This method exploits the K-nearest neighbors algorithm to identify the k-closest trained vectors, coupling with a discrete time Markov chain to determine the phases shift probability during the gait cycle. This gait detection algorithm was tested with a percentage of success of more than 95% when the subjects walked with constant and variable stride lengths.