title: Optical Enhancement of Exoskeleton-Based Estimation of Glenohumeral Angles.
abstract: In Robot-Assisted Rehabilitation (RAR) the accurate estimation of the patient limb joint angles is critical for assessing therapy efficacy. In RAR, the use of classic motion capture systems (MOCAPs) (e.g., optical and electromagnetic) to estimate the Glenohumeral (GH) joint angles is hindered by the exoskeleton body, which causes occlusions and magnetic disturbances. Moreover, the exoskeleton posture does not accurately reflect limb posture, as their kinematic models differ. To address the said limitations in posture estimation, we propose installing the cameras of an optical marker-based MOCAP in the rehabilitation exoskeleton. Then, the GH joint angles are estimated by combining the estimated marker poses and exoskeleton Forward Kinematics. Such hybrid system prevents problems related to marker occlusions, reduced camera detection volume, and imprecise joint angle estimation due to the kinematic mismatch of the patient and exoskeleton models. This paper presents the formulation, simulation, and accuracy quantification of the proposed method with simulated human movements. In addition, a sensitivity analysis of the method accuracy to marker position estimation errors, due to system calibration errors and marker drifts, has been carried out. The results show that, even with significant errors in the marker position estimation, method accuracy is adequate for RAR.
authors.affiliation: eHealth and Biomedical Applications, Vicomtech-IK4, Mikeletegi Pasealekua 57, 20009 San Sebastián, Spain; Laboratorio de CAD CAM CAE, Universidad EAFIT, Carrera 49 No. 7 Sur-50, 050022 Medellín, Colombia.
authors.forename: Camilo
authors.initials: C
authors.lastname: Cortés
authors.affiliation: eHealth and Biomedical Applications, Vicomtech-IK4, Mikeletegi Pasealekua 57, 20009 San Sebastián, Spain.
authors.forename: Luis
authors.initials: L
authors.lastname: Unzueta
authors.affiliation: Biomechanics and Technical Aids Department, National Hospital for Spinal Cord Injury, SESCAM, Finca la Peraleda s/n, 45071 Toledo, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: de Los Reyes-Guzmán
authors.affiliation: Laboratorio de CAD CAM CAE, Universidad EAFIT, Carrera 49 No. 7 Sur-50, 050022 Medellín, Colombia.
authors.forename: Oscar E
authors.initials: OE
authors.lastname: Ruiz
authors.affiliation: eHealth and Biomedical Applications, Vicomtech-IK4, Mikeletegi Pasealekua 57, 20009 San Sebastián, Spain.
authors.forename: Julián
authors.initials: J
authors.lastname: Flórez