Hybrid Inertial-Robotic Motion Tracking for Posture Biofeedback in Upper Limb Rehabilitation

Rehabilitation robotics and neuromuscular stimulation have become widespread technologies for rehabilitation training of stroke and spinal cord injured patients. In this context, real-time tracking of the performed motion facilitates real-time control of the motion support and biofeedback about undesired compensatory motions. We consider a cable-driven robotic system for upper limb rehabilitation and extend it by two wearable inertial sensors. By sensor fusion of the robotic and inertial measurements, we obtain accurate estimates of the forearm and upper arm orientation and position, which cannot be obtained by either of both measurement systems alone. A real-time biofeedback is introduced to prevent undesired compensatory motions of the trunk and shoulder. The proposed methods are evaluated with respect to an optical reference system in a series of experimental trials with and without compensatory motions. Using only the robotic sensors yields average measurement errors of up to 24 cm for the shoulder position and 19° for the elbow angle. In contrast, the proposed hybrid sensor fusion achieves accuracies better than 6 cm and 4°, respectively.