Conventional neurorehabilitation appears to have litt-le impact on impairment over and above that of spontaneous biological recovery. Robotic neurorehabilita-tion has the potential for a greater impact on impairment due to easy deployment, its applicability across of a wide range of motor impairment, its high measurement reliability, and the capacity to deliver high dosage and high intensity training protocols. We first describe current knowledge of the natural history of arm recovery after stroke and of outcome prediction in individual patients. Rehabilitation strategies and outcome measures for impairment versus function are compared. The topics of dosage, intensity, and ti-me of rehabilitation are then discussed. Robots are particularly suitable for both rigorous testing and ap-plication of motor learning principles to neurorehabilitation. Computational motor control and learning principles derived from studies in healthy subjects are introduced in the context of robotic neurorehabili-tation. Particular attention is paid to the idea of context, task generalization and training schedule. The assumptions that underlie the choice of both movement trajectory programmed into the robot and the de-gree of active participation required by subjects are examined. We consider rehabilitation as a general learning problem, and examine it from the perspective of theoretical learning frameworks such as super-vised and unsupervised learning. We discuss the limitations of current robotic neurorehabilitation para-digms and suggest new research directions from the perspective of computational motor learning.

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A previous study from our laboratory showed that when soleus electromyography was used to control the amount of plantar flexion assistance from a robotic ankle exoskeleton, subjects significantly reduced their soleus activity to quickly return to normal gait kinematics. We speculated that subjects were primarily responding to the local mechanical assistance of the exoskeleton rather than directly attempting to reduce exoskeleton mechanical power via decreases in soleus activity. To test this observation we studied ten healthy subjects walking on a treadmill at 1.25 m/s while wearing a robotic exoskeleton proportionally controlled by medial gastrocnemius activation. We hypothesized that subjects would primarily decrease soleus activity due to its synergistic mechanics with the exoskeleton. Subjects decreased medial gastrocnemius recruitment by 12% (p < 0.05) but decreased soleus recruitment by 27% (p < 0.05). In agreement with our hypothesis, the primary reduction in muscle activity was not for the control muscle (medial gastrocnemius) but for the anatomical synergist to the exoskeleton (soleus). These findings indicate that anatomical morphology needs to be considered carefully when designing software and hardware for robotic exoskeletons.

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A walking assistance device (1) has a body-mounted assembly (2) installed on the waist of a user (A), foot-mounted assemblies (3L, 3R) installed on feet, and leg links (4L, 4R) which connect the foot-mounted assemblies (3L, 3R) to the body-mounted assembly (2). The foot-mounted assemblies (3L, 3R) are provided with floor reaction force sensors (13L, 13R). Results obtained by multiplying the absolute values of floor reaction force vectors (three-dimensional vectors) detected by the floor reaction force sensors (13L, 13R) by a predetermined ratio are defined as target values of the magnitudes of the supporting forces transmitted to the leg links (4L, 4R) from the foot-mounted assemblies (3L, 3R). Actuators (20L, 20R) of the leg links (4L, 4R) are controlled such that the supporting forces having the magnitudes of the target values act on the leg links (4L, 4R) from the foot-mounted assemblies (3L, 3R) through the intermediary of joints (19L, 19R).

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Robotic gait rehabilitation faces many challenges regarding ankle assistance, body weight support and physical human-robot interaction. This paper reports on the development of a gait rehabilitation exoskeleton prototype intended as a platform for the evaluation of design and control concepts in view of improved physical human-robot interaction. The performance of proxy-based sliding mode control as a “robot-in-charge” control strategy is evaluat both in simulation and in experiments on a test setup. Compared to PID control, test results indicate good tracking performance and in particular safe system behavior.

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A previous study from our laboratory showed that when soleus electro-myography was used to control the amount of plantar flexion assistance from a robotic ankle exoskeleton, subjects significantly reduced their soleus activity to quickly return to normal gait kinematics. We speculated that subjects were primarily responding to the local mechanical assistance of the exoskeleton rather than directly attempting to reduce exoskeleton mechanical power via decreases in soleus activity. To test this observation we studied ten healthy subjects walking on a treadmill at 1.25 m/s while wearing a robotic exoskeleton proportionally controlled by medial gastrocnemius activation. We hypothesized that subjects would primarily decrease soleus activity due to its synergistic mechanics with the exoskeleton. Subjects decreased medial gastrocnemius recruitment by 12% but decreased soleus recruitment by 27%. In agreement with our hypothesis, the primary reduction in muscle activity was not for the control muscle (medial gastrocnemius) but for the anatomical synergist to the exoskeleton (soleus). These findings indicate that anatomical morphology needs to be considered carefully when designing software and hardware for robotic exoskeletons.

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