In this internship report the development of an impedance control method for an anthropomorphic lower extremity exoskeleton is described. This exoskeleton can be used to restore the gait of paralyzed people. Webots simulations are used to test the control method. Therefore a realis-tic model of both the human as the exoskeleton has to be made. The lower extremities of the human model have 6 DOF all in the sagital plane. The human model has only passive elements simulating that the human is fully paralyzed. The actuation is done by the exoskeleton. The human model is compared to a Matlab model of the TU Delft. The joint angle trajectories of both models are approximately the same. The exoske-leton model is anthropomorphic and is assumed to be rigidly at-tached to the user. The actuation is done directly at the joints, so that all sup-plied power is converted into joint rotation. The parameters of the impedance control, stiness, damping and reference trajectory, are phase dependent. They are determined using particle swarm optimization. The optimizations are able to find a gait pattern of the human model wearing the exoskeleton. This gait pattern is compared to the gait of a healthy subject, tracked by the University of Twente. The joint angles of the simulated gait have large similarities with the tracked angles. The developed model can be used to develop and test more complex control methods. By using a monotone fitness function and an adjusted fitness function the result can further improve.

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Previous studies have demonstrated that humans are sometimes capable of initiating arm movements towards visual stimuli at extremely short latencies, implying the presence of a short-latency neural pathway linking visual input to limb motor output. However, little is known about the neural mechanisms that underlie such hastened arm responses. One clue may come from recent demonstrations that the appearance of a visual target can elicit a rapid response in neck muscles that is time-locked to target appearance and functionally relevant for orienting gaze (head and eye) towards the target. Because oculomotor structures thought to contribute to ‘visual responses’ on neck muscles also target some arm muscles via a tecto-reticulo-spinal pathway, we hypothesized that a similar visual response would be present in arm muscles. Our results were consistent with this hypothesis as we observed the presence of rapid arm muscle activity (< 100 ms latency) that was time-locked to target appearance and not movement onset. We further found that the visual response in arm muscles: was present only when an immediate reach towards the target was required; had a magnitude that was predictive of reaction time; was tuned to target location in a manner appropriate for moving the arm towards the target; and was more prevalent in shoulder muscles than elbow muscles. These results provide evidence for a rapid neural pathway linking visual input to arm motor output and suggest the presence of a common neural mechanism for hastening eye, head and arm movements. (далее…)

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