Development of a myoelectric control system for a knee-mounted biomechanical energy harvester

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Our lab has developed a new wearable technology that unobtrusively generates storable electricity from the natural motion of walking. Currently, the device can extract up to 5W of electricity from each leg - enough to simultaneously power ten mobile phones. The device, which resembles an orthopedic knee brace, harvests energy from the end of a walker's stride, when the muscles are working to slow the movement of the leg. By aiding the body in decelerating the leg, the effort of the user is decreased and storable energy is harvested in much the same way hybrid cars recycle energy from braking. Currently, the device uses knee-angle and speed of movement to determine at what point in the stride to harvest energy. However, we propose to control the device with the muscle activity of the user. Using electrode sensors that indicate when muscles are contracting, we can tap into the user's nervous system and naturally integrate our device and the user. We believe this control system will harvest more energy from the body, be more comfortable for the user, and be more adaptable to changing environments and movements. To develop the control system we must, i) determine the ideal muscles to use for device control, ii) determine the optimal times during a stride to harvest energy and how these times relate to muscle activity, iii) determine how the level of muscle activity should relate to the applied resistance of the device, and finally iv) assess the new muscle activity controlled device in terms of power generation, user acceptability, and adaptability. Our device has the potential to revolutionize the meaning of portable power. The applications for such a device are vast, from powering vital communication equipment for soldiers and rescue workers to powering medical devices such as drug-pumps and prostheses. The restricting weight and limited working time of battery power can be overcome by granting humans the ability to serve as their own renewable power source.