Wearable robots including exoskeletons, powered prosthetics, and powered orthotics must add energy to the person at an appropriate time to enhance, augment, or supplement human performance. This “energy pumping” at resonance can reduce the metabolic cost of performing cyclic tasks. Many human tasks such as walking, running, and hopping are repeating or cyclic tasks where assistance is needed at a repeating rate at the correct time. By utilizing resonant energy pumping, a tiny amount of energy is added at an appropriate time that results in an amplified response. However, when the system dynamics is varying or uncertain, resonant boundaries are not clearly defined. We have developed a method to add energy at resonance so the system attains the limit cycle based on a phase oscillator. The oscillator is robust to disturbances and initial conditions and allows our robots to enhance running, reduce metabolic cost, and increase hop height. These methods are general and can be used in other areas such as energy harvesting.
In recent years, human motion tracking based on inertial sensors took a huge leap forward as a cost effective enabling technology. It overcomes the limitations of existing tracking systems such as magnetic, mechanical and optical in terms of power, cost and size. It has high impact in the areas of human performance assessment and human-robot interaction as illustrated in gait analysis and assistive devices control. It can be used as a method for alternate gait analysis overcoming the limitations of motion capture systems which are restricted to indoor environment. Also, human motion intention estimation is made possible with the help of these devices and is useful in exoskeleton control. This paper surveys the role of inertial based systems in human gait analysis and lower limb exoskeleton control. In the later part of the paper, state-of-the-art control strategies designed for lower limb exoskeletons are reviewed that show the application of human motion sensing.
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