Abstract
We present a novel assistive control strategy for a robotic hip exoskeleton for assisting hip flexion/extension, based on a proportional Electromyography (EMG) strategy. The novelty of the proposed controller relies on the use of the Gastrocnemius Medialis (GM) EMG signal instead of a hip flexor muscle, to control the hip flexion torque. This strategy has two main advantages: first, avoiding the placement of the EMG electrodes at the human–robot interface can reduce discomfort issues for the user and motion artifacts of the recorded signals; second, using a powerful signal for control, such as the GM, could improve the reliability of the control system. The control strategy has been tested on eight healthy subjects, walking with the robotic hip exoskeleton on the treadmill. We evaluated the controller performance and the effect of the assistance on muscle activities. The tuning of the assistance timing in the controller was subject dependent and varied across subjects. Two muscles could benefit more from the assistive strategy, namely the Rectus Femoris (directly assisted) and the Tibialis Anterior (indirectly assisted). A significant correlation was found between the timing of the delivered assistance (i.e., synchronism with the biological hip torque), and reduction of the hip flexors muscular activity during walking; instead, no significant correlations were found for peak torque and peak power. Results suggest that the timing of the assistance is the most significant parameter influencing the effectiveness of the control strategy. The findings of this work could be important for future studies aimed at developing assistive strategies for walking assistance exoskeletons.
Highlights
Over the last decades, several lower-limb exoskeletons have been developed for gait assistance of people with pathological gait patterns or for augmenting human performance of healthy individuals (Pons et al, 2008)
In this study we propose and validate a new myoelectric control strategy based on an ankle plantar-flexor muscle signal, i.e., the Gastrocnemius Medialis (GM) to control the flexion torque of an active pelvis orthosis
Along with the description of the control strategy, we present the results of preliminary tests with eight healthy subjects, walking on the treadmill with the Active Pelvis Orthosis (APO) providing three levels of assistance, i.e., optimal, low, and high, customized on each subject
Summary
Several lower-limb exoskeletons have been developed for gait assistance of people with pathological gait patterns or for augmenting human performance of healthy individuals (Pons et al, 2008). When people have residual lower-limb movement capabilities, the exoskeleton controller should be able to understand the user’s intended movement, synchronize with the periodicity of the gait pattern and provide additional assistance in specific phases of the gait cycle. In this case, developing a control strategy that effectively interprets the information gathered from the sensors and delivers the necessary mechanical power to the user at the right time turns out fundamental for the exoskeleton to supply effective and natural assistance (Yan et al, 2015). The control strategy of a gait assistive device should be intuitive, in order to avoid burdening the user with an additional cognitive effort (Tucker et al, 2015)
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