A Trajectory-Adaptive Walking Assistance Strategy Based on Functional Electrical Stimulation for Exoskeleton to Help Stroke Patients Restore Natural Gait

The functional electrical stimulation hybrid rehabilitation robotic system has been proved to have a positive effect on the gait rehabilitation of stroke patients in recent years, but the functional electrical stimulation walking assistance strategy combined with the exoskeleton robot is still one of the current research focuses. In this paper, a trajectory-adaptive walking assistance strategy based on functional electrical stimulation for exoskeleton is proposed, which can automatically adjust the electrical stimulation output current intensity according to the joint angle trajectory error during walking. Moreover, a small-sized four-channel functional electrical stimulation device was developed, which could be integrated inside the exoskeleton, providing a hardware platform to verify the feasibility of this walking assistance strategy. The gait data of ten healthy subjects were measured, and their joint angles during walking were used as a reference for natural gait. And another six healthy subjects were recruited to participate in the experiment. The correlation coefficient of knee joint angle between walking with exoskeleton and natural gait was used to evaluate the effectiveness of the walking assistance strategy. The mean correlation coefficient of all subjects during walking with electrical stimulation was 0.78 ± 0.1164, which increased by 0.13 compared with the condition without electrical stimulation. With the assistance of functional electrical stimulation, the mean value of range of movement of knee joint increased by 9.18 °, the mean value of the maximum knee joint angle increased by 4.69 °, and the mean value of the minimum knee joint angle decreased by 2.80 ° compared with no electrical stimulation. These results demonstrate that the walking assistance strategy can adapt to different users and have the effect of gait correction, making the user's gait more similar to the natural gait when walking with the exoskeleton.