Closed-loop control of standing neuroprosthesis using PID controller

Functional electrical stimulation (FES), applied to paralyzed or paretic muscles, can facilitate arm-free standing in patients with neurological disorders. At the same time, it has been shown that the able-bodied central nervous system regulates standing balance using a control strategy similar to proportional-integral-derivative (PID) control. The objective of this study was to investigate the capability of a PID controller for regulating an FES system applied to the ankle flexors for maintaining standing balance. We compared the performance of this controller to voluntary balance control of able-bodied individuals with compromised visual, vestibular and proprioceptive senses. According to our experimental results, the proposed PID control strategy outperformed the disrupted voluntary control of the ankle flexors while it did not require larger control efforts, in terms of the ankle torque. Therefore, this control strategy could be considered in for use in neurological patients, including spinal cord injured individuals, after further validations in the future.