Adaptive Control System for Functional Electrical Stimulation [Research Paper]

Adaptive Closed-Loop Control System for Functional Electrical Stimulation (FES)

An Approach for Improving Mobility and Control in Neuromotor Prosthesis

David Ojika

Department of Electrical Engineering

California State University Los Angles

Email: dojika@calstatela.edu

 

 

Abstract

One of the major difficulties faced by those who are fitted with prosthetic devices is the enormous mental effort needed during the first stages of training which becomes even more dramatic with myographic prosthesis were muscle fatigue causes an additional burden to the user. A lot of the approaches to FES design have considered only a smaller part of the entire neuromuscular functioning of the body and tried replicate that function in isolation with the rest of the system. The general outcome of the approach is a system that does not fully satisfy the desire of the end-user. To correct this problem, and to efficiently replicate the function of a desired part of the body via electrical stimulation, a more pervasive approach away from the linear and traditional command and control signaling is proposed. This paper focuses on possible design improvements on existing FES systems by first breaking out its major components and then proposing entirely new solutions, or combining some already existing approaches to form what may be considered as an optimal hybrid solution. The areas of focus are pattern recognition for signal processing, sensing and feedback control, the main control unit and a supervisory unit.

 

Introduction

Functional Electrical Stimulation is a technique that uses low levels of electrical current to stimulate nerves innervating extremities which have been impaired as a result of a head injury, spinal cord injury, stoke or other neurological disorders. FES is not a cure but can be used to restore function in people with disability. When used in muscular activities like walking or even in the cardiovascular aspect of breathing, it can be referred to as Neuromuscular Electrical Stimulation (NMES).

 

FES devices have been used commercially in the past to treat foot-drop problems in some patients with multiple sclerosis by stimulating the peroneal nerve during gait cycles.  Foot-drop is a condition caused by weakness or paralysis of the muscles involved in lifting part of the foot while walking. As a result of that, walking becomes a challenge and causes a person to either drag their foot or engage in irregular stepping pattern called gait cycle.

 

Generally, FES devices that are used to aid walking in disable persons are small, self-contained electronic devices which are attached to the leg just below the knee. They enable foot-lifting as a person walks, by electrically stimulating the nerve around the muscle associated with the stepping gait. During the swing phase, the device electronically stimulates the peroneal nerves, thereby activating the muscles that cause ankle dorsiflexion which may thus improve the person’s ability to walk.

 

Several of the approaches to FES design proposed by many authors in the past few years sought to address various challenges in the efficient use of FES devices especially in neuromuscular activities. Many FES devices, nonetheless, continue to exist as invasive or non-invasive, or as open-loop control systems, while newly proposed alternative designs still await long, exhaustive approval process from the FDA. A lot of the new design approaches considered a given and smaller part of the entire neuromuscular functioning of the body, and tried replicate that function in isolation with the rest of the system. The work in [1] demonstrated separately, the extraction of  Electromygraphic (EMG), Electronystagmogramic (ENG) and Electroencephalographic  (EEG) biopotentials  from the body for command and feedback purposes without a connection as to how these biopotentials relate to each other. Even though this technique might seem to be easier to design and implement, the general outcome is a system that does not fully satisfy the desire of the end-user.

 

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