An EMG-Controlled SMA Device for the Rehabilitation of the Ankle Joint in Post-Acute Stroke

Abstract

The capacity of flexing oneÕs ankle is an indispensible segment of gait re-learning, as imbalance, wrong compensatory use of other joints and risk of falling may depend on the so-called drop-foot. The rehabilitation of ankle dorsiflexion may be achieved through active exercising of the relevant musculature (especially tibialis anterior, TA). This can be troublesome for patients affected by weakness and flaccid paresis. Thus, as needs evolve during patientÕs improvements, a therapeutic device should be able to guide and sustain gradual recovery by providing commensurate aid. This includes exploiting even initial attempts at voluntary motion and turns those into effective workout. An active orthosis powered by two rotary actuators containing NiTi wire was designed to obtain ankle dorsiflexion. A computer routine that analyzes the electromyographic (sEMG) signal from TA muscle is used to control the orthosis and trigger its activation. The software also provides instructions and feed-back for the patient. Tests on the orthosis proved that it can produce strokes up to 36°against resisting torques exceeding 180 Ncm. Three healthy subjects were able to control the orthosis by modulating their TA sEMG activity. The movement produced in the preliminary tests is interesting for lower limb rehabilitation, and will be further improved by optimizing bodyorthosis interface. It is hoped that this device will enhance early rehabilitation and recovery of ankle mobility in stroke patients.

Shape Memory Actuators for Medical Rehabilitation and Neuroscience

“…Some authors [31][32][33][34][35][36][37][38][39][40][41] investigated the possibility of employing SMA to make portable or wearable devices to act as functional exercising robots.…”

“…Other papers [35][36][37][38][39][40][41] concentrated on the lower limb. In [35], a concept for a paediatric boot is described.…”

“…In the intention of the authors, a control system would activate two NiTi wires producing slow movement of the ankle and provide the possibility for home passive mobilisation. Two different implementations of a wearable ankle mobiliser were published by another group [36][37][38][39][40][41]. In the first paper [36] a description of the design procedure is presented, including mechanical and power dimensioning of SMA linear actuators based upon biomechanical considerations.…”

“…Pre-clinical trials are also reported in the text. The following publications [40][41] dealt with an amagnetic rotary actuator and its use for the construction of a biosignal-controlled ankle exerciser that could be used in two different modes: fully passive and haptic-assistive, according to the evolving state of the patient during recovery. Trials on healthy subjects are described in [41].…”

Design and Control of an EMG Driven IPMC Based Artificial Muscle Finger

“…Firstly, its hybrid actuation mechanism has the advantage of increasing the active degrees of freedom and secondly, using only two myoelectric sensors, has the potential for controlling more than three patterns of fingers movements. Pittaccio & Viscuso (2011) have developed a SMA wire device for the rehabilitation of the ankle joint where active orthosis powered by two rotary actuators like, NiTi wire are used to obtain ankle dorsiflexion and EMG signal is used to control the orthosis and trigger activation from muscle. Stirling et al (2011) have shown the potential of SMA wire for an active, soft orthotic in the knee where NiTi based SMA wires is also used.…”