چكيده به لاتين
Functional electrical stimulation (FES) with a history of more than 50 years, is one of the most commonly used techniques for therapy, function restoration and maintenance of vital functions in persons with upper motor neuron diseases. FES uses low-level electrical pulses to generate contractions in paralyzed muscles and achieve functional outcome in related joints. FES-cycling has demonstrated many physiological and psychological benefits for SCI patients. Improvements were reported in cardiovascular and pulmonary functions, peripheral circulation, muscle bulk, strength and reduced atrophy of skeletal muscles.
The main novelty of this study is to propose a new Jacobian-based stimulation pattern named free pattern which is exclusive for each patient and its determination is thoroughly automatic. In this method, each muscle is stimulated related to crank angle so fatigue effect is minimized and cycling process would be more effective than previous approaches proposed in literature. In this study, adaptive gain super twisting algorithm (ASTW) which is simultaneously robust and adaptive against disturbances and physiological system conditions is used for the first time to control the generated torque of muscles. A dc motor which is connected to ergometer shaft is responsible to control the cycling cadence.
At first, fixed and free stimulation patterns of muscle groups and control strategies (PID, STW and ASTW) were evaluated on virtual patient under three conditions of operation such as normal, fatigue effect and external disturbance. The simulation results demonstrate the privilege of free stimulation pattern and ASTW algorithm. Experimental results on three paraplegic subjects consisted of two separated protocols: passive cycling cadence control and simultaneous control of cycling cadence and torque using functional electrical stimulation (FES). Cadence tracking error using ASTW in first protocol was 4.17±0.03% and torque tracking error using free stimulation pattern and ASTW in second protocol was 5.04±0.6% which indicate the advantage of proposed method over other approaches.
Keywords: Functional electrical stimulation (FES), cycling, adaptive gain super twisting controller, free pattern stimulation, paraplegics