Development of a wireless character-Input interface controlled by Laplacian electromyographic activity

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We have developed a wireless character-input interface by combining a compact wireless electrode unit, an electromyogram (EMG)-click converter circuit and character-input software. Experiments for evaluation of the interface showed that characters could be input stably as desired by contraction of (a) the masseter muscle of the cheek, (b) the trapezius muscle of the neck, (c) the anterior tibial muscle of the right crus, or (d) the flexor carpi ulnaris muscle of the right forearm. We also confirmed that the mean integrated EMG signal (IEMG) during the character-input task was significantly decreased in seven of eight subjects when the Laplacian EMG was used as the input signal of the interface, compared with the IEMG obtained when the conventional EMG was used. The developed interface appears applicable to persons with physical disabilities, because it can utilize many sites for the Laplacian EMG measurement, hence reducing the risk of secondary disability of the muscles at these sites.A method has been proposed for sensing the surface electromyogram (sEMG) through thin cloth inserted between the electrodes and the skin of the subject. The method is based on capacitive coupling involving the electrodes, the cloth, and the skin. A pilot device using this method was assembled and evaluated to explore the feasibility of this approach. The experimental results showed that the sEMG obtained in this way was comparable and synchronized with the conventionally obtained sEMG, although its amplitude and S/N were reduced. Since the proposed method eliminates discomfort due to conventional electrode-to-skin coupling, it shows promise for use in human-machine interfaces such as Human Adaptive Mechatronics (HAM).