Development and evaluation of hand pointing system for functional electrical stimulation

Paralyzed limbs of central-nervous-system impairment patients can be restored by electrically stimulated muscle contraction. This principle is called a functional electrical stimulation (FES). In their daily lives, the function of reaching to an object is one of the essential functions as shown in eating motion. We developed a system that enables a hand to move to desired positions by FES applied to the muscles of the arm. A subject puts on a cap, which mounted a red pointing light, and a position sensor on the wrist. The forearm is laid on an orthosis that can move only in horizontal plane. The pointing light gives the red beam whose diameter is approximately 15 cm when it was illuminated from the height of 30 cm on a plane. The subject projects the light beam from his head to a position sensor on his wrist. It detects the center of the illuminated area with differentially arranged phototransistors. A computer calculates stimulation patterns from the position data in order to guide the hand to the position, and a stimulator provides current pulses to the muscles of the upper limbs. The above procedure is repeated until the hand reaches to the target. While the light is not directed on the sensor, the position of hand is maintained at the current position. Experiments with a 22-year-old normal male subject were carried out to test the system. The light pointed to any targets from 30 cm high, and his hand moved to the target position from the border of illuminated area. This system has the following advantages. 1) The hand can be moved from any initial position to any target position in horizontal plane. 2) The pointing light does not prevent subject's motion, and is easy to use.