An ultrasonic time-of-flight system for hand movement measurement

We have designed and built an ultrasonic time-of-flight system to measure the three-dimensional coordinates of up to three moving emitters. These emitters are fixed on the hand and arm of a human subject or on a hand-held stylus, to provide information concerning motor control. Three stationary receivers are suspended above the experimental space and provide three diagonal distances which are converted to x, y and z coordinates. The sampling rate for one emitter is 200-400 Hz, depending on the nature of the experiment. Multiple emitters are time-multiplexed. The piezoelectric resonator emitter is pulsed with 200 V for 12 microseconds of each cycle and rings at 40 kHz with a Q factor of four. The piezoelectric resonator receiver drives circuitry with a gain of 500 and a bandwidth of 60 kHz. The system provided highly linear results with a repeatability of +/- 1.64 mm and a resolution of 0.7 mm.