A miniature electrooptical force transducer

A 5 mm*6 mm*3 mm electrooptical force-sensing transducer has been developed from a metal U-shaped spring. Force compresses the open end of the spring so that it decreases light passing from a light-emitting diode to a light-sensing photodiode. The operating range is from 0 to 50 N, but can be changed by changing the spring metal and dimensions. Nonlinearity is less than +or-7%. Hysteresis is less than 3%. Random error is about 6% peak-to-peak. Temperature-related zero drift is less than 1%/ degrees C uncompensated and much lower compensated. When embedded in a rubber insole, this thin transducer has measured force on the sole of the foot during normal human gait.