Development of a miniature plantar shear force sensing transducer

Abstract

We have developed a circular ( 1 5 m in diameter x 3.8mm thick) shear force sensing transducer consisting of two circular metal discs and two flat springs to measure the shear between the plantar surface and insole during ambulation. Shear force causes the top disc to move in the direction of the applied force. This movement forces a wedge, located on the top disc, to either increase or decrease the amount of light transmitted from an LED to a photodiode, rela&ive to a change in the applied shear force. The operatiug range was from 0 to 22.3N shear, and could be altered by adjusting the metal spring stiffness and dimensions. The two transducer discs were assembled and bonded with silicone adhesive. Placement of the sensor into an insole allowed measurement of shear forces under the human foot during normal gait.