Development of a miniature shear sensing transducer

We have developed a circular (12.7mm in diameter × 3 mm thick) shear force sensing transducer consisting of two circular metal plates and two pin-shaped springs to measure the shear between the plantar surface and insole during ambulation. Shear force causes the top plate to more in the direction of the applied force. This movement forces a wedge to either increase or decrease the amount of light passing from an LED to a photodiode, relative to a change in the applied shear force. The operating range was from 0 to 180 N shear, and could be altered by adjusting the metal spring stiffness and dimensions. The two transducer plates 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.