Measurement of Mechanical Characteristics of a Fingerpad Surface in the Design of a Tactile Display

Abstract

To design a piezoelectric vibrator for a tactile aid, we examined the mechanical characteristics of an index fingerpad surface. First, the mechanical impedance of the fingerpad surface was measured. Specifically, a vibrating pin with a diameter of 0.6 mm was attached to the fingerpad surface to investigate how the impedance of the skin's surface changes depending on physical parameters, such as vibrating amplitude, static force, and stimulation points. From the results, we ascertained the following: the mechanical impedance increased in direct proportion to the static force, the impedance at the fingertip was larger than at other points of measurement (including the finger pulp and the area around the DIP joint), and the impedance decreased as the vibratory amplitude increased. These results also indicated that the mechanical characteristics of the fingerpad could be modeled after a spring-damper system. Secondly, the relation between vibratory frequencies and vibratory displacements was determined by using an equivalent circuit of a piezoelectric bimorph actuator.