Tactile sensors based on soft polymers

Abstract

Piezoresistive carbon black/polydimethysiloxane (CB/PDMS) is a widely used material in the field of artificial skin development because of its high gauge factor to all forms of stress, including tension, compression and shear. While its durability, inexpensive-ness and customizability make CB/PDMS makes it the quintessential active material for pressure-sensing skin, the material itself has not been well-characterized electrically or mechanically. A series of mechanical tests on 0.625" cubes of CB/PDMS revealed that the material's resistance increases monotonically with strain and that CB/PDMS have similar sensitivities to tension and compression across different CB concentrations. Shear sensitivity, however, was relatively poor and inconsistent between samples. To overcome this lack of sensitivity to shear forces, a hair-inspired "pillar" sensor was designed to detect shear forces. The pillar sensor contains two 2 mm x 2 mm x 28 mm CB/PDMS strain gauges embedded in a 3 mm thick PDMS base, and a silicone pillar that has a 5 mm diameter and 6 mm height. Unlike the CB/PDMS cubes, the pillar sensors were very sensitivity to shear forces and presented resistance changes of up to 10% per 0.5 mm until a deflection angle of 20°. These sensors also have the ability to determine the direction of pillar deflection, exhibiting anisotropic behavior when the sensor is structurally constrained.