Tactile sensor for measuring hardness and viscosity by using a bimorph piezoelectric array

In this paper, an active tactile sensor system for measurement of Young's modulus and viscosity is developed. For the active sensing, the sensor unit with the 8 bimorph piezoelectric array is bonded to the speaker that is driven by a square wave. The transient response from the sensor signal of each bimorph piezo cell is processed to reduce the noise. From the output, the first peak and the ratio of first peak to time of first peak are extracted as the indexes for the measurement of Young's modulus and viscosity, respectively. It is confirmed that the first peak has a clear correlation with the Young's modulus, and that the ratio of first peak to time of first peak has a definite correlation with the viscosity. Further, the initial contact force affects the sensitivities of Young's modulus and viscosity.