Static tactile sensing for a robotic electronic skin via an electro-mechanical impedance based approach

Tactile sensing is paramount for robots operating in human-centered environments to help in understanding the interaction with objects. To enable robots with the sophisticated tactile sensing capability, researchers have developed different kinds of electronic skins for robotic hands and arms to realize the 'sense of touch'. Recently, Stanford Structures and Composites Laboratory developed a robotic electronic skin which is based on a network of multi-modal micro-sensors. This skin can identify temperature profile and detect arm strikes by embedded sensors. However, one vital aspect of tactile sensing is yet to be investigated: sensing for the static pressure load. Current state-of-the-art tactile sensors mostly are capacitive sensors which can achieve high sensitivity. However, these sensors are liable to damage under high repeating load. In addition, capacitive sensor signals are prone to external noises which will result in complex circuitry for signal conditioning. In this work, an electromechanical-impedance based method is proposed to investigate the response of piezoelectric sensors to the static normal pressure load. The smart skin sample was firstly fabricated by embedding piezoelectric sensor into the soft silicone. Then a series of static pressure tests to the skin were performed. Test results show that this setup can reach a minimal detectable force of 0.5N by using the proposed diagnostic method. Theoretical analysis was then performed to explain the experiment results.