A Variable Sensing Range Electrical Impedance Tomography Sensor for Robot Electric Skins

While stretchable and compressible sensors are commonly used to enhance the proprioception and exteroception of soft robots, their sensitivity and sensing range are constrained by their design and stiffness, often limiting their measurement capabilities. To overcome this limitation, this paper presents a novel approach that integrates stiffness modulation with piezoresistive sensing, specifically Electrical Impedance Tomography (EIT). This approach results in a new type of artificial skin, termed Variable Sensing Range Electrical Impedance Tomography Skin (VEITS), which features an adjustable sensing range. The VEITS comprises two layers: a top layer with variable stiffness achieved through granular jamming and a bottom EIT sensing layer. By applying a vacuum to the granular layer, the sensor stiffness can be increased, enabling it to measure higher contact forces. Specifically, applying a vacuum pressure of −80 kPa extends the contact force range by 37<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\%$</tex-math></inline-formula> compared to the unpressurized state. While increased stiffness temporarily reduce sensitivity to small loads, it does not affect the EIT localization accuracy. The VEITS simple structure makes it suitable for large surface sensing on robots, and effectively expanding the sensing range. Though demonstrated with EIT and granular-jamming stiffness modulation, this novel principle is applicable to other strain-based sensors and stiffness modulation techniques.