In-Skin Pressure and Curvature Sensors for Soft Robots

Abstract

The emerging field of soft robotics has attracted much attention due to its low cost, ease of use, and the potential in handling delicate objects compared with traditional rigid robots. However, the intrinsically compliant bodies of these robots make sensing, control, and evaluation of their motion complex. Current research on soft sensors has focused on quantifying the strain or pressure applied to the surface of a soft robot, but few, if any, have attempted to differentiate between external (environmental) pressure and the robot’s own internal pressure, induced by the displacement of air within the robot’s body. In this work, we present an in-skin soft capacitive sensor to determine the curvature and body deformation under force applications. The fabrication process is rapid, simple, and uses the same soft materials as the robot itself, thereby making it easy to integrate into the skin of a soft robot. We verify the performance of the sensors using a two-button testbed while applying pressures up to 60 kPa and illustrate their capacity to sense the curvature and differentiate between internal and external pressures throughout this range. Specifically, the sensitivity of the devices were shown to be 0.0042 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for external pressures and 0.0013 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> for internal pressures above 40 kPa. Finally, we demonstrate the sensor’s ability to identify curvature and estimate the applied pressure in a case study used to prove the feasibility of this in-skin capacitive sensing.