Slip Perception via Soft Robotic Skin Made of Electroconductive Yarn

Abstract

We have developed a fabric sensor knitted of tension-sensitive electroconductive yarns. This sensor differs from other fabric-based sensors, in that the sensor itself is a piece of cloth with high density of knitted yarns. Each yarn has an elastic core, around which is wound two other separate, tensionsensitive electro-conductive threads, making this sensor inherently flexible and stretchable and allowing it to conform to any complicated surface on a robot, acting as a robotic skin. The pile-shaped surface of the sensor enhances its ability to detect tangential traction, while also enabling it to sense a normal load. Our aim is to utilize this sensor in applications involving relative sliding between its surface and a touched object, such as contact recognition, slip detection, and surface identification through a sliding motion. We carefully analyzed the static and dynamic characteristics of this sensor while varying the load and stretching force, to fully understand its response and determine its degree of flexibility and stretchability. We found that a Discrete Wavelet Transformation (DWT) may be used to indicate stick/slip states while the sensor is sliding over surfaces. This method was then utilized to detect slippage events acting on the sensor’s surface, and to decode textures in a classification test using an Artificial Neural Network (ANN). Due to its flexibility and sensitivity, this sensor can be used widely as a robotic skin in humanoid robots.