Surface Texture Detection With a New Sub-mm Resolution Flexible Tactile Capacitive Sensor Array for Multimodal Artificial Finger

Edoardo Sotgiu,Rosana Dias,Jose Fernandes,Jose Rodrigues,Joao Gaspar,Bernardo Pires,Eurico Esteves Moreira,Diogo E Aguiam,Filipe Alves,Sofia Martins,Helder Fonseca,Carlos Calaza

doi:10.1109/jmems.2020.3004584

Abstract

This work presents a flexible polyimide-based capacitive tactile sensing array with sub-millimeter spatial resolution. The sensor is conceived to be embedded in a multimodal artificial finger to detect and classify the texture morphology of an object’s surface. The proposed tactile sensor comprises a $16\times 16$ array of capacitive sensing units. Each unit is composed of a parallel square electrode pairs ( $340~ {\mu }\text{m}\,\,\times 340~ {\mu }\text{m}$ ) separated by a compressible air cavity and embedded into a flexible polyimide substrate. Standard MEMS microfabrication techniques were used to develop the sensor. The polyimide device was covered with a thin compressible PDMS layer to tune the normal pressure sensitivity and dynamic range (225–430 ${\mu }\text{m}$ thin PDMS layer resulting in 0.23–0.14 fF/kPa). The detection of the surface morphologies of a regular grating stamp for different orientation and a small metallic nut placed on the sensor is demonstrated, showing a 420 ${\mu }\text{m}$ spatial resolution. The proposed sensor represents a novel capacitive tactile sensing device with a sub-mm resolution of human fingertip sensitivity.

Highlights

T HE pleasant sensation transmitted by tactile perception influences how a user perceives the aesthetics and ergonomics and a product’s quality [1]
Despite providing tactile sensitive matrices capable of acquiring force distribution, none of the previous works have reached a spatial resolution of 0.5 mm, which is required for emulating the typical human tactile sensing
This paper presents a novel flexible tactile sensor device conceived to extract surface morphology with a spatial resolution of 420 μm

Summary

INTRODUCTION

T HE pleasant sensation transmitted by tactile perception influences how a user perceives the aesthetics and ergonomics and a product’s quality [1]. Fine textures are detected by the fast adapting receptors which are sensitive to the vibration generated by the relative motion between the skin and the object when sliding the finger over its surface On that premise, both fine and coarse texture sensing mechanisms are important to fully emulate the human touch perception on artificial sensor fingers. Tactile sensors mimicking human touch sensitivity for texture discrimination must detect normal and tangential force distribution in the 0.01-10 N range with spatial resolutions below 1 mm [6]–[8]. Despite providing tactile sensitive matrices capable of acquiring force distribution, none of the previous works have reached a spatial resolution of 0.5 mm, which is required for emulating the typical human tactile sensing. A thin compressible polydimethylsiloxane (PDMS) cover was used to tune the pressure sensitivity and the dynamic range

SENSING MODELING AND STRUCTURE DESIGN

RESULTS & DISCUSSIONS

CONCLUSION