Design and Characterization of a Multimodal Flexible Electronic Skin with CPLD-Based Data Acquisition for Tactile Intensity and Gesture Recognition

Summary

This protocol describes the fabrication and operation of a flexible, multimodal electronic skin system. It utilizes a CPLD-based backend to achieve synchronized, hybrid-frequency data acquisition from 36 sensor channels, enabling the quantitative analysis of complex tactile gestures for advanced robotic perception and human-robot interaction.

Abstract

This work presents the design and characterization of a flexible multimodal electronic skin (e-skin) platform that supports high-resolution tactile sensing and gesture recognition via a CPLD-based data acquisition system. The system integrates a 36-channel, 14-bit hybrid-frequency sampling architecture (2 kHz, 1 kHz, 100 Hz), with hardware-level support for pressure, acceleration, light, temperature, and environmental signals. A flexible FPC substrate enables conformal integration on curved robotic surfaces while maintaining mechanical stability. To demonstrate tactile perception capability, this study focuses on the pressure sensing channel, which serves as the primary modality for contact force estimation and gesture dynamics. Four representative human interactions, gentle touch, tap, light pinch, and strong pinch, were analyzed. Two dimensionless metrics, equivalent waveform skewness and equivalent load, were introduced to distinguish force intensity and gesture categories. Experimental results show that the system achieves clear gesture separation and skin-like viscoelastic response, with an average unloading time of 0.4 s ± 0.2 s. Real-time wireless data transmission at 1.5 Mbps is supported, and the modular design provides a scalable foundation for future integration of additional modalities. This work establishes a hardware framework for force- and gesture-based human-robot tactile interaction, with extendable capacity for multimodal perceptual systems.

Introduction

Tactile sensing has been extensively investigated for robotic perception^1,2, however, most electronic skin (e-skin) systems still rely on single-modality, low-density configurations that can limit the interpretation of complex human touch. Despite significant advances in flexible tactile materials and device architectures³, system-level integration of multimodal and multichannel tactile sensing with high-precision, real-time acquisition presents ongoing technical challenges⁴. Consequently, key issues such as signal synchronization, timing coordination, and data t....

Protocol

All experimental procedures described herein were non-invasive and did not involve animal or human clinical subjects; therefore, no ethical approval was required for this study. The reagents and the equipment used are listed in the Table of Materials.

1. Fabrication of sensors

1. Preparation and integration of the viscoelastic sensor
   1. Mark the target dimensions [e.g., 5 mm x 5 mm] on the viscoelastic sensing material using a precision ruler and a fine-tip permanent marker to ensure dimensional accuracy. Cut the material along the marked lines using sharp, fine-tip scissors. Perform the c....

Results

This protocol enables the quantitative characterization and differentiation of distinct tactile gestures applied to the electronic skin (e-skin). Fix the e-skin sample on the test platform. A single operator then performs four defined tactile actions, gentle touch, tapping, light pinch, and strong pinch, according to the parameters listed in Table 1. The "gentle touch" gesture involved repeatedly placing a finger lightly on a single e-skin unit for about 1 min to ensure stable and consistent repe.......

Discussion

The sensing mechanism of the e-skin is fundamentally rooted in the viscoelastic properties of its constituent polymer^6,15. This material exhibits both elastic deformation and viscous flow when subjected to an external force. The viscous component introduces a characteristic latency in the material's recovery; that is, it does not instantaneously return to its original state upon the removal of the force but instead requires a finite period to recover. These v.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Flexible Printed Circuit Board	JLCPCB	any one	Used to obtain pressure data
Analog switches	TI	TMUX1108PWR	Used for selecting different channels
Analog to Digital Converter	Analog Devices	AD7940BRMZ-REEL7	Convert analog signals to digital signals
CPLD	Intel	MAX 10M02	Data processing unit
Oscilloscope	Tektronix	TBS2000	This oscilloscope is used to measure signal waveforms.
quartus ii	Intel	any one	Programming IDE for CPLD
viscoelastic sensing material	any one	any one	This material is used to generate pressure signals.
Wi-Fi 6 module	AI-THINKER	ad-m62-cbs	Data transmission module