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Knitted RESi: A Highly Flexible, Force-Sensitive Knitted Textile Based on Resistive Yarns

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Abstract

We demonstrate a force sensing knitted textile, based on a piezo-resistive yarn. The resulting elastic, stretchable, and robust textile exhibits sensors based on the widespread Force Sensitive Resistor (FSR) principle. As a proof-of-concept, we implemented a knit consisting of multiple piezo-resistive wales, each intersecting with a single vertical piezo-resistive insert, spawning discrete FSRs at the respective intersection points. While enabling monitoring of external stress, such as pressure, stretch, and deformation, the textile features inherent pleasant haptic qualities.
Knied RESi: A Highly Flexible, Force-Sensitive Knied Textile
Based on Resistive Yarns
Andreas Pointner, Thomas Preindl, Sara Mlakar, Roland Aigner, Michael Haller
mi-lab@fh-hagenberg.at
Media Interaction Lab, University of Applied Sciences Upper Austria
abc
Figure 1: With Knitted RESi, we present a force-sensing exible textile, based on piezo-resistive yarn. The textile enables to
sense applied external stress, such as pressure (a), deformation, (b), and pull (c).
ABSTRACT
We demonstrate a force sensing knitted textile, based on a piezo-
resistive yarn. The resulting elastic, stretchable, and robust textile
exhibits sensors based on the widespread Force Sensitive Resistor
(FSR) principle. As a proof-of-concept, we implemented a knit con-
sisting of multiple piezo-resistive wales, each intersecting with a
single vertical piezo-resistive insert, spawning discrete FSRs at the
respective intersection points. While enabling monitoring of exter-
nal stress, such as pressure, stretch, and deformation, the textile
features inherent pleasant haptic qualities.
CCS CONCEPTS
Human-centered computing Interaction devices
;
Haptic
devices.
KEYWORDS
Interactive Textiles, Textile Sensor, Wearables, Smart Textiles, Con-
ductive Yarn, FSR
ACM Reference Format:
Andreas Pointner, Thomas Preindl, Sara Mlakar, Roland Aigner, Michael
Haller. 2020. Knitted RESi: A Highly Flexible, Force-Sensitive Knitted Tex-
tile Based on Resistive Yarns. In Proceedings of SIGGRAPH ’20: Emerging
Technologies (SIGGRAPH’20). ACM, New York, NY, USA, 2 pages. https:
//doi.org/10.1145/XXXXXXX.XXXXXXX
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SIGGRAPH’20, July 19–23, 2020, Washington, D.C., USA
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ACM ISBN 978-x-xxxx-xxxx-x/YY/MM. . . $15.00
https://doi.org/10.1145/XXXXXXX.XXXXXXX
1 INTRODUCTION
For millennia, textiles make up an essential and indispensable part
of human’s lives. Due to their favourable properties of being light-
weight, highly exible, and comfortable on skin, they are applied
in a wide range of use cases. Nowadays, textiles can be augmented
by electronic components, to gain additional capabilities for input
and output, including sensing, actuation, lighting, etc.
We strongly believe that textiles can be used to fundamentally
transform a range of everyday objects and provide new and exciting
possibilities that are otherwise dicult or impossible to realize. Our
primary goal is to create interactive textiles capable of sensing
both pressure and deformation input in real-time. The technical
foundation of our implementation is the usage of a conductive
yarn with piezoresistive coating [
4
], we term RESi (RESistive textile
Interfaces) yarn.
Our RESi yarn comprises a conductive metal core (copper-silver
alloy with a diameter of 50
µ
m) with a coating (15
µ
m) by an organic
polymer solution, containing conductive carbon-based particles.
Whenever external stress is applied at intersecting yarns, the coat-
ing is compressed, consequently compacting conductive particles
in the coating (cf. Figure 2), which corresponds to a change in
electrical resistance.
2 RELATED WORK
Concepts for pressure sensing in the context of fabric have been
explored and developed for a huge variety of applications. Tactile
pressure sensing on fabric has been achieved through capacitive
[
3
,
6
], resistive [
2
,
5
], and optical [
8
] methods. Resistance-based
force sensors have been in use for over thirty years and can be
easily implemented in textiles by stacking multiple layers. Rofouei
et al. implemented a smart textile composed of an array of pressure
SIGGRAPH’20, July 19–23, 2020, Washington, D.C., USA Pointner, et al.
Figure 2: We use conductive yarn with piezo-resistive coat-
ing (a), which enables sensing of stress wherever traces of
this yarn intersect (b).
sensors, by sandwiching a resistive textile in between of two con-
ductive layers [
7
]. Numerous related projects employ this method,
including SmartMat, eCushion, SimpleSkin, and FlexTiles [5].
3 KNITTED TEXTILE SENSORS
Stretchable woven textiles require elastic yarn (e.g. elastane core
in combination with a twisted non-elastic ber). In contrast, knits
provide excellent elastic and tear-resistant behaviour, even though
the yarn itself is typically non-elastic. Our proof-of-concept im-
plementation, exhibits a fully knitted solution by intersecting two
wales with a single vertical insert, cf. Figure 1. The textile itself was
manufactured with an industrial 5 gauge at-bed knitting machine
(Shima Seiki SWG091N2 5G). As a yarn we used a 12
×
80
µ
m RESi
yarn ply as presented in [
4
]. Figure 3 (a-b) shows the right and
wrong sides of the implemented result. Note that our concept can
be easily extended beyond two discrete pressure points.
Beyond the implementation we showed, our system is capable
of operating an 8
×
8 sensor matrix. A shift register applies voltage
to individual rows, while a multiplexer sequentially connects each
column to an ADC via a voltage divider. We acquire and process the
sensor data at 100 Hz using an ESP32 microcontroller, optionally
forwarding the data wirelessly to a computing device at the edge
for further processing, analysis, and utilization.
4 CONTRIBUTIONS AND LIMITATIONS
A valuable property of a knit is elasticity; consequently, beyond the
implications on durability, stretching is a promising input modal-
ity we will further investigate. In our experiments, we found that
stretch-based input is particularly easy to read, when compared
to pressure, which depends on solid, uniform, and consistent sup-
port. In contrast to coating or polymerization [
1
], we can easily
implement complex custom patterns at loop level and control the
sensors’ performance according to our requirements. Finally, the
design and implementation of our knitted textile supports multi-
ple input modalities, including continuous touch-input as well as
deformation, such as stretch and wrinkle.
At SIGGRAPH 2020 Emerging Technologies exhibition we will
demonstrate our Knitted RESi all-in-one prototype systems with
a b
Figure 3: Right (a) and wrong side (c) of our knit textile sen-
sor prototype. Two intersection points of RESi yarn (black)
are created by two wales and one orthogonal insert, result-
ing in two distinct pressure sensors on the elastic fabric.
incorporated electronics for measurement and display via an em-
bedded 2.2" TFT LCD display. Attendees will be encouraged to
experience them rst hand and get a sense of the notable haptic
quality and durability of our knit sensor. Furthermore, example
applications will be provided (both embedded and on a PC con-
nected via Bluetooth), highlighting and demonstrating valuable
sensor characteristics, such as low activation threshold and high
dynamic range.
ACKNOWLEDGMENTS
This research is part of the COMET project TextileUX (No. 865791,
which is funded within the framework of COMET - Competence
Centers for Excellent Technologies by BMVIT, BMDW, and the
State of Upper Austria. The COMET program is handled by the
FFG.
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... Rather than attaching functional objects to a soft structure, the soft structure itself might become functional. This might be achieved by the use of functional dyes [21], or by weaving or knitting fabric or clothing consisting of multi-material yarns [22,60]. Such multi-material fabrication enables creating devices with integrated sensors [48,52] as well as detailed characterization of interaction between textile design and sensor performance [84,85]. ...
... There is increasing work in combining conductive, non-traditional materials with craft techniques. Conductive materials have been used in crochet [8], knitting [14,29] and weaving [7,11] to create novel sensing capabilities and interactive displays. This work extends to machine and hand-sewing. ...
... Knitting has been uniquely favored not only for shape-changing effects but also for sensing and protection [81] due to its structural conformity. Continuous interlocking loops result in interfaces that have considerable stretch, enhancing knit fabric's ability to serve as input sensors [4,53,63,65,69,92]. For instance, Ou et al. [63] presented a machine-knit resistance-changing elastic stretch sensor. ...
... This sensor is composed of two layers of striped conductive foil with a conductive polymer fiber sheet in between, forming a 80 × 80 electrode grid. Piezoresistive yarn is used in sensors that measure contact as a change in resistance, and has been explored in conjunction with several textile assembly techniques, such as hand sewing, machine sewing, weaving, and knitting [24,26]. Conductive polymerization using piezoresistive materials has been explored to realize interactive e-Textiles [16]. ...
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