Session: Poster, Demo, & Video Presentations
UbiComp’13, September 8–12, 2013, Zurich, Switzerland
E-Textile Pressure Sensor Based on
Conductive Fiber and Its Structure
Yu Enokibori
Yuuki Shimakami
Abstract
Nagoya University
Aichi Center for Industry and Sci-
Furo-cho, Chikusa-ku, Nagoya,
ence Technology
Aichi, 464-8603, Japan
35 Aza-Miyaura, Mabiki, Yamato-
This paper proposes a novel e-textile-based pressure
sensor. Textile is a common material in our life, used in
such items as sheets, seats, and clothing. If these
items are equipped with sensor functions, they can invisibly assist humans without significant lifestyle
changes. Our sensor is suitable for mass production
and durable in daily hard use cases. The sensor is woven with common weaving machines with a special
manner and its material is a common low-cost conductive fiber that does not use special and costly materials,
such as optical fiber. The sensor mechanism is supported by the textile structure; thus our sensor has durability for frictional force and scratch occurring sometime in
daily context. In this paper, we also introduce two example usages of our textile sensor: a bed-size body
pressure sensor for anti-pressure-ulcer treatment and a
wearable foot-pressure sensor for walk and skill analyses.
[email protected]
cho, Ichinomiya, Aichi, 491-0931,
u.ac.jp
Japan
[email protected]
Akihisa Suzuki
Tsuchiya Co., Ltd.
Kenji Mase
22-4, Higashi-Namiki-Kita, Chiryu, Nagoya University
Furo-cho, Chikusa-ku, Nagoya,
Aichi, 472-0006, Japan
AkihisaSuzuki@tsuchiya-
Aichi, 464-8603, Japan
group.co.jp
[email protected]
Hirotaka Mizuno
Tsuchiya Co., Ltd.
22-4, Higashi-Namiki-Kita, Chiryu,
Aichi, 472-0006, Japan
[email protected]
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Copyright is held by the author/owner(s).
UbiComp’13 Adjunct, September 8–12, 2013, Zurich, Switzerland.
ACM 978-1-4503-2215-7/13/09.
Author Keywords
E-textile; Pressure Sensor; Foot pressure; Bedsore;
Wearable
ACM Classification Keywords
H5.2. Information interfaces and presentation (e.g.,
HCI): User Interfaces.
http://dx.doi.org/10.1145/2494091.2494158
207
Session: Poster, Demo, & Video Presentations
UbiComp’13, September 8–12, 2013, Zurich, Switzerland
Introduction
This paper proposes a novel e-textile-based pressure
sensor. E-textile-based pressure sensors are eagerly
anticipated because they can provide invisible support
for humans in healthcare and training. Textiles are
common materials in our life, used for such items as
sheets, seats, clothing, and more. If such items are
equipped with sensor functions, they can invisibly assist
humans without major lifestyle changes. For example,
if sheets and seats can sense pressure, they can alert
patients and their care-givers to the increasing risk of
pressure ulcers. If socks can sense pressure, they can
alert users to the increasing risk of falls with pattern
recognition of gait instability.
Conductive Fiber
Sensing point
Textile Sensor
Figure 1. E-textile Pressure Sensor
(left: top view, right: side view)
We introduce our e-textile-based pressure sensor in the
next section and then introduce two usage examples: a
bed-size body pressure sensor for anti-pressure-ulcer
treatment and a wearable foot pressure sensor for walk
and skill analyses.
Figure 2. Sensing Mechanism
E-textile-based Pressure Sensor
does not need sandwich layers, in contrast to that of
Sergio et al. [3]; thus, our sensor is thin.
Figure 1 provides an overview of our sensor. The dark
gray lines are conductive fibers. The cross points of the
dark gray lines are the sensing points. Each sensing
point is about 1-cm square. The distances among sensing points is about 1 cm. The thickness of the sensor is
about 0.6 mm. It is soft and flexible.
The sensor mechanism is supported by the textile
structure. It does not use embroidery, which differentiates it from those described by Shimoji et al. [4] and
Meyer et al. [1] Therefore, our sensor works continuously even if several fibers are inadvertently cut off
with frictional force or scratch. In addition, our sensor
The sensing mechanism is the capacitance measurement during the warp and weft of the conductive fiber,
as illustrated in Figure 2. If a load is placed on the
sensing point, the distance between the warp and weft
decreases, yielding a change in capacitance. The
change is measured and converted to the pressure.
The sampling rate of our sensor depends on the size
and type of conductive fiber to be used. For example,
the sampling rate of the bed-size sensor described in
the next section is 1.65 Hz per one surface. The sampling rate of the foot-pressure sensor described in Application 2 is 33 Hz per one surface.
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Session: Poster, Demo, & Video Presentations
UbiComp’13, September 8–12, 2013, Zurich, Switzerland
In addition, our sensor is suitable for mass production.
The material of our sensor is a common low-cost conductive fiber that does not use special and costly materials, such as optical fiber [1]. In addition, it is woven
with common weaving machines with a special manner;
thus, cost can be reduced and size increased in the
same manner as common textiles.
E-textile-based
Pressure Sensor
Application 1: Bed-size body pressure sensor
for anti-pressure-ulcer treatment
One application of our sensor is as a bed-size body
pressure sensor for anti-pressure-ulcer treatment. An
overview of which is illustrated in Figure 3. The current
prototype has 3,960 (88 by 45) sensing points with a
sampling rate of 1.65 Hz.
This sensor aims to reduce the pressure-ulcer prevention workload of nurses. Pressure ulcers are localized
injuries that are caused by immobility and lack of body
control, commonly known as bedsores. To prevent
pressure ulcers, nurses periodically change patient position. Using our sensor, nurses can focus on repositioning only those parts of a patient’s body parts that
are detected by our sensor, thus eliminating the need
for heavy lifting unless necessary.
Figure 3. Bed-size Sensor
The proposed sensor does not conflict with a pressurebalancing mattress, in contrast to the other thick or
hard sensors. Patients who are at high risk for pressure
ulcers use pressure-balancing mattresses. Thick or hard
sensors would interfere with a pressure-balancing mattress’ operation when such sensors are put on the mattress. Therefore, such sensors should be placed under
the mattress. However, placing sensors under the mattress will prevent the correct detection of body pressure
that can affect skin integrity. In contrast, our sensor is
Textile Sensor
Figure 4. Foot Pressure Sensor
thin and soft and can therefore be utilized on the pressure-balancing mattress. It can measure correct body
pressure related to skin integrity without interfering
with the pressure-balancing mattress.
Two examples of detected body pressure pattern (body
pressure image) are illustrated in the second and third
row of Figure 3. These body pressure images are postprocessed with smoothing and noise reduction. Rough
body shapes can be detected in both of these images.
In the middle image, high load can be detected around
the coccyx, where pressure ulcers commonly occur.
Similar characteristics can be detected on the side at
the shoulder and hip in the bottom image.
This sensor is being tested in a nursing home for the
aged and several homes performing nursing care in the
future work.
Application 2: Foot pressure sensor
Another application of our sensor is a foot pressure
sensor for gait and skill analyses, whose overview is
illustrated in Figure 4. The current prototype has 84 (6
by 14) sensing points and the sampling rate is 33 Hz.
The foot pressure sensor can be used for gait analysis
in daily life. An example of such use is illustrated in
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Session: Poster, Demo, & Video Presentations
Figure 5. As the pressure images show, changes in foot
pressure can be detected. Gait stability and fall risk
levels can be analyzed from the change in the images,
which is very beneficial for the aged. When this sensor
is incorporated in socks, it enables the same support
for people who do not wear shoes in the home and provides an advantage over insole-type sensors.
Another usage of the foot pressure sensor is the analyses of skills that generate a large frictional force between the feet and the ground, such as baseball batting,
golf swinging, and metal filing. Figure 6 shows the sensor’s use in analyzing a manufacturing skill called metal
filing. During metal filing, force is maximized at the
contact point of a file and scraped metal. The counter
force of such action force is the frictional force generated between the feet and the floor, which sometimes
causes the breakdown of embroidery based sensors,
such as the cutting off of critical fibers and peeling off
of sensing points. Our sensor works under such severe
conditions. In our project, one sensor set was shared
among 40 students during a half-year curriculum and
was still working properly at the end of the project.
Figure 5. Foot Pressure During Walk
This sensor is being tested in usages of daily gait analysis and sports skill analysis in the future work.
Conclusion
This paper proposed a novel e-textile-based pressure
sensor with two applications.
The material of our sensor is a common low-cost conductive fiber. Its sensor mechanism is supported by the
textile structure; thus it has higher durability than embroidery based sensors. In addition, our sensor is woven with common weaving machines with a special
UbiComp’13, September 8–12, 2013, Zurich, Switzerland
E-textile-based
Foot Pressure Sensor
Figure 6. Metal-filing Skill Analysis
manner. It means that cost can be reduced and size
increased in the same manner as common textiles.
Our sensor is currently utilized as a bed-size body pressure sensor for anti-pressure-ulcer treatment and a
wearable foot pressure sensor for walk and skill analyses. Both are being tested for practical use in the future works.
Acknowledgements
This research was supported by “The Knowledge Hub”
of AICHI, The Priority Research Project.
References
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