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E-Textile Pressure Sensor Based on Conductive Fiber and Its Structure
Abstract 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 in-visibly assist humans without significant lifestyle changes. Our sensor is suitable for mass production and durable in daily hard use cases. The sensor is wo-ven with common weaving machines with a special manner and its material is a common low-cost conduc-tive fiber that does not use special and costly materials, such as optical fiber. The sensor mechanism is support-ed by the textile structure; thus our sensor has durabil-ity for frictional force and scratch occurring sometime in daily context. In this paper, we also introduce two ex-ample 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 anal-yses.
Author Keywords E-textile; Pressure Sensor; Foot pressure; Bedsore; Wearable
ACM Classification Keywords H5.2. Information interfaces and presentation (e.g., HCI): User Interfaces.
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UbiComp’13 Adjunct, September 8–12, 2013, Zurich, Switzerland.
ACM 978-1-4503-2215-7/13/09.
http://dx.doi.org/10.1145/2494091.2494158
Yu Enokibori Nagoya University Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603, Japan [email protected] Akihisa Suzuki Tsuchiya Co., Ltd. 22-4, Higashi-Namiki-Kita, Chiryu, Aichi, 472-0006, Japan [email protected] Hirotaka Mizuno Tsuchiya Co., Ltd. 22-4, Higashi-Namiki-Kita, Chiryu, Aichi, 472-0006, Japan [email protected]
Yuuki Shimakami Aichi Center for Industry and Sci-ence Technology 35 Aza-Miyaura, Mabiki, Yamato-cho, Ichinomiya, Aichi, 491-0931,�Japan [email protected] Kenji Mase Nagoya University Furo-cho, Chikusa-ku, Nagoya, Aichi, 464-8603, Japan [email protected]
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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.
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.
E-textile-based Pressure Sensor 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 sens-ing 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 differenti-ates it from those described by Shimoji et al. [4] and Meyer et al. [1] Therefore, our sensor works continu-ously even if several fibers are inadvertently cut off with frictional force or scratch. In addition, our sensor
does not need sandwich layers, in contrast to that of Sergio et al. [3]; thus, our sensor is thin.
The sensing mechanism is the capacitance measure-ment 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 sam-pling rate of the foot-pressure sensor described in Ap-plication 2 is 33 Hz per one surface.
Figure 2. Sensing Mechanism
Figure 1. E-textile Pressure Sensor (left: top view, right: side view)
Textile Sensor
Conductive Fiber
Sensing point
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In addition, our sensor is suitable for mass production. The material of our sensor is a common low-cost con-ductive fiber that does not use special and costly mate-rials, 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.
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 preven-tion 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 po-sition. Using our sensor, nurses can focus on reposi-tioning only those parts of a patient’s body parts that are detected by our sensor, thus eliminating the need for heavy lifting unless necessary.
The proposed sensor does not conflict with a pressure-balancing 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 mat-tress’ operation when such sensors are put on the mat-tress. Therefore, such sensors should be placed under the mattress. However, placing sensors under the mat-tress will prevent the correct detection of body pressure that can affect skin integrity. In contrast, our sensor is
thin and soft and can therefore be utilized on the pres-sure-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 post-processed 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
E-textile-based Pressure Sensor
Figure 3. Bed-size Sensor
Figure 4. Foot Pressure Sensor Textile Sensor
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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 pro-vides an advantage over insole-type sensors.
Another usage of the foot pressure sensor is the anal-yses of skills that generate a large frictional force be-tween the feet and the ground, such as baseball batting, golf swinging, and metal filing. Figure 6 shows the sen-sor’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 generat-ed 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.
This sensor is being tested in usages of daily gait anal-ysis 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 con-ductive fiber. Its sensor mechanism is supported by the textile structure; thus it has higher durability than em-broidery based sensors. In addition, our sensor is wo-ven with common weaving machines with a special
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 pres-sure sensor for anti-pressure-ulcer treatment and a wearable foot pressure sensor for walk and skill anal-yses. Both are being tested for practical use in the fu-ture works.
Acknowledgements This research was supported by “The Knowledge Hub” of AICHI, The Priority Research Project.
References [1] J. Meyer, P. Lukowicz, and G. Troster: Textile Pres-sure Sensor for Muscle Activity and Motion Detection, , 10th IEEE International Symposium on Wearable Com-puters, 69-72, 2006.
[2] M. Rothmaier, P.M. Luong, and F. Clemens: Textile pressure sensor made of flexible plastic optical fibers. Sensors, 8(7):4318-4329, 2008.
[3] M. Sergio, N. Manaresi, M. Nicolini, D. Gennaretti, M. Tartagni, and R. Guerrieri: A textile-based capacitive pressure sensor. Sensor Letters, 2(2):153-160, 2004.
[4] M. Shimojo, A. Namiki, M. Ishikawa, R. Makino and K. Mabuchi: A Tactile Sensor Sheet Using Pressure Conductive Rubber With Electrical-Wires Stitched Meth-od. IEEE Sensors Journal, 4(5):589-596, 2004.
Figure 6. Metal-filing Skill Analysis
E-textile-based Foot Pressure Sensor
Figure 5. Foot Pressure During Walk
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