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Authors: Liu, Y. W., Wu, K. Y., Hsu, Y. L.; recommended: Yeh-Liang Hsu (2012-08-02);
Note: This paper is presented at 2012 International Society of Gerontechnology World Conference, Technische Universiteit Eindhoven (TU/e), the Netherlands, June 26~29, 2012. This paper is also published at Gerontechnology 2012; 11(2): 255; doi: 10.4017/gt.2012.11.02.590.00

An integrated motion sensing mattress for elderly living assistance applications

Purpose

For elderly people living in homes or nursing homes, the bed is an indispensable part of their daily lives. Bed activity monitoring provides valuable information of the status of the elderly people. Various sensors have been implemented for this purpose, such as static charge sensitive bed[1], force sensors[2], air cushion[3], and textile-based sensors[4]. This paper presents the development of an integrated sensing mattress, “SmartPad”, for unobtrusive sensing of physical activities in the bed. Working with a bedding manufacturer, this research aims to design a mattress with motion sensing capability using the same material and fabrication process of the bedding manufacturer, so that the mattress is comfortable, washable, inexpensive, and is closer to being a commercial product.

Method

SmartPad is in a sandwich structure of two pieces of foam 6~10mm in thickness, on which conductive fiber is knitted in a special pattern in the “sensing area”, with pieces of conductive fabric in between. As shown in Figure 1, the average resistance of 10 tests of a 20cm×20cm sensing area decreases monotonically with applied pressure in the range of 500-3,500Pa (equivalent to pressure caused by the presence of an adult). The special elastic foam provided by the bedding manufacture has passed the fatigue test of 30,000 pressure cycles. Figure 2 shows a possible layout of the mattress, with 3 horizontal sensing areas for detecting movements of the upper limbs, hip and lower limbs, and 3 vertical areas for detecting movements of the trunk.

Figure 1. Applied pressure vs. resistance

Figure 2. Pressure sensing units on the SmartPad

Results & Discussion

Integrated with information systems, SmartPad was successfully implemented in the nursing homes to facilitate real-time monitoring of on/off bed status, sleep posture and body movements, using 10 Hz sampling rate of the resistance. Service reminders and history reports were also provided[4]. Various living assistance applications are developed, such as detecting sitting posture changes on a wheelchair, motion sensing carpet for monitoring purposes, and a “touch and call” pad for elderly people with impaired motor skills who cannot handle the usual press buttons.

Keywords: bed activity monitoring, pressure sensing, living assistance.

References

[1]     Erkinjuntti et. al, “Use of the SCSB method for monitoring of respiration, body movements and ballistocardiogram in infants”, Early Human Development, 1984, v. 9, n. 2, pp. 119-126.

[2]     Brink et. al, “Contact-free measurement of heart rate, respiration rate, and body movements during sleep”, Behavior Research Methods, 2006, v. 38, n. 3, pp. 511-521.

[3]     Watanabe et. al, “Noninvasive measurement of heartbeat, respiration, snoring and body movements of a subject in bed via a pneumatic method”, Biomedical Engineering, 2005, v. 52, pp. 2100-2107.

[4]     Cheng et. al, “Development of a portable device for tele-monitoring of physical activities during sleep", Telemedicine and e-Health, 2008, v. 14, n. 10, pp. 1044-1056.

[5]     Liu et. al, “Development of a Care Management System for Nursing Homes based on SmartPad”, 1st Asia Pacific eCare and TeleCare Congress, June, 2011, Hong Kong, China.