Research>Enabling Environment
Ultrasonic Radar System for Minimally Privacy-Violative Activity Observation
Outline
We are currently developing an ultrasonic system for tracking people and objects as a way of observing activity in living spaces while keeping invasion of privacy to a minimum. Our aim is to create a system that improves quality of life (QOL). By tracking people and objects, our system would allow the observation of activities of daily living (ADL). Data from these observations could then be used to construct behavior models, which could in turn facilitate the provision of evidence-based care. We suppose an ultrasonic radar based system that can comply with the following: 1) unconstraint measurement of location for the human, 2) minimally privacy-violation, which are compounding this human activities observing system.
Ultrasonic Radar System
Ultrasonic radar detects human location by determining time-of-flight
among human head and ultrasonic sensors. Figure 1 and figure 2 show the ultrasonic
radar system for observing human daily activities. The system is composed
of 117 transmitters, 117 receivers, transmitter-controllers, receiver-controllers,
network device and a host computer. The transmitters and receivers are embedded
in a ceiling, and other devices are set on a attic.
![](UltrasonicRadarSystem.jpg)
Figure 1:Ultrasonic Radar System
![](SystemConfiguration.jpg)
Figure)BQ:System Configuration
Principle of measurement in ultrasonic radar system
In the ultrasonic radar system developed by the authors, it is assumed that
the human head is an object moving at a relatively high vertical position
in a living area, and emitting ultrasonic sounds and receiving them back as
they are reflected from the head can detect the position of the head. This
section explains the principle used to measure and calculate, that is, to
locate, the position of a human head with unconstraint.
If the positions of the i-th transmitter, j-th receiver and head are
)BC
)BC
,
respectively, and the propagation distance is
,
as shown in Figure 3, then the following equation of a spheroid can be obtained.
(1)
If
)BCand
are known, then the head position
can
be calculated from the three equations of a spheroid.
![](PrincipleRadar.jpg)
Figure 3: Principle of measurement
Resolution and measuring error
The resolution in the x, y, and z directions is illustrated
in figure, which shows the probability density distribution for 1000 locations
of head calculated by the system. The resolution in x and y directions is
about 34 mm, while that in the z direction is about 10 mm. The average of
measuring error is 43 mm.
Figure 4: Probability distributions for human head detection
Tracking result
The upper part of the figure shows the measured trajectory
of the human head when the test subject moves as shown in the lower part of
the figure. The figure shows that the system can detect the positions of the
head at a frequency of 1 Hz.
Figure 5: Tracking position of a human head
Experiment for discrimination based on the height difference among objects
The system can distinguish the detected objects by their
height difference. For example, there is the difference between the head and
a desk. The figure shows a result of experiment for discrimination. In the
figure, red squares show the highest position of an object and green squares
that of another. The figure indicate that the system can distinguish the detected
objects)B@and trace.
Figure 6: Result of experimememt for discrimination
References
- S. Murakami, T. Hori, Y. Nishida, H. Mizoguchi, )BgUsing an Ultrasonic Tagging System to Assist with Protective Care in Nursing Homes: Evidence-Based Nursing Using a Patientfs Life Log (in Japanese),h in Proceedings of the 23rd Annual Conference of the Robotics Society of Japan, pp. 3D33(1)-(4), September 2005 (Keio University).
- S. Murakami, Y. Nishida, T. Hori, H. Mizoguchi, )BgA Minimally Privacy-Violative Activity Observation System: Tracking People and Objects Using a Combined Tag-Radar Ultrasonic System (in Japanese),h in Proceedings of JSME Robotics and Mechatronics Conference 2005 (ROBOMEC2005), 1A1-N-095(1)-(4), June 2005.
- T. Hori, Y. Nishida, "Ultrasonic Sensors for the Elderly and Caregivers
in a Nursing Home," Proceedings of the 7th International Conference on
Enterprise Information Systems ICEIS 2005, Vo. 5, pp. 110-115, May 2005
- Y. Nishida, S. Murakami, H. Toshio, H. Mizoguchi, "Minimally Privacy-Violative
System for Locating Human by Ultrasonic Radar Embedded on Ceiling," in
Proceedings of 2004 IEEE International Conference on Systems, Man and Cybernetics
(SMC '04), pp. 1549-1554, October 2004
- T. Hori, Y. Nishida, S. Murakami, H. Aizawa, H. Mizoguchi, "Distributed
Sensor Network for a Home for the Aged," in Proceedings of 2004 IEEE
International Conference on Systems, Man and Cybernetics (SMC '04), pp. 1577-1582,
October 2004
- S. Murakami, Y. Nishida, T. Hori, H. Mizoguchi, )BgDetecting Human Head Location Using a Simply Installed Ultrasonic Radar System,h in Proceedings of the 22nd Annual Conference of the Robotics Society of Japan, 1A23(1)-(2), September 2004.
- Y. Nishida, S. Murakami, T. Hori, H. Mizoguchi, )BgA Minimally Privacy-Violative Human Locating System: Calculating Head Position Using Ultrasonic Radar Installed in a Ceiling (in Japanese),h in Proceedings of JSME Robotics and Mechatronics Conference 2004 (ROBOMEC2004), 1A1-H-47(1)-(4), June 2004.