Page 434 - Mechatronics for Safety, Security and Dependability in a New Era

Ch84-I044963.fm Page 418 Tuesday, August 1, 2006 5:00 PM
Ch84-I044963.fm
418
418 Page 418 Tuesday, August 1, 2006 5:00 PM
θ [de g ] ] ]
[de
[de
g
g
[deg]
ma
ma
max x x x
ma
60
60
60
60 60
50 50
50
50
50
O O O O 40
40
40
40
40
30
30
30 30
r r r r 30
w w w w 20
w
20
20 20
20
10
10
10 10
10
C C C C G G G G w/r r
w/ w/r
w/r
w/r
E E E E θ 0 0 0 0 0 0 0 0 0 0 0 0 0 0.1 0.2 0 0 0 0.3 0 0 0 0.4 0.5
.
.
2
.
0 0 0
.1
.5
.1
.1
2
.4
.4
0 0 0
.5
.5
.3
2
.3
.4
.3
0.3
0.4
0.2
0.1
0.5
Figure 3: Relationship between ball shape and maximum slope angle
infrared LEDs, a radio receiver and a battery are attached to electronic circuit boards, and the boards
are fixed to the internal surface of a small sphere outer shell with cushion material. This shell is made
of impact-resistant transparent plastic.
Ball Shape for Suppression of Rolling
Tn order to cover the weak point of no locomotion mechanisms, some kinds of technique to distribute
search balls widely inside rubble are required. For this requirement, we discuss the effect of ball shape
on "rolling". First a ball drops on top rubble and rolls to its edge, then it drops again on next rubble. If
the ball is an entire sphere, it repeats these actions until it reaches the lowest points or horizontal
planes. But some balls must stop halfway down to the bottom in order for balls to be scattered widely
and evenly inside rubble. Hence it is important to endue balls with different ability to roll. For this
purpose, we adopt the ball shape shown in Fig.3. Just like a brim of a hat, a ring is attached to the
sphere outer shell; r is the radius of the sphere, and w is the width of the ring. As an index of ability to
roll, we use the maximum slope angle 0 max for the ball not to roll. When this ball remains stationary on
the slope of angle 0, the projection of its center of mass on the slope, G, is between the contact point
of the sphere on the slope, C, and the contact point of the ring edge on the slope, E. Thus the angle 6* is
maximum when G coincides with E. Letting O be the center of the sphere,
6 max= A EOC=cos"V/(r+w)) (1)
The graph in Fig.3 shows the relationship between 0 max and the ratio w/r. By changing w/r, we can
endue the ball with different ability to roll: the greater w/r suppresses the ball's rolling. This ball shape
also has the effects of irregular rolling and bouncing of the ball. Preparing balls of different w/r and
scattering them will bring wide distribution of the balls inside rubble.
Identification of Balls and Acquisition of Sensor Information
A large number of search balls are distributed inside rubble. Thus the wireless communication
between the balls inside the rubble and monitoring computers outside requires identification of the
balls and acquisition of the sensor information from the balls. Here we suppose to search the inside of
a collapsed Japanese-style wooden house; its area is less than 100[m ]. Because balls are thrown into
the house after it is collapsed, there exists the route of entry for each ball, through which the ball
enters the inside of the rubble. This route can be a path of communication between the ball and the
outside. In this situation, one-to-one wireless communication between each ball and the outside
monitoring computer is possible.
As shown in Fig.2 and Fig.4, the designed search ball has two wireless cameras, infrared LEDs, a
motor and a radio receiver. Before balls are thrown into rubble, a unique ID number is assigned to
each ball. The radio frequency of all balls and the computer is matched. After drop, the computer
broadcasts the ID of the target ball to all balls. Each ball receives the ID and checks whether it agrees
with the assigned ID. If they agree, the target ball turns on its cameras, LEDs and motor. The
computer sends motor commands: 1 bit for switching rotation/stop and 1 bit for changing direction of