Page 72 - Mechatronics for Safety Security and Dependability in a New Era

Ch12-I044963.fm Page 55 Tuesday, August 1, 2006 9:08 PM
1, 2006
Page 55
9:08 PM
Ch12-I044963.fm
Tuesday, August
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element (upper part of the block diagram) and rotational control element (lower part). Translational
signal generates translational velocity V, and rotational signal generates difference of velocity between
left wheel and right wheel.
EVALUATION ABOUT FOLLOWING CHARACTERISTICS IN STRAIGHT DRIVING
As the first step of optimum adjustment, we determined the translational gain K{ that affects the
following characteristics. Under the condition when an assistance dog began to walk straight with
F<i=2.5[km/h], some time responses of moving speed of electric wheelchair were calculated as in figure
3(a). In the case of Kf=0.\, the maximum velocity of wheelchair was less than the velocity of
assistance dog. It resulted that the electric wheelchair could not follow the assistance dog. In the
case of K/=0.277, the length of lead has not been extended to limit and the velocity response was very
smooth. Also, electric wheelchair could move on following to assistance dog in A^=0.8. However,
the velocity of wheelchair exceeded dog's speed, and passenger's riding comfort might become worse
by speed adjustment. In figure 3(b), some typical values of time response are shown as a function of
the translational gain K{. An extent of an oblique line in figure 3(b) shows the area where the electric
wheelchair could not follow the dog. The lager K f, the earlier the wheelchair's speed would be in a
steady. However, since the amount of overshoot P m was increased, the fluctuation of velocity became
larger. In the case of Kf• =0.277, the P m was kept small and an electric wheelchair could follow an
assistance dog even with faster speed, for example F(;=3[km/h].
V dog=2.5[km/h]
±
5[%] criteria
V d=2.5[km/h] ~ ~ 2.5 ± 5[%] criteria V dog =2.5[km/h] 10 ^
V d =2.5[km/h]
10
2-5
[km/h] 1 0.1 V D F [ D S [ e s [ 2 / [
[m]
I
E 4 4 1 1 "W. E m ~ ] E ] m o ] c ] %
0.1
0.8
— 3 0.8 0.277 l 0.75 ~ l T r P m 8 8 E P m D _
0.277
0.75
V 3
P m
> ~JZ e c n a e c n a 1.5 5DF • 6 6 8 t o o
1.5

e
D F
Velocity 0.8 Towling length d d e e
8 2 0.277 V d 0.5 t S s i £ t s i m i t 1 T r 4 4 t h s r
0.8
0 25
3- 1 1 0.25 I g n i I g n i s i R 0.5 D S ' r- v O
. 1
t
K =0.1 w o t E 0.5 y 2 2 ^
e
l
0 l l S 0 0
12
0 2 4 6 8 10 12 14 o F 0 0.2 0.4 0.6 0.8 1 0
10
0.8
0.6
0.4
0.2
Time t t [sec]
Time
[sec]
Translational gain K [-]
Translational gain K l ,
(a) Time responses of velocity of (b) State values of wheelchair as functions of
wheelchair the translational gain K{
Figure 3: Simulation results to fix the translational gain Kf
EVALUATION OF FOLLOWING CHARACTERISTICS IN ROTATIONAL DRIVING
In order to determine the rotational gain K t), we considered one situation. An assistance dog walks
straight, makes one rotation on keeping constant turning radius after that, and return to walk straight
again. This situation can be deal with one part of turning corner. We used one evaluation value P
described in equation (1).
Here, the value ji was rotational angle to center of clearance circle Od drawn by assistance dog, the pd
turning radius of assistance dog and the Rw distance between the center point of assistance dog's
clearance circle Od and the center point of electric wheelchair, shown in figure 4(a). Some simulation
results were obtained, when the dog's speed was Ka^2.5[km/h] and turning radius of assistance dog
was /)rf=3[m]. In the case of small K t, the electric wheelchair turns right or left with large turning
radius compared with the assistance dog's one, because the generated rotational signal was not enough
to make velocity difference large. Especially, when K (i was too small, the length of lead exceeded
the limit and became impossible to follow an assistance dog. On the other hand, in the case of large
Kj, the turning radius of electric wheelchair was smaller than that of assistance dog. Therefore,