Page 58 - Mechatronics for Safety Security and Dependability in a New Era

Ch09-I044963.fm Page 41 Tuesday, July 25, 2006 11:58 AM
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11:58 AM
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4.0
3.5
\
3.0
r ^ 2
.
2.5 • - J = 26 [kgm ]
% • 4.a
- • - 8.4
2.0 - • - 15.9
0 1 2 3 4 5
Velocity average CO d [rad/s] Power output
Figure 5: Torque average to each averaged Figure 6: HR reserve to power output
velocity in the steady state for evaluation of wheelchair propulsion
in the steady state

5. For evaluation, figure 6 shows relation derived power output (P [W]) and heart rate reserve (I [%])
in the test of figure 5.

DISCUSSION
The wheelchair equipped with the power assist control system is needed development or an
improvement to a design based on the human-wheelchair model, not on a trial and error. Generally,
this system of the wheelchair with hand-rims, which transmit human power as source of the propelling
force, should contain not only assist power but also adjustment element corresponding to change of the
resistances that cause fatigue. For one of resistances that should be considered, we should consider
about inertia, which is resistance to change of movement and which changes with total mass of the
human-wheelchair system. For realization of this system, many relations that occur between human
and the wheelchair should be studied and evaluated quantitatively.

First, we made equipment for this study and we confirmed usefulness for the evaluation of some
characteristics at straight propulsion. Next, we obtained the steady state velocity-torque characteristic.
Finally, we acquired and verified the some relation between inertia power and human elements in the
human-wheelchair system. These contents and considerations are described to following about each.

As described by the result (Figure 3, 4), the propelling peak torque tended to vary inversely as the
propelling velocity amplitude that the change of inertia affects. Because large inertia resistance is
equivalent to increase the driving resistance, speed variation and propelling frequency, which make
operator feel like bad driving quality and too much operation, decrease. The propelling peak torque of
each cycle, however, increases for the effect of inertia. We have then deduced that heart rate reserve
increase in proportion to inertia increase from the results. On the other hand, averaged torque and
velocity of one cycle were not affected by inertia (figure 5). The case of overweight (J=15.9[kgm ]),
however, revealed an increased torque and we have considered that the reason was influence of
resistance caused by inertia on the equipment. In the steady state, theoretically of relationship
between averaged torque and velocity predict that these values were not influenced by inertia and we
made sure it. From these results, we have considered that heart rate reserve to power output varies
with inertia. The experimental result had little change to inertia (shown in figure 6) and did not agree
to the theoretical estimates. This result showed that the variation of heart rate has a tendency similar
to the power. Moreover, we found that an element, which varied heart rate by propulsion under
different inertia, dose not only depend on the peak torque but also depend on the frequency of cycling
motion and each element is adjusted by human self-directive ability of that kind.