Page 62 - Mechatronics for Safety, Security and Dependability in a New Era

Ch10-I044963.fm Page 46 Tuesday, August 1, 2006 8:42 PM
Ch10-I044963.fm
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At low load, the attendant eases to pushing, so keeps the walking speed fast. With increasing load, the
pushing becomes harder and the large pushing force needs long time period of foot's touching on the
ground, so the walking speed becomes slower. The mechanical power of the attendant is so small that
the assisted system is needed for most of attendants. The pushing force responses showing in the
Figure 4 slow, because attendants push carefully against unknown loads. The following responses
against grip movement in the Figure 5(a) and (b) provide that attendants cannot keep its relative
distance and propelling force. Attendants delay to response against the grip movement and adjust its
position slowly despite the force have already adjusted. We expected from these results that human
couldn't reproduce its position and forces exactly and settle them within certain range. The
phenomenon of the falling force was well found in the fast slider speed condition, because responding
against fast object was more difficult. Despite of the facts, well corresponding between the model and
the experiment was found in the Figure 6. Neglecting dynamics, such as sudden dropping strength
dynamics, causes some differences. This time experiment carried out only one direction, such as
increasing force, moving forward. It is probably need to investigate the experiments of the opposite
directions, because human does not always have only one linear characteristic. Lately, the proposed
model describes attendant's behavior, mainly the pushing force and the relative distance very well. We
will estimate and assess the load and the safe of attendants with the proposed model.

1
s 2
? 1 '
'I I
£ <5

0 2 4
Time [s]
Fig. 6 Validation of the proposed model

CONCLUSIONS

We proposed the model to expect the attendant's behavior for the safe and low load design of the
assisted wheelchair with high assist. The validation of the proposed model shows well corresponding
against the experiment. The model can describes attendant's behavior on various conditions. Therefore,
the model is useful for the controller design of assisted wheelchairs.

REFERENCES
Al-Eisawi, K. W., Kerk, C. J., Congelton, J. J., Amendola, A. A., Jenkins, O. C, Gaines, W. (1999),
Factors affecting minimum push and pull forces of manual carts, Applied Ergonomics 30, 235-245
Cremers, G. B. (1989), Hybrid-powered wheelchair : a combination of arm force and electrical power
for propelling a wheelchair, Journal of Engineering and Technology 13, 142-148
Resnick, M. L., Chaffin, D. B. (1995), An ergonomic evaluation of handle height and load in maximal
and submaximal cart pushing, Applied Ergonomics 26, 173-178