Biomedical Engineering Reference
In-Depth Information
on an isolated platform subjected to the pre-acting control (fifth bar). For
the second bar, the dataset is for a 90-km/h change in velocity to illustrate
the case when response criteria exceed critical values. A criterion and the
component of the wheelchair-occupant system to which this criterion is
related are indicated on the top of the diagrams.
Figure 8.6 shows kinematic diagrams of the behavior of the wheelchair
and the occupant for various types of attachment of the wheelchair to the
vehicle. The diagrams are arranged in three columns corresponding to the
wheelchair attached to the vehicle body (left), the platform controlled with-
out pre-action (middle), and the platform controlled with pre-action (right).
The diagrams are shown for
t
50 ms and then follow with an inter-
val of 25 ms. The time is measured from the beginning of the accelerated
motion of the wheelchair base, that is, from the instant of application of
the shock pulse to the vehicle for the left and middle columns and from
the instant of the beginning of the pre-acting control of the platform for the
right column.
=
0
,t
=
8.4
DISCUSSION
As indicated in Figs. 8.4 and 8.5, in the case of the 48-km/h change
of velocity, none of the response criteria exceed the critical levels. The
platform-based responses are also below all of the critical values, but some
of the criteria are significantly below the critical values. This is the case
for the injury measures involving HIC (
J
7
and
J
8
), thorax acceleration (
J
9
),
chest deflection (
J
10
), and neck injury criteria (
J
11
and
J
13
). The reduction
in the injury measures ensured by the platform system without pre-action
versus the attachment of the wheelchair directly to the vehicle ranges from
20% [for the forward head displacement (
J
4
) and criterion
J
6
] to 71% [for
HIC
36
(
J
7
)]. There is an increase in the criterion
J
5
by 18%. The reduc-
tion due to pre-acting control of the platform, as compared with the system
without a platform, ranges from 0% [for the neck compression (
J
13
)] to
91% [for HIC
15
(
J
8
)]. In view of the importance of the reduction in the
injury risk in a motor vehicle crash, especially for occupants with disabil-
ities, these results suggest that a shock-isolated platform has the potential
to reduce injury risk for wheelchair-seated occupants.
It is important to note that the isolated platform-based tiedown system
substantially reduces the load on the wheelchair (criterion
J
14
). The platform
controlled without pre-action provides a 43% reduction and the platform
with pre-acting control a 62% reduction in the tiedown strap force, as com-
pared with the system without a platform. Reducing tiedown forces reduces
the risk that the wheelchair structure, often not designed to withstand crash
loads, will fail in an undesirable manner.
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