INJURY CONTROL FOR WHEELCHAIR OCCUPANTS - Injury Biomechanics and Control: Optimal Protection from Impact - page 269

rattlespace allowed for the platform relative to the vehicle is not violated.
For the single-degree-of-freedom system considered earlier, an optimal con-
trol was constructed that ensures the absolute minimum for the peak force
transmitted to the object to be protected, provided that the rattlespace is
constrained. This single-degree-of-freedom system can be regarded as a
simplified model for the platform-based occupied wheelchair, in which the
platform, the wheelchair, and the occupant are combined into a single rigid
body (the object to be protected). In this case, the load transmitted to the
object is proportional to its absolute acceleration. The optimal time histo-
ries of the absolute acceleration have been determined as functions of the
parameters of the shock pulse applied to the base. When simulating the
behavior of the MADYMO multibody model, the optimal absolute accel-
eration calculated on the basis of the single-degree-of-freedom model is
applied to the platform. In this case, the motion of the platform in the
MADYMO model coincides with the motion of the object to be protected
in the single-degree-of-freedom model and, hence, the constraint on the
rattlespace for the MADYMO model is satisfied automatically.

8.3.3 Response Criteria

Fourteen response criteria J i , i 1 ,..., 14, are used for the simulation.

Criterion J 1 is the distance moved by the platform in response to the crash
pulse,

=

J 1 = max

t

x(t) − min

t

x(t), (8.15)

where x is the displacement of the platform relative to the vehicle measured
from some reference point. The maximum and minimum in Eq. (8.15) are
calculated over the interval on which the motion of the system is considered.
Criterion J 1 characterizes the rattlespace required for the platform for a
given design of the system.
Criteria J 2 through J 6 are defined in ANSI/RESNA (2000).
Criterion J 2 is the peak forward displacement of the wheelchair relative to
the platform. It is defined as the maximum projection of the displacement
of a reference point of the wheelchair relative to the platform onto the
direction of motion of the vehicle. This quantity must not exceed 0 . 2m.
Criterion J 3 is the peak forward displacement of the occupant's knees
relative to the platform. It must not exceed 0 . 375 m.
Criterion J 4 is the peak forward displacement of the center of mass of
the occupant's (dummy's) head relative to the platform. This criterion must
lie below a level of 0 . 650 m.