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SLACK TESTING
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Slack
Testing
Slack Testing of Q'Straint Securement
System Using Surrogate Wheelchair
Conducted by Queen's University
Department of Mechanical Engineering
Purpose of the Test
To measure the movement in four
directions of a surrogate wheelchair which was secured to a
rigid platform by a Q'Straint system.
Materials and Methods
The surrogate wheelchair was
a rigid structure made of steel and resembling a wheelchair,
with a mass of 80 kg. (176 lb). It was secured by a Q'Straint
securement system on a rigid platform resembling a vehicle floor.
The anchoring points were positioned according the manufacturer's
instructions, which in turn complies with CSA draft standard
Z-605.
The motion of reference point P, relative to a datum on the
platform, was measured with a Vernier caliper, after a force
of 1600 N, (350 lb) was applied through point P. The direction
of the load application was forward, rearward and sideways.
The procedure was according to CSA draft standard Z-605, clause
9.
Force measurements were made with a calibrated load cell and
a strain indicator.
A test was repeated 3 times without changing the overall setup
but at each trial the datum was reset. AT least 2 tests were
done for each direction. Between these two tests the belts were
released and again hand tightened according to normal practice
in wheelchair restraining. |
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Results
In the forward direction the
movement of the surrogate wheelchair during the application
of the load was between 8 and 9.5 mm, (.32 to .37 inch). In
the rearward application of the force the wheelchair moved between
13 and 17.5 mm, (.51 and .69 inch). Sideways movement was between
6.0 and 22 mm, (.21 and .87 inch). Tables 1, 2 and 3 show the
results.
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| Test
Set
A Test
Set B |
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| 1 |
9 mm |
(.35 inch) |
9,5 mm |
(.37 inch) |
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| 2 |
8,5 mm |
(.33 inch) |
8 mm |
(.31 inch) |
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| 3 |
9,5 mm |
(.37 inch) |
8 mm |
(.31 inch) |
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| Table 1. Movement of point P in the
forward direction due to ann applied load 1600 N |
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| Test
Set
A Test
Set B |
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| 1 |
17,5 mm |
(.68 inch) |
16 mm |
(.62 inch) |
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| 2 |
13,5 mm |
(.53 inch) |
13,5 mm |
(.53 inch) |
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| 3 |
14,5 mm |
(.57 inch) |
13,0 mm |
(.51 inch) |
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| Table 2. Movement of point P in the
forward direction due to ann applied load 1600 N |
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| Test
Set
A Test
Set B |
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| 1 |
14,5 mm |
(.77 inch) |
22 mm |
(.86 inch) |
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| 2 |
7 mm |
(.27 inch) |
7 mm |
(.27 inch) |
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| 3 |
6 mm |
(.23 inch) |
6 mm |
(.23 inch) |
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| Table 3. Movement of point P in the
forward direction due to ann applied load 1600 N |
Discussion
Since the surrogate wheelchair
is rigid, the forward motion of the chair and point P was determined
by the rear belts stretching, and by the rotation of the wheels.
In the rearward direction the same occurred in the opposite
direction. |
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Conclusion
The Q'Straint wheelchair securement
system kept the surrogate wheelchair and its point P within
the allowable range of motion of draft standard CSA Z-605, clause
9. As the applied force in the slack test for other jurisdictions
is less for most of the wheelchairs, (except for extra ordinary
heavy chairs exceeding a mass of 160 kg or 350 lb), the Q'Straint
system would also comply with AS 2942, ISO WD 10542, (proposed)
ADA and NHTSA regulations. |
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