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Using Stability & Fatigue Strength Testing When Choosing a Manual Wheelchair
Andrew J. Rentschler
Rory A. Cooper
Michael L. Boninger
Shirley Fitzgerald
Center of Excellence for Wheelchairs & Related Technologies, VAMC
Dept. of Rehabilitation Sciences & Technology,
University of Pittsburgh
Slide 1
Using Stability & Fatigue Strength Testing When Choosing a Manual Wheelchair
Andrew J. Rentschler
Rory A. Cooper
Michael L. Boninger
Shirley Fitzgerald
Center of Excellence for Wheelchairs & Related Technologies, VAMC
Dept. of Rehabilitation Sciences & Technology,
University of Pittsburgh
Slide 2
Background
Performance and Safety Characteristics of Manual Wheelchairs.
Gaal- of 253 reported WC incidents, 42% involved a tip or fall.
Ummat/Kirby- of 2,066 WC accidents reported to NEISS, 73.2% involved a tip or fall.
Slide 3
Methods
ANSI/RESNA Wheelchair Standards, Sections 1 and 8.
Section 1- Static Stability- Uphill, Downhill, Lateral.
Section 8- Fatigue Strength- Double Drum & Curb Drop.
Cyclic Fatigue Failure Testing.
Slide 4
Static Stability
Graphic description:
Slide 5
Double Drum/Curb Drop
Graphic description:
Slide 6
Wheelchair Footprint
Graphic description:
Slide 7
COG/Wheelbase Diagram
Graphic description:
Slide 8
Geometric Model for Static Stability
Graphic description:
Slide 9
Static Stability Tipping Angles
Graphic description:
Slide 10
Fatigue Testing
Graphic description:
Slide 11
WC’s Tested Until Failure
Graphic description:
Slide 12
Frame Failures
Graphic description:
Slide 13
Discussion
Average uphill tip angle is 11.6o. Antitip devices needed for safety.
Large range in downhill tip angle (27o).
Wheelchair set-up can significantly affect stability.
Geometric model good predictor for stability.
Slide 14
Discussion
41% of the WC’s failed to meet the minimum ANSI/RESNA standards for fatigue testing.
74% of the WC’s tested to failure experienced a frame failure.
Frame failures occurred sooner than other class III failures (297,722 vs. 658,018).
Slide 15
Discussion
Cost analysis of wheelchairs.
Cooper et al- Rehab chairs lasted 13.2 times longer than depot chairs. Depot chairs cost 3.4 times as much to operate per cycle.
Fitzgerald et al- Fatigue testing of 61 manual wheelchairs, 21 class I failures, 29 class II failures.
Slide 16
Factors Leading to Frame Failures
Welds
Type of Weld
HAZ (Heat Affected Zone)
Notches & Inclusions
Material
Steel/Aluminum/Composite
Areas of High Stress Concentration
Bolt Holes
Seat/Backrest Joint
Slide 17
Frame Failures
Graphic description:
Slide 18
Frame Failures
Graphic description:
Slide 19
Frame Failures
Graphic description:
Slide 20
Conclusions
Static stability range can be used to choose a set-up that is functional yet safe.
Geometric model useful for estimating stability.
Results from fatigue testing are useful for life cycle and cost analysis.
Performance and safety information allows consumers and clinicians to choose the safest and most practical wheelchair at a reasonable cost.
Slide 21
Acknowledgements
Students & Staff at HERL who helped with the testing & data analysis.
PVA & other organizations that provided funding.
The End
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Updated: March 11, 2002
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