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

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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

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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

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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

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Slide 5
Double Drum/Curb Drop

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Wheelchair Footprint

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COG/Wheelbase Diagram

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Geometric Model for Static Stability

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Static Stability Tipping Angles

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Slide 10
Fatigue Testing

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WC’s Tested Until Failure

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Frame Failures

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Slide 13
Discussion

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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

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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

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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

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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

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Frame Failures

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Frame Failures

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Slide 20
Conclusions

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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

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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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Please note: This information is provided a archival information from the Rehabilitation Engineering Research Center on Wheeled Mobility from 1993 to 2002.

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