Design of an Oblique Angled Suspension Fork for Wheelchairs

C. Blauch BS, R.A. Cooper PhD, W. Ammer BS, M. McCartney, T. Corfman MS, E. Wolf BS

Slide 1
Design of an Oblique Angled Suspension Fork for Wheelchairs

C. Blauch BS, R.A. Cooper PhD, W. Ammer BS, M. McCartney, T. Corfman MS, E. Wolf BS

Slide 2
Significance

Traveling over obstacles in a wheelchair cause vibrations that may lead to injury

The injuries may include herniated disks, spinal deformities, and chronic low back pain

These vibrations can also reduce fatigue life on wheelchairs

Slide 3
Background

Reducing vibrations through casters

Pneumatic, foam-filled, or polyurethane wheels help reduce shock

Frog-Legs suspension caster (vertical orienation)

Invacare suspension caster (horizontal orienation)

Graphic description: In the top picture of this slide there is a picture of the Frog-Legs caster fork with a vertically oriented shock absorbing material.

In the bottom picture of this slide there is a picture of the Invacare caster fork with a horizontally oriented shock absorbing material.

Slide 4
Statement of Problem

Vertical or horizontal orientation of shock absorbing material is not optimal in reducing shock since neither can absorb shock both vertically and horizontally

Slide 5
Rationale

Orient shock-absorbing material at an angle that will absorb energy in horizontal and vertical directions

The principal behind the new design is to have the shock absorber tangential to the axis of rotation.

Slide 6
Rationale – con’t.

Vertically oriented shock absorbing material

Graphic description: In left picture of this slide there is a picture of the Frog-Legs caster fork with arrows showing the translation of the forces of this fork when it strikes a common obstacle.

In the right picture of this slide there is a drawing of the shock absorbing material of the Frog-Legs. It shows that half of the shock absorbing material is in compression and the other half is in tension.

Slide 7
Rationale – con’t.

Obliquely Angled shock absorbing material

Graphic description: In left picture of this slide there is a picture of the oblique angled caster fork with arrows showing the translation of the forces of this fork when it strikes a common obstacle.

In the right picture of this slide there is a drawing of the shock absorbing material of the oblique angled suspension caster fork. It shows that allof the shock absorbing material is in compression.

Slide 8
Development

Dimensions – 4"x 2.5"x 1.5"

Designed to use a 3" diameter, 1" wide wheel

Aluminum alloy 6016 – high strength, high corrosion resistance, easily machined

Polyurethane elastomer –elastic material, high energy absorption, variable hardness

Graphic description: In the top picture of this slide there is a technical drawing with the dimensions of the oblique angled suspension caster fork.

In the bottom picture of this slide there is a picture of the oblique angled suspension caster fork mounted in a wheelchair.

Slide 9
Evaluation

New casters tested against conventional casters with same wheel diameter

Accelerometers placed on footplate to measure shock

Both types of casters propelled over rumble strips and a door threshold by an experience wheelchair user

Acceleration data was analyzed for peak to peak accelerations and vibration dose values

Slide 10
Discussion

New casters showed an improvement over conventional casters as determined by the data and feedback from the subject

A softer or a variable stiffness shock absorber may improve results

A more involved study between the types of suspension casters would be needed to be done to determine the effectiveness of the new casters

Slide 11
Acknowledgements

Rehabilitation Services Administration, United States Department of Education (H129E990004)

VA Rehabilitation Research and Development Service, United States Department of Veterans Affairs (F2181C)

University of Pittsburgh

The End

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Updated: March 12, 2002