Design Criteria For Manual Wheelchairs Used As Motor Vehicle Seats Using Computer Simulation

Alex Leary, BS, Gina Bertocci, PhD
University of Pittsburgh

Slide 1
Design Criteria For Manual Wheelchairs Used As Motor Vehicle Seats Using Computer Simulation

Alex Leary, BS, Gina Bertocci, PhD
University of Pittsburgh

Slide 2
Background

1990 ADA – Increased public access for people with disabilities

Some wheelchair users are unable to transfer to a vehicle seat

There is a need to produce transportable wheelchairs that offer safety comparable to vehicle seats in an impact

Slide 3
Purpose

Quantify dynamic impact loads on a manual wheelchair during a 20g/48kph frontal impact deceleration to provide design criteria for transportable wheelchairs

• Seat
• Wheels and casters
• Tiedowns and restraints
• Securement points
  

Slide 4
Significance

Bertocci G, Esteireiro J, Cooper R, Young T, Thomas C. Testing and evaluation of wheelchair caster assemblies subjected to dynamic crash loading. Journal of Rehabilitation Research and Development. Vol. 36, No. 1, Jan. 1999.

Dynamic drop tests simulating impact loads on wheelchair casters produced failure in 5 of 7 components tested

There is a need for improvement in transportable wheelchair design

Slide 5
ANSI/RESNA WC-19

Voluntary standard addressing wheelchair crashworthiness

Four point tie-down securement system

Securement device dynamically tested in 20g/48 kph frontal impact

• No major structural failure
• Excursion limits from ATD and wheelchair
• ATD and Wheelchair must remain upright
  

Slide 6
Methods

Construct a computer model of a wheelchair and occupant in a 20g/48kph frontal impact

Validate the model to sled test data

Use the model to calculate wheelchair loads

Conduct parametric sensitivity analysis

Slide 7
Methods: Model Construction

46 lb manual wheelchair with a welded aluminum frame

Hybrid III Anthropomorphic Test Dummy (ATD)

Four point tiedowns

Shoulder and lap occupant restraints

Slide 8
Methods: Model Construction

Dynaman Articulated Total Body lumped mass simulation software

Ellipsoids, planes, joints

Force deflection, friction, restitution, and energy functions describe element interaction

Slide 9
Methods: Model Validation

Gross Motion

Match acceleration histories

• Head
• Chest
• Pelvis
• Wheelchair
  

Match Force histories

• Occupant Restraints
• Wheelchair Tiedowns
  

Graphic description: A series of photographs and line drawings comparing an actual sled test with a computer modeled test.

Slide 10
Methods: Model Validation

Graphic description: A graph comparing results of shoulder belt tension,, tiedown tension, lap belt tension, wheelchair acceleration, pelvis acceleration, and chest aceleration of an actual sled test with a computer model. The restus are very similar.

Slide 11
Results: Seat Loads

Graphic description: two graphs showing the relationship between seat stiffness and seat force. As seat stiffness increases, seat force increases.

Slide 12
Rear Securement Point Locations

Graphic description: A line drawing showing 3 different wheelcchair rear tie down securement points: 5.5 inches above the hub, 1.5 inches above the hub, 2.5 inches below the hub.

Slide 13
Results: Wheel and Caster Loads

Graphic description: Two graphs: one showing the relationship between caster wheel force and tie down securement points to and the other showing the relationship between rear wheel force and tie down securement points. As the height of the tie down point increases, the caster wheel force decreases. As height of tie down point increases, the rear wheel force increases.

Slide 14
Results: Rear Securement Point Loads

Graphic description: a graph showing the relationship between the height of the tie down securement points to rear securement point force. As height of tie down point increases, the rear securement point force also increases.

Slide 15
Results: Wheelchair Design Criteria

Graphic description: a table showing the minimum and maximum force on: seat (min = 4017, max = 5407), caster wheel (min = 216, max = 1900), rear wheel min = 2011, max = 4038) and rear securement points (min = 1313, max = 1712).

Slide 16
Discussion

The model has been shown to be a reasonably valid representation of the sled test

The model efficiently determines the effect of design changes

Seat stiffness greatly influences seat load

Rear securement point position greatly affects wheel loading and wheelchair stability but has little effect on tiedown loads.

Slide 17
Questions?

The End

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Updated: March 12, 2002