Computer Simulation Validation of a Wheelchair Mounted Occupant Restraint System under Frontal Impact

Linda van Roosmalen PhD
Gina E Bertocci PhD
Alex Leary BS

Slide 1
Computer Simulation Validation of a Wheelchair Mounted Occupant Restraint System under Frontal Impact

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Linda van Roosmalen PhD
Gina E Bertocci PhD
Alex Leary BS

Slide 2
Problem: Restraint Process Case 1

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Graphic Description: a photograph of person in power chair with a laptray and an AAC device. Another person is making an attempt to restrain the individual in the wheelchair with an upper torso restraint, but the laptray, armrests and AAC device are preventing proper occupant restraint.

Slide 3
Problem: Restraint Process Case 2

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Graphic Description: photograph of a person sitting in power wheelchair and pelvic restraint is wrapped around the armrests, which could be dangerous during frontal impact and injure the wheelchair occupant’s abdominal area.

Slide 4
Problem: Restraint Process Case 3

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Graphic Description: Person sits in a manual wheelchair. The upper torso restraint is barely touching the shoulder and will most likely completely slide off the shoulder during frontal impact, posing a threat on the occupant who might impact the vehicle interior.

Slide 5
Results

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WORS in Private Vehicles:

  • Quick, Easy & Comfortable to use

WORS in Mass-Transit and Para-Transit:

  • Uncomfortable to wear
  • Difficult to reach
  • Time consuming to use

WORS in Mass-Transit

  • WORS are time consuming
  • WORS use is intrusive
  • Non-availability of WORS in mass transit
  • Reported use of non-compliant positioning belts

Slide 6
Research Objective

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Wheelchairs are designed to provide mobility to individuals. Since many wheelchair users use their wheelchairs as motor vehicle seats, there is a growing demand for wheelchairs that can be safely used in transportation.

This means that design criteria need to be established for wheelchairs and occupant restraint systems. Design criteria in the areas of crash protection, seat design characteristics, usability and comfort.

This all needs to be done to provide individuals using a wheelchair comparable level of safety and user comfort as individuals seated in an original equipped and manufactured (OEM) vehicle seat and restraint system when exposed to crash conditions.

Graphic Description: a diagram with four arrows pointing from a picture of a wheelchair with occupant restraint system towards Crash protection, Usability, seat design and comfort.

Slide 7
Seat Integrated Restraint Advantages

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Extensive research has been done in the automotive industry to optimize the effectiveness and comfort of seat belts by integrating both torso and pelvic belt in the car seat. Haberl et al. @ BMW, Ruter & Hontschik @ the Batelle Institute, Wainwright et al, and Cremer, all studied restraint effectiveness when integrating a 3 point belt in the seat of a car.

They found that restraint effectiveness was improved by a shorter belt length and a decrease in belt stretch, reducing the forward displacement of the upper body.

Keeping the belt close and horizontal to the shoulder causes the occupant to participate early in the crash, whereas and the belt wraps well around the body which causes the body to rotate less around the belt.

Integrating the torso and pelvic belt in the seat has the following benefits:

No belt adjustment necessary when moving the seat for/rearward, optimized belt geometry results in optimum comfort and a higher user acceptance of the seat belt. Furthermore integrated seat belts feature improved protection in frontal as well as side, rear, and rollover impact.

Slide 8
Plan of Study

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Develop concept Wheelchair Integrated occupant Restraint System (WIRS)

Evaluate static strength of seat belt anchors of a concept WIRS

Dynamic strength compliance of WIRS with WC-19

Occupant safety compliance with SAE J2249

Create and validate simulation model of WIRS

Optimize restraint characteristics

Establish design criteria for a WIRS

Slide 9
Sled Impact Test

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Graphic Description: two pictures. The top one shows the setup of the wheelchair and occupant restraint system. The occupant restraint system is attached to the exterior. A Hybrid III ATD is restrained by the Fixed vehicle mounted occupant restraint system (FWORS).

The bottom picture shows the test setup of the wheelchair and occupant restraint system that is attached to the wheelchair itself. A Hybrid III dummy is restrained by a wheelchair mounted/integrated occupant restraint system (WIRS).

Slide 10
Dynamic Evaluation Motion Comparison

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Graphic Description: three screenshots of the moving dummy during frontal impact at 40, 80 and 120 milliseconds for the two different restraint scenarios.

Slide 11
Dynamic Evaluation Conclusions

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WIRS and FWORS compliance

  • GM-IARV occupant injury criteria
  • SAE J2249 kinematic motion and excursion criteria
  • WIRS feasibility

Development of Computer Simulation Model

  • Evaluate the effect of wheelchair seating system and occupant restraint characteristics
  • Study the effect of these characteristics on wheelchair kinematics and occupant risk of injury

Slide 12
Research Setup

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Build computer simulation model according to sled impact information

Optimize restraint characteristics

Optimize wheelchair seat design criteria

Slide 13
Computer Simulation Model

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Sled pulse 20g/30mph

Model of SAE J2249 surrogate wheelchair

Hybrid III 50th % male ATD dummy

Belt type wheelchair tie-down system

WIRS with flexible seat-to-back

Version 3.0 Dynaman

Graphic Description: diagram of the simulation model (build in Dynaman) of a surrogate base, wheelchair seating system and wheelchair occupant restrained by a WIRS.

Slide 14
WIRS Simulation Model Validation

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Graphic Description: four screenshots of the moving dummy during frontal impact at 0, 40, 80 and 100 milliseconds for the actual sled impact test with WIRS and the computer simulation model.

Slide 15
Validation

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Graphic Description: three graphs showing the validation of the computer simulation model based upon the sled impact test for the wheelchair acceleration, upper torso restraint load and wheelchair tiedown load. All pairs of lines follow a similar trend.

Slide 16
Validation

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Graphic Description: three graphics showing the validation of the computer simulation model based upon the sled impact test for the head acceleration, chest acceleration and head excursion. All pairs of lines follow a similar trend.

Slide 17
Results

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Validated WIRS simulation model

Similar trends were found

  • Motion criteria
  • Injury criteria

Study Limitations:

  • Validation based on limited sled test data
  • Simplification of occupant restraint system
  • Simplification of flexing seat back

Slide 18
Next: Sensitivity Analysis Wheelchair Design Parameters

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Seat back angle

  • 0-30 deg. (10 deg. increments)

Seat-to-back joint stiffness

  • 25-200% of model value

Seat back support stiffness

  • 25-200% (100-1900 lb/in)

Seat support surface stiffness

  • 25-200% (500-3300 lb/in)

Seat surface energy Absorption (submarining)

  • Returned energy factor R=0-1 (0.25 increments)
  • Permanent deformation factor G=0-1 (0.25 increments)

Slide 19
Sensitivity Analysis Occupant Restraint Parameters

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Retractor with load limiter to reduce excursion and occupant loads

  • Located at upper torso anchor
  • 300- 1500 lb (150 lb increments)

Restraint pretensioner to reduce excursion and occupant acceleration

  • Located at upper torso anchor
  • -2 to +2 in. (1 in. increments)

Slide 20
Sensitivity Analysis Restraint retractor with load limiter

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Reduction of forward displacement (Haberl et al., 1989)

Use of load limiter showed improved frontal crash protection

High Load limit (>2000 lb) shows higher injury risk for elderly individuals

Reduction in HIC values and neck loads

Moderate reduction in chest compression (NHTSA: Gupta et al., 1996)

Slide 21
Sensitivity Analysis Restraint Pretensioner

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Elimination of belt slack

Reduction of forward displacement (Haberl et al., 1989)

Energy absorption during early forward travel

Chest acceleration reduction (NHTSA: Gupta et al., 1996)

Slide 22
Sensitivity Analysis Findings

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Wheelchair seat and occupant restraint parameters affect occupant injury measures

  • Seat back recline angle
  • Seat-to-back joint stiffness
  • Seat surface stiffness (H-pt)
  • Restraint pretension
  • Restraint load limit

Slide 23
Sensitivity Analysis Findings

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Wheelchair seat and occupant restraint parameters affect wheelchair seat surface loading

  • Seat back recline angle
  • Restraint retractor load limit

Parameters were varied independently

Need for optimization of parameters

Slide 24
Future Steps

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Conduct additional sled impact testing

Improve WIRS simulation model

Establish design criteria for a WIRS

Slide 25
Acknowledgements

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This study is supported through:

  • NIH-STTR
  • NIDRR: RERC on Wheeled Mobility

Slide 26
Thank You For Your Attention

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Return to Slide Series

Updated: March 14, 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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