SP-5b: Development of Guidelines and Criteria for Integrated Restraints

Task leader: Linda van Roosmalen, PhD (industrial designer/rehabilitation scientist)

Co-investigators: Miriam Manary, MS (bioengineer/PhD Student)

Other participants: Gina Bertocci, PhD (bioengineer, research scientist); Hoveround (wheelchair manufacturer); Mark Schmeler (clinician, consumers); Mike Nordquist, Sunrise Medical (wheelchair manufacturer); Lucy Spruill, United Cerebral Palsy, Pittsburgh (consumers)

Duration/ staging of task: This 24 month research task will be conducted in months 12-36 of the 60 month RERC cycle



Design of development activities

This specific task will use the WIRS design requirements generated in Task SP-5a to develop surrogate WIRS prototypes (adult and child). These test prototypes will be surrogate adjustable prototypes, which will allow for investigation of the effects of various key WIRS design features.

The objectives in this task are as follows:

  1. Design and develop WIRS testing surrogate prototypes for adults and children based on design requirements established in Task SP5-a and previously determined crash loading characteristics (van Roosmalen and Bertocci, 2001; van Roosmalen, Bertocci et al., Submitted Feb. 2001), using solid modeling techniques and FEA (Solid Works, MADYMO). Two test prototypes will be developed; one suitable for children and the other for adults. These test prototypes will be capable of providing adjustability of key restraint system characteristics, i.e. adjustable shoulder belt anchorage, provision of retractors, etc. These surrogate test WIRS prototypes will be mounted to the surrogate wheelchair base (ISO 16840-4) for testing.
  2. Dynamically evaluate the WIRS surrogate test prototype performance using ANSI/RESNA WC19 frontal impact testing. Occupant protection associated with the WIRS surrogate test prototypes will be evaluated across a range of WIRS parameters. Parameters will include restraint anchorage location, the presence or absence of retractors, etc. for adults and children. (Current ANSI/RESNA and ISO 16840-4 standard efforts include the development of a surrogate wheelchair base to evaluate the crashworthiness of seat and back surfaces and attachment hardware. The test setup in this Task proposes to utilize a comparable dynamic wheelchair test setup - prototype surrogate WIRS mounted on surrogate wheelchair base - to evaluate various WIRS scenarios for adults and children.) Two instrumented Hybrid III Anthropomorphic Test Devices representing a 50th percentile male and 6 year old child user will be used in the WIRS evaluation. Data will be collected on head and chest acceleration, neck loads, occupant restraint loads, chest compression, occupant motion and wheelchair load data.
  3. Evaluate surrogate WIRS compliance with SAE J2249 Wheelchair Tiedown and Occupant Restraint standard and GM-IARV (General Motor Injury Assessment Reference Values) occupant injury criteria (NHTSA-GM, 1983; SAE, 1996) across various WIRS scenarios.
  4. Develop computer simulation models of dynamic impact testing of the adult and child surrogate WIRS using MADYMO and validate these models using the collected data from the sled impact tests. Using these models, further investigate wheelchair seat and restraint characteristics and their effect on occupant safety during frontal impact through parametric analysis.
  5. From sled testing and computer simulation studies, compile and disseminate design guidelines and performance criteria for WIRS that can be used by wheelchair and restraint manufacturers.

Technology used in development

In a previous study conducted by the task leader, a concept WIRS for adult wheelchair users was developed and evaluated. The concept WIRS was designed using solid modeling and Finite Element Analysis (FEA). Occupant injury measures and wheelchair kinematics of the WIRS were evaluated through computer simulation and sled impact testing to test for compliance with SAE J2249 and GM-IARV recommended values. These techniques, which are proposed for use in this Task, (solid modeling, FEA, computer simulation and sled impact testing) proved to be useful in developing, evaluating and predicting feasibility of the WIRS (van Roosmalen, 2001).

Conceptual model and state-of-the-art

Wheelchair seat characteristics such as seat to back angle, seat stiffness and back stiffness have been shown to affect occupant risk of injury when integrating occupant restraints in wheelchairs (van Roosmalen, 2001). Restraint characteristics such as belt pretension, load limiter retractor and belt geometry and anchor location also have been shown to have an effect on occupant risk of injury and perceived comfort (Bertocci, 1996; (Bertocci, 1997; NHTSA, 1999; Bertocci and Evans, 2000; van Roosmalen, 2001). Additionally, when developing an occupant restraint system independent from the vehicle and integrated in the (wheelchair) seat, additional loading will act on the wheelchair structure (van Roosmalen and Bertocci, 2001; van Roosmalen, Bertocci et al., Submitted Feb. 2001). Therefore a strength analysis of the wheelchair frame, seating system, and the restraint system needs to be conducted as part of WIRS development. Solid modeling combined with FEA and dynamic computer simulation will be used to conduct the strength analysis in this task. Such an approach will enable surrogate WIRS development, without extensive production and testing costs.

The proposed approach, which relies upon the development and usage of a surrogate WIRS, is one that has been effectively used in the wheelchair transportation standards area. Such an approach will allow for investigation of key restraint system design parameters, without the need for costly wheelchair and WIRS prototypes. Development of a computer simulation of the surrogate WIRS impact event will further enhance the study of design variables through parametric analysis. Together, these state-of-the-art techniques will permit us to effectively define WIRS design guidelines for manufacturers.

Environment for development and testing

Solid modeling and FEA analysis, as well as computer simulation of both pediatric and adult WIRS designs will be conducted at the University of Pittsburgh’s Injury Risk Assessment and Prevention laboratory (IRAP). Development and fabrication of the WIRS structure will be conducted at a machine shop available at the University of Pittsburgh. 20g/30mph sled impact testing using an instrumented 50th percentile male and 6year old child Hybrid III ATD will be conducted at the sled test facility at the University of Michigan’s Transportation Research Institute (UMTRI). Wheelchairs and seating manufacturers will provide input during the development of surrogate WIRS. Evaluation of WIRS feasibility will be conducted at IRAP and UMTRI.

Cost-effectiveness and usefulness

The Task SP-5a, to be completed in year 1, will provide researchers and designers with the user requirements and manufacturing requirements for WIRS development. The feedback from wheelchair users and manufacturers on generated conceptual design drawings during the focus group meeting of Task SP5-a will help to ensure a WIRS surrogate design that can account for users’ needs regarding safety and usability. Since sled impact testing is a costly event, computer simulations will be used to conduct occupant injury and crashworthiness evaluations prior to surrogate prototyping and actual sled testing. Also, based upon preliminary FEA analysis and computer simulation, design modifications can be made prior to fabricating surrogate prototypes. Additionally, the use of test prototypes (both surrogate WIRS and surrogate wheelchair base) will save the cost of wheelchair bases and seating components.

Regarding the usefulness of the WIRS prototype development, surrogate prototypes will provide the basis for providing manufacturers with WIRS design guidance.

Potential for commercial development

This Task generates WIRS surrogate prototypes, which will provide the foundation for defining WIRS design criteria. These surrogate WIRS will permit us to study the effects of restraint system design characteristics, thereby fostering the development of commercial WIRS for adults and children.

It has been shown in previous University of Pittsburgh studies that consumers desire WIRS (van Roosmalen, Bertocci et al., 2001; van Roosmalen, Bertocci et al., Accepted for publication April 2001) since they are easier to use, less time consuming and more comfortable. Additional preliminary University of Pittsburgh studies have demonstrated the superior occupant protection associated with WIRS (Bertocci and Evans, 2000) and WIRS feasibility through sled testing (van Roosmalen, Bertocci et al., Submitted Feb. 2001). The automotive industry has also previously proven integrated restraint to provide improved occupant safety for adults and children (Cremer, 1983; White, 1994; Lynch, 1995; Gupta, Menon et al., 1996; Sances and Saczalski, 1999). For these reasons, there is a high potential for WIRS commercial development. Additionally, collaboration with standards development organizations and wheelchair manufacturers enables great potential for successful commercial development of a WIRS.

References

Bertocci, G. E., Digges, K., et al. (1996). Shoulder belt anchor location influences on wheelchair occupant crash protection. Journal of Rehabilitation Research and Development 33 (3): 279-289.

Bertocci, G. E. (1997). The Influence of securement point and occupant restraint anchor location on wheelchair frontal crash safety. Bioengineering. Pittsburgh, University of Pittsburgh.

Bertocci, G. E. & Evans, J. (2000). “Injury risk assessment of wheelchair occupant restraint systems in a frontal crash: a case for integrated restraints.” Journal of Rehabilitation Research and Development 37(5): 573-589.

Cremer, H. P. (1983). Seat integrated safety belt. Society of Automotive Engineers (SAE).

Gupta, V., Menon, S. G., Mani, A., Shanmugavelu, I. & Kossar, J. (1996). Improved occupant protection through advanced seat design. Washington, NHTSA: 181-191.

Lynch, T. (1995). “Integrated seat adds safety, design convenience.” Design News 43(October).

NHTSA (1999). Advanced integrated structural seat, EASI Eng. & Johnson Controls Inc.

NHTSA-GM (1983). General Motors submission USG 2284, app. E, NHTSA. Docket 74-14 Notice 32.

SAE (1996). SAE J2249 Wheelchair tiedowns and occupant restraints (WTORS) for use in motor vehicles, SAE.

Sances, A. & Saczalski, K., J. (1999). Studies with belt integrated vehicular seats. BMES/EMBS Conference, Atlanta, GA, IEEE.

van Roosmalen, L. (2001). Wheelchair integrated occupant restraint system feasibility in frontal impact. Rehabilitation Science and Technology. Pittsburgh, University of Pittsburgh.

van Roosmalen, L. & Bertocci, G. E. (2001). The effect of a wheelchair integrated occupant restraint system on wheelchair tie-down and occupant restraint design characteristics. RESNA annual conference, Reno, RESNA Press.

van Roosmalen, L., Bertocci, G. E., Ha, D. & Karg, P. (Submitted Feb. 2001). “Wheelchair integrated occupant restraints: Feasibility in frontal impact.” Medical Engineering & Physics.

van Roosmalen, L., Bertocci, G. E., Hobson, D. A. & Karg, P. (2001). Usability and satisfaction of wheelchair occupant restraint systems used during motor vehicle transport. RESNA annual conference, Reno, RESNA Press.

van Roosmalen, L., Bertocci, G. E., Hobson, D. A. & Karg, P. (Accepted for publication April 2001). “Preliminary evaluation of wheelchair occupant restraint system usage in motor vehicles.” Journal of Rehabilitation Research and Development.

White, C. E. (1994). “Dynamic sled test results: Integrated child seat.” (March).


Progress report May 1, 2003

To obtain occupant restraint design requirements for children, a set of three dynamic sled tests has been conducted with pediatric wheelchairs to obtain shoulder belt loads and chest compression measures from an instrumented Hybrid III ATD representing a 6 year old occupant. A commonly used vehicle mounted 3-point shoulder and pelvic restraint configuration was used. Values from these sled tests and values measured from a previous conducted sled test with a 50th percentile male ATD will be compared and used to determine design requirements and test procedures to evaluate a seat integrated restraint system.

A computer simulation model of a pediatric wheelchair is under development to assess changes in occupant and wheelchair kinematics when integrating an occupant restraint system in a pediatric wheelchair.


Progress report May 1, 2004

A usability study among adult wheelchair users has been conducted to obtain input on occupant restraint design and ease of use. Outcomes resulted in guidelines for the design of a wheelchair integrated restraint system that can be used independently by wheelchair seated individuals. A network with wheelchair manufacturers and seat belt manufacturers has been established to assist with manufacturability of prototypes. A design of a user friendly and safe pelvic restraint system is under development to work with the existing on board shoulder belt. Strength analysis of the proposed design is currently underway.


Progress report May 1, 2005

Progress to date for the adult population

Based on user testing and input from wheelchair users via the world wide web, information was gathered into a Quality Function Deployment matrix. This matrix has been communicated to wheelchair users and clinicians at RESNA. The QFD and more detailed design guidelines are now in the process of being communicated to constituents in the form of publications and online guidelines.

 

Progress to date for the pediatric population

Guidelines for pediatric integrated restraints are being developed using data from a laboratory study of 60 children weighing between 40-80 lb that examined factors in occupant restraint fit, application, and use.  The results of this study are being combined with relevant aspects of the occupant restraint design and performance requirements of Federal Motor Vehicle Standard 213 Child Restraint System, to define characteristics of effective, comfortable, and easy-to-use wheelchair-integrated harnesses.  These guidelines will be evaluated through the development of prototype hardware and dynamic testing of experimental systems.


Progress Report May 1, 2006

Two concepts of pelvic restraints for adult use have been developed. For one concept additional funding has been sought for technology transfer purposes. For the other concept, we originally had a commercial partner to assist with prototyping. However, due to a conflict regarding a license agreement, this partner has withdrawn from the project. A new partner is now being sought.

One concept is in detailing phase and should be ready for prototyping this summer. Sled testing is expected to take place in the fall of 2006, demonstrating the feasibility of this wheelchair integrated pelvic restraint. The pelvic restraint is innovative because a rotational buckle was used instead of a commonly used push button. Additionally, an adjustable stiff stalk is attached to the buckle to allow for one handed engagement and release.

This project also investigated the feasibility and design criteria for wheelchair-integrated (i.e., wheelchair-anchored) belt-type occupant restraint systems for pediatric wheelchair users, with special emphasis on five-point harness systems for children under 23 kg (50 lb) mass. The initial portion of the project defined design guidelines for integrated restraint harnesses using information from the federal motor vehicle safety standard for child restraint systems (FMVSS 213), from well established principles of occupant restraint, from ease-of-use issues for child restraint systems based on field observations, and from studies of automotive-seated child anthropometry.

During this year, the draft version of these design guidelines was used to implement five-point harnesses obtained from current FVMSS 213-compliant child safety seats on current pediatric commercial wheelchair products. The prototypes were frontal-impact tested to evaluate the crashworthiness of each prototype based on established performance criteria from FMVSS 213. The tests also provided quantitative information on forces applied by harness shoulder belts to the wheelchair seatback for use wheelchair manufacturers in designing their pediatric products for use with fully integrated restraint systems. The final phase of the effort will develop similar prototypes harnesses for lightweight folding wheelchairs.

Based on the information collected during the process of developing and testing these prototypes, the design guidelines were revised and improved, to include strength requirements and issues specific to wheelchair encountered during the prototyping process. These guidelines are now being used to augment ANSI/RESNA WC19 with design and performance criteria for wheelchair-integrated, five-point harnesses for wheelchairs used by children under 23 kg (50 lb).

Last updated: August 18, 2006

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