D-5: Development and Evaluation of Injury Prevention Wheelchair Technologies
Task Leader: Gina Bertocci, PhD, PE (bio/mechanical engineer)
Co-investigators: Patricia Karg, MS (bio/mechanical engineer); Douglas Hobson, PhD (rehabilitation engineer); Linda vanRoosmalen, PhD (industrial designer/PhD graduate student); Dongran Ha, BS (civil engineer/MS graduate student)
Other Participants: Susan Shutrump (clinician); Larry Schnieder, PhD (crash safety expert); Jean-Marc Girardin - Q'Straint (manufacturer); Julie Grubaugh - Invacare (wheelchair and seating manufacturer)
Duration/Staging of Task: This 60-month development task will be conducted throughout the entire RERC cycle, commencing January 1, 1999.
Rationale/Task Summary
Providing effective occupant protection in a motor vehicle crash is a multi-faceted problem involving the vehicle, vehicle seat, and occupant restraint system. Persons traveling seated in their wheelchairs are required to rely upon third-party add-on components to secure their wheelchair to the vehicle and restrain themselves for occupant protection.
Furthermore, their wheelchair must act as an OEM motor vehicle seat and must be crashworthy, providing a stable seating surface in a crash. The proposed ANSI/RESNA WC-19 Standard address wheelchairs used as a seat in motor vehicles (SOWHAT, 1998). WC-19 intends to reduce the risk of injury for motor vehicle occupants who remain in their wheelchair during transportation. This WC-19 standard will evaluate the crashworthiness of all types of wheelchairs using a 20g/30mph-sled test simulating a frontal crash.
A computer simulation study highlighted the special requirements for transport-safe wheelchairs by investigating the crash loads applied to a wheelchair during a 20g/30mph frontal crash (Bertocci, Digges, & Hobson, 1996). Results indicated that transport wheelchair design criteria are more stringent than design criteria for pure mobility function. Two wheelchair structures that are particularly at risk for failure in a crash and have direct impact on occupant protection are seating systems and casters. This Task addresses the crash integrity of both of these critical components.
This project aims to advance the development of transport-safe wheelchair technologies which will present rehabilitation service providers with more suitable and a wider range of options for those clients seeking to travel in their wheelchairs. Currently, service providers must prescribe products that address the client's mobility needs without assurances of product crashworthiness.
Objectives
The product-driven hypothesis addressed in Task D-5a is that injury risk associated with the use of wheelchairs as seats in motor vehicles is greater than injury risk associated with the use of an OEM vehicle seat in a crash. It is postulated that the level of occupant protection offered by wheelchairs is substantially less than that provided in motor vehicle seat design. Accordingly, this task proposes to develop a transport-safe wheelchair seating system. Through implementation of this rigorous development plan, research in support of the ANSI/RESNA Seating Standard will also be accomplished. Wheelchair-seating systems will be evaluated using Federal Motor Vehicle Safety Standards (FMVSS) established for motor vehicle seats and sled testing protocols established in applicable wheelchair transportation standards. Injury risk of the wheelchair-seated occupant will be predicted for various seating systems through the use of a comprehensive risk assessment methodology based upon biomechanical tolerances and crash response excursion limitations. Based upon the findings of these evaluative efforts and existing criteria established for motor vehicle seats, design criteria will be developed for wheelchair standards intended to guide industry. Assuming the hypothesis holds true, a prototype transport-safe prototype seating system will also be designed following design criteria, fabricated and evaluated through the pursuit of STTR program funding.
Specifically Task D-5a is designed to:
1. Evaluate commonly used wheelchair seating systems following FMVSS 207 Seating Systems Testing Methods to determine crashworthiness.
2. Provide a comprehensive assessment of wheelchair user risk of injury in a frontal crash when using common wheelchair seating systems.
3. Develop wheelchair-seating system design criteria appropriate for crash conditions.
4. Transfer and implement research findings and techniques through wheelchair standards efforts, a design and applications guidelines document, and publications.
The product-driven hypothesis to be evaluated in Task D-5b is that common wheelchair caster assemblies are not crashworthy and will compromise wheelchair user occupant protection in a crash. This hypothesis will be investigated through a comprehensive research plan which evaluates the crash performance of commonly used caster assemblies, analyzes the performance results and their influence on wheelchair injury risk, and defines crashworthy design criteria. Assuming the hypothesis holds true, a prototype transport-safe caster assembly will also be designed, fabricated, and evaluated.
Specifically, Task D-5b is designed to accomplish the following:
1. Evaluate crashworthiness of commonly used wheelchair caster assemblies.
2. Determine caster failure modes.
3. Analytically model caster assemblies and conduct stress and parametric analyses.
4. Through the use of crash simulations, evaluate the injury risk associated with common caster failures.
5. Develop caster assembly design criteria appropriate for crash conditions and transfer findings through standards efforts and publications.
6. Design, develop, and evaluate transport-safe caster assembly prototype.
Progress Report (12/31/99)
Crashworthy Wheelchair Seating
During Year 1 of this project we have focused on defining crashworthy design criteria, developing appropriate seating component test protocols and applying these test protocols to commercial wheelchair seating systems. Our commercial seating product component testing to-date consists of the following: 7 seat backs, 6 seat surfaces and 10 sets of seating attachment hardware. We have also begun to study the influence of seating system characteristics, such as surface stiffness and angle, on seat loading during frontal impact through the use of computer simulation techniques. Using the same computer simulation models, we have also begun to evaluate the influence of these seating factors on occupant crash kinematics and injury risk.
Preliminary seating system test results have shown that existing commercial seating components may not perform adequately in a crash. In tests of wheelchair seat backs, products failed at less than the target loading of 2300 lb. The maximum sustained loading of the tested seat backs was approximately 1450 lb. Wheelchair seats (horizontal surfaces) also performed poorly with failures occurring between 800-1800 lb, well below the target design load of 3800 lb. Only one seat support surface withstood the design load. Tested seating attachment hardware, which should be capable of withstanding approximately 3800 lb in a crash, failed between 600-1600 lb. Preliminary results from computer simulations indicate that seating characteristics do influence occupant crash kinematics which effect injury risk.
Wheelchair Integrated Restraint System (WIRS)
During Year 1 we have further evaluated our prototype WIRS design. The comprehensive WIRS evaluation consisted of finite element analysis, static testing (FMVSS 207) of the seating system to which the WIRS was adapted and static testing of the WIRS anchorage strength (FMVSS 210). All testing of the WIRS was successful. Dynamic frontal impact testing (20g/30mph) in accordance with SAE J2249 and ANSI/RESNA WC19 is planned for Feb, 2000. A series of sled tests will compare the occupant protection of the WIRS to a traditional vehicle-mounted occupant restraint system.
Progress Report (12/31/00)
A manuscript entitled: Wheelchairs as Motor Vehicle Seats: Seat Loading in Frontal Impact was submitted to the Medical Engineering and Physics Journal. The information contained within this manuscript will be key to aiding manufacturers in the design of transport-safe wheelchair seating.
The following papers (see publication list), which capture our 4th qtr 2000 progress on Task D5, were submitted to RESNA 2001 Conference. Each of these papers was submitted under the Whitaker Scientific Paper Competition.
Expected Outcomes
Design and operational guidelines established through this project for wheelchair casters and seating systems used in motor vehicles will provide industry direction for manufacturers and suppliers of these products. As such, a direct benefit to the wheelchair using population will be realized through improved wheelchair safety and occupant crash protection.
Publications/Reports
VanRoosmalen L, Bertocci GE, Ha D, Karg PE, Proposed Test Method and Evaluation of Wheelchair Seating System Crashworthiness. Accepted in Journal of Rehab Research and Development, Dec., 1999.
Bertocci GE, Szobota S, Ha D, van Roosmalen L, Development of Frontal Impact Crashworthy Wheelchair Seating Design Criteria Using Computer Simulation. Submitted to Journal of Rehab Research and Development, Dec., 1999.
Van Roosmalen L, Bertocci G, Adaptation of Integrated Restraint Technology for use in Wheelchair Transportation, Proceedings of IEEE EMBS Conf, Oct, 1999.
Bertocci G, Szobota S, Effect of Wheelchair Seating Stiffness on Occupant Crash Kinematics and Submarining Risk Using Computer Simulation, submitted to RESNA 2000 Conference, Dec, 1999.
Ha D, Bertocci G, Deemer E, Roosmalen L, Karg P, Evaluation of Wheelchair Seating System Crashworthiness – Wheelchair Back Surfaces and Attachment Hardware, submitted to RESNA 2000 Conference, Dec, 1999.
Deemer E, Bertocci G, Ha D, Wheelchair Seating System Crashworthiness: An Evaluation of Seating Attachment Hardware, submitted to RESNA 2000 Conference, Dec, 1999.
Van Roosmalen L, Bertocci G, Evaluation of Seat Belt Anchorage Strength of a Prototype Wheelchair Integrated Restraint System, submitted to RESNA 2000 Conference, Dec, 1999.
Van Roosmalen L, Bertocci GE, Hobson D, Karg P, Usability and Satisfaction of Wheelchair Occupant Restraint Systems Used During Motor Vehicle Transport, submitted to RESNA 2001 Conference, Dec 2000.
Van Roosmalen L, Bertocci GE, Effect of Wheelchair Integrated Occupant Restraint System on Wheelchair Tiedown and Occupant Restraint Design Characteristics, submitted to RESNA 2001 Conference, Dec 2000.
Van Roosmalen L, Bertocci GE, Leary A, Computer Simulation Validation of a Wheelchair Mounted Occupant Restraint System Under Frontal Impact, submitted to RESNA 2001 Conference, Dec 2000.
Leary A, Bertocci G, Injury Risk Analysis of a Wheelchair User in a Frontal Impact Motor Vehicle Crash, submitted to RESNA 2001 Conference, Dec 2000.
Leary A, Bertocci G, Design Criteria for Manual Wheelchairs Used as Motor Vehicle Seats Using Computer Simulation, submitted to RESNA 2001 Conference, Dec 2000.
Souza A, Bertocci G, Effects of Wheelchair Seating System Energy Absorption on Occupant Submarining Risk in a Frontal Impact Using Computer Simulation, submitted to RESNA 2001 Conference, Dec 2000.
We have also submitted a manuscript entitled: Wheelchairs as Motor Vehicle Seats: Seat Loading in Frontal Impact to the Medical Engineering and Physics Journal. The information contained within this manuscript will be key to aiding manufacturers in the design of transport-safe wheelchair seating.
Journal of Rehabilitation Research and Development
PITTSBURGH, Jan. 9, 2001
Progress Report (12/31/01)
During Year 3 of this project we have focused on defining design criteria for wheelchair seating used in transport. A primary intent of this effort is to provide manufacturers with guidance in the design of transport-safe wheelchair seating. In doing so we have attempted to assess seat loading during a crash using both experimental techniques and computer simulation. Experimental techniques have relied upon sled impact testing using the SAE J2249 surrogate wheelchair with an instrumented seating system capable of measuring loading during a crash. A manuscript detailing our results has been accepted for publication in Medical Engr & Physics. We have also worked closely with the ISO standards committee to develop a dynamic test protocol that will enable seating system testing independent of a specific wheelchair frame. This test method, in conjunction with our static seat test methods used in this study, have been compiled in a draft ISO standard. Using computer simulation we have also recently developed wheelchair design criteria for manual wheelchairs. Criteria established include seat, wheel, securement point and lap belt loading. Results of this effort have been recently presented in a Bioengineering Masters thesis.
Using computer simulation models, we have also evaluated the influence of seating design parameters on occupant crash kinematics and injury risk. We have found that seating characteristics do in fact influence occupant crash safety. A manuscript of this work is currently in review.
Publications
Bertocci GE, Ha D, Deemer E, Karg P, Evaluation of Wheelchair Seating Crashworthiness: Drop Hook Type Attachment Hardware. Archives of Physical Medicine and Rehabilitation, Vol 82 (4), April, 2001.
Bertocci GE, Ha D, van Roosmalen L, Karg P, Deemer E, Evaluation of Wheelchair Drop Seat Crashworthiness. Medical Engineering & Physics, Vol 23, No 4, May, 2001.
Bertocci GE, Manary M, Ha D, Wheelchairs Used as Seats in Motor Vehicles: Seat Loading in Frontal Impact Testing. Accepted in Medical Engineering & Physics, Oct, 2001.
Ha D, Bertocci GE, Deemer E, Karg P, Evaluation of Wheelchair Sling Back and Seat Crashworthiness. Submitted to Medical Engineering & Physics, April, 2001.
Van Roosmalen L, Bertocci GE, Ha D, Karg P, Feasibility of a Wheelchair Integrated Occupant Restraint Concept in Frontal Impact, Medical Engr & Physics, to appear in 23(10), 685-696, Dec, 2001.
Van Roosmalen L, Bertocci GE, Hobson D, Karg P, Preliminary Evaluation of Wheelchair Occupant Restraint System Usage in Motor Vehicles, to appear in Journal of Rehab Research and Development, 39(1), Dec, 2001.
Bertocci GE, Souza A, Szobota S, The Effects of Wheelchair Seating Stiffness and Energy Absorption on Occupant Frontal Impact Kinematics and Submarining Risk using Computer Simulation, submitted to Journal of Rehab Research and Development, May, 2001.
Progress Report (12/31/02)
The main purpose of wheelchair casters (front wheels) and caster-fork assemblies is to provide a stable base, and to make wheelchairs easy to maneuver. When a wheelchair is used as a motor vehicle seat, the caster and fork assembly require different strength requirements. Dynamic sled impact testing using a Hybrid III Anthropomorphic Test Dummy (ATD) seated in a wheelchair secured with a four point tiedown, revealed caster loads up to 7382N. Caster assemblies should be of sufficient strength to avoid catastrophic failure. A pendulum test instrument was developed to evaluate commonly available caster assemblies for their crashworthiness. Pendulum mass and pendulum arm length were established using methods based upon the conservation of energy. Caster and fork assemblies were then tested using the Pendulum Impact Tester (PIT) to assess their failure modes under dynamic loading. Failure modes obtained during tests of casters and forks independent of the wheelchair can be studied using the PIT and provide feedback to improve existing caster designs.Progress to date
The objective of year 4 of Task D5 was to determine wheelchair caster loading during frontal impact testing. Additionally, the effect of rear securement point location and wheelchair seat system performance on caster loading was evaluated. Another objective of this study was to develop a test method to dynamically test wheelchair caster and fork assemblies under crash level loading conditions. The final objective was to evaluate the loading characteristics of caster assemblies under dynamic impact equivalent to that experienced in a 20g/30mph frontal impact
Figure 1: Load platform to measure tri-axial front caster loading
Processes and Output
Peak caster loads (7209 N) were seen in impact scenarios where the wheelchair was secured high above the floor (457mm) and where the seat and back failed during the test. In the case where no seat failure occurred, low rear securement points lead to the highest caster loading. This preliminary study shows that seating system integrity and rear securement position can affect caster loading. Caster load magnitudes and patterns obtained from this study may guide manufacturers of caster assemblies in the design of crashworthy products.
A pendulum impact tester (Figure 2) was developed to evaluate the crashworthiness and loading characteristics of casters and forks independent of wheelchair frame. A commercial fork with a surrogate caster wheel and a commercial fork with a commercial pneumatic caster wheel were evaluated using different impact loads (based on dynamic impact test results) by varying the mass, height and angle of the PIT. Additional efforts will focus on matching the loading conditions of caster assemblies subjected to sled testing. Work is underway to test various commercial caster wheels and forks by measuring the displacement throughout the test an LVDT. Outcomes from this study will provide wheelchair and component manufacturers an inexpensive means to evaluate crashworthiness of caster-fork assemblies or other wheelchair components.
Figure 2: The Pendulum Impact Tester (PIT)
Peer Reviewed Conference papers (submitted/in progress)
Nethravathi Tharakeshwarappa BS, Linda van Roosmalen PhD, Gina E. Bertocci PhD,
John Duncan BS, Songfeng Guo PhD, and Rory A. Cooper PhD. Development Of A Pendulum Impact Tester To Evaluate Wheelchair Caster Crashworthiness, submitted for publication in the annual RESNA conference proceedings, December 2002.
Linda van Roosmalen PhD and Gina E. Bertocci PhD. Wheelchair Caster Loading During Frontal Motor Vehicle Impact, submitted for publication in the annual RESNA conference proceedings, December 2002.
Gina E. Bertocci, PhD and Linda van Roosmalen, PhD. Wheelchair Front Wheel Loading during Frontal Impact. For submission in the Journal of Rehabilitation Research and Development.
Service on Committees
ANSI/RESNA IDSA
RESNA, Journal of Rehab. R&D
Networking Activities
Wheelchair manufacturers: Sunrise Medical, Invacare, Froglegs, Pride Mobility, E&J.
Contact Person: Gina Bertocci
Acknowledgement:
The primary support for the WMRC is provided by
The Department of Rehabilitation Science and Technology (RST) of the School of Health and Rehabilitation Sciences
