Improving Wheelchair and Wheelchair Seating Crashworthiness
Other Participants: Tom Whelan (manufacturer), Sue Johnson (manufacturer), Jill Kolczynski (manufacturer), Mike Barner (clinician), Virginia Nelson (clinician), Bette Cotzin (clinician, transportation provider), Nathaniel Madura (researcher), Jennifer Whalen (student), wheelchair seating manufacturers, wheelchair users.
This is a development project that is aimed at improving wheelchair and wheelchair seating crashworthiness through three tasks:
This activity will support the long-term outcome of improved safety for wheelchair users, particularly in the van and minivan environments. The standard and test devices (SWCB and SWCSS) developed in this project will support the intermediate outcomes of increased availability and use of wheelchair bases and seating systems that are suitable and safe for occupancy in motor vehicles.
Expected Project Outputs and Short-term Outcomes
Expected short-term outcomes
Task P4.1: Completion of a Rear Impact Standard for Occupied Forward-Facing Wheelchairs and Demonstration of Feasibility in Prototype Designs
This task will begin with the revision and improvement of draft design guidelines for wheelchairs that provide enhanced occupant protection in rear impact. These draw on the work from the previous RERC and on-going complementary studies. The design guidelines will define wheelchair characteristics, head/back support geometries, and seatback and attachment hardware strengths associated with good wheelchair performance in a moderate-to-severe rear impact test. It is possible that solutions that incorporate rear-impact protection features would only be acceptable for wheelchair users who already need or use head back support during motor-vehicle travel, although rear-impact protection is an important feature for all travelers. If head/back support structures on the wheelchair are determined to interfere with the comfort and function of users, a vehicle mounted head/back support may be more appropriate, and these solutions will be explored in Project P3.
Unlike the development process for the frontal impact standards where many lightweight commercial wheelchairs already had sufficient frame strength to perform well under the frontal crash conditions, it is anticipated that most wheelchairs will require enhancements to meet the proposed forward-facing rear impact criteria. Therefore, the project will facilitate commercial wheelchair product improvement by identifying and demonstrating how wheelchairs can meet these proposed standards. Input from wheelchair manufacturers will be incorporated into the standards development process.
Specifically, the research team will work with the collaborating manufacturers to identify a set of candidate wheelchairs that represent the nominal characteristics of groups of wheelchair types (i.e., stroller-type, standard manual, pediatric power, adult power, etc). Wheelchairs that are more often used by populations that cannot easily transfer to OEM seating during motor vehicle travel, and thus can benefit most from rear-impact protection features, will be the focus. Based upon previous efforts related to identification of failure mechanisms in rear impact and determination of seat back loading in rear impact the design of the wheelchair, (particularly the seatback and head support features) will be enhanced to improve rear-impact crash performance. The improved performance will be verified using the dynamic test methods in the draft standard. The information gleaned from the process will be used to improve the forward-facing rear-impact draft standard and provide manufacturers with real solutions on how to achieve compliance.
This exercise will provide insight into the feasibility of creating successful designs, determine the potential impact on other wheelchair features/functions, and give a clearer idea of which wheelchair types are likely to be amenable to having rear-impact protection features built into the product. The activity will conclude with revision of both the design guidelines and draft forward-facing rear-impact standard to reflect new knowledge gained from the development process.
During the reporting period, the draft rear-impact wheelchair standard was approved at the committee draft (CD) level for Working Group (WG) 6 of Subcommittee (SC) 1 of ISO Technical Committee (TC) 173. The rear-impact test method and associated performance criteria will initially be implemented as a new informative Annex to ISO 7176-19 "Wheeled Mobility Devices for Use in Motor Vehicles." The comments from the CD voting process have been implemented in a new version of the Annex and it will be processed by ISO for a draft international standard (DIS) level vote.
During the reporting period, the draft rear-impact wheelchair standard was approved as a New Work Item (NWI) for Working Group (WG) 6 to Subcommittee (SC) 1 of ISO Technical Committee (TC) 173. The rear-impact test method and associated performance criteria will initially be implemented as an informative Annex to ISO 7176-19 "Wheeled Mobility Devices for Use in Motor Vehicles." The comments from the NWI voting process have been implemented in a new version of the Annex, which is being processed by ISO for a CD-level vote.
During the reporting period, the draft rear-impact wheelchair standard was revised and submitted as a New Work Item (NWI) for Working Group (WG) 6 to Subcommittee (SC) 1 of ISO Technical Committee (TC) 173. Per the working group decision, the rear-impact test method and associated performance criteria will initially be implemented as a new informative Annex to ISO 7176-19 "Wheeled Mobility Devices for Use in Motor Vehicles." We are now awaiting SC1 approval of the document as a New Work Item.
The draft rear-impact wheelchair standard was revised and reformatted with the intention to submit a New Work Item (NWI) for Working Group (WG) 6 to Subcommittee (SC) 1 of ISO Technical Committee (TC) 173. It has been agreed that the rear impact test method and associated performance criteria will initially be implemented as a new informative Annex to the existing ISO 7176-19 "Wheeled Mobility Devices for Use in Motor Vehicles." At the WG6 meeting in May 2009, new information was presented about a related standards-development effort that is underway in Germany. After discussion, the ISO working group agreed to find out more details about the German draft standard in an effort to harmonize the two standards. The resulting enhanced draft annex of ISO 7176-19 will be on the agenda for the Fall 2009 WG6 meeting, following which it will be submitted to SC1 for approval as a New Work Item.
The draft rear-impact wheelchair standard was revised and it has now gained consensus from the ISO working group to be incorporated in ISO 7176-19, Wheeled mobility devices for use in motor vehicles, as an informative annex. The latest draft is in the process of being reformatted for submission to ISO as a new work item per the ISO WG6 decision. The performance criteria for the draft standard have been reevaluated and are being revised to reflect the need to encourage or possibly require some level of seatback compliance during rearward loading. Two RESNA papers presented in June 2007 have raised awareness among manufacturers and other stakeholders on the need for improved rear-impact performance of current commercial wheelchair products as well as the types of design changes that are needed to enhance seatback performance. The next step is to submit the draft annex for ISO voting to obtain international input on the draft test procedures and performance criteria.
During the reporting period, the draft rear-impact wheelchair standard has been revised twice. The test methods in the improved standard has been used to conduct new tests and the revised performance criteria have been used to evaluate all rear-impact test data available to date. Two RESNA papers have resulted from this work. The draft standard was discussed at the last two ISO meetings and the group has decided to support an ISO new work item that will propose incorporating the draft as an informative annex to 7176-19.
This task will focus on improving the existing SWCB to expand its utility and scope of its application. The initial effort will be a sled test series to address the issues of the mass of the SWCB, particularly in the case where a seating system has a fully integrated seatback frame and attaches to the wheelchair base only through the hardware connected to the seatpan. A set of worst-case scenarios for seating failure modes and the concerns that have been identified by the wheelchair manufacturers to date will be fully defined, and a sled test series will be used to explore the key issues of, and solutions to, effective testing of these systems. Also, computer modeling will be used to investigate the effects of SWCB mass on seat attachment hardware shear loading and relative motion between the seating system and SWCB.
A second activity will use computer modeling and sled testing to explore the effect of anchoring the lap belt to the vehicle floor, the wheelchair base, and the wheelchair seating system to determine which test modes produce worst case outcomes and are therefore most appropriate for SWCB test protocols. The analysis will also assess differences in outcomes that may warrant additional tests to be added to the standard, or lap belt anchoring configurations that should be discouraged. The knowledge gained in the two activities above will be used to improve SWCB design, SWCB drawings, and relevant standards.
This past year, the standard-development efforts focused on the completion of a RESNA standard, RESNA WC-4:2010, Section 20 (aka WC20), which was approved in a ballot by the RESNA Committee on Wheelchairs and Transportation (COWHAT) in 2009, and a revised version of the standard passed the 30-day review process in May of 2012. WC20 will be published in July 2012, along with revised versions of Section 19 for complete wheelchairs (WC19) and SAE J2249 for WTORS, now Section 18 of RESNA Volume 4 (WC18). Manufacturers are currently using the surrogate wheelchair frame (SWCF) and test methods to evaluate their seating systems and there has also been interest in using the SWCF to evaluate separate seating components, such as seats and back supports, in addition to complete seating systems.
This year, the standard-development efforts focused on the completion of a RESNA standard, RESNA WC-4:2010, Section 20 (aka WC20), which was approved in a ballot by the RESNA Committee on Wheelchairs and Transportation (COWHAT) in 2009. Arevised version of the standard passed the 30-day review process in May of 2011 and WC20 is expected to be published later in 2011, along with revised versions of WC19 and SAE J2249 (now RESNA WC18). Manufacturers are currently using the surrogate wheelchair frame (SWCF) and test methods of WC20 to evaluate their seating systems and there has also been interest in using the SWCF to evaluate seating components, such as seats and back supports, in addition to complete seating systems.
This year, the development efforts related to the surrogate wheelchair base (SWCB) have resulted in a final test method and publication of an International Standard, 16840-4, that sets forth design requirements and performance requirements, criteria, and associated test methods to evaluate the suitability of seating systems for use as seats in motor vehicles. The standard also establishes requirements for seating-system labeling and seating manufacturer literature. A correspond RESNA standard, RESNA WC-4:2010, Section 20 (aka WC20), was approved in a ballot by the RESNA Committee on Wheelchairs and Transportation (COWHAT) in 2009 but is has been undergoing revisions based on comments received during the balloting process. WC20 is expected to be published later in 2010, along with revised versions of WC19 and SAE J2249 (now RESNA WC18). Manufacturers are currently using SWCB and test methods to evaluate their seating systems and there has also been interest in using the SWCB to evaluate seating components, such as seats and back supports, in addition to complete seating systems.
The development efforts related to the surrogate wheelchair base (SWCB) have focused on resolving remaining issues with regard to the test conditions that result in worst-case seating system loads in frontal-impact testing, as well as pursuing acceptance of the standards in the ISO and RESNA standards arenas. In the first part of the reporting period, a main barrier to progress was concerns raised by wheelchair manufacturers that the proposed use of a vehicle-anchored lap belt for generating worst-case loading on the seating system when testing with the SWCB is incompatible with the requirement that complete wheelchairs must be crash tested in Section 19 of the RESNA standard using a wheelchair-anchored pelvic belt. To resolve this issue, the RERC WTS conducted a series of sled-impact tests using a load-cell instrumented SWCB to quantify and compare the effects of anchoring the pelvic-belt portion of the occupant restraint to the wheelchair and to the vehicle floor, respectively, on seating-system loading. The test methods and results are presented in a 2009 RESNA paper and clarify that anchoring the pelvic belt to the wheelchair base frame produces worst-case loading on the seating system, thereby resolving this final barrier to moving ahead with completion of the seating-system standard - i.e., both wheelchairs and seating systems must be tested with the pelvic belt anchored to the wheelchair base frame or seating frame.
The ISO version of the standard on wheelchair seating systems used as motor vehicle seats, for which the SWCB was developed and designed, has advanced to the Final Draft International Standard (FDIS) level and FDIS voting was completed in early 2009. The new standard (ISO 16840-4) has now been approved although it has not yet been published. The parallel effort in the U.S. to implement a seating system test that uses the SWCB in the RESNA series of standards on wheelchairs and transportation has also moved ahead and the document (Section 20 of Volume 4 of RESNA wheelchair standards) has been approved through RESNA balloting. However, revisions to the standard based on comments received during the balloting process will be made in the next couple of months and the standard will be sent out for a recirculation ballot. It is expected that Section 20 of Volume 4 of wheelchair standards, "Wheelchairs and Transportation," will be published by early 2010. Manufacturers are already testing seating systems to the draft standard and it is expected that this number will increase when the standard is published.
Data from sled tests and computer simulations have been complied and summarized to address the remaining issues with using a SWCB to generically evaluate wheelchair seating system frontal-impact crashworthiness. These data and their implications were discussed in depth at the RESNA COWHAT meeting in June 2007 and also at the ISO WG6 meeting in October 2007. These discussions prompted further computer simulations and data analysis that are now complete, and the final recommendations for the standard have been implemented. The data show that the vehicle-anchored lap belt condition produces worst-case crash-dummy loading on seating systems during frontal impacts and that the SWCB mass of approximately 50 kg is appropriate for the scope of the standard. ANSI/RESNA WC20 is now ready to proceed to final ballot voting in the latter half of 2008. Several wheelchair seating manufacturers are now testing products to the draft standard and it is expected that this number will increase when the standard is published.
Since the project began in November 2006, three sled test series have been conducted along with associated computer modeling to address the issues of lap belt anchoring and SWCB mass. In general, the data show that a vehicle-anchored lap belt produces the worst-case loading scenario needed for testing wheelchair seating but some issues regarding the SWCB mass remain. The preliminary findings of this work were discussed at the ISO and RESNA standards meetings and the SWCB standards (ISO 16840-4 and WC20) were revised according to the study findings and the respective group consensus. The next steps to addressing the remaining questions on SWCB mass have been identified.
The success and promise of the SWCB has led to the complementary issue of how to test wheelchair frames independent of a specific seating systems, so that there are commercial products to accept the seating systems tested using the SWCB in accordance with ANSI/RESNA WC20 and ISO 16840-4. The solutions must provide wheelchair base/frame manufacturers of wheelchair frames/bases the same level of confidence and ease of testing afforded to the seating system manufacturers. The objectives of this task are to design, develop and validate a surrogate seating system for these purposes. While the primary function of the SWCSS will be to test wheelchair frames and bases, the SWCSS will also be used as a platform for limited testing supplemental postural supports. The following steps will be used in the development of a SWCSS:
During the reporting period, the latest design for a surrogate wheelchair seating system (SWCSS) was presented and made available to wheelchair transportation standards committee for incorporation in standards. The SWCSS will be implemented in a voluntary industry standard for evaluating the frontal-impact crashworthiness of wheelchair frames independent of commercial seating systems.
During the reporting period, the latest design for a surrogate wheelchair seating system (SWCSS) was evaluated in sled-impact tests and the design was finalized and documented in engineering drawings. The SWCSS will be implemented in a voluntary industry standard for evaluating the frontal-impact crashworthiness of wheelchair frames independent of commercial seating systems.
During the reporting period, the first prototype surrogate wheelchair seating system (SWCSS) was evaluated through dynamic sled testing to compare the loads it delivers to the wheelchair base frame and the crash-dummy kinematics generated with similar data from commercial wheelchair seating systems. The initial version performs well compared to planar commercial seating systems, which are the primary style of aftermarket seating for people with specific medically-related seating needs. A second-generation prototype SWCSS was then developed to allow for inward loading on base frames which typically occurs with more flexible fabric-based seating systems. The data from sled tests with this second-generation SWCSS are currently being analyzed to determine if the new design is an improvement over the initial design. In coming year, the design of the SWCSS will be further evaluated and finalized so that it can be implemented in a voluntary industry standard for evaluating wheelchair base-frame crashworthiness independent of commercial seating systems.
A series of sled tests was conducted using the load-cell instrumented surrogate wheelchair base (SWCB), which is described in Project 4.2, to quantify loads delivered to wheelchair base frame with different types of wheelchair seating. A new instrumentation array was developed and implemented on the surrogate wheelchair base to provide for measurement of triaxial loads at four points on the seat rails and four points on the back-support posts. The resulting data show that the use of fabric seating results in the highest normal and shear loads on the base frame, but loads applied to the back support are similar across seating types. These findings are consistent with the retrospective analysis of commercial wheelchair frame failure patterns in sled tests performed at UMTRI, which that showed greater frame damage with fabric seating. In discussions with wheelchair and seating manufacturers, it was decided to expand on the test series in the coming year to enhance the database and to establish dynamic loading targets for design of a surrogate wheelchair seating system (SWCSS) that can be used to conduct frontal impact tests of wheelchair base frames independent of commercial seating systems. An initial prototype of a surrogate seating system has been developed based on results of testing conducted to date, input from seating and wheelchair manufacturers, and analysis of the database of frontal-impact tests previously noted. The design of the SWCSS will be modified and further evaluated.
A retrospective analysis of the results of over 550 wheelchair crash tests was performed to determine patterns of wheelchair frame failure, and the results are being reported in a 2008 RESNA paper. The data indicate that the SWCSS needs to generate nominally worst-case downward and forward loading on the wheelchair base frame, and it must also generate nominally worst-case rebound loading of the crash test dummy into the seatback. The results of these analyses also indicate that fabric seating may deliver higher loads to the base frame than seating that includes a planar wood or metal base. These results and the implications for the design of the SWCSS were discussed with a group of manufacturers and clinicians in the Spring 2008. As a result of that meeting, a new series of sled tests using SWCB instrumented with seat and seatback load cells is planned to explore loading patterns generated on the wheelchair frame by different commercial seating systems.
During the reporting period, the process of developing a preliminary design for a surrogate wheelchair seating system was initiated through discussions with other researchers, wheelchair users, clinicians, and wheelchair seating manufacturers to determine how such a device is likely to be used and what types of commercial products will be most effected. An in-depth retrospective survey of over 500 dynamic tests was begun that will yield information on how commercial wheelchair frames fail during WC19 frontal impact tests. These data will provide information as to how surrogate seating should load wheelchair frames in order to represent a nominal worst-case seating system under frontal impact conditions. In addition, plans are underway to meet with a group of manufacturers and clinicians in the Fall of 2007 to review project findings and design ideas to date.
Last updated: 07.13.2012
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