توسعه و اعتبار تاثیر چرخ عقب در مدل شبیه سازی کامپیوتری راهنمای حمل و نقل صندلی چرخدار دستی بزرگسالان با سرنشینان

It has been shown that ANSI WC19 transit wheelchairs that are crashworthy in frontal impact exhibit catastrophic failures in rear impact and may not be able to provide stable seating support and thus occupant protection for the wheelchair occupant. Thus far only limited sled test and computer simulation data have been available to study rear impact wheelchair safety. Computer modeling can be used as an economic and comprehensive tool to gain critical knowledge regarding wheelchair integrity and occupant safety. This study describes the development and validation of a computer model simulating an adult wheelchair-seated occupant subjected to a rear impact event. The model was developed in MADYMO™ and validated rigorously using the results of three similar sled tests conducted to specifications provided in the draft ISO/TC 173 standard. Outcomes from the model can provide critical wheelchair loading information to wheelchair and tiedown manufacturers, resulting in safer wheelchair designs for rear impact conditions.

The Americans with Disabilities Act (ADA) [1] was introduced in 1990 to assure that all people with disabilities are granted equal opportunity to integrate into society. Part of the ADA mission is to establish equivalent safety with respect to transportation, so that all individuals may pursue employment, education, and recreation. There are 3.3 million adult wheelchair users in the U.S. [2], and a substantial number may not be able to transfer from their wheelchair to a motor vehicle seat during transport. These wheelchair users should have the same level of transportation safety as persons using motor vehicle seats. Wheelchairs are primarily designed to be mobile, and are often not intended to serve as motor vehicle seats, especially in a crash. ANSI/RESNA WC19 [3] wheelchairs have been designed to sustain frontal impact crashes, but because of differences in rear impact loading [4] and dynamics, they may not be able to sustain a rear impact crash. Previous studies have been conducted, investigating rear impact pediatric wheelchair and occupant behavior [5] and [6], but very little is known about adult wheelchair and occupant response in rear impact. Initial testing done at the University of Michigan Transportation Research Institute (UMTRI) found catastrophic failures [7] when ANSI WC19 wheelchairs were subjected to a rear impact crash pulse (25–32 km/h, 12–14 g) [8]. Rear impact collisions account for 43.5% of all motor vehicle crash related injuries [9] and 5.4% of fatalities [10]. Therefore it is important to further investigate the effects of rear impact collisions on the occupant, wheelchair, and wheelchair tiedown and occupant restraint system (WTORS). Sled testing is one method to perform this investigation, but has certain drawbacks. Sled test limitations include their time consuming nature, relatively high costs, and the inability to provide detailed wheelchair structure loading data. Computer simulation modeling addresses some of these limitations and can be an effective tool to supplement sled testing.

The dynamics of a frontal impact event differ from rear impact dynamics. In a frontal impact the ATD primarily loads the occupant restraints as it moves forward, while the rear tiedowns primarily secure the wheelchair by preventing forward excursion. The front tiedowns and seatback are then loaded minimally during the rebound phase of a frontal impact event. In rear impact however, the front tiedowns serve as the primary means of maintaining wheelchair securement and preventing rearward excursion, while the seatback serves as the primary means of restraining or containing the occupant in the wheelchair seat. Only during the rebound phase of a rear impact are the occupant restraints loaded. The 50th percentile Hybrid III ellipsoid ATD was developed by the software manufacturer, TNO, and was imported from the provided MADYMO™ database. TNO validated this particular Hybrid III ellipsoid model using frontal impact crash testing (48 km/h, 20 g), but the validation process involved only two sled tests and did not statistically compare the ATD model to the sled test outcome measures, but relied on ‘engineering judgment’ to confirm validity [22]. The imported ATD model was amended by adding an additional ellipsoid to the posterior upper torso (T1/T2 level) and by adding a contact between this ellipsoid and the ATD head. This was done because the ATD used our sled tests had a more prominent protrusion at the same location than the imported ATD model. Additionally, in all of our sled tests, the ATD head made contact with the posterior upper torso (T1/T2 level). The imported ATD model originally lacked this posterior head-torso contact because it was only validated in frontal impact [22]. In frontal impact, the ATDs head does not contact the posterior upper torso; rather, the chin contacts the anterior torso.