XVI. Wheelchairs and Powered Vehicles


A. General



Nigel Shapcott, MSc; Steven Garand, MS
University of Pittsburgh, Pittsburgh, PA 15238; email: shapcott@pitt.edu

Sponsor: Department of Veterans Affairs, VA Rehabilitation Research and Development Service, Washington, DC 20420
(Project #B685-3DA)

PURPOSE--Current wheelchair users and prescribers have a large and increasing selection of wheelchairs to choose from, each having a variety of accessories that tune the wheelchair to individual need. Thus, users have the opportunity to select the wheelchair that is closest to being ideal. However, opportunity does not always translate into reality due to three factors. First is an information overload: a number of companies make wheelchairs in a variety of models with many configurable options for each: therefore, a huge quantity of information has to be searched in order to make the best selection. This information continually changes as new models, options, and companies enter the scene, and information from different manufacturers may be difficult to compare. Wheelchair standards information is not easily available. Secondly, there is the possibility of incorrect prescription or purchase of wheelchairs, particularly among first-time, inexperienced wheelchair users. Thirdly, there is a procedural barrier: time-consuming written reports and justifications are required to obtain funding for wheelchairs.

  The purpose of the Computer-Aided Wheelchair Prescription System (CAWPS) project is to develop a computer program that provides an effective, easy to use, and affordable wheelchair prescription aid to assist the team normally associated with such prescription: the user, the therapist, and the vendor. The computer program will provide easy access to expert prescription methodologies and currently accurate and comparable wheelchair information based on the ANSI/RESNA wheelchair standards. The computer program will provide assistance with the preparation of written reports and justifications necessary to obtain funding.

METHODOLOGY--CAWPS is being developed to address these problems. Based on information from ANSI/RESNA wheelchair standards, experts in wheelchair prescription, expert wheelchair users, and information from manufacturers, it will incorporate an interface that updates the system with new information on new wheelchair models that have been tested according to the ANSI/RESNA wheelchair standards.

PROGRESS--We have completed the CAWPS user interface, continue to develop linked databases of prescription rules, and have displayed and demonstrated CAWPS at RESNA, along with three papers on the system. We are engaged in ongoing negotiations with two companies to develop CAWPS as a product.

PRELIMINARY RESULTS--The analysis of approximately 200 questionnaires shows a need for the project among wheelchair prescribers, confirming our perception of a great interest in CAWPS: at RESNA approximately 20 organizations requested that they be considered as Beta test sites. The rules and information already exist to develop the system.

FUTURE PLANS--The system is being designed to enable the collection, recording and analysis of information on wheelchair prescription practices over time which could be used to provide input to educators, manufacturers, funding agencies, prescribers, and users. A proposal to develop an Internet-based database of wheelchair information ancillary to CAWPS is under development.



Rory A. Cooper, PhD; David P. VanSickle, MS; Brad M. Lawrence, BS; Michael L. Boninger, MD; Jess P. Gonzalez, BS; Rick N. Robertson, PhD
Department of Rehabilitation Science and Technology, and Bioengineering Schools of Health and Rehabilitation Science, Engineering, and Medicine, University of Pittsburgh, Pittsburgh, PA 15261; Human Engineering Research Laboratories, VA Medical Center, Pittsburgh, PA 15206

Sponsor: Department of Veterans Affairs, VA Rehabilitation Research and Development Service, Washington, DC 20420
(Project #B805-2RA)

PURPOSE--The number of individuals who use wheelchairs as their primary mobility is rising. This change is a result of improved technology: more people live longer and may require a wheelchair in their later years, and more survive the violent incidents that result in spinal cord injury. However, wheelchair rider comfort is only recently being addressed. During the last 10 years, there has been a great quantity of literature devoted to whole-body vibration leading to the development of the ISO 2631 standard. Among this literature, though, only a few articles deal directly with individuals with disabilities or specifically with wheelchair users. ISO 2631 will be used as a starting point for this investigation. It is the purpose of this research to acquire and analyze acceleration and ground reaction force data so that a wheelchair may be designed to minimize user discomfort from road irregularities.

METHODOLOGY--A simulated road obstacle course has been constructed and will be used with four rehabilitation and three depot wheelchairs from three different manufacturers. These wheelchairs have been instrumented with ground reaction force sensors (SMARTHUB) to determine the force and moment input from the road surface at the axles. During separate tests, the wheelchairs will be loaded with an ISO-ANSI/RESNA test dummy instrumented with accelerometers, and with a human subject. The subjects will use a bite-bar to measure acceleration at the head. Acceleration at the seat will be determined through an adaptation of the ISO 2631 standards. Data-logging will also be used to determine the acceleration profile of a typical day for five individuals who regularly use a wheelchair as their primary mobility. The acceleration data from the data-logging studies and the acceleration and ground reaction force data from the simulated road course will be used to validate and calibrate the existing ISO-ANSI/RESNA wheelchair fatigue tests. This data will also be analyzed to determine dynamic models for the wheelchair and rider. In addition to a ride comfort analysis, nine depot wheelchairs and nine rehabilitation wheelchairs (three models each from each manufacturer) will be tested to failure using the ISO ANSI/RESNA wheelchair fatigue tests, providing life-cycle information on the different types of wheelchairs. These results will allow clinicians and wheelchair riders to compare the ANSI/RESNA test results with comfort criteria when selecting a wheelchair.

PROGRESS--The SMARTHUB ground reaction force sensor and the acceleration system necessary for data collection have been designed and constructed. The SMARTHUB takes the place of one of the wheels on the user's own wheelchair. The accelerometer system is designed to clamp onto a frame member below the wheelchair seating surface. Both systems use a data logger based on a 68HC11 microcontroller (Motorola), designed and constructed especially for this research.

PRELIMINARY RESULTS--Preliminary results show that the transmission of vertical acceleration through the human body can be represented by an auto-regressive model. This model consists of four poles and two zeros. Nine depot wheelchairs have also been fatigue tested using the ISO/RESNA Double-Drum and Curb-Drop Machines. Only one wheelchair of the nine surpassed the ISO ANSI/RESNA Standard requirement of 200,000 Double-Drum cycles and 6,666 Curb-Drop cycles. Of the remaining eight wheelchairs, only one wheelchair completed the initial 200,000 Double-Drum cycles.

FUTURE PLANS--We plan to expand our testing by considering the effect that the seat cushion has on the transmittance of vibration to the wheelchair user. We also plan to increase the number subjects and conditions tested. These future studies will be aided by the extensive development of sensors done in the current research.




Pascal Malassigné, MID, IDSA; Audrey L. Nelson, RN, PhD; Mark W. Cors, BFA; Carl H. Sutton, MD; Thomas L. Amerson, PhD
Clement J. Zablocki VAMC, Milwaukee, WI 53295-1000; James. A. Haley VAMC, Tampa, FL 33612-4798; Department of Physical Medicine and Rehabilitation, Medical College of Wisconsin, Milwaukee, WI 53226

Sponsor: Department of Veterans Affairs, VA Rehabilitation Research and Development Service, Washington, DC 20420
(Project #B768-DA)

PURPOSE--The purpose of this project was to design a new bowel care/shower chair that can be safely and efficiently used by SCI and other disabled users who cannot transfer to the toilet. The chair must provide access for caregivers. Because bowel care procedures by SCI individuals can take from 30 to 90 minutes, proper seating posture and comfort is necessary in order to prevent pressure ulcers, a serious threat in older designs of bowel care chairs. During a pilot study, several features of existing models were found to be less than optimal: space access for digital stimulation, seat design and cushioning, armrests, footrests, backrest, brakes and the size of the wheels in relationship to the positioning of the chair to the wall.

METHODOLOGY--The procedure used by the investigators to design this new chair included three phases: 1) design development and fabrication of bowel care/shower chair prototypes; 2) testing of the prototypes according to the ANSI/RESNA wheelchair standards; and 3) clinical evaluation of the prototypes with patients and caregivers at the Milwaukee and Tampa VA Medical Centers.

PROGRESS--Eight chair prototypes were fabricated by Ortho-Kinetics, the collaborating manufacturer, and clinically evaluated with SCI participants. This evaluation involved the use of data instruments to collect caregivers and participant's opinions. From this clinical evaluation, design adjustments were made to the chairs.

  Wheelchair frame. The final design provides a proper seating position and hand access for digital stimulation without interference from frame and wheels. A production frame tubing of 3.2 cm was selected. This frame is designed for static stability of 15 degrees in forwards and rearwards tipping.

  Seat design. A final "C" shape seat was designed that allows hand access in three positions (front, left, and right) and safe transfer from another wheelchair. Various foam densities were evaluated with a pressure mapping system to determine an ideal density. The selected density distributes evenly the pressure created by the buttocks and the legs on the seat.

  Hand-ring development. A preference study, using three hand-ring diameters (27, 34, and 42 mm) led to the selection of the 34 mm as the preferred diameter for grasping. In addition, a coated finish provides grasping under wet conditions.

  Footrest development. A footrest providing a larger support area for the feet and an overall contoured shape for comfort and positioning was finalized. In addition a foot-lift to ease cleaning of legs and feet was successfully evaluated in the prototypes. This new foot-lift will be incorporated in the production chairs.

FUTURE PLANS--Following testing of the final chair design according to the ANSI/RESNA wheelchair standards, final production considerations will be addressed with Ortho-Kinetics the collaborating manufacturer before commercialization of the chair.




L.H.V. van der Woude; Dirkjan H.E.J. Veeger Dr; Rients H. Rozendal
Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Faculty of Human Movement Sciences, 1081 BT Amsterdam, The Netherlands; email: L_H_V_van_der_Woude@FBW.VU.NL

Sponsor: Institute for Fundamental and Clinical Human Movement

PURPOSE--We are conducting a systematic analysis of manual wheelchair propulsion from a combined biomechanical and physiological perspective, with the objective of eventually improving the mobility of the wheelchair-user combination. Central areas of interest are the impact of wheelchair design characteristics upon the physiology and biomechanics of the wheelchair user, with special reference to functional load and mechanical efficiency and kinetics, loading of structures during mere manual wheelchair propulsion. From this, a set of theoretically based guidelines for wheelchair design and wheelchair fitting emerges.

  We also study the factors that determine work capacity and power output (among others, functionality and propulsion technique) of the wheelchair user. This should lead to guidelines of wheelchair training in sports and rehabilitation, as well as serving in the development of design and fitting guidelines.

METHODOLOGY--Wheelchair propulsion is studied during standardized submaximal aerobic wheelchair exercise and sprint tests on a motor-driven treadmill and during simulated conditions on different computer-controlled wheelchair ergometers. During the treadmill tests (used in studies on prototype evaluation, performance capacity, and propulsion technique), physiological measures are combined with 3-D kinematics and electromyography. Force measurements and kinematics during propulsion on the wheelchair ergometer enable an additional 3-D reconstruction of the movement pattern of arms and trunk, and the study of force and power production. Together with electromyography of upper extremity and trunk muscles and overall physiology, phenomena of the mechanical efficiency in manual wheelchair propulsion may be studied from a biomechanical and anatomical perspective.

  A detailed model of the shoulder-arm complex allows calculation of the contribution of different muscles on power production during static and dynamic activity of shoulder and elbow in wheelchair arm work and other tasks. Thus the high prevalence of repetitive strain injuries (RSI) in the shoulder and hand-wrist) among the wheelchair-user population may be understood more clearly. Arm work during different forms of manual wheelchair propulsion is thus studied: lever, crank, hubcrank, and handrim propulsion.

PROGRESS--Detailed studies were conducted on lever and (synchronic and asynchronic) crank propulsion in relation to different gear ratios. Results on crank propulsion indicated a significantly better performance using the synchronic mode. The levers showed a better performance when using a "high resistance-low speed" condition. Overall levers and cranks are much less straining and more efficient than handrims. The latter also holds for hubcrank propulsion: a continuous cyclic motion where both hands apply force to a crank mounted to the hubs of the rear wheels. This clearly is associated with the more natural coupling of the hand to the hand grip, its continuous bimodal motion and power transfer, and a more effective power transfer. The more natural coupling also appears beneficial to the stresses upon the hand-wrist area, which tend to be high in hand rim propulsion. Recent study of hand-wrist motions indicated, as before, large excursions around the flexion/extension axis and ulnar/radial deviation axis.

FUTURE PLANS--Fitting quidelines will be further refined for groups of disabled subjects, also during the process of rehabilitation. Detailed analysis of wheelchair arm work during handrim and other propulsion mechanisms must contribute to a better understanding of the mechanisms and risks of RSI and possible preventive measures in terms of wheelchair design or propulsion technique. Obviously, also the efficiency question will be further addressed.




Sheldon R. Simon, MD; Wayne E. Carlson, PhD; Donald L. Stredney; Rebecca Jackson, MD; Rosalind Batley, MD; Torsten Moeller; Po-Wen Shih
The Division of Orthopaedics and the Department of Physical Medicine/Rehabilitation, The Ohio State University, Columbus, OH 43210;

Sponsor: National Institute on Disability and Rehabilitation Research, Washington, DC 20202

PURPOSE--In an effort to utilize technology that can have a direct and immediate relevance to the problems confronting the disabled, we propose to examine human performance in negotiating barrier-free environments through the use of computer-generated virtual simulations. The project will be instrumental in defining standards for use in evaluating user proficiency, which will provide information for more suitable selections of enabling technology for the disabled. In addition, this research will demonstrate direct implications for the development of enabling technology through virtual testing and analysis, and provide improved methods for the design of barrier-free environments.

METHODOLOGY--We intend to interface Invacare's Action Power Evaluation and Training simulator with the capabilities for generating advanced computer simulations found at ACCAD. We will incorporate real world architectural databases, so as to maximize transfer from the simulator to actual user environments. We propose that this research will lead toward a practical interface for the disabled. The prototype can become a generic tool for use in analyzing and evaluating human performance, and provide us with new insight into the nature of disabilities and new understanding of certain limitations.

PROGRESS--We have developed a virtual-structure prototyping system that allows navigation by a person using a power wheelchair. The system is a tool for three groups of people: for architects and designers, it provides structure previsualization and analysis that can both improve the handicapped accessibility of building designs and test a structure for the compliance with the Americans with Disablities Act of 1990, which requires handicapped accessibility for (almost) all public structures. For wheelchair users, it provides more appropriate device fitting and training with wheelchair control systems. For health care professionals, it provides a system for assessing user performance and for determining the best power chair control mechanism for a particular patient.

  The system consists of an instrumented, joystick-driven power wheelchair connected to a high-performance graphics workstation that simulates the actual speed and maneuverability of the particular wheelchair within a virtual structure. The display generates realistic interiors containing multiple light sources and surface textures and is viewed in stereo through lightweight polarized glasses. The system maintains a hierarchical data structure that detects collisions between the virtual wheelchair and the environment.

  Pilot trials were run at the Ohio Supercomputer Center. Subjects included individuals with disabilities of varying severity and individuals from the nondisabled population. Simple steering tasks were performed and evaluated. Subjects were asked to navigate through a simple environment using the joystick controller. The hypothesis is that force feedback technologies can provide significant improvements in user performance.

RESULTS--To date, we have developed a robust system that provides previsualization of architectural data sets and assists in assessment for ADA compliance. In addition, the system provides an immersive environment for users to train themselves in the use of a power chair, therefore limiting the application of unsuitable technology that may never be fully, or even partially utilized.

  Current efforts include the completion of a communications protocol to allow a health care provider, working on a remote machine, to place moving objects in the path of the user. Currently, the system tracks and records specific tasks, performance time, and number and exact location of collisions (e.g., front-right, back-left). Recording collision positions is useful in assessing cognitive disorders such as side neglect. Additional tracks will include reaction times, and location of the object upon initial recation in relation to the user's field of view.



B. Seating Systems



Maurizio Ferrarin, PhD; Giuseppe Andreoni, DrEng; Antonio Pedotti, PhD
Centro di Bioingegneria, Fondazione Pro Juventute Don C. Gnocchi IRCCS, Politecnico di Milano, I-20148 Milano, Italy; email: ferramau@ipmel2.elet.polimi.it

Sponsor: Italian Ministry for University and Scientific Research

PURPOSE--This project, started 2 years ago, seeks to develop and apply an evaluation protocol to compare different types of seat cushions for wheelchairs. The aim is to define and measure some parameters (physical measurements, postural parameters, functional parameters, and so forth) useful for evaluating and comparing the performances of the different cushions under analysis. Applications are in the design of innovative products and in the optimal choice and adaptation of a product for the single subject characteristics.

METHODOLOGY--The main considered biomechanical data are the interface pressure between subject and cushion. In order to measure this variable, we use a device consisting of a thin matrix (42 rows × 48 columns) of piezoresistive pressure sensors (1 cm2 of area each) put into a pad connected with a personal computer with a particular software that allows us to store and represent all collected data. The PC runs dedicated software that elaborates data after acquisition to deal with artefact rejection, temporal and spatial filtering, spline interpolation of missing data, and then computes automatically the desired parameters. The main computed parameters are maximum peaks and mean pressures in particular areas under the buttocks. The most involved areas under the bony prominences are the ischial tuberosities, great trochanters, sacrum, and coccyx. Pressure distribution maps are also used to evaluate some postural parameters such as the asymmetry of load distribution, position of pressure centre with respect to the anatomical reference system and seat contour characteristics. These parameters are acquired both in static and in dynamic conditions, that is, during wheelchair propulsion.

  The cushions considered in this study are both commercially available and innovative prototypes. They present different characteristics: one is a contoured firm foam base covered by a gel pad, another is composed by rows of air-filled rubber balloons connected by narrow air channels in a flat rubber base, and the last two are formed by gel-filled and foam-filled rubber balloons with a foam base.

  A subjective evaluation of matters such as comfort and stability, taken from a dedicated questionnaire, is also considered and will be correlated with the measured parameters.

RESULTS--Three groups of patients have been selected: spinal cord injured patients without sensibility in lower limbs, multiple sclerosis patients with intact sensibility, and elderly subjects with motor problems. A total of 30 patients have been acquired, both in static and dynamic conditions, and data elaboration is still in progress. The already available data show interesting differences both between cushions and between groups. Moreover, the dynamic data seem very promising to evaluate stability properties of cushion.

FUTURE PLANS--This procedure will be applied on a more consistent number of patients, and the obtained data will be statistically analyzed looking for significance. The trend in time during long-term acquisition will be considered too.

  In the long term a new protocol will be developed to study particular variables that allow the change of some cushion parameters like thickness, gel distribution, and gel amount, in order to adapt the cushion to the single patient characteristics. The aim is to change in the best way the shape of the cushion to reduce pressures peaks and to improve patient comfort.




Steve Ryan, BESc, PEng; Denise Reid, PhD, OT(C); Patty Rigby, MHSc, OT(C); Wes From, MASc; Joy Sommerfreund, MEd, OT(C); Michael Doell, OCA; Kubet Weston; Ruth Wescott
Bloorview MacMillan Centre, Toronto, Ontario, Canada M4G 1R8; The University of Toronto, Department of Occupational Therapy, University of Toronto, Toronto, Ontario, M5T 1W5; Thames Valley Children's Centre, London, Ontario, N6C 5Y6; email: ortcsr@oise.utoronto.ca; ortcdr@oise.utoronto.ca

Sponsor: Ontario Rehabilitation Technology Consortium (funded by the Ontario Ministry of Health)

PURPOSE--The purpose of this project is to develop alternatives and improvements to the lap belts traditionally used to provide pelvic stabilization for some children who use wheelchairs. Consumers have identified a number of areas where current belting systems need to be improved. The end result will be a system that is easier to use and will provide children with better pelvic stabilization, resulting in better seating posture.

PROGRESS--Since fall 1994, we have completed the first phase of involved applying qualitative methodologies to acquire information regarding the product needs of consumers. The consumer groups included: occupational and physical therapists, parents and children, clinical technicians, and others. We have also completed an extensive review of relevant clinical and theoretical literature and have conducted a comprehensive product search. In consultation with consumers, a number of designs were proposed and critiqued, resulting in the development of four concepts to the prototype stage. Further in-house laboratory evaluations and the feedback from consumers have resulted in the further development of two prototypes: one concept enhances the function of traditional belts and the other replaces the belts with a completely different system. In collaboration with the Bloorview MacMillan (MacMillan site) Seating Service, one of the of the prototypes is currently in extended field trials with encouraging results. The second prototype is currently undergoing modifications with the expectation of field trials in the near future.

FUTURE PLANS--In the final phase of this project, we will complete the field trials and make the final design modifications before production. The dissimilar nature of the two current designs will allow us to market them both without competing with each other.




Steve Ryan, BESc, PEng; Patty Rigby, MHSc, OT(C); Wes From, MASc; Michael Doell, AOCA
Bloorview MacMillan Centre, Toronto, Ontario, Canada M4G 1R8; email: ortcsr@oise.on.ca

Sponsor: Rotary Club of Leaside (Toronto) Ontario Rehabilitation Technology Consortium (funded by the Ontario Ministry of Health)

PURPOSE--Many children with physical disabilities need custom-made seats to be comfortable and well-supported while in their wheelchairs. This creates safety concerns for automobile transport. Commercially available car seats are often not suitable because many of these children do not fit into them. As a result, parents use the custom-made seat from their child's wheelchair for this purpose. This arrangement may not provide adequate protection in case of a motor vehicle collision. The intent of this project is to develop a custom car seat for school-aged (5-12 years) children weighing from 40 to 75 pounds (18-34 kg) to meet general safety standards as well as their special needs for comfort and support.

  Another issue that concerns parents is how to transfer their child safely to and from the car without incurring back injury. To deal with this problem, the project includes the development of a portable lift and transfer device that can be conveniently used for this purpose.

PROGRESS--We completed a study to understand the ability and willingness of seating clinics to build custom car seats using a carrier restraint system. This research was significant because it showed for the first time that this new technology could be used to offer children with physical disabilities both custom support and the same level of occupant protection as other motor vehicle passengers. We proceeded to engineer changes to the prototypes for the restraint system and lift and transfer device. We conducted a series of crash tests to optimize the design of the restraint system and re-engineered the lifting device to enhance its consumer appeal and versatility. With the endorsement of our consumer advisory panel, we are now developing a new product: a modular seat to fit into our carrier restraint. This strategic move will allow us to establish a presence in the specialty car seat market. Ontario-based companies are being approached to determine their commercial interest.

FUTURE PLANS--If we are to manufacture these specialty products in Ontario, we need to actively support our partners during the commercialization phase. The prototypes for the restraint and lifting device are mature, but design enhancements and cost-cutting features will need to be incorporated before commercial products are realized. We will also finalize the standard restraint seat design. Since the production restraint must be certified to federal standards, we will oversee compliance tests and complete consumer and clinical instructions. In collaboration with our Ontario-based partners, new market niches and relevant distribution channels will be established for these products in North America and abroad. With appropriate industrial linkages, we hope to have these products available in 1997.




Steve Ryan, BESc, PEng; Patricia Rigby, MHSc, OT(C); Wes From, MASc; Michael Doell, AOCA; Jonathan Kofman, MASc, PEng
Bloorview MacMillan Centre, Toronto, Ontario, Canada M4G 1R8; email: ortcsr@oise.utoronto.ca

Sponsor: Rotary Club of Leaside (Toronto); Ontario Rehabilitation Technology Consortium (funded by the Ontario Ministry of Health)

PURPOSE--Modular seating systems are attractive to seating service providers because a variety of components can be combined to produce a functional product for many of their clients. However, these systems are reported by both clinicians and consumers to be unreliable, incompatible with many commercial wheelchair bases, and unusable for children with simple seating needs.

  The purpose of this project is to develop a new generation, modular wheelchair seating system to serve school-aged children who have mild-to-moderate seating problems. The system will include novel features that address needs identified by consumers and service clinicians.

PROGRESS--To help us understand how the product should be designed, we asked the opinions of more than 300 students, parents, and rehabilitation professionals through self-report questionnaires, focus groups, and group discussions. Various design concepts and models of the proposed system were created. During 1995, under contract from Special Health System Limited (Aurora, Ontario), we engineered two major design changes to adapt to more cost-effective manufacturing processes.

FUTURE PLANS--We plan to complete the development of a mature prototype of the new seating system over the next fiscal period. To evaluate the efficacy of the design, we will conduct both mechanical proof tests, clinical trials, and consumer testing. During this time, linkages will be established with a new industry partner.




Thongsay Vongpaseuth, BS; Beth A. Todd, PhD; Tera S. Bunn; Jared Box
University of Alabama, Tuscaloosa, AL 35487-0276; email: tvongpas@eng.ua.edu; btodd@coe.eng.ua.edu

Sponsor: None listed

PURPOSE--Open cell foams provide cushioning and precise positioning in many medical applications. One of the major applications is for wheelchair seating, where prolonged use can cause serious problems such as decubitus ulcers, or pressure sores, in the elderly and disabled because of inadequate pressure relief between the wheelchair cushion and the buttocks. In order to design cushions and supporting surfaces with open-cell foams, a thorough investigation and understanding of the foam material properties is necessary. In this study, three different types of commercially available open-cell foams are tested in accordance with the American Society for Testing Materials (ASTM) standards.

METHODOLOGY--For this study, three types of open-cell foams were used. These foams are Fire Resistant (FR) Polyurethane (PU), #6 PU, and PU Beige. Both coated and uncoated samples of these materials were tested according to ASTM D-3574-91, "Standard Methods of Testing Flexible Cellular Materials--Slab, Bonded and Molded Urethane Foams." Large and small deflection compression tests are used for this study. Samples dimensions of 15×15× 4 in (38.1×38.1×10.16 cm), 12×12×4 in (30.5×30.5×10.16 cm), 1.57×1.57×1.97 in (4×4×5 cm), and 4 in (10.16 cm) disks with a 4 in (10.16 cm) radius are being tested with the Instron Universal Testing Machine. For better data collection, a Data Acquisition System is being used.

PROGRESS--At this time, the compression testing of the foams is not yet completed. Data are still being collected and analyzed. However, some initial results are available.

PRELIMINARY RESULTS--As expected, the material property curves for the foam have both linear and nonlinear regions. It must also be noted that the sample size appears to affect the stress strain curve due to the contact between the foam and the sides of the indentor.

FUTURE PLANS--The current objective is to investigate the linear region of the material property curve. The analysis of the nonlinear portion of the data will also be performed along with further investigation of the viscoelastic behavior of the open-cell foam material.



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Last revised Wed 05/26/1999