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Journal of Rehabilitation Research and Development

Rehabilitation R & D Progress Reports 1987

V. Wheelchairs and Powered Vehicles

A. General

B. Powered Controllers

C. Seating Systems

V. Wheelchairs and Powered c es

A. General

Evaluation of the Neutral Posture for Handicapped Utilizing Wheelchairs

Michael Krebs, M .D. and Jerome J . Congleton, Ph.D., P .E.Texas A&M University, College Station, TX 77843

Sponsor : VA Rehabilitation Research and Development Service

Purpose—The objective of this project was to buildand fit the neutral posture chair to three wheelchairs(Amigo, Everest/Jennings, and Alexis) . The neutralposture chair is a unique combination of a forwardsloping cultivator seat and an English saddle, withwrap-around leg trough support.

Progress/Methodology—I) Modify and install a neu-tral posture chair to fit existing Amigo hardware.The chair provided pneumatic adjustment of heightand, while seated, adjustment of seat pan tilt andbackrest angle and included a manual lock to stopseat rotation when desired as well as optional arm-rests . The handle bars and steering post were mod-ified to allow greater leg clearance, provide bend insteering post, and provide speed control linkage tohandle . A deflector guard was developed for thedual rear wheels.

2) Modify Everest/Jennings wheelchair and neu-tral posture chair for compatible attachment . Amodified wheelchair that can be collapsed and stowedin the rear seat of a vehicle by the user was provided.A Pos-chair with adjustment of independent seatpan and back rest tilt angle as well as armrestcontrols for actuation of seat pan and back rest tilt,mechanisms was provided . Materials and designmodifications to reduce overall weight of chair was

investigated.3) Modify Alexis wheelchair and neutral posture

chair . A Pos-chair was designed with electricalheight and tilt actuation and a seat pan and backrest bladder system . The mounting hardware on thewheelchair was redesigned to accommodate the newPos-chair interface and the armrest with controlassembly and footrests was added.

Preliminary Results—The prototype of the neutralposture chair for the Amigo is complete and userevaluation and feedback began in July, 1987 . Theprototypes for the Everest/Jennings and Alexiswheelchairs were completed and the user evaluation/feedback began in August, 1987.

Future Plans/Implications—Assuming user evalua-tion/feedback is positive and considerable advan-tages can be obtained, additional funding will besought . The neutral posture designed wheelchairswill then be compared to currently utilized wheel-chairs . The scientific methods utilized will be : but-tocks and thigh pressure measurements, stability ofthe chair and person (by measuring center of grav-ity), anthropometric measurements for work-placedesign criteria, and measuring the effect of bodyposture on force-generating capability.

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Wheelchairs and Powered Vehicles

Wheelchair Graded Exercise Test for Patientswith Lower Limb Disabilities

W.E. Langbein, M .S . ; D.K. Murdock, M .D.; C.J . Robinson, D.Sc . ; M.H. Hwang, M.D. ; B.A . Nemchausky, M .D.;R.D. Wurster, Ph .D. ; L. DynastHines Veterans Administration Hospital, Hines, IL 60141 and Loyola University School of Medicine,Maywood, IL 60611Sponsor : VA Rehabilitation Research and Development Service

Purpose—Wheelchair locomotion even under idealenvironmental conditions can result in elevatedlevels of exertion and fatigue . For some elderlypersons, and patients with cardiovascular and/orpulmonary impairments, manual wheelchair loco-motion may pose a significant health risk . If healthcare professionals must make judgments regardinga patient's capacity to endure the exertional stressof operating a manual wheelchair, give exerciseprescriptions for rehabilitation and/or develop aero-bic conditioning regimens, they must have appro-priate measurement tools for patient evaluation.

The problems addressed in research are to : 1)develop a device that will utilize the patient's ownwheelchair for graded exercise testing and aerobicfitness training ; 2) establish standardized maximaland submaximal wheelchair graded exercise tests toaccurately measure the cardiorespiratory fitness ofpatients who are restricted to the manual wheelchair;3) evaluate the sensitivity of the testing system fordetecting abnormal cardiovascular and pulmonaryresponses to exercise stress in spinal cord injured(SCI) and other persons with lower limb disabilities;and, 4) compare wheelchair experimental testingprotocol test data against data obtained from con-ventional arm crank ergometry.

Progress—New experimental graded exercise testprotocols are being designed and empirically eval-uated . These tests are analogous to the well estab-lished procedures for lower limb exercise testing,i.e ., bicycle ergometer, treadmill . Because the inten-sity of exercise on the Wheelchair Aerobic FitnessTrainer can be controlled it is possible to test patientswith very low to very high exercise tolerance. TheWAFT graded exercise protocols to be evaluatedare: a) sub-maximal, b) maximal discontinuous, c)

maximal continuous for the highly physically fit, d)maximal continuous for the average fit, and e)maximal continuous for the low fit and those at highrisk of coronary heart disease . Exercise tests ad-ministered on the WAFT, in accordance with theestablished protocols, can provide valid and clini-cally useful information regarding the locomotorperformance capacity and cardiorespiratory fitnessof SCI patients and others with lower limb disabil-ities.

Project tasks include : 1) recruitment of an ade-quate sample of subjects ; 2) complete modificationsto the WAFT ; 3) hire cardiac nurse with currentcertification in advanced life support ; and, 4) con-tinue laboratory bench testing of the WAFT toestablish the work done by the user at differentvelocities and magnetic resistance settings.

Preliminary Results—A prototype device called theWheelchair Aerobic Fitness Trainer (WAFT) hasbeen constructed and undergone pilot testing. TheWAFT was developed and is being evaluated by theRehabilitation, Research & Development Center,Edward Hines, Jr . Veterans Administration Hos-pital, Hines, Illinois . This device enables the patientto use his or her own wheelchair as a means ofexercise . Thus graded exercise testing on the WAFTcan give a more realistic evaluation of a patient'sfunctional capacity for wheelchair locomotion thanalternative modes of exercise . The exercise stresstest protocols to be utilized in this research projectwere explicitly created for the WAFT . The conceptof task specificity as applied to wheelchair loco-motion has been of paramount importance in thedevelopment of both the testing device and thegraded exercise test protocols .

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Rehabilitation R&D Progress Reports 987

Ergonomics of Manual Wheelchair Propulsion

R.H. Rozemdu ;L.H,V . van der Woode:I8.E.J . VeegerDepartment of Functional Anatomy, Faculty of Human Movement Sciences, The Free University, Amsterdam,The Netherlands, 1007MC

Sponsor: Innovative Research Programme/Aids fir the Handicapped

Purpose—ManualPurpose-Manual wheelchair propulsion is less eficient (8 percent) than other ways of human am-bulation (e .g., cycling, 25 percent) . The nature andcauses of this apparent drawback have to be under-stood if optimalization is to be realized.

The objective of the present research is to analyzethe driver-wheelchair interface in search of kiuc-ain!ogioa!, biomechanical, and exercise-physiologi-cal aspects of wheelchair propulsion on a straighttrajectory and on the dependence of driver, vvbceicbair, and interface-related variability.

Progress-.—Wheelchair types were tested on a motordriven treadmill : lever- and crank-propelled wheel-chairs proved to be more efficient and less energy-costing than normal hand-rim propelled wheelchairs.A special racing wheelchair appeared the least ef-ficient (7 .5 percent max) . However, cardio-respira-tory responses, frictional losses due to rolling drag,and air resistance were lower . Hand-rim diameter

vvauofi_, ,ortaocc the smaller rims leading to moreefficient driving . Physiological responses and move-ment technique in propulsion depended on poweroutput (velocity, resistance) and on interface factors,such as seat height and shoulder position . Speedadaptation in hand-rim wheelchair propulsion oc-curred primarily by adapting cycle-frequency, push-duration, and work/push . Duration of the recoveryphase showed only a minor decrease, whereas thepush range remained constant.

Future Plans/Implications—A wheelchair simulatorwill become available in late 1987 . It will be com-puter-controlled, with dual controls and simulationsystems for asymmetric driving . Force transducersin the propulsion system, as well as the seat andback rest, will enable amore &boroughhionmecbuo-icul analysis . Movement registration and EMG willcomplete the kinesiologica analysis.

A Model for Optimization of Wheelchair Lever Propulsion

Clifford E. Brubaker, Ph.D. and Pradip N. Sheth, Ph .D.University of Virginia Rehabilitation Engineering Center, Charlottesville, VA 22903Sponsor : National Institute on Disability and Rehabilitation Research : Field-Initiated Research Program

Purpose—The purpose of the project is to developa model to predict and simulate optimum wheelchairpropulsion performance, from dimensional variablesand a limited number of performance factors, forwheelchair users . A necessary and more fundamen-tal goal is the development of a model to predictindividual force vectors for selected muscles of theupper extremity during a motion cycle.

There are four components of the project . Theseinclude: I) the determination of architectural modelsfor the selected upper-extremity muscles ; 2) theacquisition of kinematic, force, and muscle-activa-tion data for a range of wheelchair propulsion cycles;3) the formulation and evaluation of load-sharingalgorithms for the muscles during motion cycles ;

and, 4) the development of software for mathemat-ical

as has been made in the first threeof these areas . Data from cadaver dissections todetermine volume, belly length, pennation angle,optimum fiber length, and length and volume ratiosrelative to segment lengths and joint-to-muscle at-tachment distances have been obtained for eightupper-extremity muscles . These data are being com-pared with measurements acquired from MRI scans.

The development of the architectural model isbased on the work ofVVoddez et ul ., in the Neth-erlands. A 3-dimensional skeletal-link model basedon kinematic data has been formulated using IMP,

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a CAE software system for linkages and mecha-nisms . The initial model included 4 d .o.f. and 2segments . This model is currently being extendedto include motion for 5 segments (trunk, scapula,arm, forearms, and hand) with compatible d .o .f. forthe involved joints . IMP is being used to formulatethe equations of motion for the skeletal link model.

The IMP system has also been used to drive thelink model through wheelchair propulsion cycles tocalculate the mechanical advantages of the differentmuscles over a cycle. These data will eventually beused, along with the architectural model, to for-mulate the algorithms for prediction of the individualmuscle force vectors.

Preliminary Results—The results obtained to dateare of a preliminary nature . Dissections have beenlimited to two cadavers ; however, the results fromcomparison of measurements of lengths and volumefrom the MRI scans with direct measurements ob-tained by dissection have been quite good . Meehan-

ical advantages for simulated muscles (line forces)have been quantified as a function of joint torquesabout the shoulder and elbow axis in a preliminarymodel using the IMP system.

Future Plans—The activities to date represent lessan 1 year of work on a 3-year project . More data

will be collected to obtain representative values toestablish ratios for the architectural model variablesfor the selected muscles . One task to be performedduring the next period is the evaluation of severalload-sharing algorithms, based on optimum controltheory, that have appeared in the literature . Thisevaluation will be accomplished using kinematic andEMG data obtained during simulated level propul-sion.

Publication Resulting from This Research

A Spatial Musculoskeletal Model for Wheelchair Lever Propul-sion . Sheth PN, Brubaker CE, Proceedings of the 10thAnnual RESNA Conference 7 :486-488, San Jose, CA, June1987.

Functionality and Durability of Manually-Propelled Wheelchairs

R.H. Rozendal ; L.H.V. van der Woude; M.E . RoebroeckDepartment of Functional Anatomy, Faculty of Human Movement Sciences, The Free University, Amsterdam,The Netherlands, I007MC

Sponsor : Research Programme on Quality and Functionality of Aids for the Handicapped

Purpose—The purpose of this study was to analyzeindividual complaints and appreciations regardingmanually-propelled wheelchairs under daily use con-ditions, related to impairment, intensity of daily use,and wheelchair brand and type.

Progress—Instruments developed for the whole sam-ple were : a telephone questionnaire (180 items) takentwice, a failure-diary kept during a nine-monthinterval between interviews, and an activity-diaryduring a week in Spring 1987 . In 10 percent of therespondents, a technical examination of the wheel-chair, and an odometer mounted to the rear wheelof the wheelchair during a nine-month period, wereadministered in order to validate the instruments.Samples were drawn from populations of wheel-

chairs provided in 1982, 1983, and 1984 by the twomajor social welfare corporations in this country.Non-response amounted up to 75 percent or more,resulting in a total sample of N =609 respondentsfor the first telephone questionnaire.

Progress Testing is well under way and was to becompleted in the Fall of 1987.

Future Plans/Implications—The research will giveanswers to questions formulated, in as far as thecombinations of the variables will result in a con-siderable number of different cases ; contribute tothe methodology of this type of consumer research;and provide a basis for realistic and valid lab testson wear and tear of wheelchairs .

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Development of a Motorized, Adjustable Standing Frame

Bowker, Ph .D. and A.B. Liggins, M,Se.Department of Orthopaedic Mechanics, University of Salford, Salford M5 4WT, UK

Sponsor : University of Salford Venture and Enterprise Fund

PurposesFor handicapped, as for able-bodied chil-dren, the erect weightbearing position has immenseadvantages in maintaining health, compared withthe sedentary posture . For children for whom walk-ing or standing is impossible or difficult, the weight-bearing position can be obtained through the use ofa standing frame in which the child is held by three-point support in front of the knees and chest andbehind the buttocks . Understandably, however, thedaily standing session is not welcomed by thesechildren, who see it as twenty minutes of boring,wasted time, during which they are deprived of themobility of their electric wheelchair . The objectiveof this project was, therefore, to produce a motorizedstanding frame which combined the mobility of theelectric wheelchair with the therapeutic value of thestanding frame.

Progress—To date, a prototype suitable for childrenin the age range of 6-11 years has been designed,built, and subjected to trials with a group of hand-icapped children.

The prototype device consists essentially of asimple standing frame, which can be swung into thehorizontal position to facilitate the fitting of thechild, mounted on a motorized base. This basecarries two twelve-volt traction batteries, which

differentially drive two motors slung behind its rearwheels . Control is via a joystick mounted on apivoted arm, which gives a top speed of 3 .5 mph.All the components of the drive and control systemsare standard electric wheelchair parts, which enablesa system of proven quality to be assembled atminimum cost . The batteries and motors have aprotective cover, featuring lights which flash whenthe batteries are in need of charging . The detachabletable is suitable for schoolwork, for toys or games,or for feeding.

Preliminary Results—The frame has recently beentested with four children at a school for the physi-cally handicapped, and although a number of detaildeficiencies were highlighted, the overall conceptand execution were found to be most successful.Indeed, that the device had achieved the aim ofcombining the mobility of the electric chair with thetherapeutic value of the standing frame, was con-firmed when the children who tested our prototypechristened it, "The Stand-up Wheelchair ."

Future Plans—We now plan to build a pre-produc-tion model, making use of the experience gainedwith the prototype and improve the engineering ofthe main structure of the frame.

Development of a Protective Foot and Leg Guard for Use in Wheelchair Sports

S. Naumann, Ph.D., P .Eng.Hugh MacMillan Medical Centre, Toronto, Ontario, Canada M4G 1R8

Sponsor : Variety Village Sport Training and Fitness Centre, Toronto, Canada

Purpose—This study had the following objectives:1) to gather information on participation of theadolescent and teenage wheelchair population insports activities ; 2) to develop a guard which protectsthe lower legs and feet of adolescent and teen-agedathletes while playing wheelchair sports ; 3) easilyattaches to and detaches from a variety of wheel-chairs : and 4) will be manufactured at a reasonablecost .

Progress—A survey was conducted of children whocharacterize the subject population of this project.Information from the questionnaires served to clarifythe design criteria by identifying the cause andnature of injuries experienced by children playingvarious sports, their attitudes toward participation,and the potential for injury.

The guard is a rigid U-shaped structure, protectingbut not touching the shin and calves of the child's

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legs. It is constructed of a tubular aluminum frameinto which is fastened a polyethylene sheet . (Dif-ferent colors of polyethylene could be used todesignate different teams .) Prototypes of the guardhave been produced and evaluated for electricwheelchair floor hockey and manual wheelchairbasketball.

This project has proceeded through the combinedefforts of Variety Village and the RehabilitationEngineering Department at the Hugh MacMillanMedical Centre. The need was first identified by thestaff at Variety Village, who, with their clients,contributed design input and tested and evaluatedthe guards . Design development and prototype con-struction has been carried out at Hugh MacMillanMedical Centre.

Preliminary Results—Sixty-eight amateur athleteswere surveyed; thirty-seven in manual wheelchairsand thirty-one in electric wheelchairs . Only occa-

sional minor injuries (bruises) have been experi-enced and/or observed by the players, despite fre-quent collisions . Concern over potential injury tothemselves (including other parts of their bodies)was expressed by nineteen respondents . Game trialsshowed that the necessary shape of the guard causedsome limitations in the player's vision and move-ments. As well, the athletes indicated a generalresistance to the imposition of more protectiveequipment in their game . This is consistent with thelow incidence of injury and the lack of concern forinjury by the majority of players . From the results,it was determined that the provision of a guard toprovide physical protection is not necessary.

Future Plans/Implications—Future efforts should fo-cus on the development of new equipment andgames which have a low risk of injury inherent inthem in order to encourage greater participation inwheelchair sports.

Testing of Gel-Electrolyte Batteries for Wheelchairs

William E . Fisher, Ph.D. ; Rob E. Garrett, B .Teeh . ; Barry R . Seeger, Ph .D.Rehabilitation Engineering Department, Regency Park Centre for Young Disabled, Kilkenny, S .A. 5009 AustraliaSponsor : None Listed

Purpose-The charge capacity of a liquid-electrolytelead-acid battery can be determined by measuringthe electrolyte density using a hydrometer, but thisis not possible with gel-electrolyte batteries . Con-sequently, test equipment was needed to measurethe charge capacity of gel-electrolyte batteries.

Progress—A simple test rig was developed to meas-ure the capacity of the gel-electrolyte batteries usedto power wheelchairs . It has been shown that dis-charge testing with a simple resistive load is a goodindicator of battery performance when fitted to awheelchair . Our battery tester comprises a resistiveload, a timer, and a box housing the control switchesand electronics . The system was designed to be

simple to operate and suitable for use in a wheelchairmaintenance workshop.

Preliminary Results—Results of 166 tests revealeda wide scatter of battery life with different usersand also showed that, in many cases, the twobatteries used in a wheelchair became unequal incharge capacity after some time in use. It is rec-ommended that pairs of batteries should be chargedin series to overcome this problem . A scientificpaper describing the test rig and our results hasbeen accepted by the Journal of RehabilitationResearch and Development for publication in Vol.25(2), Spring, 1988 .

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B . Powered Controllers

UNISTIK Vehicle Controller : Safety, Reliability and Human Applications

Catherine W . Britell, MM.Spinal Cord Injury Service, Veterans Administration Medical Center, Seattle, WA 98108


Purposes—A control system (the UNISTIK VehicleController) has been designed to enable people withhigh quadriplegia and limited extremity function todrive a motor vehicle . In this study, engineeringsafety and reliability testing has been done on thesystem installed in a van . Engineering testing in-cluded lifetime testing of all servomechanisms andextended testing at elevated temperatures of thesteering servomechanism . A flexible driver stationfor training and evaluation was developed and in-stalled. Clinical evaluation of the van will be donein order to identify the types of disabled individualswho would benefit from the Controller and to createguidelines for evaluating and training prospectiveusers of the Controller.

Progress—Engineering safety and reliability testingincluded lifetime testing of all servomechanisms andextended testing at elevated temperatures of thesteering servomechanism . Following the tests, theservomechanisms were disassembled and checkedfor wear . Extensive road testing included simulatedfailures of van and controller subsystems . Clinicaltesting will consist of training 20 - 30 participants inthe use of the system . Participants will be high-level

quadriplegics, amputees, post-polio individuals, andindividuals with cerebral palsy and muscular dys-trophy. Training will include preliminary evalua-tions, in-vehicle instruction and on-road drivingskills and will be done at the Seattle VAMC.

Preliminary Results—Results of engineering safetyand reliability testing showed servomechanismswithstood lifetime and temperature testing . No ex-cessive wear was found on gears or bearings in theservomechanisms . Simulated failures of van andcontroller subsystems produced predicted and reli-able responses and proved the effectiveness of back-up systems for braking and steering.

Future Plans/Implications—The van will be clinicallytested at the Seattle VAMC . Results from clinicaltesting and engineering safety and reliability testingwill be incorporated into a production model of theUNISTIK Vehicle Controller system . Clinical test-ing will also identify who would benefit from thecontroller and define guidelines for training pro-spective users of the UNISTIK Vehicle Controllersystem.

Ultrasonic Head-Controlled Wheelchair and Interface

David L . Jaffe, M.S.E.Rehabilitation Research and Development Center, Veterans Administration Medical Center, Palo Alto, CA 94304

Sponsor : VA Rehabilitation Research and Development Center Core Funds ; Paralyzed Veterans of America

Purposes—The Ultrasonic Head Control Interface(UHCI) is a device designed to provide severelydisabled individuals (quadriplegics) with a means ofcontrolling devices such as wheelchairs in a sociallyacceptable and aesthetically pleasing manner.

Progress—In order to perform some tasks inde-pendently, severely disabled individuals must findcommunication pathways to replace the ones that

have been totally lost or amplify the ones that areimpaired . High-level quadriplegics have a particu-larly difficult time in replacing lost or diminishedchannels to the outside world since many of themcan only control muscles at their neck level andabove.

In this project, two Polaroid ultrasonic distance-ranging sensors are the basis for a new type ofhuman-machine interface . They emit inaudible high-

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frequency sound waves which propagate throughthe air until reflected by an object . A portion of thesignal incident on the object is reflected as an echoand is detected by an electronic system . The elapsedtime from transmission of the signal to the receptionof its echo is proportional to the round-trip distancefrom the sensor to the object . In this rehabilitationapplication, two separated sensors are directed atthe user's head . The , two resultant distance ranges,one from each sensor to the head, and the fixeddistance between the stationary sensors, describe atriangle whose vertices are the two sensors and theuser's current head position . A geometric relation-ship allows the offset from the base line and centerline of the two sensors to be calculated . Thisinformation is then used to map the user's headposition onto a two-dimensional control space . Thearray of distance ranging sensors can monitor thehead position of a severely disabled quadriplegicoperator to obtain command and control informationfor the operation of mobility, communication, androbotic devices.

In operation, the user of an UHCI merely tiltsthe head off the vertical axis in the forward/backwardor left/right directions . The translation of head po-sition information into electrical signals can mimicthe output of a joystick . Both can be used to controldevices to which they are attached, such as awheelchair, a communication aid, a video game, ora robotic arm.

The main advantage of this type of interface isthat no mechanical contact between the sensors andthe user's head is required . This effectively separatesthe user from the device being controlled . With thisunit, the user does not feel confined as with devicesin close proximity to the face or body, as frequentlyoccurs with other interfaces . He/she would thereforenot feel "wired-up" using it ; an important factor inits acceptance . The use of the remote sensing abilityof the UHCI should result in rehabilitation devicesthat are socially acceptable and cosmetically pleas-ing.

Preliminary Results—UHCI have been installed ontwo electric wheelchairs . The first is an E&J model3P equipped with a reclining Recaro seat and is inuse in France by a quadriplegic woman . The secondis mounted on an Invacare Rolls IV with a SoloProducts Power Pack and is being evaluated byspinal cord injury patients at this facility .

Both units have been operational since June, 1983.User evaluation has been performed with ten quad-riplegic individuals . After a short demonstration andtraining session, they were transferred into the chairand most were able to successfully navigate thechair without problems. Users stated that theypreferred the ultrasonic head control to the chin-controlled joystick wheelchairs that they had used.The device has proven to be easy to use . Its intuitiveoperation requires little focused concentration andthus does not result in user fatigue.

A generalized interface for a robotics applicationhas also been developed . As with the UHCI, therobot user will be able to select tasks and controlthe operation of a mobile robotic arm via headposition . Specifically, the vehicle's navigation pathwill be under the control of the user—its trajectorybeing "drawn" on a CRT with head motions.

A technical manual documenting the work on theUHCI, including background material, electronicschematics, computer program listings, explana-tions, and illustrations has been compiled . Its in-tended purpose is to provide information that wouldallow a technically knowledgeable and adequatelyequipped engineer to construct a duplicate UCHIand apply it to the control of devices such as poweredwheelchairs . This manual has been made availableto over fifty interested investigators around theworld who are considering the UHCI for researchor commercialization.

Future Plans/Implications—Within the VA, a Re-quest for Evaluation has been submitted to theEvaluation Unit and approved . The funds for theproduction of four commercial prototype units havebeen received . A solicitation has also been publishedand a manufacturer is about to be selected from theresponses . The delivery of the four units is expectedone year after the award of the funds . These deviceswill then be evaluated at VA Medical Centersthroughout the country . Finally, a decision will bemade regarding the prescription of electric wheel-chairs using the UHCI technology for appropriateseverely disabled veterans.

Current Publications Resulting from This Research

Polaroid Ultrasonic Ranging Sensors in Robotic Applications.Jaffe DL, Robotics Age, March, 1985.

Human-Machine Interfaces . Jaffe DL, IEEE Short Course onRehabilitation Engineering, Palo Alto, CA, February, 1986 .

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A Study of Powered Wheelchair Controllers

Mark Hartridge, M .I .E. Aust . ; Barry R . Seeger, Ph .D.Rehabilitation Engineering Department, Regency Park Centre for Young Disabled, Kilkenny, S .A . 5009 Australia

Sponsor : Channel 10 Children's Medical Research Foundation of S .A.

Purpose—The number of children using electricwheelchairs has increased rapidly . New types ofwheelchair controllers permit alteration of thewheelchair response to user-input by limiting thewheelchair acceleration and by filtering the user'sinput signals in various ways . However, the extentof driving improvements, if any, has not beenobjectively demonstrated . With the provision ofindependent adjustments for aci -ration and signalfiltering, a practical problem al s in determiningwhich combination of settings /ill give the bestwheelchair control for

km' user. On currentcommercial products, wl ra p ; of accelerationand filter settings are provided s well as an ad-justment for maximum speed . At present, we areunaware of any information which could assist in

identifying combinations of settings likely to helpthe driving ability of various types of users . Suchinformation would be valuable in assisting wheel-chair users and therapists to optimize driving ability,and also in assisting manufacturers to improve theinternal software of their controllers, thus providingmore effective products for wheelchair users.

The aims of this study are : 1) to determine if newconcepts in electronic wheelchair control are effec-tive in improving wheelchair driving performanceof children with cerebral palsy, and to quantify anyimprovements; and 2) to establish procedures foradjusting controllers to obtain optimum driving per-formance . The outcome will be a protocol for es-tablishing optimum controller settings in order tomaximize benefits to users of electric wheelchairs.

The Development and Clinical Assessment of a Universal Wheelchair Controller System

M. Milner, Ph.D., P.Eng.,Hugh MacMillan Medical C

Toronto, Ontario, Canada M4G, 1R8

Sponsor : The Easter Seal Rese ,,Th Institute, Toronto, Canada

Purpose—This study — the following objectives:I) to develop a clo

wheelchair controllerthat will respond to 'tional and non-propor-tional interfaces ; 2) to t hnically and clinicallyevaluate the performance of the prototype controllerand the relative user driving response ; and 3) todevelop a manufacturing prototype of the controllerand seek a manufacturer.

Progress A unique wheelch s controller has beendeveloped that can interchal

, ly respond to bothproportional and r" ;dal el

interfaces . Thiscontroller income need control-loopwhich behaves in a n anion slim - to cruise controlsin modern automoLdes and au , radically compen-sates for environmental factors such as sidewalkslant, varying terrain and torque demands . For theclinician's convenience, the input circuitry of thecontroller was designed in such a manner that it

automatically recognizes the type of interface beingconnected to it and selects the appropriate decodingstrategy . Rapid interchanging of interfaces is there-fore possible for assessment purposes or as anindividual's physical condition deteriorates.

The back electromotive force (HEW) generatedby the permanent magnet motor, proportional to theangular velocity of the motor's shaft, is used inclosed-loop speed control circuit . An analogue errorsignal, proportional to the difference between theselected speed and the BEMF signal, modulates twobi-directional pulse train outputs in proportion toits amplitude and polarity . An analogue data selectoris used to direct the modulator's signals to theappropriate inputs of the MOSFET power bridge,and thereby derive the desired response from themotor.

A power MOSFET "H" bridge was developedto provide more efficient power switching to the

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wheelchair motors when operated at 20 kHz . Closed

ation rates are each independently adjusted vialoop dynamic and static braking circuitry was im-

potentiometers.plemented in the design. Acceleration and deceler-

Assessment Protocol for Prescription of Powered Mobility Devices

S. Jarvis, B .Sc., P.T . ; W . Lotto, M .D., F .R.C.S.(C), F .A.C .S . ; J . Staub, M.A., C. Psych . ; M. YoungHugh MacMillan Medical Centr e, Toronto, Ontario, Canada M4G 1R8Sponsor: The Hospital for Sick Children Foundation, Toronto, Canada

Purpose-This project studied predictors of suc-cessful powered mobility driving, with the goal ofpreparing an assessment protocol for the prescrip-tion of powered mobility devices . Currently, sucha protocol does not exist. It appears that eachprescribing Centre has a method of prescribingpowered mobility devices which is based in part onthe prescriber's clinical experience, and in equalpart on trial and error . The approach taken in thisstudy was to first determine which, if any, measurespredict powered mobility control, and then base anassessment on these predictors.

Progress—Fifty-seven subjects were seen in thisstudy: twenty-four were able-bodied subjects, andthirty-three were disabled. All were subclassifiedinto three age groups (i.e., 4-5, 6-7, and 8-9 yearsold).

Subjects were further classified according to phys-ical ability level (i .e., able-bodied, walk-with-aid,walked into clinic, non-walker) ; according to ex-perience with mobility devices (i .e., no experience,manual wheelchair, electric wheelchair, and pas-sively mobile) ; and, according to diagnosis (cerebralpalsy, diplegic and quadriplegic involvement, spasticand athetoid, spina bifida, spinal muscular atrophy,hemiparesis, and one subject each with quadrilateralamputations and head injury).

A large battery of standardized motor, perceptual,and intelligence tests was administered, including:Motor : Peabody Motor Development Scale ; Per-ceptual : Motor Free Perceptual Test and AyersSpace Visualization Test ; Intelligence : WISC-R orWIPPSI MAZES ; Raven Colored Progressive Mat-rices ; Peabody Picture Vocabulary Tests ; WISC-R

Picture Completion Subtest ; WISC-R Picture Ar-rangement Subtest; Representative Stencil DesignTest ; Vision Examination : carried out with 30 per-cent of the disabled subjects.

All tests in this battery were administered andscored in the standard way . In addition to this testbattery, four computer-based pre-driving tests, twocomputer-simulated driving tests and two actualdriving tests (wheelchair and remote-controlled driv-ing tests) were performed by the students . Pre-driving tests consisted of a targeting test, a trackingtest, a test of dynamic perception and a simplemaze. All driving tests (simulated and actual) usethe same five courses which were to be traversedin one of two speeds . These courses consisted of:1) straight-away ; 2) S-curve ; 3) sharp (90 degree) leftturn ; 4) backing up and sharp left turn ; and 5) twosharp right turns . For simulations and remote-con-trolled driving tests the courses were scaled to thesize and speed of the moving object.

Preliminary Results—Data collection was completedduring the summer and data coding and analysiswas commenced . All data processing is being carriedout using SYSTAT (version 2 .1) . Analysis steps tobe completed are : a) comparisons of means bysubject groups and age groups ; b) testing of regres-sion models for each of the test domains (motor,perceptual, spatial, verbal, pre-driving, simulationand remote) ; c) selection of predictors by test domainand subject (ability) group.

Publications Resulting from This Research

Assessment Protocols for Prescription of Powered Mobility De-vices . Jarvis S, Lotto W, Staub J, Young M, Verburg G,Rehabilitation Digest, 17(2) :12, 1986 .

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A. "Smart" Controller for Electric Wheelchairs

Ian R. Loudon and Paul NisbetBioengineering Centre, Princess Margaret Rose Orthopaedic Hospital, Edinburgh EHIO 7ED Scotland

Sponsor: Lothian Health Board, Scottish Education Department

Purpose—The aim of this study is to produce anadaptable and programmable controller which canbe used with a standard electrically-powered wheel-chair so as to allow the severely disabled user adegree of independent mobility . The controller willalso operate as a simple communication devicewhich will enable the same switches to be used forboth functions, thereby simplifying the learningprocess and providing greater incentive for thedevelopment of control skills.

Progress'We have produced two prototype con-trollers which are based on the Rockwell R65F12microprocessor and which are programmed in Forth.The controller is capable of monitoring bump de-tectors, proximity sensors, wheel position sensors,a line follower and several user inputs . The inputdevices include single and double switches, switchedand analogue joysticks and direct input from portablecomputers or communication aids.

The control software is written in Forth and iscurrently under development . It is based on a queueddata structure and uses a modular program construc-tion. By connecting the controller to an externalcomputer, the appropriate operating mode can beselected to suit the individual needs of the user.

The degree of assistance which the controller

provides varies from following a preprogrammedcourse to a completely user-controlled mode . Thespeed and acceleration of the chair can be limitedwhere appropriate and a number of experimentalcontrol systems involving feedback to the user byspecial joysticks are being investigated.

The safety of users with limited control abilitieshas been enhanced by the incorporation of bumpand proximity detectors which slow the chair downas it approaches obstacles and stop it in the eventof collision. Other sensors keep the chair moving ina straight line on uneven surfaces or allow it tofollow a path marked on the ground.

Future Plans/Implications—Trials will begin soonwith a group of wheelchair users who have no meansof controlling their chairs at present . This groupcovers a broad spectrum of physical and mentalhandicaps with several multiply-handicapped sub-jects . A variety of control schemes based on theprinciples of external physiological proprioception(developed by the Bioengineering Centre while in-vestigating the control of arm prostheses) will beadapted to wheelchair control by means of specially-produced joysticks . This work should improve thequality of control for all joystick users.

C . Seating Systems

Seat Cushions for the Paralyzed

Bok Y. Lee, M.D. and Leon Bennett, M .A.E.Veterans Administration Medical Center, Castle Point, NY 12511 and Veterans Administration Medical Center,New York, NY 10001


Purpose—The purpose of this project is to evaluatethe role of shear in pressure sore causation, toassess cutaneous buttocks blood flow of paraplegicsubjects with respect to pressure sore trauma, and

develop an instrument capable of sensing buttocks

blood flow for clinical prescription purposes.

Progress—Thirty-four paraplegic subjects have been

149


evaluated employing standard segmental Dopplerultrasound techniques, as used in the assessment ofocclusive arterial disease, and also local cutaneousblood flow in the region of the ischial tuberositieswhile seated, as given by harmonic analysis ofphotoplethysmographic pulsatile waveform . Thecorrelation is sought between known pressure soretrauma, as determined from a subject's medicalrecords over a prior 5-year period, and the variousblood flow measurements.

Serving as a control group, 23 normal subjectshave also been tested while sitting, yielding data onblood flow, pressure, and shear.

Preliminary Results—To test the hypothesis thatrepeated pressure sores in a given paraplegic subjectmay be simply the result of pure chance, a Poissondistribution has been constructed, employing theaverage possibility of an initial pressure sore onset,as evidenced by the subject pool (50 percent). Theresults suggest that chance is unlikely to explain thedistribution of multiple pressure sores : approxi-mately 5 times as many subjects develop 3 or morepressure sores over the test period as may beexpected to arise through chance . It follows thatthere is reason to seek a physical cause for at leastthose subjects exhibiting multiple pressure sores.

Analysis of paraplegic ankle pressure testing (an-kle/brachial) data, when plotted against the fre-quency of pressure sore occurrence, does suggestthat there is some connection between these events.That is, a least squares regression, based on a

straight-line relationship, indicates the likelihood ofmultiple pressure sores to increase as ankle pressuredecreases, implying a connection between multiplepressure sores and an impaired peripheral arterialcirculation . However, the level of significance(P=0 .08) is low, implying considerable scatter inthe results and a lack of specificity of application.

Testing for local buttocks circulation character-istics via photoplethysmographic harmonic analysis,and also plotting against the frequency of pressuresore occurrence, yields a similar qualitative trend:the more impaired the circulation, the greater thenumber of pressure sores . However, with this ex-perimental procedure, the quantitative aspects areimproved ; the level of significance (P=0 .008) maybe regarded as highly significant . In summary, ourresults strongly imply a connection between localbuttocks cutaneous flow and multiple pressure soreoccurrence.

Results concerning vertical shear effects uponanimal pressure sore threshold experimentation in-dicate that those tests conducted with small pistonsimpart much of the test load in the form of verticalshear, rather than pressure . Computations have beenprepared to illustrate the extent of the misassignedload, as a function of piston diameter.

Future Plans Additional measurements of circula-tion are to be assessed for pressure sore associationand all results will be incorporated into a technicalmanuscript.

A Comparative Evaluation of Special Seatingfor Severely Disabled Children

William E . Fisher, Ph.D., and Barry R. Seeger, Ph .D.Rehabilitation Engineering Department, Regency Park Centre for Young Disabled, Kilkenny, S .A. 5009 Australia

Sponsor : Channel 10 Children's Medical Research Foundation of S .A.

Pur' ose In recent years a number of special seatingsystems have become commercially available, andthis study was undertaken in order to comparespecial seating systems for use in Australia.

Progress—The subjects for this study were eightchildren with cerebral palsy or traumatic braindamage, who were selected because they requiredmore contoured seating than padded flat surfaces.The categories of cerebral palsy involvement and

seating options defined by Hobson and Trefler (1984)were used to define appropriate seating types.

We purchased a Pin Dot Modular System, aCanadian Posture and Seating Center Modular Sys-tem, a Matrix Body Support System, a MedicalEngineering Resource Unit Matrix, a Canadian Pos-ture and Seating Center Foam-in-Place System, andwe also included a Hexcelite seat and a Foam-andPly seat .

150


Results—A very satisfactory result was obtainedwith each seating system . They all rated very highlyin terms of both comfort and appearance, and theattainment of functional goals was dependent on theinitial setting of achievable goals regardless of theseating system chosen. The most dramatic differ-ences between seating systems were in terms ofcost, with the Pin Dot Modular being the mostexpensive, followed by the CPSC Modular, MERUMatrix, Matrix Body Support, CPSC Foam-in-Place,Hexcelite, and Foam-and-Ply being the least expen-sive . Other comments were that the Pin Dot Modularlooks very good, the CPSC Modular is easy to clean,

the MERU Matrix and the Matrix Body SupportSystem are easily adjusted, the Hexcelite Systemallows good ventilation and the Foam-and-Ply seatis highly versatile.

Publications Resulting from This Research

Towards Matching Needs with Technical Approaches in Special-ized Seating . Hobson DA

,iceedings ofthe 2nd International C

abilitation Engi-neering, Ottawa, 486-489,

A Comparative Evaluation of 3p

ting for Severely DisabledChildren . Fisher WE aid

, Australian Physicaland Engineering Sciei

li ne . Vol . 10, No . 3,September 1987.

Computer-Aided Prescription of Specialized Seats for Wheelchairs

Steven I . Reger, Ph .D.; Donald Meth, M .S . ; Thomas McGovern, M.S.Department of Musculoskeletal Research, The Cleveland Clinic, Cleveland, OH 44106

Sponsor : The Cleveland Clint( Foundation Research Institute

Purpose—This project will develop and evaluate thecomputer-aided measurement and prescription ofwheelchair seating supports . The scope of the pro-posed project does not include computer-aided man-ufacture of the personal body support : the focus ison the accuracy and validity of the computer-aidedmeasurement and prescription prm

A new concept in clinical data collection is pro-posed through the use of a computer-aided prescrip-tion seat (CAP-seat). The design will allow passivemeasurement of posture, pressure, and body con-tours. For the measurements, the patient will bepositioned in a subjectively established sitting pos-ture . Interactive adjustments will be carried outunder operator control using the pressure and con-tour information provided by the instruments . Theprototype fitting seat (prescription seat) will beevaluated with children and adult disability groupsselected from the clinical load of the ClevelandClinic Foundation . Postural and support data willbe transferred through a telephone modem to acentral location, removed from the sites of patientevaluation and fitting, for computer-aided manufac-turing of seat and supports .

Progress—Two sets of an 8-by-8 array of contourgauges have been built and mounted on the backand seat of the chair for the determination of backand buttocks contour . The software used in therapid collection of data from the fitting seat hasbeen developed and debugge n the IBM AT, usingPascal programming langui

he software hasbeen interfaced with the I/O na

1cluding anA/D board and a par d" Pt ' ma. u . 'a he contourgauges have also beer

'd and test data havebeen gathered. A soft\

n Me which transformsthe data points into contours has been written.These contours can be viewed

the computerscreen or they can be output to f

'hie plotter.

Future Plans/Implicatiom—Actua hiipe adjust-ments will be made by an array of low-pressurepneumatic cylinders acting under operator controlto deform the support surfi

wh le the Jbject issitting on it . Work is en

i thecomputer interface to the pneuma

ors .

151


Weightbearing Characteristics of Soft Tissuesfor Body Support Applications

Steven Reger, Ph .D. : George ET, selhobek, M.D.; Thomas McGovern, M .S.Depart ,,

Musculo

no

.'eh, The Cleveland Clinic, Cleveland, OH 44106

Sponsor: The Ci 'veland Clime inn tion Research Institute

Purpose—Ai

serials used in orthopaedics for

paraplegic male and female subjects lying supine onbody srnpot carry the risk of causing soft-tissue

3-inch-thick polyurethane foam cushions . The load-tra in

,e ause of the lo ad transfer at the interface .

ing conditions were : 1) no compression (unsup-How

, an objective . . sment of the support

ported, free-hanging) ; 2) body weight ; and, 3) a 10kgmate its for individual eed has not been devel-

sandbag resting on the right iliac crest for maximumoped. The efficacy of the load transfer from the

compression, Surface pressure was measured forsupport cushion to tht I ssues is limited by the

each load and location, and the soft-tissue springstiffness of the structm

carrying the load . For

constants were determined . The stiffness of theequal loads, a difference hi stiffness results in higher

support cushions were determined using the stand-deformation of the lower-stiffness component, which

and indentation load deflection test.leads to shear lo

id hammocking at the soft-tissue interface .

Results—Thicker tissues were observed in the nor-

The purpose of this work is to obtain a preliminary

mal subjects, leading to the conclusion that highercomparison of the vertical spring characteristics

pressure gradients must exist in the paraplegic Bs-(stiffness) of the composite soft tissues (muscle, fat,

sues than in the normal. Bony prominences in theskin) near bony prominences versus the vertical

paraplegic tissues "bottomed out" under body weightspring characteristics of common foam support cush-

alone, increasing the risk of tissue trauma. Theions .

stiffness of the Durafoam cushion showed a reason-able match to the spring constant of the paraplegic

Progress—In vivo soft tissue deformations under

trochanteric area . The performance of other (vis-three compressive loading conditions were obtained

coelastic) foam tested did not match the mechanicalfrom magnetic resonance images of normal and

properties of the soft tissue areas.

Toward Further Development of a Seating Systemfor the Physically Handicapped

W. Lotto, M.D., F .R.C .S .(C), F .A.C .S . and M. Milner, Ph .D., P.Eng., C.C.E.Hugh MacMillan Medical Centre, Toronto, Ontario, Canada M4G 1R8Sponsor : Easter Seal Research Institute, Toronto, Canada

Purpose—The eim of this project is to develop amodular seati system to meet the postural supportneeds of chit

with cerebral palsy . The specificgoals of the idy are twofold : 1) to design anddevelop a cost-effective modular seating system tomeet the postural support needs of children withcerebral palsy ; and 2) to assess the performance ofthe two types of modular seating systems fabricated.

Progress—A rev i

sett 1 its dispensed at theCentre demonst es tha trge percentage ofchildren with cerebral palsy have common posturalsupport requirements . It is intended that this pop-

ulation be fitted with a cost-effective modular seatingsystem.

A tubular steel frame was designed to hold theseat and back components of the seating system.Commercially available modular seat and back cush-ions were purchased and secured to the frame byindependent vacuum-formed ABS pans . An adjust-able headrest and polyester restraint straps for thetrunk and pelvis were also secured to these pans.

Two types of frames were designed : the first type,intended for mildly-involved children, is the "fixed"frame . The angle at which the entire frame isattached to the wheelchair is fixed at assembly . The

152


second type of frame, intended for moderately-involved children, is the "tilting" frame . While fixedto the mobility base, the entire frame is adjustableto any angle from the upright position back to a 40degree inclination . The angle between the seat andback remains constant . Both types of frames haveadjustable telescoping tubes to allow for growth ofthe child . Also, both frames have flush bases to

permit them to be positioned on a chair whenremoved from the mobility base.

Preliminary Results—Two of each type of the sys-tems have been dispensed as part of the study . Theresults of clinical and technical evaluations weremade available in 1987.

Comparison of Pressure Monitoring Systems

Thomas McGovern, M .S . ; Sandy Magnano, R .N. ; Thomas P . Stewart, Ph.D.; Steven I . Reger, Ph .D.Department of Musculoskeletal Research, The Cleveland Clinic, Cleveland, OH 44106 and Gaymar Industries,Inc ., Orchard Centre Industrial Park, Orchard Park, NY 14127

Sponsor: The Cleveland Clinic Foundation Research Institute

Purpose—The importance of pressure evaluation inclinical assessment of body-support systems is nowclearly recognized and used in many progressivehospitals and rehabilitation institutions . However,the transducers used in pressure evaluation areinconsistent, and the measurement technology ispoorly defined and varies among the institutions.

Factors affecting the results of pressure evaluationare many, but the important ones are : 1) the trans-ducer size and material ; 2) load shape and itsinteraction with the support material ; 3) the methodof endpoint detection ; and, 4) the uniformity of themeasurement technique.

The objective of the work was to establish agree-ment among the three most common pressure-evaluating systems, using a clinically acceptableprotocol . These results may subsequently serve todevelop correction factors for shape, size, andmaterial variations among transducers.

Progress—Interface pressures were measured by theScimedic, TIRR, and Gaymar pressure transducerson 10 normal volunteers by two experienced inde-pendent observers . The subjects were tested in thesitting and recumbent positions, using all threetransducers on three support systems successively.In the sitting position, the pressure was measuredunder the coccyx, ischial tuberosities, and trochan-ters . In the lying positions, the trochanteric andsacral pressures were observed . All measurementswere repeated three times by each observer, relo-cating the transducers each time . All pressure valueswere recorded, but only the highest of each threeobservations was used for the statistical analysis .

The support materials were blue "egg crate" foam(EC), high resiliency 3-inch-thick polyurethane foam(HR), and the constant-pressure "Sof-care" airinflation system (SC). The support materials weremade into seat-cushion and bed-cushion size padsfor the measurement of contact pressures . Recum-bent pressures on the egg crate foam were measuredon both single and double layers, but sitting pres-sures were measured only on double layers of thisfoam.

Results—Interface pressures were measured up to100 mmHg to minimize hysteresis effects in thevinyl transducer bags . The lower limit of the meas-urements was set by the Scimedic transducer, whichdid not provide readings less than 20 mmHg.

Linear regression analysis was performed on datacollected at the Cleveland Clinic, at Gaymar Indus-tries, and on the combined data from both locations.At each location, pressure values collected from 10subjects using one instrument were regressed onvalues measured on the same 10 subjects with asecond instrument . For the combined data, theregression was repeated using all 20 subjects.

All transducers tested behaved reliably and cor-related well to a significant degree. When the meas-ured pressure distributions were examined for cor-relations among transducers, the standard deviationswere 10-to-15 mmHg . The standard deviations amongcushion types, however, were in the range of 14-to-21 mmHg. This indicates more variance amongcushions using the same transducer at the sameanatomic location than among transducers on thesame cushion at the same anatomic location .

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Wheeled Mobility and I mproved Seating Systems

Warren G. Stamp, M .D. and Clifford E . Brubaker, Ph .D.Department of Orthopedic Surgery and Rehabilitation, University of Virginia Medical Center, Charlottesville, VA22908 ; and University of Virginia Rehabilitation Engineering Center, Charlottesville, VA 22903

Sponsor : National Institute on Disability and Rehabilitation Research ; Rehabilitation Engineering Center Program

Purpose—The University of Virginia RehabilitationEngineering Center (REC) is in the fifth year of a5-year program for research and development onwheelchairs and seating for the disabled . A part ofthe work on seating has been conducted in collab-oration with the University of Tennessee Rehabili-tation Engineering Program at Memphis under con-tract.

The emphasis at the REC is to conduct technicalstudies on all aspects of wheelchair and seatingdesign and function that will lead to a better under-standing of the principles involved, and therefore,contribute to improved design, fabrication, and pre-scription of wheelchairs and seating.

Progress—The REC has conducted some 23 tasksgrouped under 5 areas . The work accomplished ineach of these areas during the current period ispresented as follows:

Ergonomics : Propulsion efficacy was evaluatedat multiple work intensities for hand-rim and leverpropulsion in treadmill and dynamometer simula-tion, and for hand-rim, lever, and "poling" underreal conditions. Further model development wascarried out for optimization of wheelchair propulsionefficiency . Upper-extremity motion was evaluatedwith respect to variation in position over a three-dimensional array and at various work intensities.

Analysis and Design of Structural Componentsand Systems : Work has continued on the double-drum fatigue tester (which was adopted as the ISOstandard test device) to investigate the efficacy ofdifferent attachment procedures and to determinethe appropriate configuration and number of cyclesfor the test standard . Work has been completed onthe development of equations to describe the dy-namic behavior of castored mobility devices as afunction of load, speed, and perturbing forces.Structural analyses have been conducted on twolightweight commercially available wheelchairs, in-cluding finite element analysis . A PC-based finite-

element analysis program for wheelchair frames hasbeen completed and is being distributed at nominalcost.

Seating and Body Support .. The anthropometricdata base, which includes 80 variables relevant tospecialized seating, has been expanded for cerebralpalsy (CP) and spinal cord injury (SCI) populations.Work has continued to determine the effects ofvariation in position on spasticity in CP children.Comparisons were made for different cushions todetermine compression, shear and surface tensioncharacteristics . An evaluation was made of differ-ences in pressure distribution at the seat interfacefor flat and custom-contoured cushions of differentdensity foams. Comparisons were made for pressuredistribution of commercially available cushions amongpopulations of paraplegics (both spastic and flaccid)and quadriplegics.

Electromechanical Propulsion : A patent applica-tion has been filed for a contained-electrolyte proc-ess that could result in a significant cost reductionin the manufacture of extended-life batteries . Abattery charger control algorithm has been devel-oped and tested that predicts the optimum time tostop the charging process . Work has continued ondevelopment of fault-detection capability for pow-ered wheelchair components.

Product Design and Development : The UVA leverdrive has been redesigned as an add-on unit . It hasbeen successfully attached to commercially avail-able lightweight wheelchairs . The compact user-adjustable wheelchair has been redesigned to reduceweight and fold more compactly . Dynamic brakeshave been designed and fitted to commercially avail-able wheelchairs : these provide control on slopesor at high speed . They also function as parkingbrakes . A computer-aided manufacture (CAM) sys-tem for carving custom seat cushions is near com-pletion. This system utilizes data obtained frommeasurement of client surface contours to producethe three-dimensional seating surface .

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