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4 RERC ON WHEELCHAIR TECHNOLOGY

I. WHEELCHAIR TECHNOLOGY TASKS

♦PM-1 Improved Electric and Electromechanical Systems

♦PM-1 a Computer Simulation Electromechanical Systems

♦PM-1 b Power Wheelchair Batteries

♦PM-1 c Power Wheelchair Controllers

♦PM-1 d Improved Wheelchair Motor Drives

♦PM-2 Advanced Materials and Mechanisms

♦PM-3 Improved User Input Devices and Control Concepts

♦PM-4 Integration of Improved Mobility Components (removed from work program)

♦PM-5 The Use of Integrated Controls by Persons with Physical Disabilities

♦PM-6 New Concepts in Powered Mobility

♦PM-7 Powered Mobility Simulator

♦MM-1 Structural Improvements to Manual Wheelchairs

♦WP-1 Consumer Responsive Mobility Prescription Process

♦WP-2 Wheelchair Prescription Software Project

♦STD-1 Research in Support of Wheelchair Standards

5FINAL REPORT: 1993-1998

Approach and Background

The research approach taken was to address each

of the major electromechanical components of the

powered wheelchair independently within Tasks PM-

1-3. Task PM-4 was intended to integrate the

component results into a complete ‘idealized’ system.

Task PM-1 investigates each of the major drive system

components (batteries, controller, motors, and power

train) as interrelated sub-tasks.

The four sub-tasks of PM-1 are as follows:

PM-1a Electromechanical System Simulation

PM-1b New Technology for Wheelchair Batteries

PM-1c Improved Power Controllers

PM-1d Improved Wheelchair Motor Drives

The initial two years of the Task PM-1 involved a

major subcontract with Westinghouse Corporation.

Unfortunately, Westinghouse has undergone

significant downsizing and restructuring which has

lead to a reduction in resources (staff and laboratories)

that were initially available to this task. Progress was

impeded by this unforeseeable event as new resources

had to be identified and new team members brought

up to speed during Year III. By the end of Year III,

most collaborative work with Westinghouse had been

terminated and other resources identified.

PM-1ACOMPUTER SIMULATION OF

ELECTROMECHANICAL SYSTEMS

Investigators: Douglas Hobson, Dave Brienza, Fazal

Mahmood, Jonathan Evans

Rationale

Designers of powered wheelchairs have few tools

to assist in the design and development of new

powered wheelchairs. This task focuses on the

development of a computer simulation tool that can

aid designers during the decision-making process

regarding the selection of various electromechanical

components. The primary strategy is to optimize the

design towards the lowest energy consumption.

Other variables, such as tipping stability, can also be

optimized.

The initial thrust of this task was to model the

components of the wheelchair using a proprietary

simulation tool (HEAVY) developed by

Westinghouse, Inc. When it became evident that the

Westinghouse tool was not appropriate for

wheelchair simulation and considerable new code

would be required, the task was scaled back to focus

on a more limited design tool for industry. This

direction was taken at the advice of our Advisory

Board at its May 1995 meeting.

Goals

To develop a computer-based design tool to

facilitate the design of powered wheelchairs for use

by wheelchair designers.

Methods Summary

A computer program called HEAVY, originally

developed by Westinghouse Inc. when it was

involved in battery powered car research, was used

as the conceptual model for the simulation program.

Many algorithms had to be modified and others

added to make the model applicable to wheelchairs.

The original program was Fortran based therefore not

readily useable by desktop computers. Prior work

done at the University of Virginia-RERC on rolling

resistance, wind drag and power consumption was

used to make the model more applicable to

wheelchairs. Comments were solicited from industry

designers regarding the desirable outcomes of the

model. Once the simulation model was completed,

validation by actual wheelchair testing using a

prescribed test course was done to check the accuracy

of the simulation model. Refinements to the

TASK: PM-1 IMPROVED ELECTRIC AND

ELECTROMECHANICAL SYSTEMS


simulation tool was done over time by continued

validation testing using different types of

wheelchairs.

Outcomes Summary

Conversion to C ++ code for the simulation

program was completed. The simulation program

now includes program code to carry out the

simulations as illustrated in the following flow

diagram. First stage validation of the simulation was

completed. This was done using an on-board data

measurement/collection system while driving two

production wheelchairs through a prescribed test

course. Energy consumption was measured and

compared to the simulation results.

In order to verify the accuracy of the energy

consumption model, two powered chairs were

monitored while they completed the test track

outlined in the ISO standards (ISO 7176/6) for

determining the energy consumption and range of

powered wheelchairs. Our test course covered 200

feet with the dimensions of the rectangular track

measuring 50 feet on each side. Throughout the test,

the voltage and current were recorded using a lap

top computer, which acquired readings 200 times per

second. The results of the validation were then used

to compare the results obtained when running an

identical course in the computer simulation model.

Since we were unable to obtain the specific motor

and battery characteristics for the wheelchairs that

were tested, the program used data obtained for

motors and batteries with similar characteristics.

However, due to the power capacity of the Invacare

chair tested, the characteristics were thought to be

sufficiently different to effect the results of the

simulation program. Therefore, only the results from

the Quickie P-190 are were used.

For the Quickie P-190, the measured average

speed over the ISO test track was 5.67 ft/ second. The

distance traveled was 2000 ft. and the energy

consumed was 22.7 watt-hours. By using the ISO

guidelines for determining the range of the chair, the

range for the P-190 was determined to be 6.67 miles.

For the simulation, the motor data that was used

was the Fracmo M453-W30 24-volt DC motor. The

battery data was based on the MK 22NF Gel Battery.

Using the speed of 5.67 ft/sec. as input data, the

program then calculated the drag, the gear-box losses

and the air drag to determine the torque required to

overcome these losses at the specified motor RPM.

The drag losses calculated for P-190 was 35.5 pounds.

The wheel diameter is 12.5 inches; therefore, the

torque required to overcome these losses is 221.9 in./

lb. Use the look-up tables for the motor

characteristics, the available energy of the battery is

monitored at each 1-second interval in order to

determine the range. From the simulation, the energy

Figure 1 - Flow diagram of simulation process

• • • • • • • • ••

• • • • •

•

• • •


used while driving through the virtual ISO test course

was 52.86 watt-hours, yielding a total range of 3.86

miles.

The results of the simulation program vs. the

validation test show that the computer model

computes a range 42% less than the actual measured

results. This difference makes the use of the

simulation program impractical at its present stage.

More work is required to determine the source of

error.

It seems that the method used for determining

the drag may be incorrect. From studying how the

air, motor, and rolling drag are calculated, it appears

that the rolling resistance equations yield a larger

value than expected (32 lbs.). Accurate battery and

motor characteristics are also necessary for precise

comparative validation. Also, the effects of caster

drag, even on a firm rectangular test course, are not

adequately addressed by the simulation model. If

these deficiencies can be corrected, it appears that the

computer model can be a useful tool in studying the

effects that different batteries, motors, mass and frame

and wheel configurations have on the range and

energy efficiency of powered wheelchairs.

Recommended Future Research and Development

The C++ code for the simulation program

functions as intended. Additional experimental work

must now be done to refine the algorithms in order

to reduce the disparity between actual and simulated

values. Initial C++ code work was also done on the

modeling for static stability. However, now that the

newly revised versions of the ISO standards for static

(Part 1) and dynamic stability (Part 2) tests have been

completed, these simulations could be added to the

battery of tests. All information on the above

algorithms, program code and energy consumption

testing will be maintained on file, at least until

January 2003. This information can be made available

to any persons seriously contemplating additional

development of this simulation tool.

Publications

Alva, P and Hobson, DA, Computer simulation of poweredwheelchair electro-mechanical systems, Proceedings of theRESNA ‘96 Annual Conference, Salt Lake City, UT, June 1996

Hobson DA (in preparation)

PM-1B POWER WHEELCHAIR BATTERIES

Investigators: David Brienza, Douglas Hobson,

Mostafa Khondukar

Collaborators:Rick Blanyer, Steve Addington

(Electrosource, Inc.)

Rationale

The key component in any electrically powered

vehicle is the battery—the heaviest, most expensive,

and least reliable system component. The need for

improved battery technology is clear. Current

technologies used and the configurations made

available are far less than optimal for wheelchair

applications. For example, the basic configuration of

lead-acid batteries [Bode, 1977] limits frame design,

space for respirators, etc. Virtually every commercial

electric vehicle, including wheelchairs, uses a lead-

acid battery. For many years, lead-acid has been the

most reliable, cost-effective, and practical battery

available. It exists in its present form due to the

billions of dollars worth of research and development

aimed at improving both the battery and the mass

production process. These efforts, which were fueled

and funded almost entirely by the automobile

industry, have led to the optimization of a lead-acid

battery with respect to economics and the task of

starting a car engine. For application in wheelchairs

[Kauzlarich, 1990; Petersen, 1986; Lavanchy, 1992], the

lead-acid battery is much less than ideal. It is heavier,

more costly, and less reliable than desired, which is

not a surprising situation considering the fact that

the lead-acid battery was not originally engineered

and developed for motive power applications.

Project Goals

Our objectives for this task were:

• Review current and developing batterytechnology and evaluate its efficacy for use inpowered wheelchair systems,

• Identify one or more candidate batterytechnologies, acquire prototypes and evaluateperformance relative to wheelchair applications,and

• Disseminate findings and facilitate technologytransfer to wheelchair manufacturers.


Methods and Outcomes Summary

A comprehensive review of emerging battery

technology was completed and published as an RERC

Technical Report No. 2 (Bayles, 1995) and presented

at a national RESNA Conference (Bayles et al., 1994).

As a result of that effort, one candidate battery

technology was selected to evaluate for possible

application in powered wheelchairs. That

technology—the Horizon® battery—is an advanced

lead-acid technology developed by Electrosource, Inc.

of Austin, Texas. The Horizon battery is shown along

side a standard 22NF lead-acid battery in Fig. 2.

Although other technologies were considered, the

Horizon® was selected as the best battery available

for evaluation. The potential advantages are

improved energy density, improved specific energy

and a low profile design. A test plan including bench

testing and dynamometer testing was developed. The

load cycle used for testing is a variable discharge cycle

and is intended to be representative of typical indoor

and outdoor wheelchair driving. Bench testing has

been completed. Compared to commercially available

22NF gel electrolyte, lead-acid batteries, the Horizon®

battery demonstrated a 74% increase in specific

energy (40.6 Wh/kg vs. 23.3 Wh/kg).

A meeting was organized, including technical and

marketing staff from Electrosource, representatives

from three major wheelchair manufacturers, a

representative from one scooter manufacturer, and

the RERC staff was organized. At the meeting an

introduction to the new technology and preliminary

test results were shared. The research staff has no

knowledge of any further communication between

Electrosource and the wheelchair manufacturers.


Development of new battery technology has been

progressing more slowly than was anticipated in

1993. However, we expect that significant

improvements will be achieved. For this reason,

wheelchair industry representatives are advised to

stay informed and in the development loop so that

the specific requirements of the power wheelchair

may be accommodated in the packaging of any new

and significant battery technology.

Figure 2 - Horizon (right) and standard 22NF (left) lead-acid batteries

Publications

Bayles, G. New Power Source Technologies for Electric

Wheelchairs, Technical Report #2, RERC, University of

Pittsburgh, Pittsburgh, PA 1995.

Bayles, G., Ulerich, P., Palmer, K., and Brienza, D.M., New

Battery Technology for Powered Wheelchairs, Proceedings

of the 17th Annual RESNA Conference, Nashville, TN, June

1994.

References

Bode, H., Lead-Acid Batteries, John Wiley & Sons, NY, 1977.

Kauzlarich, JJ. Wheelchair batteries II: Capacity, sizing, and

life, J Rehab Res and Devel, 1990; 27(2):163-70.

Lavanchy, C. Comparative evaluation of major brands of

lead-acid batteries, Proceedings of the 1992 RESNA

International Conference, 1992;pp.541-43.

Peterson. HA. Development of test procedures for batteries

in electric wheelchairs, Report No. 86022, Energy Research

Laboratory, Niels Bohrs Alle 25, 5230 Odense M, Denmark.

PM-1C POWER WHEELCHAIR CONTROLLERS

Investigators: David Brienza and Wonchul Nho

Collaborators:Theodore Heinrich (Westinghouse

Inc.)

Rationale and Goals

Very little innovation has occurred in the

methodology used to control the power from the

batteries to the motors, which is the job of the power

controller. The objective of this development task was

to adapt an alternating current (AC) motor controller


technology developed for an electric automobile for

use in a wheeled mobility device.


An AC power controller using the vector control

technique was designed. An existing design

produced by the Westinghouse Corporation for

electric vehicles (EV) was modified and updated to

fit specifications developed for powered wheelchairs.

The vector controller consists of two portions,

software and hardware. Our initial work on this task

concentrated on the hardware dedicated to the high

current output stage of the controller, the motor drive.

The role of the motor drive is to convert stored energy

in the batteries to electrical power for the motors

according to the magnitude of a control signal

generated by the controller section of the device. A

block diagram of a typical electric wheelchair power

train is shown in Figure 3 below. The design for the

power controller has been completed. The new design

of the motor drive has been enhanced as compared

to the original EV design. The power switching

integrated circuits were upgraded using IGBT devices

and important performance gains were achieved with

the addition of a dead-time generator.

The design of the dead-time generator in the

motor drive has involved the theoretical

determination of three important parameters: carrier

ratio, modulation index, and time-delay. Depending

on the values and combinations of values of these

parameters, harmonic and wave form distortions can

be significant or negligible. The effect of the

significant distortions is a reduction in efficiency and

a momentary loss of control. Distortions in the

voltage-wave form have been investigated through

simulation. Distortions were determined as a function

of carrier ratio, modulation index, and time-delay.

Optimal values that minimize the distortion for both

fundamental and harmonic components of the

voltage-wave form in the output of the motor drive

were selected for three representative operating

conditions. The results of the simulation indicate that

the modulation index must be near unity, carrier

frequency is good at 15 kHz and a time delay of 10

msec is adequate. The application of these optimal

values should allow for significant improvement in

the output wave form of the motor drive.

Original plans for this task included the

fabrication and testing of a prototype controller; these

plans were not executed.

CONTROLLER

DRIVER

INPUTDEVICE

(JOYSTICK)

BATTERY

MOTORDRIVE

MOTORDRIVE

COMPUTER

IM

IM

Figure 3 - Schematic of the prototype controller

Publications

Nho WC, Brienza DM and Boston R. The development of

and AC motor drive in power wheelchair Proceedings of

15th Annual RESNA Conference, Salt Lake City, Utah, June

7-12, 1996.

PM-1D IMPROVED WHEELCHAIR MOTOR

DRIVES

Investigators: Douglas Hobson, David Brienza

Collaborator: Jules Legal

Rationale

Advancement of powered wheelchair options is

restricted by the availability of motor drive

configurations. This task explored motor

developments and specifically, motor/drive

combinations that will open new opportunities for

alternate wheelchair designs.

This task initially focused on the potential use of

AC motors and the improvement of DC motors.

However, it quickly became evident that the size of

the wheelchair market limits the development of new

motor technology specifically for use in the

wheelchair industry. Therefore, the focus was

redirected to identify existing technologies that can

be “re-packaged” in such a manner to offer new drive

options, such as a steerable in-hub motors and gear

train combinations.


Project Goals

1. To improve the availability of alternate wheelchair

motors/drive systems through forming working

partnerships with Federal labs and/or motor/

gear drive developers and manufacturers,

2. To work with wheelchair manufacturers in

evaluating the feasibility of introducing new

motor/train concepts and devices into new

wheelchair designs.

Figure 4 - Schematic of powered steering for front wheeldrive wheelchair

Outcomes Summary

Information and supplier literature was collected

on available motors and gear drives, such as the

Fracmo line. Direct communication was established

with Fracmo, which was followed by a joint meeting

with the Pitt-Westinghouse team in November 1994.

As a result, several prototype motor drives were

obtained and used in tasks PM-2 and PM-6. A

conceptual design was prepared and sent to a list of

manufacturers with the goal to identifying a firm that

wished to pursue a joint development project. The

same specifications were distributed throughout the

NASA technology transfer network in an effort to

identify new sources of motor/drive technology.

Finally, the following conceptual drawings were

prepared, complete with more detailed views and

specifications on the operational characteristics

required. These drawings and their contained

specifications will be used for future communications

with prospective motor/drive manufacturers.

Rearch and Development

As will be discussed in Project PM-6 below, the

commitment of a motor development and

manufacturing company will be necessary before any

new significant motor drive options will be made

available to the wheelchair industry. As part of the

PM-6 continuation plans, SBIR funding will be sought

to allow active participation by a motor company and

a wheelchair manufacturer in this effort to provide

alternate drive systems for indoor power wheelchairs.


Rationale

Powered wheelchair maneuverability is critically

important to many people that need to maneuver their

wheelchair in confined spaces. Most products today

use the same control strategy that was used in the

first powered wheelchair introduced by Everest and

Jennings in the mid 1950s. It relies on the independent

control of the two powered wheels, usually in the rear,

and the free motion of pivoting front caster wheels.

This task and PM6 are investigating alternate methods

for enhancing wheelchair maneuverability by

changing the fundamental manner is which the

steering is accomplished. Application of successful

findings to future products will increase the number

of environments accessible to persons using these

products.

The ability of a powered wheelchair user to

maneuver in tight spaces is closely related to the

chair’s drive and steering configuration. The most

common drive configuration, differential rear wheel

drive, consists of fixed and driven rear wheels with

front caster wheels. Direction changes are made by

individually varying the speeds of the rear wheels.

In this configuration the point about which the

wheelchair pivots lies on the line perpendicular and

running through the center of the rear wheels. The

minimum turning radius is achieved when the pivot

point is directly between the rear wheels. The

minimum space required to turn the wheelchair is

then determined by the maximum distance from that

point to any other point on the wheelchair. This is

usually the front corner of the footrests or the user’s

feet (Figure 5).

To minimize the turning radius for the rear wheel

differential drive configuration, the point between the

rear wheels must be located as close to the geometric

center of the chair as possible. Several commercially

available power chairs have achieved reduced turning

radius using this approach. Another benefit of this

approach is that a larger portion of the total weight

of the wheelchair is born by the drive wheels and

less by the caster wheels. The more weight there is

on the caster wheels, the more difficult it becomes to

change directions when caster wheels must reverse

directions and rotate through 180°. The approach,

however, causes the designer to take extraordinary

steps to provide stability. Typically, stability is

achieved by counter balancing the user’s mass over

and in front of the main drive wheels with the center

of mass of the batteries located approximately at or

just rear of the axis of the main drive wheels. It is

often necessary to provide anti-tip wheels in the rear

of the chair to avoid tipping backwards while

accelerating forward. The addition of these extra

wheels may compromise the chairs ability to climb

over low obstacles if the wheels are small or close to

the ground.

Figure 5 - Rear wheel differential drive configuration

Methods Summary

An alternate approach to minimizing the turning

radius is to steer all four wheels. Steering all four

wheels avoids the problems associated with caster

wheels yet retains minimum turning radius,

maximizes stability, provides tracking of the front and

rear wheels along the same path, and provides for

enhanced obstacle climbing capability.

TASK: PM-2 ADVANCED MECHANISMS

Investigators: Clifford Brubaker, David Brienza, Douglas Hobson

Collaborators: Jules Legal, Edmund LoPresti

front

caster wheelsin front

pivot point forminimumturning radius

fixed drivewheelsin rear


The challenge in designing a mechanical four-

wheel steering mechanism is to design a device with

the ability to turn each wheel through 180° while

minimizing misalignment of the wheels. Steering

linkages such as those used in automobiles owe their

simple design to the relatively small turning angles

required by that type of vehicle. For highly

maneuverable small vehicles such as wheelchairs, the

range of steering angle is much greater. Furthermore,

the wheels must maintain proper alignment over the

entire range of steering angles to avoid undesirable

wheel scrubbing when the wheelchair turns. The

wheels are properly aligned whenever the

perpendicular bisectors of all four wheels intersect

at a single point. In four wheel steering, this point

lies on a line between the front and rear wheels

running perpendicular to the fore-aft direction of the

base. This is illustrated in Figure 6. In two wheel

steering, the perpendicular bisectors of the front

steered wheels intersect at a point along the line

through the centers of the fixed rear wheels (Figure

5).

Outcomes Summary

A photograph showing a section of the

prototype steering linkage is shown in Figure 7.

A working platform that can demonstrate the

potential of the four-wheel drive configuration was

completed but the testing remains to be completed.


Future research and development should begin

by investigating the control issues concerning the

operation of a four wheel steered wheelchair. The use

of four wheel steering in the wheelchair application

introduces a dilemma for the control of that vehicle.

Optimum performance is likely attained when the

wheels can be left at arbitrary, but a known, steering

angle while the wheelchair is idle. Under these

conditions the driver knows which direction the chair

will initially go and there is no delay in initiating a

move. However, to make the direction of the wheels

known to the driver while the chair is at rest requires

the driver to observe the direction using a visual

inspection of the wheels or the direction information

must be provided using some other feedback

mechanism. Three options come to mind: 1) a visual

display on the controller panel; 2) tactile feedback

through the control stick using a rotation about either

the unused vertical axis or a rotation about the

steering axis; 3) no feedback at all. Although no

solution is ideal, a rotation of the stick seems more

desirable from the users perspective because it will

not require the driver to read a display, thereby

diverting his or her attention away from the

surrounding environment. The rotation option is

fronttypical pivotpoint

pivot point forminimumturning radius

Figure 6 - Wheel alignment for four wheel steering about asingle pivot point

Figure 7 - The complete linkage consists of two slidingmembers (A), four cam follower slots (B) cut into a flat plate(C), and two links (D) for each wheel.


likely more complex and expensive to implement. The

third option, no feedback at all, will require the driver

to sense the wheel direction by sensing the direction

of travel once motion is initiated; this option is likely

to be problematic in confined spaces where the chair

is close to obstacles.

The other alternative for control of the vehicle is

to program the controller to self-center the wheels

each time the chair stops. This solution is also less

than ideal. In this configuration, there will be a delay

between the time when the user steers the wheels and

when the chair is able to travel in the desired

direction. If there is no direction feedback for the

wheels, the user is required to perform a visual

inspection of the wheel direction or sense the direction

after initiating a move by observing the direction of

travel.

Publications

Brienza, DM and Brubaker, CE. A four-wheel steering

mechanism for short wheelbase vehicles. Proceedings

RESNA Annual Conference, Pittsburgh, PA, June 1997

Brienza DM and Brubaker CE. A steering linkage for

short wheelbase vehicles:Design and evaluation in a

wheelchair power base. Journal of Rehabilitation Res &

Dev.1999;36(1)

US Patent No. 5,862,874.


TASK: PM-3 INPUT DEVICES AND CONTROL CONCEPTSInvestigators: David Brienza, Wonchul Nho, James Protho, Patricia Karg,

Jennifer Angelo and Kimberly Henry

Rationale

The interface between the wheelchair user and

the wheelchair itself is often the most critical

component of the powered wheelchair. Hand

operated joysticks with proportional control are now

the traditional method of interface for most

wheelchair users. Sip and puff control, head control,

chin control, single switch are further options for

those that are unable to access the joystick.

Goals

The objective of this task was to review existing

input and controller technology and explore technical

options for enhanced performance, reliability and

safety given current market needs and the evolving

national standards for microprocessor-based

wheelchair controllers.


The results of a focus group meeting to identify

the most significant issues impacting input devices

and control concepts for powered mobility devices

held during the first funding period has been reported

(Brienza, et al, 1995).

A research and development plan consistent with

the needs identified by the focus group and

compatible with the goals and objectives of the RERC

was conducted. The long-term goal of this research

is to develop a control system that integrates

navigational and obstacle detection sensors into a

control system that assists the driver of a wheelchair

in both known, i.e., mapped, and unknown

environments. Potential applications of the system

include obstacle avoidance in known and unknown

environments, execution of predefined maneuvers

such as traversing through a doorway or following

along a wall, assisted navigation along predefined

paths through a known environment and as a driving

skills training device for powered wheelchair users.

Developments during the first project period

concentrated on the application of assisted obstacle

avoidance using a force feedback joystick. During the

second period the two control algorithms were

further developed.

Two philosophies have guided the design process:

1) ultimate control of the wheelchair must remain

with the driver and not with the control algorithm;

and, 2) mobility efficiency must be maximized.

Providing the user with the ability to apply the

decisive control input signals distinguishes this

wheelchair control system from that of an

autonomously guided vehicle. The driver remains in

control of the decision making element of the system

and at no time is an action initiated without allowing

the user to override the suggested action. Also, any

input action should result in a predictable response

from the system so that the user is not required to

decipher the control algorithm in order to accomplish

a desired task.

The object of the control system is to assist the

driver in negotiating obstacles as fast as possible and

with as little cognitive and physical effort as possible.

It is undesirable to slow down the wheelchair. This

would decrease efficiency or burden the driver with

excessive monitoring tasks, making the wheelchair

more difficult to drive. Instead our objective is to

influence the steering of the wheelchair using force

feedback from the active joystick. Note, however, that

the user may choose to counter the suggestions of

the control system by overcoming the joystick’s force

resistance.

Since the conceptual development of these control

modalities, this task concentrated on implementation

of a system for the evaluation of the concept.

An evaluation of a force feedback joystick for a

powered wheelchair was performed. The study aim

was to determine if the device enhanced the driving

performance of experienced wheelchair users. A

prototype device was constructed and used with a

virtual reality system for the evaluation phase of the


study. The force feedback joystick is shown in Figure

8. Test subjects used the force feedback joystick as a

prototype to navigate a wheelchair through a virtual

environment with and without the force feedback

algorithm activated (Figure 9). According to the

position of the wheelchair in the virtual environment,

the force feedback algorithm changed the compliance

of the joystick making it more difficult to move the

joystick in the direction of an obstacle. The factors

that were used to determine the compliance of the

joystick were 1) the angle between the wheelchair

velocity vector and the displacement vector of the

closest obstacle, and 2) the speed of the wheelchair.

The subjects were experienced power wheelchair

users with marginal ability to control a wheelchair

using a conventional proportional joystick. Their

performance using the force feedback joystick was

measured using the time needed to complete a run

through the course and the number of collisions with

the obstacles. The test course is shown in Figure 10.

The results showed that one out of the five subjects

who participated in the study had fewer collisions

when the force feedback algorithm was activated

compared to their performance when the algorithm

was not activated.

Figure 8 - Picture of force feedback joystick

Figure 9 - Picture of a subject using the system

Figure 10 - Diagram of test course.

Publications

Brienza, D.M., Angelo, J.A., Henry, K. Consumer

participation in identifying research and development

priorities for power wheelchair input devices and

controllers. Assistive Technology, July 1995.


Rationale

Persons with limited motor abilities and multiple

technical needs are able to access assistive

technologies through either many individual

switches or integrated controllers. There are no

guidelines to assist clinicians or consumers in

identifying persons who will be successful users of

integrated controllers.

Goals

1. To determine criteria necessary for successful use

of integrated controls by persons with multiple

technology needs and complex physical

conditions.

2. To identify service delivery components which

support the recommendation and provision of

integrated controls.

Methods Summary

A survey for interviewing successful users of

integrated controls was developed in conjunction

with the Office of Research at the University of

Pittsburgh. Survey topics included, but were not

limited to, user characteristics, environmental factors,

amount and type of training and back up and

maintenance of systems. Respondents were located

through clinicians that worked in North American

institutions that were multidisciplinary and known

for their work in assistive technology. Thirty

clinicians were contacted and assisted in the

recruitment process. The survey was administered

over the telephone and results tabulated and

analyzed. A Likert type ranking system was used to

analyze survey results.

Outcomes Summary

Twenty-four people with severe physical

disabilities, who used integrated controls,

participated in the telephone survey. The survey

focused on their satisfaction with areas related to use

of an integrated control device. Respondents were

generally satisfied with their integrated control

devices. A moderate correlation coefficient was found

between gadget appeal and satisfaction with devices.

The sample was self-selected and voluntary.

Three areas were identified as leading to

satisfaction with integrated controls. One, the

introduction of the integrated controller gave the

respondents a method of accessing devices that, prior

to receiving the controller, they were unable to

operate. Second, some form of training took place.

Either the trial or error or trial and error plus a manual

were used for training in cases where persons were

satisfied with their integrated controllers. This

information might help clinicians select a training

method. Finally, persons who liked gadgets were

more likely to be satisfied with integrated controllers.

A second survey was completed with clinicians that

recommend integrated controls. Issues affecting their

recommendation of integrated controls included the

availability of technical support and the comfort of

the clinician with the technology.

Due to the small sample size and the fact that the

group was self-selected, the results must be

interpreted carefully and should not be generalized

to the population of persons using integrated control

devices. Further studies need to be conducted to

support or refute these findings. One group that may

be surveyed is the population that has abandoned

integrated control device to examine why the devices

were abandoned. Another area that should be

investigated is how these results differ when

surveying children. The device procurement,

receiving devices all at once or over time, the learning

curve, and type of training may be quite different

depending on the age and experiences of the

individual user. This survey demonstrated that

persons using integrated control devices were, in

general, satisfied with them.

TASK: PM-5 THE USE OF INTEGRATED CONTROLS BY

PERSONS WITH PHYSICAL DISABILITIES

Investigators: Jennifer Angelo and Elaine Trefler


Recommended Future Research

Authors propose that a survey should be

conducted on the population that has abandoned

integrated controls. Another area that should be

investigated is how these results differ when

surveying children rather than adults. Finally,

training methods utilized with complex high

technology systems need to be investigated.

Publications

Angelo, J., Trefler, E. (1996). Surveying satisfaction of

integrated controls users. Proceeding of the RESNA

‘96 Annual Conference, Salt Lake City, UT, June 1996:

212-214.

Trefler, E and Angelo, J. Surveying Users of

Integrated Controls - A Pilot Study. Proceedings,

ARATA. Adelaide, Australia, October 1995: 17-19.

Angelo J and Trefler E, (1998), Satisfaction of Persons

Using Integrated Controls, Assistive Technology, 10.2.

77-83.


Rationale

Very few powered wheelchairs have been

optimized for activities conducted in tight indoor

environments. Reaching up and down, transferring

and maneuvering in confined spaces are examples

of these activities. Many older persons with

disabilities have need for such mobility products, but

will often reject the notion if it makes a statement

about their disability. Aesthetics is an important

component to acceptance and, therefore, it was given

high priority in this task.

Goals

1. To provide increased indoor powered mobility

options for consumers of all ages and disabilities

with emphasis on environments of older persons.

2. Refine commercially promising designs and

facilitate transfer to the marketplace.

Methods Summary

The PM2 Advanced Mechanisms task addressed

the wheelchair steering problem by using a

mathematically designed cam and linkage steering

arrangement. This task addressed the need for

increased indoor maneuverability by using two

software-controlled servo-steering motors to control

the position of the two front drive motors. A

prototype, termed the PM6-MKI was developed

which also featured a novel tiller-type joystick control.

The software algorithm compensates for the

difference in turning radius of the two front driving

wheels and thereby minimizes any wheel scrubbing

effect. (Figure 11). The front wheel drive motors used

in the prototype were Fracmo, Model: M453-W30,

previously developed by Legal and Hobson. First

stage comparative maneuverability testing was done

using existing powered wheelchairs typically used

indoors as the benchmark.

A second design, the MKII, which grew out of

TASK: PM-6 NEW CONCEPTS IN

POWERED INDOOR MOBILITYInvestigators: Douglas Hobson, Linda van Roosmalen

Collaborators: Jules Legal, Steve Stadelmeier

our relationship with the students and faculty in the

Design Department at Carnegie Mellon University,

is shown in Figure 12. The Quality Function

Deployment (QFD) [Jacques et al., 1994; Logan &

Radcliffe, 1997] tool was used to establish the design

criteria. This prototype addresses the need for

improved esthetics and self-adjustability of seat

height and angulation. Re-cycled motor drives

combined with a standard controller were used to

power the prototype. Two linear actuators control the

height and inclination of the seat.

The task plan called for the combining of the best

features of each prototype into a final demonstration

product. The full implementation of this plan was

dependent on the availability of a new motor drive

system, which was the focus of MK I prototype and

task PM-1d. In spite of several efforts at working

directly with motor drive manufacturers, we were

unsuccessful in convincing a company to invest

resources in a newly configured motor drive system.

Illustrations of the MK I and MK II designs follow.

Figure 11 – PM6-MK I Evaluation Prototype

TILLER-TYPE CONTROL

POWEREDSTEERING

STEERINGMOTOR


Concept illustration based on QFD criteria Working Prototype

Figure 12 - MK II Prototype

Figure 13 - Corridor Figure 14 - Bathroom


Outcomes Summary

a) Laboratory Feasibility Testing of the PM-6 (MK

I) Prototype

The purpose of the feasibility test was to compare

the maneuverability of the MK I prototype to that of

production wheelchairs designed for similar usage.

Two production wheelchairs, Quickie P190 and the

E&J Tempest, were selected for the tests. The tests

consisted of running the three wheelchairs through

three typical environmental spaces setup as a

laboratory test course. Each space was laid out

according to the dimensions of the Uniform Federal

Accessibility Standards.

The course setup consisted of the following three

spaces as shown in figures 13-16 below. The

dimensions of the test spaces are as follows:

Corridor: w=91.7 cm; Bathroom: w x d=152.3 x

142 cm; Elevator: w x d= 171.2 x 129.3 cm

Walls for each space were fabricated from

replaceable 3/4” thick polystyrene foam sheets,

which showed damage marks each time they were

contacted by a wheelchair.

Test Method

The MK I, Quickie P190 and the Tempest

wheelchairs were randomly assigned to 4 test

subjects, all non-experienced wheelchair users. The

subjects were all given the same time to become

familiar with the standardized test course. They were

then asked to maneuver through the test course, twice

with each wheelchair.

Time was measured for each wheelchair to

maneuver through each space. The time started when

the front feet of the test wheelchair passed the space

threshold line. The time was stopped when the

wheelchair exited past the space threshold line. Also,

within each space the number of hits with the course

“wall” was recorded.

The first space, the corridor, was entered in a

forward direction. The subject had to first steer the

Figure 15 - Elevator

Figure 16 - Overview of the complete course layout. Thelines indicate the required maneuvers.

Wheelchair Powered by Front wheel type Footprint

MK I Powered front wheels Steered powered wheels 80 x56 cm

Quickie P190 Powered rear wheels Swivel caster 107 x 61 cm

E&J Tempest Powered rear wheels Swivel caster 94 x 65 cm

TEST WHEELCHAIR DATA


wheelchair into the right corridor and proceed until

they could touch a designated point on the wall with

their hands. They then backed down the corridor until

they could turn right and exit through the entrance

corridor.

The bathroom space had to be entered in a

forward direction. An object on the simulated vanity

was touched. The subject then backed out of the

bathroom.

The elevator space was approached in a forward

direction. The subject then turned 180 degrees and

touched the simulated control buttons for the elevator.

The subject then exited the elevator forward facing.

Results

The test results were analyzed in such a way that

the maximum speed of each wheelchair did not

influence the outcome of the test. The sample results

of the tests are shown in the following graphs. The

first two graphs are for a single subject; the last two

are the averages for all subjects.

Figure 17 - Average test time of subject #1 per space for the three test wheelchairs

The graphs indicate that in most cases the PM6 -

MK I wheelchair resulted in the shortest test time and

the least number of inadvertent walls impacts. Little

difference was seen in the time needed for the

washroom test. The reason for this may be that the

overall maneuvering requirements of the space were

not extensive. Whereas, in the corridor test, most

subjects took substantially longer to maneuver with

the Tempest and the Quickie wheelchairs than with

the MK I wheelchair. Finally, the elevator test was a

time consuming task for all three wheelchairs. In

terms of wall impacts, the graphs indicate that the

PM6-MKI wheelchair clearly performed better then

the other two test wheelchairs.

Average Test Time 1

0

10

20

30

40

50

60

Corridor Elevator Washroom

Average time (sec)

PM-6: 4.48m2Tempest: 6.11m2Quickie P190: 6.53m2


Figure 18 - Average number of wall impacts by subject #1 for each test wheelchair

Figure 19 - Average number of wall impacts for all subjects for the three wheelchairs/spaces

Amount of Hits per W/C 1

0

1

2

3

4

5

6

7

8

9

1 2 3

Averageamount

of hits (n)

PM-6: 4.48m2Tempest: 6.11m2Quickie P190: 6.53m2

Average Number of Hits

0

2

4

6

8

10

12

14

Numberof hits (n)

PM-6: 4.48m2 0.5 2.5 1

Tempest: 6.11m2 12.5 12 4

Quickie P190: 6.53m2 11.5 8.5 2



Figure 20 - Average test time for all subjects for the three wheelchairs/spaces

Discussion

All wheelchairs used in the tests had different

‘footprints’, the MK I being the smallest. Therefore,

direct comparisons and any conclusions from the

results must be done with caution. For example,

reduction in the footprint size of the production

wheelchairs to that equal to the MK I wheelchair

would most likely improve their wall impact

performance. Also, the difference in maneuverability

times could be effected by the larger footprint size of

the production wheelchairs and not be totally due to

the enhanced maneuverability of the MK I prototype.

The Tempest and Quickie wheelchairs have front

swivel casters, which makes it impossible to

maneuver backwards from a forward maneuver

without first causing a lateral ‘shift’ of the front end

of the wheelchair. This was, in some cases, the reason

for higher number of wall impacts of the production

wheelchairs. Whereas, the MK I wheelchair, having

powered steering of the front wheels, does not exhibit

lateral shifting when reversing course.

Finally, because of the small size of the test

sample, no statistical analysis was attempted.

Therefore, it is only an observational conclusion that

can be drawn from this simplified feasibility test.

As mentioned, the MK I design also features a

uniquely designed tiller-type joystick. The idea is that

most elderly people will intuitively relate better to

tiller control (side to side movement to steer up and

down for reverse and forward, respectively). Also, the

direction of the tiller could be coupled electronically

to the direction of the steered wheels, so at start-up

there would be no directional surprises. Although this

joystick design worked well during the tests, no

comparative tests with the conventional joystick were

possible.

b) Development of the MK II Design

In brief, the purpose of the MK II design was to

explore the following criteria for an indoor wheelchair

that would provide:

• an alternative to the scooter for indoor/home use,

• an economic way to give elderly people mobility

in institutional settings,

• an alternative for the indoor/outdoor for home

to office use,

• an alternative for ADA accessibility into tight

workspaces, offices,

Average Test Time

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

40.0

45.0

Time (sec)

PM-6: 4.48m2 21.0 15.0 10.2

Tempest: 6.11m2 37.4 19.2 15.3

Quickie P190: 6.53m2 40.1 20.7 9.4



• a better way to vary the sitting height of a person

in a W/C, and

• a more esthetic and less stigmatizing way of

providing powered mobility.

Focus groups, user surveys and the Quality

Function Deployment (QFD) tools and the MK I

experience were used to explore questions and solicit

concepts leading to a list of weighted design criteria.

A sample questionnaire containing comments from

wheelchair users can be reviewed in Appendix A. The

summary results of the QFD analysis are also

contained in Appendix A. The MK II prototype shown

in figures 21-22 resulted from these intensive

planning efforts. The working prototype embodies

the following key features:

• a nontraditional frame and elevating/tilting seat

system,

• a ergonomically designed seat with swing up

armrests for ease of transfer,

• powered front wheels, castered rear wheels

allowing increased maneuverability in tight

indoor spaces. (Steered front wheels were

planned but suitable units were not possible to

obtain for the prototype construction),

• miniature integrated joystick control,

interchangeable between left and right armrests,

and

• a non wheelchair-like appearance intended to

minimize the stigma of disability.

The Mark II design was featured at the 1998

RESNA Conference exhibit. Interest was

demonstrated by clinicians, wheelchair users and two

prospective wheelchair manufacturers. Below are

several photos showing some of the features of the

MK II design.

Recommended Future Development

Given that both demonstration outcomes were

basically positive, this development now requires

significant resources to integrate the best of the

demonstrated MK I & II features, complete with a

newly developed motor drive system. It will require

the formation of a partnership between the

developers, and, at least, a committed wheelchair

Figure 21 - Seat raises and tilts to aid in standing. Foot rests

drops to floor.

Figure 22 - Arm rests flip back to aid in transfer and work

place access .


manufacturer and motor/drive developer-supplier

to transition the development towards commercial

availability. The investigators have made plans for

the formation of such a partnership and an SBIR

submission is under preparation to help finance the

venture. Assuming success with the SBIR submission,

the plan calls for the development of an integrated

MK III design. The MK III will then be subjected to

more rigorous laboratory and user testing as part of

its Phase I feasible evaluation.

Publications (in preparation)

References

Jacques GE, Ryan S, Naumann S, Milner M, Cleghorn WL

Application of Quality Function Deployment in

Rehabilitation Engineering, IEEE Transactions on

Rehabilitation Engineering, Vol. 2, No. 3, September 1994.

Logan GD, Radcliffe DF Potential for use of quality matrix

technique in rehabilitation engineering. IEEE Transactions

on Rehabilitation Engineering, Vol. 5, No. 1, March 1997.

Brown PG, QFD: Echoing the voice of the customer, AT&T

Technical Journal, March/April, 1991, pp. 18-32.

Hauser JR, Clausing D The house of quality, The Product

Development Challenge, Harvard Business Review Book,

eds. Kim B. Clark and Steven C. Wheelwright, pp. 299-

315, 1995.


TASK: PM-7 POWERED MOBILITY SIMULATORInvestigators: Douglas Hobson, Nigel Shapcott, Mark Schmeler

Collaborators: Robert Lang, Jules Legal

Rationale

Evaluation for powered mobility can be a difficult

and time consuming process for both service

providers and wheelchair users. The decision to

recommend or purchase a powered wheelchair must

be done carefully and with maximum consumer

involvement as the costs are often high and the

mistakes are difficult to rectify after the fact. For

individuals with severe disabilities, the selection

process can often involve trials with different types

of input controls in an effort to determine if powered

mobility is even a viable option. For others who have

been long time manual wheelchair users, manual

propulsion may become increasingly more difficult

as a result of progressive disability or older age. A

powered wheelchair simulator is a multi-purpose tool

that allows consumers and clinicians to experiment

with powered mobility options at a relatively low cost

in an effort to make informed decisions prior to the

purchasing process. It allows a person in their manual

wheelchair, in their typical seated posture, to

experience the sensation of being in a powered

wheelchair. The concept is based on having a

powered platform or simulator onto which a person

can wheel their manual wheelchair. Controls can be

readily selected and positioned to meet the individual

needs of the user. Assuming the trial is positive, the

clinician, working closely with the user and assistive

technology supplier, can then more confidently

formulate the specifications for the definitive

powered wheelchair. This approach can be a

significant improvement over the typical trial and

error approach, as well as reduce the chances of

prescription error and ultimate disappointment by

the user. Research work conducted by Mark Schmeler

and Nigel Shapcott, while at the University of Buffalo,

indicates that the sensation experienced by users

while on the simulator closely parallels the motor/

perceptual sensations experienced in an actual

powered wheelchair (Schmeler, ’95).

Methods Summary

A first generation prototype simulator was

constructed during the latter part of Year II.

Evaluation of the first generation prototype was

performed in the University of Pittsburgh Medical

Center’s Center for Assistive Technology (CAT). A

local assistive technology supplier was invited to

participate in the prototype implementation and

evaluation. The results of this interaction were

positive, including suggestions for MK-II design

improvements. A mechanical designer (Jules Legal)

was added to the team. An unsuccessful STTR

proposal was prepared and submitted to NIH/

NCMRR in partnership with two local firms in Yr.

III. Year IV focused on continued refinement and

testing of the MK-II design with consumers in the

CAT. Based on the positive local experiences, a

second, revised STTR grant proposal was submitted.

It was not successful. The CAT also produced several

units for use by other clinical facilities.

Figure 23—Powered Mobility Simulator prototype based on the

Suny-Buffalo design.


Outcomes Summary

Transfer of this development to the marketplace

was dependent on a commercial partnership and the

receipt of technology transfer support from external

sources. As indicated above two attempts at securing

the necessary federal support were unsuccessful.

Several reviewers questioned the viability of such a

product given its limited application and therefore

numbers that can be potentially sold. This may

possibly be the case. However, we were gratified that

Mark Bresler, [Bresler, ML, 1990], one of the early

proponents of the wheelchair simulator concept,

exhibited a new prototype at the 1998 RESNA

conference. Hopefully he has captured the interest of

a commercial entity that will make this “orphan”

development available to those clinicians in most

urgent need.

Publications

Schmeler, M.R. Performance Validation of a Powered

Wheelchair Mobility Simulator, Proceedings of theEleventh International Seating Symposium, Pittsburgh,

PA, February 1995

References

Bresler, MI Turtle trainer: A way to evaluate power

mobility readiness. Proceedings of the Thirteen AnnualRESNA Conference, 1990


Rationale

The purpose of this project was to design and

develop a novel wheelchair with a unique

combination of features. This wheelchair design was

intended to address a market need for a wheelchair

capable of folding compactly for stowage (e.g.,

overhead compartments during commercial air

travel), accessing narrow passageways and other

areas requiring a compact profile and footprint, and

providing a high degree of maneuverability. Our

intent was to design an “Enhanced Access

Wheelchair” to achieve these capabilities without

sacrificing the performance characteristics essential

for everyday use (Figure 24). We also attempted to

determine the feasibility of incorporating fiber

reinforced material technology.

TASK: MM-1 STRUCTURAL IMPROVEMENTS TO

MANUAL WHEELCHAIRSInvestigators: Clifford Brubaker, David Brienza

Collaborators: Phil Ulerich and Catherine Palmer, Westinghouse Corp.

Figure 24 - Enhanced Access Wheelchair.

Goals

The goals of this project, as originally proposed,

were to design, fabricate and evaluate an aesthetically

pleasing, general-purpose wheelchair that could be

easily stowed, manipulated and maneuvered through

narrow corridors. The conceptual design was

proposed to meet this objective by providing several

important features:

• Compact folding frame;

• Light weight (using composite materials);

• Three position (anti-tip, rear support and folded)

auxiliary wheels; and

• Attractively shaped solid side frame members

that allow for subtle incorporation of mechanisms

like brakes, releases and structural members.

Three prototype wheelchairs were designed,

fabricated and tested in the course of this project. The

final design incorporated side frame members made

from inexpensive, molded thermoset materials. Other

frame components were eventually machined

individually from aluminum stock due to difficulties

with machined composite parts. It was (and is) our

expectation that these parts could be manufactured

more efficiently in production models. The

dimensions of the folded frame are 5.5 inches wide

by 21 inches deep by 12 inches tall with the footrest

mounts and main wheels removed and not including

the back rest. The wheelchair is shown folded in

Figures 25 and 26. Auxiliary wheels are included to

allow passage through openings as narrow as 18

inches (overall width is defined explicitly by the seat

width) when the main wheels are removed (Figure

27). The development effort has focused on the

incorporation of these novel features and

manufacturing processes. Weight reduction will be

an objective for subsequent design iteration.

An important secondary goal of this project was

to demonstrate alternative materials and

manufacturing techniques for the production of

wheelchairs. Our experience with this option is

summarized in the following section of this report.


Figure 25. - Side view of folded wheelchair.

Methods

A CAD design for the prototype wheelchair was

executed using CADKEY. This design was exported

to a more sophisticated CAD system at Westinghouse

Corp. Science and Technology Center where the

design was further refined. A structural analysis

using ANSYS, a finite element analysis program, was

conducted to determine the necessary material

strengths for the different parts. Stress analyses were

performed on individual components and for an

articulated model of the prospective prototype. Upon

completion of the design and computer simulation

phases, the project proceeded to the development of

the physical prototype. Thermoset materials were

considered as a low-cost production option for

wheelchair structures.

Inexpensive, molded thermoset materials offer

several advantages for use as low cost wheelchair

structures. Two major disadvantages are

manufacturers’ lack of experience with thermoset

molding and the high initial cost of molds. Both of

these problems were considered in this project.

The structural elements of the wheelchair were

designed as compression molded, glass filled

polyester components. One reason for this selection

is the very low cost of this material. It is used

commonly in industry for electrically insulated

structural parts. Since it is an engineered plastic, an

entire range of material strengths, weights and costs

are available. This allows for trade-off between

weight and cost in the design and manufacture of

wheelchairs. The basic design and geometry of this

wheelchair was defined substantially by the novel

folding mechanism of the chair and by common

structural requirements for wheelchairs.

A few iterations of weight reduction analysis were

done on the parts to save some material. Considerably

more refinement is possible. The chair was modeled

as plate elements and loaded with a 200 kg dummy

at 3 g’s. Consideration was given to both the

maximum von Mises stress and the maximum

deflection. Acceptable deflection was based only on

assumed aesthetic perceptions for the prototype

development. The stress limit was determined from

isotropic treatment of the maximum allowable tensile

stress.

The high cost of mold fabrication precluded mold

development for parts other than the side frame. Parts

were initially machined from sheet stock. This

decision was made with the knowledge that

machined composite parts typically have structural

strengths on the order of 40% less than comparable

Figure 26 - Folded (front).


molded parts. This loss of strength is well

documented and results from surface cracks and

defects left from milling the smooth, fiber free

surfaces. The use of machined composite parts proved

not to be a viable solution in subsequent testing. The

parts (other than the side panels) were subsequently

machined from aluminum sheet and bar stock.

wire is fed into the spray head and electrically melted.

Repeated layers of sprayed metal were applied until

a shell was created from 1/8 to 1/4 inch thick. This

shell was backed with an aluminum-filled epoxy to

provide strength and stiffness and placed into a cold

rolled steel frame about 1/2 inch thick. This process

was repeated to form the other half of the mold.

Unfortunately, the mold was incorrectly developed

as a conventional injection mold, rather than as a

compression mold. For injection molding the mold

is parted at the midline with two symmetrical (in this

instance) halves that are held in opposition while

material is injected. In contrast, a compression mold

has a “force” component and a “cavity” component

as the two “halves.” Without a force and cavity, it

was difficult to assure that sufficient material would

be incorporated into the mold to fill the part. After

six attempts the proper charge of bulk molded

material to fill the part was determined. After the

third piece was molded, the ejector system failed and

the molder was forced to pry subsequent pieces out

of the mold using hand tools. This was difficult, as

the mold must be stabilized at 350 degrees before the

molding process can begin. The failure required a

modification of the mold. It became necessary to

machine away extra material. This ultimately

weakened the parts.

The molding technology chosen for this project

is based on spray metal tooling. This technique for

mold making takes about a month and costs less than

$8,000. This process is rather new and has seldom

been used on compression molded parts of this size.

Only 20 to 150 parts would be expected from this tool.

By contrast, standard mold construction (using steel)

for comparable sized parts would require 4 to 6

months to complete at a cost on the order of $70,000.

These steel molds could be used to produce 500,000

to 5,000,000 parts. Standard aluminum molds are less

expensive ($45,000), quicker to machine

(approximately 3 months), and would be suitable for

producing 5,000 to 25,000 parts. The project provided

an opportunity to consider the efficacy of

compression molded parts at modest cost.

The mold was fabricated over the course of 8

weeks and was received at Penn Compression near

Pittsburgh, PA. The mold was made from a wood

model of the final part, which was placed in an inert

bed up to the mold parting line. An electric spray head

was used to sputter-coat thin layers of a zinc-

aluminum alloy onto the pattern. Zinc-aluminum

Figure 27 - Side view with main wheels removed.

Figure 28 - Narrow access.


The molded side-frame had four “through

holes,”including a 1" diameter main axle hole and

three 1/4 inch diameter holes to stop the auxiliary

wheel in its various positions. Of the parts produced,

five did not fill completely and several others were

broken while being ejected from the tool. In the end,

six acceptable parts were made, allowing for the

assembly of three prototypes.

Prototype assembly

Fabrication of an initial prototype resulted in the

discovery of weaknesses in the original design. As a

result of the initial fabrication phase, a substantial

number of the components were redesigned with the

goal of increasing the structural integrity of the

wheelchair frame. The modified designs were used

to fabricate two additional prototypes, which were

evaluated using applicable ISO standard test

procedures. The modified version is shown in Figure

29 and 30.

fatigue strength). The chair passed all static and

impact strength tests with the exception of armrest

upward weight bearing. The armrest upward force

test is not applicable to our design since the armrests

were designed to release with upward force. The chair

successfully completed 200,000 cycles on the two-

drum fatigue strength test without failure, but failed

after 2055 cycles of the curb drop test. This failure

was a fracture of the side frame where the footrest

and front caster wheels are attached. Prior to the

testing, we observed cracks in the frame resulting

from a poor fit between the molded side frame and

the footrest/caster wheel mount. It will be necessary

to address this area of structural weakness in the

design of future prototypes using molded

components.

Consumer Evaluation of the Prototype

Initial evaluation was provided by an

experienced wheelchair user and resulted in several

comments and suggestions:

• The concept of the design is attractive. The ability

to remove the rear wheels and use 8 inch auxiliary

wheels to roll down an airplane aisle or in a small

rest room would be useful. (Figure 28)

• The ability of the chair to fold and break-down

into small components makes it attractive for

storing in overhead compartments of aircraft or

in compact automobiles.

• The folding mechanism is awkward and

cumbersome. The wheelchair can become difficult

to fold if the central pin loses alignment with the

cross-braces. The dovetail joints bind and are

prone to jamming from dust and dirt.

• The wheelchair is much too heavy. The materials

need to be changed and the overall design

lightened.

• The wheelchair is too tall and the leg rests are

positioned too far forward.

• The auxiliary wheels do not perform adequately

as anti-tip devices and are cumbersome to use.

• The wheelchair and center of gravity are not

adequately adjustable.

• The backrest folding mechanism is bulky and

does not provide adequate lateral stiffness.

Figure 29 - Assembled Prototype.

ISO Test Evaluation of the prototype

The first of the modified prototypes was tested

according to ISO 7176-8 (Wheelchairs - Part 8:

Requirements and test methods for static, impact and


• The chair has multiple pinch points that need to

be eliminated

• The wheelchair provides a proof-of-concept and

would require additional refinement prior to

being acceptable to consumers.

wheelchair that allows access to narrow corridors and

is rigid and durable enough for everyday use is now

several years old, there is still considerable need for

such a product by many wheelchair users. As a result,

we feel that the market potential for a wheelchair with

these features is still significant. This initial funding

provided the basis to take the most critical step in the

research and development process: from conceptual

design to full-scale working prototype. There are still

several important engineering problems to solve

before the eventual development of a commercial

product; however, we have successfully

demonstrated the feasibility of producing the

wheelchair for enhanced access. Although it was not

our primary objective, we have also shown the

possibility of using parts manufactured with

inexpensive techniques and materials.

External Evaluation

A more thorough demonstration and evaluation

was conducted by the RERC on Technology Transfer

at SUNY Buffalo. The Enhanced Access Wheelchair

was evaluated by three focus groups of 30 consumers

who had used a manual wheelchair for a minimum

of five years. Some general results from comparisons

with existing commercial products were particularly

encouraging:

1. 55% of the consumer participants preferred the

prototype to existing products.

2. Consumers were willing to pay up to $200 more

for the features incorporated in the Enhanced

Access Prototype.

3. Consumers increased the additional amount they

would pay for the prototype features to $370

(mean) after viewing the features of a competing,

production model wheelchair.

4. Among features valued by the consumers were

the folding mechanism, the folded size, and the

3-position deployment of the auxiliary wheels, the

“solid” seat, and the aesthetics of the side-frame.

Disadvantages identified included the

imprecision and “awkwardness” of the

mechanisms, the overall weight, and the lack of

tie-down points. Suggestions were generally on

ways to improve the mechanisms and decrease

Figure 30 - Front view of assembly

Several of these problems have already been

addressed. For example, the seat was redesigned to

eliminate the possibility of pinching while it is being

opened. The backrest support brackets were

redesigned since this initial evaluation was made.

Amelioration of all other shortcomings is being

considered. The design will require further iteration

to become viable for commercial development.

Outcomes Summary

Our initial impression of the prototype relative

to its performance is positive. The solid seat together

with the cross braces and side frame members form

a support structure that feels significantly more rigid

than typical “X” cross brace frame, folding

wheelchairs. Even with the large main wheels

removed for narrow access, the wheelchair was

sturdy and stable. In informal trials in our laboratory,

varying users have found the chair’s performance to

exceed their expectations for a folding frame

wheelchair. A formal beta test program will be

developed as the next stage of development.

Although the concept of a compactly folding


the weight. One of the strongest preferences for

the prototype over production folding chairs was

the folding mechanism. It was perceived to be

more stable and to allowed more compact folding.

Recommendations for Future Development

The project has progressed to the point of

successful demonstration of several valuable features

of a manual wheelchair. We believe that the

evaluation information is sufficiently positive to

warrant further development. Initial plans for a

second generation prototype have been completed.

We believe that it will be necessary to produce a metal

frame model to gain the interest of current

manufacturers. If we can obtain additional funding

for this project we shall proceed with development

of an all metal prototype in which we shall refine the

mechanisms and reduce the weight of the wheelchair

as suggested by the consumer panels.

Publications and Technical Reports

Brienza, DM, CE Brubaker (1996) Design and Development

of a Wheelchair for Enhanced Access, RESNA Proceedings,

16:250-252.

Brubaker CE, Brienza DM, Ulerich P “Design and

Development of a Wheelchair for Enhanced Access,” Final

Progress Report, SCRF Grant #1218, Paralyzed Veterans

of America, November 10, 1995.

Ulerich P, Palmer, K, Stampahar,M, Brubaker, CE “Design

and Development of a Wheelchair for Enhanced Access,”

First Annual Report to the Paralyzed Veterans of America

Spinal Cord Research Foundation, Grant #1218-01, March

16, 1994.


TASK: WP-1 CONSUMER RESPONSIVE MOBILITY

PRESCRIPTION PROCESS

Investigators: Elaine Trefler, Heather Rushmore

Rationale

Consumers who use manual wheelchairs have

expressed the view that their first wheelchair did

not meet their personal needs. The purpose of this

study is to develop a consumer responsive wheel-

chair prescription process for first time wheelchair

users who are functioning as paraplegics.

Over the past several years, consumer-respon-

sive services have become the highly studied

means of providing assistive technology and

rehabilitation services. In the past, consumers were

not given ample choices nor were they often asked

to contribute to the decision making process.

Often, all decisions were, and at times still are

today, made by the medical/therapy team. Due to

the lack of involvement by the consumer, he/she is

often dissatisfied with the assistive technology

received.

Goals

1. To determine the components of a service

delivery process that support consumer satis-

faction both with the process and the product

during the provision of their first wheelchair.

2. Propose enhancements to the service delivery

model based on the findings.

Methods Summary

The following steps were taken to address the

above goals:

1. Develop an interview instrument to determine

consumer satisfaction with the prescription

process for a first time wheelchair user, admin-

ister it to at least one individual to obtain input

into the areas that need refinement and gather

feedback to develop discussion areas and

questions for a focus group.

2. Form a focus group to gather ideas on ways to

improve the wheelchair prescription process.

Use input from the focus group to further refine

the interview instrument.

3. Identify and interview 30 consumers (15 who

received services from a multidisciplinary

clinical setting and 15 from a non-

multidisciplinary setting) with the interview

instrument developed to determine consumer

satisfaction with service delivery and wheel-

chair technology.

4. Review current practice based on information

and data collected from the focus group and

interviews.

5. Develop and propose enhancement to the

service delivery model based on the data

collected in steps 1-4.

Outcomes Summary

A focus group of five expert wheelchair users

was assembled to generate ideas on improving

current prescription processes. The group

brainstormed 31 ideas and ranked the top six ideas,

which were:

1. focus on the person;

2. consumer testing of different wheelchairs;

3. education on different wheelchairs for different

activities;

4. evaluation of the consumers home;

5. wheelchair user as a team member; and

6. peer counselor/mentor as part of the team.

Publications were prepared for both consumer

and professional publications, which summarized

the results of the focus group. The main themes

were that consumers wanted to be involved as full

partners in the decision making, to be able to try

different options in their own environment and

access to advice from other wheelchair users.


Recommended Future Research

Based on the above experience we recommend

the following areas for further investigation:

1. Investigate effectiveness of education and

training methods for consumers. Document

consumers’ perceptions of training practices

and determine compatibility with active prac-

tice.

2. Compare consumer’s first prescription process

to their most recent to determine features and

satisfaction level.

3. Investigate the possible differences between

satisfaction and adjustment levels of individu-

als with acquired and congenital disabilities

and how this might relate to components of the

service delivery process.

Publications

Trefler, E and Rushmore, H. A consumer responsive

mobility prescription process: The summary of a focus

group. Team Rehab Report, June 1997, 41.43.

Trefler, E, Fitzgerald, S, and Rushmore, H. Manual

Wheelchair Prescription Process: Consumer Satisfaction

with Multidisciplinary and Non Multidisciplinary

Approaches, In revision.


TASK: WP-2 WHEELCHAIR PRESCRIPTION SOFTWARE

PROJECT (WPSP)Investigator: Nigel Shapcott

Rationale

Current wheelchair users and prescribers (OT, PT

and RTS students are the target population) have a

large and increasing selection of wheelchairs to

choose from, each having a variety of accessories that

customize the wheelchair to individual need. Thus,

the goal is to provide users the opportunity to

participate in the selection of the wheelchair that is

closest to being ideal for their needs.

Information overload caused by the significant

number of companies making wheelchairs, which

come in a variety of models with many configurable

options for each, leads to a large quantity of

information that has to be searched in order to make

appropriate selections. Information continually

changes as new models, options and companies enter

the market. Added to this is the fact that the

information between different manufacturers may be

difficult to compare because the wheelchair standards

testing information is not readily available.

Incorrect prescription or purchase of wheelchairs,

particularly among first time inexperienced

wheelchair users, is common among individuals with

spinal cord injury and other diagnoses where needs

change over time. There is a lack of training

opportunities that teach and inform prescribers on

the strategies of wheelchair prescription, taking

account of physical needs, functional environment,

funding and other issues, and relating these to the

priorities of a particular individual.

This collaborative project, to develop wheelchair

prescription software, has been funded mainly

through the Department of Veterans Affairs,

Rehabilitation Research and Development Service

(VA RR&D) as a component of the Computer Aided

Wheelchair Prescription System (CAWPS).

Goals

1. Develop a computer program that provides an

effective, easy to use wheelchair prescription

teaching aid.

2. Provide easy access to expert prescription

methodologies.

3. Commercialize the software in order to provide

a mechanism for widespread availability at

reasonable cost.

Methods Summary

An interactive computer based wheelchair

prescription system, using expert system

methodologies, has been developed. As part of this

development process, internal evaluation and

interactive evaluations were carried out using known

case studies.

Outcomes Summary

1) The software structure was stabilized January

1997. Educational features include:

• Quicktime videos to show different wheelchair

types and activities to educate and raise

expectations about what may be reasonable

achievements in education, work, leisure and

ADL activities.

• Graphics to explain dimensional information.

• Incorporation of a publication on wheelchair

selection as resource material (text and graphics).

(Axelson et al, 1994)

• Each question has an accompanying explanation

which can be accessed by a simple mouse click

(“Why Button”).

• Each feature of the final generic wheelchair can

be examined (simply by a ‘click’) to determine

which questions (and accompanying answers)

were factors in the selection of that feature.


2) A demonstration version is available at:

ftp.pitt.edu/users/s/g/sgarand.

3) Logic developed has been largely completed

and is currently in the testing and editing phase.

4) Formal testing was not carried out in order to

secure funds and protect confidentiality pending

completion of negotiations with a potential

commercial partner (see below). The input from

informal testing has been very positive for this

educational version.

5) The project has been successful in attracting

commercial interest. An agreement, through the VA

RR&D Technology Transfer Section with a major

health care company who expressed interest in

commercializing CAWPS, failed. The company had

intended to further develop CAWPS and make it

widely available through Intranet and Internet links

as well as in a stand alone format. Task WP-2, WPSP

was planned to be released as a low cost (possibly

free) version of the main CAWPS program as part of

the commercialization plans. In December 1998,

negotiations ceased.

6) Plans are now under way to obtain funding

for further testing.

Individuals interested in obtaining a

demonstration version of CAWS should contact Nigel

Shapcott preferably by e-mail at [email protected]

or through the RERC at 412-647-1273.

Recommended Future Development

1. Investigate the use of CAWPS as an

educational tool.

2. Investigate the use of CAWPS as an clinical

tool.

Publications

Shapcott, N and Garand, S. Computer-Aided

Wheelchair Prescription System, paper submitted to

Canadian Seating Symposium, Toronto, Canada, Sept

1996.

Shapcott, N and Albright, S. Computer-Aided

Wheelchair Prescription System, paper submitted to

Pittsburgh International Seating Symposium,

Pittsburgh, PA February 1997.

Reference

Axelson P, Minkel J, Chesney D. Guide to wheelchair

selection: How to use the ANSI/RESNA wheelchair

standards to buy a wheelchair, PVA 1994


TASK: STD-1 PARTICIPATION IN THE DEVELOPMENT OF

WHEELCHAIR STANDARDS

Investigator: Rory A. Cooper

Rationale

Development and application of performance

standards is perhaps the most productive activity in

terms of affecting the improvement to the quality of

wheelchair products for the largest number of users.

However, standards development requires research

and testing in order to validate the test procedures

prior to their acceptance in national and international

standards. Standardized disclosure of test and

measurement data in presale brochures is a means

by which consumers can accurately compare

products prior to purchase commitment.

Goals

1. To participate in the development and revision

of wheelchair standards to ensure product quality

for consumers.

2. To participate in the development and revision

of wheelchair standards to provide sufficient

information for product comparison.

Methods Summary

Three basic methods were employed. The first

methods consisted of active participation in the

standards meetings at both the ANSI/RESNA and

ISO levels. This included chairing several of the

working groups, and for two years chairing the

RESNA Technical Guidelines Committee. The second

method was to provide supporting research and

development for the creation and revision of

standards. Without supporting data or devices,

reasonable standards can not be developed. The third

method employed applying the standards to

commercial products to provide comparison data.

This information was published to assist clinicians,

consumers, payers, and manufacturers.

Outcomes Summary

The key outcomes from this task can be

summarized as follows:

• coordinated the development of a complete

electric powered wheelchair/scooter

electromagnetic compatibility standard which is

in the voting process as of 12/98,

• contributed to the development of an electronic

integration interface standard (ISO CD7176/17)

being developed through TIDE, a program of the

European Economic Community,

• conducted a study to compare the results of

common hospital type wheelchairs with active

duty ultralight wheelchairs,

• conducted a study to analyze the performance of

selected lightweight wheelchairs.

• standards which consumers, practitioners,

manufacturers and purchasers can rely upon

more complete information by which to compare

products,

• quality of wheelchairs will be improved.

Recommended Future Developments

Work on the development of standards must

continue in order to ensure improvement in

wheelchairs. Moreover, product comparisons are

required to provide consumers, clinicians, and

manufacturers information about the safety, quality,

and value of wheelchairs. There are a substantial

number of wheelchair standards in development and

in revision. The application of wheelchair standards

continues to produce higher quality wheelchairs.

Publications

Cooper RA, Boninger ML, Rentschler A, Evaluation of

Selected Ultralight Manual Wheelchairs Using ANSI/

RESNA Standards, Archives of Physical Medicine and

Rehabilitation, Vol. 80, 1999.


Cooper RA, O’Connor TJ, Gonzalez JP, Boninger ML, and

Rentschler A, Augmentation of the 100 kg ISO Wheelchair

Test Dummy to Accommodate Higher Mass, Journal of

Rehabilitation Research and Development, Vol. 36, No. 1, 1999.

Cooper RA, Gonzalez J, Lawrence B, Rentschler A,

Boninger ML, and VanSickle DP, Performance of Selected

Lightweight Wheelchairs on ANSI/RESNA Tests, Archives

of Physical Medicine and Rehabilitation, Vol. 78, No. 10, pp.

1138-1144, 1997.

Cooper RA, A Perspective on the Ultralight Wheelchair

Revolution, Technology and Disability, Vol. 5, pp. 383-392,

1996.

Cooper RA, Robertson RN, Lawrence B, Heil T, Albright

SJ, VanSickle DP and Gonzalez J, Life-Cycle Analysis of

Depot versus Rehabilitation Manual Wheelchairs, Journal

of Rehabilitation Research and Development, Vol. 33, No. 1,

pp. 45-55, 1996.

Cooper RA, Harmonization of Assistive Technology

Standards , Proceedings 20th Annual IEEE/EMBS

International Conference, Hong Kong, CD-ROM, 1998.

Gonzalez J, Cooper RA, Rentschler A and Lawrence B,

Frame Failures of Welded Tube Manual Wheelchairs,

Proceedings 20th Annual RESNA Conference, Pittsburgh,

Pennsylvania, pp. 184-186, 1997

Lawrence B, Cooper RA, VanSickle DP and Gonzalez J,

An Improved Method for Measuring Power Wheelchair

Velocity and Acceleration Using a Trailing Wheel,

Proceedings 20th Annual RESNA Conference, Pittsburgh,

Pennsylvania, pp. 251-253, 1997

Cooper RA, Gonzalez J, Robertson RN, and Boninger MD,

New Developments in Wheelchair Standards, Proceedings

18th Annual IEEE/EMBS International Conference ,

Amsterdam, Netherlands, CD-ROM, 1996.

Cooper RA, Robertson RN, Boninger ML, A Biomechanical

Model of Stand-Up Wheelchairs, Proceedings 17th Annual

IEEE/EMBS International Conference, Montreal, Canada,

CD-ROM, 1995.

Cooper RA and McGee H, Wheelchair Related Accidents

and Malfunctions, Proceedings 18th Annual RESNA

Conference, Vancouver, BC, pp. 334-336, 1995

Cooper RA, McGee H, Apreleva M, Albirght SJ, VanSickle

DP, Wong E and Boninger ML, Static Stability Testing of

Stand-Up Wheelchairs, Proceedings 18th Annual RESNA

Conference, Vancouver, BC, pp. 349-351, 1995.

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