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TECHNOLOGY AREA
As with any product, the selection of materials for wheeled mobility
products impacts both the manufacturer and the end user. Materials impact characteristics
such as durability, strength, cost, appearance, design and manufacturing flexibility,
and weight. Although there have been significant improvements in materials for wheeled
mobility, excellent improvement opportunities still exist. Some of the areas that could
benefit from new technologies include:
- Frames - Strength-to-weight ratio, reduced manufacturing steps,
finish characteristics.
- Tires and Wheels - Improved wear without compromising ride and
traction, non-conductive, non-marking, durable.
- Seating Materials - Comfort, durability, appearance, ease of
cleaning, fire retardant qualities.
THE NEED
Materials have been the basis of major evolution in wheelchair products.
Newer chairs benefit from specialty designs originally intended for sports activities
- racing, basketball, etc. Specifically, the development of lighter-weight products
based on advanced materials has been one of the biggest breakthroughs in wheelchair
technology. High-performance materials have enabled designs offering comparable
strength with greatly reduced weight and thus smaller and more maneuverable products,
a direct benefit to users. Most of the users who have benefited from reduced weight
materials have been in manual chairs, where the frame is a major portion of the mass.
For power wheelchairs, unfortunately the frame is often a small part of the total mass,
which is dominated by components like batteries. In many cases, costs have been reduced
when materials have enabled new manufacturing methods and reduced material, machining,
and assembly costs. Reduced costs translate into benefits not only for manufacturers but
also end users and third-party reimbursers. One example of this is the use of the
injection-molding processes for power scooter bodies that greatly reduces not only weight
but also assembly time and thus manufacturing costs.
Today, even with the excellent material improvements over previous product
generations, there are still significant needs for materials. Some of the newer, lighter
chairs have not maintained previous levels of durability required for long-term use. In
addition to improvements in the frame, both manual and power chairs stand to benefit from
better materials for wheels, tires, and seating. Increased chair and component life
translates to reduced costs for end users, third-party reimbusers, and manufacturers,
especially if parts fail within a product's warrant period. Material cost has often been a
direct trade-off with certain performance improvements. For example, the use of composite
materials may require hand lay-up or other expensive fabrication processes. These higher
costs may translate into significantly higher retail sale prices, or more frequently
result in selection of a cheaper, lower-performance material. During the stakeholders'
forum, we will be discussing these types of trade-offs related to materials.
BASIS FOR DISCUSSION
The following problems have been identified from literature and
communication with experts, end users, and manufacturers. The goal of the forum discussions
is to select a priority, high-impact problem and to begin to develop a problem statement
that specifies the requirements for a commercially viable solution. The problem statement
will be used to solicit solutions from technology producers. Please come prepared to
discuss these topics and to choose the most important. It would greatly benefit discussions
if manufacturers come prepared to discuss non-competitive issues regarding materials and
related manufacturing methods that are limiting manufacturing and design improvements.
FRAMES
Statement of the Problem
There is a need for frame materials that reduce weight, increase
aesthetics, enable novel designs including modular components, maintain durability, fit
manufacturing requirements, and do not increase cost.
Current Solutions
Most chairs today are made of tubular aluminum or alloy steel. Some frame
designs have incorporated advanced materials such as plastics, titanium, composites, and
alloys like chrome-moly; however, the majority of chairs do not use these high-performance
materials due to the high cost. A good example of how advanced materials and manufacturing
methods can reduce cost is the reduced assembly and associated costs resulting from the use
of injection molding to create a unibody for power scooters.
Issues to Consider
Material improvements can enable frame designers to reduce weight and cost
while increasing durability, functionality and aesthetics of the chair. This can be achieved
by using materials that offer a greater strength-to-weight ratio, improved processing
characteristics, and better mechanical performance; however, incorporating high-performance
materials, such as titanium, results in increased cost. Also, the strength and durability of
a frame design is not strictly dictated by material strength; fatigue strength is strongly
influenced by tubing dimensions and shape, welding characteristics, and other
assembly-related design aspects. Modular design may provide the solution. There are several
advantages associated with modular design, the biggest one being the ease of replacement and
repair. Modularity may provide for easy transportation and handling of chairs, especially
light weight chairs. Modularity may not address some of the issues relating to product
customization and specific end user needs. One expert reported that up to 50 % of chairs are
customized. Also, to ensure the safety of the wheelchair users when they are traveling in
public or private transportation, caster assemblies and frames should be strong enough to
withstand the shocks which they are subjected to during a crash.
Aesthetics of a wheelchair are directly related to the frame design and
materials. Chairs in the European market are aesthetically better than in the U.S. This is
largely due to the fact that the higher-cost aesthetic features are not accepted by third
party reimbursement agencies in the U.S. Based on these issues, please consider the following
questions:
- Are aesthetics, strength, weight, and cost of the wheelchair frame issues
for both manual and power wheelchairs?
- Is there market potential for improvements to wheelchair frames in general?
Will third party reimbursers fund these improvements?
- Is modularity a good option for addressing the need for customization and
serviceability? How modular would a design need to be? What would the benefits be to:
manufacturing? use? cost?
- Will manufacturers be willing to adopt modularity, considering that
modularity might open gates for the competition from low-end manufacturers?
Also, a better understanding of frame dynamics, especially for power chairs, is
needed. It is still unknown whether frame design can help in reducing or perhaps eliminating
vibration. There is a need to determine a vibration standard for the wheelchair industry. The
current vibration standards are based on standards for trucks and other heavy vehicles. A
wheelchair user has different stability requirements than a heavy vehicle user and so there
is a need to develop a more appropriate standard.
- Is vibration still a problem in manual and/or power chairs?
- Does the frame design contribute to vibration? If yes, then how can
vibration damping be achieved with respect to frame design and materials?
- How should the vibration standards for wheelchairs be defined and who
should define them?
Both limited sales volume and small production volume, resulting from limited
commonality in parts across product lines, contribute to manufacturers' hesitation to develop
and implement novel designs. Manufacturers will often hesitate in redesign without proven demand,
a situation that delays design evolution. The evolution of frames based on designs originally
developed for high-performance sports models illustrates the tendency to introduce revolutionary
concepts into niche, rather than broad markets. Standardization of components/frame across
various product lines could help increase production volume of any component/frame.
- What is the barrier that prevents manufacturers from standardizing their
components across various product lines?
- Are current issues related to frame designs and materials related more to
material performance, manufacturing processes, or design demands?
- Is there a need for adjustability options such as multiple axle
placements?
Tires/Wheels
Statement of the Problem
There is a need for improved tire wear without compromising ride and traction.
Tires must be functional on varied surfaces - sand, rugs, snow, and smooth and rough surfaces -
and must be non-marking. Tires should allow discharge of static electricity to prevent shocks
to the user and damage to the electronics associated with power chairs. At the same time, tires
and wheels should be light and inexpensive. In a 1994 study related to power wheelchairs, users
reported that tires were the second most frequent repair behind batteries. Wheels have yearly
maintenance problems 24% of the time. Although significant research has had a positive impact
on manual wheelchair tires, little advancement has occurred with power chairs tires. This
problem stems from the varied wheel diameter and the design and performance parameters
associated with power chairs. Also, power wheelchairs introduce much larger stresses on the
wheels and tires than manual chairs due their heavier loads.
Current Solutions
Common materials used include rubber, urethane, polyurethane, composite nylons,
and kevlar-reinforced thin tubes. Research is in process on solid polyurethane foam tires,
which combine the best features of the pneumatic (comfort, low rolling resistance) and solid
tires (low maintenance). These materials have a microcellular structure that reduces weight
while maintaining wear and rider comfort. One problem with the new solid tire designs is the
tendency for the tire to become unseated from the rim. Radial tires, semi-pneumatic designs,
and inserts are also being researched.
Issues to Consider
In the area of tire and wheel performance, the main issues are reliability
and durability without losing comfort and safety. Pneumatic tires provide great comfort but are
a potential inhibitor of independent living, due to flat tire etc. The goal is to achieve the
comfort level offered by pneumatic tires along with the reliability and durability offered by
solid tires. Increase in durability will also provide economic relief to the end user. At
present, power wheel chair tires cost almost $100. This is a big expenditure considering that
present tires have a short life span and are therefore replaced quite frequently. There is a
need to innovate or use materials and design that can bring down the cost of the tire, increase
the durability of the tire while maintaining reliability and comfort level. And most
importantly, tires should be non-marking. Black tires meet most of the requirements of an ideal
tire but suffer from the big disadvantage that they are marking and are therefore not used in
the industry.
Are the problem of static charge build up and durability more critical to
the power wheelchair industry than manual wheelchair industry? Are the newer solid urethane and polyurethane foam tires meeting users'
needs adequately? If not, why not?
An issue relating to wheel improvement brings into question if it is beneficial
to reduce the wheel weight for power chairs. Spoke wheels performs well but requires a lot of
maintenance. Probably an ideal wheel will be one that has the weight and power of spoke wheels
while the cost and maintenance of plastic wheels. A misaligned wheel requires a lot more effort
to push. It is frame structure that mainly controls wheel alignment. For manual wheelchairs,
wheels should require minimum effort to push. Technology innovation, like geared hub wheels,
is required to make the wheels easier to push. Though considerable improvements have been done
in the wheel bearing, it is still a high maintenance item. Further improvement is required in
this field.
- For power chairs, is weight irrelevant? Is the goal for wheel materials
to merely match the weight and strength of spoke wheels but improve in the area of cost and
maintenance?
- Wheel misalignment affects tires wear rate as well as rolling resistance.
Is this a serious problem?
In the literature we found articles that cited the major barrier in the area
of tires and wheels as the fact that the total market is not large enough to support
investment in R&D by traditional tire and wheel manufacturers. Some believe that development
of better tires will require government funding for research at universities. Another concept
discussed in the literature is that all wheelchair manufacturers should cooperate to develop
a specification with a single tire supplier who could then address the industry's problem.
- Is an industry consortia on tires and wheels feasible as a means to
develop adequate R&D to meet the industry's needs?
- Are varied customer needs a problem inherent in tire and wheel product
selection? Could modularity apply to tires/wheel systems?
Seating
Statement of the Problem
Seating materials and components have a significant impact on cost and
customer satisfaction. Pressure sores is a very big problem for wheelchair users. The chair
needs to fit the user well even when there are changes with clothing, physique, or age.
Seating materials must withstand daily use in varied weather and climate and thus must be
durable. Customer preference regarding aesthetics and comfort also are important variables.
A well-designed suspension can contribute a lot towards the designing of a comfortable
seating system. Cushions can reduce shocks considerably. Upholstery must allow for air
circulation and provide user comfort, yet it also must be able to be wiped clean or
laundered easily for hygienic and aesthetic reasons. Fire retardance is essential for users
who smoke or are around smokers; seating material must not ignite. Ride quality and
durability are tightly linked to selection of seating materials and design of seating
systems.
Current Solutions
Seating comes in many forms: sling-type, armchair, plastic bucket,
automotive-type, and custom. The materials used for these seating systems vary greatly,
including wood, leather, plastics, textiles, foams, and gels. Simple seats can be made
from plastic molding with no cushioning or upholstery; whereas others, like the
automotive-type, may incorporate a sophisticated design with subforms, multiple types of
cushioning materials, and upholstery. Air permeable fabrics based on a pore size that does
not permit liquid to pass have best solved the conflicting needs for comfort - relating to
breathability of a seating material - and for waterproof characteristics.
Issues to Consider
To accommodate the various requirements of the end user, seating system
needs to be adjustable/adaptable. Modular seating can lead itself to adaptive seating.
Seating is most comfortable when there is a zero shear force for back upholstery and
head rest. Sensors and actuators could be used on the seating system to achieve this
zero shear force target. Similarly there is a need for an improved suspension system which
can improve the ride quality. An active suspension system can reduce vibration a lot but
due to the cost factor is suitable for niche market only. A suspension system that is
variable - capable of being soft for mobility comfort and hard for end user transfer - may
have benefit to the end user.
- Have aspects of custom seating, that could benefit the broader market,
been adopted by manufacturers? If not, what prevented their use?
- Is the "pressure sore" problem being adequately addressed by the
industry? If no, why not?
- Is there a need for adjustability / adaptability features in seating
systems? If yes, how could these features be best integrated?
- Are varied customer needs a problem inherent in seating designs?
- What are the issues regarding shock absorption at the casters versus shock
absorption at the main axle?
The Reference List
- Clifford E.Brubaker (1989). Wheelchair IV, Report of a conference on the
state-of-the-art of Powered Wheelchair Mobility, December 7-9,1988.RESNA Press.
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