Innovation boosts wheelchair safety and lifespan

Written by: Paul Fanning | Published:

It is estimated that there are as many as 750,000 full-time wheelchair users in the UK, of whom a significant proportion are under 18. Clearly, while a chair for a fully-grown adult may have a lifespan as long as that of the user, a wheelchair for a child has to take account not only of their smaller size, but also of the fact that they are growing and developing physically, meaning that chairs must be replaced at regular intervals.

As children grow their physical and developmental needs change rapidly, and are at greater risk of deterioration if their wheelchair is not appropriate. Since many of these younger wheelchair users rely on the National Health Service for their chairs, the need for regular replacement of chairs represents a considerable cost for the public purse. With this in mind and following clear statements of clinical need from parents, carers, users and health professionals for a wheelchair that promotes user independence and is easily adaptable for a growing child, the NHS National Innovation Centre (NIC) launched a competition entitled 'Chair4Life'.

Aiming to revolutionise the design of wheelchairs for both children and adults, the NIC issued a competition tender to facilitate the next stage of research and development; the production of a fully working prototype for further evaluation. The project was ideally suited to organisations that could bring a range of experience, competencies and expertise to build on existing research and design work and develop a prototype that will transform the lives of disabled children and young adults.

The challenge was taken up by product design consultancy Renfrew Group International, which set about developing a powered, modular wheelchair designed to grow with the child. The new design was arrived at in a mere 18-week development cycle and is aimed at maximising mobility and independence for disabled children as they grow into adulthood.

However, the need to be adaptable to a child's development was just one of the design factors that Renfrew had to consider. Indeed, this was in one sense very much a bottom-up redesign of the wheelchair.

Factors that had to be taken into account by the design included: discretion; the ability to talk to people face-to-face; usability on uneven ground; comfort; manoeuvrability in tight spaces; smart stability control; the ability to climb kerbs; ease of customisation; and light weight.

"It was a very broad brief," says Bruce Renfrew, design director of Renfrew Group. "When we first looked at it we decided that it would be very difficult – if not impossible – to achieve all the aspects of the brief. So we decided to compartmentalise it in the sense that not only is it modular, but it uses interfaces between each module that are an assemblage of components that go to make the mobility chassis and, in the other largest module, the seat itself."

This was achieved by designing the chair around a universal, modular platform that can be readily updated and modified through a standard catalogue of attachments and bespoke components. It centres on a standard chassis that is retained throughout a child's development, which greatly reduces disruption to their lives caused by lengthy waiting times for new chair systems.

The seat grows with the child via the implementation of ISO Mount, a universal modular docking system that attaches the seat to the chassis lift mechanism, allowing swift replacement of successive seating modules. The universal ISO Fasten system ensures that the chair can be swiftly and easily modified to accommodate changes such as monitoring and care equipment, storage and accessories. A triangular section extrusion that runs under the bottom of the seat, around the back and over the top, it allows anything to be attached as long as the correct clamp is in place – either fixed-screw or over-centre.

This innovative system gives third party manufacturers the ability to provide a raft of upgrading features and components within a fixed base platform. This, according to Renfrew, means more patient choice, improved quality of products and new components to drive innovation within the industry. He says: "So Iso Mount, IsoFasten and IsoConnect all created a sort of conduit through which the whole project could be developed and meant that we could develop a snapshot of what Chair4 Life would be like… So in other words, we didn't have to design the whole system, we just showed how development could take place and things could slot into place using Iso Mount as the conduit."

The adaptability and modularity dealt with, the next stage of the process was to look at the other requirements of the design. Chief among these was the requirement that the wheelchair user should be able to sit at a height that allowed for eye-to-eye interaction with the able-bodied.

Says Renfrew: "We designed the chassis to do certain things: principally to have on board a standard elevating column that would allow the user to achieve peer eye level while conversing. This was a very strong requirement that came as part of the feedback for the project from our user groups as we were doing the design." This was achieved using a lightweight 320mm vertical chair lift that employs a ballscrew.

However, with greater elevation comes lower stability. Says Renfrew: "If a user wants to travel over rough terrain with the column at a higher setting to be at a peer group eye level, there is a danger of instability." To combat this, the chair features an electronically-controlled, expandable track and wheelbase. This 'Varitrak' adjustable wheelbase allows the user to adjust the wheels to suit indoor or outdoor conditions, providing stability when it is needed and compactness for manoeuvrability in smaller spaces for greater freedom.

In fact, with a retracted width of 550mm, and wheelbase of 450mm, the Chair4Life has a turning radius of just 550mm, and is suitable for moving around school classrooms, shops, public transport and other tight indoor spaces. Equally, however, it is very stable on uneven ground. With an expanded width of 720mm, and a wheelbase of 630mm an extremely stable platform is provided for children and young adults to go where they want.

Further stability is provided by sensors in the base, which monitor the height of the seat lift and the angle of the wheelchair on uneven ground. These either provide warnings or automatically adjust the wheelbase, seat lift or tilt to ensure safe stability if there is tipping or if the user angle from a static baseline is exceeded.

Lightweighting was another major concern within the design and for this purpose, as well as the lightweight lift, the chair uses lithium ion batteries, a stressed lifting column, hub motors, and all aluminium construction the unloaded weight of the wheelchair is 80kg. 20-40kg less than current paediatric wheelchairs.

Says Renfrew: "We're using hub motors so that the motors are in the wheels themselves and they are mounted at the end of independently-suspended arms that can be extended by 150mm. We're using a Lithium Ion battery pack, which is lightweight and compact. We've created space for the electronics that are in a slice that sits alongside the column, so again those are very compact.

"We've got suspension on the castors and what in production will be a die-cast aluminium base that carries the pivot for all the suspension mounting points and all the fixing for the column. That's pretty much it. It is very, very simple."

As well as technological considerations, however, there were aesthetic concerns to be accounted for. Chief among these was an idea that can best be summed up with the phrase 'Look at me not the wheelchair'. Thus, for instance, the chair offers discreet storage for medical equipment, keeping the emphasis on the user and not on the wheelchair.

"The chassis is designed to be minimal not only in terms of components, but also in terms of how it looks," says Renfrew. "Again, one of the important features to have come out of research with the user groups was that they wanted to be seen as an individual in their own right. They didn't want people to look at the chair. So we wanted the chair to blend into the background and the way for us to do that was to ensure that the bulk of the chassis in particular was as compact as possible."

Because the Chair4Life is designed to be used from aged four onwards, it is obviously desirable that it should be able to reflect the changing tastes and personalities of its users as they mature. Says Renfrew: "It has been designed with adaptation and customisation in mind. It was therefore quite important to design a chair that would allow the young person to adapt and customise it to their own tastes. So we've designed it in such a way whereby there are areas of trim and trim panels that can be adapted in that way."

Given that the design has been put together in association with the NHS, its cost is clearly a major consideration. However, claims Renfrew, while there is a rise in cost, this is easily outweighed by the chair's longer lifespan. He says: "Because this is a chair for life and therefore can be used for very much longer than a current prescription chair that is supplied to a user aged four and changed at very regular intervals of 18 months to two-and-a-half years, it has a much longer life and can have additional modules and upgrades applied to it. So, although the overall cost is rather higher than a standard wheelchair, that cost is easily amortised over the life of the chair."


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