Wheelchair handrim alternative image

In a project financed by the Austrian Science Fund FWF, a research group from Vienna set out to find the optimal drive for wheelchairs; the outcome passed initial practical tests and patent approval is awaited.

The group of researchers was headed by Margit Gföhler, a specialist in biomechanics and mechanical engineering at the Vienna University of Technology.

For many people with reduced mobility or disabilities, they rely on wheelchairs to get around. A lot of the manual wheelchairs that individuals use have handrims attached to the rims.

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However, the researchers have found disadvantages with these handrims, stating that their efficiency level is limited to just ten percent and that they require extreme positions for the arm and hand joints, which often result in excessive strain and injuries of the wrists or shoulders.

As wheelchair users use their mobility devices on an everyday basis, these afflictions often become chronic, notes the group.

To tackle this issue, the researchers sought a better alternative to the handrim.

Margit explained: “When a wheelchair is driven by means of a handrim, the human body has to adapt to this simple mechanism. However, human joints are not really designed ideally for these movements.”

According to her, more practiced wheelchair users are particularly prone to reaching far back on the handrim, which requires extreme wrist bending.

“Especially in extreme positions, this puts a great strain on the joints,” she added. “The idea behind the project was to look at the problem from the flip side. We tried to find out what sort of drive mechanism would be most suited for the human upper body.”

The researchers used their own creativity alongside computer simulations to find the optimum design. The only criteria were to avoid extreme body positions and to achieve the highest possible degree of efficiency.

In order to identify optimal movement, Margit’s team created a simulation environment. “We used a musculoskeletal system of the upper extremity and then optimised the movement for maximum performance at minimum muscular effort,” explained the scientist.

The result of the computer simulation was an oval-shaped mechanism, similar to pedalling on a bicycle, but a little further towards the front and a little further up than where a handrim would be.

The next step was to test the system and a prototype was built and installed on a wheelchair ergometer.

“We carried out performance tests in which we were able to prove that this type of drive actually requires less power input than a handrim drive,” said Margit.

One of the aspects the researchers measured in the test was the carbon dioxide content of the breathing gas under load conditions. The project partner for this step was the Weißer Hof Rehabilitation Centre, where the tests were carried out.

One requirement for the prototype was that it must not increase the wheelchair’s width or length, a requirement which the group says has been fulfilled. According to the researchers, power is transmitted to the axle via toothed belts with only minor friction losses.

Margit added that the advantage of the better motion sequence greatly outweighs any disadvantages created by the belt.

The project was not only successful from a scientific point of view, but the personal feedback of the test participants was also very good, reports the researcher.

She commented: “It took a little time for people to get used to, but then they were all happy with it.”

The researchers are now looking for business partners to develop a marketable product from the prototype.

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