16-05-2012, 12:58 PM
DESIGN AND OPTIMIZATION OF A WHEELCHAIR FOR BASKETBALL USING CAD
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Abstract
During last decades sport activities for disabled people are practiced by many and many athletes,
both amateurs and professionals. In order to give the possibility to play safely a variety of sports, the
equipments have to be designed with more care than those for able people. Many factors have to be
taken into account: athletic performance, safety of both player and opponents, comfort and reliability.
For this reason modern computer aided design methodologies seem to be a valid instrument to
improve quality of equipments and fulfil the regulations as well. In this paper the authors describe the
application of CAD-Multibody techniques to an optimization of a wheelchair for basketball. The target
of the investigation is to give to the athlete the possibility to perform quick forward accelerations
without rollover tendencies. For this purpose a chair with a self adjustable cushion has been designed.
The behaviour of several mechanisms has been virtually simulated and compared: simple pendulum,
slider-crank assembly and a combined-multilink. Performances have been assessed simulating the
working operation using a virtual dummy embedded into CAD.
Keywords: sport engineering, virtual model.
Introduction
During last years the interest for sport activities for disabled people is increased enormously.
The causes of this success are due to the organization of dedicated tournament, the improvement of
sport equipments and to the attention paid by the media. This positive trend has allowed disabled to
play a lot of activities: tennis, rugby, ski, basketball. In order to make easier this practice many
equipments have been redesigned, others have been reinvented, others just modified. For these reasons
interesting research activity have been started up [1]. The target is to design new devices to improve
the performance of the athletes looking at their less abilities, comfort, and respecting the regulations.
During last years a lot of international patents have been registered concerning different sport
activities for disabled.
Figure 1: Images from wheelchair basketball match, and main limits imposed by regulations
Among sport activities for disabled, the basketball (or better the wheelchair basketball) is one of
the first to be played and at present it is one of the most practiced. All people with upper limb
functionality may play this sport. In Europe, the International Wheelchair Basketball Federation
(IWBF) indicates a quote of 5160 professional athletes and 500 teams of first and second division.
In Italy there are 380 professional athletes who play in 16 teams.
Since there are different kinds of disabilities, international regulations [2] state that each player
has to be evaluated by a medical committee that assign him a coefficient of disability (from 1, highly
disabled, to 4.5 lowly disabled). The overall coefficient of disability for each team is computed by
summing the one of each player of the team and it can not exceed the value of 14. This rule ensures a
uniform physical penalty for every team. As concern the wheelchairs the regulations are quite strict.
They may have a cushion of maximum 10 cm of thickness (for players with disability coefficient from
1 to 3) or 5 cm (for players with disability coefficient from 3.5 to 4.5). The foot rest can not be placed
more than 11 cm above ground level, and it must have a smoothed shape. In order to reduce the risk of
rearing, one or two additional wheels (anti-tip device) may be mounted not exceeding the rear wheel
silhouette and not exceeding the distance of 2 cm from the ground level. The plane of sitting may not
exceed 53 cm (at the highest point) from the ground level. The wheelchair must also have two driving
wheels with external rings for propulsion. These rings must have a diameter lower than 69 cm. The
wheelchair must not have steering or braking systems or gearboxes.
In order to find out the design target we have to investigate the recently proposed solutions. The
first one is described in the U.S. Patent n° 5,851,018 (1988). It is about a wheelchair with rear wheel
camber angle which can be adjusted to improve player stability. This feature is obtained with a set of
wheel axle different supports which can be easily changed in order to get the desired camber.
A more interesting solution is described in the U.S. Patent 6,161,856 (2000) where the rear axle
is mounted by means of a suspension system using a four bar mechanism and a rubber element. When
the chair meets an obstacle the suspension system push on the rubber element which dump the
dynamic action. This feature improves both comfort and stability.
Figure 2: Us Patent 5,851,018: an overall image (on the left) and a detailed view of the camber
adjusting system (on the right)
Figure 3: Us Patent 6,161,856: an overall image (on the left) and a detailed view of the four bar
mechanism (on the right)
Biomechanical interaction between player and wheelchair
Before proposing improvements let us investigate a common wheelchair for basketball. The
main components of this equipment are:
• the frame
• the rear axle and the two wheels
• the front wheels
• the footrest
• the backrest
• the anti-tip device
All these components have been modelled into a CAD application referring to actual
dimensioning (Figure 4).
In order to simulate the dynamic behaviour of the system the wheelchair has been assembled together
with a virtual dummy (anthropometrical data are chosen according to [3] and [4]). The interaction
between the dummy and the equipment has been investigated in depth in order to have an accurate
assessment about the force exerted by the player and transferred to the equipment, following the
approach in [5].