Page 286 - Handbook of Electronic Assistive Technology

Chapter 9 • Powered Mobility 275

• Types of tilting mechanism: There are different types of tilt-in-space available. To
determine which is the most suitable, the first question is how much tilt is required.
Some individuals will need a large amount for true pressure relief and to assist
with their management of posture within the chair, while others may only require a
little tilt to stabilise their position and to help them rest in the daytime. The second
question is how much tilt will be required in the future – with some conditions,
typically motor neuron disease, deterioration can be foreseen and so it is advisable
to build in additional features, such as tilt, from the start, thereby future-proofing
the chair. Fitting these at a later stage is usually financially costly (parts and
labour).

There are two prevalent mechanical designs of tilt-in-space mechanisms:

1� Pivot tilt has a single pivot about which the seat tilts. This tends to be at the back and
is now less frequently used. The stability of the chair becomes impaired with larger
amounts of tilt because the person’s weight is transferred backward as the mechanism
moves through its arc. As a result, it tends to offer less of a range of tilt, typically only
15–25 degrees; this will be sufficient for some people but not all.
2� ‘Centre of gravity’ tilt or ‘floating’ tilt tends to be offered by the more advanced
chairs/seating systems and usually goes hand in hand with a greater degree of tilt. As
the seating is tilted it is drawn forward concurrently, thereby maintaining the centre
of gravity very close to its position when the chair is upright; this is achieved by using
four pivots and two link arms each side, which allows the chair to move within its
own chassis footprint and means that the chair remains stable (largely). It can have a
shorter overall length as the tilt is articulated within the frame, but the weight is kept
central to the chair.
a� Disadvantages of a tilting system:
i� The increased number of mechanical components can add weight but with a
powered chair this is less of an issue.
ii� Tilt generally adds cost and the upcharge can vary widely.
iii� Some tilting chairs are longer than those without the feature, which may have
implications for access around the home, although those with centre of gravity
shift are less affected.
iv� Individuals with intellectual disabilities sometimes struggle to understand the
concept of a tilting system, and so may struggle to use it effectively. The person
can be respectfully encouraged to use the feature but it cannot be enforced
where the person has capacity to make their own decisions.
v� In some situations people are left in a tilted position where ideally they should
be in a more upright posture (e.g., to complete a functional task).
b� Transportation:
i� It can be challenging to manoeuvre a bulky powered chair up a ramp into a
vehicle, either for an occupant or an attendant.
ii� The additional height of some powered chairs can make car door apertures and
inner roof heights challenging.