Page 278 - Handbook of Electronic Assistive Technology

Chapter 9 • Powered Mobility 267

The vast majority of joysticks operate proportionally, that is to say small deflections
induce small movements of the chair and larger deflections a proportionally larger
response. The joystick can be moved in any direction, which allows easy correction of
directional changes without loss of speed.
Manufacturers offer a range of joystick and control modules of differing complexity
to suit the needs of the person. For those who cannot use a standard joystick, there are a
variety of options:
• Alternative joysticks:
• Heavy duty, but tend to be simple switched movements rather than proportional.
• Tray mount, where the arms require full support or where a mid-line position is
required for postural reasons.
• Light touch, where the person’s primary issue is muscle weakness.
• Mini-joystick, where the person can make only very small movements.
• Switched input:
• An array of simple on/off switches (between one and five).
• A switch or switches in combination with a clock face scanner (the user hits the
switch when the clock face is lit in the direction of intended travel).
• Sip/puff tubes which the person holds in their mouth. The four directions of
movement are commonly provided by short sip/long sip/short puff/long puff.

It should be noted that switched input is only used where proportional control is not an
option because the client does not have sufficient manual dexterity to control a proportional
joystick effectively with their hands, or sufficient range of movement in their head to use a
chin joystick, or may have no hands at all. In which case other body parts can suffice. For
example head, arms, knees and feet. It is quite possible to approximate proportional driving
with an array of switches that can control and modify the direction of the chair in real time.
Driving with a scanning direction controller using switches can be slow and tedious. The
small directional changes used with a joystick to correct for undulations in the floor/ground
or for the pile of carpet indoors are corrected much more slowly with switched input – one
must stop, turn left/right slightly and then carry on ‘straight’ until a further directional cor-
rection becomes necessary; this results in repeated stops and slow progress. More recent
systems do however allow a degree of directional adjustment “on the fly” but these become
increasingly more complex to set up for the wheelchair service, and more complex to use by
the driver of the chair. You could for example have someone driving with a scanner using a
foot switch as the main input, and then have two head switches for left and right “Nudge”.
With complex systems such as this it becomes even more important that the technical teams
putting these systems together are familiar with good electronics engineering practice, as a
number of connectors will be needed to allow removal of the headrest and footplates etc.
And these components must be robust and reliable to cope with heavy repeated usage. In
addition, to possible misuse they receive when out in the real world. That being said, if it is
the only option for independent driving, there is still significant potential benefit.
This is not an exhaustive list of control system inputs and the market is developing
constantly, so other options will be available.