The usability criterion was pursued by designing the navigation
module with two levels of autonomy and making use of
the M3S protocol for the design of the user interface. In fact,
the use of this protocol allows a rapid and low-cost substitution
of the user command devices, which depends on the types
of remaining functional abilities of the user, without the need
to re-adapt the other modules of the system. Moreover, the different
levels of autonomy of the navigation module allow the
tailoring of the system to different levels of users’ disabilities.
The user interface was developed to be flexible (in accordance
with the M3S choice) and to have a low level of complexity with
respect to the controls/activities required to the user.