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"Implementing force feedback on a wheelchair"
Background
All human-computer interaction is enabled and
thus also limited by the interfaces. The computer does not understand
human signals and the human does not understand computer signals.
The most common input interfaces are keyboard and mouse, the most
common output interface is the monitor. The experience of the
interaction with the computer has to go through these devices.
Much of the experience is limited by the interfaces, in the real
world you don't have separated "interfaces". In the
real world you don't navigate with your body and get only visual
feedback, you use all senses when you interact with the world.
When moving around you normally use three of them (sight, hearing
and touch). Example: If you walk into a wall the major experience
you can feel that the wall contact you in the face, torso and
so on, the minor experiences are that your eyes has to focus on
a object close, the sounds echos in a special way (taste and smell
is often not involved).
In VR (Virtual Reality) there are other navigating devices such
as, wand, tracking devices (tracks sensors which are wearable),
wheelchairs. Wheelchairs and trackers are more intiutive then
wands, but are more expensive, they are also more limited to each
device natural behavour (try to imagine navigate a aeroplane using
a wheelchair).
The disadvantages with tracking and wheelchairs is that if you
exeeds the limits of the virtual world you can't get any feedback
other then visual, and this could get very confusing.
The advantages with a wheelchair is that it has a real world existance,
many users have tried it before, no disturbing cables, very intuitive
to navigate.
Haptic devices.
Haptic devices differs from the normal input
devices, they are two-way communication devices, you give an input
signal and get an output signal from the same device.
When using haptic devices the exceeding limit advantages mentioned
above can be eliminated, which when simulating the real world
will strongly extend the experience of the presence and make the
interaction easier for both the novice and experienced.
The haptic device presents the limit in some way, often by preventing
the interacting device from advance any further.
Wheelchair navigation
Navigating with a wheelchair in a simulated world
is very intuitive even without feedback from the wheelchair, when
sitting in a wheelchair you can only control your movement by
rotating the two steering wheels. Sitting in a wheelchair you
have a "frame" around you, when you collide with a wall(with
a not to high velocity) your body will remain in the wheelchair
and the only thing you feel is the wheelchair shaking and you
can't move the wheels any further in that direction. This restricted
feedback is an ideal situation when used as a interface to control
computer generated enviroments, when you sit in a wheelchair you
will automaticly expect limited feedback.
Wheelchair haptics
The feedback you can get from a wheelchair when
moving around is:
The steering wheels can accelerate and deaccelerate, eg. you need
to use more or less force to make the wheel rotate in desired
velocity. The wheel rotation feedback is the major feedback for
fine grained motion control, it is also adds experience of the
velocity.
Vibrations & impulses transplanted through the seat. This
is the major feeback for coarse motion feedback, like collisions.
These two parts are clearly distinguished from each other, and
the second part can be solved by using already existing motionplatforms.
This project implements the first part, simulating the steering
wheels rotation. When moving slowly against the wall, you can
feel a little bump, but after that the only feedback is that you
can't rotate the wheel anymore in that direction.
The components involved for the haptic feedback are:
- MTS SFD-230 servomotor controller
- MTS servomotor S561D130R000
- Computer with rs-232 interface.
- osgVortex
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