Biomedical Engineering Reference
In-Depth Information
Users of this first prototype, however, felt uncomfortable due to pressure exerted
by the parachute-like harness. In subsequent work, the harness was therefore replaced
with a belt around the waist [
8
]. A brake pad was placed at the toe of the roller skate
in order to increase the stability of the walker. While the walker steps forward, the
break-pad enhances the friction force in the rear foot.
In 1992, the improved Virtual Perambulator was utilized to study the sense of
travelled distance [
8
]. The test course for the experiment was a straight path. The
scene of the test space provided to the subjects was a plain wall and floor as well as
a flag. Subjects were asked to walk along the path from the starting area to the goal
while watching the CG image in the HMD. The width of the path and the height
of the walls were 3 m. The starting area is 5 m deep and the depth of this area was
reported to the subjects. As subjects moved along the course, they memorized the
distance between the starting line and the flag. After they finished walking, they were
asked to plot the position of the goal on a data sheet in which the walls and starting
area were marked. The results showed that Stevens' power law [
26
] could be applied
to explain the estimated distances.
This second prototype still exhibited two major flaws: (1) The waist belt restricted
vertical and turning motions of walkers' bodies, and (2) The weight and height of
the roller skate affected natural motion. In order to overcome these problems, a new
frame and sliding device was developed [
9
]. A hoop was set around the walker's
waist in which he/she could physically walk and turn about. The diameter of the
hoop was 60 cm. The walker could freely change the direction of walking. Novice
users of the system could hold the hoop so that they can easily keep the balance of
their bodies, while trained users of the system could push their waists against the
hoop and learn to walk fast or can even run. Since no harness is used, walker's body
had no restriction. A new sliding device based on rubber sandals instead of steel roller
skates was also developed. A layer of low friction film was placed at the middle of
the sole. Rubber in the toe region played the roll of a brake pad. Material of the floor
surface was selected for compatibility with the low friction film and brake pad. The
device was demonstrated at the Interactive Communities venue at SIGGRAPH'95.
During the five-day conference, 235 people experienced the device. The behavior of
the walkers was observed, and 94 % of them were found to succeed in rhythmical
walking [
9
]. The main limitation of the Virtual Perambulator was found to be that
the device itself is passive. Walkers had to slide their feet by themselves and they
had to get accustomed to the sliding action.
9.2.2 Powered Shoes
Powered Shoes is a locomotion interface using motorized roller skates [
15
]. A com-
pact and light-weighted drive mechanism is put underneath the sole. A large force is
required to move the walker so that the motor for the locomotion interface could not,
itself, be placed underneath the sole. A flexible shaft was instead used in order to
separate the motor from the roller. Motors and batteries are the heaviest parts of the
