Biomedical Engineering Reference
In-Depth Information
Fig. 9.7
Overall view of
Torus Treadmill
9.3.3 Control Algorithm of the Torus Treadmill
A scene of the virtual space is generated corresponding with the results of motion
tracking of the feet and head. The motion of the feet and head are measured by a Polhe-
mus FASTRAK. The device measures 6 degree-of-freedom motion. Sampling rate of
each point occurs at a rate of 20 Hz. A receiver is attached to each knee. Sensors cannot
be put near the motion floor because a steel frame distorts magnetic field. The length
and direction of a step is calculated by the data from those sensors. The user's view
point in virtual space moves corresponding with the length and direction of the steps.
To keep the walker in the center of the walking area, the Torus Treadmill must be
driven in correspondence with the walker. A control algorithm is required to achieve
safe and natural walking. The walker is not connected to a harness or mechanical
linkages, since such devices restricts the motion and inhibits natural walking. The
control algorithm of the Torus Treadmill must be safe enough to allow removal of
the harness from the walker. At the final stage of the Virtual Perambulator Project,
the harness could be successfully removed using a hoop frame. The walker could
freely walk and turn around in the hoop, which supports the walker's body while
he/she slides the feet. The function of the hoop in the control algorithm of the Torus
Treadmill was simulated by putting circular deadzone in the center of the walking
area. If the walker steps out of the area, the floor moves in the opposite direction so
that the walker is carried back into the deadzone (Fig.
9.8
).
