Biomedical Engineering Reference
In-Depth Information
Composite
Plate
Voice-coil
Actuator
Suspension
Element
Force
Sensor
30 cm
Fig. 12.7
Vibrotactile floor interface hardware for a single tile unit.
Left
(View) showing main
components.
Right
Side view with top dimension
impacts with the plate, and low-frequency forces generated by active human motions,
limited in bandwidth to no more than 10 Hz [
9
,
110
]. A haptic simulation provides
feedback approximating the vibration response felt during interaction with a virtual
object. The rendering algorithms are of admittance type, computing displacements
(or their time derivatives) in response to forces applied to the virtual object. Force
sensing is performed via four load cell force transducers (Measurement Systems
model FX19) located below the vibration mount located under each corner of the
plate. Although the cost for outfitting a single-plate device with these sensors is not
prohibitive, potential applications of this device to interaction across distributed floor
surface areas may involve two dimensional
m
×
n
arrays of tiles, requiring a number
4
mn
of sensors. As a result, in a second configuration, four low-cost resis-
tive force sensors are used in place of load cells. After conditioning, the response
of these sensors to an applied force is nonlinear, and varies up to 25 % from part
to part (according to manufacturer ratings). A linearization and calibration of force
sensing is performed [
112
] ensuring a response accurate to within a few percent.
Analog data from the force sensors is conditioned, amplified, and digitized, and used
as an input to drive a physically-based simulation of a ground surface such as sand,
snow, or ice. Vibromechanical feedback is provided by a single Lorentz force type
inertial motor (Clark Synthesis model
N
=
) with a usable bandwidth of about
25 Hz to 20 kHz, which is driven using standard digital and analog audio hardware.
The Fig.
12.8
provides an overview of the system.
TST429
12.3.4.2 Actuated Shoes
Actuated shoes provide a mobile solution to foot-floor interaction setups, not requir-
ing the use of large floors laid out in specific spaces. However, the realization of
a mobile device delivering the same cues as a static actuated floor poses serious
technical questions. While the size of the device needs to remain small enough not
to impair the natural walking gait of the user, the intensity of the signals it delivers
must allow the rendering of perceivable interaction cues. Power supply as well as
