Biomedical Engineering Reference
In-Depth Information
[
33
,
71
,
80
], although design issues affecting their perceptual transparency have
often been neglected. As case studies, two approaches are described below, starting
with floor-based stimulator and continuing with a shoe-based stimulator.
12.3.4.1 Actuated Floors
Floor-based systems for providing multimodal feedback to the foot offer the advan-
tage of easy accessibility, since users are not required to wear any special footwear
or equipment in order to use them. Furthermore, they can be readily designed with an
extensible architecture, which allows them to be networked and powered easily, as
they can be integrated within existing room infrastructures. However, on the negative
side, such systems can be said to be somewhat invasive, since they require modifica-
tions to the existing floor infrastructure of a building, thus requiring a comparatively
permanent installation space. The workspace available to users—that is, the amount
of real space within which they can interact—depends on the size of the actuated
floor, with a larger workspace inevitably entailing higher costs and complexity.
The vibrotactile floor tile interface developed by Visell et al. [
106
,
107
,
110
,
111
] represents the first systematically designed device of its type for haptic human-
computer interaction. Passive floor-based vibrotactile actuation has been used to
present low frequency information in audiovisual display applications, for special
effects (e.g., vehicle rumble), in immersive cinema or VR settings [
99
]. The fidelity
requirements that must be met by an
interactive
haptic display are, however, higher,
since users are able to actively sample its response to actions of the feet. The device
of Visell et al. is based on a high fidelity vibrotactile interface integrated in a rigid
surface, with visual feedback from top-down video projection and a spatialized,
eight-louspeaker auditory display. The main application for which it was envisioned
is the vibrotactile display of virtual ground surface material properties for immer-
sive environments. The device consists of an actuated composite plate mounted on
an elastic suspension, with integrated force sensors. The structural dynamics of the
device was designed to enable it to accurately reproduce vibrations felt during step-
ping on virtual ground materials over a wide range of frequencies. Measurements
demonstrated that it is capable of reproducing forces of more than 40 N across a
usable frequency band from 50 to 750 Hz. In a broader sense, potential applications
of such a device include the simulation of ground textures for virtual and augmented
reality simulation [
112
] or telepresence (e.g., for remote planetary simulation), the
rendering of abstract effects or other ecological cues for rehabilitation, the presenta-
tion of tactile feedback to accompany the operation of virtual foot controls, control
surfaces, or other interfaces [
111
], and to study human perception. In light of the
latter, an effort was undertaken to ensure a high fidelity response that would avoid
the reproduction of vibromechanical stimuli.
The interface of the device (Fig.
12.7
) consists of a rigid plate that supplies vibra-
tions in response to forces exerted by a user's foot, via the shoe. The total normal
force applied to the plate by a user is measured. It can be assumed to consist of
two components: isolated transients with high frequency content, generated by foot
