Biomedical Engineering Reference
In-Depth Information
Figure 7.2
Softness display prototype [6] (See Plate 14)
using a computer model and a tactile force-feedback device (ERGOS [5]). Their experi-
ments illustrated that the addition of tactile feedback (virtual finger deformability in this
investigation) to force feedback, increases both accuracy and the number of tasks accom-
plished (in this investigation, following the task, they modeled a virtual bridge contour
for evaluation of feedback accuracy).
In work conducted by Scilingo
et al
. [6, 7], a combination of a kinesthetic and tactile
display was proposed and developed. This system is capable of independent and accurate
rendering of both kinesthetic and cutaneous cues in order to provide perception and
precise discrimination of softness. In their early work [8], they illustrated that most of
the cutaneous information can be derived from contact force and contact area (spread rate
of contact area). In order to render softness, they proposed a novel softness display [8]
consisting of a pneumatic device that contained a set of cylinders with different radii,
as shown in Figure 7.2, and combined this in series with a commercial force-feedback
interface, the Delta Haptic Device (DHD). In this system, they assigned two independent
control inputs (chamber pressure and DHD force) to the cutaneous and kinesthetic parts
of their simplified system.
Mechanical interaction during contact causes several complex stimulations of receptors
in the skin and in the proprioceptive system [9]. To illustrate the complexity of contact,
and the need for integrating kinesthetic and cutaneous cues, Scilingo
et al
. [6] proposed an
experiment to show how two objects having an equal kinesthetic cue can present different
cutaneous cues, and vice versa. To assess the impact of integration and performance
of their proposed integrated display, they conducted psychophysical experiments, and
compared the subjects' indirect perceptions of softness with those obtained by direct touch
on physical objects. It can be observed from their results that the subjects interacting with
the integrated haptic display were able to discriminate the softness better than by using
either purely kinesthetic or cutaneous displays. By referring to Srinivasan and LaMotte's
work [10], it can be concluded that for compliant objects with rigid surfaces, a combination
of both tactile and kinesthetic information (active touch) is essential, otherwise, if only
one or the other were used, maximum discrimination would not be possible, as indicated
by Lederman and Klatzky [11].
