Biomedical Engineering Reference
In-Depth Information
These sensors are the tactile array sensor, fingertip force-torque sensor, and various
dynamic tactile sensors.
At present, the types of contact information required for manipulation control have still
to be fully established. Depending on the details of each task, the sensing requirements
will certainly vary and will range from little or no sensing at all, as in the case of a
simple pick-and-place operation in assembly operations, or a great deal of sensing and
contact information as when rolling, sliding, or regrasping an unknown object during
manipulation. One important distinction is between continuous sensing that is used in
real-time control of the fingers, and simple threshold detection that is used in 'guarded
moves.' There have been few reports of experimental investigations of manipulation with
robot hands. Thus the sources of the hypotheses about sensing in manipulation presented
here are mainly human contact sensing and robotic grasp analyses [115, 117, 118].
10.10 Virtual Environment
More and more research and corporate resources are being invested in the development of
VEs. The challenge of virtual reality technology is to provide users with sensory stimu-
lations that are as 'realistic' as possible, that is, for a given situation, producing a sensory
flow giving rise to the same perception as that experienced in 'real' life. Most of the
VEs built to date contain visual and spatialized sound displays of high fidelity, whereas
haptic display technology that allows for manual interactions with these environments
clearly lags behind. Yet, being able to touch, feel, and manipulate objects, in addition
to seeing and hearing them, is essential for realizing the full promise of VEs. Indeed,
haptic perception provides a sense of immersion in an environment that is otherwise not
possible. In addition, one of the most important potential applications of virtual reality
displays is the development of training and simulation systems, especially in the domains
where real practice presents risks for the involved persons. In this regard, haptic displays
have a critical role to play since the main part of our interactions with the environment
involves tactual and manipulative skills. For instance, a haptic-based virtual reality display
can be very useful in providing 'safe' surgery or medical exploration training to novice
surgeons, in both the human and veterinary fields [119 - 122], in which any mistake can
have life-threatening consequences. Unfortunately, even by employing the most advanced
technological approach it is still not possible to construct a haptic device that generates a
satisfactory facsimile of the real world, due to mechanical, temporal, and frequency con-
straints. In virtual reality environments, a person interacts with a simulated environment
within which the person perceives virtual objects through the senses with a high degree
of freedom. He/she can move objects, react to them, and manipulate them at their natural
size as would be possible if they were real. For instance, monitors cannot display real
movements of objects, but they are able to create an illusion of movement by succes-
sively displaying single pictures faster than human visual perception can resolve them.
This example illustrates how taking into account the specificities of human perception,
and exploiting its limits, can allow us to by-pass these technical limitations. Psychophys-
ical experiments have traditionally used three methods for testing the subjects' perception
in stimulus detection and difference detection, which include the
method of limits
,the
method of constant stimuli
,andthe
method of adjustment
. In the method of limits, some
property of the stimulus starts out at a level so low that it cannot be detected; then this
level is gradually increased until the participant reports that they are aware of it. In the
