Biomedical Engineering Reference
In-Depth Information
1
Introduction to Tactile Sensing
and Display
1.1 Background
Throughout the ages, humans have become accustomed to the environment by using their
five senses: sight (vision), hearing (audition), touch (taction), smell (olfaction), and taste
(gustation). Most of us subjectively experience the world through these five dimensions,
although only two of these, sight and hearing, have been reliably harnessed for the work
of objective scientific observation. For the senses of smell, taste, and touch, however,
objective and accurate measurements are still being sought. This chapter will deal mainly
with the under-represented sense of touch, which perceives temperature, force, force
position, vibration, slip, limb orientation, and pain. The sense of touch confers upon us a
haptical experience without which it would be difficult to write, grasp a light object, or
to gauge the properties of objects [1]. Given the importance of touch (tactile sensing) in
scientific work and daily life, researchers have been striving to understand this sense more
thoroughly, with the goal of developing the next generation of tactile-based applications.
Though the concept of replaying audio and visual recordings is quite familiar to us, the
applications and devices for gathering tactile information and rendering it into a useful
form is not, as yet, well understood or characterized.
A conceptual comparison between collecting and displaying information for visual,
auditory, and tactile systems is shown in Figure 1.1.
Viewed objectively, touch is perceived when external stimuli interact through physical
contact with our mechanoreceptors. Contrary to our other senses, which are localized
in the eyes, nose, mouth, and ears, the sense of touch is a whole-body experience that
comprises arrays of different nerve types and sensing elements. Our skin is capable of
sensing force, the position of applied force, vibration (pulsation), softness, texture, and
the viscoelasticity of any object with which it comes into contact. This permits us to
determine things about any object we touch, such as mass distribution, fine-form features,
temperature, and shape. To some extent, these senses that are felt by the fingers can be
simulated by using signals from tactile sensors in order to provide proportional input
control to any grasping application [2]. Although touch is a whole-body experience,
research on touch-based (haptic) systems focuses primarily on the hand and particularly
the fingertips, which contain the greatest number of tactile receptors. Tactile information is
