Haptic Technology

If you thought the Apple iPhone was amazing, then feast your
eyes -- and fingers -- on this phone from Samsung. Dubbed the
Anycall Haptic, the phone features a large touch-screen
display just like the iPhone. But it does Apple's
revolutionary gadget one better, at least for now: It enables
users to feel clicks, vibrations and other tactile input. In
all, it provides the user with 22 kinds of touch sensations.

Those sensations explain the use of the term haptic in the
name. Haptic is from the Greek "haptesthai," meaning to
touch. As an adjective, it means relating to or based on the
sense of touch. As a noun, usually used in a plural form
(haptics), it means the science and physiology of the sense
of touch. Scientists have studied haptics for decades, and
they know quite a bit about the biology of touch. They know,
for example, what kind of receptors are in the skin and how
nerves shuttle information back and forth between the central
nervous system and the point of contact.

Unfortunately, computer scientists have had great difficulty
transferring this basic understanding of touch into their
virtual reality systems. Visual and auditory cues are easy to
replicate in computer-generated models, but tactile cues are
more prob­lematic. It is almost impossible to enable a user
to feel something happening in the computer's mind thro­ugh
a typical interface. Sure, keyboards allow users to type in
words, and joysticks and steering wheels can vibrate. But how
can a user touch what's inside the virtual world? How, for
example, can a video game player feel the hard, cold steel of
his or her character's weapon? How can an astronaut, training
in a computer simulator, feel the weight and rough texture of
a virtual moon rock?

Since the 1980s, computer scientists have been trying to
answer these questions. Their field is a specialized subset
of haptics known as computer haptics. Over the next few
pages, we'll cover how haptic technology works by:

* relating computer haptics to related fields of haptics
research
* characterizing the types of h­aptic feedback required
for realistic virtual touching
* examining haptics systems either in development or
currently available on the market
* exploring current and potential applications

Of course, the prom­ising future of haptics owes much to its
history. In the next section, we'll examine this history to
understand that computer haptics falls on a continuum of
haptics research.

The Haptics Continuum

As a field of study, haptics has closely paralleled the rise
and evolution of automation. Before the industrial revolution,
scientists focused on how living things experienced touch.
Biologists learned that even simple organisms, such as
jellyfish and worms, possessed sophisticated touch responses.
In the early part of the 20th century, psychologists and
medical researchers actively studied how humans experience
touch. Appropriately so, this branch of science became known
as human haptics, and it revealed that the human hand, the
primary structure associated with the sense of touch, was
extraordinarily complex.

With 27 bones and 40 muscles, including muscles located in
the forearm, the hand offers tremendous dexterity. Scientists
quantify this dexterity using a concept known as degrees of
freedom. A degree of freedom is movement afforded by a single
joint. Because the human hand contains 22 joints, it allows
movement with 22 degrees of freedom. The skin covering the
hand is also rich with receptors and nerves, components of
the nervous system that communicate touch sensations to the
brain and spinal cord.

Then came the development of machines and robots. These
mechanical devices also had to touch and feel their
environment, so researchers began to study how this sensation
could be transferred to machines. The era of machine haptics
had begun. The earliest machines that allowed haptic
interaction with remote objects were simple
lever-and-cable-actuated tongs placed at the end of a pole.
By moving, orienting and squeezing a pistol grip, a worker
could remotely control tongs, which could be used to grab,
move and manipulate an object.

In the 1940s, these relatively crude remote manipulation
systems were improved to serve the nuclear and hazardous
material industries. Through a machine interface, workers
could manipulate toxic and dangerous substances without
risking exposure. Eventually, scientists developed designs
that replaced mechanical connections with motors and
electronic signals. This made it possible to communicate even
subtle hand actions to a remote manipulator more efficiently
than ever before.

The next big advance arrived in the form of the electronic
computer. At first, computers were used to control machines
in a real environment (think of the computer that controls
a factory robot in an auto assembly plant). But by the 1980s,
computers could generate virtual environments -- 3-D worlds
into which users could be cast. In these early virtual
environments, users could receive stimuli through sight and
sound only. Haptic interaction with simulated objects would
remain limited for many years.

Then, in 1993, the Artificial Intelligence Laboratory at the
Massachusetts Institute of Technology (MIT) constructed
a device that delivered haptic stimulation, finally making it
possible to touch and feel a computer-generated object. The
scientists working on the project began to describe their
area of research as computer haptics to differentiate it from
machine and human haptics. Today, computer haptics is defined
as the systems required -- both hardware and software -- to
render the touch and feel of virtual objects. It is a rapidly
growing field that is yielding a number of promising haptic
technologies.

Types of Haptic Feedback

When we use our hands to explore the world around us, we
receive two types of feedback -- kinesthetic and tactile. To
understand the difference between the two, consider a hand
that reaches for, picks up and explores a baseball. As the
hand reaches for the ball and adjusts its shape to grasp,
a unique set of data points describing joint angle, muscle
length and tension is generated. This information is
collected by a specialized group of receptors embedded in
muscles, tendons and joints.

Known as proprioceptors, these receptors carry signals to the
brain, where they are processed by the somatosensory region
of the cerebral cortex. The muscle spindle is one type of
proprioceptor that provides information about changes in
muscle length. The Golgi tendon organ is another type of
proprioceptor that provides information about changes in
muscle tension. The brain processes this kinesthetic
information to provide a sense of the baseball's gross size
and shape, as well as its position relative to the hand, arm
and body.

When the fingers touch the ball, contact is made between the
finger pads and the ball surface. Each finger pad is
a complex sensory structure containing receptors both in the
skin and in the underlying tissue. There are many types of
these receptors, one for each type of stimulus: light touch,
heavy touch, pressure, vibration and pain. The data coming
collectively from these receptors helps the brain understand
subtle tactile details about the ball. As the fingers
explore, they sense the smoother texture of the leather, the
raised coarseness of the laces and the hardness of the ball
as force is applied. Even the thermal properties of the ball
are sensed through tactile receptors.

Force feedback is a term often used to describe tactile
and/or kinesthetic feedback. As our baseball example
illustrates, force feedback is vastly complex. Yet, if
a person is to feel a virtual object with any fidelity, force
feedback is exactly the kind of information the person must
receive. Computer scientists began working on devices --
haptic interface devices -- that would allow users to feel
virtual objects via force feedback. Early attempts were not
successful. But as we'll see in the next section, a new
generation of haptic interface devices is delivering
an unsurpassed level of performance, fidelity and ease of
use.