preface to haptics

The term “haptics” unlike the terms “optics” or “acoustics” is not so well-known
to the majority of people, not even to those who buy and use products related to
haptics. The words “haptics” and “haptic” refer to everything concerning the sense
of touch. “Haptics” is everything and everything is “haptic”, because it does not
only describe pure mechanical interaction, but also includes thermal- and pain- (nociception)
perception. The sense of touch makes it possible for humans and other
living beings to perceive the “borders of their physical being”, i.e. to identify where
their own body begins and where it ends. With regard to this aspect, the sense of
touch is much more efficient than the sense of vision, as well in resolution as in the
covered dihedral angle, e.g.: In the heat of a basketball match a light touch on our
back immediately makes us aware of an attacking player we do not see. We notice
the intensity of contact, the direction of the movement by a shear on our skin or a
breeze moving our body hairs - all this is perceived without catching a glimpse of
the opponent.
“Haptic systems” are divided into two classes1. There are the time-invariant systems
(the keys of my keyboard), which generate a more or less unchanging haptic effect
whether being pressed today or in a year’s time. Structures like surfaces, e.g. the
wooden surface of my table, are also part of this group. These haptically interesting
surfaces are often named “haptic textures”. Furthermore, there are active, reconfigurable
systems, which change their haptic properties partly or totally dependent on
a preselection - e.g. from a menu. Finally, there are combinations and hybrid forms
of systems, which are presented and explained in the corresponding chapters. The
focus of this book is on the technological design criteria for active, reconfigurable
systems, providing a haptic coupling of user and object in a mainly mechanical un-derstanding. Thermal and nociceptive perceptions are mentioned according to their
significance but are not seriously discussed. This is also the case with regard to passive
haptic systems.
The fact that you have bought this book suggests that you are interested in haptics.
You might have already tried to sketch a technical system meant to fool haptic perception.
And this attempt may have been more or less successful, e.g. concerning
your choice of the actuators. Maybe, you are just planning a project as part of your
studies or as a commercial product aimed at improving a certain manual control or
at introducing a new control concept. Approaches of this kind are quite frequent.
Many of the first active haptic systems were used in airplanes, to make aware of
critical situations by a vibrating control handle. Nowadays, the most wide-spread
active haptic system surely is the vibration of a mobile-phone. It enables its user to
notice the reception of a message without visual or auditory contact, whereby even
the type of the message - SMS or phone call - is coded in this buzzing haptic signal.
More complex haptic systems can be found in automotive technology, as e.g. reconfigurable
haptic control knobs. They are typically located in the center of the control
console and are usually part of complex luxury limousines. Today, multidimensional
haptic interaction is no longer limited to navigation- or modeling purposes of professional
users, but has also found its way into interaction during computer gaming.
Maybe, you are a member of the popular group of doctors and surgeons actively
using haptics in medical technology. There has been a continuous increase of, the
complexity of the tools for minimally-invasive surgery - longitudinal instruments
with a limited degree of freedom to inspect and manipulate human tissue through
small artificial or natural openings in the human body. This automatically results
in the loss of the direct contact between surgeon and the manipulated tissue. For
decades, the wish to improve the haptic feedback during such kinds of applications
and/or the realization of training methods for minimally-invasive surgery has been
a high motivation for researchers in haptic device design, however without a satisfactory
commercial breakthrough, yet significant improvements in telemanipulation
and simulation have been achieved.
Despite of or even because of the great variety of projects in industry and research
working with haptic systems, the common understanding of “haptics” and the terms
directly referring to it, like “kinaesthetic” and “tactile” are by no means as unambiguous
and indisputable as they should be. In this book, we, the authors, intend to
offer you a help to act more safely in the area of designing haptic devices. This book
will begin with the presentation of the terminology and its usage according to what
we regard as appropriate. Then it will provide a deeper understanding of haptics and
a simplified engineering description, and will finally lead to concrete instructions
and recommendations for the design of technologically complex haptic systems.
Besides the intention to generate real hardware design, there is another reason for
dealing with haptic device design: A continuing ambition to extend one’s knowledge
of haptic perception. This discipline, named “psychophysics” is an “unsharp”,
non deterministic science formulating hypotheses and systematically checking them
with the help of experiments and observations. These experiments are paramount to
any progress. Consequently, special attention has to be paid to their quality and theparameters observed. As a by-product of this important science of haptic research
a plurality of devices and technical systems have been built. In fact psychophysics
uses expertise in many different disciplines to solve its problems. As a consequence,
important and creative engineers and scientists like Prof. HONG TAN and Prof. VINCENT
HAYWARD have not only been designing high fidelity and very efficient haptic
devices, but are also heavily involved in the research on psychophysical parameters.
Psychophysics with emphasis on haptic questions is a very dynamic science. Every
year, an uncounted number of results and experiments are published at congresses
and in journals. Lately, MARTIN GRUNWALD [79] has published a notable summary
of the latest state of knowledge. The book you are holding in your hands
does not claim to keep up with every detail of this psychophysical progress. However,
it tries to include as many of its findings as possible into the design of haptic
devices. This book has been written by and is addressed to engineers of all the disciplines
mentioned before: Design-engineers representing mechanical engineering,
hardware-near electrical engineering, control-engineering, software-engineering or
as a synergy of expertise in all disciplines of mechatronics.
As said before, the haptic sense is doubtlessly gaining in importance. This can be
concluded from the great number of scientific publications on this subject and from
the fact that all relevant distal senses like the senses of sight and hearing have already
been provided with synthetic information in almost perfect quality in every-day life.
“Perfect quality” may have different meanings depending on the actual context. A
realistic rendering of a sensual experience can be an important requirement. The
resolution of a 3D-monitor has to be below the resolution capability of the human
eye in color dynamics and spatial distances between the picture elements (pixels).
Sounds have to be traceable in space and must not interfere with artifacts of the
storage- or transmission medium. In different circumstances attracting attention can
be another “perfect quality”. Typically, warning signals in the dashboard of a car
are visual examples, so are acoustic signals in the cockpit of an airplane. Another
demand on “perfect quality” can be the simultaneous requirement of high discriminabilty
and large range - just think of navigational signals for ships. Both areas -
optics and acoustics - have been subject to intense research for decades and have
been provided with numerous intelligent device designs. In many cases the borders
of the human capability of perception of the information provided have been reached
or even crossed nowadays. At this point it is obvious to make use of another human
sense to transmit information. Another motivation is the true-to-life simulation of
virtual environments. After visual and auditory presentation having reached a high
quality, the focus is directed to the haptic sense as being the next important one.
Only this sense enables us to experience our physical borders and the synergy of
interaction and perception.
Further areas of haptic research are telepresence and telemanipulation systems. In
these cases, an intuitive and immediate feedback is a prerequisite for a safe handling
of e.g. dangerous and / or valuable materials. There are reasons enough and
to spare for dealing with the design of haptic devices which are demanded by the
market. However, experts are rare and the access to this subject is difficult. The design
of haptic devices demands interdisciplinary knowledge which should includethe basics of the properties of haptic perception and its dynamic-dependence on amplitude
and frequency. Furthermore an overview of technological solutions, like the
designs of actuators, kinematics or complete systems including software-solutions
and the interfaces to simulations and virtual reality systems may be extremely helpful.
For designing virtual reality systems it is also necessary to know the concepts of
haptic renderings to enhance communication between soft- and hardware engineers.
The authors of this book regard their task as being fulfilled as soon as this book
helps to fascinate more design-engineers by the development of haptic devices, thus
speeding up the creation of more and better haptic systems available on the market.