ABSTRACT
Multi-touch technology is an advanced
human-computer interaction technique
that recogonises multiple touch points and also includes the hardware devices that implement it, which
allow users to compute without
conventional input devices . Multi-touch consists of a touch screen (screen, table, wall, etc.) or
touchpad, as well as a software that recognizes multiple simultaneous touch
points, as opposed to the standard
touchscreen which recognizes only one touch point at a time. Multi touch using
Frustrated Total Internal Reflection is a simple, inexpensive, and scalable technique for
enabling high-resolution multi- touch sensing on rear-projected interactive
surfaces. Different applications for
multi-touch interfaces both exist and are being proposed. Some uses are individualistic eg iPhone, iPod
touch, MacBook Pro, MacBook Air. The use of multi-touch technology is expected
to rapidly become common place.
TABLE OF CONTENTS
1. INTRODUCTION
1.1
TOUCH SCREEN
1.1.1
TECHNOLOGIES
1.1.2
DEVELOPMENT
2. MULTI TOUCH
2.1
HISTORY
2.2
RECENT DEVELOPMENTS
2.3
FUTURE
3. FTIR
3.1
PRINCIPLES
3.2
DESIGN
3.3.1
REQUIREMENTS
3.3.1.1
HARDWARE
3.3.1.2
SOFTWARE
3.4
WORKING
3.5
ADVANTAGES
3.6
APPLICATIONS
4.CONCLUSION
5.APPENDICES
5.1
APPENDIX I
6.REFERENCES
1. INTRODUCTION
1.1 TOUCH SCREEN
A touch screen is a display which can
detect the presence and location of a touch
within the display area. The term generally refers to touch or contact to the display of the device by a finger or hand. Touch
screens can also sense other passive objects,
such as a stylus. However, if the object sensed is active, as with a light pen,
the term touch screen is generally not
applicable. The thumb rule is: if you can interact with the display using your finger, it is
likely a touch screen - even if you are using a stylus or some other object. Up until
recently, most touch screens could only sense one point of contact at a time, and few have had the capability to sense how
hard one is touching. This is starting to change with the emergence of multi-touch
technology - a technology that was first seen in the early 1980s, but which is now
appearing in commercially available systems.
The touch screen has two main attributes. First, it enables you to interact
with what is displayed directly on the
screen, where it is displayed, rather than indirectly with a mouse or a touchpad. Secondly, it lets one do
so without requiring any intermediate device,
again, such as a stylus that needs to be held in the hand. Such displays can be
attached to computers or, as terminals,
to networks. They also play a prominent role in the design of digital appliances such as the
personal digital assistant , satellite navigation
devices and mobile phone
1.1.1 TECHNOLOGIES
There are a number of types of touch
screen technology
Resistive
A resistive touch screen panel is
composed of several layers. The most important are two thin metallic electrically conductive and
resistive layers separated by thin space. When some object touches this kind of touch
panel, the layers are connected at certain point; the panel then electrically acts
similar to two voltage dividers with connected outputs. This causes a change in the
electrical current which is registered as a touch event and sent to the controller for
processing. Surface acoustic wave SAW
technology uses ultrasonic waves that pass over the touchscreen panel. When the panel is touched, a portion of the wave is
absorbed. This change in the ultrasonic waves
registers the position of the touch event and sends this information to the controller for processing. Surface wave touch
screen panels can be damaged by outside
elements. Contaminants on the surface can also interfere with the functionality
of the touch screen.
Capacitive
A capacitive touch screen panel is
coated with a material, typically indium tin oxide that conducts a continuous
electrical current across the sensor. The sensor therefore exhibits a precisely controlled field of
stored electrons in both the horizontal and vertical axes - it achieves capacitance. The
human body is also an electrical device which
has stored electrons and therefore also exhibits capacitance. When the sensor's
'normal' capacitance field (its
reference state) is altered by another capacitance field, i.e., someone's finger, electronic circuits
located at each corner of the panel measure the resultant 'distortion' in the sine wave
characteristics of the reference field and send the information about the event to the controller
for mathematical processing. Capacitive
sensors can either be touched with a bare finger or with a conductive device being held by a bare hand. Capacitive
touchscreens are not affected by outside elements and have high clarity. The Apple
iPhone is an example of a product that uses capacitance touchscreen technology.
Infrared
An IR touchscreen panel employs one of
two very different methods. One method uses
thermal induced changes of the surface resistance. This method is sometimes slow and requires warm hands. Another method
is an array of vertical and horizontal IR
sensors that detect the interruption of a modulated light beam near the surface
of the screen.
Optical imaging
A relatively-modern development in
touchscreen technology, two or more image sensors are placed around the edges (mostly
the corners) of the screen. Infrared backlights
are placed in the camera's field of view on the other sides of the screen. A touch shows up as a shadow and each pair of
cameras can then be triangulated to locate
the touch. This technology is growing in popularity, due to its scalability, versatility, and affordability, especially for
larger units.
Dispersive signal technology
Introduced in 2002, this system uses
sensors to detect the mechanical energy in the glass that occur due to a touch. Complex
algorithms then interpret this information and provide the actual location of the touch.
The technology claims to be unaffected by
dust and other outside elements, including scratches. Since there is no need
for additional elements on screen, it
also claims to provide excellent optical clarity. Also, since mechanical vibrations are used to detect
a touch event, any object can be used to generate these events, including fingers and
stylus. A downside is that after the initial touch the system cannot detect a motionless
finger. 1.1.2 DEVELOPMENT
Virtually all of the significant
touchscreen technology patents were filed during the 1970s and 1980s and have expired. Touchscreen
component manufacturing and product
design are no longer encumbered by royalties or legalities with regard to patents and the manufacturing of
touchscreen-enabled displays on all kinds of devices is widespread.
The development of multipoint
touchscreens facilitated the tracking of more than one finger on the screen, thus operations that
require more than one finger are possible. These devices also allow multiple users to
interact with the touchscreen simultaneously.
With the growing acceptance of many kinds of products with an integral
touchscreen interface the marginal cost
of touchscreen technology is routinely absorbed into the products that incorporate it and is
effectively eliminated. As typically occurs with any technology, touchscreen hardware and software
has sufficiently matured and been perfected
over more than three decades to the point where its reliability is unassailable. As such, touchscreen displays
are found today in airplanes, automobiles, gaming consoles, machine control systems,
appliances and handheld display devices of
every kind. The ability to accurately point on the screen itself is taking yet
another step with the emerging graphics
tablet/screen hybrids.
2.MULTI TOUCH
Multi-touch is a human-computer
interaction technique and the hardware devices that implement it, which allow users to compute
without conventional input devices e.g., mouse, keyboard. Multi-touch consists of a
touch screen like screen, table, wall or touchpad, as well as software that recognizes
multiple simultaneous touch points, as opposed
to the standard touchscreen i.e. computer touchpad, ATM, which recognizes only one touch point. This effect is achieved
through a variety of means, including but not limited to: heat, finger pressure, high
capture rate cameras, infrared light, optic capture, tuned electromagnetic induction and
shadow capture.
2.1
HISTORY
Multi-touch technology dates back to
1982, when the University of Toronto developed the first finger pressure
multi-touch display. The same year, Bell Labs at Murray Hill published what is believed to be
the first paper discussing touch-screen based
interfaces.
Bell Labs
In 1984 Bell Labs engineered a
multi-touch screen that could manipulate images with more than one hand. The group at the
University of Toronto stopped working on hardware and moved on to software and
interfaces, expecting that they would have access to the Bell Labs work.
A breakthrough occurred in 1991, when
Pierre Wellner published a paper on his multi-touch
Digital Desk, which supported multi-finger and pinching motions.
Finger works
In 1998, FW, a Newark-based company run
by University of Delaware academics John
Elias and Wayne Westerman, produced a line of multi-touch products including the iGesture Pad and the TouchStream keyboard.
Westerman published a dissertation in
1999 on the subject. In 2005, after years of maintaining a niche line of keyboards
and touch pads, Finger works was acquired by Apple Computer.
2.2 RECENT DEVELOPMENTS
Various companies expanded upon these
discoveries in the beginning of the twenty- first century. Mainstream exposure
to multi-touch technology occurred in the year 2007, when Apple unveiled the iPhone and
Microsoft debuted surface computing. The iPhone in particular has spawned a wave of
interest in multi-touch computing, since it permits greatly increased user interaction on
a small scale. More robust and customizable
multi-touch and gesture-based solutions are beginning to become available, among them TrueTouch, created by
Cypress Semiconductor. The following is
a compilation of notable uses of multi-touch technology in recent years. Microsoft
Surface In 2001 Steve Bathiche and Andy Wilson of Microsoft began work on an
idea for an interactive table that mixes
both physical and virtual worlds. Research and Development expanded rapidly in 2004, once the
idea caught the attention of Microsoft
Chairman Bill Gates. In 2007 Microsoft introduced MS, a functional multi- touch
table-top computer based on a standard PC platform including an Intel Core 2 Duo processor, Windows Vista, and 2 GB of RAM
Perceptive Pixel
PP is a company founded by New York
University consulting research scientist Jefferson Y. Han that creates wall displays
and tables that can accommodate up to 20 fingers. Han introduced the FTIR technique to
multi touch screens. The displays use light
emitting diodes along with infrared light to determine the point of contact.
Han envisions large collaborative spaces
that will allow multiple users to work and interact. PPâ„¢s technology is currently being
utilized, in the form of the Multi-Touch Collaboration Wall, by CNN and an unspecified
government contractor everyday programs
with ease and most importantly more than one user can operate the system at any given time.
Apple iPhone, iPod touch, MacBook Air,
and MacBook Pro In 2005, Apple acquired Fingerworks. In 2007 they introduced
the iPhone, marking the first time
multi-touch technology was used on a phone. The iPhone includes such components as a web browser, music player,
video player, and a cell phone without the
use of a hard keypad or stylus. Following the release of the iPhone, Apple also
expanded its use of multi-touch computing
with the new iPod Touch, as well as the new MacBook Air. Multi-touch was later added to the 2008 MacBook Pro line
in the form of a trackpad. Apple is currently
in the process of trying to patent its Multi-touch technology and to trademark the term "multi-touch".
2.3 FUTURE
The use of multi-touch technology is
expected to rapidly become common place. For example, touch screen telephones are expected
to increase from 200,000 shipped in 2006,
to 21 million in 2012. Developers of the technology have suggested a variety of
ways that multi-touch can be used
including:
·
Enhanced dining
experience
·
Concierge service
·
Governmental use
·
Concept mapping
·
Collaboration and
instruction on Interactive Whiteboards
3.FRUSTRATED TOTAL INTERNAL REFLECTION
3.1 PRINCIPLES
Total internal reflection is an optical
phenomenon that occurs when a ray of light strikes a medium boundary at an angle larger
than the critical angle with respect to the
normal to the surface. If the refractive index is lower on the other side of
the boundary no light can pass through,
so effectively all of the light is reflected. The critical angle is the angle of incidence above
which the total internal reflection occurs. When light crosses a boundary
between materials with different refractive indices, the light beam will be partially refracted at the
boundary surface, and partially reflected. However, if the angle of incidence is greater
(i.e. the ray is closer to being parallel to the boundary) than the critical angle â€
the angle of incidence at which light is refracted such that it travels along the boundary
â€
then the light will stop crossing the
boundary altogether and instead be totally reflected back internally. This can
only occur where light travels from a
medium with a higher refractive index to one with a lower refractive index. For example, it will
occur when passing from glass to air, but not when passing from air to glass.
The critical angle is the angle of
incidence above which total internal reflection occurs. The angle of incidence is measured
with respect to the normal at the refractive boundary. The critical angle is given by: where
n
is the refractive index of the less
dense medium, and n
is the refractive index of the denser
medium
An important side effect of total
internal reflection is the propagation of an evanescent wave across the boundary surface. Essentially,
even though the entire incident wave is reflected
back into the originating medium, there is some penetration into the second medium at the boundary. Additionally, the
evanescent wave appears to travel along the
boundary between the two materials. This wave can lead to a phenomenon known as frustrated total internal reflection.
Under "ordinary conditions" it
is true that the creation of an evanescent wave does not affect the conservation of energy, i.e. the
evanescent wave transmits zero net energy. However, if a third medium with a higher
refractive index than the second medium is placed within less than several wavelengths
distance from the interface between the first
medium and the second medium, the evanescent wave will be different from the one under "ordinary conditions" and
it will pass energy across the second into the third medium.
3.2 DESIGN
3.2.1 REQUIREMENTS
Multi touch is designed using the FTIR
technology. FTIR describes the internal reflection
of light .It is force-sensitive, and provides unprecedented resolution and scalability .Large enough to accommodate both
hands and multiple users.This phenomenon
is also used in fingerprint and robot sensors.Allows us to create sophisticated multi-point widgets for
applications 3.2.1.1 HARDWARE
The basic design has a hardware and
software part. Hardware requires basically IR ledâ„¢s,acrylic,camera,projector and a
computer. Infra red light has a higher wavelength than that of visible light .Therefore it has
more intensity and will be felt everywhere inside the denser medium. Acrylic is the
denser medium .It is a synthetic fiber having half the density of glass.An infra red camera
or a webcam is used to catch IR light . A IR block filter of the camera has to
be removed since it blocks IR light. It also consists of a projector and a computer. The object has
to be projected on top of the acrylic from
a computer . Thus acrylic is a virtual display. The IR LEDâ„¢s about 10-20 are arranged on both sides of the acrylic along
its edges .The camera below the acrylic and
the projector located behind to acrylic.
3.2.1.2 SOFTWARE
Computer applications are necessary to
communicate between a multi touch display and a computer.These applications can be developed
within several languages / programming
environments.For example: Processing (P5), Flash, C, C++, Java and others. Because of the usability of certain
APIâ„¢s and the relatively simple visualisation possibilities, P5 or Flash 9, in combination
with Actionscript 3.0 will make a great combination
3.4 WORKING
FTIR describes the internal reflection
of light, inside a certain material. In our case, it will be infrared light, that internally
reflects inside is a piece of acrylic, also known as plexiglas.This way, infrared light is beamed
inside the acrylic and reflects internally.In a simple way, you can say that, IR-light
bounces inside the acrylic, from one side to another.As soon as a finger touches the
acrylic surface, the internal reflection of the IR-light, is interrupted.The infrared light
scatters on the finger tips.Infrared light is invisible to the human eye, but by placing an
infrared camera behind the acrylic your fingertips
will be visible on the infrared camera.The images that are generated by the camera, contain white blobs (caused by the
fingertips). These blobs will be analyzed by software. Every blob corresponds
to certain coordinates. Software can by
analyzing these coordinates perform certain tasks, for example move, resize or rotate objects. Multiple points are obtained on the camera
.Each point is a pixel position. Either a single pixel or a group of pixel . Each point
locations are identified and all operations are performed .Suppose if we want to zoom a picture
we use 2 fingers and move it in or out
to perform zoom in and zoom out respectievely . Two coordinates will be located on the camere .The difference is found
which is put as the offset and it is either
added or subtracted with the locations to zoom out and zoom in respectievely.
3.5 ADVANTAGES
·
Multi touch based on
FTIR is a simple and inexensive technique .It constructs a multi touch display with the
available and less costly materials .
·
Scalable technique that
enables high-resolution graphics .It provides support to any resolution possible as all
multiple points could be generated on a
camera
·
It acquires true touch
image information at high spatial and temporal resolutions.The actual finger print of the
touch is obtained .This could be used to
determine the force sensitivity on displays , either too hard or soft touches can be analysed.
·
It is scalable to large
installations.Any kind of applications can be made to suit multi touch using FTIR . Allows
us to create sophisticated multi-point
widgets for applications
·
Larger shared-display
systems ie it is well suited for use with rear- projection like wall
screens,table tops .All this lead to high resolution graphics.
3.6
APPLICATION
A myriad different applications for
multi-touch interfaces both exist and are being proposed. Some uses are individualistic e.g.,
iPhone, iPod touch, MacBook Pro, MacBook
Air, HTC Diamond . However, multi-touch technology is mainly used to incorporate collaboration into the computing
experience .
A multi touch display can be used in
·
Personal
computers,Laptops,Tabletops,Graphics Tablets .
·
It supports both LCD
and CRT monitors .
·
Telephones ,Watches
,PDAs, Mobile phones.
·
Advanced multi touch
Gaming with high graphics support
·
Governmental,office and
business purposes
·
An enhanced multimedia
experience including audio,video and photo sharing
·
Enhanced dining
experience
Applications for a multi touch display
are never ending . We can even convert a computer to a mere piece of display attached
to a wall or a
4.CONCLUSION
Touch screens are the interface for the
21 st century. Touch screens address the conflicting demands for smaller portable
electronics with larger displays, by eliminating
traditional buttons without sacrificing screen size. The recent release of the iPhone has created a buzz around touch
screen interfaces and its multi-touch acrobatics
have caught the eye of many industry leaders. There are many ways to make a
multi-touch screen. Some of the early designs measured the change in electrical resistance
or capacitance on a surface when fingers touched it. But these devices have limited
resolution, are relatively complex, and don't easily and inexpensively scale up
to large dimensions. Multi-touch technologies have a long history. This technique using FTIR is
simple and easy to implement . It provides
any resolution displays supported with high graphics .The applications being both
made and proposed are plenty in number . A drawback of the approach is that, being
camera-based, it requires a significant amount
of space behind the interaction surface, though we primarily expect application scenarios where rear-projection
would have been employed anyway (e.g. interactive
walls, tables). Also, as an optical system, it remains susceptible to harsh lighting environments.
6.REFERENCES
ü Low-Cost
Multi-Touch Sensing through FTIR by Jefferson Y. Han
ü Buxton,
W., Hill, R., and Rowley, P. 1985. Issues and Techniques in
ü Touch-Sensitive
Tablet Input
ü Donald
Hearn ,M Pauline Baker, Computer Graphics C version, 2/E
ü Pearson
Education ,2003
ü Buxton,
Bill. 2008. Multi-Touch Systems that I Have Known and Loved.
ü http://www.billbuxton.com/multitouchOverview.html
ü How
to build a multi touch by Harry Vaan Der
ü Opensource,MultitouchDisplay,http://www.technologyreview.com/Infotec
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