TOUCH SCREEN TECHNOLOGY
A touch screen is a display that can detect the presence and location 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.
The touch screen has two main attributes:
First, it enables one to interact with what is displayed directly on the screen, where it is displayed, rather than indirectly with a mouse or 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 (PDA), satellite navigation devices, mobile phones, and video games.
A touch screen display has three:
the touch sensor, the controller, and the software driver.The software driver is the application program that transcribes touch sensations into commands and
communicates with the operating system installed on the computer.
The controller is a PC card that connects the touch sensor to the PC. It is a small gadget that translates information from
the touch sensor into information that is comprehensible to the PC.
A touch screen sensor is a clear glass panel with a touch responsive surface. The touch sensor/panel is placed over a display screen so that the responsive area of the panel covers the viewable area of the video screen.
History:
Touch screens emerged from academic and corporate research labs in the second half of the 1960s. One of the first places where they gained some visibility was in the terminal of a computer-assisted learning terminal that came out in 1972 as part of the PLATO project.
The HP-150 from 1983 was probably the world's earliest commercial touch screen computer. It doesn't actually have a touch screen in the strict sense, but a 9" Sony CRT surrounded by infrared transmitters and receivers which detect the
position of any non-transparent object on the screen.
Until the early 1980s, most consumer touch screen 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 commercialization of multi-touch
technology.
Touch screens are popular in heavy industry and in other situations, such as museum displays or room automation, where keyboard and mouse systems do not allow a
satisfactory, intuitive, rapid, or accurate interaction by the user with the display's content.
Development:
The development of multipoint touch screen 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 touch screen simultaneously.
With the growing acceptance of many kinds of products with an integral touch screen interface the marginal cost of touch screen technology is routinely absorbed into the products that incorporate it and is effectively eliminated. As typically
occurs with any technology, touch screen hardware and software has sufficiently matured and been perfected over more than three decades to the point where its reliability is unassailable.
With the influence of the multi-touch-enabled iPhone and the Nintendo DS, the touch screen market for mobile devices is projected to produce US$5 billion in
2009. .
Technologies:
The types of technologies that can be found are as follows:
·
Resistive:
The resistive touch screen uses a glass panel with a uniform conductive ITO (Indium Tin oxide) coating on the side
surface. A PET film is a tightly suspended over the ITO coating surface of a glass panel. The glass substrate and the PET film are separated by tiny, transparent insulating dot spacers. The Pet film has a hard coating on the outer side and a conductive ITO coating on the inner side. The structure is
film glass process. The early process is film-film-glass structure.
Resistive Touch Screen Structure
Working Principle
:1. When the screen is touched, it pushes the conductive ITO coating on the PET film against the ITO coating on the glass. That results the electrical contact, producing the voltages. It presents the position touched.
2. The pins (X left) and (X right) are on the glass panel, and the pins (Y up) and (Y down) are the PET film.
3. The microprocessor applies +5V to pin (X left) on the glass panel, and the voltage is uniformly decreasing to pin (X right) for 0V because of the resistive ITO coating on the glass
substrate, and the PET film is grounded. When the touch
screen is not touched, the controller detects the voltage on the PET film is zero. The next electric cycle, the microprocessor applies +5V to pin (Y up) on the PET film, and the voltage is uniformly decreasing to pin (Y down) for 0V. When the touch screen is not touched, the controller detects the voltage on the glass panel is zero.
4. When the touch screen is touched, a voltage on the glass substrate proportional to the X (horizontal) position of the touch appears on the PET film.
This voltage is digitized by the A/D Converter and subjected to an averaging algorithm. Then it is stored and transferred to the host. Hence, the X position is produced.
The next electric cycle, a voltage on the PET film
proportional to the Y (vertical) position of the touch appears on the glass substrate. This voltage is digitized by the A/D Converter and subjected to an averaging algorithm. Then it is stored and transferred to the host. Hence, the
Y position is produced.
Features:
Resistive touch screen deliver cost-effective, consistent and durable performance in environment where equipment must stand up to contaminants and liquids, such as in restaurants, Factories , and hospitals. Include only 75% optical
transparency and the fact that a sharp object can damage the resistive layers. The Analog Resistive technology is perfect for PDAs, web phones, and other handheld consumer
applications. Resistive touch screen can also support Multi touch.
Surface acoustic wave:
On the pure glass substrate, there are four piezoelectric
transmitting and receiving transducers on the three corners for both the X and Y axes. Around the glass, there are four 45- degree reflectors around the glass, divert the ultrasonic bust across touch screen.
SAW Touch screen Structure
Working Principle
:1. The SAW controller sends a 5 MHz electrical signal to the X-axis and Y-axis transmitting transducers. They convert the signal into ultrasonic waves to the reflectors.
These waves are changed direction across the front surface of the touch screen by 45-degree array of reflectors. The 45- degree reflectors on the opposite side gather and redirect
the waves to the X-axis and Y-axis receiving transducers, which reconvert them into an electrical signal. The signal is represented by a wavy curve on a oscillograph.
2. When the touch screen is touched, the finger absorbs a portion of the wave passing across the surface of the panel. The signal received by the receiving transducers is then
compared to the wavy curve that is produced when the touch screen is not touched. The microprocessor in the controller recognizes the change of the wave and calculates a coordinate. This process happens independently for both the X and Y
axes. The coordinates are transmitted to the host for processing. Y- axis transmitting transducer Y-axis
Receiving transducer. Array of reflectors X- axis receiving transducer X- axis transmitting transducer Edge of Active Area.
Features:
The touch screen made by surface acoustic wave is incomparable for clarity and reliability, even in public
environment. It mainly features pure glass for durable scratch resistant surface, superior image clarity, and light
transmission.
The SAW can be used in public places in open environment. Furthermore, it is sensitive and fast on response, accurate touch position performance.
The SAW system works much like the resistive system,
allowing a touch with almost anyobject, except hard and small objects like a pen tip.
SAW can be used in any and all applications for the best possible image clarity an unlimited life.
Capacitive
:Capacitive touch screen is a four multi-layer glass. The two sides of the glass substrate are coated with uniform
conductive ITO (indium tin oxide) coating. The thickness of 0.0015 millimeter silicon dioxide hard coating are coated on the front side of ITO coating layer.
There are electrodes on the four corners for launching electric current.
Construction of Capacitive Touch Screen
Working Principle:
1. Small amount of voltage is applied to the electrodes on the four corners
2. A human body is an electric conductor, so when you touch the screen with a finger, a slight amount of current is drawn, creating a voltage drop.
3. The current respectively drifts to the electrodes on the four corners. Theoretically, the amount of current that drifts
through the four electrodes should be proportional to the distance from the touch point to the four corners.
4. The controller precisely calculates the proportion of the current passed through the four electrodes and figures out the X/Y coordinate of a touch point.
Features:
One advantage of the capacitive system over the resistive system is that it transmits almost 92% of the light emitted from the monitor, whereas the resistive system transmits only about75%.
Also the capacitive system has very long life (about 225 million clicks).
is not damaged by running water applied to the active area. Our capacitive touch screens withstand contaminants such as grease, dirt, water, running liquid and harsh chemicals.
Infrared:
Use an array of photodiodes on two adjacent screen edges with corresponding photo sensors on the opposite edges. These diode/sensor pairs establish an optical grid across the screen.
Any object that touches the screen breaks the optical-grid lines that cross the touch point, causing drops in the
corresponding photo sensor output signals. These drops indicate the touch point coordinates.
Rather than simultaneously establishing all grid lines, IR screen controllers typically scan through the array. This type has no glass panel construction that may reduce visibility of the display.
Infrared Touchscreen
Features:
Widespread adoption of infrared touch screen has been hampered by two factors: the relatively high cost of the technology compared to competing touch technologies and the issue of performance in bright ambient light. This latter problem is a result of background light increasing the noise floor at the optical sensor, sometimes to such a degree that the touch screen’s LED light cannot be detected at all, causing a temporary failure of the touch screen.