TOUCH SCREEN TECHNOLOGY

Abstract:

A touchscreen is a display that 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. In the last decade, touchscreen equipped displays have become common features in applications such as kiosks, point of scale systems, industrial control, and medical instrumentation. There are more of choices in touchscreen technologies from the branded manufactures. This paper presents the choices that are available to the product designer and integrator, and to assist in the selection of the most appropriate touchscreen options.

Introduction:

Touchscreens can also sense other passive objects, such as a stylus. The touchscreen 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 primary components that allow it to function: 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.

History:

Touchscreens 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. They have subsequently become familiar in kiosk systems, such as in retail and tourist settings, on point of sale systems, on ATMs and on PDAs where a stylus is sometimes used to manipulate the GUI and to enter data. The popularity of smart phones, PDAs, portable game consoles and many types of information appliances is driving the demand for, and the acceptance of, touchscreen.

The HP-150 from 1983 was probably the world's earliest commercial touchscreen computer. It doesn't actually have a touchscreen 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 touchscreen could only sense one point of contact at a

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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.

Touchscreens 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.

Historically, the touchscreen sensor and its accompanying controller-based firmware have been made available by a wide array of after-market system integrators and not by display, chip or motherboard manufacturers. With time, however, display manufacturers and chip manufacturers worldwide have acknowledged the trend toward acceptance of touchscreen as a highly desirable user interface component and have begun to integrate touchscreen functionality into the fundamental design of their products.

Development:

The development of multipoint touchscreen 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. With the influence of the multi-touch-enabled iPhone and the Nintendo DS, the touchscreen market for mobile devices is projected to produce US$5 billion in

2009.

Construction:

There are several principal ways to build a touchscreen. The key goals are to recognize one or more fingers touching a display, to interpret the command that this represents, and to communicate the command to the appropriate application.In the most popular techniques, the capacitive or resistive approach, manufactures coat the screen with a thin, transparent metallic layer. When a user touches the surface, the system records the change in the electrical current that flows through the display.

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Dispersive-signal technology which 3M created in 2002, measures the piezoelectric effect — the voltage generated when mechanical force is applied to a material — that occurs chemically when a strengthened glass substrate is touched.

There are two infrared-based approaches. In one, an array of sensors detects a finger touching or almost touching the display, thereby interrupting light beams projected over the screen. In the other, bottom-mounted infrared cameras record screen touches. In each case, the system determines the intended command based on the controls showing on the screen at the time and the location of the touch.

Technologies:

The types of technologies that can be found are as follows

Resistive:

The Structure of resistive touch screen

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.

Figure.1: Resistive Touch Screen Structure

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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 touchscreen 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 touchscreen is not touched, the controller detects the voltage on the glass panel is zero.

4. When the touchscreen 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.

Figure.2: Construction of Resistive Touch Screen

Resistive touchscreen deliver cost-effective, consistent and durable performance in environments where equipment must stand up to contaminants and liquids, such as in restaurants, factories, and hospitals. Disadvantages of Resistive technology include only 75% optical transparency and the fact that a sharp object can damage the resistive layers. The Analog Resistive technology is

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perfect for PDAs, web phones, and other handheld consumer applications. Resistive touchscreen can also support Multitouch.

Analog resistive touch technology is suitable for applications that require ease of integration, low power consumption, light weight, portability, cost effectiveness and compact mechanism. It is used in outdoor applications where environment is dusty.

Surface acoustic wave:

The structure of a SAW touchscreen:

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 touchscreen.

Figure.3: SAW Touchscreen 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 touchscreen by an 45-degree array of reflectors. The 45-degree reflectors on the opposite side gather and re-direct 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 touchscreen 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 touchscreen 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

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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.The touchscreen 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 any object, 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. The SAW is specially designed to prevent dust or water from influencing the SAW touchscreen performance. The transducers are completely hidden and protected inside the covering eliminating risk of damage during integration. It is easy to install and maintain inside the kiosk.

Capacitive:

The structure of a Capacitive touchscreen:

Capacitive touchscreen 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.

Figure.4: 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.

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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.

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 about 75%. This gives the capacitive system a much clearer picture than the resistive system. Also the capacitive system has very long life (about 225 million clicks). The bad news is that this touchscreen type cannot be activated by contact with inanimate objects (e.g., the gloves that being used for wearing). There are mainly two subtypes: one cannot register more than one touch at a time, while the other called ‘Multitouch’ (used in Apple iPhone and iPod) does. It 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:

Conventional optical-touch systems use an array of infrared (IR) light-emitting diodes (LEDs) on two adjacent bezel edges of a display, with photosensors placed on the two opposite bezel edges to analyze the system and determine a touch event. The LED and photosensor pairs create a grid of light beams across the display. An object (such as a finger or pen) that touches the screen interrupts the light beams, causing a measured decrease in light at the corresponding photosensors. The measured photosensor outputs can be used to locate a touch-point coordinate.

Widespread adoption of infrared touchscreen 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 touchscreen’s LED light cannot be detected at all, causing a temporary failure of the touch screen. This is most

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pronounced in direct sunlight conditions where the sun has a very high energy distribution in the infrared region.

However, certain features of infrared touch remain desirable and represent attributes of the ideal touchscreen, including the option to eliminate the glass or plastic overlay that most other touch technologies require in front of the display. In many cases, this overlay is coated with an electrically conducting transparent material such as ITO, which reduces the optical quality of the display. This advantage of optical touchscreen is extremely important for many device and display vendors since devices are often sold on the perceived quality of the user display experience.

Another feature of infrared touch which has been long desired is the digital nature of the sensor output when compared to many other touch systems that rely on analog-signal processing to determine a touch position. These competing analog systems normally require continual re-calibration, have a complex signal-processing demand (which adds cost and power consumption), demonstrate reduced accuracy and precision compared to a digital system, and have longer-term system-failure modes due to the operating environment.

Figure.5:Infrared Touchscreen

Comparison of touchscreen technologies

Technology Resistive SAW Infrared Capacitive

Durability: 5 year 5 Year 3 Year 2 Year

Stability: High Higher High Ok

Transparency: Ok Good Good Ok

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Installation: Built-in/On wall Built-in/On wall On wall Built-in

Touch: Anything Finger/Pen Sharp Conductive

Intense light- resistant:

Good Good Bad Bad

Response time: <10ms 10ms <20ms <15ms

Following Speed:

Good Low Good Good

Monitor option: CRT CRT CRT CRT or LCD

Waterproof: Good Ok Ok Good

Advantages & disadvantages:

Advantages:

User friendly. Fast response.

Error free input.

Easy to install.

Use finger, fingernail, gloved hand, stylus or any soft-tip pointer to operate.

Easy to clean and maintain.

Compatible with Windows, Macintosh and Linux.

Does not interfere mouse and keyboard function.

Make computing easy, powerful and fun.

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Disadvantages:

It has two types of problems

1. Finger stress:

An ergonomic problem of touchscreen is their stress on human fingers when used for more than a few minutes at a time, since significant pressure can be required for certain types of touchscreen. This can be bared by some users with the use of a pen or other device for more accurate pointing. However, the introduction of such items can sometimes be problematic depending on the desired use case (for example, ATMs). Also, fine motor control is better achieved with a stylus, because a finger is a rather broad and ambiguous point of contact with the screen. Ordinary styluses do not work on capacitive touchscreen nor do fingers gloved in insulating materials.

2. Fingerprints:

Touchscreens can suffer from the problem of fingerprints on the display. This can be reduced by the use of materials with optical coatings designed to reduce the visible effects of fingerprint oils, such as the oleo phobic coating used in the iPhone 3G S, or by reducing skin contact by using a fingernail or stylus.

Applications:

Public Access

• Museums• Library resource guides• Corporate information• Public Transportation Schedule / Status• Airport terminal passenger internet and email systems• Automated travel and entertainment ticket dispensers • Shopping mall directory

Business

• Gas stations• Point of sales• Restaurants• Grocery stores• Hospital and hotel directories (check-in, registration)• Banks and Financial Reporting• Bank cash advance and teller machines• Corporate presentation• Employee relation information

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Education:

• Assistive technology• Computer Aided Instruction for Children• Edutainment• Professional training and presentations• Employee orientations

Entertainment:

• Interactive computer games• Casinos

Government:

• Government voting facilities• Military control system• Scientific research lab

Industry:

• Industrial Equipment and Instrument Control

Conclusion:

Twenty years ago, PC’s were just arriving on the scene and simple GUI interfaces were almost unheard of. Designers strove to use touchscreen to simplify compute input commands for largely unsophisticated computer users. The proliferation of touch-enabled self-service kiosks, the conversion from cash registers to point of sale systems, and countless automotive, medical training, and industrial products that use touchscreen as operator interfaces have validated touch screen concept.

Today, a larger share of population is PC literate, yet the touchscreen has become adopted by computer users of all abilities because it is simple, fast, and innovative. Today’s product designer or system integrator would be served to remember yesterday’s technology adoption challenges and flexibly adopt new technological approaches if they wish to solve today’s application challenges.

References:

1. Howstuffworks2. MERL - Mitsubishi Electric Research Lab (MERL)'s research on interaction with touch tables.

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3. Jefferson Y. Han et al. Multi-Touch Interaction Research. Multi-Input Touchscreen using Frustrated Total Internal Reflection.

4. Dot-to-Dot Programming: Building Microcontrollers.

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