Touch screens make work easy & fast

By: Chamil Kulatunga

A touch screen is an input device similar to a mouse or keyboard in purpose, but easier to use than either of these devices because the computer is operated simply by touching the key locations on the screen. The first touch sensor, the Elograph was developed by Dr. Sam Hurst in 1971, and was patented by the University of Kentucky Research Foundation. Following this a touch screen that could determine polar coordinates implemented this new touch sensor technology in 1974.

Touch screens can be used in situations where there is no space to handle a mouse or keyboard, or where it would be easy to remove or damage them. In cases where only a few simple commands are necessary touch screens can be especially useful for people who are not familiar with computers. Or where speedy turnaround is important, for example the vegetable weighing scales in supermarkets, where bottlenecks can cause delays. More examples can be found in point of sales systems, public information displays, real time industrial control and automation systems, automatic teller machines, vending machines, air plane TVs, computerized gaming, electronic catalogs, fast restaurant outlets and many more self services areas.

Touch screens work by using a sensor, a controller and a software drive. There are several technologies that can be used in the sensor of the touch screen to make it work. And just as humans have their five senses to interact with the world touch screen sensors can also use several different technologies and some of them are quite similar to the human senses. Currently touch screen sensors are activated using either resistance, capacitance, acoustics, optics or mechanics.
Some sensors work by using resistance where a thin, flexible membrane is separated from a glass or plastic substrate. These metallic coatings meet when a finger or stylus presses against the screen, thus closing an electrical circuit. The advantages of this mechanism are high-touch resolution and resistance to dirt, dust, water or light. The disadvantages are poor clarity and a sharp object can damage the resistive layers.

Other sensors use capacitance. This is where voltage is applied to the corners of the screen with electrodes spread uniformly across the field. When a finger touches the screen, it draws current from each side proportionately. The frequency changes are measured to determine the X and Y coordinates of the touch event. Advantages to using this system include high clarity, good resistance to dirt, grease and moisture and high touch resolution.

Other sensors use acoustics. These sensors detect a touch event when a finger touches the screen resulting in absorption of sound energy. Bursts of high frequency acoustic energy are launched from the edges of the screen. Arrays of reflectors at the edges divert the acoustic energy across the screen and redirect the energy to sensors. A touch causes a dip in the received energy waveform for both axes. The timing of dips indicates the X and Y touch-point coordinates. The advantages of this system are high-touch resolution, high clarity and durability with no drift operation thus ruling out the need for recalibration. But, this sensor is susceptible to dust, dirt and moisture since it can't be completely sealed.

Sensors can also use optics where touch screens use infrared light between an array of photodiodes on one edge and corresponding photo sensors on the opposite edges. Any object that touches the screen disturbs this infrared sensing layer that leads to drops in the signals. This then indicates the coordinates. The advantage of infrared sensors is good clarity and immunity to drift. But it is susceptible to dust, needs special bezels for daylight use, and has parallax problems on curved screens. Since the optical grid floats above the screen, a touch event can be registered before the user's fingers reach the screen.

Sensors can also be worked through the use of mechanics. This kind of touch screen uses strain gauge or platform force-sensing technologies that transform mechanical force into an electrical signal. When you touch the strain gauge screen, the stresses produced are measured at each corner. The mathematical calculation of the four readings indicates the touch-point coordinates. The controller tracks out static forces, such as gravity and repetitive forces such as vibration. This sensor is the easiest to install but it needs frequent recalibration. It might give false readings because of the shocks on the screen.

Recently touch screens have been introduced where the keyboard cannot be read by anyone unless they are directly in front of the screen. This improves security in places like ATMs since no one can see users entering their PIN numbers.
Very interesting questions arise about this technology, which we may only know the answers to at some point in the future. For example will notebook computers upgrade with touch technology? Will touch technology be used in future web browsing. The future of touch technology will depend on the economic and social environment, but at the moment it looks like it is here to stay.