Touch Technology

Touch Technology

Touch screens emerged from corporate research labs in the 1960s. Yet it was Apple iPhone, which incorporates a touch technology called projected capacitive, that touch screens entered the mainstream and subsequently, the hearts and minds of consumers around the world. While touch may seem simple and intuitive to the end-user, the technology behind it is anything but: there are more than a dozen different touch screen technologies used today in cell phones, PCs, and displays.
Some of the more popular touch technologies include resistive, surface capacitive, projected capacitive, infrared, surface acoustic wave (SAW), and optical imaging. Other technologies include: dispersive signal technology (DST), acoustic pulse recognition, LCD in-cell optical, and force sensing.


Resistive Touch Technology


Resistive is the most common type of touch screen technology. It is a low-cost solution found in many touch screens, including hand-held computers, PDAs, consumer electronics, and point-of-sale-applications. The resistive screen is popular because of its relatively low price (at smaller screen sizes), and ability to use a range of input objects (fingers, gloves, hard and soft stylus).

How it works A resistive touch screen uses a controller and a specially-coated glass overlay on the display face to produce the touch connection. The touch screen panel consists of two thin, electrically conductive layers separated by a narrow gap. When an object, such as a finger, presses down on a point on the panel's outer surface the two layers become connected and then cause a change in the electrical current which is registered as a touch event.

Limitations and considerations

  • The primary types of resistive overlays are 4-wire, 5-wire, and 8-wire. The 5-wire and 8-wire technologies are more expensive to manufacture and calibrate, while 4-wire provides lower image clarity.
  • Two options are generally available, polished or anti-glare. Polished offers clarity of image, but generally introduces glare. Anti-glare will minimize glare, but will also diffuse the light, thereby reducing clarity.
  • One benefit of using a resistive display is that it can be accessed with a finger (gloved or not), pen, stylus, or a hard object.
  • Resistive displays are less effective in public environments due to the degradation in image clarity and the need for periodic recalibration caused by the breakdown of the layers of resistive film, and its susceptibility to scratching.
  • Resistive displays are susceptible to vandalism, and touches will not register if the resistive sheet is cut or scratched.

Surface Capacitive Touch Technology


Capacitive touch screens are all-glass and designed for use in ATMs and similar kiosk-type applications. It has better clarity than resistive technology and is durable making it suitable for industrial applications.

How it works A small current of electricity runs across the screen, with circuits located at the corners of the screen to measure the capacitance of a person touching the overlay. Touching the screen interrupts the current and activates the software operating the kiosk.

Tech Global's Dynamic-Touch

Limitations and considerations

  • Because the glass and bezel that mounts it to the monitor can be sealed, the touch screen is both durable and resistant to water, dirt and dust. This makes it practical in harsher environments like gaming, vending retail displays, public kiosks and industrial applications.
  • The capacitive touch screen is only activated by the touch of a human finger.
  • Because the technology was originally created for small screens, it will not scale to larger screens easily and can require periodic recalibration.

Projected Capacitive Touch Technology (PCT) (also PCAP)


Capacitive touch screens are all-glass and designed for use in ATMs and similar kiosk-type applications. It has better clarity than resistive technology and is durable making it suitable for industrial applications, Outdoor operability, multi-touch supports gesturing, true flat front surface possible with no bezel and can be activated by a thin gloved hand

How it works Projected Capacitive Touch (PCT) (also PCAP) technology is a variant of capacitive touch technology. All PCT touch screens are made up of a matrix of rows and columns of conductive material, layered on sheet of glass. This can be done either by etching a single conductive layer to form a grid pattern of electrodes, or by etching two separate, perpendicular layers of conductive material with parallel lines or tracks to form a grid. Current applied to this grid creates a uniform electrostatic field, which can be measured. When a conductive object, such as a finger, comes into contact with a PCT panel, it distorts the local electrostatic field at that point.

Limitations and considerations

  • Because the glass and bezel that mounts it to the monitor can be sealed, the touch screen is both durable and resistant to water, dirt and dust. This makes it practical in harsher environments like gaming, vending retail displays, public kiosks and industrial applications.
  • The capacitive touch screen is only activated by the touch of a human finger.

Surface Acoustic Wave (Saw) Touch Technology

SAW technology provides good image clarity because it uses pure glass construction. Compared to resistive and capacitive technologies, SAW provides superior image clarity, resolution and higher light transmission. However, it was originally designed for smaller screens and may not scale easily to screen sizes over 30."

How it works SAW technology uses ultrasonic waves that pass over the touch screen 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. When sound waves are transmitted across the surface of the display, the following sequence of events occurs:

  • Each wave is spread across the screen by bouncing off reflector arrays along the edges of the overlay.
  • Two receivers detect the waves.
  • When the user touches the glass surface, the user's finger absorbs some of the energy of the acoustic wave and the controller circuitry measures the touch location.

SAW technology is used in ATMs, amusement parks, kiosks, and in banking applications.

Limitations and considerations

  • Because the technology cannot be sealed, it can be adversely affected by surface contaminants and water, making it unsuitable for many industrial or commercial applications. The contaminants can cause dead spots on the screen, requiring periodic cleaning of the sensor and sometimes recalibration.

Due to the way the technology works it can also be susceptible to data “noise."



Infrared Touch Technology

How it works Infrared technology relies on the interruption of an infrared light grid in front of the display screen. The touch frame contains a row of infrared LEDs and photo transistors, each mounted on two opposite sides to create a grid of invisible infrared light. The frame assembly comprises printed wiring boards, on which the electronics are mounted and is concealed behind an infrared-transparent bezel. Infrared touch screens are often used in manufacturing and medical applications because they can be completely sealed and operated using any number of hard or soft materials.

  • The bezel shields the electronics from the operating environment while allowing the infrared beams to pass through
  • The infrared controller sequentially pulses the LEDs to create a grid of infrared light beams
  • When a stylus, such as a finger, enters the grid, it obstructs the beams
  • One or more phototransistors detect the absence of light and transmit a signal that identifies the x and y coordinates

Limitations and considerations

  • The major issue with infrared is that the seating of the touch frame is slightly above the screen. Consequently, it is susceptible to early activation before the finger or stylus has actually touched the surface.
  • Contaminants can also cause false activation on the screen inside the thick border that is required for the frame.

Costs to manufacture infrared bezels are significant.

           


Optical Touch Technology

How It Works Working together, two optical sensors track the movement of any object close to the surface by detecting the interruption of an infra-red light source. The light is emitted in a plane across the surface of the screen and can be either active (infra-red LED) or passive (special reflective surfaces).

At the heart of the system is a printed circuit controller board that receives signals from the optical sensors. Its software then compensates for optical distortions and triangulates the position of the touching object with extreme accuracy.

By using optical sensors at two corners of the screen, Optical Touch “sees” the touching object from two angles. The result is a high degree of accuracy, with no contact pressure required. No special coatings and films are needed—there’s nothing to scratch, wear out, or cloud the display image. The screen can be sealed against dirt, dust, and moisture, ideal for heavily used kiosks in public areas.

Multi-touch capable. Optical Touch accommodates multiple touch points with a high degree of precision. You can touch the screen anywhere, with anything—a finger, a pen, a credit card. Even the lightest touch will be registered. Annotations are fast and precise.

Limitations and considerations

  • Contaminants can cause false activation on the screen inside the border that is required for the frame. 
  • Anything can activate the screen (Fly on the screen issue)
  • Cameras can become confused with direct light
  • Dust can collect on the boarders, confusing the cameras 

Dispersive Signal Technology (DST)

How It Works Traditional touch technologies detect "touch" by interrupting acoustic waves, optical fields or infrared light above the surface of the touch screen. What's different about DST is that it precisely calculates touch locations by analyzing the bending waves within the glass substrate that are created by the user's touch. This allows for fast, accurate, reliable touch performance that is unaffected by contaminants, scratches, or static objects on the screen. Able to be activated by gloved hand, stylus or any object. The glass is chemically strengthened with a Anti-glare coating.
Sizes 32"-55".

DST Customer Briefing.pdf

Limitations and considerations

  • Single-Touch with simple gestures
  • Size constraints: 32"-55"
  • Cannot resolve touch and hold or constant touch. Requires slight tap.