TouchSystems - Types of Technology

Touch Screen Technologies

3M Dispersive Signal Technology (DST)

MicroTouch DST touch systems offer a chemically-strengthened glass, stylus-independent touch solution with fast-accurate-repeatable response and operation unaffected by contaminants, static objects or other touches on the screen. DST is ideal for large-format LCD displays used for interactive digital signage and point-of-information applications 3M Dispersive Signal Technology (DST) is poised to become the touch technology standard for large-format interactive displays. Traditional touch technologies detect touch locations by interrupting acoustic waves, optical fields or infrared light above the surface of the touch screen.

What’s different about MicroTouch 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 and reliable touch performance that is unaffected by contaminants, scratches or static objects on the screen, as well as enabling stylus support and multi-user capability.


Click Here to View the DST Surface Impact Video	Click Here to View the DST Difference Video

Optical Imaging

Optical Imaging is a newly developed touch technology that offers ease of use, low cost and flexible sizing. This technology uses optical sensors to detect the touch point allowing the touch to register just before the physical touch on the screen, meaning that users can apply zero or light touch to the screen to initiate a response. Any input device, such as a paintbrush, finger, pen or stylus will work with the touch screen.

Surface coating overlays are not used on the touch screen surface, creating a crystal clear image. In addition, scratches on the touch surface will not affect the touch screen operation which is important for high-use environments such as a lobby or kiosk.

Optical Imaging scales easily to very large displays (120 inches), making it possible to create genuinely collaborative, interactive conference and teaching settings.

Optical Imaging provides a solution without calibration drift. Once the touch screen has been calibrated it does not require any further adjustments eliminating maintenance costs.

Resistive

The sensor consists of a piece of glass with a conductive coating on top, plus a polyester top sheet with a conductive coating on the bottom. The conductive surfaces are held apart by “spacer dots”, usually glass beads that are silk-screened onto the coated glass. On a 5-wire design (the most commonly used type of resistive in large screen POS applications); a voltage is applied to the 4 corners of the glass layer. When a person presses on the top sheet, it is deformed and its conductive side comes in contact with the conductive side of the glass, effectively closing a circuit. The voltage at the point of contact is read from a wire connected to the top sheet.

Advantages

Can be activated with any device
Low cost solution
Low power consumption
Disadvantages
Less durability compared to other technologies
Less transmittance and overall optical quality
Requires periodic recalibration

Surface Acoustic Wave (SAW)

A SAW touch screen consists of a piece of glass with “sound wave reflectors” deposited along all 4 edges. Two emitting transducers are mounted in two corners and receivers are mounted in the opposing two corners. A sound wave travels parallel to the borders of the glass. As it encounters the sound wave reflectors, some of it is passed through to the next sound wave reflector, and some of it is reflected across the touch screen. On the opposite side, the wave is passed through the sound wave reflectors to the receivers. The receivers can detect a drop in amplitude of the sound wave when a sound absorbing material (such as a finger) is placed in contact with the glass.

Advantages

Very high transmittance
Very high durability

Disadvantages

Cannot be sealed
Requires “soft” input device
Surface obstructions can cause a false touch

Capacitive

The capacitive sensor has a conductive coating on the front surface with wires connected to each corner. A small voltage is applied to each of these 4 corners. The operation relies on the capacitance of the human body. When a person touches the screen, a small current flows to the point of touch, causing a voltage drop which is sensed at the 4 corners.

Advantages

More durable than resistive (because the top layer is not plastic
Higher transmittance than resistive (fewer layers

Disadvantages

Accepts input from finger only (or a special, tethered conductive stylus
Susceptible to electromagnetic interference can cause an erratic cursor location
Accuracy is dependent on capacitance of person touching the display
Requires periodic calibration

Scanning Infra Red (IR)

IR uses of a Printed Circuit Board (PCB) “frame” around the perimeter of the display. On two sides there are closely spaced IR LEDs and on the opposing two sides there are matching photo transistors. The LEDs are turned on in sequence and the signal is read from the matching transistor. If no signal is read, then that indicates a blocked IR beam, meaning a touch. No actual touch “screen” is required for operation, however a plate of glass is generally used to protect the underlying display from damage and to provide anti-glare.

Advantages

Highest quality of underlying image
Very high transmittance (no conductive layers, only glass between image
Excellent anti-glare, with use of chemically etched glass
Can be activated with almost any device
Higher accuracy than other technologies<br>
Very high durability and reliability
One time factory calibration
Can be sealed
No wear mechanism

Disadvantages

Surface obstructions can cause a false touch