Touchscreens have traditionally not been suited to harsh industrial applications because of their limited ability to withstand heavy abrasion, impact and contaminants such as dirt, grease, oil, water and solvents. Some touchscreen technologies, for example, offer good resistance to impact and scratching, but aren’t simple to seal against liquid ingress. Others can be sealed, but are susceptible to EMI.
Zytronic Displays, a UK company (distributed by Transcity ), has developed a touchscreen technology which it claims “has outstanding potential for use in harsh environments”.
The touchscreen element is based on the company’s patented “projected capacitive” Zytouch. This employs embedded microfine wires within a toughened laminate material. Depending on the screen resolution and size, between 25 and 32 individual wires are embedded to divide up the screen area into pixel-sized sensing cells. Figure 1 demonstrates how pattern skew is used to ensure that optical fringing does not occur.
Each wire is small enough to be practically invisible when viewed against a powered display. The company explains that the wires are connected to an integrated controller board, which establishes an oscillation frequency for each wire. When a conducting stylus touches the glass surface of the sensor, a change in capacitance occurs. This results in a measurable oscillation frequency change in the wires surrounding the contact point. According to the company, the integrated controller calculates the new capacitive values, the data is transferred to a host controller and the sensor contact point is translated to an absolute screen position.
Designed for industrial applications
The Zytouch sensor is constructed from a combination of two plies of soda lime fully tempered glass with a total thickness of 7.8 mm (3 mm for the viewing face, 4 mm at the rear, and 0.8mm for the sensor layer). The company claims that this makes the sensor resistant to accidental and malicious damage, wear and tear and severe scratching on the glass surface. It adds that even complete failure of the outer glass face of the sensor will not prevent operation of the sensing technology. The screen can be operated by both bare and gloved fingers.
No additional sealing is needed to prevent the ingress of water, solvents, harsh cleaning fluids, grease and dirt.
It is also possible to position the sensor behind a sacrificial glass or polycarbonate layer up to 25 mm thick. This provides additional protection from all types of contaminants.
The company says that Zytouch-based touchscreens deliver uncoated light transmission ratings of up to 88%. Resolution is below 1 mm, and the positional accuracy of the sensor is rated at 1 percent error within the recommended viewing area. Response times of 13 ms are said to be comparable with the best conventional technologies.