You Can Touch This

Touchscreen Technologies Ready for Prime Time

The touch sensors and sensor interface controllers used in resistive touchscreens are getting cheaper, and there are many communication interfaces available.

Touchscreens have followed an evolution common to many industrial control technologies. First, there's the premature introduction of not-ready-for-prime-time products.

Vendors learn from that, so the second evolutionary step incorporates user input and results in acceptable products. The third step is convincing industrial machine builders and other users that the products really have changed and now are ready for industrial use. If the third step goes well, then the fourth step is widespread acceptance.

Touchscreens are well into the fourth step and are used extensively in industrial OEM applications. "In our seven-year history, the ratio of touch to non-touch systems shows a continual increase and is more than 75% today," says Rick Tomfohrde, vice president of Christensen Display Products (www.christensendisplay.com).

Why touch rather than non-touch? That's easy, according to George Liao, HMI product manager for Advantech (www.advantech.com/ia). "Touchscreens make machines easier to use," he says. "If the operator can see what he or she is doing with the machine directly via a graphical interface, the chances of mistakes are reduced."

"Touchscreens allow operators to be faster and more precise when directing a machine," says Haroon Rashid of HMI product marketing for Schneider Electric (www.us.telemecanique.com). "Touchscreen displays make particular sense for OEMs because they can deliver a machine that's ready for the customer to plug in and run."

There are four main types of touchscreen technology. Resistive touchscreens are the least expensive and most widely used, capacitive types are next in terms of cost and acceptance, and the most expensive, infrared, are in third place. A fourth type, standing acoustic wave appears to be an also-ran.

Resistive touchscreens are inexpensive, offer a high resolution of touch, and are fairly durable. "Resistive touchscreens can be operated with gloved hands, support on-screen, slide-type controls, have good chemical and environmental resistance [can be NEMA 4X rated], and don't require frequent calibration," says Michael Budai, CTC business unit hardware engineering manager for Parker Hannifin (www.ctcusa.com).

The only drawback to resistive touchscreens is screen durability. "Susceptibility to surface abrasion is the most common limitation of resistive touchscreens," confirms Tomfohrde. "The front surface is polyester over glass, so when abrasives are present in the environment or just happen to see a lot of use, the screen's plastic surface can become worn or scratched."

The touch sensors and sensor interface controllers used in resistive touchscreens are getting cheaper, and there are many communication interfaces available including serial, USB, PS/2 and data bus. Most touchscreen vendors also provide software drivers for operating systems such as Windows 2000/XP/CE, Linux and QNX.

Capacitive touchscreens are enjoying a technological resurgence because Near-Field Imaging (NFI) provides excellent durability, overcoming the one weakness of resistive touch.

NFI projects the capacitive sensor field from the inside to the front outside of the viewing surface. When the operator penetrates this field, the touchscreen is activated, emulating a mouse click. The exposed physical front surface is therefore inactive and can be well-sealed and made from a durable material such as chemically hardened glass.

NFI technology is more expensive than resistive, but this type is easy to seal to NEMA 4 (or better) specifications and virtually abrasion and shatter proof. In certain environments, capacitive touchscreens can last twice as long resistive types and thus worth the price premium.

NFI technologies do allow for gloved hand operation and are not affected by surface abrasions, which were the two primary limitations of older capacitive technology. "It's still a fraction of total touchscreen sales, but we expect tremendous growth," predicts Tomfohrde.

Providing the ultimate in performance, but at the highest price is infrared; particularly as implemented by Dolch Computer Systems (www.dolch.com). "Our EnhancedInfrared touchscreen technology uses non-visible infrared light transmitted by LEDs and detected by mil-spec light-receiving phototransistors," says Chris McDonald, director of marketing with Dolch. "We use a scratch-resistant and shatter-proof acrylic faceplate, but scratches and gouges won't affect operation."

How durable is the technology? To demonstrate how tough these things are at trade shows, Dolch provides booth visitors with large hammers to strike the screens,something I tried with no ill effect.

Unlike an electromechanical push button, there is no immediate sensory indication of activation with a touchscreen. At least one vendor is addressing this shortcoming. "We offer unique technology that gives an operator positive tactile feedback through a plastic overlay," says Rajiv Salhotra, director of sales with IDEC (www.idec.com).

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