Wednesday, April 25, 2018
Publication Date: 10/1/2007
Archive >  October 2007 Issue >  Partnering > 
Touch Screen Technology: Managing Multiple Choices

Though increasingly widespread and user-friendly, touch screen technology is still very much a specialty, and is therefore outsourced by equipment manufacturers. But outsourcing any electronic subassembly can be a slippery slope for OEMs, since ultimately the end product will have their brand name on it. Global manufacturers in the automotive, aircraft and other major industries are experiencing quality issues that will certainly testify to that. OEMs that are developing new and innovative applications for touch screen interfaces, whether hand-held devices or elaborate systems, would do well to resolve some important issues before committing to a touch screen design and supplier.

Partnering with the Supplier
Biolase Technology, Inc. (Irvine, CA), a manufacturer of laser-based dental systems, found that partnering with a highly experienced touch screen manufacturer can help OEMs avoid design pitfalls and even accelerate new product speed to market.

"The touch screen panel is integral to our laser dental system. Since this is still a new technology, it is crucial that this interface be user-friendly, accurate and error-resistant for users," says Dimitri Boutoussov, vice president of Biolase engineering. "To ensure the acceptance and satisfaction of our product line, we decided it was best to have a collaborative relationship with a highly experienced touch-screen supplier, one who could validate or assist with design and testing as well as manufacturing our panels." Boutoussov adds that their supplier was exceedingly dedicated in supporting Biolase in order to make deadlines. "They were working literally nights and days and over the weekends to deliver a quality TouchView® Plus interface for our product launch," he says. "Touch-based systems can get very complex and confusing," says Manny Cardinale, president of CAM Graphics. "Naturally, vendors might specialize in a certain touch screen technology or market segment to make them more competitive, but that also limits their flexibility, so they might not be the best supplier for other applications." CAM Graphics is a developer and manufacturer of human interface and display technology. Since 1969, the company has pioneered the development of high-rel touch screens, membrane switches, graphic overlays and the integration of those and other related technologies. The company specializes in such applications as industrial controls, medical equipment, instrumentation, military systems and office automation.

Cardinale says that engineers should also consider the volumes normally produced by a supplier. "Some companies are geared to make large runs of a certain type of design, others are not. For instance, our company covers a whole gamut of touch screen technologies, but we are a relatively small-to-mid volume manufacturer."

He adds that it is necessary to confirm what is practical for products like these. CAM Graphics, which works with FDA-certified customer products, is a couple of steps above state-of-the-art, yet they must ascertain that incorporating more advanced features or functionalities are justified for a given application.

Which Technology?
There are different digital and analog touch screen technologies to choose from that will work in most applications. Analog resistive touch has achieved the greatest market acceptance and penetration. However, this technology can present certain problems, such as `drift' (deviation) under certain conditions, whereas digital touch screens do not exhibit this problem.

In general, touch screen designers and integrators should consider a variety of properties depending on the application. While reliability is a must, other considerations include size, image quality, sensitivity-to-touch, power consumption, durability and environmental factors. Some of these factors may dictate that the display contain a combination of touch screen technologies, such as membrane switches, analog keypads, LCDs and LCMs.

Environmental Design
While touch screens are generally useful in most environments, they are affected by such factors as extreme temperatures, humidity, corrosive atmosphere, lighting conditions, electromagnetic interference and even sound.

"Some of these factors are fairly obvious," says Cardinale. "Yet we all have experienced situations where touch screen displays are hard to read due to lighting. That can be quite a handicap, and it results from not using the optimum materials, coatings or filters." In the case of Biolase, the glare of bright lights in the dental office require that touch screens offer sufficient brightness as well as anti-reflective coatings on top surfaces.

Touch screen sensitivity was another Biolase concern. Boutoussov says the challenge was to produce a touch screen with the same pressure sensitivity required to actuate buttons that are also located on the controller. Achieving this was sufficiently difficult, making two prospective vendors pull out of the touch screen development project.

"We also needed a good size display," says Boutoussov. "That meant engineering the panel so that the frame should be very narrow. Because all the electrical traces are contained in the frame, that was quite a challenge. And three reputable manufacturers replied with `no bid' to our specification. CAM Graphics helped us find a reliable solution."

"Drift" Pitfalls
One of the more serious pitfalls of touch screen technology is drift — the phenomenon of a touch screen falling out of calibration so that the touch point does not correspond to the touch of the finger or stylus. Most often this deviation occurs with analog electronic touch screens that are exposed to extreme temperatures.

"The standard acceptable linear deviation is 1-1/2 percent," explains Cardinale. "That may be easy enough to achieve when a touch screen is manufactured. But if it falls to 4 percent out of calibration, touch response could go off the map, and the consequences would be disastrous."

Cardinale says that drift often occurs because of conditions outside of the OEM's control, when the equipment is in the field for awhile. Drift can occur because of the materials the touch screen manufacturer has used, or rough treatment by users.

"We test the touch screen ITO (Indium Tin Oxide) through 5-10 million cycles, and very little normally happens to it. But you have to realize that at some point in time you're going to have a fracture of that surface. And that can certainly cause some amount of drift.

There are other preventive design methods as well, he advises. For example, when deemed appropriate, the manufacturer will use glass as one layer with an ITO deposit on glass, which is generally a harder, more durable surface than the ITO on more flexible, sputter-coated polyester.

For more information, contact: CAM Graphics Company, Inc., 166 New Highway, Amityville, NY 11701 631-842-3400 fax: 631-842-1005 E-mail: Web:

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