Touch Screen Technology — Managing Multiple Choices

Increasingly widespread, touch screen technology is a specialty that is typically outsourced by equipment manufacturers. But outsourcing any electronic subassembly can be a slippery slope for OEMs, since the end product will ultimately carry their brand name. Therefore, OEMs developing new applications for touch screen interfaces, whether hand-held devices or elaborate systems, would do well to resolve some important issues before committing to a designer and supplier.

Biolase Technology, Inc., a manufacturer of laser-based dental systems, found partnering with an experienced human interface manufacturer can help OEMs avoid design pitfalls and accelerate product to market.

“The panel is integral to our system. It is crucial that this interface be user-friendly and accurate,” says Dimitri Boutoussov, vice president of Biolase engineering. “We decided to collaborate with an experienced supplier, one who could validate or assist with design and testing as well as manufacturing.”

“Touch-based systems can get complex and confusing,” says Manny Cardinale, president of CAM Graphics, a manufacturer of human interface and display products for 30 years. “Naturally, vendors might specialize in a certain technology to make them more competitive, but that limits flexibility, so they might not be the best choice for other applications.”

There are digital and analog screen technologies that will work in most applications. Analog resistive touch has achieved the greatest market penetration. However, this technology can present problems, such as “drift” (deviation) under certain conditions, whereas digital screens do not exhibit this problem.

Along with reliability, designers and integrators must consider size, image quality, sensitivity-to-touch, power consumption, durability and environmental factors. Some of these factors dictate a combination of human interface technologies, such as membrane switches, analog keypads, LCDs and LCMs.

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

For example, we’ve all experienced situations where displays are hard to read due to lighting,” says Cardinale. “That can be a handicap, and it results from not using the optimum materials, coatings or filters.”

In the case of Biolase, the bright lights in the dental office dictated the need for screens with sufficient brightness as well as anti-reflective coatings.

One serious pitfall of touch screen technology is drift — the phenomenon of a 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 screens 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 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 drift often occurs when the equipment is in the field and can occur because of the materials used or rough treatment by users. There are other preventive design methods, however. When appropriate the manufacturer will use glass as one layer with an ITO deposit on glass, which is generally a 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; Phone (631) 842-3400; Fax (631) 842-1005; E-mail: sales@camgraphics.com; Visit the web site www.camgraphics.com.