Appliance Design - February 2008 - (Page 25) CONTROLS & SENSORS Infrared Innovations Fig. 1. Infrared light is emitted where it touches the finger and then is reflected back to the photosensor. he applications for infrared energy are wide ranging and include imaging and cooking, nondestructive tests and home heating, motion sensors and remote controls for consumer electronics. For at least two decades, infrared has also been used in touch-control technology. Here, too, infrared technology’s uses may grow as new innovations emerge, such as improved slide controllers. Infrared-based touch controllers are especially useful for appliances that require robustness such as cooking appliances or clothes dryers, which can face heat, cleansing agents, grease and other challenging conditions, says Martin Zapf, product manager of controls and sensors for Cherry GmbH, a German-based company with North American offices in Pleasant Prairie, Wis. In the 1980s, Cherry was one of the first companys to develop touch controls for cooktops and is one of the companies utilizing IR technology in an expanding number of touch-control uses. Infrared touch controls operate by using www.applianceDESIGN.com T a transmitter to send a beam of infrared light through a glass surface. When a finger touches a keypad, the infrared light is reflected off the finger to an IR receiver and a microprocessor analyzes the reflection. (See Fig. 1.) To ensure the touch is intentional, Cherry uses various methods, including the use of barycenter algorithms to determine if the finger falls within the sensitive operating area of the focused sensors. The software also looks at other factors, including reflection speed rate and plausibility factors, such as whether two buttons were to be pressed simultaneously in a specific scenario. According to Zapf, accidental switching caused by cleaning, children or pets, pans boiling over, or outside light sources is almost impossible. Cleaning the cooktop is a good example of how the controls can be touched, but not activated. “Cleaning the glass above the sensor area with a cloth will not affect the heat settings of the control.” Zapf says that Cherry’s IR Focus Technology concentrates IR light on the finger and creates a “good coupling coef- Improvements lead to expanded uses. by larry adams applianceDESIGN February 2008 25 http://www.appliancedesign.com
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