Appliance Design - February 2008 - (Page 24) CONTROLS & SENSORS mance. Vasseur says that to get high volume and good performance, designers from the OEM and Sensitive Object need to work together to determine the optimal location. ReverSys’ software engine, which can be implemented in a PC or embedded in a microprocessor, discriminates touches based on the acoustic signature and triggers any set of actions that are programmed to occur when a button at that precise location is touched. For instance, the company’s S16 embedded system features built-in sensors that feed the acoustic information to a printed circuit board, which digitizes the signal, enhances it via a proprietary process and then compares it to a library of pre-loaded acoustic signatures. The unit can store up to 64 acoustic signatures in a standard configuration, with expansion being possible. In other technologies, having 64 touch points might require 64 sensors. This acoustic approach allows designers to reduce the number of components needed and the subsequent cost for developing a complex interface. This technology can work with the touch of a stylus, a pen, or corner of a credit card, which can be advantageous when using a point-of-sale, or point-of-service system. However, unlike other technologies, this acoustic sensing technology can’t follow a moving touch, so therefore cannot be used to create a slide-type actuator, which would require multiple touches. The ReverSys technology can be designed to work independently of the object’s shape, meaning that the touch interface can be a traditional flat or three-dimensional object. The touch control surface can utilize virtually any type of material, including glass, plastic, metal, wood, and even soft materials such as leather. The system does not require there to be a line of sight between the object touching the control and the sensor. This is an advantage over other technologies such as infrared that requires a line of sight. In fact, when using acoustic signal processing, the substrate material can be damaged, dirty and impossible to see through, and it will still work as a touch control interface, adds Vasseur. The system’s robustness is linked to the substrate material that the product designer chooses. The material and the thickness doesn’t matter, Vasseur says, whether that material is a 1 mm thick glass panel or a 5 A user controls consumer electronics from several feet away. mm glass panel, because once the system is programmed to recognize a signature through a particular material it will do so every time. As a general rule, the technology can employ any material possessing a homogenous composition. “The technology is based on the way the object is resonating, if the noise is propagating through a material that is not reasonably homogenous, the level of performance could suffer,” Vasseur says. Given that the acoustic properties of most materials are well known, materials don’t need to be customized for any particular acoustic control application. One critical challenge that arose during the development of the technology was dealing with ambient environmental noise, an issue that Vasseur says has been resolved. The problem was that any external or internal noise impacting the control surface or sensors product could “pollute” the acquisition of the acoustic signal. The solution was to model the touch signatures so that the system could be programmed to recognize the difference between the acoustic signatures of a deliberate touch and the vibrational signatures induced into the surface by ambient sound. On the electronics side, the company put in a lot of work developing protection for the different platforms. For instance, a touch screen that the company currently sells can withstand 15 kV of electrostatic discharge. The nature of acoustic touch control also makes EMC issues less of a concern. “By not using electricity, we are much less sensitive to electromagnetic interference issues than other technologies such as capacitive technology.” The first application based on the technology was a virtual keyboard (VBK), an ultra thin acoustic keyboard that can be used to create a fully functional 108 key computer keyboard on any surface. Two sensors mounted underneath the surface enable the entire keyboard face to be made tactile sensitive. Today, they are currently in use in a variety of applications such as household appliances, vending machines, medical equipment and industrial automation. The technology has evolved to include uses in touch screens, control panels or in embedded platforms — some applications may require multiple platforms to be used. For instance, a vending machine might have a keypad as well as a touch control interface. The systems can be easily reprogrammed so that a touch might mean something different. For instance, if the price of a soft drink goes up, the unit can be reprogrammed so that a touch system will reflect the new cost. Vasseur says that another opportunity for OEMs is in terms of releasing new appliance models without having to develop new tooling. The appliance maker can use the same physical piece of glass or polycarbonate for the touch interface on two or three different models by changing the graphic overlay on each touch panel and then programming each microcontroller to recognize the different set of touch points. < For more information, enter . . . . . . . . . . . . . . . . . . 301 Or email: contact@sensitive-object .com 24 applianceDESIGN February 2008 www.applianceDESIGN.com http://www.appliancedesign.com
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