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Illuminated thin-film keypads with OLEDs

Push-buttons on coffee dispensers and large industrial machines are often hard to see unless they are illuminated. A structured flat thin-film keypad based on organic light-emitting diodes provides users with information via illuminated symbols.

Time for a coffee – yet on large coffee makers, it is hard to tell which button to press for cappuccino or espresso unless they are illuminated. And once the drink has been selected, usually only a tiny LED reveals whether the appropriate button on the machine has been pressed hard enough and the desired coffee drink is about to bubble into the cup. In a joint project with colleagues at the Potsdam University of Applied Sciences, the University of the Arts HfK in Bremen and the Neuruppin-based company TES-Frontdesign GmbH, scientists at the Fraunhofer Institute for Applied Polymer Research IAP in Golm have developed a keypad based on organic light-emitting diodes, OLEDs for short. The really striking feature is that the illuminated symbol can change and is itself the switch. In other words, the buttons do not need captions, the function can easily be recognized by the respective illumination. If the “espresso” button has been selected on a coffee dispenser, for instance, the selected button will indicate a half-filled cup instead of an empty cup. If the button has been pressed twice for a double espresso, the full-cup symbol will light up. There is no need for any additional illumination of the buttons. “The novel OLED keypad has numerous advantages – and that applies equally to the control panels of large machines used in industrial production,” says IAP head of department Dr. Armin Wedel. “The buttons even show the user whether the machine is switched on and which application is running – even in very dark rooms.” The keypad comprises two layers, the flat OLED display and the thin-film keypad. These two layers must be superimposed with great accuracy, as otherwise the button that the user sees and pushes will not fulfill the desired function. There is another challenge to overcome, too: The OLED is rigid. When the user presses a button the finger pressure is distributed too evenly across the underlying keypad, making the switching mechanism inaccurate. “To ensure that the finger pressure on the appropriate button really does trigger the desired function, we have slightly raised the top of the switching element to focus the pressure on the button,” explains Wedel. The first prototypes of the thin-film keypad, which are only two millimeters thick altogether, are already in use: The keypad is integrated in a coffee machine. TES Frontdesign GmbH will be applying the technology primarily in mechanical engineering applications. The project was promoted by a grant from the Investitions- und Landesbank Brandenburg through the Brandenburg Economic Development Board (ZAB) in Neuruppin.


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