If a genuine tactile operating feel with pressure points and distinct key strokes is essential, real keyboards are the top option. And even where cognitive operator control is not possible, conventional electromechanical solutions are the first choice. They include, in the broadest sense, keyboards featuring single components (discrete keys) and flat input systems (membrane keypads, silicone rubber keypads).
The classic one: Keyboard comprising single components
When we think of keyboards, we mostly think first of all about a computer. While this type has a limited variety of keys, it does meet certain requirements in terms of key stroke and actuating force. This is easiest to implement using single keys. This type of keyboard is ideal especially for typing lengthy text.
A major disadvantage of it is handling: Large numbers of single components have to be soldered onto a printed circuit board, and each solder point is critical in terms of the keyboard's reliability. Each key cap needs its own imprint, which incurs cost in materials management and stockholding. And lastly, the rather bulky structure has to be safe installed in or mounted on the device.
The robust one: Membrane keypad
Membrane keypads protect displays, digits or LEDs behind a plastic film membrane. The film is indented so as to guide the user's finger around the keys. Common features are indented key surrounds, full key cap indents, and bubble-shaped indents. Key labeling in braille is also possible. The design possibilities for graphic films are virtually unlimited - that is why they are also referred to as graphic films: In contrast to keyboards consisting of individual components, which only allow for round or square keys, membrane keypads enable any shape of key at no additional cost. Colors can be customized in line with a corporate design, or to provide a visual subdivision of the keypad surface. The film is imprinted from the back, so adhesion is not a problem. Membrane keypads are used primarily on sports equipment such as ergometers, cross-trainers and treadmills, on vending machines, and on robust mobile equipment such as measuring devices or robot lawnmowers.
The membranes are made of strong, temperature-resistant polyester or polycarbonate film. This makes the keypads resistant to oil for factory or workshop applications. It also means they remain color-fast in outdoor use. In addition to the indenting and imprinting variants, there is also a choice of different finishes: glossy, mat, textured, or combinations of all. Extra features such as electrical shielding, interchangeable labels and various illumination modes round off the application options. And contrasting their complex design, the keypads are very easy to assemble: Detach the protective paper on the back, lay the cable, stick it down - and it's done!
Incidentally, membrane keypads can also create an effect that is otherwise only achievable with sensor keys or touch panels: If the key stroke is kept very small, there is no discernible lift or pressure point, yet the evaluation remains absolutely simple. Since they are "real" electromechanical contacts neither auxiliary energy nor controllers are necessary. That results in lower cost, simpler design, and higher energy efficiency.
There is, however, a disadvantage to counter those advantages: the third dimension. If the keypad is to be not only long and wide but also high in terms of the keys' shape and/or lift, a film membrane encounters physical limits. This problem can be bypassed using silicone keys.
The three-dimensional one: Silicone rubber keypad
Silicone rubber keypads are used for remote controls in the multimedia field for example.
The silicone rubber enables more lift, and so a characteristic tactile feedback. Actuation strokes of up to 4mm can be realized quite easily.
For everything to work mechanically and electrically, there is a conductive disk - sometimes more than one - on the underside of each key. The disks are conventionally made of carbon (carbon pills), or alternatively of various conductive material combinations, or even with gold surfaces. A gold surface has lower resistance, which cuts power consumption and so extends the operating time of the application - a plus-point especially for battery-powered equipment. The counterpart is an electrode pattern on a printed circuit board: The conductive pill creates a short circuit between two contact areas on the PCB while pushing the silicone rubber key.
Silicone rubber keypads are a practical solution particularly thanks to their inherent material characteristics, such as a wide operating temperature range and easy - and therefore low-cost - shapeability. They also make for a longer keypad life. In view of that, of course, optimum fastness of the key labeling is all the more important. Abrasion-resistant screen-printing inks, a variety of different coatings (such as from varnish to PU) and laser labeling are ideal. In conjunction with different rubber colors (multiple colors on a single keypad are also possible) and illumination, this results in attractive options for customizing silicone rubber keypads.
And for something out of the ordinary: If the front panel and key caps are made of stainless steel, the keypad looks robust, while the substructure is a cost-saving flat keypad.
The custom made one: Combinations of various technologies
Keypads combining the attributes of multiple technologies offer flexibility for custom solutions. Based on the motto "the best of both worlds", a silicone rubber keypad can, for example, be fitted with cutouts for displays or the like, and the surface - apart from the keys - clad in a PE film. These keypad types are used in medical technology and in the care sector, for example, where distinct touch feedback allied to good cleanability is required.
Custom adaptation to the specific application is key to every solution. That is true in terms of the dimensions, the requirements of the operating environment, or design wishes. To achieve an optimum balance between meeting the requirements and cost, Rutronik's field application engineers and product managers work closely with membrane and silicone rubber keypad specialist Knitter-Switch to support customers worldwide. The German manufacturer has been at the forefront of switch technology for roughly 50 years, with customers profiting from tried-and-tested, state-of-the-art products, extensive experience, and exceptional knowledge. knitter-switch develops all its solutions in Germany, thus offering uncomplicated on-site support and effective coordination.