Published in PC & Industrie 09/2021
Article as .pdf (German) >>
Robust, reliable and easy to operate
The crane is controlled with dirty work gloves, the keyboard is exposed to permanent vibrations and grinding dust in the assembly hall – no question, industrial application areas demand a lot from input units.
A robust design, simple operation and reliable function are the decisive parameters here. The input unit must be optimally protected against vibration and shock or even designed to be explosion-resistant. They should be resistant to water, dust, dirt, oils and chemicals, and be able to withstand temperature fluctuations. Despite the high requirements, different keyboard and key solutions come into question depending on the area of application.
Stainless steel tasers
The first thought when asking for a robust input solution is obvious with robust stainless steel keyboards. Especially in public areas or local traffic, as well as in industrial machine control systems, vandalism-proof keyboards are used. Visually, they are similar in standard design to any conventional PC keyboard and thus benefit from wide acceptance. Another advantage for customers is that there is a very wide product range of stainless steel keyboards and thus no initial costs, as is the case for customer-specific input keyboards. Despite the standard, individualization is also possible here through the key layout, printing and backlighting in smaller frames. The inscription of the keys is done by laser engraving or etching, which makes the key symbols wear-free. Colored graphics or raised symbols, such as Braille or other customer-specific lettering, are also possible.
High protection class
The housing and buttons are made entirely of stainless steel and are usually accompanied by fully sealed switching mat technology. Both the front-mount and rear-mount versions have a protection class of up to IP67 and an impact class of up to IK10. Fully encased desktop keyboards even achieve an IP class of 68 and are thus protected against permanent submersion. The integration of touchpads and trackballs is also possible without loss of protection class.
Different installation variants
Thanks to various installation variants and common interfaces, stainless steel keyboards can be integrated very well into existing working environments. With an average operating range of -20°C – +60°C, they can also withstand fluctuating temperatures. In addition, many suppliers also offer pure number blocks and function keys in various sizes made of stainless steel.
If only individual buttons are required, pushbuttons made of stainless steel or also of robust plastic are an option. The pushbuttons often take on the functions of a pure command transmitter, so that signals such as start and stop or forward and reverse or emergency stop, are clearly communicated. With engraved or printed pushbutton covers, colored Satus LEDs and various housing colors, these are given an individual appearance. Multicolor illumination even makes it possible to display multicolored status indications. The pushbuttons are installed directly in a front panel or housing and achieve a protection class of up to IP68/IP69K thanks to appropriate seals. The service life of several million cycles also makes the pushbuttons very reliable. Virtually maintenance-free are piezo switches made of metal. By eliminating a mechanical stroke, wear and contamination are virtually eliminated. Lifetimes of over 50 million cycles are now the standard.
Areas of application
Stainless steel input solutions are often used in areas where vandalism, damage, or exposure to environmental stress and user interaction is expected.
When the standard product is not enough, a customized HMI interface is needed. Especially control units of construction and agricultural machines, as well as mobile input devices in outdoor use are mainly custom-made. The devices often need a smaller number of functions, but good visibility, sufficiently large keys with haptic and sometimes also acoustic feedback, and a long mechanical service life. The working environment here demands reliable operation, even with heavy work gloves, high noise levels and sometimes extreme weather conditions. Therefore, membrane keyboards and silicone keypads are currently used in industrial environments due to their design freedom, closed surface, resistance to chemicals and their impermeability to liquids and dust.
Silicone Rubber Keypad
The silicone rubber keypad adapts it to its construction and is extremely flexible and space-saving. Key caps made of metal and plastic, different key shapes and individual key colors can easily be realized in one mat. Special lacquers can be used to make the individual keys abrasion-resistant. It triggers a direct switching function on the circuit board underneath and determines the haptics, the visual as well as tactile impression and, via the integrated contact elements, the electrical behavior. In addition, the switching mat often performs a sealing function on the printed circuit board.
Button designs with integrated seals ensure dust- and moisture-proof housing integration up to IP67. A higher protection class can be achieved by completely overmolding a housing with integrated keypad layout. The mechanical service life with up to 10 million switching cycles makes the silicone keypad a durable and virtually maintenance-free input solution. The illumination of individual keys or the entire mat can be realized by LEDs in combination with transparent silicone or integrated light guides. The display of status indications in individual buttons is also possible thanks to a very precise 2K injection molding process. Without LEDs, silicone keypads made of phosphorescent silicone acquire luminous properties. Illumination offers users an advantage in avoiding incorrect entries in the often diffuse lighting conditions in industrial halls.
Adaptable and inexpensive
The force-displacement behavior of a silicone switching mat can be customized to meet the requirements of the specific application. This means that even the high actuating forces of 200g – 500g and actuating travels of 0.3 to 5.0 mm typical of industry are possible. The silicone switching mat can particularly show its advantages when large quantities are required. The high one-time costs for the tools make small series very cost-intensive. However, compared to equipping them with individual switches, they are significantly less expensive even in medium series.
Membrane keypadThe membrane keypad can also take on any shape through the use of tools and is the more favorable variant compared to the silicone keypad in smaller quantities. There are almost no limits to the design options through screen and digital printing processes, as well as specially embossed foils and surface coatings. Even the illumination of a membrane keypad can be easily realized by integrating LEDs, while retaining its flat design. The decorative foil as the top layer of the keyboard is made of polyester or polycarbonate and is printed on the reverse side to ensure the highest possible protection against abrasion. Compared with other flexible materials, polyester in particular has a convincing life cycle of over 1 million switching cycles, very high abrasion resistance and resistance to chemicals.
To ensure concise finger guidance, the decorative foil can be embossed. There is the possibility of key, dome and edge embossing with which very ergonomic key shapes can be realized. A high-quality epoxy coating gives the keys a three-dimensional appearance. Tactile feedback is provided by integrated snap domes which, when pressed, create a tangible tactile sensation and, depending on the version, an audible “click” sound. This direct feedback reduces file entry errors. The combination of metal snap domes with a high actuation force and key embossing is common in the industrial environment.
In addition, it is possible to replace the upper polyester film with a silicone surface. This silicone cover with keys can be laminated onto the circuit package of a normal membrane keypad as a pure actuation layer. The resulting hybrid of a classic membrane keypad and a silicone switching mat gives scope to combine the advantages of the individual input solutions in one keypad. With the silicone surface, a three-dimensional design can be realized, a point at which the membrane keyboard is naturally severely limited. This makes it possible to have protruding keys with a free design, guide elements such as offset rings around a key, Braille inscriptions or cursor keys. At the same time, the surface is visually and haptically enhanced.
For reinforcement, the membrane keyboard can be mounted on custom-made carrier plates with press-in studs. Aluminum plates are used as standard, but other metals or plastic plates are also possible. The membrane keypad is glued onto the carrier plate over its entire surface. A complete assembly with display and printed circuit board is also possible. By integrating seals, a membrane keypad can achieve protection class IP67.
Multi-touch display solutions
Capacitive multi-touch display solutions are also suitable for use in industrial environments, at least in terms of their protection classes and technical parameters. However, the restriction of gloveless operation does not fit into every working environment. However, if displays are desired to simplify complex machine control, a resistive single touch display may be an option. In combination with push buttons, a membrane keypad or silicone keypad as an additional input element, user-friendly menu navigation can also be promoted. Recurring input commands or preset parameters can be called up quickly, easily and clearly using the mechanical keys. Due to the haptic feedback of the mechanical command transmitters, user-related input errors can be avoided, which increases the safety of operation. For easier handling, the displays can be equipped with anti-reflective and anti-fingerprint coatings.
Conventional input keyboards and pushbuttons remain strong, especially in the industrial environment. The trend towards miniaturization, as in other application areas, plays less of a role here. Instead, the requirements in terms of service life, protection class and technical equipment are increasing.
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