Technical article: Keyboard technologies. A comparison.

Item no. 1861

Typical applications of key keyboard technologies.

Description

How do membrane keyboards, rubber keyboards, silicone keyboards, vandal-resistant keyboards and touchscreens work?
Technical article by Gert Breidenbach, GeBE Elektronik und Feinwertechnik GmbH
The author attempts to categorise important keyboard technologies on the basis of some salient requirements from typical areas of application. He discusses the technical solutions, special features and possible combinations with other I/O devices such as mouse, trackball and touch screen. Typical criteria are fast typing, operation of machines, required protection against vandalism in publicly accessible areas, high functional safety for medical devices and special protective measures in explosion-proof installations. In the author's opinion, in addition to functionality and operational safety, the design and software support of input technologies are playing an increasingly important role. The development of interactive technologies will have more and more influence on traditional I/O technologies, so that a slowdown of the currently rapid development of I/O technologies is not foreseeable.
Fast typing, good feeling -- long-travel keyboards
Experience has shown that high speed data entry can only be achieved with long-travel keys. In addition to the classic areas of application, long-travel keyboards are also often preferred in industrial environments because of their ease of use. However, a great deal of effort is required to prevent soiling, which makes these keyboards not exactly cheap. High-quality long-travel keyboards, which are sealed against water by rubber membranes under the keys, compete with simple covers moulded from soft plastic material, which offer a certain degree of protection against liquids and dust on the upper side even if the keyboard is not protected to IP65 all round. However, the foils lying loosely on the keys have a decisive negative effect on the feeling during operation, so that safe and fast data entry will not be achievable in the long run.
Membrane keypads - Safe data entry in harsh environments
Foil-covered keyboards are particularly suitable for use in harsh environments and are much easier to clean than long-stroke keyboards. However, there are major differences not only in the use of language but also in the quality of keyboards constructed with foils, which are of course also noticeable in the price. Classic membrane keyboards, where the individual keyboard elements are also made of membrane, are primarily suitable for mass-produced articles and large series. For smaller series, on the other hand, discrete switching elements covered with foil are used, such as metal switching domes (Knackfrosch) and short-travel keys. In the meantime, strongly raised reliefs up to lenticular key caps are also applied to the foil in special screen-printing processes, thus avoiding the weakening of the foil that occurs during embossing. If the flexible foil only serves to cover the keypad, which is otherwise made up of discrete switching elements, the initialisation costs for the entire keyboard are lower. Because foils are normally flat, the application of this technology is mainly limited to 2-dimensional objects such as front panels. But it is precisely here that foil-covered keyboards dominate the market.
Rubber keyboards - Three-dimensional design
If, on the other hand, one wants to free oneself from the 2-dimensional restrictions of membrane keyboards, the technology of silicone rubber keyboards is available. The rubber key technology offers an immense number of design options in the third dimension. However, practically nothing works without tools. Due to the not too high pressure in the mould, these are relatively inexpensive and amount to about one eighth to one fifth of the cost of an injection moulding tool for comparably sized objects. The closed surface of the rubber keypads makes it relatively easy to keep devices clean and sealed. By completely moulding the keyboard base body with silicone compound, the often mechanically very critical individual key bushings through the housing can be dispensed with. For the installation of the keyboard, only a complete breakthrough, which is easy to control, is provided. If, on the one hand, protection against vandalism is required and, on the other hand, the good dynamic properties of the key element are to be used, the rubber mat is reinforced with a steel armour. The rubber mat, which is inexpensive to produce, then fulfils sealing and sensory functions. For large series, a full-travel keyboard designed in this way can fulfil its many tasks unrivalled in price and safety.
Vandal resistant keypads - applications in public areas
Vandal-proof keyboards are in great demand in a steadily growing market for vending machines and information terminals. Good protection against vandalism is offered by metal keyboards where the keycaps are inserted into a stainless steel front plate. Scratching does not immediately lead to rusting. Technologies under the "stainless steel armour" are manifold. Great importance is attached to sealing to the inside. In the meantime, keycaps with profiling protruding over the front are also available, so that the feel of these keyboards is increasingly approaching that of long-travel keys, which is very much in line with the need for use, e.g. in publicly accessible Internet terminals. The ball of the sometimes integrated trackball is also made of steel.
Touchscreen - New interactive techniques
In the future, complex processes and complicated, software-controlled machines will require more and more intuitively operable interactive input/output systems. The touch-sensitive input surface is combined with a graphically freely designable output medium. Above the LC display, which is mostly used today, a touch sensor is arranged, which can dedicate the place where the finger touches its surface by means of analogue-digital working electronics. Various physical principles are used, such as infrared sensing from the edge or resistance measurement in a so-called foil touch screen. The basic idea behind these interactive keyboards is, of course, to be able to change the layout of the input medium on the display - the assignment between the key symbol and the triggered command - quickly and almost in any desired form at any time. There can be no doubt that in areas where interactive input/output is becoming more and more important, e.g. at vending machines and Internet terminals, the touch screen display will become an increasingly strong competitor to the traditional keyboard. Often today, a picture output is available on the machine anyway, so that the use of a touch screen for data input is obvious and the arrangement of additional discrete keys becomes practically superfluous.