Keyboards in medical technology

Hygiene, functional safety and usability - keyboards in medical technology

The demands on devices in medical technology have always been extremely high. Inconceivable when a ventilator simply stops working, or when an input error in an infusion pump leads to an overdose. The three parameters are decisive here: hygiene, functional reliability and usability. Hygienically closed user interfaces with a high resistance to detergents and disinfectants are almost mandatory, because many viruses can survive on surfaces for several hours.

Depending on the field of application, the control devices are exposed to multiple people accessing them every day and can thus become a vector for disease. The MMI interface should also be reliable and easy to use. This is because, particularly in emergency situations where users are under time pressure and stress and often have to operate different devices at the same time, a complicated design can encourage incorrect input.

In addition to purely display-oriented operating technologies, classic input elements for controlling medical devices continue to play an important role. Whether ultrasound devices, patient monitors or bed controls - most human-machine interfaces in medical technology are still implemented or supplemented with a classic keyboard.

Published in the meditronic-journal 3/2021

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membrane keyboards

Due to its diverse design and equipment options, the classic membrane keyboard a preferred choice in the medical environment. A membrane keyboard consists of several individual layers that are placed on top of each other to form the overall structure. With the help of tools, it can take on almost any shape.

The decorative film, as the top layer, is made of extremely durable polyester or polycarbonate and is printed on the back to ensure the highest possible protection against abrasion. In addition, the material can be coated with a antimicrobial agent be supplemented and thus limit or eliminate the spread of germs.

Membrane keyboards medical technology

Haptic feedback from membrane keyboards

The user benefits from a membrane keyboard from haptic feedback, so that user-related input errors can be avoided. For a secure finger guidance and tactile feedback ensure embossed buttons. In addition to the metal snap disks, there is also an acoustic feedback in the form of a “click” sound. The metal snap domes are available in a wide variety of sizes, shapes and actuation forces. They are preferred for applications with a high number of operations.

Capacitive solutions

Senso-Touch membrane keyboard
Senso-Touch membrane keyboard

Mechanical sliders and knobs can also in one membrane keyboard However, in hygiene-sensitive areas, a capacitive solution with a closed surface is recommended. The raised areas, gaps, and crevices associated with conventional controllers and encoders pose a high risk of contamination.

Cursor keys can also be capacitive solution be realized and replace the classic mouse as an input unit. Another advantage of this technology is an increased service life, since there is no mechanical wear. The user can also experience acoustic or optical feedback through the integration of LEDs or signal transmitters.

Touch displays with keyboard

If more complex menu navigation is required, the Membrane keyboard with a Touch display can be addedThe membrane keyboard as a keypad allows quick access to recurring input commands or preset parameters, while the touch display with its graphic visualization options enables interactive communication.

For a closed surface, the connection between film and display is achieved by integrated viewing window with a highly transparent adhesive layer Depending on requirements, these windows can be individually specified as glossy, matte, anti-reflective, scratch-resistant, UV-resistant, and colored.

The membrane keyboard retains significant design aspects even when the display is off and black. Even if functional reliability is the primary focus, product design contributes to the purchasing decision. It's also important to consider intercultural differences among users. A red start button, for example, would be unusual in Germany, but not in Asia.

Keyboard lighting

Touch display with membrane keyboard
Touch display membrane keyboard with disappearing effect

The room lighting in medical work environments is often dimmed, so that the lighting of input elements is essential for safe operation. Here she scores membrane keyboard due to the easy integration of LEDs and the advantage of the printed surface, which can also be seen from a 180° rotated viewing angle.

The LEDs often function as status indicators for individual keys and are sufficiently bright even in daylight. Fully backlit membrane keyboard or individual keys is through the Use of LGF (Light Guide Film) possible. The typically flat design and flexibility are retained.

With LGF technology, LEDs are embedded at the edge of an extremely thin, highly refractive film. Due to the high light refraction, only a very few LEDs are required for homogeneous illumination. Backlighting of each key can be done in different colors, in addition, LGF technology does not require a high-frequency alternating voltage source.

A special feature is the disappearing label. This is a label that is invisible when the keyboard is unlit and only becomes visible when illuminated. This allows a clear ON/OFF mode to be signaled.

EMC shielding for interference-free operation

Reliable and trouble-free operation of input devices is absolutely essential, especially in medical technology. Membrane keyboards of all types are characterized by long service life with over 1 million switching cycles When using multiple electrical sources in one location, such as in an operating room, inadequate shielding against electrical or electromagnetic effects can lead to malfunctions and interference with individual devices.

The EMC shielding of a membrane keyboard is realized, among other things, with an aluminum or copper-coated polyester foil. This shielding film prevents the device from malfunctioning due to the ingress of unwanted signals, as well as interference in its own electromagnetic environment. In connection with integrated displays, a segmented EMC shielding of the keyboard and conductor tracks is used.

Partial EMC shielding of a membrane keyboard
Partial EMC shielding of a membrane keyboard

Fully protected with silicone coating

In addition to the membrane keyboard as a control element, especially for handheld devices or desktop keyboards, a completely closed silicone coating possible. A flat keyboard layout is sprayed onto the front panel of the housing. After the electronics have been installed, they are welded to the back shell using an ultrasonic process. The result is an optimal bond between the individual components and a completely closed surface.

The keyboards are protected against water and dust ingress and thus allow complete and thorough cleaning. With a Protection class up to IP68 They are also suitable for immersion disinfection. Depending on the silicone used, steam sterilization is also possible.

In combination with a membrane keyboard or a pure touch solution, the Housing with sprayed-on seals im multi-component injection moulding be equipped. The integrated seal ensures that there are no gaps that are difficult to clean and that the electronics are protected from the ingress of foreign bodies and liquids. A protection class of up to IP65 can be achieved with a well-coordinated design from the outset.

advantage of Multi-component injection molding technology is also that only one component needs to be constructed. This significantly reduces the investment and the effort required for production and quality assurance. Ultimately, profitability always plays a role in every product. For example, the financial outlay for programming a graphical user interface between man and machine is a significant factor.

It is true that not everything that is technically possible is also economically viable. Especially in devices with a small number of functions that require good visibility and constant user interaction, proven input components such as that membrane keyboard, therefore the preferred choice. Due to the lower one-off tool costs, the cost remains significantly lower than for most alternatives – especially for project volumes with small and medium quantities.

Plastic plate with molded-on silicone keyboard as assembly
Plastic plate with molded-on silicone keyboard as assembly

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