A decision-making aid for keyboard developers
Published in Meditronic 05/2023
In medical technology, keyboards and user interfaces are an essential aspect of device design. These components must not only be functional and reliable, but also meet the high standards of hygiene and usability required in clinical environments.
From ultrasound machines to patient monitors to bed controls, the human-machine interface is a critical factor in the quality of patient care.
Hygiene is paramount when it comes to medical keyboards. Pathogens can survive on surfaces and potentially lead to infections. This makes it essential to use materials and technologies that are easy to clean. In addition, these surfaces must be resistant to aggressive cleaning and disinfection agents that are often used in medical facilities.
Classic input components: membrane keypads and silicone keypads
Most often, classic keyboards are used: membrane keypads and silicone keymatsBoth technologies have their own strengths and weaknesses, and the choice of the appropriate keyboard solution depends on a number of factors, including unit volume, budget, technical requirements, and the specific application of the device.
Structure of a membrane keypad
membrane keypads
Membrane keyboards are often the first choice for applications where a flat input solution and easy installation are desired. They can often be integrated by adhesive bonding to a standard housing, making them particularly attractive for applications where quick solutions or customization are required.
This keyboard consists of several individual layers that are combined to form a very flat overall structure. Special printing techniques allow more complex circuit diagrams to be printed directly onto the membrane.
The top layer is often made of durable polyester or polycarbonate and can be treated with antimicrobial agents to limit the spread of germs. Embossed keys provide for a haptic feedback, which minimizes user-related input errors. In addition, metal snap domes provide acoustic feedback through a "crack" sound, which is particularly advantageous in environments with high actuation frequency. The integration of flat signal generators is also possible for acoustic feedback.
Membrane keyboards in medical handheld devices
Illuminated membrane keypads
The room lighting in medical work environments is often dimmed, so the lighting of the input elements is essential. The membrane keypad scores points here with the easy integration of LEDs for backlighting of key symbols or for status messages. The user also receives visual feedback through integrated LEDs.
More complex menu navigation can be achieved by adding the membrane keypad with one Touch display be facilitated. The membrane keypad allows quick access to recurring input commands and preset parameters, while the touch display offers graphic visualization options for interactive communication.
Compatibility shielding (EMC) for membrane keypads
When several electrical sources are used simultaneously in one place, such as in an operating room, inadequate shielding measures against electrical or electromagnetic influences can lead to impairments and interference with the individual devices. To ensure trouble-free operation of a membrane keypad in this environment, a electromagnetic compatibility shielding (EMC) which consists, among other things, of a polyester film coated with aluminum or copper.
This protective film not only prevents unwanted signals from entering the device, but also minimizes potential interference in the device's own electromagnetic environment. In terms of price, membrane keypads have an advantage over silicone keypads for small to medium quantities, as they require a lower initial investment.
silicone keymats
Silicone safety mats in medical applications
Hygiene requirements
Regarding hygiene requirements, the use of silicone keymats in medical technology may initially appear to be suboptimal. The main concern is potential cavities and gaps that could arise when integrating them into a housing. These may supposedly not be sufficient to meet the high hygienic standards of medical technology.
In addition, the initial investment in tools and molds for silicone keypads should not be underestimated, which makes them expensive for small series. However, it has been shown that silicone keypads higher production numbers more cost-efficient as membrane keypads.
Silicone safety mats for flexible design
Another crucial one Advantage of silicone safety mats lies in their extraordinary design flexibility and adaptability. In contrast to membrane keypads, which have physical limitations, particularly in the spatial extent of the keys, silicone keys offer considerable design freedom and allow keys with a height of several centimeters. This flexibility extends across a wide range of possible applications: from variable key shapes and sizes to customized color options and specific surface textures.
Additionally, targeted elevations or depressions in the keys differentiated haptic feedback that significantly enhances the user experience. Furthermore, special surface coatings such as polyurethane (PU) or epoxy resin provide lasting protection against mechanical abrasion.
The way food is Integration of modern lighting technologies such as status LEDs or backlighting in combination with transparent elastomers is easily possible.
To effectively seal gaps and gaps in the housing and protect the underlying electronics from moisture, individual keys can be equipped with peripheral seals. This is a critical factor, especially in medical environments where regular cleaning and disinfection of equipment is essential.
Multi-component injection molding technology for diverse integration
Patient wristband in multi-component injection molding with a modified keyboard layout
The Overmolding process also opens up completely new perspectives, especially with regard to handheld devices, desktop keyboards and larger operating devices such as ultrasound devices. A flat keyboard layout is applied directly to the front panel of the case. After the electronics have been installed, they are welded to the back shell using the ultrasonic process. This results in a seamless connection of the individual components and a surface that is completely finished.
The resulting keyboards are highly resistant to water and dust ingress and therefore allow for thorough and comprehensive cleaning. With a Protection class up to IP68 Immersion disinfection is even possible. Depending on the choice of silicone material, steam sterilization is also possible, which can largely alleviate any initial concerns about hygiene suitability.
Another feature of the Multi-component injection molding technology The efficiency of manufacturing is key: only one component needs to be developed and produced. This not only reduces initial investment but also significantly lowers resource expenditure for production and quality assurance. The scalability of this approach can often more than offset the initial costs for tools and molds, making this method a cost-effective alternative to separate membrane keypads and housing components.
In addition, the technology allows for seamless integration of additional functional elements such as magnetic connectorsthat require minimal installation depth while ensuring a robust connection. This simplifies the design logic and optimizes the space required in the device.
In medical applications, these connectors offer a convincing alternative to conventional connector systems, whose corners and edges could pose a contamination risk, thanks to their easy-to-clean and disinfectable surfaces. Their cleaning efficiency can even be increased by using special seals or directly overmolding the connector.
Not a simple either/or
Both membrane keypads and silicone keypads offer high durability and reliability, so choosing between them isn't a simple either/or decision. Rather, it requires a careful analysis of the specific needs of the respective medical device.
Factors such as usability, usage context and cost structure should be considered in a holistic approach over the entire product life cycle in order to select the optimal keyboard solution. In this complex decision-making landscape, both the membrane keypad and the silicone keypad can be the more convincing options, both technologically and economically.
The final decision ultimately depends heavily on the individual requirements and needs of each project.
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