Electromechanical Components for Medical Engineering - For Versatile Protection and Maximum Reliability

02/03/2021 Know-How

Developers of medical devices must be in a position to get increasingly complex technologies ready for serial production as quickly as possible. But they also need to meet the highest quality and safety standards – after all, their ability to work flawlessly can literally mean the difference between life and death in a worst-case scenario.

Medical engineering often requires compact end systems that are easy to clean and sterilize. Electromechanical components help to achieve this, offering protection from usage mistakes, overcurrents and overvoltages as well as overheating. User-friendly design for medical devices requires modern control concepts that minimize human/machine interaction errors as much as possible. But they also need to provide a sterile and easy-to-clean device with IP67 protection.

The ability to easily operate a device manually can be ensured using robust rocker switches, rotary switches and pushbuttons manufactured from high-grade materials, for example using ENC series optical encoder switches from C&K (Figure 1). These components, available with two-channel, 2-bit output, provide robust haptic feedback with clear lock-in feedback.

Tact switches enable reliable operation due to the tactic feedback they offer. C&K's KSC series models (Figure 2) are designed for more intensive usage, offering a long service life of up to 10 million cycles. Their silicone and rubber actuators offer specified haptic feedback and audible reactions depending on the force and actuator hardness, and also enable the switch to be easily integrated.

Customized metal keyboards offer many ways to handle operate medtech devices often equipped with various applications. These keyboards, which are highly resistant to liquids, can also be easily cleaned and sterilized.

Complex, modern devices can make use of human-machine interfaces to enable their control. The corresponding functions are controlled using the control unit via a signal and/or MOSFET relay. MOSFET relays such as the G3VM from Omron (Figure 3) guarantee a high number of silent switching cycles. No light arc is generated when the contacts are switched, which means that there is no failure as a result of contact wear and tear. These components therefore offer the advantage of a long service life.

High-Performance Power Supply

Like any technology, new medical developments and enhancements of these depend on a reliable, custom-built supply of power, which is provided by a power supply unit. However, a safe deactivation mechanism that switches to a backup power supply such as a rechargeable battery must also be ensured for faults such as short circuits. Various fuse mechanisms such as cartridge fuses, 5mm/¼" axial lead fuses and brick fuses are used for this purpose. Brick fuses in particular are defined by their small and compact construction.

The surface-mountable 6125 series brick fuses from Eaton Bussmann are especially recommended for applications where work needs to continue in the event of a fault without resulting in damage to components. They not only protect the power supply from short circuits but also serve as EMI filters. The fast-acting types (6125FF) are specially designed for high switch-on currents. The 6125TD series with time-delay action corresponds to the EIA-IS-722 standard and can conduct rated currents for at least four hours. The 6125FA models guarantee overcurrent protection up to 125V AC/DC.

The 1025 series from Eaton Bussmann (Figure 4) comes into play when even higher currents are involved. These conventional surface-mounted fuses offer protection from the highest current level. Their higher melting integral also allows for higher switch-on currents. With an operating temperature of -55 to +125°C, they are also suitable for use in harsh environments.

Eaton Bussmann also offers fuse brackets for panel or PCB mounting, with many being suitable for 5mm and ¼". They are available in a variety of IP protection classes.

Resettable fuses are ideal for difficult-to-access circuits, especially in applications that need to be continuously available or where overcurrents are common. These PTC components (positive temperature coefficient) increase resistance when the temperature rises as a result of excessive current. Once the problem has been fixed and the temperature drops again, the resistance is automatically "reset". The largest selection of PTC components is found at Littelfuse, for example the PolySwitch and Poly-Fuse series. The nano SMD series from Littelfuse also has especially small dimensions that help to save space and cut costs. With the large selection of different models, it also provides versatility in design. Thanks to their high voltage ranges, they can also be integrated into newer applications.

Can't Stand the Heat

Heat emissions from components during operation present a certain risk for the flawless function and lifetime of the components, which is why thermal management tailored to the application and specific installation conditions is essential. Board-level heatsinks (pin heatsinks) are an established method of cooling PCBs that host not only power semiconductors but also controllers and signal processors. As they are directly mounted on the component in question, they can be used to cool them specifically and efficiently. Fischer Elektronik and Assmann WSW are among the providers with the largest range of aluminum or copper board-level heatsinks with various sizes, form factors and installation mechanisms.

Thermally conductive foils as thin as 10µm to 100µm help to save even more space (Figure 5), and also offer a high thermal conductivity of up to 1,950W/mK. They are simple to handle as they are easy to cut to the desired size. Thermally conductive foils are available on the market from suppliers such as 3M and Panasonic.

Where very large amounts of heat are generated, fans are the method of choice. They are superior to passive cooling both in terms of performance and in terms of cost. If the focus is on maximizing air flow, the AD12032 from ADDA comes recommended (Figure 6). If noise levels are a factor, on the other hand, for example in devices used in patient rooms, models with floating bearings such as the AD12032 series from ADDA or the JV0620-00 from Jamicon are recommended (Figure 7). The dual ball bearing models from Jamicon have an especially long service life.


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