A Clean Break: Breakaway Connectors in Medical Devices
Breakaway connectors can quickly disconnect to protect people and equipment, yet still provide the same pin and housing durability as their mechanically secured counterparts.
By Steven Lassen, Product Applications Engineer, and Julie Carlson, Marketing Communications, LEMO Breakaway connector
Breakaway connectors break the rules of device design that expect electronic connectors to make a secure attachment — whether between a cable and a device or two cables to each other. Typically, we want connectors to be stronger than the weight of the device or the limits of the cable holding them together. In a surgical setting, for instance, mechanically secured connectors can ensure that an accidentally snagged cable doesn’t lose power in the middle of a procedure.
Mechanically secured connectors typically employ push-pull, lever-actuated, partial-turn, or other manual locking mechanisms that are designed to release only with specific user intervention initiated directly at the connector interface and are otherwise engineered to hold tight — sometimes withstanding a pull force of dozens or even hundreds of pounds.
However, in many applications there is a need for connectors that are engineered to hold tight up to a predetermined point and then, when that force is reached, smoothly and cleanly let go. Breakaway connectors, which are also known as quick-release or quick-disconnect connectors, are often employed in applications including aviation helmets and headsets that attached to cockpit consoles with cables, mobile medical monitoring equipment attached to patients, and unmanned vehicles designed to release payloads in order to prevent cord entanglement, snags, and pulls from hindering or harming the people and equipment they’re attached to.
How to Specify Breakaway Connectors
When specifying breakaway connectors, design engineers should first identify the number of pins needed in order to calculate the desired amount of force needed to successfully unmate the connector. Too little force could lead to overly frequent unmating, and too much force could contribute to bodily injury or equipment damage. As a rule of thumb, the more contact pins there are, the greater the inherent friction, which creates an immediate minimum amount of force that the breakaway connector design must be sure to account for and overcome. In practice, most breakaway connectors are made to hold tight until subjected to forces between 4 and 15 pounds, although some can go much higher, and they are almost never specified for an exact figure (e.g., 5 pounds of force), but rather for a narrow range (e.g., 4–6 pounds of force) to allow for small variances.
Breakaway Connector Technologies
Once the force range is decided upon, designers can select from a number of breakaway connector technologies capable of satisfying both the force requirement and other application demands. Latched breakaway connectors are one common solution since they employ latch or tab features similar to those employed in most mechanically secured connectors. However, instead of being designed to grip the inside of the connector housing until purposefully released through user intervention, the latches or tabs in breakaway connectors are designed — through careful engineering and precision machined tolerances — to release when the specific level of force is reached. Hence, they are often referred to as reduced-latch-force connectors.
Another group of breakaway connector technologies relies upon friction rather than mechanical means to create quick-release connections. These types of breakaway connectors are sometimes referred to as latch-less solutions and are precisely engineered — often using one or several rubber or plastic O-rings or canted coil springs — to create the exact amount of drag needed to provide the desired level of breakaway force. The O-rings employed in breakaway connector designs are usually wrapped around grooves machined into the connector housing with a high degree of accuracy and tight tolerances to ensure that they achieve the desired drag and quick-release forces. The use of O-rings can also provide breakaway connectors with environmental sealing, water resistance, temperature resistance, and other useful properties. For example, Viton rubber is highly resistant to jet fuel and other chemicals, EPDM elastomer is radiation resistant, and silicone can be resistant to temperatures ranging from -50°C to 200°C. So O-rings made of these and other specialized materials are often specified for use in harsh-environment breakaway connector applications.
Canted coil spring breakaway connector technologies are also designed directly into connector housings to provide the desired breakaway force and can provide higher retention forces than O-rings even they still rely on friction, rather than latching mechanisms, to achieve it. In addition, they too can be specified in a number of different materials — typically metals such as brass, copper, or tungsten — to achieve various properties, including excellent temperature resistance and EMI/RFI shielding.
Another breakaway connector technology, the snap-ring design, works roughly like snap-on apparel fasteners, with the connector clicking in, holding securely, and sliding back out over the connector only when appropriate force is exerted. Like canted coil spring variants, these types of breakaway connectors can be also engineered to achieve greater breakaway forces.
Lanyard technology is yet another common breakaway connector solution. In this method, a lanyard or ring-shaped wire is attached to the outside of a connector that must otherwise be released at the connector juncture by means of standard mechanical security mechanisms, such as push-pull or rotation features, and will override the manual unmating method, enabling quick release, if subjected to the specified degree of pull force. These lanyards can easily be marked with a tag or label for clear visibility and can also be easily manipulated with gloves or other low dexterity means, such as a robot, which can be advantageous in some medical, industrial, and aviation applications.
Matching Application Demands to Connector Characteristics
In addition to identifying the desired unmating force for a given breakaway connector solution, it’s also vital to examine the operating environment in which it’ll be deployed, taking into account potential exposure to environmental conditions — including heat, flame, cold, sand, mud, salt water, rain, radiation, chemicals, vibration, ice, RFI/EMI, crushing forces, unusually high pulling forces, cutting forces, and other hazards — as the influence of such factors can be mitigated by proper component specification. Functional and aesthetic issues relating to the application also loom large in the connector selection process, including pin count, wire size, color-coding, shell size, and weight.
A wide variety of materials, including various plastics and metal alloys, can be used to manufacture breakaway connectors, and each delivers their own set of pros and cons. For example, plastic can provide lower weight and lower cost over time, but requires an investment in tooling. Aluminum is more resistant to wear than most plastics and is relatively lightweight compared to other metals, but it is less corrosion resistant. Other metals, such as stainless steel or brass, are heavier but can offer higher degrees of wear resistance, durability, and corrosion resistance.
Plating Materials and Finishes
In many cases, a connector’s base materials can be plated to provide additional properties or overcome limitations. For example, a designer may be able to leverage the low weight and other beneficial properties of aluminum in a potentially corrosive environment by specifying chrome plating to provide the required corrosion resistance and durability, and even improved aesthetics.
Plating materials and other finishes can be specified for both functional and aesthetic reasons. For example, connectors might be color-coded to match their mating partners to enable quicker, easier assembly in high-density electronics, for brand differentiation, or to blend into the device design, which can be desirable for connectors employed on the outside of electronic systems, like medical monitors. Color-coding intended to support proper mating may appear as small dots or markings, while coloration intended for branding or glint reduction, like a black matte finish, is often all-over.
Another consideration when specifying plating materials and other finishes is durability, which should match that of the connector itself. A colored finish or plating that degrades before the end of a connector’s useful lifetime can significantly detract from the benefits its meant to provide.
In general, the more pins there are in a housing, the larger the shell size needs to be. Similarly, higher breakaway forces also tend to require larger shell sizes. However, these generalizations are just that and are not universally true. There can be vast differences in relative abilities to pack more pins or greater forces into smaller connectors based on factors including the size of a given manufacturer’s connector housings and mechanism designs, as well as machining and engineering skills.
Mating Cycles and Consistent Performance
As with all mechanical components, the edges of the pins, housings, and other elements of breakaway connectors exposed to friction can become blunted and worn over time, leading to lower minimum unmating force requirements and increased electrical resistance. However, the point at which this starts to happen can vary considerably, with higher quality connectors designed to reliably perform for several thousand cycles. Most connector manufacturers offer either approximate guidelines or a guarantee regarding the number of mating cycles their products are designed to provide based on factors including material and engineering quality, as well as testing and field experience.
Cable Interface Reinforcement
A common concern among product designers is the strength of the termination point between the connector and the cable, and especially so in applications that employ breakaway connectors and are thus likely to be subject to high pull forces. Additional reinforcement methods, such as overmolding and potting, can help protect the cable terminations and ensure that the connector will unmate as expected rather than rip the cable and wiring out of the connector when subjected to a sudden yank or extreme vibrations.
It is also important to consider the total cost of ownership for a given breakaway connector design rather than just the component cost. For instance, a part that can provide several thousand more mating cycles but is priced slightly higher than a similar part might be well worth the investment of even several extra dollars, especially since specifying cheap alternatives over proven name-brand solutions can result in downstream costs including equipment damage, warranty issues, safety and liability issues, equipment downtime, and loss of business. Some connectors also come with value-added services, such as product traceability and access to technical experts or repair technicians, which positively factor into total cost as well.
The relationship between the cost of the equipment and the relative cost of the connector should also be considered. For example, specifying a low-cost connector on a $500,000 portable X-ray machine that’s expected to deliver high accuracy and durability is unlikely to result in long-term success.
The Value of Customization for breakaway connectors
These are just a few of the many specification considerations and opportunities for breakaway connectors. Depending on the target application, these connectors can also be designed with shielding that resists electromagnetic radiation or radio interference, with breakaway capabilities from several different angles, and with touch-proof protections to mitigate the risk of electric shock. Many breakaway connector manufacturers also offer to work in partnership with design engineers to develop semi- to fully-custom solutions that take every conceivable element of a given application environment, desired connector performance, and overall value into account.
This article is excerpted from LEMO’s white paper, “How to Specify a Breakaway Connector.” See the article in its entirety on LEMO’s supplier page on Connector Supplier.