Staying Connected - April 2014

Locking and Non-Locking Medical Connectors

Medical connectors can be divided into two broad groups based on how they are retained by the devices to which they are connected:  locking - also referred to as latching - and non-locking.  Each offers advantages and disadvantages and design and manufacturing challenges

Locking and Non-Locking Connectors


USB connectors are examples
of non-locking connectors

Custom locking defibrillator
connector latches securely



Example of “MS” – mil-spec
type connector commonly used
in early medical devices


Early medical cable assemblies used connectors adopted from military and industrial applications.  These “MS” (mil-spec) metal connectors had knurled threaded couplers.  Once screwed down to the receptacle, this connector would not come loose inadvertently.  While this type of connection met the requirement that the cable not be disconnected unintentionally, they were difficult for clinical users to connect and disconnect and provided no safety disconnect feature which is often desirable for medical applications.


Custom overmolding of RJ connector helps
prevent the latch mechanism from breaking off


The Registered Jack Connector

An example of a locking connector used in medical devices is the Registered Jack, or more commonly called the “RJ” connector.  While some RJ plugs are rated for up to 1,000 mating cycles, the latch is typically exposed and easily broken.  Once the latch breaks, the plug is poorly retained by the receptacle and the cable requires replacement.

One solution to improve the service life of an RJ connector is to overmold the body and include a flexible hood.  The hood should allow the latch to be depressed but should also prevent the latch from being bent upwards and breaking off.

Locking Connector with Safety Disconnect

It is often desirable for a medical cable assembly, particularly those that connect between a patient and a stationary device, to lock to avoid unintended disconnection.  In some instances, it is equally desirable for the connector to safely disconnect if axial force is applied to the cable such as when it is caught in a moving bed.



A safety release has been designed into
the plug (red feature) which will allow safe
disconnection above a pre-established load


This design requires that a minimum retention force be established for the locked connector over which the plug will disconnect.  By carefully designing the locking mechanism, the connector will be held securely in the connected condition until the specified axial force is applied.  Above that load, the connector will disconnect without causing harm to the patient, device or cable assembly.

Non-Locking Connectors

Medical cables require a positive connection between the plug and receptacle.  Any looseness in the connection may cause intermittent contact, resulting in unwanted noise or poor signal quality which may make diagnosis or therapy difficult, if not impossible.

How firmly the plug is held by the receptacle is referred to as retention force and is a controllable characteristic.  Pin and socket selection, as well as the physical design of the plug and receptacle, allow control over both insertion and retention force.  If the connector is expected to have a high number of mate and un-mate cycles, it is generally desirable to achieve retention force from the friction between metallic pins and sockets rather than plastic parts that wear more easily.

Connector Retention Force


The interface and friction between pins and
mating sockets plays a large role in the
retention force of a mated connector


Retention force of a connector pair - plug and receptacle - is nominally made up of the sum of the retention force of each pin and socket as well as any friction between the plug and the receptacle.  For connector pairs with few contacts, friction, whether intended or unintended, between the insulator and receptacle wall may be the largest factor in determining the total retention force.  For units with a larger number of contacts, little or no friction may be needed between insulator and receptacle wall.

An additional factor to be considered is that in a connector with more than a few contacts, the total retention force is greater than the sum of each pin to socket retention force.  This characteristic is detailed in a paper by Robert S. Mroczkowski, Sc.D “The Mating Game” in “Connector Specifier” magazine, December, 2001.  In the article Mroczkowski states that “mating force will always be greater than that value (if all contacts mate at the same time) because of tolerance and housing interaction effects.”

Enhancing Connector Retention Force

If the retention force achieved by pin-to-socket and friction of the connector housing is insufficient, one method to effectively increase retention force is to design the connector so that axial force applied to the cable does is not directly applied to the removal-axis of the connector.


Custom, non-locking connector can
be disconnected by axial force applied
to the cable

Custom, non-locking right-angel
version resists disconnection when
axial force is applied to the cable

Retention Force Specification

For non-locking connectors, one of the specifications established early in the project is the retention force of the plug to receptacle.  The amount of retention force as well the required number of mate and un-mate cycles are factors considered in contact selection and part design.

Once mating and retention forces are established and documented, molds are designed in a “tool safe” manner.  Tooling is designed to produce plastic parts that have retention force below the desired level.  By removing metal from the tool, the connector becomes larger and retention force is increased.  Done in very small increments, this method allows retention force to be “dialed in.”  Sharing mold trial parts the design team allows insertion and retention force to be evaluated and adjusted before production parts are manufactured.

Connector Retention Force Testing

Once production parts have been manufactured, verification testing will confirm that all specifications, including connector retention force, are met.  For non-locking connectors, Design Verification Testing will typically include measuring retention force at pre-established intervals during mate and un-mate cycle testing.  This will confirm that retention force is maintained over the design life of the connector.


Engineering technician, Eric Yamane,
performs Mate/Un-mate cycle testing
by hand to more closely simulate actual use

David Moreno measures
retention force at pre-defined intervals
of mate/un-mate testing

Summary

Choosing to use a locking or non-locking connector for a medical cable assembly is a decision that should be made early in the life of the project and should consider the user and also how the cable may be used.

The Affinity engineering team has decades of experience designing both locking and non-locking medical connectors and the associated cable assemblies.  Let us partner with you on your cable or connector project.

For additional information, contact your local Molex Sales Engineer or Account Manager or call us at +1 949.477.9495 or email us at custcare2@molex.com.

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Meet Jorge G. Olalde – Shipping and Receiving Associate



Jorge Olalde, Affinity Shipping
and Receiving Associate


Hearing from his mother-in-law who works at Affinity that the company was hiring, Jorge applied for a job “five or six times.”  “I came in so often, that Janett, the receptionist, knew who I was.  Finally, first shift production supervisor Eric Schnitzler called me to come in for an interview.

Jorge joined the Affinity Medical team in 2010 as a temporary Production Associate in Work Cell 21, one of the work cells that manufacture electrophysiology cables.  About six months later, when a position in Shipping and Receiving opened, Jorge applied, “without hesitation and eager for a new challenge.”  Moving to Shipping and Receiving, Jorge had the opportunity of transitioning from a temporary to regular employee.

“Working as a Production Associate gave me a good background for Shipping and Receiving,” said Jorge.  “I understand what goes into manufacturing the products that we ship out.  Only after our customer receives their product in perfect condition with the proper paperwork, is our job done.”

Jorge also works in receiving, applying knowledge and training he received as a Production Associate.  “Everything that comes in the door is inspected.  Nothing leaves the receiving department until we have confirmed that meets the requirements of the inspection plan.  Only then, is it allowed to move from receiving into the warehouse.”

“Shipping and Receiving has really changed in the past three to four years.  We have gotten much busier and occasionally ship more in a single day that we did in several weeks,” said Jorge.  “Affinity’s heaviest shipping is towards the end of the month.  When it is really busy, we often work from six in the morning to six in the evening.  We have to get the shipments out because we know that our customers are counting on us.”

Asked what the biggest challenge has been in Shipping and Receiving, Jorge discussed international shipments.  “We now ship to customers in other countries almost every day.  We coordinate international shipping with carriers such as Expeditors, ABF, DHL Global, Stevens Global, and FedEx Trade Network.  Last year we took on the challenge of filing Electronic Export Information (EEI) ourselves using AES Direct rather than paying our carriers to do this for us.  It was difficult at first because there is no room for errors.  Everything has to be perfect.”


Shipping must be done accurately –
there is no room for errors” – Jorge Olalde


 “When we received our first several monthly reports from the U.S. Census Bureau I was really pleased that Affinity had zero errors – perfect reports,” said General Manager, Bob Frank.  “Our shipping and receiving team, which Jorge is part of, did a great job of implementing the program saving us time and money.”

Jorge met his wife Cynthia at church five years ago.  They live in nearby Garden Grove and have a three-year-old son, Joshua.

When not working, Jorge enjoys family time and also drawing.  “I have always liked to draw and I get a lot of pleasure out of art,” said Jorge.

Asked if he had any other comments, Jorge replied, “I would like to thank my supervisor, Maria Alcaraz and also Isidro Rivas for supporting me and helping me become the man I am today at Affinity.”. 

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Reduced Cost Lead Interface

Reducing cost is often required as medical devices are intended to be sold in emerging markets.  Often, one of the most costly components of a cable assembly is the connector.  In this example, cost was reduced by eliminating an external connector.

For the application pictured, the device maker intended the two ECG leads to be semi-permanent with the cable only being changed infrequently.


Custom interface is designed to be
captured by top and bottom halves
of the device case

A Flexible circuit with a low-cost pin
header plugs directly into the PCB
eliminating a more costly connector

The assembly, molded of very durable Santoprene® was designed with groves to be captured and held securely by the top and bottom halves of the device case.  Instead of using a pair of connectors – plug and receptacle - the interface was simplified and the cost reduced by using a small flexible circuit and a pin header.  The four-pin connection on the end of the flex circuit is plugged directly into the PCB within the device.

The assembly described is custom and proprietary, however unique interconnects like this can be designed and manufactured to meet your specific requirements.

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Announcements, Information and Trivia


 


The equator is marked in
Uganda and the Sun will be
directly overhead during the
twice-a-year equinoxes


The Sun appears to rise
before it actually does

Twice a Year - The two annual equinoxes are the only times when the center of the Sun is exactly overhead at the Equator.  The Vernal, or spring, equinox took place on March 20th, 2014 16:57 Universal Time and the autumnal equinox will take place on September 23rd, 2014 at 2:29 Universal Time.

Equinox - Equinox is Latin for aequus (equal) and nox (night) meaning, roughly, “equal night”.  At the vernal and autumnal equinox, day and night are nearly equal!

Sunshine – Because the Sun is so much larger in diameter than the Earth, slightly more than half of the Earth is in sunlight all of the time!

Sunrise – Sunrise is commonly referred to as the time when the top of the Sun’s disk rises above the horizon.  Because Earth’s atmosphere refracts sunlight, sunrise appears to happen – that is the sun appears to peek above the horizon – before it actually does.