Staying Connected - March 2011

Strain Relief Design Options

A strain relief, also commonly called a bend relief, is important to the electrical and mechanical integrity and overall performance of a medical cable assembly.



A combination strain relief and grommet
designed to be captured and held in place
by an opening in the enclosure

A strain relief typically provides a transition from a flexible cable to a rigid connector or connection point.  A well designed strain relief will prevent mechanical force applied to the exterior of a cable from being transferred to the electrical terminations within the connector which could lead to failure.  A strain relief should prevent an axial load or any flexing being applied at the wire termination point within the connector or device.

Grommets with integrated strain reliefs are also commonly used when a cable is permanently attached to a device.  Cables that pass through an opening into a device typically employ a grommet to anchor the cable to the device and provide protection against tensile force.  If it is likely that the cable will be flexed it is common to use a combination grommet and strain relief for through-hole applications.

Pre-manufactured and CustomStrain Reliefs


Pre-manufactured flexible
slip-on strain relief

Pre-manufactured metallic
spring-style strain relief

Strain reliefs can be either pre-manufactured or custom designed for a specific application.  Custom strain reliefs can be designed to be applied as a separate piece or can be designed to be molded over the cable, capturing the connector.)

Pre-manufactured strain reliefs typically slip over the cable before the connector is terminated.  After the cable conductors are terminated to the connector, the strain relief is screwed or glued onto the connector assembly.  Most off-the-shelf connectors have corresponding pre-manufactured strain reliefs available to fit a variety of cable diameters and are also often available in different colors.


A custom strain relief pre-molded and
designed to fit into plastic housing.
Cable clamp increases tensile strength

An off-the-shelf connector and screw-on
boot with segmented strain relief

In most instances, a custom designed and overmolded strain relief will offer superior flex life, tensile strength, and moisture protection performance than a pre-manufactured strain relief.

Flex Life and Tensile Strength Performance

A well designed strain relief can enhance both flex life performance and tensile strength.  Typically raw cable or wire will withstand a higher number of flex cycles and have a higher tensile strength than a cable assembly.  The point where the cable or wire is terminated is generally considered the most likely point of failure in terms of flex life and tensile strength.  A well designed strain relief should prevent any force from being applied to termination points.



Flat surfaces show cable clamp that has
been crimped onto the cable jacket
increasing tensile strength when
captured in overmold

Design considerations for a strain relief include not only the geometry of the part, but also the interaction of the strain relief and cable jacket material.  Tensile strength performance will be increased if the strain relief bonds to the cable jacket and connector body.  The union of the strain relief to the connector can be improved by providing features that will allow the strain relief to physically attach to the connector body.

Additional tensile strength can typically be achieved by incorporating a clamp which is crimped onto the cable jacket prior to molding.  When the strain relief is overmolded, the clamp is embedded into the mold material which greatly increases the tensile strength of the assembly.

Segmented or Smooth Design Considerations

Strain reliefs can be solid and smooth or segmented.  A solid strain relief is easier to clean which can be an important consideration for many medical applications.  If the material, size and shape are the same, a segmented strain relief typically offers the more flexibility than a solid strain relief.


A segmented strain relief can be more
difficult to clean as compared to
a smooth strain relief

A smooth, solid strain relief is typically
less flexible but is easier to clean as
compared to a segmented strain relief



The bending action
of a well designed
segmented strain relief

Strain Relief Design

A well designed segmented strain relief will feature walls and spaces designed to allow the bend radius to increase a greater distance from the connector or connection point.  The size of the solid sections and the size of the gaps between solid portions are varied to achieve the desired bend radius.  Segmented strain reliefs are generally designed so that the segment closest to the fixed point closes first and the segment furthest from the fixed point closes last.  This provides the greatest amount of bend relief, protecting the wire terminations within the connector.

Strain reliefs are typically designed to flex in either one axis – unidirectional or in two axes – multidirectional.   A unidirectional strain relief is typically used when the cable or wire exiting the strain relief is not round.  This is commonly the case with bonded cable or wire.  In this instance, the flex is limited to one axis by the cable design, not by the strain relief design.


Anticipating how a cable will
be stored when not in use is
important design considerations

The length of a strain relief also contributes to performance.  Generally, the longer the strain relief, the better the bend and tensile strength performance.  However, consideration should be given to how the cable will be stored in clinical use.  Experience has shown that cables are often left attached and wound around portable devices, placing continuous strain on the assembly.  In this instance, a shorter strain relief may offer better performance than a longer strain relief.


Custom Overmolded or Off-the-shelf Strain Relief

It is generally accepted that an overmolded strain relief offers superior performance on several levels when compared to a pre-manufactured strain relief.

An overmolded strain relief typically provides a higher degree of moisture resistance as compared to a pre-manufactured strain relief due to bonding of the overmold to the cable jacket and connector.  This can be an important consideration for cables that are cleaned often or otherwise subjected to contact with liquids.  Similarly, an overmolded strain relief will typically offer improved tensile strength when compared to a pre-manufactured strain relief because of the bonding achieved by molding. 

Two factors that may lead to selecting a pre-manufactured strain relief instead of a custom overmolded strain relief are lead-time to design and produce tooling and the cost to have the tooling fabricated.

Affinity has developed a variety of strain relief tooling that can be used by our OEM partners.  Depending on the design of the connector and diameter of the cable jacket, some tooling can be used as-is with no additional cost.  Other molds may require modification but with less cost and time required than designing and fabricating tooling from scratch.  The Affinity engineering team can often guide customers design decisions allowing them to use available tooling, saving both time and money.



The Affinity engineering team is anxious
to help with all aspects of your medical
cable or connector design

Summary

By understanding performance and design requirements, the Affinity engineering team can help you choose the appropriate strain relief system, whether it is an off-the-shelf or custom molded solution.  A well designed strain relief can improve both the performance and useful life of a medical cable assembly.

For more information or to discuss any aspect of medical cable design, contact Affinity Customer Care at 949-477-9495 or email to customercare2@affinitymed.com.

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Meet Janett Lopez – Administrative Assistant



Janett Lopez
Affinity Administrative Assistant

“Administrative Assistant does not describe all that Janett does,” said Affinity Business Development Manager, Hank Mancini.  “Besides being the first voice you hear when calling Affinity, the Janett helps out in just about every other department here at Affinity.  And, everyone appreciates her warm smile and friendly demeanor.”

Janett joined Affinity in 2005 starting as a production associate.  Recognizing her experience and organizational skills, she moved to the front office as Administrative Assistant less than a year later.

Before joining Affinity, Janett worked in several customer-focused jobs, including working for a major cosmetic manufacturing and distribution company in Orange County.  When the company relocated farther away to south Orange County, Janet decided to look for work closer to home allowing her to spend more time with her family.

As Administrative Assistant, one of Janett’s duties is receptionist.  She answers most calls to Affinity and directs them to the proper team member.  “We want a person to answer the phone, not a machine,” said Mary Phillipp, Affinity President and CEO.  “Our OEM customers always tell us how much they appreciate being greeted by Janett when they call.  Even if they do not know exactly who they need to talk to, Janett will get them to someone who can help them.”

Janett also greets visitors, signing them and giving them visitor badges.  She also helps those looking for work, giving them applications and showing them where they can sit and complete their application.


Janett training production team members
in proper data entry

Besides receptionist duties, Janett helps entire management team.  She compiles data for quarterly Management Review, helps with special projects, prepares presentations, and maintains company files. She also keeps the Quality Manual up-to-date and helps our Affinity’s Quality Manager prepare for both internal and external audits.

Janet is responsible for arranging catering for customer visits, audits, vendor meetings and for company-wide events.  She also arranges cakes and candles for Affinity’s monthly employee birthday celebrations.  On the sales and marketing side, Janett helps out with customer inquiries and preparing for trade shows.  She also supervises Affinity’s card mailings that go out monthly throughout the year.



Janett helping out during Affinity’s recent move

Janett is fluent in both English and Spanish.  Her bi-lingual skills are often called upon to help out with Human Resource issues.  “All of our employees speak English, but for many, it is their second language.  If they have difficult questions regarding insurance or benefits, I am glad to help out,” said Janett.

When asked what she likes most about her job, Janet replied,” I really enjoy helping to organize our company events such as our Christmas luncheon and anniversary parties.  It is worth all of the effort to know everyone has a good time and is pleased with the outcome.”

Janett, her husband and two children live not far from Affinity.  As a family they enjoy spending time together going to movies and visiting nearby Disneyland.  They also have fun with their chihuahua Princes.

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Keying and Marking to Facilitate Proper Connection



Keyway prevents improper connection

In a well-designed cable and connector system, the user should instinctively know how to properly plug the cable into the device it is intended to be connected to.  Too often, designing an intuitive and easy-to-use interface is overlooked due to all attention being focused on the electrical and mechanical requirements of the project.

Keyways

Keyways are commonly used to assist in proper mating.  Keyways can also be used to prevent a connector from being plugged into the wrong receptacle.  Keyways should be large and strong enough to prevent either misalignment or damage that would make the keyway ineffective


Large raised arrow facilitates plugging
connector into receptacle

Markings

Often markings on the connector are employed to help users understand how the connector is mated to the device.  When markings are used, care should be taken to ensure that they are large enough to be effective.  If the design calls for a custom connector, raised markings can be molded into the connector which provides both a visual and tactile reference.

Another option for marking is printing or applying a permanent label directly onto the connector.  The materials and shape of most connectors limit printing to simple graphics in a single color.  If multiple colors or complex graphics are desired, a permanent and durable label can be affixed to the connector.  In either case, printing or graphics should be easily read or recognized to be effective.



Color-coded connector plugs
into color-coded receptacle

Color-Coding

One way to achieve an intuitive cable design that is easy to use is to use color-coding on both the cable and device.  This is especially helpful when the device has more than one receptacle.  To achieve color designations on the connector, it is common to overmold the strain relief in a color that will match the color indicators on the receptacle.  If a slip-on boot is desired, many off-the-shelf connectors can be ordered with colored strain reliefs.  In addition, the pin insulator can be color coded to the device receptacle

Summary

When designing a medical interconnect device (a cable assembly or a connector), consideration should be given to making the intended connection as intuitive to use as possible.  If the design of a medical connector or cable is intuitive, the intended user should be able to connect or disconnect with little or no thought and without the opportunity to damage the device or connector.

The Affinity engineering team can help you design an interface that is intuitive, robust and cost effective.   Take advantage of our experience and expertise and help complete your project on-time by making us part of your team.

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Affinity Customer Care and Hours of Operation



Candy, Suzann and Cesar – the Affinity Customer
Care team - the Affinity Customer Care Team

At Affinity Medical, we don’t have a customer service department.  In place of customer service, we have Customer Care Coordinators.  While our Customer Care Coordinators perform many of the same functions that customer service representative would, we strive to offer our OEM partners more than that.  The job of our Customer Care Coordinators is to take care of our OEM customer partners.

Affinity’s Customer Care team consists of Candy Golding, Suzann Sitka and Cesar Jara.  Candy is the team supervisor and has over twenty years experience working with medical cables.  Suzann joined Affinity over five years ago.  She has extensive experience having worked for several medical device manufacturers before joining Affinity.  Cesar is the newest member of the team, joining Affinity in mid 2009.

Affinity Medical Technologies Customer Care specialists are available to assist you from 7:00 A.M. until 4:00 P.M., Monday through Friday, U.S. Pacific Time, except holidays

 

Affinity Medical Technologies

New Address:
3545 Harbor Boulevard, Suite 150
Costa Mesa, CA 92626 USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499

Email: Customercare2@affinitymedical.com
Website: www.affinitymedical.com
Blog: http://blog.affinitymed.com