Cable fatigue

[udirn1]

I have a devices that incorporates hand pieces that are used very rigorously , and I am experiencing a cable fatigue phenomenon. The hand piece is moving in circular motion on the patient body .The breaking point occurs at the entrance point of the cable onto the plastic housing.

I seek for a prompt solution to this cable fatigue problem as a first aid.I came to learn that my application needs a cable that could withstand both twisting and bending.

Redesign would take a lot of time but I need now some guidance on how to improve the situation with what I have.

I would appreciate your guidance and assistance on what would be the best way and fastest way to solve this problem.
A picture of the inside of the handpiece is attached.
Udi

 

[KENAT]

There are all kinds of strain relief solutions for this type of situation.

Some 'connectors' have a boot on them with becomes gradually more flexble the further out you get.

I've seen 'coil springs' used to similar effect.

What unique requirements do you have, cleanliness concerns or the like?

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[udirn1]

Thanks for the reply.
I need nothing special, but need it it avilable fast and to match to current plastic design with minimum changes.
Could you direct me to the connectors solution? does it come on top of the plastic sleeve?

Udi

 

[udirn1]

anyone???

 

[BrianE22]

A gradual change in stiffness is important. Electrical cables frequently use something like this:

http://heyco.com/products/sec_02/2-04.html

Not sure how to handle the twisting problem though.

 

[chicopee]

When stating "cable", are you refering to the inner electrical conductor or the outer corrugated sheath?

 

[KENAT]

Brian gave a link to one of the types of things I was thinking. Or like I said, just putting a coil spring in a similar manner can work. you may be able to bond it to your existing handle with little other change.

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[IRstuff]

> change the material. supposedly, oxygen-free copper wire can tolerate bending and resultant work-hardening better than conventional copper

> reduce the incremental bending, i.e., keeping the deflection to less than ~10% of the incremental length. precoiled cable like telephone cord might work

TTFN

FAQ731-376

 

[udirn1]

Hi Guys

Thanks for your support-
brian- will look into the pig tail connector.Thnaks

Chicopee - I was referring to the inner conductors.This cable is comprised of 4 thick wires to conduct an RF signal and 8 thin ones for control.Usually the thinner ones break.

Kenat - I tried using a spring .it did extend the lifrtime of the cables but problem only moved downwarth...I can place a spring on all the cable length as it will stiffen it and it wont be comefortable for work.

IRstuff- the telephone cord might be interesting.can you give me alink to such wire or charachtristic as I am not from this field.

If you have any more ideas, you are most welcomed!
Udi

 

[KENAT]

That's the problem with a simple spring, you still have an abrupt change of stiffness where you go from spring to unsupported cable - though not as bad as from rigid handle to cable.

A conical spring (or other way of gradually decreasing stiffness) may alleviate this or something like the specially designed items from Brian. Heck a simple leaf spring that gradually tapers aligned to the primary bending direction might work, but I don't think it's the best way.

Strain relief of this kind isn't exactly a new problem or idea. Try looking at similar items and see what they do for it.

http://www.cablescience.com/

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[IRstuff]

They're typically less than 22 gauge:

http://www.telephonecentral.com/Departments/Cable--Jacks--and-Cords/Telephone-Cords.aspx

TTFN

FAQ731-376

 

[chicopee]

From the section view that you presented, the hand held piece seems to rotate about the outer corrugated sheath, thereby subjecting the restrained inner conductor to torsions. If you can stabilize the rotation about the outer sheath, you problem should be solved.

 

[KENAT]

OK, here's an idea for a simple and dirty temporary fix until you get a good one.

Multiple layers of heat shrink but with each layer being slightly shorter than the previous to give a gradual transition of stiffness.

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[RoarkS]

I like that idea... In fact I think Im going to do that... I have a nibbler that I have put off fixing for this same reason.
Great Idea!

 

[ScottyUK]

I'd look at strain-relieved glands in the medium term. Maybe adapt the cable entry to accept a gland? Something like

http://www.lappusa.com/Spec_Template2.asp?nGroupID=11060

for example. The gland anchors the cable against tension, and the spiral relief provides relief against damage from bending.


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If we learn from our mistakes I'm getting a great education!

 

[udirn1]

Scotty and all

Thanks again.

I was looking through "heyco" site, and I came about the following :

http://heyco.com/products/sec_03/3-17b.html

Whats the difference from what scotty had mentioned?
Udi

 

[ScottyUK]

Similar principle for sure. The gland I listed provides a watertight transition through a bulkhead and has a threaded portion which can either pass through the bulkhead and accept a nut on the reverse side or can be directly screwed in to it, where the Heyco type clips in and doesn't provide a watertight entry.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[dbaird]

1.Talk to the robotic suppliers. They have continuous bending hi-flex cables and accessories.

2.Check out this conduit system for robots:

http://www.mtgmoltec.com/robotic.html

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.