×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Measuring fiber optic wire vibration during manufacturing

Measuring fiber optic wire vibration during manufacturing

Measuring fiber optic wire vibration during manufacturing

(OP)
What would be the best method to measure the vibration of a .007" fibre optic wire?  The manufacturing process is likely causing the wire to vibrate and I want to measure the frequency that it is vibrating at, the phyical displacement of the vibration etc. Laser or strobe is about all I can come up with since it must be done without contact to the wire.  I'll need to gather as much information on the wire as I can before I can decide how to proceed with determining the source and stopping the vibration.  Let me know your ideas!

Thanks!

RE: Measuring fiber optic wire vibration during manufacturing

In addition to the laser you already mentioned, would it be possible to sense the vibrations via monitoring of the fiber tension?

RE: Measuring fiber optic wire vibration during manufacturing

(OP)
Hmmm.. measuring the tension may be even harder, how would it (tension) relate to vibration frequency etc.?

RE: Measuring fiber optic wire vibration during manufacturing

I was assuming that there was probably some sort of web tension control system in place that may have a tension signal that could be monitored.  If not, then adding it would probably be more trouble than a laser doppler vibrometer.

To answer your 2nd question, higher tension will cause higher frequency of vibration.  An example of this is how a guitar or piano is tuned.  The fundamental frequencies of a vibrating string is given by:

fn = Kn/(2*Pi)*sqrt((T*g)/(w*L^2)), where

fn = Natural frequency (hz)
Kn = Pi, 2*Pi, 3*Pi, etc.
T = String tension (lbf)
g = 386 lbm*in/lbf/s^2
w = Weight of string (lbm/in)
L = Length of strin (in)

This is assuming small displacements and zero bending stiffness of the fiber.  For large displacements, the tension will fluctuate with displacement and cause a nonlinear stiffness increase.

RE: Measuring fiber optic wire vibration during manufacturing

Another thought.  If the tension and theoretical frequency are known, could an acoustic sensor with appropriate signal processing monitor for vibration?

RE: Measuring fiber optic wire vibration during manufacturing

(OP)
Thanks for the information.  Our research has shown this is a very new diagnostic field (fiber optic) and we have some been getting some good feedback from people like yourself.  I'll post again if and when we figure out what the final results/test equipment will be.

Thanks again!

RE: Measuring fiber optic wire vibration during manufacturing

(OP)
One more question... what does Kn equal (stand for) in this formula?

fn = Kn/(2*Pi)*sqrt((T*g)/(w*L^2)), where

                         fn = Natural frequency (hz)
                         Kn = Pi, 2*Pi, 3*Pi, etc.
                         T = String tension (lbf)
                         g = 386 lbm*in/lbf/s^2
                         w = Weight of string (lbm/in)
                         L = Length of strin (in)

RE: Measuring fiber optic wire vibration during manufacturing

Kn is a constant.  K1 is Pi, K2 is 2*Pi, K3 is 3*Pi, etc.  These correspond to the fundamental frequencies f1, f2, f3, etc.  In theory, there are infinitely many modes and frequencies.  In practice, only the first few modes are likely to have any significant amplitude.  

RE: Measuring fiber optic wire vibration during manufacturing

Greetings,

Is it totally impossible to send a laser signal down the length of the fiber?  Is the free end of the fiber accessible (even there's a mile of fiber between it and the vibration source)?  Maybe there is a sharp enough impedance change at the point of extrusion to bounce a laser off of it.  I ask because I have a friend at MIT who's doing part of his PhD work on phase smearing due to acoustical waves inside installed fiber optics.  He would know.

Barring that, maybe a good question to ask would be: where exactly does the vibration input matter?  If the problem is occurring at the point of extrusion and goofing up the cross-sectional integrity, then maybe measuring equipment displacement would be a good proxy for displacement in the fiber.

Also, have you considered modeling any parts of the system?  Depending on where the vibration input is occurring, maybe a bit of finite element work on the equipment design would give you some direction on what to look for.

Byron

J. Byron Davis
Vibro-Acoustic Consultants
byron@va-consult.com

RE: Measuring fiber optic wire vibration during manufacturing

I believe Dr. Bob Jones of SKF has done vibration analysis on Fiber optic wire - he may be contacted at Bob.M.Jones@skf.com

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources