DIY 2 Plane Balancing Machine

[dynaman]

Hi all

I have successfully built a 2 plane balancing machine using the trial weight method. However, it is getting very tedious to run the method again for trimming the balance weights.

I would like to build the system that shows the amount of weight I need to trim after each run (without using trial weights). I see commercial units that do this. How can I do this?

regards

Dynaman

 

[GregLocock]

My guess is that they'd be soft bearing machines, measuring the force input to each bearing. Then you don't need to know too much about the item under test. For whatever reason our driveshaft balancers were stiff bearing units but then we knew exactly what the driveshafts were.

Cheers

Greg Locock


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[electricpete]

So you want to build a balancing machine, sounds pretty ambitious.

An overview here:

http://www.irdbalancing.com/balancing-machines---types,-classification,-and-methods.html

and here

https://en.wikipedia.org/wiki/Balancing_machine

There are two basic types as Greg mentioned - hard and soft balancing machines.

To my thinking the hard balance machine is a very rigid or massive support with rotor operated at low speed such that motion of rotor is negligible, rotor acceleration forces are negligible, and all balance force is transmitted to the support where it is measured. Soft balance machine supports the rotor flexibly (rotor is operated at a speed far above it's mounted rigid-body resonance but of course below any flexible rotor critical) and accordingly it is a mass controlled system and displacement of rotor mass is measured (portions of the balance machine that move with rotor are known as parasitic mass and must be compensated for).

Lots more at the links including advantages and disadvantages for each. Seems to me these are carefully engineered products... and buying would typically make more sense than trying to build one yourself unless you have a whole lot of time on your hands.



=====================================
(2B)+(2B)' ?

 

[Strong]

If you are periodically rebalancing the same item or balancing multiple of same items, then you can use the One Shot method. Basically you run the balancing calculation after one (baseline) run using the data (influence coefficients) from the first balance job and perform a Trim Balance. With careful setup and linear response the result (vibration level or Residual Unbalance) should meet your criteria.

Walt

 

[dynaman]

Thanks guys,

I'm more interested in the mathematics behind the soft bearing machines. Those machines seem to work on a method where the vibration is measured at the bearing locations and use laws of statics to determine the imbalance, depending on how the rotor is configured.

Thanks Walt for your suggestion. I'm not sure how to use those influence coefficients for the trim balance? Also, after each trim, do you have new influence coefficients to calculate for further trimming?

regards

dynaman

 

[GregLocock]

No, the influence coefficients are constant for a given machine+test item, in theory.

You should have 3, one for each plane and one for the crosstalk (IC11, IC22,IC12). In practice you have 4 because you use different ones for IC21 to IC12 because you have different radii, but I vaguely remember that in theory in terms of mass*radius they are the same (bit shaky on that).



Cheers

Greg Locock


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[shell18]

Hi!
Initial + 2 trial runs are required to calculate influence coefficients. When influence coefficients are known, you can apply it to any input vibration vector.
So, instead initial vibration vector (initial vibration value\phase) you can use vibration value\phase after mounting of the correction weights.

 

[Tmoose]

"My guess is that they'd be soft bearing machines, measuring the force input to each bearing. "

Hi Greg,

I think traditional definitions consider "hard bearing" (also known as “Sub-critical), ” as “Force Measuring.”
Conversely “Soft Bearing” (also known as “Super-critical” or “Displacement Measuring”) machines measure motion, or something related to motion, at the support bearings.

http://www.irdbalancing.com/assets/...f-strategic-rotating-machines----may-2009.pdf

http://www.irdbalancing.com/phone/dynamic-balancing-machines,-soft-bearing-vs.-hard-bearing.html

Regards,

Dan T

 

[GregLocock]

Makes sense to me, thanks.

Cheers

Greg Locock


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