Re : Re: Rotary Balancing

[RL]

Some time back I asked about a Rotary Balancing Toolset and got a few replies but was not able to buy any software.  Does anyone know where to get the 2 plane algorithms that could be used in Labview?  I am using a 4452 (4 simultaneous channels).  I would prefer software i.e. VI  but that does not appear to be likely for less than several thousand dollars.

Raymond

[Abhinav T]

Raymond,

National Instruments does not have a specific toolkit for Rotary Balancing. Do you have more details about this application so what we can find something similar?

Abhinav T.
Applications Engineer
National Instruments

[RL]

I want to 2 plane balance a rotor.  This requires the sampling of two velocity sensors (one at each end of the rotor) and a rotary position sensor.  The position sensor can be as simple as recognizing the same point each time the rotor rotates, that point becomes 0 degrees while the distance to the next 0 is equally divided, on the screen (polar graph), into 360 equal parts. 

The challenge is calculating where the imbalance is located (between 0-360 degrees) and where the correcting weights have to be applied to correct the imbalance and at which end of the rotor.   I am trying to find out if someone has those algorithms and if they will share them.

I planned to use a 4452 board to minimize the signal skew that could introduce itself especially when turning rapidly.

Raymond

[Abhinav T]

Raymond,

There isnt an algorithm that National Insturments has for this specific application. You can probably write your own control feedback loop, provided you can control the weighting of the rotor electronically.

Abhinav T
Applications Engineer
National Instruments

[Kevin_Price]

Is this an industrial application or an academic project?  It sounds a little underspecified, though I can't claim any special knowledge in the field.

In generic terms, it would seem that a rotary imbalance implies a motion perturbation.  I would have expected this kind of app to use a controlled constant velocity while measuring a difference in bearing reaction forces due to the imbalance.  Since you want to measure a velocity variation, I assume you plan to deliver a constant torque to your rotor and allow the velocity to fluctuate as an indication of imbalance?  Is your shaft horizontal such that gravity contributes a fluctuating torque due to the mass imbalance?

With this in mind, I'd think you'd also benefit from a fairly high resolution encoder rather than just an index mark.  An index mark alone might be more useful at purely constant velocity, but less optimal for your case.

Wouldn't the "algorithm" just be Newton's Laws?

-Kevin P.

[Conseils]

I think Kevin seems to have the hang of it despite his comments

On the systems I have previously worked on there was usually an absolute encoder of some type, but this is often used to allow the subsequent adjustment operation to position the specimen correctly statically. On one system I worked on there was a once per pulse reference for a turbocharger balancing operation on a wig-wag mechanisim. The rotor assembly was then placed in a grinding machine on centres and the pulse reference used as the potision reference for the angle. This was to reduce any added interia to an absolute minimum. The measurement system had two displacement sensors (lLVDT's) one on each arm of the wig wag machine. The drive to the shaft was provided through a belt onto the turbine wheel and as the shaft rotates the imbalance causes the wig wag mechanisim to be vibrated at some frequency and in such a way (displacement amplitude versus time) that it was possible to determine the highest and lowest point of imbalance. The belt was obviously intended to have limited effect on the measurement process. Obviously the two systems (measurement and adjustment) had to determine the reference in the same way, but these days that's easy with modern sensor systems.

ON a Schenk (valve based system) I used to work on they used an absolute rotary encoder (RVDT), I think it was actually a Lucas Schaevitz sensor. But I have also seen Baumer absolute optical encoders used as well.

Unfortunately all this was (still is) done electronically in the days when I used to bash bits of chips and components about. So whilst I could possibly work back to the solution, I never got round to coding an example in LabVIEW (sorry).

But I hope this sheds a little light.

[RL]

Yes, an absolute encoder is more precise but I don't believe that it is essential if an accurate 0 degree position can be established. When the unit is stopped I planned to mate a degree wheel (360 degree protractor) to the rotor to determine where material has to be removed. Since the metal removal will cover several degrees the idea is to straddle the theoretical degree mark as centered as possible. The metal removal should be in diminishing amounts each time therefore it will be easier to be close to the required degree position.

Certainly it is possible to calculate the amount of metal and where on the periphery it should be removed by taking into account the turning speed, the radius of the area where metal will be removed, the sideways velocity of the rotor due to imbalance, and the position of the rotor when the imbalance is at its maximum (will probably be different for the two supporting points. Considering that it may take 3 to 6 iterations to get it right I imagine that there is half a day of calcultions which is not all that appealing nor financially advisable.

It is also possible to test with calibrated weights in predetermined positions to get the measured imbalance and measurement skew.

Already, it is a good sign that someone is familiar with the topic. The other good thing is that at this time I only want to balance one type of rotor.

Raymond

[Boris8135]

Hello,
I know that this is an od topic but this might help
http://zone.ni.com/devzone/cda/tut/p/id/4381

I am also very interesting in balancing rotors( service company for electromotors)
I would be very happy to evolve this matter further

Regards
Boris

[RL]

Thank you Boris,

Yes I am still interested in doing this in Labview.  I skimmed the link you included and hope to spend more time on it.  It did not exist at the time we were posting the earlier messages.  Some people had a Balancing VI but did not want to release it because the engineer doing the support had left the company another company ceased communications when I offered only $1000 for their VI. Most people tie their software to their hardware which is sold at a premium.  I would like to use my 4 channel simultaneous DAQ PCI board alternatively, it might be a good idea to get a newer USB based system so that it will work with the laptop.

Raymond

[RL]

There is now a tutorial  bal_2_plane_pda.zip which is designed for a pda. It uses an optical tachometer but does does not describe what type.  It appears that the tach would recognize the 0 positions and divide the space into 360 points (or a multiple thereof) to establish phase angle.  An encoder would be much more accurate.  Is anyone familliar with the VI's compatibility with various sensors.

Raymond