Pitch Error Compensation

[crow36]

Dear all,

Would like to find out if anyone out there could tell me how exactly i can use a pitch master gauge to recalibrate the error compensation for the entire length of the ballscrew. There should have some formulas involve for the calculation if i not mistaken.

Appreciate the assistance given.

Cheers
crow

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[One of Many]

If your machine has what is called a ballscrew compensation table as part of the control parameters, it is only a matter of mapping the screw with a high resolution dial indicator to a known good standard. The dial indicator should have at least the same resolution as the axis being checked. Screw compensation tables may have variables that can map the screw at stations every XXmm-Xcm or .XXXin-1in. Each station within that table will get a +/- offset value to compensate that portion of the screw. You end up with a table of say 10 numbers that may be + .018mm, -.023mm and so on. What ever the deviation from the commanded verses actual against the standard ends up being input data for the compensation table. It is also a good idea to map it in both travel directions, since you may find backlash or greater ball path wear affect in some places more than others. Considering this is done in a no load condition, there may still be some additional deviation under load besides the normal way wear and machine deflection.

OEM's will usually do laser mapping on a ballscrew and many OEM's retain the original mapping of the screws as stored parameters for the compensation table in their archives. As long as the screw has not been replaced and wear isn't excessive, it would be easier to request a backup copy than mapping it yourself. There is still some peace of mind in knowing if there are any faulty areas of concern. At best, you end up taking the happy medium for the compensation table correction value on any given station along the screw, but you have only one backlash compensation value for the entire screw.

No compensation formulas that I know of for the equipment I have worked on. Unless someone is taking some other miniscule anomoly into account to compensate for.

DC

[crow36]

One of Many,

Thanks alot for the explanation given. Will try it out when i have the chance. I have always thought that there is a formula involved but since there is none, it'll be so much easier.

Thanks again

crow

[mangalmoorthy]

Dear all,

Would like to find out if anyone out there could tell me how exactly i can use a pitch master gauge to recalibrate the error compensation for the entire length of the ballscrew. There should have some formulas involve for the calculation if i not mistaken.

Appreciate the assistance given.

Cheers
crow

First thing is you please specify the CNC system you are working. Because each CNC system has different type of Pitch error compensation procedure. for example in Fanuc system we can give compensation in incremental pattern. In seimens system we can give compensation in Abosulte pattern. So first you specify which system u want to calibrate then surely i will let you know the procedure to do Pitch error compensation.
Regards,
Mangalmoorthy.A
(Head Calibration department)

[Adhithya]

First thing is you please specify the CNC system you are working. Because each CNC system has different type of Pitch error compensation procedure. for example in Fanuc system we can give compensation in incremental pattern. In seimens system we can give compensation in Abosulte pattern. So first you specify which system u want to calibrate then surely i will let you know the procedure to do Pitch error compensation.
Regards,
Mangalmoorthy.A
(Head Calibration department)

Is there any way to give compensation in Siemens in an incremental pattern? Through programming some calculations or formulae? I'm using simotion D motion controller with TIA Portal and simotion software(step 7).

[joeavaerage]

Hi,
there are two types of pitch errors with ballscrews:
1) Absolute, when you rotate the ballscrew such that the nut moves 300 mm....how close to 300mm is it? A rolled C7 ballscrew which abound on Ebay and elsewhere are +-50um over 300mm.
A ground C5 ballscrew is about ten times the price and within +-18um over 300mm. A C3 is even more and about +-8um over 300mm, C1s and C0s are special order, who knows what they cost.
2) Cyclic, this is the deviation from perfect in each rotation. C7 ballscrews are up to +-30um per rotation. This is a problem, and is very hard to compensate for. C5 ballscrews are +-8um per rotation
and C3s are better again.

The procedures previously posted work well with ground (C5 and better grades) ballscrews but C7 rolled screws are a problem. You'd have to plot the error within each rotation...and that would
be a battle.

What type of ballscrews do you have?.

Craig