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Calibration Error- Probe Reading Wrong

MatthewHaines
Straight to it. All measurements in metric. Versions: PCDMIS 2013 & 2013 MR1.

We calibrated our probes, using the usual method in probe utilities. But now they are all reading wrong. Up to 25 microns too small to be precise.

We calibrated a probe last week, then we ran a job today which had a 11.000 mm bore, it measured it as 10.980. Yet a 11.030 plug gauge slips in fine. We then ran it around a UKAS verified 8.000 setting gauge and it was reading 7.975. We recalibrated the probe and ran both again, and it still measured small on both the 11.000 and the 8.000. I edited the probe file manually (adjusted the diameter size) until it read precisely 8.000 on the setting gauge, then I ran it round the 11.000 bore again. This time it came out at 11.040 (which explains why the plug gauge went in fine). We checked the calibration spheres and they are measuring fine with a micrometer (which in itself is reading fine on UKAS verified slips). We then did this entire process on our other CMM and exactly the same thing has happened. Something is going wrong between the probe measuring the sphere and the software adjusting the probe data to bring it in line with the sphere size.

So why is PCDMIS not properly adjusting itself when it measures the calibration sphere? Why does it think everything is small?

We have deleted the probes files and rebuilt them to remove any possible accumulative error, but we are getting the same issue. We have verified everything and the probes are definitely reading wrong, this isn't a "maybe the job is wrong issue". The probes aren't damaged either, and we have tried swapping them over. This error is occurring on all 18 of our probes across 2 CMM's.
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  • A few points here...


    1) The tip diameter which you get after calibration should be smaller than the tip diameter as measured with a micrometer. This is because you need to move slightly past contact point to trigger a hit, and there will be some bending of the stylus also. This is why I refer to it as the effective diameter.

    2) It does sound like possibly the calibration isn't holding for some reason. After calibration (and viewing the results) make sure to say Okay on the probe utilities dialog and not Cancel. After that, F9 the probe again, click on tip A0B0 and then Edit (as you have done when modifying the tip diameters) and just double check that the Diameter matches the diameter reported in the Results file.

    3) What tip diameters and lengths are we talking about here (I can see it's a1mm tip in the results you've posted, in the first instance I'd stick to a shortish fairly large tip whilst we figure out what's going on here)

    4) Calibration settings - How many hits and what touch speed?


    Having a look at those results again they don't look right.

    Here are mine from a 1by50mm tip on a Std Force Module using 13 hits on 3 levels @ 2mm/sec (Note for a longer tip you usually get a smaller diameter and higher Std Dev) 

    T1A0B0         THEO X   0.0000 Y   0.0000 Z 191.5200 D 1.0000
T1A0B0         MEAS X   0.6036 Y   0.1514 Z 191.6765 D 0.9842 StdDev 0.0020
Reply
  • A few points here...


    1) The tip diameter which you get after calibration should be smaller than the tip diameter as measured with a micrometer. This is because you need to move slightly past contact point to trigger a hit, and there will be some bending of the stylus also. This is why I refer to it as the effective diameter.

    2) It does sound like possibly the calibration isn't holding for some reason. After calibration (and viewing the results) make sure to say Okay on the probe utilities dialog and not Cancel. After that, F9 the probe again, click on tip A0B0 and then Edit (as you have done when modifying the tip diameters) and just double check that the Diameter matches the diameter reported in the Results file.

    3) What tip diameters and lengths are we talking about here (I can see it's a1mm tip in the results you've posted, in the first instance I'd stick to a shortish fairly large tip whilst we figure out what's going on here)

    4) Calibration settings - How many hits and what touch speed?


    Having a look at those results again they don't look right.

    Here are mine from a 1by50mm tip on a Std Force Module using 13 hits on 3 levels @ 2mm/sec (Note for a longer tip you usually get a smaller diameter and higher Std Dev) 

    T1A0B0         THEO X   0.0000 Y   0.0000 Z 191.5200 D 1.0000
T1A0B0         MEAS X   0.6036 Y   0.1514 Z 191.6765 D 0.9842 StdDev 0.0020
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