probe calibration?

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  • probe calibration?

    Hey Guys, A couple of questions here??

    I posted the other day regarding probe calibration problems were we are getting large deviations. A collegue recently adjusted our auto probe changer so it changed probes more smoothly, since then we have experienced problems when calibrating. Is this because the auto changers co ordinates have changed in relation to the calibration tool? (we use a 3 sphere tool by the way) see pic! we also think that the probe tool may of been knocked or moved slightly. What is the best way of resolving this problem?

    Also how do we delete probe calibration data, we were told on training that it's good practice to delete when re adding calibration tools and probes. I know its >Edit >Path search, but struggling after that.

    Any help would be greatly appreciatedIMAG0147.jpg

  • #2
    You should calibrate a probe and answer "yes" to the question about the sphere move. I believe that there's no link between the changer and the sphere, but the sphere can "change" of location after a homing (depends on the accuracy of zero location, on different cmms).
    When you calibrate, you can choose between add or overwrite results of calibration. You can also go in the probe folder, and delete the .res of the probe.

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    • #3
      Thanks jefman, I deleted the results data from the probe files, I wil re Install the calibration tools and see if that improves the results. Is there a way of calibrating the PH10M unit?? It may of been knocked? It would be good to know if there's a way to qualify the ph10m for pece of mind. We have started calibrating our probes the french way (12 hits)

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      • #4
        I don't think you can calibrate the PH10 "alone". A good way to check the calibration is to calibrate for example A0B0, A90B90 and A90B-90 (in a parameter set), then measure a sphere (if possible another one than calibration sphere) with the three angles, and look at the results...

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        • #5
          Hold on a second...

          Deleting the .RESULTS file does nothing, it's simply a text file to display the results.

          On later versions there is a Reset Tips button on the probe utilities window which will reset the tips to Theo values.




          If you're using a probe changer and multiple probes the following will be of MASSIVE importance to you.



          1) Nominate one probe to be your MASTER probe, ideally use your shortest with the biggest tip diameter.

          2) Reset the tips for this probe

          3) Qualify T1A0B0 with this probe - when prompted say 'Yes Reference sphere has moved'
          This probe at A0B0 has now defined your Ref Sphere Position (if you look in the results file you will see it's position defined above the Tip results)
          You will also notice the THEO and MEAS xyz for T1A0B0 are identical (basically your pretending this probe is perfect, and offsets in this probe are passed into the location of the reference sphere)

          4) Reset all tips on any other probes

          5) When you go to qualify them, say 'No sphere has not moved'


          Now...

          NEVER EVER say 'Yes Sphere has moved' with any other probe than your Master probe.

          NEVER EVER say 'No, Sphere has not moved' when qualifying T1A0B0 with your master probe (You can say Yes - DCC hits' if you want)

          Make sure EVERYONE who uses the CMM knows which is MASTER probe, and knows the two 'NEVER EVERS' above


          Notes

          If a tip won't calibrate (i.e. missed the reference sphere or crashes into it) try increase prehit/retract, or failing that, do a MAN+DCC calibration of it first, once it's calibrated manually or semi-manually, it will use the measured values and should qualify in DCC next time)

          As you're using multiple Ref sphere's each one should be defined with T1A0B0 of your master probe. (i.e. Answer 'Yes Sphere has moved with T1A0B0 of your master probe)

          If you ever notice the THEO and MEAS xyz for T1A0B0 aren't identical someone's broken the rules and also your calibration chain (the 'chain' which means each tip relates correctly to every other tip).

          Likewise, if you ever notice the line in the results file showing the ref sphere position defined with any other probe tip than Master probe A0B0 someone's broken the rules and also your calibration chain (the 'chain' which means each tip relates correctly to every other tip).
          Automettech - Automated Metrology Technology

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          • #6
            Thanks for the help NinjaBadger we have been meaning to use a master probe so have decided nows the time. We have followed your instructions and get these results


            Probe file=6X10_MASTER_PROBE Date=15/12/2014 Time=11:35:43

            T1A0B0 THEO X 0.000 Y 0.000 Z 195.070 D 6.000
            T1A0B0 MEAS X 0.006 Y -0.060 Z 195.072 D 5.975 StdDev 0.002

            Any idea why we are getting these results?

            one thing i didnt mentions is that we have 2 heavy fixtures parked on the back of the cmm bed, could this affect the results, I know it's not good practice buit we are short on space.
            Also how many hits and levels would you use when qualifying a probe?

            Thanks for your help and input.

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            • #7
              From those results it doesn't look like you said 'Yes the sphere has moved'

              If you had I'd expect a line above T1A0B0 which showed the reference sphere position.

              Try again.

              1) Reset tips
              2) Qual A0B0 saying 'Yes, ref sphere moved'
              Automettech - Automated Metrology Technology

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              • #8
                Yes we reset and selected tool has moved, we were using a 6x10probe we have since changed the master probe to 4x20 and got these results which seem to be better.

                Probe file=4X20_MASTER_PROBE Date=15/12/2014 Time=11:57:54



                Probe file=4X20_MASTER_PROBE Date=15/12/2014 Time=11:59:42

                19mm_Sphere_(+Z) CENT X 247.295 Y -331.718 Z -925.579 D 19.000
                T1A0B0 THEO X 0.000 Y 0.000 Z 205.070 D 4.000
                T1A0B0 MEAS X 0.000 Y 0.000 Z 205.070 D 3.967 StdDev 0.003

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                • #9
                  Looks good, you've got the Ref tool's position shown there now which is correct.

                  One comment: it's wise to avoid anything but letters and numbers in any ID's (alignment, feature and dimension names), but I extend this to program, probe and ref tool names also

                  Symbols like +-*/@'.,?~#() can cause unexpected things to happen. I'd rename that ref sphere to '19mm_sphere_zplus'
                  Automettech - Automated Metrology Technology

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                  • #10
                    Thanks for the advice, we are now re calibrating the other 5 probes in the auto changer following your instructions, we have added a few angles but unfortunately standard deviations for probe calibration exceeds the limit.Capture.PNG

                    Any Ideas!!

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                    • #11
                      Shanking out, dirt or loose components?

                      What settings are you using? Speed/Prehit/Retract/Num hits/Num Leves/Angles etc?

                      Check all components are tight.

                      Can you post the actual results?

                      StdDev is out (I'm guessing) because the Diam is out.
                      Automettech - Automated Metrology Technology

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                      • #12
                        Is it just the angle the photo was taken at or is the set of qual spheres set at an angle? If so you could be hitting the shank(s)?
                        sigpic

                        James Mannes

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                        • #13
                          Make sure your not shanking and the tips & sphere have been cleaned. If that didn't work, I would try not doing a partial calibration. Have it do the scans & hits. Even if you say the sphere hasn't moved. This is a setting in the probe calibration box. That's what I've done in the past and that usually works. If not, delete the angle & add as new. New angles can't have partial calibrations done.
                          Kymberly..."It is what It is"

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                          • #14
                            Thanks for the tips guys, especially NinjaBadger!

                            We have re run the calibration again this morning and got the same exceed deviation error message, we selected re run calibration but this time it passed. We decided to run a further 2 times to prove repeatability, We have succesfully run the rest of the probes apart from a knuckle. The problem we have now is when we come to calibrate a 2x20x30┬░knuckle we select the tool has not moved like suggested, but it will not run without us taking a hit on the sphere! What do you guys suggest? Please see attached screen shot of hit and calibration settings.Knuckle.jpg

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                            • #15
                              When you say it won't run, do you mean it misses (or crashes into) the sphere? Or is it simply prompting you to take a hit instead of entering DCC?

                              Also I notice from your screen shot that you've got calibration and move speeds set as %'s instead of mm/sec (% is the default setting but it's a complete nonsense.)

                              Hit F5 (or Edit > Pref > Setup) and go to the Part/Machine Tab, tick the 'Display Absolute Speeds' check box.

                              Everything (your programs and qualification settings will now in mm/sec - I'd recommend 2 or 3 mm/sec for the TP20 probes.)

                              Without knowing what CMM you have 2% could be way too fast (however it looks like an old machine) on some machines that's 10mm/sec!

                              Unfortunately it will mean running qualification - again - but might as well get it right from the start yeah?


                              Also make sure your qualification touch speed is the same as your programs touch speed. I simply always use 2mm/sec for everything.



                              Also, as you're getting some odd results (and your original question was about checking the probe head) it might be worth having a quick probe check prog.

                              I'll see if I can find an example I posted a while back, but basically I write a program which origins xyz on cal sphere, then proceeds to measure it with a couple of angles per probe, depending on your machine spec you check location and diameter are all within so-and-so (I use ┬▒0.005), my CMM should be good to around half of that, but it just highlights if there's something seriously wrong (i.e. it's had a knock, damaged ruby, of there's a loose tip etc)

                              Nice program to run first thing whilst you have nice cup of tea!
                              Automettech - Automated Metrology Technology

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