Bug in calibration routine?

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  • Bug in calibration routine?

    In version 3.2063. Anytime I rotate the renishaw head I see deviation errors in the rotating axis. For example I am measuring two bores 180 degrees from each other. Rotating the head I see a deviation of .0061" in the rotating axis and a concentricity of .0113. Now if I go thru the part and measure the two bores with out rotating the head I have a deviation of .0003" in the axis I would have rotated in and a concentricity of .0013". I was told that it is a bug in the version I am running with how the calibration relates to the PH10MQ head. Does anyone know a work around for this problem? There are features that I have to rotate to be able to measure.

  • #2
    Have you tried squaring the probe head?
    PC-DMIS CAD++ 3.7 from 4.2 MR1

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    • #3
      2D features or 3D features or a combination? My first susspicion in cases like this is always the feature vectors.
      <internet bumper sticker goes here>

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      • #4
        Are you using 2 head positions to measure one feature? PC-DMIS only compensates for the LAST TIP used in a feature.
        When in doubt, post code. A second set of eyes might see something you missed.
        sigpic

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        • #5
          two separate features 2d circles. 1 circle is the datum origin the other circle I rotate the head from 90,90 to 90,-90 and measure on the other side of the part( think of a box with bearing bores in each of the four walls) A guy at our corporate office said in ver 3.7mr1 they added a dcc+dcc calibration routine and this gets rid of the deviation errors but I am not able to run that version and 3.2063 doesn't have that option.

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          • #6
            Originally posted by Ceeph View Post
            In version 3.2063. Anytime I rotate the renishaw head I see deviation errors in the rotating axis. For example I am measuring two bores 180 degrees from each other. Rotating the head I see a deviation of .0061" in the rotating axis and a concentricity of .0113. Now if I go thru the part and measure the two bores with out rotating the head I have a deviation of .0003" in the axis I would have rotated in and a concentricity of .0013". I was told that it is a bug in the version I am running with how the calibration relates to the PH10MQ head. Does anyone know a work around for this problem? There are features that I have to rotate to be able to measure.
            Is it possible that your probe is shanking out in one bore and giving you the error?

            You have qualified probes with the appropriate probe to measure the bores...right?

            You do a fairly simple test. Use a larger diameter stylus. If you are using a 3 mm. , try using a 6mm and see if it is possible you are shanking out.

            You should not be seeing those kinds of differences.

            The most obvious error sources would, IMO, be whether or not the probe is mechanically square with the machine or a probe calibration issue.

            Could be either or a combination of both.
            HTH
            Hilton Roberts

            "Carpe Cerveza"

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            • #7
              I run 3.2063 and have never seen a problem like that. I actually have a part that I use exactly those rotations to measure a cylinder. My alignment is from one side and I verify the hole from the other side. There is never a difference. Are the tips calibrated at the same time and do they relate to each other?

              Just read Hilton's post. Never thought of the shanking. Good thing to look at.
              When in doubt, post code. A second set of eyes might see something you missed.
              sigpic

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              • #8
                Do you do any alignments (specifically level) in between the first circle being measured and the second? What is your leveling feature and are you absolutely positive it is square to the bores? What do you get when you do 2 cylinders or at least what do you get if you do one cylinder then level to it then measure the other as a circle? You are getting a lot of error and this "bug" this guy is talking about I don't believe is the issue.
                <internet bumper sticker goes here>

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                • #9
                  Originally posted by Hilton Roberts View Post
                  Is it possible that your probe is shanking out in one bore and giving you the error?

                  You have qualified probes with the appropriate probe to measure the bores...right?

                  You do a fairly simple test. Use a larger diameter stylus. If you are using a 3 mm. , try using a 6mm and see if it is possible you are shanking out.

                  You should not be seeing those kinds of differences.

                  The most obvious error sources would, IMO, be whether or not the probe is mechanically square with the machine or a probe calibration issue.

                  Could be either or a combination of both.
                  HTH
                  Probes are qualified at each tip orientation and the probe is not shanking out. It occurs with a 2mm, 3mm, and 4mm probe.

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                  • #10
                    MQ probe head shouldn't move because of the quill but try this just to see...

                    Place a pen with point up in one of threaded hole on surf plate, make sure you have enough travel for 90,90 & 90,-90.

                    Place the stylus on top of pen point (lock y axis) then rotate the head to 90,-90 (if you satrted with 90,90) see if centers same - if not then you need to adjust so that when you change probe attittude it is true.
                    PC-DMIS CAD++ 3.7 from 4.2 MR1

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                    • #11
                      Originally posted by craiger_ny View Post
                      Do you do any alignments (specifically level) in between the first circle being measured and the second? What is your leveling feature and are you absolutely positive it is square to the bores? What do you get when you do 2 cylinders or at least what do you get if you do one cylinder then level to it then measure the other as a circle? You are getting a lot of error and this "bug" this guy is talking about I don't believe is the issue.
                      I am leveling to the machined surface that the datum bore is cut in and rotating to a line through the origin bore and the other datum(dowell pin hole). No alignment changes between features.

                      The guy was getting similar deviation errors until he changed his calibration method. It was brought to his attention by one of our Suppliers and he started looking into it further and passed the info on to me.

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                      • #12
                        What do you get if you measure them as 3D features?
                        <internet bumper sticker goes here>

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                        • #13
                          Have not tried it as a cylinder yet.

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                          • #14
                            If it is a bug or not I don't know. I do know I have to figure this out because the bore measures almost dead nuts nominal if I don't rotate the head and .006" different when I do. If it is the software or my programming it is unacceptable to have that much deviation when I have to show capability to 1.33 cpk on a .0020" total tolerance.

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                            • #15
                              I went back and recalibrated the tips to make sure they were all done at the same time. The deviations between rotating and not rotating got better. It is now .0025" in the rotating axis and .0005 when I don't rotate but this is still unacceptable when I have .0020 total positional tolerance.

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