Basic CMM Methodology

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  • Basic CMM Methodology

    Here I come again with some basic methodology needs of explanation for some co-workers. I have tried to explain to them that you must measure with the same touch speed as you calibrate with. Or else the calibration will not be valid for that particular measurement, or vice versa. I was faced with the suggestion that the move speed changes the accuarcy of the measurement, which I countered with: that would be a valid statement IF the touch speed was ALSO faster than the calibrated speed, thereby not allowing enough time for the prepositioning of the probe for it's actual measurement, otherwise the move speed has no effect on the accuracy of the hits. My statement that the measure touch speed needing to equal the calibration touch speed is the main ingredient for accuracy of probe hits was then nulled and has been ignored. To which I say the notion that move speed is paramount to accuracy of measured points is wrong, but go ahead and adhere to that philosophy and I will stick to my philosophy. Can I get some help here? Either straighten me out about this or give me another way to enlighten my co-workers. Thanks in advance.

  • #2
    I would agree with you. If they need further enlightening though, I would maybe perform a few studies with different move speed and touch speed settings. They can argue with theories, but not with numbers. Just an idea.
    Kevin

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    • #3
      I agree with you. I assume the CMM has to account for overshoot much the same way a machining center does with a spindle probe. The probe could teleport to the other side of the table and still measure accurately if the measure speed is correct. The overshoot is a fixed value determined during calibration, this same fixed value is then used to compensate during the hit. As long as the measure speed is the same, the hit will be compensated correctly. Am I right?

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      • #4
        Give them one word, tell them this is what percision is made from, Like a swiss watch. So is a CMM.

        synchronize

        2 entries found for synchronize.
        To select an entry, click on it. synchronizesynchronized swimming Main Entry: syn·chro·nize http://webster.com/images/audio.gif
        Pronunciation: 'si[ng]-kr&-"nIz, 'sin-
        Function: verb
        Inflected Form(s): -nized; -niz·ing
        intransitive senses : to happen at the same time
        transitive senses
        1 : to represent or arrange (events) to indicate coincidence or coexistence
        2 : to make synchronous in operation
        3 : to make (motion-picture sound) exactly simultaneous with the action
        - syn·chro·niz·er noun
        sigpicSummer Time. Gotta Love it!

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        • #5
          Touchspeed should be the only real factor involved, but there are always limits, right? I mean I would think that if you were running a movespeed of 100, and a prehit distance of .001, then definately the movespeed would have a negative affect, regardless of the touchspeed. But if you are doing that, you're never touching my machine!
          Kevin N. Thompson - Thompson Digital Image
          Quality Manager - Rj Link International

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          • #6
            I would disagree with kthompson in that, touch speed and movespeed are directly related. Touch speed is a percentage of the move speed, hence they are directly related. Same can be said of the jog box. If you have a move speed of 80% and a touch speed of 1%, and you have your jog box set to 50% during qualification, then you need to run your program with those same parameters to get the best correlation.


            Edit:
            Brown and Sharpe Technician in house today says I am full of guano. Please accept my apologies for making an inaccurate statement.
            Last edited by JamesMannes; 06-29-2006, 10:31 AM.
            sigpic

            James Mannes

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            • #7
              Learn something new every single day - it never ceases to amaze me.

              I for some reason thought the touch speed was just a percentage of total.

              Interesting. Congrats, you've made a better CMM user out of me today!

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              • #8
                So now, touch speed is a percentage of move speed? I, like CFisher always assumed move speed was a percentage of max speed of machine and that touch speed was also a percentage of max speed.

                If I write a program to run at a certain speed and then my operator runs the program with the speed decreased on the jog box she is changing the accuracy of measurement? How do I get around this? Is there a way to lock out the speed control on the jog box?

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                • #9
                  Is it true that touchspeed is a percentage of movespeed? I was not aware of this either. I did understand the setting of speed on the jogbox will affect both touch and move speeds. I think we need a Wilcox/Hexagon/B&S comment on this. I'll PM Don Ruggeri.
                  When in doubt, post code. A second set of eyes might see something you missed.
                  sigpic

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                  • #10
                    Guys, please question my comments because this was not based on any fact, just what I thought to be correct. If I am wrong I am sorry and I have also learned something. SIA (sorry in advance?).


                    Edit:
                    Brown and Sharpe Technician in house today says I am full of guano. Please accept my apologies for making an inaccurate statement.
                    Last edited by JamesMannes; 06-29-2006, 10:31 AM.
                    sigpic

                    James Mannes

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                    • #11
                      Originally posted by JamesMannes
                      Guys, please question my comments because this was not based on any fact, just what I thought to be correct. If I am wrong I am sorry and I have also learned something. SIA (sorry in advance?).


                      Edit:
                      Brown and Sharpe Technician in house today says I am full of guano. Please accept my apologies for making an inaccurate statement.
                      You are correct, I was to busy earlier to post that, I knew someone would.

                      Also I am just sitting here waiting to pounce on a wrong answer from you, Mister. hahahahahahaha
                      sigpicSummer Time. Gotta Love it!

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                      • #12
                        I do not know for sure, but based on my experience accuracy of calibration depends on move speed - (?) means touch speed depends on move speed.
                        N.

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                        • #13
                          Accuracy of calibration would depend on move speed if prehit and touch speed were such that the machine does not have time to "settle" after a move. This is a fact. If your prehit is .001, your touch speed 1%, and your move speed 100% the machine will most likely "coast" into the sphere and not get a good hit.

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                          • #14
                            Originally posted by Goodluck
                            Accuracy of calibration would depend on move speed if prehit and touch speed were such that the machine does not have time to "settle" after a move. This is a fact. If your prehit is .001, your touch speed 1%, and your move speed 100% the machine will most likely "coast" into the sphere and not get a good hit.
                            No this is not the case, I have enough prehit distance for probe "settle".
                            N.

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                            • #15
                              Touchspeed is a Percentage of of MAX Maxhine Speed, Not to Exceed 20%.
                              according to helpfile.
                              Move Speed is percentage of max machine speed, can be set to 1-100%..

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