CMM to CNC integration to make automated offsets
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  1. #1
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    Cool CMM to CNC integration to make automated offsets

    Does anyone have experience with setting up a robotic cell with a CMM that can do the inspection and have some sort of output that can be read by the lathe/vmc and change the offsets? Ex...Part Ø is .001 over, CMM reads that and tells the cnc to change comp by .001 (or more to be closer to nom)?

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    It is possible. You will have to work with both the CNC and CMM vendors and your EE to determine how best to handle this. Most CMM's can't do record keeping / spc / averaging so this is best handled in the CNC via macro or by a separate SPC computer that feeds info to the CNC. You do not want an adjustment for every measured part, you want some moving average and you need limits on the adjustment amount.

    For instance, if it measures 0.008 mm from nominal, and your tolerance is +/-0.100 mm, do you really want to make an adjustment? - probably not.
    If you get a reading of 1.3mm from nominal when the tolerance is +/-0.100 you don't want to make an adjustment then either. So there are lots of things to think about.

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    What kind of error you want to eliminate ?

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    By far the talking between them is the most painful integration part.
    Then there is the simple bang-bang adjust and having some "smarts" in between as very correctly noted by Tony (whom has a whole shitload of experience in good/bad here).

    Tighter example let's say you have 50 microns and are out by 25. An experienced operator may only go 12 so as to not overshoot.
    A bang control system will go for zero, often over-adjusting ending up with a worse process than needed as it bangs back to the other side so you end up overcontrolling the machine and not letting it "play" a bit.
    New real human operators doing the same measure-adjust often (if not always) do the same and you have to tell them to back off a bit.

    So now to make it work nicely you need a controls guy/gal for the interfacing and a SPC guy/gal to smooth out the corrections being passed.
    The combination explains why so many try such, end up not happy and turn off the gauging system.

    I do truly love such a system as you describe but it's not as easy as it appears from the outside as it is not a perfect or absolute world.
    The gage has errors, the machine bounces around but all this is way past the first point of making one tell the other what I want done and that is a controls/interfacing problem that you have to deal with first.

    I have seen this "autogauge" concept go very good and most certainly built and sold some very bad ones over the years.
    Bob

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    Yea, you typically want to adjust about 1/2 of the error amount. We have such systems running. This lets it creep up on the machine capability limits over time. But there is testing that needs to be done, such as what is your machine capability? What is your gauge R&R? These two must be taken into account when you design your macros or set up your SPC computer. It isn't as simple as it seems to have a robust solution from the controlling standpoint. The interface will typically be solid once designed and implemented, the control side is where the real development must come.


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