If your CMM is equipped with PH20, but you're not fully utilizing 5 axis PCS measurement then it's a waste of your investment. To save your time for reading, let's go straight into a real case study. One of my client who's running a PH20 cmm with Open Dmis wants to know how to handle this part efficiently:
First, a little bit background story: before they retrofitted their cmm to PH20, they've been checking these parts with PH10 in pc-dmis but soon they realized that the PH10 got worn out so quickly because this high volume inspection and imagine the probe rotates for small angle change hundreds if not thousands times every day. And obviously it's time consuming for probe calibration, programming etc. So after some consulting and research they decided to retrofit with PH20. All the teeth width/angular positions are critical on this part so the program must verify every single tooth. They're quite happy with the PH20 capability in that the calibration time cut down tremendously and the probe doesn't get worn out easily. Both of my trainees are smart cmm tech., who realized quickly that they can use Notepad ++ to quickly create dmis codes whenever applicable.
But after a while they called me back to resolve this struggle: even though you can create loops with alignment rotation to take care all teeth measurement, but how about the probe angle? How to let the PH20 change its angle automatically for each tooth during the loop? As I mentioned they're experienced cmm people so they tried to manipulate angle A and B with different ways, but really these are not necessary at all if, you understand how the PCS works on 5 axis PH20.
Whether you use Open Dmis or Modus (or maybe other dmis package that supports PH20), if you create a point measurement with PCS (not head touch, not 3 axis), you'll see below codes:
F(PT_RIGHT) = FEAT/POINT,CART, 83.9998, -4.3735, 104.5000, -0.582, -0.813, -0.000
MEAS/POINT, F(PT_RIGHT), 1
PTMEAS/CART, 84.000, -4.374, 104.500, -0.582, -0.813, -0.000, PCS, 180.273, 21.843, 236.131, ALLAXESTOUCH
Without getting into too much details, the PCS codes defines a tool alignment according to your current Part Co-ordinate System, which means if your alignment changes then with the exact same dmis code your PH20 will change its A/B angles to maintain the same relationship between probe and the target hit. In this particular case, we have 32 pair of points all around so we need to rotate our alignment by 11.25 degrees for 32 times, with the same dmis codes, without need of coding probe changes. One important note is that do NOT try to manipulate those 3 parameters following PCS because they're not that straight forwarded as you think, so always create your 1st "seed" measurement thru software interface.
This strategy works not just on points, but really any feature, so you can program same way on these slots:
Next thing they need to know is how to use variables so after the loop all features are labelled uniquely, reported individually, not get overwritten. I might write another article to show how it works. But at the end my client was so happy that the program became so short, so easy to modify yet runs most efficiently.
Currently I can also offline program on following software:
PC-Dmis , Open Dmis, Camio, Modus, Mcosmos, CMM Manager
CGP Certified (ITAR equivalent)
CMM Application Specialist
RX Metrology Solutions Inc.
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