hexagon logo
Register Sign in
  • Replies 13 replies
  • Subscribers 223 subscribers
  • Views 228 views
  • Users 0 members are here
Options
Related

Understanding Calibration Results

TheBradish
I don't usually look at the probe calibration results because I don't really understand what I'm looking at. I'd really like to gain a firm understanding of the data and what it should mean to me.

I've been digging through old threads, and I'm getting closer. What I think I get is that StdDev is the standard deviation of single-point error of the measured sphere for each tip angle. (I was told by another inspector here that that number should be .0002 or less.) I also understand that the MEAS D determines the effective probe diameter for each tip, and is used for probe size compensation.

I don't fully understand the THEO/MEAS XYZ (where the THEO comes from, what the MEAS means), or what is a maximum permissible error. What do you guys look for when you read your calibration results? What do you hope to learn from the numbers? What do you consider to be a red flag?
Parents
  • From looking at my results, it looks like my probe head might be slightly out of square. But if the qualification routine compensates for that, will it really make a difference? How much is too much?

    The qualification mathematics take care of this, and if you calibrate manually there shouldn't be a problem (except that it has only been done manually).

    But if you calibrate in DCC, PC-DMIS assumes that the tips are as specified theoretically. For the probe angle A90B0, applying simple geometry gives (assuming I have understood the problem):

    The difference between where the tip actually is, and where PC-DMIS thinks it is (when running in DCC with THEO definitions) is roughly "Length of tip from rotation point" times SIN(angle between probe tip A90B0 and the closest machine axis [X or Y]). If this value gets as large as the prehit distance, you should expect problems.

    To this should be added that you get a small cosine error in the measuring points as soon as the hits are not exactly normal to the surface. I don't know (or have the time to calculate) if that will be significant.
Reply
  • From looking at my results, it looks like my probe head might be slightly out of square. But if the qualification routine compensates for that, will it really make a difference? How much is too much?

    The qualification mathematics take care of this, and if you calibrate manually there shouldn't be a problem (except that it has only been done manually).

    But if you calibrate in DCC, PC-DMIS assumes that the tips are as specified theoretically. For the probe angle A90B0, applying simple geometry gives (assuming I have understood the problem):

    The difference between where the tip actually is, and where PC-DMIS thinks it is (when running in DCC with THEO definitions) is roughly "Length of tip from rotation point" times SIN(angle between probe tip A90B0 and the closest machine axis [X or Y]). If this value gets as large as the prehit distance, you should expect problems.

    To this should be added that you get a small cosine error in the measuring points as soon as the hits are not exactly normal to the surface. I don't know (or have the time to calculate) if that will be significant.
Children
No Data
© 2024 Hexagon AB and/or its subsidiaries. Privacy Policy | Cloud Services Agreement