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Rmeas help

mjdevries
I've been trying to figure out what PC-DMIS does with the RMEAS statement with the different numbers of Hits. I found some info that refers to the Rmeas with 3 hits as the "Flush/Gap" measurement. Can anyone explain the difference between the RMEAS with 1 hit versus the RMEAS with 3 hits? From analyzing the data I believe it has to do with the vector that is used when it takes the actual measurement. From what I've seen looking at data is the single hit RMEAS would be considered a "Surface/Edge" measurement where the edge is too thin to consider it having any thickness/depth.

From my own analysis it appears that the single hit version uses an approach vector that is perpendicular to the reference points vector. The vector I believe is derived by the unit vector of (|V1| X |V2|) X |V1|, where V1 is the vector on the surface point and V2 is the vector on the point being measured with RMEAS. The X represents the Cross Product function. The first cross product is done between the 2 vectors to obtain a vector normal to the 2 vectors. The cross product of the resulting vector & the surface vector then gives you a vector that is perpendicular to the surface vector V1, but in the same plane as V2.

Does anyone know what the 3 hit version does? 

F(F0954M009B) = FEAT/POINT,CART,2531.99,860.834,605.15,0.0437,0.9651,0.2584
  MEAS/POINT, F(F0954M009B), 1
  ENDMES
 T(XTOL_4)=TOL/CORTOL,XAXIS,0.0,0.0
 T(YTOL_4)=TOL/CORTOL,YAXIS,-0.15,0.15
 T(ZTOL_4)=TOL/CORTOL,ZAXIS,0.0,0.0
 T(VECTOL_4)=TOL/PROFP,0.0,0.0
 TEXT/OUTFIL,'F0954M009B - POINT - INSP=D METAL=0.686'
 OUTPUT/FA(F0954M009B),TA(XTOL_4),TA(YTOL_4),TA(ZTOL_4),TA(VECTOL_4)

  GOTO/2536.032,864.531,605.704
F(G0954M009B) = FEAT/POINT,CART,2524.03,857.084,605.007,0.9667,-0.2002,-0.1595
  RMEAS/POINT, F(G0954M009B), 1, FA(F0954M009B)
  ENDMES
 T(XTOL_5)=TOL/CORTOL,XAXIS,-0.15,0.15
 T(YTOL_5)=TOL/CORTOL,YAXIS,0.0,0.0
 T(ZTOL_5)=TOL/CORTOL,ZAXIS,0.0,0.0
 T(VECTOL_5)=TOL/PROFP,0.0,0.0
 TEXT/OUTFIL,'G0954M009B - HEDGE - INSP=D METAL=0.686'
 OUTPUT/FA(G0954M009B),TA(XTOL_5),TA(YTOL_5),TA(ZTOL_5),TA(VECTOL_5)
  GOTO/2536.032,864.531,605.704
  • Matthew,
    Where did you go?

    Do you know what the theo thickness and edge theo thickness are when you use the edge measurement? I'm assuming they are perpendicular to each other. See my image and let me know if it makes sense what I labelled as the Theo Thickness and the Edge Theo Thickness.

    I have a few things wrong with the measurement I think. The Indent is wrong I believe. When I measure from the Surface point to the edge point on the wrong side of material perpendicular to the surface normal I get what they have in the CMM Program as the Indent. I believe the indent should be the distance from the surface point to the edge point on the correct surface. This error gives me the 0.711 mm material thickness shift.

    If the Edge Theo Thickness is actually the thickness of the part in the direction that would be tangent to the edge surface (perpendicular to the edge surface normal vector), then that woud be the other 0.711 shift I am seeing in the target point that PC-DMIS is taking the hits on.

    Now the target point is on the wrong side of material so I also have that shift to along the measurement direction that also needs to come out of the data.

    It is crazy how much can be wrong with one stinking dimension when someone really screws it up. Unfortunately they use some offline programming here and some automation to create the cmm programs. I believe I will find that we have this issue in a couple hundred CMM programs. Yippee!

  • In that picture, what you are calling an edge point, isn't an edge point, and (IMO) shouldn't be an edge point. It should be a vector point.

    INDENT is only used if INIT and PERM do NOT equal zero. If INIT and PERM are set to zero, then NO sample hit is taken on the surface at the INDENT value from the dge of the part.

    Edge Points:
    THEO/ACTL THICKNESS = SURFACE
    THEO/ACTL EDGE THICKNESS = EDGE

    Here is an example of what is what for which type of feature and what the different thickness values will give you.

    Well, I would have posted an image, but the STUPID site will not let me DELETE any attachments I have already uploaded. I'll have to try something else.
  • In that picture, what you are calling an edge point, isn't an edge point, and (IMO) shouldn't be an edge point. It should be a vector point.

    INDENT is only used if INIT and PERM do NOT equal zero. If INIT and PERM are set to zero, then NO sample hit is taken on the surface at the INDENT value from the dge of the part.

    Edge Points:
    THEO/ACTL THICKNESS = SURFACE
    THEO/ACTL EDGE THICKNESS = EDGE

    Here is an example of what is what for which type of feature and what the different thickness values will give you.

    Well, I would have posted an image, but the STUPID site will not let me DELETE any attachments I have already uploaded. I'll have to try something else.

    Looks like crap, but here it is:
  • I'll have to study that one. You are correct, Images must be resized when you upload them and it really degrades them. I believe I can read this well enough though.

    The section that shows what they are measuring using the edge check is an extreme sample of trying to use the wrong tool for the job. We have trim edges and hem edges that they use this on which are fine if set up properly. They also attempt to use it on Flush/Gap points. I was not here when they started doing this. It has been going on here for years. I'm just trying to understand this the best I can so I can make an argument that we need to change some of the things we are doing. You have been around long enough to know how difficult it is to "Change" a process. Especially if it has been automated and everyone believes that it is being done correctly because the automation could not possibly be wrong.

    Thanks again for you time and efforts helping me understand this better.

    Mike
  • They are trying to use the edge measurement here for measuring the edges of bent corners. This would be more of a bent corner. I believe the the 'Theo Thickness' and the 'Edge Theo Thickness' may be dependent on the surface vector of the cad where the edge point is defined. The sketch you posted is for a trim edge where the cad design is flat surface that gets thickened, so the design vector of the surface that the edge point is on would be perpendicular to the edge you want to measure. The edge measurement does not use the vector on the edge point for the approach. It does some math where it finds the vector that is perpendicular to the surface point and uses that for the approach. Which in the sketch you drew, would still be normal to the edge surface.

    With that in mind I think that the design I am looking at where the design surface is bent and the edge point is on a surface with a vector the 'Theo Thickness' and 'Edge Theo Thickness' would be like this sketch. This would give me the results that I am seeing where the actual measurement points are all skewed because the hit is being taken where the 'Edge Theo Thickness' point is shown.

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