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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
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  • Matthew - Thanks for the response.

    I do not have PC-DMIS. I analyze data coming off PC-DMIS, and when the CMM data reports that parts are out of spec significantly and we are building assemblies that are within spec it concerns me. I'm trying to understand what the data is actually telling me.

    The number of hits I'm referring to comes from the DMIS Standard and the RMEAS function as defined by the DMIS Standard, I believe DMIS.org is their website. I'm trying to figure out exactly how PC-DMIS is interpretting the DMIS RMEAS statement when it is imported. PC-DMIS has many more settings/options than the DMIS standard. The number of hits in the DMIS standard from my understanding is that it determines the vector of the actual measurement. Using 1 you would get what PC-DMIS calls an Edge point. This is where the vector that is used for taking the measurement is perpendicular to the surface hit vector in the same plane as the surface and gap points. Using 2 hits the vector is normal to a line defined by 2 sample hits along the edge. Using 3 hits is commonly referred to as the Flush/Gap measurement from what I have read on line. This is for when you have a corner where you have enough surface on the edge to take 3 hits to get the normal vector for the measurement. It still uses the target that is defined by the offset of the surface, but there are 3 different approach vectors that can be used to take the actual measurement.

    The part I'm trying to understand is the XYZ coordinate measurements include the deviation of the surface point. If you have a 90 degree edge you can subtract out the surface point deviation easily. But when you get away from 90 degrees it deviates away from being straight math and you need to start doing vector math. I have one measurement that for some reason is adding 0.984 mm to the deviation along the direction of the surface vector. This is in addition the the actual surface deviation. I'm just trying to figure out where that 0.984 came from because it is a constant on all the measurements. When your tolerance is +/- 0.5, having 0.984 unexplained meanshift in your measurement system is not acceptable.
Reply
  • Matthew - Thanks for the response.

    I do not have PC-DMIS. I analyze data coming off PC-DMIS, and when the CMM data reports that parts are out of spec significantly and we are building assemblies that are within spec it concerns me. I'm trying to understand what the data is actually telling me.

    The number of hits I'm referring to comes from the DMIS Standard and the RMEAS function as defined by the DMIS Standard, I believe DMIS.org is their website. I'm trying to figure out exactly how PC-DMIS is interpretting the DMIS RMEAS statement when it is imported. PC-DMIS has many more settings/options than the DMIS standard. The number of hits in the DMIS standard from my understanding is that it determines the vector of the actual measurement. Using 1 you would get what PC-DMIS calls an Edge point. This is where the vector that is used for taking the measurement is perpendicular to the surface hit vector in the same plane as the surface and gap points. Using 2 hits the vector is normal to a line defined by 2 sample hits along the edge. Using 3 hits is commonly referred to as the Flush/Gap measurement from what I have read on line. This is for when you have a corner where you have enough surface on the edge to take 3 hits to get the normal vector for the measurement. It still uses the target that is defined by the offset of the surface, but there are 3 different approach vectors that can be used to take the actual measurement.

    The part I'm trying to understand is the XYZ coordinate measurements include the deviation of the surface point. If you have a 90 degree edge you can subtract out the surface point deviation easily. But when you get away from 90 degrees it deviates away from being straight math and you need to start doing vector math. I have one measurement that for some reason is adding 0.984 mm to the deviation along the direction of the surface vector. This is in addition the the actual surface deviation. I'm just trying to figure out where that 0.984 came from because it is a constant on all the measurements. When your tolerance is +/- 0.5, having 0.984 unexplained meanshift in your measurement system is not acceptable.
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