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Noob measuring question

jero pero
Hi.

I am measuring with PC dmis Vision.

I want to measure outer dimensions of a square piece (40x40mm) that was cut with a laser.

I know how to measure a straight line along the edge, but how do you measure the outer points along that line (because edges are never perfect straight lines)?

To clarify this : If I measure my piece with the caliper I get the dimension 40.00mm, but when I measure it with Vision, I get 39,93mm.

I hope this makes any sense....
  • When you're using the calipers, you're measuring a tangent line, i.e. the line formed by the two highest points on each surface. The CMM is calculating out a best fit line, one with the least amount of deviation based on the sum of the squares. So already you're using a different method than the CMM.

    You can replicate it, though it's not intuitive and not really a beginner's method, but... 

    LIN1       =FEAT/CONTACT/LINE/DEFAULT,CARTESIAN,UNBOUNDED
            THEO/<0.25,0,0>,<1,0,0>,<0,1,0>,<0,0,1>,10
            ACTL/<0.25,0,0>,<1,0,0>,<0,1,0>,<0,0,1>,10
            TARG/<0.25,0,0>,<1,0,0>,<0,1,0>,<0,0,1>
            SHOW FEATURE PARAMETERS=NO
            SHOW CONTACT PARAMETERS=YES
              NUMHITS=3,DEPTH=0.1181
              SAMPLE METHOD=SAMPLE_HITS
              SAMPLE HITS=3,SPACER=0,INDENT1=0,INDENT2=0
              AVOIDANCE MOVE=NO,DISTANCE=0.3937
            SHOW HITS=NO
LIN2       =FEAT/CONTACT/LINE/DEFAULT,CARTESIAN,UNBOUNDED
            THEO/<-0.25,-0.25,0>,<1,0,0>,<0,-1,0>,<0,0,1>,10
            ACTL/<-0.25,-0.25,0>,<1,0,0>,<0,-1,0>,<0,0,1>,10
            TARG/<-0.25,-0.25,0>,<1,0,0>,<0,-1,0>,<0,0,1>
            SHOW FEATURE PARAMETERS=NO
            SHOW CONTACT PARAMETERS=YES
              NUMHITS=3,DEPTH=0.1181
              SAMPLE METHOD=SAMPLE_HITS
              SAMPLE HITS=3,SPACER=0,INDENT1=0,INDENT2=0
              AVOIDANCE MOVE=NO,DISTANCE=0.3937
            SHOW HITS=NO
            ASSIGN/V1=MININDEX(LIN2.HIT[1..LIN2.NUMHITS].Y)
            ASSIGN/V2=MAXINDEX(LIN1.HIT[1..LIN2.NUMHITS].Y)
MAX_Y      =GENERIC/POINT,DEPENDENT,CARTESIAN,$
            NOM/XYZ,<LIN2.HIT[V2].X,0.25,LIN2.HIT[V2].Z>,$
            MEAS/XYZ,<LIN2.HIT[V2].X,LIN2.HIT[V2].Y,LIN2.HIT[V2].Z>,$
            NOM/IJK,<0,0,1>,$
            MEAS/IJK,<0,0,1>
MIN_Y      =GENERIC/POINT,DEPENDENT,CARTESIAN,$
            NOM/XYZ,<LIN1.HIT[V1].X,-0.25,LIN1.HIT[V1].Z>,$
            MEAS/XYZ,<LIN1.HIT[V1].X,LIN1.HIT[V1].Y,LIN1.HIT[V1].Z>,$
            NOM/IJK,<0,0,1>,$
            MEAS/IJK,<0,0,1>
DIM DIM_1= 2D DISTANCE FROM POINT MIN_Y TO POINT MAX_Y PERP TO LINE LIN2,NO_RADIUS  UNITS=IN,$
GRAPH=OFF  TEXT=OFF  MULT=10.00  OUTPUT=BOTH
AX       MEAS    NOMINAL       +TOL       -TOL        DEV     OUTTOL
M       0.2500     0.5000     0.0004     0.0004    -0.2500     0.2496 <--------
  • Thank you very much, will try this first thing in the morning.

  • Maybe using the size option with SX modifier could give the result ? (in the feature control frame).
    You can also construct a 2D width, which should give the result that you're looking for. (depends on the version)
  • You can measure lines along the edge, and construct an intersect point to get the corners (I believe)
  • Another possibility is to check the Filter Settings (if you have any applied) Filtering can have quite a pronounced effect on your end results... (but I'm no filter guru.... you need to ask Mr. Gauss himself Rolling eyes )
  • +1 Dr. JEFMAN!
    The world of filtering is indeed a black box. (much like a metrology software vendor's 'certification' of their product)
    Great link.
    In my world of Optiv 2D Vision, I wish Hexagon went a bit further in the Help file to explain the finer points of filtering. Alas, I am guessing it is
    needed to go get some additional training at one of their facilities........ cha-ching!!
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