Scanning Holes

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  • Scanning Holes

    My apologies if these questions were answered in another post somewhere - I did spend quite a bit of time searching and reading and didn't find anything that specifically answered my questions.

    I (and the engineer I work with) am/are very new to PC-DMIS. We have jumped right past touch probe stuff and are trying to make scanning work. We are measuring a piece of 1/4" mild steel which is lying horizontal and has several holes in it with diameters ranging from 0.571 inches to 0.189 inches. We intend to scan these holes as three circles - one near the top, one halfway down, and another near the bottom (for various reasons we don't really want to scan a cylinder at this point).

    Initially we had problems with the scanning. When using a basic circle scan the probe would move pretty fast, but stop about halfway through the scan, start over, and then move very slowly. We were able to reduce the incidents of this happening by taking three touches at the top of the hole and aligning to the center. We could then further reduce problems by taking touches at the depths of the other scans, but this is time consuming.

    Is there a way to open up the tolerance a bit so that realigning for every scan is not necessary? Is there a way to reduce the number of rescans? Is there a way to raise the speed of the second pass scan so that it's not inspiring extra coffee breaks?

    Also, when we get down to the smaller holes we are often times unable to have any success and have problems with the probe crashing. Any ideas on how to stop that?

    One idea we had, which sometimes helps, is to take the diameter reported by the initial three touches and put it in as the nominal for the scan. It seems we either need to allow PC-DMIS to tolerate a hole which is far (0.025" or so) from the expected nominal, or somehow change the nominal of the scan via a variable (no, I don't like the sound of that either).

    Our CMM is a Sheffield Discovery D-12 with a PH6M, SP25M, SM25-1 and we are running PC-DMIS version 4.1.

    Any help is greatly appreciated.


    Guy

  • #2
    Originally posted by PlasmaGuy View Post
    My apologies if these questions were answered in another post somewhere - I did spend quite a bit of time searching and reading and didn't find anything that specifically answered my questions.

    I (and the engineer I work with) am/are very new to PC-DMIS. We have jumped right past touch probe stuff and are trying to make scanning work. We are measuring a piece of 1/4" mild steel which is lying horizontal and has several holes in it with diameters ranging from 0.571 inches to 0.189 inches. We intend to scan these holes as three circles - one near the top, one halfway down, and another near the bottom (for various reasons we don't really want to scan a cylinder at this point).

    Initially we had problems with the scanning. When using a basic circle scan the probe would move pretty fast, but stop about halfway through the scan, start over, and then move very slowly. We were able to reduce the incidents of this happening by taking three touches at the top of the hole and aligning to the center. We could then further reduce problems by taking touches at the depths of the other scans, but this is time consuming.

    Is there a way to open up the tolerance a bit so that realigning for every scan is not necessary? Is there a way to reduce the number of rescans? Is there a way to raise the speed of the second pass scan so that it's not inspiring extra coffee breaks?

    Also, when we get down to the smaller holes we are often times unable to have any success and have problems with the probe crashing. Any ideas on how to stop that?

    One idea we had, which sometimes helps, is to take the diameter reported by the initial three touches and put it in as the nominal for the scan. It seems we either need to allow PC-DMIS to tolerate a hole which is far (0.025" or so) from the expected nominal, or somehow change the nominal of the scan via a variable (no, I don't like the sound of that either).

    Our CMM is a Sheffield Discovery D-12 with a PH6M, SP25M, SM25-1 and we are running PC-DMIS version 4.1.

    Any help is greatly appreciated.


    Guy
    PlasmaGuy, Welcome to the forum.

    As you are just getting your feet wet using PC-DMIS, could you please post your program code for us to look at? The reason I say this is I would be interested in how you are setting the alignments for this part, and then I will go on to the scanning part, because if you're not starting out correctly you can't hope to end where you need to be eh?
    Anyways, post some code and the forum junkies will pick it apart. Also,this is to CAD correct?
    sigpic

    James Mannes

    Comment


    • #3
      You may be seeing the limitation of the SP25. It does not have a great deal of dynamic range and if you are off center it may lose contact with the surface. maybe the "scanning heads" here can offer a solution with regards to PCDMIS. There should be a way to keep tracking the surface instead of scanning a nominal path and measuring the deviation. You may find trying to stay in contact with the surface may take more time that the nominal path type of scan but it has to be quicker than what you are experiencing now.
      Links to my utilities for PCDMIS

      Comment


      • #4
        Thanks for the warm welcome. This part is to CAD, although we had similar results without CAD. Slower scans are fine, as long as it works.

        Here's the first part of the code. We were experimenting with both the basic circle scan and the linear closed scan near the bottom:

        STARTUP =ALIGNMENT/START,RECALL:,LIST=YES
        ALIGNMENT/END
        MODE/MANUAL
        PREHIT/ 0.125
        RETRACT/ 0.125
        MOVESPEED/ 25
        MANRETRACT/0.1181
        FLY/ON,0.1181
        FORMAT/TEXT,OPTIONS,ID,HEADINGS,SYMBOLS, ;MEAS,NOM,TOL,DEV,OUTTOL, ,
        LOADPROBE/SCANNING
        SCANSPEED/ 3
        OPTIONPROBE/MAXFORCE=0.15, LOWFORCE=0.025, UPPERFORCE=0.075, TRIGGERFORCE=0.12,
        PROBEACCURACY=1, POSACCURACY=10, #RETURNDATA=0,
        RETURNSPEED=1, SCANPNTDENSITY=6,
        SCANACCELERATION=10, SCANOFFSETFORCE=0.32,
        PROBINGMODE=DFL, MANFINEPROBING=NO
        TIP/TIP1, SHANKIJK=0, 0, 1, ANGLE=0
        LINE1 =FEAT/LINE,RECT,UNBND
        THEO/2.0701,0,-0.0958,1,0,0
        ACTL/10.8842,16.4418,-18.9005,0.9999997,0.0008146,0
        MEAS/LINE,2,WORKPLANE
        HIT/BASIC,NORMAL,2.0701,0,-0.0904,0,-1,0,10.8842,16.4418,-18.9012,USE THEO = YES
        HIT/BASIC,NORMAL,6.8257,0,-0.1012,0,-1,0,15.3238,16.4454,-18.8999,USE THEO = YES
        ENDMEAS/
        POINT1 =FEAT/POINT,RECT
        THEO/0,2.3855,-0.1145,-1,0,0
        ACTL/8.4199,19.7194,-18.829,-0.9997969,-0.0000348,0.0201552
        MEAS/POINT,1
        HIT/BASIC,NORMAL,0,2.3855,-0.1145,-1,0,0,8.4199,19.7194,-18.829,USE THEO = YES
        ENDMEAS/
        PLANE1 =FEAT/PLANE,RECT,TRIANGLE
        THEO/5.2658,2.3649,0,0,0,1
        ACTL/13.7078,18.8109,-18.827,-0.0002948,0.0004735,0.9999998
        MEAS/PLANE,3
        HIT/BASIC,NORMAL,7.637,2.9692,0,0,0,1,16.0881,19.7343,-18.8268,USE THEO = YES
        HIT/BASIC,NORMAL,7.6718,0.7146,0,0,0,1,16.0098,16.9183 ,-18.8254,USE THEO = YES
        HIT/BASIC,NORMAL,0.4886,3.4108,0,0,0,1,9.0254,19.7802,-18.8289,USE THEO = YES
        ENDMEAS/
        MANUAL =ALIGNMENT/START,RECALL:STARTUP,LIST=YES
        ALIGNMENT/LEVEL,ZPLUS,PLANE1
        ALIGNMENT/ROTATE,XPLUS,TO,LINE1,ABOUT,ZPLUS
        ALIGNMENT/TRANS,XAXIS,POINT1
        ALIGNMENT/TRANS,YAXIS,LINE1
        ALIGNMENT/TRANS,ZAXIS,PLANE1
        ALIGNMENT/END
        MODE/DCC
        PLANE2 =FEAT/PLANE,RECT,TRIANGLE
        THEO/5.4536,2.4579,0,0,0,1
        ACTL/5.453,2.4588,0.0001,0.0000005,0.0001768,1
        MEAS/PLANE,3
        HIT/BASIC,NORMAL,7.8829,3.1464,0,0,0,1,7.8819,3.1476,0 ,USE THEO = YES
        HIT/BASIC,NORMAL,7.6476,0.7707,0,0,0,1,7.647,0.772,0.0 004,USE THEO = YES
        HIT/BASIC,NORMAL,0.8303,3.4565,0,0,0,1,0.8301,3.4569,0 ,USE THEO = YES
        ENDMEAS/
        AUTO Z =ALIGNMENT/START,RECALL:MANUAL,LIST=YES
        ALIGNMENT/LEVEL,ZPLUS,PLANE2
        ALIGNMENT/END
        MOVE/POINT,NORMAL,-0.382,3.4825,0.1719
        MOVE/POINT,NORMAL,-0.3823,3.4827,-0.024
        POINT2 =FEAT/POINT,RECT
        THEO/0,3.4824,-0.024,-1,0,0
        ACTL/-0.0063,3.4826,-0.0235,-1,0,0
        MEAS/POINT,1
        HIT/BASIC,NORMAL,0,3.4824,-0.024,-1,0,0,-0.0063,3.4826,-0.0235,USE THEO = YES
        ENDMEAS/
        MOVE/POINT,NORMAL,-0.4344,3.4824,-0.024
        MOVE/POINT,NORMAL,-0.3451,3.4327,0.8635
        MOVE/POINT,NORMAL,2.2017,-0.3109,0.8607
        MOVE/POINT,NORMAL,2.2005,-0.3106,-0.024
        LINE2 =FEAT/LINE,RECT,UNBND
        THEO/2.2005,0,-0.024,1,0,0
        ACTL/2.2002,0.0028,-0.0234,0.9999997,0.0007856,0
        MEAS/LINE,2,WORKPLANE
        HIT/BASIC,NORMAL,2.2005,0,-0.024,-0.0000007,-1,0,2.2002,0.0028,-0.0234,USE THEO = YES
        MOVE/POINT,NORMAL,2.1988,-0.4707,-0.024
        MOVE/POINT,NORMAL,2.199,-0.626,1.1345
        MOVE/POINT,NORMAL,7.0124,-0.5118,1.1352
        MOVE/POINT,NORMAL,7.0114,-0.511,-0.024
        HIT/BASIC,NORMAL,7.0116,0,-0.024,-0.0000007,-1,0,7.0107,0.0066,-0.0235,USE THEO = YES
        ENDMEAS/
        MOVE/POINT,NORMAL,7.0094,-0.3902,-0.024
        MOVE/POINT,NORMAL,7.0102,-0.4089,0.5
        MOVE/POINT,NORMAL,1.248,2.752,0.5
        AUTO XYZ =ALIGNMENT/START,RECALL:AUTO Z,LIST=YES
        ALIGNMENT/LEVEL,ZPLUS,PLANE2
        ALIGNMENT/ROTATE,XPLUS,TO,LINE2,ABOUT,ZPLUS
        ALIGNMENT/TRANS,XAXIS,POINT2
        ALIGNMENT/TRANS,YAXIS,LINE2
        ALIGNMENT/TRANS,ZAXIS,PLANE2
        ALIGNMENT/END
        MOVE/POINT,NORMAL,1.248,2.752,-0.024
        0.571 TOP TOUCH=FEAT/CIRCLE,RECT,IN,LEAST_SQR
        THEO/1.248,2.752,-0.024,0,0,1,0.571
        ACTL/1.2516,2.7622,-0.0231,0,0,1,0.5724
        MEAS/CIRCLE,3,WORKPLANE
        HIT/BASIC,NORMAL,1.5335,2.752,-0.024,-1,0,0,1.5375,2.7489,-0.0239,USE THEO = YES
        MOVE/CIRCULAR
        HIT/BASIC,NORMAL,1.1053,2.9993,-0.024,0.5,-0.8660254,0,1.0977,3.0036,-0.0229,USE THEO = YES
        MOVE/CIRCULAR
        HIT/BASIC,NORMAL,1.1052,2.5047,-0.024,0.5,0.8660254,0,1.1086,2.5143,-0.0225,USE THEO = YES
        ENDMEAS/
        0.571 AXIS TOP=ALIGNMENT/START,RECALL:AUTO XYZ,LIST=YES
        ALIGNMENT/TRANS,XAXIS,0.571 TOP TOUCH
        ALIGNMENT/TRANS,YAXIS,0.571 TOP TOUCH
        ALIGNMENT/END
        0.571 LCS SCAN TOP=FEAT/SCAN,LINEARCLOSE,SHOWHITS=NO,SHOWALLPARAMS=NO
        MEAS/SCAN
        BASICSCAN/LINE,SHOWHITS=NO,SHOWALLPARAMS=NO
        ENDSCAN
        ENDMEAS/
        0.571 TOP SCAN=BASICSCAN/CIRCLE,SHOWHITS=NO,SHOWALLPARAMS=NO
        ENDSCAN

        Comment


        • #5
          Look at your PM box.
          sigpic

          James Mannes

          Comment


          • #6
            a public thank you

            Many, many thanks to all who replied to this thread - and a special thank you to James who went far above the call of duty and helped me out via emails.


            Guy

            Comment

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