Parametric Programming - Part Families

Do you manufacture and inspect Part Families?  Meaning, variety of parts having similar overall geometry but with varying dimensional characteristics?  Instead of cresting one program for each unique part, you can realize significant time savings by creating one parametric program that can inspect a variety of parts.

The following KB article describes a simple parametric program that will inspect cubes (blocks) or varying size.  This article will serve as an example that can be expanded upon as needed.  In this simple example we will only vary 3 dimensions for the work-piece, of course a more complex parametric program is possible.  The short video below shows the results of the example we'll review.

First we'll consider, how should we specify the parameters?  We could prompt the CMM operator to enter individual dimensions, we could prompt for a Rev Number and then lookup parameters that have been pre-configured in the VB Script, or we could refer to an outside data source such as a Sql database or simple text file.  The third option is best as it allows you to add new part configurations by simply adding data to this external data source.  In our example we'll use a simple text file.  Contents of three unique files as shown below:

	File # 1 contents:	File # 2 contents:	File # 3 contents:
Part # / ID	MyPart123,	MyPart246,	MyPart112,
Length, Upper & Lower Tolerance	76.2,0.5,0.5,	152.4,0.5,0.5,	50.8,0.25,0.25,
Width, Upper & Lower Tolerance	50.8,0.5,0.5,	101.6,0.5,0.5,	15,0.75,0.75,
Height, Upper & Lower Tolerance	25.4,0.5,0.5	50.8,0.5,0.5	12.5,0.75,0.75

We'll need to give the CMM program operator a chance to specify which file should be used.  This can be done with VB Script as follows:

1. Set objWShell = CreateObject("WScript.Shell") 
2. Set ChooseFile = objWShell.Exec( "mshta.exe ""about: <input type=file id=X><script>X.click();new ActiveXObject('Scripting.FileSystemObject').GetStandardStream(1).WriteLine(X.value);close();resizeTo(0,0);</script>""" )
   
3.  MyFile = ChooseFile.StdOut.ReadAll
4. 
   
5.   ChrPos = InStr(MyFile, Chr(13))
6.   ChrPos = ChrPos -1
7.   MyFile = Left(MyFile, ChrPos)

This will create a VB variable "MyFile" that contains the complete file path / name of file picked by operator using standard Windows dialog.

Better yet, we can prompt user to enter part ID and then look for file xxxx.txt in the specified folder, then fall back to file picker method if file cannot be located, like this:

1. 'Locate Job Config Txt File
2. Set objFSO = CreateObject("Scripting.FileSystemObject")
3. Set objWShell = CreateObject("WScript.Shell")
4. 
   
5. MyJob = InputBox("Please Enter Job Number")
6. MyFile = "C:\Users\Public\Jobs\" + CStr(MyJob) + ".txt"
7. 
   
8. 'check to see that Jobxxx.txt file exists
9. If objFSO.FileExists(MyFile) Then
10. 'If not - then prompt user to pick file manually
11. Else   
12. 
    
13.   MsgBox "Job not found - Please locate Job config .txt file"
14. 
    
15.   Set ChooseFile = objWShell.Exec( "mshta.exe ""about: <input type=file id=X><script>X.click();new ActiveXObject('Scripting.FileSystemObject').GetStandardStream(1).WriteLine(X.value);close();resizeTo(0,0);</script>""" )
16.   MyFile = ChooseFile.StdOut.ReadAll
17. 
    
18.   ChrPos = InStr(MyFile, Chr(13))
19.   ChrPos = ChrPos -1
20.   MyFile = Left(MyFile, ChrPos)
21. End If

Now that we know what file to open / read, we can open the file and extract contents to VB Script variables - these variables will be used to adjust measured feature sizes and report tolerances:

Parsing the input file could be done more efficiently using the VB Split() function  for comma separated files.  The example below has overhead Script to deal with inconsistent line format, some ending in comma, others do not.

1. ' Open file and read line by line
2. Set objFile = objFSO.OpenTextFile(MyFile, 1)
3. If objFile.AtEndOfStream = False Then
4.   Line1 = (objFile.ReadLine)
5. Else
6.   Line1 = "custom_job"
7. End If
8. 
   
9. If objFile.AtEndOfStream = False Then
10.   Line2 = (objFile.ReadLine)
11. Else
12.   Line2 = "777,1,1"
13. End If
14. If objFile.AtEndOfStream = False Then   
15.   Line3 = (objFile.ReadLine)
16. Else
17.   Line3 = "50.8,1,1"
18. End If 
19. If objFile.AtEndOfStream = False Then   
20.   Line4 = (objFile.ReadLine)
21. Else
22.   Line4 = "25.4,1,1"
23. End If
24. objFile.Close
25. 
    
26. MsgText = "Job file contents:" + Chr(10) + "   Job Number:  " + Line1 + Chr(10) + "   Length:  " + Line2 + Chr(10) + "   Width:  " + Line3 + Chr(10) + "   Height:  " + Line4
27. DoEdit = MsgBox(MsgText, 64, "Job Setup Info")
28. 
    
29. 'parse read lines into variables
30. 'Remove comma from end of Line1
31.   DelimPos = InStr(Line1, ",")
32.   strJobNum = Left(Line1, DelimPos-1)
33.   'MsgBox(strJobNum)
34. 
    
35. 'split Line2 into Length and Tol Variables
36.   DelimPos = InStr(Line2, ",")
37.   Length = Left(Line2, DelimPos-1)
38.   Line2 = Right(Line2, Len(Line2) - DelimPos)
39.   DelimPos = InStr(Line2, ",")
40.   LenLoTol = Left(Line2, DelimPos-1)
41.   LenLoTol = LenLoTol * -1
42.   Line2 = Right(Line2, Len(Line2) - DelimPos)
43.   DelimPos = InStr(Line2, ",")
44.   LenUpTol = Left(Line2, DelimPos-1)
45.   'MsgBox(CStr(Length) + Chr(10) + CStr(LenLoTol) +Chr(10) + CStr(LenUpTol))
46. 
    
47. 'split Line3 into Width and Tol Variables
48.   DelimPos = InStr(Line3, ",")
49.   Width = Left(Line3, DelimPos-1)
50.   Line3 = Right(Line3, Len(Line3) - DelimPos)
51.   DelimPos = InStr(Line3, ",")
52.   WidLoTol = Left(Line3, DelimPos-1)
53.   WidLoTol = WidLoTol * -1
54.   Line3 = Right(Line3, Len(Line3) - DelimPos)
55.   DelimPos = InStr(Line3, ",")
56.   WidUpTol = Left(Line3, DelimPos-1)
57.   'MsgBox(CStr(Width) + Chr(10) + CStr(WidLoTol) +Chr(10) + CStr(WidUpTol))
58. 
    
59. 'split Line4 into Height and Tol Variables
60.   DelimPos = InStr(Line4, ",")
61.   Height = Left(Line4, DelimPos-1)
62.   Line4 = Right(Line4, Len(Line4) - DelimPos)
63.   DelimPos = InStr(Line4, ",")
64.   HtLoTol = Left(Line4, DelimPos-1)
65.   HtLoTol = HtLoTol * -1
66.   Line4 = Right(Line4, Len(Line4) - DelimPos)
67.   'DelimPos = InStr(Line4, ",")
68.   'HtUpTol = Left(Line4, DelimPos-1)
69.   HtUpTol = Line4  'last line has no trailing comma
70.   'MsgBox(CStr(Height) + Chr(10) + CStr(HtLoTol) +Chr(10) + CStr(HtUpTol))

Finally, we'll create the variables that drive the motion of each measured feature.  In this case Length, Width, Height, and some associated clearance and edge offsets:

1. 'set variables for PtMeas and Move Points
2. XLeft = 3
3. XRight = Length - 3
4. XCenter = Length / 2
5. 
   
6. YFront = 3
7. YRear = Width - 3
8. YCenter = Width / 2
9. 
   
10. Z = Height
11. ZClear = Height + 10
12. XClear = Length + 5
13. YClear = Width + 5

Now to apply VB Variables to the Measurement and Reporting Operations.  Look for the Set Variable button.  This can be used both for Features Nominal but also for underlying Path and Point locations.  Note - the Measurement Commands that facilitate VB Variable will begin with "@" - this will serve as a quick visual indicator when reviewing the measurement operation.  In the example below, the X & Y location of Move Point is set by VB Variables XLeft and YClear when program runs.

While i n this example, the reported Length by VB Variable  Length  when program runs.

We recommend that you pick one part from the similar part family and write the initial program.  Create a program for this one part, then after it's tested and operates as expected add the VB Script and references to Variables as described above.  See the attached CMM-Manager Project file and associated job config files.  You can run this program easily if you have access to a 1,2,3 and 2,4,6 block.  Alternately, you could modify the attached job files to accommodate any sized blocks- i.e. gage blocks - that you have available.

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