Looping

[JamesMannes]

Hi folks,
New to looping and having a problem. What I have is 4 parts in a row going left to right. I first tried to use my original alignment and program for this part, which consisted of a manual Iterative Alignment and a DCC Iterative Alignment(CAD), followed by an alignment per the print. It didn't work quite well because the part is rather small and the leveling and translating to the part itself skewed the measurement of the 3 other parts so much so that by the 4th part it would not touch the part.

So, I then made an alignment to the fixture I have and then translated to get back to the actual part. At this point I did a CAD=PART. I then went on to do the print alignment(I'll call it ABC_ALIGN). I inserted the LOOP command here. I then recalled my ABC_ALIGN alignment. I measured 1 point and reported out the "T" deviation". At each successive loop of the program I am getting a larger and larger deviation, which indicates to me something is not right.

My question(s) for the user group is this...
1. Does it sound like I did this correctly?

2. Is it wrong to put an alignment recall command inside of a of a LOOP command?(HELP file indicates that I shouldn't do this if the features used for the alignment are not within the LOOP).

3.Does the insertion of a LOOP command into a part program have any of the ramifications like when inserting a CAD=PART into a program? It seems like the program gets funky when I have inserted and/or removed the LOOP command from the program.

4.Any hints/tips/comments/questions?

[mkopesky]

I've always been partial to using external alignments to offset your loop. This has two benifits.

First you dont need to rely on the fixture having exact offsets, or the program offsetting along the part axis like you described.

Second, you dont need to worry about PC-DMIS updating THEO values when executing the LOOP command (this is probably what you described being similer to CAD = PART which also updates Theo values). This can cause the "funky" behavior you described if you cancel execution at the wrong time, or try and step into the program.

$$ NO,******************ALIGNMENT LOOP*********************
V1         =LOOP/START, ID = NO, NUMBER = 4, START = 1, SKIP = ,
               OFFSET: XAXIS = 0, YAXIS = 0, ZAXIS = 0, ANGLE = 0
            IF/V1==1
            RECALL/ALIGNMENT,EXTERNAL,station1,STATION1:station1
            END_IF/
            IF/V1==2
            RECALL/ALIGNMENT,EXTERNAL,station2,STATION2:station2
            END_IF/
            IF/V1==3
            RECALL/ALIGNMENT,EXTERNAL,station3,STATION3:station3
            END_IF/
            IF/V1==4
            RECALL/ALIGNMENT,EXTERNAL,station4,STATION4:station4
            END_IF/

Just create a loop with no offset, and then use the loop variable to recall each stations alignment. Just make sure you uncheck the "Reset Global Variables" box in general setup options.

[JamesMannes]

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