Arghh, Iterative Alignment

**vpt.se** · 07-23-2008, 02:22 PM

Some hefty nominals you got there...

**Matthew D. Hoedeman** · 07-23-2008, 02:23 PM

Originally posted by All Parts R Good View Post

Good afternoon all,

I seem to be having a bit of a problem today with an iterative alignment. I have the CAD model, selected 6 points from it and measured them. I then went to create an iterative alignment and was greeted with the "Iterative alignment error". Below are the points that I took. 3 in the "Z" level. 2 in the "Y" rotate and 1 in the "X" origin.

What am I missing. I ran a part earlier that was very similar and it worked just fine.

Any help would be DEEPLY appreciated...

Code:

PNT1       =AUTO/VECTOR POINT,SHOWALLPARAMS = YES
            THEO/5247.826,659.181,755.547,0.0523353,0.0985408,0.9937559
            ACTL/186.114,284.904,-356.793,0,-0.0004579,0.9999999
            TARG/5247.826,659.181,755.547,0.0523353,0.0985408,0.9937559
            THICKNESS_OFF = 0,RECT,SNAP = NO,$
            AUTO MOVE = BOTH,DISTANCE = 10

PNT2       =AUTO/VECTOR POINT,SHOWALLPARAMS = YES
            THEO/5238.81,671.557,754.733,0.0523356,0.1068476,0.9928971
            ACTL/201.556,292.19,-358.05,0,0,1
            TARG/5238.81,671.557,754.733,0.0523356,0.1068476,0.9928971
            THICKNESS_OFF = 0,RECT,SNAP = NO,$
            AUTO MOVE = BOTH,DISTANCE = 10

PNT3       =AUTO/VECTOR POINT,SHOWALLPARAMS = YES
            THEO/5263.939,680.74,752.409,0.0523353,0.1086898,0.9926971
            ACTL/208.454,269.309,-360.018,0,0,1
            TARG/5263.939,680.74,752.409,0.0523353,0.1086898,0.9926971
            THICKNESS_OFF = 0,RECT,SNAP = NO,$
            AUTO MOVE = BOTH,DISTANCE = 10

PNT4       =AUTO/VECTOR POINT,SHOWALLPARAMS = YES
            THEO/5254.972,686.891,781.626,0.052336,-0.9985409,0.0133027
            ACTL/214.221,273.887,-329.695,-1,0,0
            TARG/5254.972,686.891,781.626,0.052336,-0.9985409,0.0133027
            THICKNESS_OFF = 0,RECT,SNAP = NO,$
            AUTO MOVE = BOTH,DISTANCE = 10

PNT5       =AUTO/VECTOR POINT,SHOWALLPARAMS = YES
            THEO/5260.25,686.871,759.424,0.052336,-0.9985409,0.0133027
            ACTL/213.805,273.89,-353.21,-1,0,0
            TARG/5260.25,686.871,759.424,0.052336,-0.9985409,0.0133027
            THICKNESS_OFF = 0,RECT,SNAP = NO,$
            AUTO MOVE = BOTH,DISTANCE = 10

PNT6       =AUTO/VECTOR POINT,SHOWALLPARAMS = YES
            THEO/5268.997,692.675,756.04,0.9272134,0.3661024,0.0790212
            ACTL/220.37,266.12,-353.21,0.0004272,-0.9999998,0.0004272
            TARG/5268.997,692.675,756.04,0.9272134,0.3661024,0.0790212
            THICKNESS_OFF = 0,RECT,SNAP = NO,$
            AUTO MOVE = BOTH,DISTANCE = 10

Well, when I do an iterative alignment, I always create the points, but do not measure them, then create the alignment. THEN I go back and execute them.

OK, the ONLY issue I see is PNT6 has an ACTUAL vector 90 degrees from the theo vector, is that the issue? Take the hit again.

**Paul Sarrach** · 07-23-2008, 02:26 PM

You need to use only 3 edge point with 5 sample hits. two on the lenth of the part and one on either end, then construct a 3D line and then construct a point to be your origin. Then in the iterative use the 3 points for level, the the two points for rotation and then use the constructed 3D point for origin, then us measure all always and go for it. Make sure your move distance is high enough to cleear all obstacles.

**Paul Sarrach** · 07-23-2008, 02:28 PM

Originally posted by Paul Sarrach View Post

You need to use only 3 edge point with 5 sample hits. two on the lenth of the part and one on either end, then construct a 3D line and then construct a point to be your origin. Then in the iterative use the 3 points for level, the the two points for rotation and then use the constructed 3D point for origin, then us measure all always and go for it. Make sure your move distance is high enough to cleear all obstacles.

Matt, try this, this is a little secret I have created years ago and only have told a few about it. I use it a lot on fixtures with no tooling balls. But will use it on parts that do not have and 3D features or holes.

**All Parts R Good** · 07-23-2008, 02:28 PM

Thanks guys...

The nominals are a little high as the part is the back up light in body position on an Escalade.

Now, after I posted my original message, I went back to tinkering. I added one more point to "rotate" around and the alignment works fine??

No idea why but I am not complaining!!

Thanks again....!!!!

**Matthew D. Hoedeman** · 07-23-2008, 02:32 PM

Originally posted by Paul Sarrach View Post

Matt, try this, this is a little secret I have created years ago and only have told a few about it. I use it a lot on fixtures with no tooling balls. But will use it on parts that do not have and 3D features or holes.

Ya know, I only do iterative alignments once in a blue moon. Even on fixtures without tooling balls (about half and half these days) I do not use iterative alignments. I use the 'called out' edges and faces of the fixture. If the locators do NOT then check in tolerance (I always check them, always!), I tweak the 3-2-1 alignment. If there is ANY WAY to NOT do an iterative alignment, that is what I do. It is not from NOT knowing how, it is from the fact that adjustments are MUCH easier in a 3-2-1 then they are in an iterative.

**All Parts R Good** · 07-23-2008, 02:46 PM

Hi again,

The day is getting better. The last part ran fine (after adding another rotation point) so I put a another part on the table, ran it through the 7 points I have, and when it says to "position probe at point 1" I do and it goes off to a different spot.

I gotta tell ya that this is a little un-nerving!!

**wicked_tattoo** · 07-23-2008, 03:51 PM

I would stick with no more than 6 pnts all together, i have tried woth more and it usually goes crazy. I am not sure why but it does. Its the DEMON.

**Paul Sarrach** · 07-23-2008, 04:05 PM

Originally posted by All Parts R Good View Post

Hi again,

The day is getting better. The last part ran fine (after adding another rotation point) so I put a another part on the table, ran it through the 7 points I have, and when it says to "position probe at point 1" I do and it goes off to a different spot.

I gotta tell ya that this is a little un-nerving!!

Do like I said, then make a nest for the part, then clear all, then F9 the alignment, say yes to it doing it now, then put cursor at beginning of program and hit Alt U. You will not have to touch your joy stick again.

, or depending on the which Joy Stick,

Or you could touch it more,

**Davis** · 08-05-2008, 11:04 AM

My first alignment w/o tooling balls..

Hello guys im a newb at pcdmis I am using 4.3 release and have allways used tooling balls for my alignment. I have a project to do that has no tooling balls.

I have a CAD model with all the points provided that need to be taken on the CMM. What I am scaning is a back window of a Honda SUV. It has allready been formed to its shape and Is a curved piece of glass. I have it supported on the CMM table laying flat but raised up about 2 inches. So I can do size hits around the outside of glass.

Now my problem is how do I do a alignment on this part so I can do the glass scan? I have never done a alignment without tooling balls before. If someone would please give me instructions on how to do this im sure its a simple thing. A how to Steps 1-? would help me the best.

Thx guys

**Paul Sarrach** · 08-05-2008, 11:44 AM

Let me see a picture or a print. It can be done but I need to see what I am looking at.

**winston** · 08-05-2008, 01:06 PM

Originally posted by Matthew D. Hoedeman View Post

Ya know, I only do iterative alignments once in a blue moon. Even on fixtures without tooling balls (about half and half these days) I do not use iterative alignments. I use the 'called out' edges and faces of the fixture. If the locators do NOT then check in tolerance (I always check them, always!), I tweak the 3-2-1 alignment. If there is ANY WAY to NOT do an iterative alignment, that is what I do. It is not from NOT knowing how, it is from the fact that adjustments are MUCH easier in a 3-2-1 then they are in an iterative.

when do you have to adjust your alignments? i've been using iterative alignments 99% of the time almost everyday for the past 8 years and i can't remember once having to adjust an alignment. if you're using cad and locked into the primary datums why would you have to adjust?

**Matthew D. Hoedeman** · 08-05-2008, 01:20 PM

Originally posted by winston View Post

when do you have to adjust your alignments? i've been using iterative alignments 99% of the time almost everyday for the past 8 years and i can't remember once having to adjust an alignment. if you're using cad and locked into the primary datums why would you have to adjust?

For using holding fixtures, basically automotive. Too many place are STILL getting their machines calibrated using ONLY the ball-bar, which does NOT do anything for the linear of the machine, so the numbers stamped on the fixture base might not be correct, in any of the 3 possible directions.

Almost all that I do is done with a holding fixture (auto sheet metal). You put the fixture up on the table, and align the fixture to the fixture datums (not the part datums). Once you are aligned to the fixture datums (common is top of base, front of base, side of base, for level, rotation and 3 axis origins). Then you check the locators. If the locators (part datums) all check LOW, then you tweak the alignment offsets to correct for it, then check them again. Once they are all correct, you are good to go.

NOW, before you say it, I'll say it, "Why not just do the iterative alignment on the part locators?" Well, I've been doing this forever, back before there even WAS a Pcdmis, let alone the iterative alignment method. In fact, it wasn't until there was a WINDOZE version of Pcdmis that there even WAS an iterative alignment option (and NOT even in the first windoze version, if I remember correctly). It is quicker in a lot of cases, especially when you DON'T have XYZ locations for the locators either on a print or in the cad, so you don't know where on the cad to pull these points. Yes, this is VERY common in automotive. So, the ONLY place you got to start from is the fixture datums. Sure, you could THEN go and do the DCC iterative alignment since you can then touch the nets on the fixture to get XYZ values to find on the cad, but you already HAVE the XYZ values for the fixture datums at this point from the touches you made doing the manual alignment, so it is quicker to re-program them in DCC to get the second alignment. Then you make the tweaks to THAT alignment to get the locators to check good. Benefits: You can align the fixture WITH a part on the fixture, loaded and ready to check if you are going to only check ONE part, no need to tie it all down to the table and you can quickly get it back out of the way.

Also, when MAKING fixtures, you WILL run into cases where not ALL the part datums ahve been put on the fixture yet, but you NEED to check what IS there to see if they have the pick-up right, so, you use the fixture datums, then check the available locators to the fixture datums. You can tweak and adjust the alignment to get what is there correct and give them the numbers needed for pick-up to do the rest.

There are LOTS of cases where using fixture datums are a lot easier to use and SOME where you ahve no choice. So, if you are going to start with a 'no choice' scenario, why not stick with it through the entire process. Why change from A to B when you can stay with A for the whole thing?

**Peter Warcholyk** · 08-05-2008, 02:49 PM

Now, now Paul,

Your comments may not be suitable for the "younger" viewers!

ZydecoPete

Arghh, Iterative Alignment

Arghh, Iterative Alignment

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