Base alignment loop formula

[[Cl...]]

I'm very familiar with the formula and use it for virtually every program. What I'm not sure about is what sigma
value to use? Zeiss wrote us a program for a very small part with complex geometry and tight tolerances.
Their programmer added a Base Alignment loop with a sigma value of .005. What would I base this value on?


baseSystem().valueA<0.001?

[[Ke...]]

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I usually start with <0.005, and "loosen it up" as needed.
As an example: inspecting an assembly of molded components with huge tolerances.
I would determine what to set it based on studying how many iterations it took to get it below a certain sigma value and/or IF it would ever get below a target. lol.
I'm not sure of what, if any, benefits there are to target below 0.005. For simple base alignments, it seems like if I put in a 0.005 break, then it will actually be at or below 0.003 (based on Empirical evidence of many samples)

[[Cl...]]

Makes sense. Thanks.

[[Mi...]]

I basically have 2 values I use, we have custom fixturing that is *almost* foolproof however there's always some risk of the part not quite being seated correctly and rocking.

0.005 On a program with finished tight tolerance machined features.

0.10 on a program with loose, unfinished or simple features where cycle time is more important, the only time I want these programs to loop is if the part is truly moving.

In all cases I set it to maximum 5 loops and with PCM I have the program stop if the delta value is not met.

[[Da...]]

My understanding was that the sigma value pertained to how close the base alignment is to the actual correct values of the base alignment. It is used to "tweak " the alignment to as close as you can to a perfect alignment. If the last part of your alignment was to hit a Z point and it turns out to be higher than expected, then the circles that were checked before it, were at the wrong height.

So, the alignment repeats at the new location. This will reduce the sigma value from the first alignment . The BA will repeat until the sigma value is met, or surpassed.

This will improve the repeatability of your program, since the BA was done almost exactly in the same place on each piece.
We use this on pretty much every program.

[[Ni...]]

Is this sigma value (<.005) always in metric or is it setting specific for each program?

Thanks

[[Ev...]]

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AFAIK this is a unitless value

[[Ni...]]

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What is valueA?

[[Aa...]]

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It's not unitless. This value should depend on the units of the program. If they wrote it as .005 for a metric program, that's a value of 5 microns. (For inch programs, that would be roughly 0.0002".) I would say it depends on your application. Since most of our programs are only run a handful of times (job shop, not production), we don't bother trying to "loosen it up", because we would spend more time finding that "sweet spot" than it would cost us to leave it at 5 microns or 2 tenths.

[[Si...]]

How does one loop an alignment? Recently been getting unstable parts id have to fight with, we do alot of free state inspections, 3 points.. but supplier is not too good at grinding and we see wobble or potatoe chipping. i want to make sure I am not producing a bad alignment and get it as good as I can.

[[Mi...]]

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When you're in the window to create a new Base Alignment there is a Loop button at the bottom that you've likely never paid attention to before.

it'll open up a new window, The right hand side of that window there is an Insert button, click it.

Now under Start, End, Step there will be a 1 under each.
That is a loop counter, If you change it to 1 5 1, That means the loop count starts at 1, and goes to 5 counting up by 1's.

If you changed it to 1 10 2, it would start at 1, ending at 10, counting up by 2's.

In the break condition put the formula(If metric):

baseSystem().valueA < 0.005

If you have PCM you can go a step farther and make the program stop if the break condition is never satisfied by clicking the parameter button and putting the following code or something like it in the Postsettings

align_value = baseSystem().valueA

if align_value > 0.005 then
	message("The alignment value was "+align_value+ "  (Max: 0.005), this means the part is dirty, loaded incorrectly or moved during probing, so the program will stop"+cr()+cr()+cr()+"																Please reload the part and try again")
	endInspection("NO_DATA_OUTPUT")
endif

[[Si...]]

Ok thanks. Ya i use the Loop alot. Thought it was a different action specifically for Alignments. Thanks.

[[Ni...]]

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Thanks, I have been using this and for programs programed in inches I was afraid that it was still looking for a metric value. .0005mm would be a little over kill.

[[Ow...]]

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If I remember correctly, there was a time back several years/versions ago that it only used MM.

What I don't understand is why Zeiss hasn't given us the ability to stop the program without PCM if valueA is not met.
I think I submitted a suggestion years back to put it in the start menu screen where you choose what alignment to run and could also choose a tab/button to loop it and stop program if alignment loop is not satisfied. You can report the value using a result element so, you know it was or wasn't met but, that's too late.

[[Th...]]

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I think this change was somewhere around 6.4. Used to have it written down since I had to be careful not to do unit conversion in bad places, but that notebook's long gone.

[[Je...]]

Please review the ZEISS PORTAL KNOWLEDGE BASE

https://portal.zeiss.com/knowledge-base ... &id=420709
https://portal.zeiss.com/knowledge-base ... &id=410949