Product wrongly aligned but still measured.

[[Me...]]

Hello,

We have a lack of clarity about a problem at our Quality and Control department. I hope you can help us out... Here is the problem:

We put a relative large to us product ( (200x400x100) (x,y,z) ) on our Zeiss Contura CMM. we get it delivered by us at the Quality department when its coming of an 5 axis milling machine. We keep the product in the clamp of the milling machine directly on our Contura. When we put the clamp on our Contura the operator accidentally put the clamp crooked on the measuring table. The clamp (and so the product also) were misaligned bij 2 milimeters on the X and Y axes. The operator did not noticed the the product was misaligned and started the program.

The CMM starts the alignment and did not give any errors. So the assumption is that even when a product is a (little) bit out of alignment that the CMM automatlicly adjusts the alignment in the software. (i hope i am clear enough, please tell me when i'm not). When the top side was measured there were no problems. But on the side of the product is a hole (around 4 milimeters) when the probe gets inside the hole the probe tip did not touched the side of the hole but the shaft touched the side of the hole, this is due to the mis aligment of the product.

So a long story short: due to the misaligment of the product we get wrong measuring value's, wich means that the CMM did not corrected the alignment of the product.

The Question:

How is this possible that the CMM did not give any errors when it is finished with its alignment?

And

Why didn't the CMM gave an error when its measuring the hole but got very far out of tolerances by around +/- 1 mm?
By my knowings the CMM gives an error with other products when the measured vallues are way out of tolerances or are out of 'reach'. Than the program is stopped and the stopsign is turned to red.

I would love to hear from you and hopefully with some answers! Also if some things are not clear enough, please let met know.

Kind regards,

Mark Hoefsmit.

[[Re...]]

This is why it is critical to loop your alignments. Also the results could be drastically different depending on if you have an active or passive head. But then if your part is out to the point where you are shanking your probes, this may not be picked up without some sort of logic, such as looking at the roundness of the hole.

[[Cl...]]

Base on all you stated, and without moving the work-piece to a more square position, my
initial solution would be to use a more robust start alignment & loop the base alignment.

[[Ow...]]

Not a simple answer and you really need to have a good amount of experience to use it but, I'll try.

I’m guessing the base alignment isn’t being looped.
Apparently, the clamp wasn’t off far enough to cause a crash (which would have stopped the measurement) and it wasn’t off far enough to exceed the feature search distance you have it set to (by default I think it’s 10mm). It was off far enough to cause the probe to shank out (shaft instead of tip) and report the wrong size.
To make that you're always measuring the part the exact same every time for the base alignment, you should loop the base alignment.
To loop the alignment, open up the base alignment and in the 1st window that opens up, you’ll see a tab in it that says “Loop”, click that tab and in the next window put 1 in the start, a 5 in the end and a 1 in the step.
Put a break condition in so the program knows to stop re-measuring the alignment when the condition is met. Your break condition should read like this: baseSystem().valueA<0.005. The numerical number (0.005) it’s trying to meet is the Delta value (explained below) .
What’s the Delta Value?
The Delta Value is a measurement of how much the Coordinate System has shifted from one measurement of the Base Alignment to the next. Delta is the accumulation of the X,Y,Z,X-Y Rotation and X-Y Tilt. The shift is the result of the data points being taken in slightly different locations each time the alignment is looped.

Using the condition ensures the part is in the exact same base alignment position it was when the base alignment was originally set. The program will run the base alignment features until it’s met the condition, as many as five times. THE PROBLEM could be that the condition is never met in the 5 times (you could adjust it to 10 or as much as 75) and if it’s not met, the CMM will still run. The only way you can stop the CMM from running if the base alignment condition is not met is if you have PCM.
If you want to cancel the run if the condition is not met, put this into the pre-settings of the first feature measured;

if (baseSystem().valueA>0.5) and (LOOP3==2)
cncBreak()
endif

[[Ow...]]

Wow, looks like 2 others replied while I typed mine...lol

[[No...]]

Calypso only gives an error if there is a serious problem, like:
* unexpected collision with the part
* no probing point found
* an essential calculation failed (e.g. alignment)

An out-of-tolerance measurement is not considered a serious problem (opinions differ here 🤣 ). However, a serious problem can of course go hand in hand with an out-of-tolerance measurement, so this explains why another program errored.

Long story short: If Calypso somehow makes it through a program without a serious problem, it won't ever throw a red-light error. Everything else is up to you as the operator. It's not uncommon that a Calypso program makes it through a misaligned part, but you have to expect the side effects you mentioned. It's entirely up to you to avoid them. For example, Calypso doesn't really know in which direction the probe shaft is pointing (it only knows the size and location of the probe tip), so it can not detect whether the shaft touches the part during a measurement or not. Exception: when this situation also causes a serious problem, see above...

[[De...]]

The machine has no method for knowing whether it is the probe tip or the shank of the probe that is contacting the part.
There is no underlying tech built in to the cmm for it to recognize when a probe is shanking.

Fortunately there is a tool for this; the human eye. There is no substitute for trained operators.

In order to avoid shanking it is not only critical for the part to be aligned properly, but the probes to be as well, given most probes only have something like 0.25mm clearance from the ball to the shank they need to be aligned precisely.

If you want to verify the part alignment, it is possible to create an alignment to the CMM coordinate system and then make a check between a feature measured on the part and a copy of it with recalled points in the CMM coordinate system, then stop the program if the angle is more than whatever angle you set. This likely will require you to have PCM to work.

So far as why the machine did not stop, the answer is pretty simple really, the machine is made to measure real world parts, and some people's / industries tolerance bands are wide open. Would you want your machine to stop every time you went to measure a +/- 2mm diameter simply because the machine's designers designers said so.

You could probably modify the default values for what kind of tolerances, although I am not sure what exactly you would want to modify without trying it myself.

I would have to assume this gave failing results, thats when the operator should have analyzed the results to determine the source of the error. I would expect that a simple check of the feature in question would have shown a massive amount of form error.

[[Re...]]

Like Derek stated - There is no substitute for trained operators and there is no tool like the human eye and experience.
Managers normally do not get the concept that it is very difficult to make a program dummy proof. Most of them believe that you can take anyone off the street and have them trained in days to be a metrologist. If they only knew the many things that can go wrong with inexperience. Of course I know that I preaching to the choir.

[[Ne...]]

The CMM will adjust the alignment of the part if it can successfully complete the base alignment. What the CMM will not
do is adjust the angle of probes to this new alignment. For example if you are using 3 planes to make your base alignment, along
as probing points are more than 2mm from an edge, the CMM could have taken the points and have a success full alignment.
As long as program was measuring the top of the part (which I assume is at 0,0 angle) the program ran fine. Once it tried to measure the hole on the side it tried to use the angle of the probe assigned to that feature and shanked out.

Neil

[[Ma...]]

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To answer your questions I agree you should loop the alignment. I would also, in addition to the other suggestions, add a characteristic at the top of my report that reported the deviation, or delta, of the looped alignment. To do this add a Result Element and create a formula as shown



Change the title to be something like "Alignment Deviation" this will show your operators that the alignment is good or not so good.

But your question is why didn't the CMM give any errors, well the alignment was created so no errors were given. And the questions about the hole. With the part so skewed you shanked the probe. The CMM will calculate the average circle based on the input data so it is most likely it had such bad data from measuring the ruby on one side of the hole and the shank on the other side of the hole. It is the not surprising you received such an out of tolerance hole.

To avoid the shanking issue, and I don't know if you have PCM, you could add a pre-setting that will check the squareness of the part. This example measures a plane that should be 17.9 degrees to the fixture

getActual("Error Proof Plane Measure").z
A1 = abs(deg(getActual("Error Proof Plane").a1) - 17.9)
A2 = abs(deg(getActual("Error Proof Plane").a2))

if A1 > 0.5 then
stepRS(0,150,50,())
message(" PART IS LOADED INCORRECTLY ",cr()," RELOAD PART AND RESET TRAFFIC LIGHT ")
cncBreak()
endif

if A2 > 0.5 then
stepRS(0,150,50,())
message(" PART IS LOADED INCORRECTLY ",cr()," RELOAD PART AND RESET TRAFFIC LIGHT ")
cncBreak()
endif


Mark

[[SH...]]

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If you want to verify the part alignment, it is possible to create an alignment to the CMM coordinate system


May I know how to create wrt Cmm coordinate??

[[De...]]

Create an new Alignment. Menu -> Resources -> Utilities -> Alignment

Then choose CMM System from the dropdown.

[[Ün...]]

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Mark merhaba,

Sapmaları görmek için bir sonuç elemanı ekledim ama değerler çok yüksek çıktı. Bir yerde yanlış mı yapıyorum

[[SH...]]

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Which language, Spanish??

[[Ün...]]

Hello Mark,

I added a result element to see the deviations, but the values were too high. Am I doing somewhere wrong

[[Jo...]]

Hi,
Quality master says "Do it right the first time", so why not adjust the part on your CMM table more carefully before running, or you can manully use your probe touch the hole inside to check whether your shank touches.
Looping your alignment is a better way to see alignment deviation,but if "valueA" is not satisfied,probe tip can touch,that means it is not necessary to adjust your part.So you can add pcm conditions at post-settings of the alignment features if you run by Feature Orderd to check the "form" value.From the "form"value you will decide to clean the feature or adjust your part. 🤣