Self Correct Alignment

[[Lo...]]

Good afternoon. I have a question regarding alignment features. I was taught it was best practice to never use features that are being used for alignment, for measurement. In order to accomplish good measurement, you have to first align, and then measure the features again for dimensioning. However, I am being told that Zeiss has a capability to correct its calculations so that you can use alignment features for measurement. Is this correct? Thank you.

[[Ma...]]

You want to have robust and stable base alignment - so here it can be done by various strategies and evaluations depending on norm you are using.

So it depends on your features and it's measured data.

If your features are measured on correct places ( aka not touching other elements ) then it can be used for characteristics. Otherwise make copy of those features and make new strategy and so on.

[[Mi...]]

My favourite method for aligning a part in Calypso:

Simple, Fast Start Alignment, always done with points/point strategies in circles or planes. Often only controls 5 DoF for ease of manual alignments. Large Clearance/Retract/Search distances to help find the part.

Then a complete Base Alignment that measures all the features as completely as they would need to be measured for their use in a program, so they do not have to be measured again. Most often I try to use at least 1 of main datums. However if the features are extremely large or complicated I will pick something else because of the next step.

Add the loop to the Base Alignment which will remeasure the Base Alignment features multiple times essentially until you get 2 times in a row with a very small error (a limit you set).

IF you setup the Base/Start Alignments properly, and measure them with good strategies, there is no reason not to use those features for evaluation. If fact, since they will loop, the argument could be made that they were measured better than anything else.

[[Lo...]]

Thank you both for the replies! Greatly appreciated.

[[Lo...]]

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Hello again Michael
Thank you for your reply here, I would like to clarify if I am understanding this correctly. So the start alignment locates the part in the CMM coordinate system, then the Base alignment sets a basis for measurement?
Right now, my concern is that we are currently just setting a base alignment, and then we are using features from that base alignment to create dimensions. I was always trained to not use alignment features for measurement. The idea being that until your alignment is complete, your 6 degrees of freedom are not controlled yet, so that data from those features is not complete.
You would want to remeasure those features after alignment to create dimensions with. The XYZIJK in the alignment features essentially becomes "old data"

[[Mi...]]

Calypso updates all the features after calculating the alignment. That's why it's safe to use them.

To prove this, if you have PCM, in the Postsettings of the features put display(getActual().x).

When the program runs it will display the initial value that is relative to the previous base alignment... but if you check stop the program sometime after the base alignment calculates you'll see a different number in that feature's actuals than what is in the display window. If you stop it before it calculates the alignment, it will be the same number.

That plus looping the base alignment makes it safe to use your features for measurment.

[[Lo...]]

Amazing. Zeiss is powerful software. Can you explain to me in laments terms the difference between the start and base alignment? I have had to no training yet and I am trying to get my fundamentals down. Thank you for all your help.

[[To...]]

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The base alignment consists of the features you want to use to control the 6 degrees of freedom. The start alignment allows you create a simpler alignment so operator doesn't have deal with a more complex base alignment. After the operator performs a manual start alignment, the cmm performs the base alignment in cnc mode. You will need to create the base alignment first, then you can create the start alignment.

For example, let's say you have a base alignment on a block and you are scanning polylines on all of the planes. You can create a plane on the top for the Spatial rotation and the Z origin. Next, you can create a plane on the front or the Planar rotation and the Y origin. Then, you create a plane on the right side for the X origin. Now, you could then create a start alignment but creating a plane with 3 points on the top, a line with 2 points on the front and a point on the right side.

[[Lo...]]

Thank you for the help Tom! This is very helpful, I will use this. I am still wrapping my head around how easy Zeiss makes things. The fact that the software goes back over the alignment and updates it so you don't have to remeasure those features for measurement is amazing!

[[To...]]

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Start alignments are not required. You will need to determine when to use them or not.

In the example below, the top is the spatial and z origin, the 2 sides are the planar and the cone underneath is the x and y origin. It would be tough to ask an operator to manually probe the cone. A start alignment was created on the ball to the right using a sphere for x, y and z origin. We leave the spatial and planar features blank, as the fixture holds the part square to the table. There is a second component of the fixture that clocks the part using the 2 holes in the fixture.

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