How to measure 321 alignment and iterate alignment

huangyhg

Alignments:
  
First of all, to do ANY alignment, 3-2-1 or iterative, you MUST have XYZ values for whatever you use for the alignment.
  
Step #1  
Do this no matter WHAT type of alignment you are going to do.
1) Place the part on the table the way it will sit for your inspection
2) Import your model data BEFORE you do any measuring
3) Using the CTRL-F3 option (3-D rotate), rotate the cad data until it matches the way the part sits on the machine, remembering that as you look at the screen you are looking DOWN on the machine
4) Once you have the cad data rotate (you are actually ONLY rotating the VIEW of the cad data), use F5 to open the setup options.
5) Go to the Part/Machine tab and while looking at the 3-D rotate cube, set your CAD to MACHINE axis
6) Click OK
7) Set your workplane to the ‘top’ of the cube (if the top, facing YOU face of the cube is X-, use the X- workplane)
  
You are now ready to do an alignment.
  
Iterative alignment
1) You need to know WHAT the datums are that you have to use for alignment. Use CTRL-F to open the AUTO FEATURES window
2) Select the type of feature you are going to use (vector, surface, circle, etc.) and pick that feature from the model
3) Create the feature, BUT DO NOT MEASURE IT!
4) Continue until you have all the features you need for your alignment, remember, ALL circular feature types NEED a minimum of 3 surface sample hits (circles, cylinders, cones, slots)
5) Print out the graphics screen for a reference of where the points need to be measured
6) Mark all the features and execute them, measure them as close to where they need to be as you can. OPTIONAL, do this here or at STEP 13
7) Go into the alignment and then into ITERATIVE alignment
Select the (minimum of) 3 ‘level’ features
9) Select the (minimum of) 2 ‘rotate’ features
10) Select the (minimum of) 1 ‘origin’ feature
11) Set the tolerance to high values, I use 10mm radius and 1mm fixture
12) OK out of the iterative window and the alignment window
13) Mark all the features an execute the program, and measure the features as close to where they go as you can, this is the second place you can do this, but if you didn't do it as step 6, DO IT NOW!
14) You are now aligned
15) Turn on DCC mode and repeat steps 1 to 10, making the program executable, meaning it will run without crashing. HOWEVER, for the tolerances, at this point, I use 0.5 for radius and 0.05 for fixture. ALSO, mark the MEASURE ALL ALWAYS box in the iterative window
16) Now, program the checks of the part
  
3-2-1 alignment (mostly for holding fixtures)
This is a very easy alignment, however, you will have to think back to 2nd or 3rd grade when they taught you to use a number line (you’ll see)
1) All the alignment features on the fixture SHOULD have XYZ values stamped on them. For this example, I will use a plane, and 2 lines (top corner of the fixture base)
2) Measure the plane, making sure that all the touches are EXACTLY where you want them to be
3) Measure a line (the longer edge of the base) for the ROTATE, making sure of the DIRECTION of the line
4) Measure the second edge of the base (direction makes no difference)
5) Construct a point at the intersection of the 2 lines
6) Now, you need to know exactly WHAT each of those features represent. We will say that the PLANE is for the X+ axis, the rotate line points in the Y+ direction (first to last point taken on the line) and we need to know they XYZ value for that corner of the fixture base
7) Open the alignment window
Level X+ to the plane
9) Rotate Y+ ABOUT the X+ axis to the rotate line
10) Set the X origin to the plane
11) Set the Y axis to the corner point
12) Set the Z axis to the corner point
13) Now, it is time to offset the origins. This is where the number line comes into play
IF the X value for the top of the base is equal to 1250mm, then you need to offset the X origin –1250mm. What you are doing is telling Pcdmis the direction (in this case -) and the amount to move the ZERO point, which right now is located at the corner of the base. This will make the base equal to X1250.
  
Do this for each of the axis, remembering that you are telling it the DIRECTION and AMOUNT to move the origin AWAY from where you have the origin set to.
  
So, for the corner values of the fixture at X1250, Y-250 and Z2321, your offsets will be X-1250, Y250 and Z-2321
  
14) Click on CAD=PART
15) Close the alignment window.
You model should now be ‘floating’ in space about the alignment features just like it does on the fixture.
16) Go into DCC mode and program the alignment as an executable program (one that will run without crashing). The reason for this is simple, the machine will give better, more accurate touches than you, the operator can. The speed of the touch CAN and DOES have a big impact on the final results Pcdmis see for the touch. Faster or slower can change the comp of the point, so use DCC. Not only that, but if you have to re-home the machine or re-calibrate the probes (for whatever reason), you need ONLY run the DCC portion of the alignment, the manual can be left un-done, as long as the fixture has not been moved on the table
16) Program and check the part.
  
I use non-iterative alignments almost exclusively and I never have any problems or issues with them. I also keep the alignment as a separate program, saving the alignment to an external file, then recalling that external file in my check programs. In this way, I can have multiple programs to check various portions/operations of the part WITHOUT the need to align multiple times. Sure, you can cram it all into one program, but that will slow Pcdmis down. Also, by using separate check programs, I can send the various data sets to different Datapage files.
  
The biggest advantage to the 3-2-1 CAD=PART alignment is it's ease in adjustment. You can easily adjust your pick-up values to fine-in a holding fixture without trying to figure out what-in-the-hell each individual point in the iterative alignment needs to be to get the desired effect, just change the offset for that axis, find and click on CAD=PART again (do it twice, in V3.7 MR3 it does not 'cathc' it the first time) and re-check the features.