There are numerous means to get the same resultant alignment. One way will be shown in this article. Seeing as most people today utilize CAD models, the iterative alignment methodology will be shown along with a blueprint alignment. First, the CAD model must be imported; this is accomplished by going to FILE>IMPORT>IGES and browse to the specific CAD model needed for the project. Once the CAD file is imported, a probe must be selected, choose one that is in your library. Make sure that the correct angle is chosen; for this article the A0B0 tip will be used. When using CAD models generally a manual alignment and a Direct Computer Control (DCC) iterative alignment is created. The manual alignment basically tells the CMM where the part is on the table and the DCC alignment will further refine that location.

To begin creating the manual alignment, the AUTO-VECTOR window needs to be opened and points must be collected. The points that are collected are going to represent the six degrees of freedom that need to be constrained in order to have stopped all movement of the part. The points will first be collected by choosing them off of the monitor without actually measuring the created points. The first 3 points will be taken on the top of the demo block…

Next, 2 points are taken on the front edge…

And lastly 1 point is taken on another edge…

From these 6 points, an iterative alignment can be created. This alignment will establish a relationship between the machine’s 0,0,0 ; or “home” of the CMM, and where the part sits on the CMM’s table. Once the points have been created theoretically, it is time to measure them with the CMM. Once measured, go to INSERT>ALIGNMENT>NEW…

...from this window, the programmer will choose the button, “Iterative”, and begin selecting the points they want to include in the iterative alignment.  The first points chosen will be the planar points…

Next the programmer will choose the rotational and origin points (origin in one axis).

And finally the programmer chooses the last point to lock in the other origin axis.

This method follows the 3-2-1 alignment methodology and constrains all 6 degrees of freedom such that the part is locked into a complete alignment. Before clicking “OK”, the programmer must tick the checkbox “Meas All Once” and input a target radius…

… in manual mode PC-DMIS will then instruct the programmer to locate the probe such that it is clear to move to the points used in the alignment. It will now measure these points using the Point Target Radius as its way of gaging when the points have been measured precisely enough to the programmers satisfaction. This is the essence of an Iterative alignment. Merriam-Webster dictionary defines iterate as,”to say or do again or again and again”. So, until the points are found to lie within the radial boundary the programmer has input, the software will continue to align the part getting the points closer and closer to the CAD and part relationship until the boundary requirement is satisfied.
Once the manual alignment is completed the next step is to create points in the same manner as for the manual Iterative alignment except that the points will be measured during the construction of the DCC alignment.  Click the DCC icon and then set up a clearplane 1 inch above the part. Open the Auto-vector Point window and choose 6 points in about the same area as the manual points were chosen.

Once the points have been created, open the alignment window and go to the Iterative alignment window. Choose points PNT7, PNT8, and PNT9 for the planar portion of the iterative alignment, choose points PNT10 and PNT11 for the rotational and origin (origin in one axis). The next step is to tick the checkbox “Meas All Always”. This will instruct PC-DMIS to iterate the alignment/points via DCC until the radial requirement is met. Notice in the DCC alignment the radius requirement is smaller than the requirement placed upon the manual alignment. This is again, part of the theory behind Iterative alignment methodology. Each successive alignment is further refined such that the best alignment is achieved.

The last step in completing the alignment process is to now create an actual alignment that uses features on the part other than points. Create 4 points on the top surface of the demo block. With those 4 points create a constructed plane.

Next create an Auto-Circle in the I.D. on the left hand side…

Then create an Auto-Circle in the I.D. on the right hand side…

Between the 2 circles, create a constructed line…

With these features created, an alignment to actual features on the part can be constructed. Open the new alignment window (CNTRL;ALT;A), choose the plane (PLN1) that was created and click the “Level” button making sure that the plane will be leveling to the Z axis.

Next choose the line constructed (LIN1) for the rotational feature making sure that the X axis is chosen for the “rotate to” function, and the Z axis is chosen for the “rotate about” function. The X axis was chosen instead of the –X axis because of how the line was created. Cir1 (on the left) was chose first and then CIR2 (on the right), thus the vector of the line starts in the –X axis and aims towards the +X axis, click the “Rotate” button…

Next, the circle on the left will be the origin point, so it will be chosen for the X and Y axis origin, click the “Origin” button…

The last thing to do to create a part alignment is to lock the Z axis from movement. This is accomplished by choosing PLN1 to be the origin for the Z axis, click the “Origin” button…

Click “OK”, the part alignment is now completed. Measure another circle at the X=0 and Y=0 I.D. and the programmer ensures that the alignment has been completed successfully…

Note - This is only one example of how to complete the alignment process. Other methods may be more appropriate than another.

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