# How to correctly use the RPS With Tolerances Alignment? ## Recommended Posts Often I have problem using the RPS With Tolerances alignment. I would like to know the correct usage. I want to align my particular using 2 circles for XY (that I want to be at zero) and 2 more points in Y for block the rotation (Y1 and Y2). For the Z only a point (Z). How can i do this with the RPS with tolerances alignment? NB: I have 16 cavities of this particular.  ##### Share on other sites Hi,

I think you don't need a RPS with tolerances, use a simple RPS but with one further construction step. Create a Division point from Y1 and Y2  and introduce this division point in the RPS calculation instead Y1 and Y2.

But it seems that there is another possible problem: Circle 1 and Circle2. You can't derive these circles directly from the geometry (it's position depends on the current alignment), therefore you have to define an alignment where these circles are calculated (and set the Required alignment option at the actual sections and the actual fitting circles), otherwise you have to use iterations in your RPS and these iterations will not lead always to a stable result (because we are automatically probe these circles again after switching into the calculated alignment if you haven't set a Required alignment). As a stable alignment for calculating the circles, I would recommend to use Geometric alignment with a cylinder (fitting cylinder), the bottom plane (fitting plane) and the division point for stopping the rotation.

Hope this helps?

Regards,

Bernd

##### Share on other sites I think that using only 1 Y it's not the correct thing to do, because I want that the possible error are divided in both Y (Y1=+0.05 and Y2=+0.05 for example) and putting only 1 Y can make this wrong (Y1=0 and Y2=+0.10). In attachment you can see the result of the RPS alignment with only RPS using 1 Y (division point from Y1 and Y2_ the first image is thw result with preallignment, the second with RPS and the third is the RPS alignment. I don't understand why RPS with tolerances don't use a simple gerarchy, so I can use circle for fix X and Y, and Y1 and Y2 only for block the rotation.

I tried to use the geometrical alignment with fitting cylinder, 1 point for Z and a line (costructed between Y1 and Y2) and the result is not what i want. See 4th and 5th images. So, how can resolve this problem?     ##### Share on other sites Hi,

unfortunately the forum is limited regarding analysis  of concrete data problems. It's not obvious to me why the division point still shows a deviation in your RPS.
Usually the deviation is symmetrically splitted on the points which are used for the construction (in your case Y1 and Y2). Are the normals of Y1 and Y2 are really pointing into the direction Y?

Regarding the Geometric alignment: The deviation in the points Y1 and Y2 are not forced during the alignment to be symmetrical . Therefore this result is reasonable.

Why is tolerance based approach no choice? You have to specify a tolerance bigger than zero for the point Y1 and Y2 and the algorithm only tries to compute a transformation where the target points are inside of the tolerance after the transformation. But it does not establish a symmetrical deviation (your input parameters could vary a lot, e.g a lot of points in Y direction).

If you can't find the reason for your problem, you have to contact your local GOM partner in your country and supply this project for a deeper investigation.

Regards,

Bernd

##### Share on other sites Ok, i send the project to my local GOM partner, but I think that a gerarchy could be a (simple) solution. If I have 16 stages, I can't define a + and - tolerance for all in the RPS with tolerance alignment. If I put XY circle to block the X and Y movement, the X and the Y rotation in the first and the second position, the third and the 4th position (Y1 and Y2) block only the Z rotation and with the last point I block the Z movement. I think this is easier and more stable than put manually a tolerance in the RPS that in the stages project could be a problem.

##### Share on other sites Why not? I used a line constructed between the 2 points. I really don't understand why for GOM is so difficult to put a cylinder to zero, a teorical line simmetrical to real line and a point at zero in Z.

##### Share on other sites Hello Marco,

I think it's best if your GOM partner has a look at the project. There are many possible reasons for the deviation but this analysis would be out of the scope of this forum. I'm sure with the data we'll find a solution.

Regards,

Nanno