Pro/Engineer February 2004 Tip-of-the-Month
When Reference Patterns Get Confused
When using multiple Ref Patterns, there are times when the patterning algorithms in Pro/E get confused as to how a pattern is to be controlled. This happens when a feature or assembly component references more than one other patterned member. In these cases, Pro/E doesn't know which to follow, so the pattern fails. (Or sometimes says it succeeds, but the patterned members are all coincident.)
Here is a very simple assembly example of another method. Figure 1 shows an animation.
Starting with the lead pattern part (green) a second, opposite part (blue) is assembled with a vertical constraint to the green part for a Ref Pattern. The 3rd part (white, partially hidden in the picture) is assembled to the first (green) part, with a vertical offset dimension from a datum of the green part. A 4th part (red) is assembled to the second (blue) part and by intent is assembled to the white part as well (for vertical reference).
(Note: In this case the red part could be place with a similar offset using a blue part datum, but to keep the intent, a relation would be needed.)
It is easy to create a Ref Pattern for the blue and white parts, but when the red part Ref Pattern is created, it fails. (X) Why? Because Pro/E can't distinguish which previous Pattern to Reference (Should it follow the blue part? Or the white? --- It has references to both.)
Solve this problem by the order in which the Ref Patterns are created. Assemble all 4 components first, then make the green part Ref Pattern. Next, pattern the white part with a Ref Pattern, then the red (also as a Ref Pattern). True, it hangs in space, but there is only one pattern for it to follow (because the blue part has not been patterned). Finally, create a Ref Pattern for the blue part.
Even though the pattern for the blue part is regenerated prior to the pattern of the red, because of the order of pattern creation, all the red parts reference the first blue part only and ignore pattern information for the other blue parts.
As with many things in Pro/E, order is important in controlling parent / child relationships. For more related reading, see the August 2002 Tip-of-the-Month on Understanding and Interrogating Parent/Child relationships, and the July 2001 Tip-of-the-Month on Modeling Tricks for Making Patterns.