Change Manager: The Gateway between Parametric and Direct Modeling

Several years ago, the concept of a mechanical CAD program that let you go back and forth between parametric and direct modeling environments seemed like a fantasy. In February, Autodesk announced its development team was on this quest. The Holy Grail of the coveted bidirecional workflow was to be Inventor Fusion. In Release 1, or Technology Preview 1, Fusion offered a way into direct modeling, without a way back to parametric modeling (for more, read "Autodesk Inventor Fusion, Ready for Inspection," June 24, 2009). But the most recent release, Technology Preview 2, fixed that.

Enter Change Manager, a plug-in for Autodesk Inventor 2010. The latest download of Fusion 2 contains two installation packets: a new version of Fusion and a plug-in for Inventor. (The later requires updates made available to subscription customers, so if you're not on maintenance contract, it might not work.)

I've seen a demonstration of Fusion 2 and Change Manager, seemingly showing how you might make a series of direct edits on a parametric part in Fusion and convert them into parametric edits upon import (that is, when you open the part again in regular Inventor), but I wanted to put this workflow to test on my own.

This week, I did just that. You can see the result in the video clips below:

Change Manager is, indeed, capable of translating direct edits into parametric features. But there are some limitations. Whereas it can easily recognize and convert direct edits that have correlating parametric counterparts (for example, dragging a face forward in direct editing is the same as adding extrusion distance in parametric editing), it has some trouble digesting direct edits involving rounded corners and blended edges.

Overtime, Fusion's direct-to-parametric translation algorithm is bound to improve, but I think it also illustrates the inherent differences in the two modeling methods. There are some direct edits that just don't have parametric equivalents. In a direct editing program, you might, for instance, rotate an extruded feature built with a complex profile into an odd angle, but it's highly unlikely such an edit can be translated into a series of parametric steps. I'm not suggesting that it's the shortcoming of parametric modelers, merely acknowledging that parametric programs aren't designed to accommodate such edits.

Eventually, Autodesk plans to incorporate the functions found in Fusion into standard issue Inventor, so parametric editing, direct editing, and Change Manager may all reside in the same environment.