Synchronous Features vs History Based Parametric Features

In my series on Synchronous Technology in Solid Edge ST3 I referred to synchronous features as a collection of faces. While this is true, thinking of synchronous features merely as face sets does tend to simplify the concept a bit. My idea was to keep it simple for my readers and concentrate more on the new concepts involved in the the feature tree in Solid Edge ST3.

Back in 2008, Dan Staples, the Director of Development of Solid Edge, wrote a paper titled “Explaining ‘Features’ To A Traditional CAD User“. It was an internal document and not designed to be external facing. In one of our conversations he shared the paper with me and I asked him if I could publish it on this blog. I’m glad he agreed because I really couldn’t do a better job of explaining synchronous features and how they compare with traditional history based parametric features.


Explaining “Features” To A Traditional CAD User

Dan Staples (12-May-2008)

Synchronous Technology has been described as “feature-based”. However, features in Synchronous Technology have some differences from those in Traditional CAD. For existing users, it’s important to understand these differences at the outset. Looking at what really defines a feature can help clear this up.

At the highest level, one can think of a feature as a “unit of the model that one can address to perform various functions”. If one were to abstractly consider the desirable aspects of a feature, the following would be the key points:

  1. A feature is an identifiable unit in the “model content list” (called the tree view in some systems – known as Pathfinder in Solid Edge)
  2. A feature can be renamed
  3. A feature can be deleted as a unit
  4. A feature can be moved as a unit
  5. A feature can be edited using the original creation parameters
  6. A feature can be regrouped as an alternate feature
  7. Editing a feature should not regenerate unrelated features. The edit should be localized.

Considering  Traditional vs. Synchronous Technology and features, we can draw the following table:

Obviously the first three rows of the table are identical. In both technologies you can see the feature as a unit and rename or delete it directly. Let us then consider the last 4 rows and how the two technologies differ, though both are feature-based.

Edit as Created* — The notion here is that the parameters used to create the feature will be valuable during feature editing – and this is often true. In a traditional system, this is accomplished by keeping the sketches around and using them to drive the model. Thus, to edit a feature, you edit its sketch. With Synchronous Technology, the dimensional information from the sketch is automatically transferred to the 3D model, so the sketch is not used to do the editing. However, you still edit the feature using the dimensions you used to create it, or you can apply alternate dimensioning schemes for even more flexibility. A special type of feature, called a Procedural Feature, is created for holes and patterns where the key parameters are largely non-dimensional (hole type, count, etc.).

Move as Unit – Since traditional editing is done solely via the sketches, it is not possible to simply pick a feature in the Pathfinder and move it or rotate it. You instead, have to roll back the model and redefine the feature or move the sketch to accomplish this. In contrast, Synchronous Technology features, can be picked in the Pathfinder and moved by cursor or by dimensional value to a new location.

Alternate Feature Grouping – In traditional technology, the creation method permanently establishes the edit methodology. In other words, if you create two adjacent pockets which result in a rib between them, you will forever edit this as two pockets (unless you completely delete them and replace the construct with a rib). In contrast, in Synchronous Technology you can create it as two pockets, and later choose to dimension it as a rib construct, and even create a user defined “rib” feature to also appear in the Pathfinder.

Localized Edit – In traditional technology, any feature which comes later in the tree than the feature being edited will be regenerated, even though it has no relation to the feature under edit. In contrast, in Synchronous Technology there is no linearly regenerated feature tree. Rather, when a feature is edited, only those faces specifically addressed by the edit will be modified.

In summary, Synchronous Technology is truly feature-based, but in a more advanced way than traditional technologies. It enjoys the notion of a feature being an addressable unit, but with the flexibility of being able to change that definition at will, while localizing geometric modifications, significantly speeding design.