Mixing Synchronous and History

Sometimes I think the Synchronous message gets a little bit garbled. We get so caught up in stressing the strengths of Synchronous Technology and dinging history-based modeling that we tend to forget what we are really promoting is not one method, but a combination of the two. It’s true. History-based modeling has strengths, although they might not be strengths you recognize. To me, the most important strength of history-based modeling is the ability to remember topology that gets eliminated by subsequent features. The most limiting weaknesses of history-based modeling are that the design intent is hard to change and that parent/child relationships make feature failures common, and force the concept of “rebuild time” which users of direct editing methods haven’t even heard of.

Synchronous Technology belongs to the direct edit family of CAD tools. Synchronous is really direct edit plus several other tools (driving dimensions on the model, live rules, face relations, procedural features, features as face selections, selection methods, and other stuff). Synchronous Technology’s main strengths are the tools that allow you to determine design intent at the time of the edit, and the ability to make changes directly to the model without working indirectly through a series of sketches and dialog boxes. The main weakness of direct edit methods is that they cannot remember topology that has been removed from the model.

What do you notice about these strengths and weaknesses? That’s right: they line up. The weaknesses of one are the strengths of the other.

Now if you had to pick one method or the other, you’d be kind of up the creek, so to speak. But the lucky thing is that by using the two methods together, each method counterbalances the weaknesses of the other. This makes it easy to determine when to use which method. To avoid parent/child entanglements, use Synchronous. To avoid problems with topological changes, use history.

Here’s a practical example.

Prismatic/analytical model faces can be broken up into several types, as shown below.

Using faces with identifiable topological forms make it easy to edit and extend those faces. Complex faces cannot be extended because they are made from splines that are not predictable – the form of the spline can be any shape the user wants to make them, so the software is not able to predict what the user wants. The word “topology” means the type, number and connections between the faces in a model. A cube has 6 planar faces connected at linear edges. A sphere has a single spherical face. A cylinder has one cylindrical and two planar faces. These are all descriptions of topology.

Sometimes, an edit may remove a face from a model.

Notice that the boss on the left has a couple of fillets that cover over the planar and cylindrical faces of the original. The faces shown in the green image are removed from the gray image. This is where direct edit methods, including Synchronous Technology fall short. This demonstrates the problem, now let’s demonstrate the solution by bringing Synchronous Technology together with history-based modeling.

In this screenshot, you can see the Solid Edge Pathfinder, which is the equivalent of the Works FeatureManager. Notice there is a Synchronous section that lists the synchronous features, which to a Works user is going to just look like a selection of faces for each feature. And you also have an Ordered section of the tree. The Ordered section is really history-based in the same way that your SolidWorks FeatureManager is history-based. A Works user will think of the Synchronous section of the tree as an imported body, although it is more than that, we can work with that definition to get you rolling.

If any of the fillets were to totally consume any face, you would not be able to use Synchronous to make an edit and get the missing face back, as shown in the 3 images above, but if the fillets are ordered you can.

This is what I consider to be the best way to use the strengths of both Synchronous and Ordered modeling methods in a single Solid Edge model. The most common source of failures in Synchronous edits is fillets/rounds. So by making those Ordered features, you eliminate that weakness. The adaptability of fillets is a strength of history-based modeling. So for this part, you can edit the overall prismatic part using Synchronous/direct methods, and you edit the fillets using history/ordered methods.




Updated: October 3, 2013 — 12:07 pm


Add a Comment
  1. I fully agree. And when we get to our industrial design customers, history based modeling is still the king! And ST6 gave them some very good enhancements on the surfacing area. In this case, their use of synchronous is minimal. Also, parts with patterns of hundreds of features (holes, ribs, etc), must have those features done in history, or else ST will have a really hard time to dinamically apply the live rules and make everything change respecting the design intent. So, I believe that mixing both methods will bring the best of both worlds into the 3D modeling process.

  2. I run into this all the time with procedural features in synch (holes, rounds, etc.) They are kind of like an ordered feature except they fail often. I keep trying them but a lot of the time I just do this type of feature in ordered. Remember, you can always base an ordered feature on a synchronous sketch and edit it dynamically.

  3. Matt

    Thanks for the honest pros and cons. I hope SE marketing types don’t panic. What I hate the most is being sold a product that promises far more than it can deliver event when it delivers a lot and claims of miracles are not needed or appreciated.

    I had just the opposite mind set before reading this article for the second time. I thought the main structure was better in history/structure approach with the rounds added with the ST/direct approach as the final details. But it sounds like it is just the reverse.

    So if I were to create in SE using the structured approach for 100% of a design. When it comes time to edit can I use just ST/direct method for changes and retain the history. I know nothing is 100% but for the most part would I not need to go back into the sketches to make the edits?

    As I have said in the past my hands-on experience with 3D is very limited. I have had the training and worked with engineers using PTC and SW. When trying to work out a geometry leaving the model to go to the sketch trips my thought pattern. Doing a push or pull for a what if situation without a model failure would be big plus.


    1. Joe, while Solid Edge does have a form of direct edit in the Ordered mode, to be able to edit it in Synchronous, the features must be moved to Synchronous.  This happens by selecting the point in the Ordered tree where you want to edit and select a command that moves it and all upstream features to Synchronous.  Once there, you cannot move them back to Ordered.

    2. Joe, what kind of products do you make? That will help decide how much to put in Synchronous vs Ordered. In general, extremely complex castings and molds should go in a mixed tree. Machined and most straight brake sheet metal are stars in Synchronous. And there is a spectrum in between (in the example Matt used, I would have put it all in Synchronous because there are no consumed faces — but that is the point — to each his own — we don’t dictate your favorite flavor).



      1. Dan

        I just started out on my own and really don’t know who my clients will be. First project needed very little CAD and 2D was plenty. Very thin ME market in WY. I worked in what would best be described as a consultant mode in an extension program with a university. Did that for about 5 year and previous 30 years, auto, aerospace, capital equipment. 20 of the 30 yrs in management with limited CAD assignments. During the five years a real mix, plastic prototypes, small structures, lifting equipment, jack stands for CAT trucks, work platforms and special ladders. Most jobs one off one time deals. The only one that needed 3D was the plastic prototype. A coworker used my 2D to make a 3D model for the 3D printer. Other companies use 2D or paper, pdf prints. I am now researching both business niches in WY and CO, and CAD systems.

        I am glad someone mentioned you can’t go back and forth between ST and ordered. One company I would like to become a contractor with uses Inventor for heavy equipment. But there is no guarantee of work so that is not a good reason to go with Inventor. The ME manager said they are Ok with other 3D systems. So if I get an Inventor model and change some of it to ST there is no going back. So how would the client using Inventor handle the model 1) made with all ST, 2)part ST, or 3)an Inventor file revised in SE with a mix of structured and ST?

        1. Look first at JT file format and see if you can achieve something.

          Then parasolid and Step might be the next logicical step to look at

  4. I’ve been working in a mixed ordered/sync environment for a while, but SE does not allow you to freely go back and forth between sync and ordered for the reasons mentioned already.  That is something that is often overlooked in the demos, but becomes more of an obvious issue after some time running sync.

    Perhaps the live rules from sync should also be added to the direct edit commands in ordered.  This would give a lot more design freedom, plus would be useful for those people not as willing to move to sync.  For ordered parts that have a short recompute time sometimes it is nice to keep that history tree even if it has been removed from the topology, because you may want to go back to them and they cause very little overhead.

    ST6 has come a long way, but in the big picture that is very short for CAD software.  After you get used to sync, it is not hard to see there are still many big enhancements that will be coming for a few years before key modelling tool changes slow down like the modelers that have been around a while.




Leave a Reply

Your email address will not be published. Required fields are marked *

On The EDGE © 2013 Frontier Theme