Monday, July 25, 2011

Some Fun Direct Modeling with Chain and Sprocket

I hear the term "direct modeling" being used and abuse to describe many different things. To me direct modeling refers to a CAD systems ability to interact with edges, faces, features, parts and assemblies directly during the design process. It means that the CAD system is intelligent, not necessarily the geometry. It means that the CAD system can intelligently interact with geometry regardless of how or where the geometry was created – basically; “what you see is what you get”. There is already a lot of useful information in a solid body. A direct modeling system should be able to recognize this and take advantage of it. Here's an example.
Below is a video I created after doing some direct modeling with some drive chain and a sprocket using Creo Elements/Direct Modeling. As I mentioned in the video I am not sure how useful this is in the real world, but I found it interesting and wanted to share it. I personally have not done much design with drive chain since my brother and I designed and built a go-cart, about a thousand years ago. The chain kept falling off on those tight corners, (and I lost part of my eyebrow on another tight corner. "Wear a helmet, stupid" - Whatever!).
Chain is interesting simply due to the relationship from one link to the other. By recognizing the physical properties of the solid bodies that make up the chain, you can visualize some of these interesting behaviors, especially as it interacts with the sprocket.
For this example I started out by downloading the sprocket and chain in STEP format from a 3D content web site. I then created the simple shaft in the center of the sprocket. All parts are dumb solids, and there are no assembly relationships to begin with. In the “Position” function of Modeling there is an option called “Physical”. If you turn this option on, the system will recognize the physical properties of the 3D solid models, and recognize the relationships between models in real time (or very close to it). You will notice that I do eventually put a fixed relationship onto the shaft, but I apply no other relationships to the models or assembly. There are no “user defined” relationships defined between the chain and the sprocket, and there are no assembly references. What you see is what you get.

What I find interesting is the various ways of using the “Relations” capability together with the “Physical” option when moving parts. The system doesn't recognize gravity, acceleration or anything like that so it’s not doing kinematics. It simply knows moments of inertia, CG and the fact that these models are solid. And best of all – it makes no difference how the models were created or assembled, and on what CAD system they were created or assembled, (just had to throw that in).

Monday, July 18, 2011

Direct Modeling and Variant Design

Designing products with the help of a CAD tool that is history-based (some call it parametric modeling) has been the norm for many years now. However there are thousands of companies around the world that have been successfully designing products with CAD tools that do not retain modeling history. We call this technology direct modeling. It’s more than just modeling however. Depending our your product characteristics and processes, the flexibility that comes with direct modeling may provide a better environment and methodology for supporting your particular design environment. This direct modeling methodology is catching on and now spreading rapidly.

The technology behind this methodology is experiencing substantial improvement. With some of the CAD systems out there that are based on this technology it is now possible to parametrically control models and assemblies – without recording modeling history in an ordered way. The term “parametric modeling” can no longer be used to describe history-based modeling. Parametric modeling can be done with or without history.

The benefits include the fact that with the direct modeling methodology there is no need to plan ahead. Users can create and manipulate geometry anyway possible. Relations and constraints (design intent) can be added on the fly as need. There is no need for strict and consistent modeling practices. It simply makes no difference how you come up with the geometry. And it can work on any geometry; 2D, 3D wires, surfaces, and solids, regardless of where it comes from or how it was created. With direct modeling, geometry is the master, rather than the proprietary history tree.

In the past there were several areas where history-based modeling and the ordered model provided many advantages over history-free direct modeling. One of those areas was in regards to the development and management of family , or variant parts. The ordered structure made it relatively simple to represent a part in several slightly different states or configurations. With adherence to modeling standards and careful development of the 3D history-based model, the model can be “programmed” to support the family variants simply by changing a parameter.

Below is a video of doing something similar with history-free direct modeling using the PTC Creo product “Creo Elements/Direct Modeling” (“CoCreate” or “SolidDesigner” for the old guys like me.)
In this case I am starting with an IGES file just to highlight the fact that with the direct modeling methodology, it makes no difference where or how the geometry came into existence, or if proper methods were used in creating it. Perhaps this is an example of a model coming from a supplier that uses a different CAD tool. In this scenario we need to add some design intent to the model so that we can represent other variants that may be required of this part. With traditional history-based modeling this would require a model rebuild.

Perhaps in another video I can show you how the assembly configuration can actually be used to drive the configuration of this part.
Imagine a design process that does not involve planning ahead, ordered models, model rebuilds, strict modeling practices, proprietary data, regeneration failures and the mind-numbing web of relationships and references. Well, it’s not too far away.