Introduction

One of my favorite features of modern CAD systems is that you can use kinematic relationships of “mates” or “constraints” to position parts and assemblies relative to each other in a structure. This has the added benefit of creating a kinematic system that also mimics the movement of the structure when there are dynamic relationships in the design. These “dynamic” relationships can affect how these product s are visualized on the 3DEXPERIENCE platform in viewing applications such as 3DPlay, 3D Navigate, and 3D Compose. 

To better understand the challenges of viewing this data, let’s first take a close look at these kind of assemblies in CATIA V5 and SOLIDWORKS. Let's consider the dynamic assembly below, in CATIA V5,  which changes the direction of rotational power 90 degrees without the use of gears.

The designer has two ways they can structure the product and the constraints:

• Build a flat assembly with all constraints at the top level of the assembly
• Build a more realistic system where sub-assemblies are created and instantiated into the top assembly. This option reduces the number of overall constraints that must be created as they are already defined in the sub-assembly. This also results in product structure that closely mimics the assembly process downstream once the product reaches the manufacturing stage of development.

Flexible Assemblies

The example illustrated utilizes the second way mentioned above:

it uses two instances of a sub-assembly (Crankshaft Assembly). These assemblies have their own kinematic joints that must be defined. As you can see in the example, this introduces a problem – the subassembly cannot be “rigid” since the parts that make it up are different in each instance at  any point during rotation. This is the reason  CAD systems offer “flexible assembly” functionality:

 the system has the ability to ignore the static relationship that exists within the sub-assembly for different instances.

The various CAD systems on the market today provide different methods to create fleoxible assemblies:

 In  SOLIDWORKS, we assign the flexible characteristics through the Component Property page of the sub-assembly.

In CATIA V5,  this is applied directly to the sub-assembly though a context sensitive menu.

NOTE that in both of these CAD systems, a flexible assembly can be defined on a specific instance of the sub-assembly.

Managing flexible assemblies on the 3DEXPERIENCE platform

Since the CAD system allows different positioning of sub-assemblies in different instances, this presents challenges fo the current viewing technology of the 3DEXPERIENCE platform. The various viewers look at the CAD data in a specific “static” state (at one pont in time) when images and orientations are captured in the various players using CGR representations. 

If sub-assemblies exist, the derived CGR output is created from the sub-assembly and then used in the upper assemblies. This is true of all CAD systems managed by the 3DEXPERIENCE platform to offer an agnostic view of CAD in multi-CAD environments. This results in the 3D imagery not always being accurate as illustrated in the video below.

In the current releases of the platform, the only effective way to address this issue is to handle dynamic assemblies like this by moving all the parts that are affected to the top level of the dynamic assembly. Note that this is not always the top level as the dynamic part of the structure may be defined within the context of a larger machine system. We can see the result of a flat assembly in the video below...

3DEXPERIENCE viewing technologies continue to evolve to address these kind of CAD capabilities.