Automatic CAD Assemblies Generation by Linkage Graph Overlay for Machine Learning Applications
Communication avec acte
Abstract
Enlarging 3D model databases by shape synthesis is a large field of research. Indeed, the use of
machine learning techniques requires a huge amount of labeled CAD models, and it is therefore
crucial to rely on large and varied databases. Most of existing works in shape synthesis focus on
everyday life objects generation [1]. However, these methods often do not work on assemblies
composed of several CAD models, and it is the aim of this paper to develop a new shape synthesis
method to enlarge existing CAD assembly databases.
Today, there exist lots of free databases of non-labeled CAD models (e.g. GrabCAD, 3D Warehouse,
Turbosquid) often available as STEP or IGES files. Unfortunately, very few of these databases are
labeled. Other databases like PartNet [2] and ShapeNet [3] are currently labeled by crowdsourcing, but
they do not contain complex mechanical assemblies.
Current works in shape synthesis often use auto-encoders to generate new coherent CAD
assemblies [4]. Moreover, there are probabilistic models to create diversity in large 3D Database [5] or
to classify 3D assemblies [6]. Those techniques often use linkage graphs [7] to classify and generate
new coherent assemblies. Furthermore, information within the linkage graphs differs according to the
method, and those graphs are not suitable for complex CAD assemblies like hydraulic pumps. But the
main issue of all methods is still that those databases have to be labelled.
The method explained in this paper consists in creating new labeled CAD assemblies from existing
ones by linkage graph overlay. Here, the STEP file format has been adopted in order to be the most
reproductible and to be adaptable. The linkage graphs are automatically created thanks to the
identification of the linkages between the components. Indeed, linkages are not included in the STEP
files and they need to be computed. Theses linkage graphs are then analyzed and components with
similar linkages are detected. Finally, once the similarities detected, the corresponding components
can be exchanged to created new assemblies for which the labels can be directly inherited from the
source assemblies.
The contribution is threefold: (i) a method to create linkage graphs from existing non-labelled CAD
assemblies; (ii) a method to recognize basic components using linkage graphs; (iii) a smart overlay
method to replace some components while keeping the coherence between all the components of the
assembly. The algorithm has been implemented in Python on FreeCAD and it has been tested on
several test cases. Figure 1 shows the overview of the method, from the graph synthesis to the
components overlay, finishing with the replacement of the components. The results are presented and
discussed, and a conclusion ends this extended abstract while discussing the next steps.
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