Package CAD model: cve.util.cad.bom

Import instruction :

import cve.cad.bom

About :

CAD Package

Content

Mechanism
Bill of material (BOM)
Converting CAD data to BOM
B-REP model information
Kinematics constraints
Producing urdf files
Reference API

Mechanism

A Mechansim is a complete scene including several independent mechanical systems. Every system is referred by its bill of material. But a mechanism manages also the kinematic constraints between articles.

The Mechanism class implements the concept.

Bill of material (BOM)

The bill of material describes the hierarchical decomposition of a mechanism. It is made of assemblies which can be decomposed into sub-assemblies until basic components (or part)

Both assembly and component inherits from the abstract Article class.

Converting CAD data to BOM

The cadconverter tool read a STEP file and returns a json file containing a full description of a BOM plus detailed information of comppnent B-REP model. Every component is also converted into a wavefront file.

step2asm.py stepdirectory output resolution scale

An article of the BOM manages its colors and mechanical informations of the parts, mass, inertia, center of gravity, etc. The part is associated to a topological surface

B-REP model information

A B-Rep model (Boundary representation) is the core model of most Manufacturing CAD software. A component (part) is a volume which is described by a compact surface, ie, a closed, orientable, oriented and not self-intersecting surface.

Such a surface is usually described by a set of connected patches. We call it a Topologic Surface, which is a set of Faces. A face has shape among various types: either a sphere, a cylinder, a torus, a plane, a cone or a free-form. Each shape has its own definition parameter.

Kinematics constraints

Kinematics constraints define potential mobilities between components.

Producing urdf files

Classes

Class	summury
Article	A class modelling any item in an assembly tree from root assembly to part sheet.
Assembly	An assembly is a node of a bill of material that contains sub-nodes
Ball	Center of T1 and T2 are merged
Component	A Component is the deeper node of a bill of material.
Configuration
Constraint	A Constraint makes a link between two articles
Cylinder	A Cylindric constraints two articles lines to be alined
FrameSequence	A Frame sequence is just a list of frame names
Gear	A gear constraints two articles to get connectes speeds
Joint
Mate	A mate defines a connexion of two faces
Mechanism	Define a complete Mechanism
Plane	planes (x,y) of the two articles are parallel at distance d
Revolute	Article1 and article2 have a common z axis
Rigid
Screw	z axis are alined and d depends on alpha or this versa through the step definition
Slider	Article1 and article2 have a common the z axis

Functions

Function	summury
extract_article_bodies(articles=set(), article_body={})	Extract articles bodies : set of articles with fixed connexions (more…)
extract_bodies(articles=set())	Extract bodies : set of articles with fixed connexions (more…)
extract_body_constraints(b1, b2)
extract_kinematic_model(bodies=[])

Functions details

extract_article_bodies

def extract_article_bodies(articles=set(), article_body={})

Extract articles bodies : set of articles with fixed connexions Provides a set of articles and go inside the article tree to extract the fixed subsets

Article is fixed respect to is father when it is locked or fixed with another article when an explicit fixed constraint is existing

→ articles : root articles
→ article_body : a dictionary : for each article the set of parts which in a fixed constraint
← article_body : the updated value

extract_bodies

def extract_bodies(articles=set())

Extract bodies : set of articles with fixed connexions Provides a set of articles and go inside the article tree to extract the fixed subsets