Origin in CATPart a brief overview

Among the first things you have to consider starting the design of a new part, is where to place the origin. In the early releases of Catia V5 there were no coordinate systems and the origin was only represented by the three baseplanes xy, yz and xz. Under the pressure from especially the car producers Catia V5 also become coordinate systems. They are crucial for this industry.

Two types

If we look as an example at the components of a car, you have two types of parts regarding positioning. Parts like the body panels, which have an absolute position in the car lines e.g. the hood, and parts placed relative other parts e.g. wheels and engine components.

Absolute Position

The first group are placed fixed relative a general coordinate system of the car. This general car coordinate system is placed using the front axle as reference. One example is to place the x-axis along the length of the vehicle, the y-axis on top of the front axle and z axis vertical. In this case you will have right hand system with negative x-values in front of the axle and negative z-values underneath the front axle. Some companies have therefore moved the origin of the car a certain distance in front and underneath the car to avoid negative coordinates.

In common these car parts are positioned by superposition of the CATParts origins. Important are that the corresponding geometry has the correct position and orientation regarding the origin of the part. These parts will hang around in space at their position in the car lines. When being used as carry over parts their position has to be controlled.

Relative Position

The engine has its own reference coordinate system in a CATPart, in which a general skeleton is included. In this case constraints are used to position the engines sub-assemblies and components on the skeleton with assembly constraints. There are numerous levels of sub-assemblies in which sub-skeletons are found . It is here to recommend that the origin of the parts is placed on a clearly specified interface position. An origin which is used to assemble the parts.

These CATParts are examples of the second group. Their position is explicitly a result of the environmental components. Just as the wheels are being moved by a modification of the rear axle position, the position of the pistons are changed by a distance modification between the cylinders. Important is to have a placement of the origin, which adopt to the functional constraints.



Positions are important
Thomas