Creating Correlated Deviations   

This task shows you how to create correlated deviation annotations on an assembly component.

Correlated Deviation AnnotationsTop

A correlated deviation annotation represents a set of measures at specific locations in a certain directions. its values are defined using a measurement data file.
A correlated deviation annotation is created either on an assembly component (leaf assembly components type), on the assembly itself (parent assembly components type) or on a single flexible support.

 Refer to Creating Flexible Supports.

The correlated deviation annotation of an assembly component or support is contained in its annotation set:

A correlated deviation annotation is always associated with a positioning system in order to specify how the component is positioned when measured.

The correlated deviation must not overlap with a degree of freedom used by its positioning system, therefore a point already used by a mechanical joint of the positioning system cannot be used by the correlated deviation.

Input AnnotationsTop

Correspond to the correlated deviation annotations created on leaf assembly components or supports, they represent the input annotations or initial variation  of the component before the assembly process

The variation in the degrees of freedom restrained by the positioning system is null by definition.

The supports referenced by the mechanical joints of the positioning systems should be free of deviation (not referenced by a deviation)

Output AnnotationsTop

Correspond to the correlated deviation annotations created on Parent assembly components, they represent the output annotations, annotations to be verified or measured during the assembly process.

Note: the output annotations' positioning system is not taken into account during computation, the positioning systems being taken into account are the ones associated to the activities.

Positioning SystemTop

Reminder: a positioning system represents a set of mechanical joints for which you can lock or unlock translations or rotations.

The deviation positioning system must:

  • Be isostatic at least.

  • Be associated with the assembly component where the correlated deviation is created.

  • Contain joints between support and the assembly component where the correlated deviation is created.

  • Be empty when creating a correlated deviation on a support.


  • Component's correlated deviation annotations always have the same positioning system.

  • Datum reference frame created with the 3D Functional Tolerancing & Annotations workbench can be used instead of a positioning system in a deviation.

  • Clicking Generate Points button in the Deviation Definition dialog box generates default annotation points. These points are typical points where the component is the more flexible.

    Note: Generate Points button remains grayed out until you select a positioning system

Creating Correlated Deviations (Step-by-Step Scenario)Top

Open the BasicTaaProcess2.CATProcess document.

  1. Click Correlated Deviation in the Annotations sub-toolbar.

  2. Select the Plate Two Assembly component.

    The Correlated Deviation Definition dialog box appears.
In the Statistics Law frame you can select a measurement file to define the correlated deviation law.
When no measures file in the Statistics Law field is specified, each point of the correlated deviation is created according to a normal law with a mean of 1mm and a standard deviation of 0.1mm.
See Measurement Data.
  Selecting the Local Deviation check box lets you take into account the deviation where it is defined or to interpolate it on the assembly component.
  1. Keep the Normal law and default parameters.

  1. Select Positioning System.6 as the deviation's positioning system.

  2. Select the Deviation Points 2 open body on Plate Two where the annotation will be created.

  3. Click OK.

    Deviation Correlated.2 is created.