About Constraints

An engineering connection is generally made of a set of constraints between geometrical elements of components or existing engineering connections.

This page discusses:

Constraint Types

Constraints define a mechanical relation between two components.

The following constraints can be created in an engineering connection.

Constraint Type Constraint
Advanced Symmetry
Compound
Projection
Tangency
Angle Angle
Parallelism
Perpendicularity
Hinge
Axis-Based Planar
Prismatic
Cylindrical
Revolute
Spherical
Universal
Common Contact
Coincidence
Offset
Curve Curvilinear distance
Roll
Slide
Fix Fix together relatively
Fix together
Fix in space
Fix

For more information about advanced constraints, see About Coupling Engineering Connections and About Coupling Engineering Connections.

Important:
  • A constraint can be created from scratch or by preselecting geometrical elements.
  • In case of preselection of geometrical elements, the first compliant constraint with the selection is created from the list defined in the Constraint Creation Order settings.
  • When you select only one geometrical element, the list of constraints is refined with constraints based on this geometrical element at least.
  • When you replace an existing constraint, compliant constraints with the geometrical elements of the current constraint are suggested.

    When geometrical elements defining the constraint are not compliant with the new one, a warning message appears and the previous constraint is deleted. You will have to select new geometrical elements.

Constraint Modes

The constraint mode defines the constraint behavior during the PLM Update.

Three constraints modes are available:

Option Description
Driving Restrains the relative motion of connected products during simulation (kinematics, Robot manipulation).

The constraint definition is applied during the PLM Update.
Measured Deducts the constraint value from its definition and other constraints of the engineering connection.

The constraint definition is applied during the connection edition and the PLM Update.

Note: Set Measured type to specify a sensor value (kinematics).
Controlled Defines the constraint controlled by the user (for example, the angle of a revolute).

The constraint definition is applied during the PLM Update.
Note: The variable value of a Controlled constraint can be:
  • Assigned to a controlled constraint in the kinematics command.
  • Defined between bounds.
  • Unset in the dialog through a contextual menu. This allows you to compute the value from the current position.
Important:

When a constraint leads to an unpredictable state, a warning symbol appears on all controlled constraints.

Constraint Options

Some types of constraints require orientation options in order to define the mechanical relation.

Orientation options are taken into account during the PLM Update. For more information, see Constraint Options.

Axis-based Constraint Options

Axis systems are the only geometry available for selection when creating an axis-based constraint. Coincidences are created between the planes or the axes of the axis system, depending on the selected constraint.

Note: Axis coincidence is available for revolute, cylindrical, planar and universal constraints.

The axis or plane can be selected in the Options column of the Engineering Connection Definition dialog box. By default, the two axis systems are aligned along the z axis. For more information, see Axis Systems Constraint Mode.

The two axis systems correspond to 3 unit vectors and 3 planes bound together in a 3D space. The value of each axis-based constraint is determined according to its mode and value type.

Constraint Mode Value Type Solving
Revolute Controlled

Angle between PA3 and PB3

Axis coincidence between A1 and B1

Plane coincidence between PA1 and PB1
Prismatic Controlled

Distance between PA1 and PB1

Plane coincidence between PA3 and PB3

Plane coincidence between PA2 and PB2
Cylindrical Controlled

Angle between PA3 and PB3

Distance between PA1 and PB1

Axis coincidence between A1 and B1
Spherical Driven

N/A

Point coincidence between O and Q
Planar Driven

N/A

Plane coincidence between PA1 and PB1
Universal Driven

N/A

Point coincidence between O and Q

Perpendicularity between A1 and B2

Constraint Supports

Constraints are based on supports that can be geometrical elements or existing engineering connections.

The following table lists the available geometrical elements that can be used as supports.

Element/Geometry Icon
Axis system
Circle
Computed Line
Computed Plane
Cone
Curve or Continuous curves or Sketch containing continuous curves
Cylinder
Linear edge or Line (from Generative Shape Design)
Planar face or Plane (from Generative Shape Design)
Product
Sphere
Surface
Vertex or Point (from Generative Shape Design)

For more information about engineering connections used as support see About Coupling Engineering Connections.

Important:
  • Some symbols can be displayed on the support icon to indicate its status:
    Status OK Error
    Free
    Locked
    Published
    Locked & Published
  • A support is automatically locked when the engineering connection is created or when you click Engineering Connection Templates .