Documentation

Constraint-Joint Mapping in Simscape Multibody First Generation

In Pro/ENGINEER®, unconstrained parts have six mechanical degrees of freedom (DoFs) that describe how the parts move with respect to each other. Of the six degrees of freedom, three are rotational and three are translational. Applying a constraint between two parts eliminates degrees of freedom between the two parts. Constraints can remove between zero and six degrees of freedom.

Degrees of Freedom in Simscape Multibody

Simscape™ Multibody™ First Generation assigns zero degrees of freedom to an unconstrained rigid body. Connecting the rigid body to a joint or constraint block increases the mechanical degrees of freedom available to the rigid body.

Rigid Body ConditionFirst-Generation DoF
Not connected to joints, constraints, or World Frame0
Connected to Joints or Constraints blocksAdd degrees of freedom according to joint or constraint

CAD Constraint – Simscape Multibody Joint Mapping

During CAD export, Simscape Multibody Link maps Pro/ENGINEER constraints between parts to Simscape Multibody joints between rigid bodies. CAD constraints and Simscape Multibody joints do not follow a one-to-one correspondence — multiple constraints can map into a single joint. All Simscape Multibody joints contain a combination of three joint primitives: Prismatic, Revolute, and Spherical. The Weld Joint block contains zero joint primitives, and therefore zero degrees of freedom. The following table identifies the degrees of freedom of each joint primitive.

PrimitiveAbbreviationMotion TypeNumber of DoFs
PrismaticPTranslational1
RevoluteRRotational1
SphericalSRotational3

Supported Constraint Entity

Depending on the constraint combination, Simscape Multibody Link utility supports the following Creo™ constraint entities:

Entity Description
Circle/ArcCircular edge/arc sketch segment*
Ellipse/ArcElliptical edge/arc sketch segment*
ConeConical face
Cylinder Cylindrical face
Line Linear edge/sketch segment/reference axis
Plane Reference plane or planar face
Point Vertex/sketch point/reference point

* A complete circle or ellipse is a special case of a circular or elliptical arc.

Supported Constraint Entity Combinations

The following sections list the constraint-entity combinations that Simscape Multibody Link supports for different constraint types.

    Note:   If the Simscape Multibody Link exporter cannot translate a constraint–constraint entity combination into a supported Simscape Multibody joint with DoFs, it converts the combination into a weld (W) primitive.

Coincident Constraint

The following table identifies supported constraint-entity combinations for constraints:

  • Align without offset

  • Mate without offset

  • Point on Line

  • Edge on Surface

  • Point on Surface

A ✓ indicates the combination is supported.

Constraint-Entity 2
PointLinePlaneCylinderConeCircle/Arc
Constraint-Entity 1Point     
Line    
Plane   
Cylinder   
Cone   
Circle/Arc  

Insert Constraint

The following table identifies supported constraint-entity combinations for the Insert constraint. A ✓ indicates the combination is supported.

Constraint Entity 2
PointLinePlaneCylinderConeCircle/Arc
Constraint Entity 1Point      
Line    
Plane     
Cylinder  
Cone  
Circle/Arc  

Align or Mate Constraint with Translational Offset

The following table identifies supported constraint-entity combinations for the Align or Mate constraints with translational offset. A ✓ indicates the combination is supported.

Constraint Entity 2
PointLinePlaneCylinderConeCircle/Arc
Constraint Entity 1Point    
Line     
Plane   
Cylinder      
Cone      
Circle/Arc      

Align or Mate with Rotational Offset

The following table identifies supported constraint-entity combinations for the Align or Mate constraints with rotational offset. A ✓ indicates the combination is supported.

Constraint Entity 2
PointLinePlaneCylinderConeCircle/Arc
Constraint Entity 1Point      
Line     
Plane     
Cylinder      
Cone      
Circle/Arc      

Supported Simscape Multibody Joints

The Simscape Multibody Link utility supports the following Simscape Multibody joint-primitive combinations.

Limitations

The following limitation applies to CAD export from Pro/ENGINEER.

Weld is Default Joint

If the Simscape Multibody Link utility fails to translate a CAD constraint, a Weld joint replaces the constraint.

Was this topic helpful?