# Documentation

## Mate-Joint Mapping in Simscape Multibody First Generation

In SolidWorks®, unmated parts have six mechanical degrees of freedom (DoFs) that describe how the parts can move with respect to each other. Of the six degrees of freedom, three are rotational and three are translational. Applying a mate between two parts eliminates degrees of freedom between the two parts. Mates can remove between zero and six degrees of freedom.

### Degrees of Freedom in Simscape Multibody

Simscape™ Multibody™ assigns six degrees of freedom to an unconstrained rigid body. The unconstrained rigid body behaves as a free body — it can rotate and translate, about or along three mutually orthogonal axes. The following table lists the degrees of freedom of a rigid body in different configurations.

Rigid Body ConditionDegrees of Freedom
Not connected to joints, constraints, or World Frame0
Connected to Joints or Constraints blocksAdd degrees of freedom as specified by joint or constraint

### CAD Mate – Simscape Multibody Joint Mapping

During CAD export, Simscape Multibody Link maps SolidWorks mates between parts to Simscape Multibody joints between rigid bodies. CAD mates and Simscape Multibody joints do not follow a one-to-one correspondence — multiple mates 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 Inventor® 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 the Coincident constraint. A ✓ indicates the combination is supported.

 Mate-Entity 2 Point Line Plane Cylinder Cone Circle/Arc Mate-Entity 1 Point ✓ Line ✓ ✓ Plane ✓ ✓ ✓ Cylinder ✓ ✓ ✓ Cone ✓ ✓ ✓ Circle/Arc ✓ ✓ ✓ ✓

#### Concentric Mate

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

 Mate-Entity 2 Point Line Plane Cylinder Cone Circle/Arc Mate-Entity 1 Point Line ✓ ✓ ✓ Plane ✓ Cylinder ✓ ✓ ✓ ✓ Cone ✓ ✓ ✓ ✓ Circle/Arc ✓ ✓ ✓ ✓

#### Perpendicular Mate

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

 Mate-Entity 2 Point Line Plane Cylinder Cone Circle/Arc Mate-Entity 1 Point Line ✓ ✓ Plane ✓ ✓ Cylinder Cone Circle/Arc

#### Parallel Mate

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

 Mate-Entity 2 Point Line Plane Cylinder Cone Circle/Arc Mate-Entity 1 Point Line ✓ ✓ Plane ✓ ✓ Cylinder ✓ Cone ✓ Circle/Arc

#### Distance Mate

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

 Mate-Entity 2 Point Line Plane Cylinder Cone Circle/Arc Mate-Entity 1 Point ✓ ✓ Line ✓ Plane ✓ ✓ ✓ Cylinder Cone Circle/Arc

#### Angle Mate

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

 Mate-Entity 2 Point Line Plane Cylinder Cone Circle/Arc Mate–Entity 1 Point Line ✓ Plane ✓ Cylinder Cone Circle/Arc

### Supported Simscape Multibody Joints

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

#### Tips for Specific Mates

• The point-point coincident mate maps onto a spherical joint.

• The point-point distance mate maps onto a spherical-spherical massless connector.

### Limitations

The following limitation applies to CAD export from SolidWorks.

#### Weld is Default Joint

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

#### Restriction on Point-Point Distance Mate

For Simscape Multibody Link to successfully map the CAD point-point distance mate onto a Simscape Multibody spherical-spherical massless connector, the mate must not connect to any other mates.