Engineering Connections and Degrees of Freedom

Engineering connections restrict the number of available translation and/or rotation degrees of freedom. The table below summarizes the predefined engineering connections, their associated number of degrees of freedom (DOF), whether they can include controlled constraints, and which types of controlled constraints can be used as commands in the mechanism.

Engineering Connections Translation DOF Rotation DOF Can be Controlled? Command Types
User Defined Depends on the combination of constraints Depends on the combination of constraints NO N/A
Rigid 0 0 NO N/A
Spherical 0 3 NO N/A
Cylindrical 1 1 YES Length, Angle, or both
Planar 2 1 NO N/A
Prismatic 1 0 YES Length
Revolute 0 1 YES Angle
Point Curve 1 3 YES* Length
Roll Curve 1 1 YES Length
Slide Curve 2 1 YES Length
Point Surface 2 3 NO N/A
Universal 0 2 NO N/A
Gear 0 1 YES Angle
Rack 1 1 YES Length or Angle
Screw 1 1 YES Length, Angle, or both
Cable 1 0 YES Length
Fix 0 0 NO N/A
* Point curve connections must be created using either a controlled curvilinear distance constraint or a coincidence constraint (for an engineering connection that cannot be controlled by commands). Point curves engineering connections using driving curvilinear distance constraints or measured curvilinear distance constraints cannot be simulated.

Important: For compound engineering connections, roll curve connections, and screw connections, multiple degrees of freedom (DOF) can be controlled. The commands are linked (changing one command value automatically updates the other command value) and can not be run simultaneously.

When defining controlled constraints, you must use specific geometry types as supports. Restricted geometry combinations can lead to ambiguous configurations in the mechanism, and you are not able to assign commands to these constraints in the Mechanism Manager (see Setting Up a Mechanism). The following table lists the allowed and restricted geometry combinations for controlled constraints in mechanisms.

Controlled Constraint Type Allowed Geometry Combinations Restricted Geometry Combinations
Selection 1 Selection 2 Selection 1 Selection 2
Offset Plane or Face Plane or Face Point or Vertex Point or Vertex
Plane or Face Line or Edge Point or Vertex Line or Edge
Plane or Face Point or Vertex Line or Edge Line or Edge
Angle Plane or Face Plane or Face Line or Edge Line or Edge
Plane or Face Line or Edge