About Joints

Joints are mechanical relations between bodies used to drive the motion of the mechanism. You can create joints automatically, based on existing defined mates, or manually.

Note: A joint is usually defined between two markers. It describes the translation and rotation of the second marker according to the translation or rotation of the first marker.

This page discusses:

Automatic Joints

By default, at the creation of a mechanism, the app creates a joint for every mate associated with the mechanism.

Note: For example:
  • A revolute joint is created from an existing revolute mate.
  • A curve tangency joint is created from an existing roll curve or slide curve mate.

Joints created from existing mates have the same properties as the associated mates. The app computes the joint properties. You can review them but not edit them.

To edit the properties of an automatic joint, you must convert it into a manual joint. To do so, you need to modify the joint type and select a joint type different than Automatic from mate.

Important: If you modify the type of an automatic joint, the joint is no longer associated with the mate and is considered a manual joint.

Manual Joints

If no mate is associated with the mechanism, you can create joints under the mechanism by selecting the joint types to create and by specifying their properties.

To define the position and orientation of a joint, you can associate a joint to a marker. For more information, see Creating Markers.

Note: By default, at the creation of the joint, the app creates automatic markers to define the application point and the orientation of a joint automatically. The application point and orientation correspond to the definition of the associated mate.For more information, see About Markers.

Joint Limits

If joint limits are reached during the dynamic simulation of a mechanism, the joint behaves as a unilateral spring-damper and the following contact properties apply:

  • Restitution coefficient: 0.666
  • Stiffness: 1.0e8 N_m (translation) or 1.0e8 Nxm_rad (rotation).
Note: You cannot access these properties nor modify their value.