Joint with zero degrees of freedom
This content is specific to Simscape™ Multibody™ First Generation software. First-generation features are slated to be deprecated and should be avoided.
The Weld block represents a joint with no degrees of freedom (DoFs). The two Bodies connected to either side of the Weld block are locked rigidly to one another, with no possible relative motion.
A Joint block represents the relative degrees of freedom between two bodies, not the bodies themselves.
You must connect any Joint block to two and only two Body blocks, the base and the follower. All Joints have two connector ports for these connections, defining the direction of joint motion (base to follower). You connect each side of the Joint block to these Body blocks at a Body coordinate system (CS) port.
You specify the joint primitive axes, if any, in the Joint dialog.
This Joint block is assembled and places restrictions on the connected Body CSs.
If the Joint has one or more prismatic primitives, the origins of the connected Body CSs must lie in the span of the prismatic axes:
|Number of Prismatic Primitives||Span of Primitive Axes|
|One||Along the primitive axis|
|Two||In the plane of the primitive axes|
|Three||Anywhere in three-dimensional space|
The dialog has two active areas, Connection parameters and Parameters.
When you connect the base (B) connector port on the Weld block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following figure, Weld Base and Follower Body Connector Ports.
The base Body is automatically connected to the joint primitive
the primitive list in Parameters.
When you connect the follower (F) connector port on the Bushing block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following figure, Weld Base and Follower Body Connector Ports.
The follower Body is automatically connected to the joint primitive
the primitive list in Parameters.
Using this spinner menu, you can set the number of extra connector
ports needed for connecting Joint Sensor blocks to this Joint. The
You cannot actuate a Weld joint, and a Weld joint undergoes no motion. A Joint Sensor measures zero motion, but in general nonzero reaction forces, at this joint.
Weld Base and Follower Body Connector Ports
Switch between the Axes and Advanced tabs.
The entries on the Axes tab are inactive for Weld. This block has no DoF primitives.
The primitive list states the names and types of joint primitives
that make up the Weld block: a rigid primitive
This field is inactive.
Using the pull-down menu, choose the coordinate system (World,
the base Body CS, or the follower Body CS) whose coordinate axes the
vector axis of action is oriented with respect to. This CS also determines
the absolute meaning of forces/torques and motion along/about the
joint axis. The default is
The Advanced tab is optional. You use it to control the way Simscape Multibody simulation interprets the topology of your schematic diagram.
In a closed loop, the simulation internally and automatically cuts one and only one joint.
If you want this particular joint to be weighted preferentially for cutting during the simulation, select the check box. The default is not selected.
See Modeling Degrees of Freedom for more on representing DoFs with Joints.