Revolute-Spherical (SimMechanics)

Represent a composite joint composed of a revolute and a spherical primitive spatially separated by a massless connector of constant length

Library

Joints/Massless Connectors

Description

The Revolute-Spherical block represents a composite joint composed of a revolute and a spherical joint primitive. The base Body coordinate system (CS) on one side of the Joint is connected to the revolute primitive, and the follower Body CS is connected to the spherical primitive. The primitives are separated spatially by a vector of constant length but variable direction connecting the two Body CS origins. Both primitives are assembled.

Caution This joint becomes singular if the revolute primitive axis aligns with the vector separating the primitives. The simulation stops with an error in this case.

You specify the revolute axis of the revolute joint primitives in the dialog box. The distance separation between the two axes is computed automatically from the Body CS origins to which the Joint is connected. This distance separation (the magnitude of the vector between the Body CS origins) remains fixed at its initial value during the simulation. This initial value must be nonzero.

You cannot connect a Massless Connector to an Actuator or a Sensor block.

You can connect any Joint block to two and only two Body blocks, and Joints have a default of two Connector Ports for connecting to base and follower Bodies.

A Joint block represents only the abstract relative motion of two bodies, not the bodies themselves. You must specify a reference CS to define the direction of the joint axis.

Massless Connector between Revolute and Spherical Joints

Dialog Box and Parameters

The dialog box has two active areas, Connection parameters and Parameters.

Connection Parameters

Current base: When you connect the base (B) Connector Port on the Revolute-Spherical block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following Revolute-Spherical base and follower Body Connector Ports figure.
Current follower: When you connect the follower (F) Connector Port on the Revolute-Spherical block to a Body CS Port on a Body, this parameter is automatically reset to the name of this Body CS. See the following Revolute-Spherical base and follower Body Connector Ports figure.

The base (B)-follower (F) Body sequence determines the sense of positive motion. Positive rotation is the base rotating in the right-handed sense about its rotation axis or the follower pivoting as shown for the Spherical Joint.

Revolute-Spherical base and follower Body Connector Ports

Parameters

Toggle between the Axes and Advanced panels with the tabs.

The entries on the Axes pane are required. They specify the direction of the rotation axis of one of the DoFs that Revolute-Spherical represents.

Name: This column automatically displays the name of each primitive joint contained in the Joint block. For Revolute-Spherical, there are one revolute and one spherical primitive, labeled R1 and S, connecting to base and follower, respectively.
Primitive: This column automatically displays the type of each primitive joint contained in the Joint block. For Revolute-Spherical, there are two primitive types, labeled Revolute and Spherical.
Axis of action [x y z]: Enter here as a three-component vector the directional axis about which the rotational DoF can move. The default vector is [0 0 1]. The axis is a directed vector whose overall sign matters.; This field is not active for the Spherical primitive.
Reference csys: 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 rotation is oriented with respect to. This CS also determines the absolute meaning of torque and motion about the primitive axis. The default is WORLD.; This field is not active for the Spherical primitive.

The Advanced pane is optional. You use it to control the way SimMechanics interprets the topology of your schematic diagram.

Mark as the preferred cut joint: In a closed loop, one and only one joint is cut during the simulation. SimMechanics does the cutting internally and automatically.; If you want this particular joint to be weighted preferentially for cutting during the simulation, select the check box. The default is unselected.

See Also

Revolute, Spherical

See Modeling Joints for more on representing DoFs with Massless Connectors.

See Checking Schematic Topology and How SimMechanics Works for more on closed loops and cutting.

Revolute-Revolute RotationMatrix2VR