Revolute-Spherical

Constant-length joint connector with spatially separated revolute axis and spherical pivot point

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.

    Warning   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.

Massless Connector Between Revolute and Spherical Joints

Satisfying Joint Requirements

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 a default of 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) point.

You specify the joint primitive axes, if any, in the Joint dialog.

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

Assembly Restrictions on Massless Connectors

Both joint primitives are assembled but spatially separated. That is, the connected Body CS origins must not be spatially collocated points.

The distance separating the two ends of the connector is computed automatically from the Body CS origins to which the Joint is connected. This distance (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.

Dialog Box and Parameters

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

Connection Parameters

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.

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 figure, Revolute-Spherical Base and Follower Body Connector Ports.

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 figure, Revolute-Spherical Base and Follower Body Connector Ports.

Revolute-Spherical Base and Follower Body Connector Ports

Parameters

Switch between the Axes and Advanced tabs.

Axes Tab

The entries on the Axes tab 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 CS

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.

 Restricted Parameters

Advanced Tab

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

Mark as the preferred cut joint

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 Also

Revolute, Spherical

See Modeling Degrees of Freedom for more on representing DoFs with Massless Connectors.

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

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