Spherical (SimMechanics)

Represent an assembled spherical joint with three rotational degrees of freedom

Library

Joints

Description

The Spherical block represents three rotational degrees of freedom (DoFs) at a single pivot point, a "ball-in-socket" joint. Two rotational DoFs specify a directional axis, and a third rotational DoF specifies rotation about that directional axis. The sense of each rotational DoF is defined by the right-hand rule, and the three rotations together form a right-handed system. A spherical joint is one of the SimMechanics primitive joints, along with prismatic and revolute.

The Spherical block is assembled: you must connect each side of the Joint block to a Body block at a Body coordinate system (CS) point, and the origins of these Body CSs must be spatially collocated points, within assembly tolerances.

You cannot connect a Spherical block to an Actuator block. Unlike the Gimbal block, the Spherical block cannot become singular.

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

Any Joint block represents only the abstract relative motion of two bodies, not the bodies themselves.

Spherical motion of follower (blue) relative to base (red)

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 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 Spherical base and follower Body Connector Ports figure.
Current follower: When you connect the follower (F) Connector Port on the 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 Spherical base and follower Body Connector Ports figure.
Number of sensor/actuator ports: Using this spinner menu, you can set the number of extra Connector Ports needed for connecting Joint Sensor blocks to this Joint. The default is 0. A Spherical cannot be connected to an Joint Actuator.; The motion of a Spherical is three DoFs specified in quaternion form.

The base (B)-follower (F) Body sequence determines the sense of positive motion. Positive rotation is the follower rotating in the right-handed sense as shown in the figure above.

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 automatic. They specify the orientation of the spherical DoF that the Spherical represents.

Name: This column automatically displays the name of each primitive joint contained in the Joint block. For Spherical, there is only one primitive joint, a spherical, labeled S.
Primitive: This column automatically displays the type of each primitive joint contained in the Joint block. For Spherical, there is only one primitive type, labeled Spherical.
Reference orientation [x y z]: This field is not active.
Reference csys: This field is not active.

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 Modeling Joints for more on representing DoFs with Joints.

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

Six-DoF Spherical-Spherical