SimMechanics™

Revolute-Rotational Interface

Connect revolute primitive to one-dimensional Simscape™ mechanical rotational elements

Library

Interface Elements

Description

This block connects a SimMechanics™ revolute joint primitive with mechanical rotational elements from the Simscape Foundation library. Dynamically, such a connection is equivalent to connecting the mechanical rotational elements between the two bodies that are connected to the revolute primitive. The validity of the connection is guaranteed only if the SimMechanics and Simscape mechanical modeling rules are both respected.

Simscape software supports a domain representing one-dimensional rotational motion. In a Simscape mechanical rotational circuit, torque flows through a connection line, while angular velocity is defined across nodes connected by connection lines. The Revolute-Rotational Interface block rigidly couples a SimMechanics revolute primitive to a Simscape mechanical rotational degree of freedom. By itself, this interface adds or removes no degrees of freedom (DoFs) to or from the combined machine-circuit. Revolute-Rotational Interface preserves torque through and angular motion across the block, conserving mechanical power.

The mechanical connector port acts, on the SimMechanics side, like a torque-actuated Joint Actuator, feeding torque from the circuit through the connected Joint to its connected Bodies, while maintaining the angular velocity across the block. The torque exerted by the Simscape mechanical rotational elements is applied between the two SimMechanics bodies about the Joint revolute primitive axis.
The physical conserving ports act, on the Simscape side, like a motion actuator, feeding a prescribed motion from the machine into the circuit, while preserving the flow of torque through the block. The motion of the SimMechanics bodies about the Joint revolute primitive axis is applied as relative motion between the Simscape mechanical rotational ports of the block.
The directionality of motion (base-to-follower, or B-to-F) is preserved across the interface, from the directionality of the connected Joint to the directionality of torque and angular motion in the Simscape circuit.

You interface the machine and the mechanical circuit through the block ports.

Connect the SimMechanics port P to a Sensor/Actuator port on a Joint. In the Interface block dialog, you then choose which revolute primitive in that Joint should be connected to the Simscape circuit through this interface.
Connect the Simscape mechanical rotational ports (B and F) along the circuit connection line, which in turn connects to Simscape mechanical rotational elements.

Joint Block Required for Complete Interface

The complete interface between a SimMechanics machine and a Simscape mechanical circuit includes both an Interface block and its connected Joint block containing the joint primitive chosen to couple to the one-dimensional circuit.

Avoiding Inertias in the Interfaced Simscape™ Circuit

Warning Simulating with inertia elements in a Simscape circuit interfaced to a SimMechanics machine leads to unphysical results.

To avoid such unphysical situations, model all inertias in your machine using SimMechanics Body blocks, and do not include inertia elements in the Simscape circuit interfaced to a SimMechanics machine.

The dynamics of a Simscape inertia element is simulated only:

About one dimension (the chosen revolute primitive axis)
With torques on the inertia element explicitly modeled by blocks and connections in the circuit

If a Simscape mechanical circuit is interfaced to a SimMechanics machine and includes inertia elements:

The acceleration of the circuit's frame within the larger machine and thus noninertial pseudoforces are neglected in the dynamics of the circuit's inertia elements.
The interfaced Joint, from the point of view of the machine, effectively carries any inertias modeled in the interfaced circuit. SimMechanics Joints are assumed massless.

Dialog Box and Parameters

The dialog has one active area, Primitive. The block parameters are not displayed unless you connect it to a specific Joint block.

Primitive

When connected to a Joint block, the dialog lists all the revolute primitives present in the Joint.

Connected to primitive: From the pull-down menu, select the revolute primitive in the Joint that you want to connect to the mechanical rotational elements.

Examples

These demos illustrate how to interface between a three-dimensional machine and a one-dimensional mechanical rotational circuit.