SimMechanics™

Prismatic-Translational Interface

Connect prismatic primitive to one-dimensional Simscape™ mechanical translational elements

Library

Interface Elements

Description

This block connects a SimMechanics™ prismatic joint primitive with mechanical translational elements from the Simscape Foundation library. Dynamically, such a connection is equivalent to connecting the mechanical translational elements between the two bodies that are connected to the prismatic 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 translational motion. In a Simscape mechanical translational circuit, force flows through a connection line, while velocity is defined across nodes connected by connection lines. The Prismatic-Translational Interface block rigidly couples a SimMechanics prismatic primitive to a Simscape mechanical translational degree of freedom. By itself, this interface adds or removes no degrees of freedom (DoFs) to or from the combined machine-circuit. Prismatic-Translational Interface preserves force through and motion across the block, conserving mechanical power.

The mechanical connector port acts, on the SimMechanics side, like a force-actuated Joint Actuator, feeding force from the circuit through the connected Joint to its connected Bodies, while maintaining the velocity across the block. The force exerted by the Simscape mechanical translational elements is applied between the two SimMechanics bodies along the Joint prismatic 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 force through the block. The motion of the SimMechanics bodies along the Joint prismatic primitive axis is applied as relative motion between the Simscape mechanical translational 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 force and 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 prismatic primitive in that Joint should be connected to the Simscape circuit through this interface.
Connect the Simscape mechanical translational ports (B and F) along the circuit connection line, which in turn connects to Simscape mechanical translational 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 Masses in the Interfaced Simscape™ Circuit

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

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

The dynamics of a Simscape mass element is simulated only:

Along one dimension (the chosen prismatic primitive axis)
With forces on the mass element explicitly modeled by blocks and connections in the circuit

If a Simscape mechanical circuit is interfaced to a SimMechanics machine and includes mass 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 mass elements.
The interfaced Joint, from the point of view of the machine, effectively carries any masses 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 prismatic primitives present in the Joint.

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

Examples

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