Learn more about SimMechanics

Cutting Machine Diagram Loops

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Rules for Valid Machine Diagram Loops Rules for Automatic Loop Cutting Specifying a Loop Joint for Cutting Displaying the Cut Joints For More About Disassembled and Cut Joints For More About Constraints and Drivers

Rules for Valid Machine Diagram Loops

In a SimMechanics model, you form a closed loop by the closure of SimMechanics blocks, of any type, on themselves. From a starting point, you can trace a path around a closed loop back to the starting point with no jumps or cuts. A closed loop is valid if it contains:

• At least one Joint block

• No more than one Disassembled Joint block

• No more than one Constraint or Driver block

To simulate a model containing closed loops, the SimMechanics simulation internally converts a closed-loop model to an open-topology tree model. This is accomplished by internally cutting each of the model's closed loops once, at a joint, constraint, or driver block, then replacing each cut by an additional internal constraint.

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Rules for Automatic Loop Cutting

A SimMechanics simulation follows these loop-cutting rules.

• If a loop contains a constraint, driver, or disassembled joint, the simulation cuts the loop at one of those blocks. Selecting a preferred cut joint has no effect.

• If the loop does not contain a constraint, driver, or disassembled joint, the simulation cuts the loop at the preferred cut joint if you have specified one.

• If the loop does not contain a constraint, driver, or disassembled joint, and you have not specified a preferred cut joint, the simulation cuts the loop at the joint with the most degrees of freedom.

Note   A SimMechanics simulation cuts a closed loop at a Disassembled Joint, Constraint, or Driver block, if one or more of these blocks is present, regardless of other Joints also present in the loop or of your preferred cut choice.

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Specifying a Loop Joint for Cutting

You can specify a joint to cut if the loop does not contain a disassembled joint, constraint, or driver. Open the joint's dialog box and select the Mark as the preferred cut joint check box on the Advanced tab in that joint's dialog Parameters area.

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Displaying the Cut Joints

To display automatically cut joints in your model, select the Mark automatically cut joints check box in the Diagnostics area of the SimMechanics node of your model's Configuration Parameters dialog. See Configuring SimMechanics Simulation Diagnostics in the Running Mechanical Models chapter).

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For More About Disassembled and Cut Joints

Refer to Modeling Disassembled Joints for more on disassembled joints. Consult Verifying Model Topology to learn more about closed loop analysis.

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For More About Constraints and Drivers

A SimMechanics simulation represents a cut Joint, Constraint, or Driver as an additional internal constraint. See Constraining and Driving Degrees of Freedom following for more about these specialized blocks.

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Constraining and Driving Degrees of Freedom

Applying Motions and Forces

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