Defining a Mechanism

You can set up a mechanism by specifying which engineering connections are enforced and which degrees of freedom are controlled by mechanism commands.

The Mechanism Manager confirms when enough specifications have been defined.

Before you begin: Define a mechanism as current and select it.
See Also
About the Mechanism Manager
About Limits
  1. From the Mechanical Systems Design section of the action bar, click Mechanism Manager .

    In the Mechanism Manager dialog box, you can specify commands and include or exclude engineering connections from the mechanism. Engineering connections included in a mechanism are referred to as joints.

  2. Under Status, indicate the Computation status used to calculate the degrees of freedom in the mechanism:
    OptionDescription
    Automatic Recalculates the degrees of freedom each time you add or remove connections and commands. Use this mode for small mechanisms.
    Manual Recalculates the degrees of freedom manually to avoid performing a time-consuming calculation each time you change a connection or a command.
    Note: To display the current degrees of freedom at any time, click Update status.
  3. Select the joints to include or to exclude from the mechanism:
    • To include an engineering connection as a joint, select it in the table and click Include.
      Tip: Alternatively, select the check box from the first left column .
    • To exclude a joint, highlight it in the table and click Exclude.
      Tip: Alternatively, clear the check box from the first left column .
    • To include every available engineering connection as joints in the mechanism, click Include All.
    • To exclude every available joint from the mechanism, click Exclude All.
    Warning:
    • If you have compound joints in your mechanism linking two elementary joints, exclude the joint to unlink the elementary joints. However, if you exclude one of the elementary joints, the compound joint is excluded as well.
    • Dressup joints (rigid engineering connections) appear in the table with the Included status marked in the first left column.

    To highlight engineering connections, select them in the table or in the tree, or select a product or mechanism representation in the tree. If you select a product or representation, every engineering connection associated with that object is highlighted in the table.

    Tips:
    • Parts not impacted by the selected engineering connection become transparent in the work area. It helps you better visualize the parts involved in the mechanism.
    • Right-click an engineering connection in the table to display a context menu to navigate or configure the mechanism:
      • Select Include or Exclude to include or exclude the connection.
      • Select Center Graph or Reframe On to focus the tree or viewport, respectively, on the selected connection.
      • Select Preview to display a preview of the connection in a new window.
      • Select Edit to open the Engineering Connection Definition dialog box and modify the connection.
  4. To change a command in the mechanism:
    1. Select an engineering connection including a controlled constraint.
    2. Under Command Management, specify the Length or Angle. The label in the appropriate Command column changes to reflect the type of command assigned to the joint.

    You can only assign commands to the following types of engineering connections:

    • Cylindrical
    • Prismatic
    • Revolute
    • Point curve
    • Roll curve
    • Slide curve

    You can use Compound connections to link the behavior of prismatic and revolute joints. In this case, the commands are still assigned to the prismatic and revolute connections. You can use the following compound connections:

    • Gear
    • Rack
    • Cable

    For more information, see Engineering Connections and Degrees of Freedom.

  5. To reverse the sense of motion of a command, modify the command value parameters:
    1. To edit an engineering connection that is specified as a command, right-click the command in the tree and select Edit Connection.
    2. In the Engineering Connection Definition dialog box, right-click the controlled constraint and change the type of the first option.

      For more information about the types of controlled constraints to use as commands in the mechanism, see About Engineering Connections.

      Command Type Controlled Constraint Type
      Angle-based commands (prismatic or cylindrical connections) Hinge or Angle
      Length-based commands (cylindrical or revolute connections) Offset

      The selection in the Options column differs whether the engineering connection specified as a command has been assigned a length or an angle parameter. See the specific tables below for a detailed description of the various situations.

    3. Specify the new parameter value manually in the Engineering Connection Definition dialog box.

    • For length-based commands, the table below describes the specificities for each selected option:
    To reverse the command orientation... Select
    If Below type is specified as the first option .* Above.
    If Above type is specified as the first option.* Below.
    If Undefined type is specified as the first option.* Above or Below.
    * For this combination of options, you must edit the value manually. If the value of a length parameter equals 200, define its value to -200.

    • For angle-based commands (cylindrical or revolute connections), the tables below describe the specificities for each selected option:

    For a controlled-hinge constraint :

    To reverse the command orientation... Select...
    If Sector 4 is selected as the first option. Sector 1
    If Sector 3 is selected as the first option. Sector 2
    If Sector 2 is selected as the first option. Sector 3
    If Sector 1 is selected as the first option. Sector 4
    For these cases, the angle value is automatically changed. For example, an angle parameter marked is automatically set to 360° - .

    For a controlled -angle constraint :

    To reverse the command orientation...Select...
    If Angle is selected as the first option. Hinge Sector 4 For example, an angle parameter marked α is automatically set to 360° - α .
    For more information, see the dedicated article in the Knowledge Base.
  6. Repeat Steps 2 and 3 until the status icon in the Mechanism Manager turns green and a message indicates that the mechanism can be simulated.
  7. To assemble mechanisms, click the Assembly tab.

    For more information on mechanism assemblies, see Defining an Assembly of Mechanisms.

  8. Click OK.

Tip: To edit a dressup, double-click a Dressup node in the tree.