Joints

This section provides an overview of the Joint entity in MotionView.

Theory/Background

Joints create lower pair constraints. A lower pair is an idealized form of constraint where the constraint can be represented using two reference frames, or coordinate systems, belonging to two different bodies. The origin, axis, or plane of one reference frame is said to be constrained with respect to the origin, axis, or plane of another reference frame. For example, a translation joint constraints a point on one body with regard to coordinate planes on another body. In this case, the point can only translate along a vector of the coordinate system. The body is said to have only a translation degree of freedom free, while the remaining two translational and all rotational degrees of freedom are restrained.

The figure below shows the various types of Joints that are supported in MotionView:

joint_diagram_mv

Creating/Adding Joints

To learn how to add an "Entity" to a model, please see the Entity Manual topic.

1.	A Joint entity can be added to the model using two different methods:

•	From the Constraint toolbar, right-click on the Joints icon to create any of the Lower Pairs or Joint Primitives.

•	From the Project Browser, right-click on the Model label (or on any System/Analysis of your choice) and select Add > Constraint > Joint from the context menu.

joint_prjct_brwsr_cntxt_menu_mv

The Add Joint or JointPair dialog is displayed.

add_joint_or_jointpair_dialog_mv

2.	Specify a Label for the joint.

The label can be a descriptive name.

3.	Specify a Variable for the joint.

The recommended naming convention for creating joints is that all joint variable names should begin with j_. Further, the variable name can be descriptive however it should not contain any special characters (other than ‘underscore’).

4.	Select the desired joint type from the drop-down menu.

5.	Click on the entity Type radio button and select the desired joint type: Single joint or Pair joint.

A Joint entity, like most of the entities that are created in MotionView, can be a Single Entity or a Pair Entity. Pair entities help in creating models which have symmetric properties.

6.	If required, you can make the joint to allow compliance by activating the Allow Compliance check box.

A Joint when made compliant, will be treated as a Bushing entity and all the properties of the Joint will now be the same as the properties of a Bushing.

7.	Optionally, you can also specify a descriptive Comment for the joint.

8.	When you are finished specifying the properties, click OK, Apply, or Cancel.

-	Clicking OK will add/create the joint entity and close the dialog.

-	Clicking Cancel will cancel the joint creation operation and close the dialog.

-	Clicking Apply will add/create the joint; however the dialog will remain open so that more joints can be added in the same way.

9.	Once a Joint entity has been added to the model, the panel for the joint will automatically be displayed in the panel area. See the panel example below:

joint_panel_example_mv

The Connectivity tab displays the type of joint that was created. The joint type can be modified using the drop down menu. Other members/tabs in the panel will vary depending on the type of joint.

10.	If the Allow compliance option was checked when adding the joint, the panel will look as shown in the image below:

joint_panel_example_compliant_mv

The drop-down menu below the Joint type drop-down menu is activated and the joint can be made compliant if need be.

11.	Use the drop-down menu to change the setting from Non-compliant to Compliant. The panel will then look as show in the image below:

joint_panel_example_compliant2_mv

Additional tabs are added to the panel which allow the specification of Translation Stiffness, Rotational Stiffness, Translational Damping, Rotational Damping, and Preload. These are tabs are similar to the tabs located on the Bushings panel, and the behavior of a Compliant joint is exactly the same to the behavior of a bushing entity.

The table below shows the list of joints that can be created in MotionView along with the Degrees of Freedom (DOF) that each joint removes:

Joint Type	Translational Constraints	Rotational Constraints	Total Constraints
AtPoint	3	0	3
Constant Velocity	3	1	4
Cylindrical	2	2	4
Fixed	3	3	6
Inline	2	0	2
Inplane	1	0	1
Orientation	0	3	3
Parallel Axes	0	2	2
Perpendicular Axes	0	1	1
Planar	1	2	3
Revolute	3	2	5
Screw	0.5	0.5	1
Spherical/Ball	3	0	3
Translational	2	3	5
Universal	3	1	4

Note	Click on the individual links (above) to learn more about each specific joint type.