Perpendicular Axes Joint

This section describes the Perpendicular Axes joint entity of MotionView and shows the various usage, creation, and editing methods.

Theory/Background

A Perpendicular Axes joint is a five degree-of-freedom primitive constraint. The constraint is imposed such that the Z axis of a reference marker on one body (Body 2) remains perpendicular to the Z axis of a reference marker on the other body (Body 1) connected by the joint. All three translations are free along with two rotations about the Z axis of markers on both of the bodies defining the joint orientation. Joint primitives like Perpendicular Axes joints may not have a physical existence. These types of joints can be used to impose unique constraints where using a regular joint would not be possible.

perpendicular_joint_diagram_mv

Perpendicular Axes joint construction

Joint Definition

The Perpendicular Axes joint is represented using Markers when exported to an MBD Solver. The representation can be visualized as shown in the figure below:

perpendicular_axes_joint_marker_diagram_mv_ug

Parallel Axes joint - coincident origins

The bodies that are constrained by the Perpendicular Axes joint are represented using two markers: Marker I and Marker J. Marker I belongs to Body 1 and Marker J belongs to Body 2. The constraints are applied on the Marker I with respect to Marker J. Both of the markers will have a common point of origin, the same as the joint’s Origin point. The Z axis of Marker I will be constrained to remain parallel to the Z axis of Marker J.

Entity Data Members

The topological information required to define an Perpendicular Axes Joint is shown in the figure below:

perpendicular_joint_diagram2_mv

The data members of the Perpendicular Axes Joint can be classified into the following members:

Connectivity

An Perpendicular Axes Joint needs the following:

•	Body 1 and Body 2 - Specify two Bodies between which the joint is to be created.

•	Origin - Specify Point, which defines the location of the joint.

•	Orientation Method - A Perpendicular Axes joint needs an two axes to be specified for the constraint to be imposed. This can be done by specifying vectors or points which identify the direction of the axes.

•

Compliant Mode (Optional) - If the Allow Compliance option is selected while adding the joint to a model, the joint's compliance state can be toggled between Compliant and Non-Compliant. If the joint is made Compliant, it no longer remains a rigid connection and the joint will then be treated as a bushing.

The joint can be modeled as a Single entity or as a Pair entity.

Properties

There are no editable properties for a Perpendicular Axes Joint.

Creating and Editing Joints

To learn how to add a Perpendicular Axes joint to a model, please see the Joints topic.

1.	Once a Perpendicular Axes joint has been added to the model using any of the "entity" creation methods, the panel for the joint will automatically be displayed in the panel area. See the panel examples below:

perpendicular_joint_panel_conn_tab_mv

Joints Panel (Perpendicular Axes Joint) – Connectivity Tab - Single Entity

perpendicular_joint_panel_conn_tab_pair_mv

Joints Panel (Perpendicular Axes Joint) – Connectivity Tab - Pair Entity

2.	The joint definition needs two bodies which are connected by the joint. Select Body 1 by picking the body from the graphics area, or double click the Body 1 collector to open to the model tree (from which the desired body can be selected).

3.	Similarly, pick Body 2 from the graphics area by clicking on the desired body (or use the collector and model tree method).

4.	Select the Origin Point from the Project Browser, or the graphics area, to specify the point of origin for the joint.

5.	The Perpendicular Axes joint needs two axes (Axis 1 and Axis 2) that are mutually perpendicular and each belonging to Body 1 and Body 2 respectively. Use the corresponding drop-down menus and collectors to specify each axis.

6.	Define Axis 1 using either of the following methods:

-	Point – Select a point that lies on the desired Alignment axis for the joint.

-	Vector – Global axes can be used for vectors by clicking on the desired axis (X, Y, or Z) in the graphics area (or by browsing through the model tree).

alignment_axis_vector_example_mv

7.	Define Axis 2 using the same process outlined in the step above.

8.	When defining a Pair Perpendicular Axes joint use pair entities for Body 1, Body 2, Origin, etc.

Note - The same steps as shown above can also be used to define Pair Perpendicular Axes Joint entities.

1.	Left click the Joints panel icon on the Constraint toolbar.

The Project Browser will filter the entities and display only the Joints in the model.

2.	Select the desired joint in the Project Browser.

The corresponding panel is automatically displayed.

3.	From the Connectivity tab, use the Joint type drop-down menu to change the joint type, or use the collectors to change the bodies and origins, alignment points, etc. of the joint.

perpendicular_axes_joint_drop_down_menu_mv_ug

Joints panel - Connectivity tab - joint type drop-down menu

Perpendicular Axes Joint in MDL and XML Formats

The model containing the Perpendicular Axes Joint can be saved in MDL format from MotionView and exported in the MotionSolve XML format.

The Perpendicular Axes Joint can be of the following types:

1.	Non-Compliant - Single and Pair

2.	Compliant – Single and Pair

These four types of entities can be added to the model using the MDL Statements shown below:

Syntax:

*PerpAxesJoint(joint_name, "joint_label", body_1,

body_2,

origin,

POINT|VECTOR,

point_1|vector_1,

POINT|VECTOR,

point_2|vector_2,

[ALLOW_COMPLIANCE])

To understand the complete syntax of the MDL statement please refer to the *PerpAxesJoint topic.

Syntax:

*PerpAxesJointPair(joint_name, "joint_label", body_1,

body_2,

origin,

POINT|VECTOR,

point_1|vector_1,

POINT|VECTOR,

point_2|vector_2)

[ALLOW_COMPLIANCE])

To understand the complete syntax of the MDL statement please refer to the *PerpAxesJointPair topic.

To learn how to create a complete model using MDL Statements please refer to tutorial MV-1060: Introduction to MDL.

The Perpendicular Axes joint when exported to the MotionSolve XML format is defined as a Constraint_Joint or Constraint_Jprim statement.

Syntax:

<Constraint_Joint [or Constraint_Jprim]

id = "integer"

label = "Name of Joint"

type = "JOINT TYPE"

i_marker_id = "integer"

j_marker_id = "integer"

Example:

<Constraint_Joint [or Constraint_Jprim]

id= "301001"

label = "Perpendicular Axes Joint"

type = "PERPENDICULAR"

i_marker_id = "30103050"

j_marker_id = "30101050"

In the above XML Model statement the i_marker_id and j_marker_id represent the I and J markers of the Joint which belong to Body 1 and Body 2 respectively. To understand the complete syntax of the Constraint_Joint XML model statement, please refer to the MotionSolve Reference Guide Page for Constraint_Joint or Constraint_Jprim.

Creating a Perpendicular Axes Joint using the Tcl Command Layer

In MotionView, the Tcl command layer can be used to add any MDL entities to the model. There are two Tcl commands that can be used to add an entity:

Syntax:

mdlmodel_handle InterpretEntity new_handle keyword varname label

In case of the Perpendicular Axes Joint the statement will look as shown below:

mdlmodel_handle InterpretEntity PerpAxesJt_handle PerpAxesJoint j_Perp_Axes "\"Perpendicular Axes Joint\"" b_1 B_Ground p_ori "POINT" p_1 "VECTOR" "V_Global_Z" "ALLOW_COMPLIANCE";

*This command is not applicable for Perpendicular Axes joint entities.

The InterpretEntity command is used to add entities to the model and the InterpretSet command is used to set the entity properties (which is not applicable for this type of joint). Extended definitions for InterpretEntity and InterpretSet can be found in the HyperWorks Desktop Reference Guide.

Note - When using the InterpretEntity and InterpretSet commands, it is important to also use the Evaluate command in order for the changes to take effect immediately.

To learn how to create a complete model using Tcl commands, please refer to tutorial MV-1040: Model Building Using Tcl.

Example Model

The example file below shows a Perpendicular Axes joint connecting two bodies:

*BeginMDL( the_model, "Model", "12.0.110.40" )

*StandardInclude(FILE)

*Point( p_0, "Single Joint Origin" )

*PointPair( p_1, "Pair Joint Origin" )

*Body( b_0, "Single Body 1", p_0, , , , )

*BodyPair( b_1, "Pair Body 1", p_1, , , , )

//Perpendicular Axes joint definition

*PerpAxesJoint( j_PerpAxesjsingle, "PerpAxes Joint Single", b_0, B_Ground, p_0, POINT, p_1.l, VECTOR, V_Global_Z )

//Perpendicular Axes joint pair definition

*PerpAxesJointPair( j_PerpAxesjpair, "PerpAxes Joint pair", b_1, B_Ground, p_1, VECTOR, V_Global_X, VECTOR, V_Global_Z )

*Point( p_2, "Point for ori" )

*SetPoint( p_2, 0.0, 50.0, 0.0 )

*SetPoint( p_1, LEFT, , -100 )

*EndMDL()