Joint Editor View

Overview

The Joint Editor view allows you to create passive and active Physics Joints between two or more body assemblies created with the Kinematization Menu.

The Physics Joint is configurable in the editor and allows you to lock, unlock or limit movement within the six degrees of freedom (DOF) individually.

For a joint, one reference is considered the stationary reference (rigid), while the other is considered the moving reference (physics). The moving and the stationary references of the joint must be located on two different body assemblies.

Example of a Physics Joint configuration in the Joint Editor:

The editor automatically verifies the configuration and indicates detected configuration issues by a red triangle in each box that is affected. A tooltip is provided that indicates a solution. The total number of issues detected in the editor is displayed in the lower left corner.

The Joint Editor provides two buttons in the upper right corner:

Button

Description

Moves the camera to position 0.0.

Click to move the camera view of the editor to the upper left edge.

Fits all nodes within the view

Click to zoom in or out of the editor view so that all available objects are displayed.

Creating Physical Joints

To create a physical joint between two assemblies, proceed as follows:

Step

Action

1

Right-click in the Joint Editor view and run the command Add Body from the contextual menu.

Result: A new body block is displayed in the Joint Editor.

2

Create a relationship between the block in the Joint Editor and an assembly in the scene by selecting the assembly in the scene or in the Solution Explorer, right-clicking the block in the Joint Editor and running the command Link to assembly from the contextual menu.

Result: The name of the assembly is assigned to the selected block in the Joint Editor.

3

Repeat steps 1 and 2 to create a second block in the Joint Editor and to link it to a second assembly in the scene.

Result: Two blocks representing two different assemblies are available in the Joint Editor.

4

Right-click in the Joint Editor view and run the command Add Physics Joint from the contextual menu.

Result: A Physics Joint block is added to the Joint Editor.

5

Click in the frame of the first assembly, hold down the left mouse button and draw a connecting line to the Origin connection point of the Physics Joint block.

Result: The first assembly is defined as origin or stationary reference for the joint and the Origin connection point is highlighted in blue.

6

Verify the configuration of the body assembly that is connected as Origin:

The Dynamics parameter Type must be set to Rigid or Physics (refer to the Properties of Body Assemblies). If the Type = Bodiless is selected, correct the configuration.

7

Click the Child connection point of the Physics Joint block, hold down the left mouse button and draw a connecting line to the second assembly.

Result: The second assembly is defined as child or moving reference for the joint, the Child connection point is highlighted in blue.

8

Verify the configuration of the body assembly that is connected as Child:

The Dynamics parameter Type must be set to Physics (refer to the Properties of Body Assemblies).

If this is not the case, a red triangle is displayed at the upper right corner of the body block. To adapt the configuration, right-click the assembly that is defined as child and run the command Set to Physics from the contextual menu.

Result: The Dynamics parameter Type is set to Physics and the red triangle is removed.

9

Configure the Physics Joint. For further information, refer to Configuring Physical Joints.

Configuring Physical Joints

By default, the six parameters representing the six degrees of freedom are set to Axis Mode > Locked, meaning that motion of the joint is not allowed:

  • Linear X

  • Linear Y

  • Linear Z

  • Rotation X

  • Rotation Y

  • Rotation Z

To allow motion in one or more directions, select Axis Mode > Free from the list for the respective parameters.

To restrict the motion of the moving reference for one degree of freedom, select Axis Mode > Limited and configure a force that corresponds to a spring to keep the body assembly within the defined limits.

The following constraints apply to the configuration of the Axis Mode with respect to the three axes and are restricted within the software:

Case

Axis 1

Axis 2

Axis 3

Description

Valid case 1

Limited:

-75°...75°

Limited:

-75°...75°

Locked

General rule: At least one axis must be Locked to help ensure stability.

If one axis is Locked, allowed Limits for the other two axes are between -75° and 75°.

Valid case 2

Limited:

-180°...180°

Locked

Locked

If two axes are Locked, the allowed Limits for third axis are between -180° and 180°.

Invalid case

Limited:

-75°...75°

Free

Locked

This is an invalid case because if one axis is Locked.

The software does not allow you set one of the other axes to Free.

With Axis Mode > Limited selected, configure the following parameters:

Parameter

Description

Limits

Configure limits for the motion of the moving reference.

Min

Enter the maximum movement (in mm) in the negative direction for the remaining axis or axes if one or two axes are set to Locked.

The valid range depends on the configuration of the Axis Mode for the three axes of motion as indicated in the table above:

  • -75°...75° with one axis set to Locked

  • -180°...180° with two axes set to Locked

Max

Enter the maximum movement (in mm) in the positive direction for the remaining axis or axes if one or two axes are set to Locked.

The valid range depends on the configuration of the Axis Mode for the three axes of motion as indicated in the table above:

  • -75°...75° with one axis set to Locked

  • -180°...180° with two axes set to Locked

Spring

Configure the physical properties that correspond to springs and that act on the moving reference to keep it within the configured limits.

Stiffness

Enter a value >0 to configure the stiffness of the spring (in N/m) that is the extent to which it can resist deformation in response to an applied force.

Damping

Enter a value >0 to configure the damping of the spring (in N·s/m) that is the resistance against fast changes in displacement and that contributes to bring the spring to rest quickly.

Enable Drive

Select this option to use active joints. Refer to Configuring Active Joints.

NOTE: In the Properties of the Child assembly, set the Dynamics Parameters to Type = Physics for allowing the physical simulation to display the motion in the scene.

By combining the physical joints feature with the functions provided in the Kinematization menu, you can create customized robot kinematics.

Configuring Active Joints

You can also configure active or motorized joints that interact with the geometry by using forces. To achieve this, set the Axis Mode to Free or Limited and configure the following parameters:

Parameter

Description

Enable Drive

Select this option to use active or motorized joints to keep a moving reference within the configured limits.

Drive Type

Select an option from the list to define the controller input that is valid for the motor:

  • Velocity: A velocity value for the motor (in Units) is provided by a variable from the controller.

  • Forward/Backward: Boolean forward/backward signals are provided by a variable from the controller.

  • Custom: Select this option to use customized motors or positioners. If they meet the requirements defined in Customized Motors or Positioners, they are available for selection in the Custom Drive list and can be added to the selected joint. You can configure them in the Properties view (see the How to Use Device Catalogs User Guide).

The motor is configured with the parameter Drive > Motor.

Drive

Active joints are controlled by drives. The drive is a proportional derivative drive that applies a force according to the following formula:

F = stiffness * (target position - position) + damping * (target velocity - velocity)

Motor

Configure the motor according to the selection for the parameter Drive Type.

The motor parameters are configured as described in the How to Use Device Catalogs User Guide. Alternatively, you can right-click the motor node in the Solution Explorer and control the motor manually with the Stop, Start, Forward, Backward commands.

Spring

Configure the coefficients used by the spring drive to move the child body assembly (moving reference) through forces.

Use the Stiffness parameter to apply a force that is proportional to the detected position error.

Use the Damping parameter to apply a force that is proportional to the detected velocity error.