The Collision Dialog

The model by default does not have collision testing enabled. Without collision testing of the model, VM will not detect when a tool, part or fixture touches a component of the machine. However, even with model collision testing disabled, VM will continue to check for collisions and gouging between the tool and the part, in-process stock and fixtures.

Setting collision testing for the entire model is a simple step. Right-mouse on the machine object (e.g., “Machine01” ) and select the “Test for collision” menu entry. When the Collision dialog appears, first select the “Entire branch” radio button, then select the “Enable” check box, and finally press OK to set the collision status. A green dot will now be shown in the model navigator in front of each physical component of the model. This green dot indicates that collision testing is enabled for that component; a red dot would be shown if collision testing is disabled. Note: if you have been following the steps up to this point in the manual, the model will now appear in a transparent red color signifying that its objects are colliding.

Collision testing takes CPU. Model performance can be improved by only testing for collisions on objects that are of concern. You can select individual components or a range of components to apply or remove collision testing.

To apply or remove collision testing; right-mouse on the highest component (hierarchically speaking) of interest in the navigator and select the “Test for collision” menu entry. You can enable or disable collision testing on a range of components in the model, starting at the selected component, as follows:

• Current selection: Sets the collision testing status for the object that was selected. This choice is only available if the selected object is a physical component.

• Current selection and direct children: Sets the collision testing status for the object that was selected and all objects directly below it (i.e., a single level only). This choice is only available if one or more of the objects (i.e., selected or children) are physical components.

• Branch to any axis: Sets the collision testing status for the object that was selected and all objects in the branch below it, but no further in the branch than any axis component. Note that a Reference Axis is an “axis” by definition. This choice is only available if at least one of the objects in the branch is a physical component.

• Branch to movable axis: Sets the collision testing status for the object that was selected and all objects in the branch below it, but no further in the branch than any movable axis component. Note that a Reference Axis is not a movable axis. This choice is only available if at least one of the objects in the branch is a physical component.

• Entire branch: Sets the collision testing status for the object that was selected and all objects in the branch below it. This choice is only available if at least one of the objects in the branch is a physical component.

  The following entries on the dialog will be applied to the range of components selected by your choice above:

  • Enable: Set or clear this check box to enable or disable collision testing on the selected objects. When multiple objects are involved, a third “grayed” state is available for the button, which can used to change the safety distance for collision-enabled objects without affecting the collision state of the objects in the branch.

  • Safety zone: Use this field to specify a safe clearance distance around collision enabled objects. A collision will be signaled when another object intersects with the safety zone, which is offset from the original surface by the distance specified. Safety zone testing can use considerably more CPU, so use this feature only where necessary. You can see the effect of the safety zone around objects by toggling Simulation»Show»Safety Zones from the menu bar. This field will be blank if the selected objects have different safety settings.

The collision testing status and safety zone value can also be viewed and modified from the Properties dialog of physical components.

VM tests for collisions only between objects that can move with respect to each other. Another way of saying it is that VM tests for collisions only between objects that are separated from each other in the model navigator by a movable axis (i.e., linear, rotary or curve). A collision occurs when two such objects touch or overlap each other.

Objects are drawn in a red transparent color when colliding, with a highlighted yellow line marking the intersection between the surfaces of the colliding objects. If the safety zone around the object is violated, then the safety zone is drawn in a yellow transparent color, with a high-lighted yellow line marking the intersection between the safety zone surface and the surface of the object that is too close.

Collision testing takes CPU time. Safety zone testing can take considerably more CPU time. You should disable collision testing for any objects where collision testing is not required.