## Updating Dependent Commands When the Alignment Changes

An alignment consists of two transforms:

1. Machine origin to Part origin (termed "Machine-to-Part")

2. CAD origin to Part origin (termed "CAD-to-Part")

If either of the transforms is modified, PC-DMIS will display a Yes/No message similar to the following, letting you choose how the commands dependent on the alignment will be updated:

Yes/No message asking if PC-DMIS should update dependent commands

The text in the message indicates which types of commands and command values may be updated for each alignment change.

Different commands and command values may change depending on the transform that is changed. This table lists the commands and/or command values that may update after a changed transform:

Commands and command values that may update after a changed transform: | Transform Change
Machine-to-Part | Cad-to-Part | Both

- Move commands

- Feature command ACTL

- Feature command THEO

- Feature command TARG

- Move commands

- Feature command THEO

- Feature command ACTL

- Feature command TARG

There are two general scenarios in which you will need to decide how to update the commands in the part program in response to an alignment change:

1. Loading a part program that recalls an external alignment file. See "Updating Commands When Loading a Part Program" below.

2. Adding a new alignment or modifying/deleting an existing alignment while in ‘Learn’ mode. See "Updating Commands While in Learn Mode" below.

Updating Commands When Loading a Part Program

Part programs that include RECALL/ALIGNMENT, EXTERNAL commands attempt to re-load the referenced external alignment files each time the part program is opened.

The correct answer to the question "Update dependent commands?" depends on why the external alignment file has changed:

- If the alignment file has changed because the part has been moved on the CMM then the theoretical and actual values of the commands dependent on that alignment should remain fixed relative to the part (see figure below). The Machine-to-Part transform has been modified. It’s possible the Cad-to-Part transform has also been modified, but that is not very common. In this case, you should choose No at the Yes/No message so the values of the dependent commands are not changed. This allows the position and orientation of the part to change while retaining the previous dimensional information, similar to equating an alignment. This is the most common scenario.

Part Moved on CMM

- If the file has changed because small adjustments have been made to the alignment to see how it affects the measured results without actually re-measuring the part then the values of the dependent commands should be updated to the new alignment coordinate system. The Machine-to-Part transform has been modified, but the Cad-to-Part transform has not changed.

Note: This usually requires the SAVE/ALIGNMENT command be configured to only include the Machine-to-Part transform, not both transforms

In this case, you should choose Yes at the Yes/No message.

- If the file has changed because the alignment origin itself was moved to a new location on the part (for example, the level, rotate, and/or locate features were changed to different features), but the part itself has not moved on the CMM then the theoretical and actual values of the commands dependent on that alignment should be updated to the new alignment coordinate system. The Cad-to-Part transform has been modified, but the Machine-to-Part transform has not changed.

Note: This requires the SAVE/ALIGNMENT command to be configured to include both transforms.

In this case, you should choose Yes at the Yes/No message so that the measured data will not be shifted away from the CAD geometry. This is not a common scenario.

Updating Commands While in Learn Mode

When editing a part program in ‘Learn-mode’, if changes are made that modify or delete an existing alignment command or create a new one, PC-DMIS will display the Update Dependent Commands dialog box letting you choose how the commands dependent on that alignment command will be updated.

The correct answer to the question "Update dependent commands?" depends on why the alignment definition has changed:

- If the alignment definition has changed because the alignment command origin was moved to a new location on the part (for example, the level, rotate, and/or locate features were changed to different features) then the theoretical and actual values of the commands dependent on that alignment command should be updated to the new alignment coordinate system (see the figure below). Both transforms have been modified.

Alignment moved on part

In this case, the you should choose Yes at the Yes/No message so that the measured data will not be shifted away from the CAD geometry. This is a common scenario.

- If the alignment is from a RECALL/ALIGNMENT, EXTERNAL command and the file reference is changed to a different external alignment file that represents the part at a different location on the CMM then the theoretical and actual values of the commands dependent on that alignment should remain fixed relative to the part. The Machine-to-Part transform has been modified, but the Cad-to-Part transform should be the same.

In this case, you should choose No at the Yes/No message so that the values of the dependent commands are not changed. This is a less-common scenario. It allows the position and orientation of the part to change while retaining the previous dimensional information, similar to equating an alignment.