270 Rockwell Automation Publication MOTION-UM003K-EN-P - January 2019
Chapter 12 Homing
APR Fault Generation
A project download, restore from a memory card, or a ControlFLASH
firmware update after one of these events can cause an APR fault:
• Axis configuration
– Change in any of the axis attributes that impacts the absolute
machine position.
• Attribute changes
– Offline edits of the axis attributes or configuration do not cause an
APR fault until after download occurs.
– Online edits of certain attributes result in an immediate APR fault.
Changing the axis feedback device or feedback polarity without
downloading the project also generates an immediate APR fault.
• Axis hardware change or malfunction.
• Axis hardware resource insufficiency.
– Hardware resource insufficiencies are detected only during download
or ControlFLASH firmware update.
• Reconnection of the drive axis.
When an APR fault occurs, the actual position of the axis is set to the feedback
reference position of the axis. This value is read from the absolute encoder of
the axis. The APR Fault clears the axis homed status bit.
Downloading of a Project
The following checks are made during a download of a project:
1. Does the Axis exist? If not, then it is a new axis and no APR fault occurs
or is generated.
2. Does the Scaling Signature match the saved Scaling Signature?
3. Does the Feedback Serial Number match the saved Feedback Serial
Number?
If these three checks pass, absolute position is restored.
During operation, the system monitors changes to that following attributes.
These attributes do not affect the Scaling Signature or result in the loss of the
absolute machine reference and therefore do not generate an APR Fault.
•Conversion Constant
• Position Unwind
•Travel Mode
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