User manual

182 Rockwell Automation Publication MOTION-UM003F-EN-P - March 2015
Chapter 8 Home an Axis
Absolute Position Recovery
(APR)
APR is the recovery of the absolute position of an axis that has been machine
referenced after a power cycle, or reconnection. The terms Absolute Position and
Machine Reference Position are synonymous.
APR Terminology
This table describes terminology related to the APR feature.
APR Supported Components
There are differences in the way the 1756-L6x, 1756-L6xS, and the 1756-L7x
ControlLogix controllers recover machine position:
• The 1756-L6x and 1756-L6xS controllers have a battery and use a
CompactFlash card to save information.
• The 1756-L7x controller has a 1756-ESMxxx module and uses a Secure
Digital (SD) card to save information.
• The 1756-L6x and 1756-L6xS series A controllers have a battery to
recover the position after a power cycle but does not support APR.
• The 1756-L6 and 1756-L6xS series B controllers recover the position after
a download or restore from CompactFlash software card or a firmware
update from the ControlFLASH utility. A battery is not required.
• The 1756-L7x controller with a ControlLogix Controller Energy Storage
Module (ESM) works the same as the 1756-L6x series B controller with a
battery.
• The 1756-L7x controller without a ControlLogix Controller Energy
Storage Module (ESM) works like a 1756-L6x series B controller without
a battery.
Term Description
Absolute Feedback Position Position value read from an absolute feedback device.
Incremental Feedback Position Position value read from an incremental feedback device.
Feedback Position Value read from a feedback device, absolute or incremental.
Absolute Position
Absolute Machine Reference Position
Machine Reference Position
Position registers in the 1756-L6x
(1)
, 1756-L6xS, and 1756-L7x controllers
after the following instructions have been executed on a machine with an
absolute or an incremental feedback device:
• MAH, machine home
• MRP, machine redefine position
(1) The 1756-L6x controllers are not supported in the Logix Designer application, version 21.00.00 and later.
A machine home/reference Establishes a Machine Reference Offset as follows:
HomeOffset =
ConfiguredHomePosition - AbsoluteFeedbackPosition
AbsoluteMachineReferencePosition = AbsoluteFeedback Position
+ HomeOffset
Absolute Position Recovery (APR) Recovers the Absolute Machine Reference Position by maintaining the
Home Offset through various scenarios as described on page 183
.