Behavior models used in CIP Motion
Rockwell Automation Publication MOTION-RM003I-EN-P - February 2018 43
See also
Motion Control Axis Behavior Model on page 51
State Behavior on page 61
Fault and Alarm Behavior on page 41
Absolute Position Recovery (APR) provides support for establishing and
maintaining absolute position referenced to a specific machine, commonly called
the machine referenced absolute position or just absolute position.
Absolute position is established by a homing procedure initiated by successful
execution of an MAH instruction. Once the homing procedure has successfully
established a machine reference, the Axis Homed bit is set in the Motion Status
attribute, indicating that actual position and command position now have
meaning with respect to the associated machine.
It is good application programming practice to qualify dynamic machine operation
with the Axis Homed bit being set. Otherwise, absolute moves to a specific
position may not have any relationship to the position of the axis on the actual
machine.
Since the homing procedure usually requires the machine to be taken offline and
placed in a manual operating mode, for example, not making product, anything
that would require you to rehome one or more axes on the machine is undesirable.
This is downtime and costs money. The APR feature maintains the machine
reference or absolute position through power cycles, program downloads, and even
firmware updates.
Absolute Feedback Device
The absolute feedback device lets absolute position to be retained through a power
cycle. These devices take various forms, but they all are capable of maintaining
absolute feedback position while power to the drive and to the feedback device is
off.
When power is turned back on, the drive reads the feedback referenced absolute
position from the feedback device and, by applying a saved absolute offset to this
absolute feedback position, the motion control system can recover the machine
referenced absolute position.
Most drive products provide this capability. But what happens if the drive is
swapped out, or the drive firmware is updated? Absolute Position is generally lost.
CIP Motion lets you recover the absolute position not only through power cycles,
but also program downloads, and even firmware updates.
Absolute Position Recovery
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