Rockwell Automation Publication MOTION-RM002H-EN-P-February 2018 181
cleared. The motion controller keeps track of the master axis and slave axis
positions relative to the first profile at the time of the change and uses this
information to maintain synchronization between the profiles.
If the Execution Schedule of an MAPC instruction is set to Immediate and a
position cam profile is currently in process, the MAPC instruction errs. This is
true even when the axis is waiting to lock onto the master axis.
If an Execution Schedule of Pending is selected without a corresponding position
cam profile in progress, the MAPC instruction executes but no camming motion
occurs until another MAPC instruction with a non-pending Execution Schedule
is initiated. This allows pending cam profiles to be preloaded prior to executing
the initial cam. This method addresses cases where immediate cams would finish
before the pending cam could be reliably loaded.
After a Pending position cam has been configured, the Position Cam Pending
Status bit of the Motion Status word for the specified slave axis is set to 1 (true).
When the pending (new) profile is initiated and becomes the current profile,
Position Cam Pending Status bit is immediately cleared as shown below.
Master Reference
The Master Reference parameter determines the master position source to link to
the cam generator. This source can be actual position or command position of the
master axis. Smoother motion is derived from command position but in some
cases, for example when a physical axis is not controlled by a ControlLogix motion
module, actual position is the only practical option.
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