180 Rockwell Automation Publication MOTION-RM002H-EN-P-February 2018
Pending Cam Execution
Alternatively, the MAPC instruction’s execution can be deferred pending
completion of a currently executing position cam. An Execution Schedule
selection of Pending can thus be used to seamlessly blend two position cam
profiles together without stopping motion.
The Pending execution feature is particularly useful in applications like high-speed
packaging when a slave axis must be locked onto a moving master axis and
accelerate using a specific profile to the proper speed. When this acceleration
profile is done, it must be smoothly blended into the operating profile, which is
typically executed continuously. To stop the slave axis, the operating profile is
smoothly blended into a deceleration profile such that the axis stops at a known
location as shown in graphic Pending Cam Execution.
By executing the position cam profile as a Pending cam profile while the current
profile is still executing, the appropriate cam profile parameters are set up ahead of
time. This makes the transition from the current profile to the pending profile
seamless; synchronization between the master and slave axes is maintained. To
ensure smooth motion across the transition, however, the profiles must be
designed such that no position, velocity, or acceleration discontinuities exist
between the end of the current profile and the start of the new one. This is done
using the Logix Designer application Cam Profile Editor.
Once a pending position cam instruction has been executed, the new cam profile
takes effect automatically (and becomes the current profile) when the master axis
passes through either the start or end point of the current profile. If the current
cam is configured to execute once, the new profile is initiated at the completion of
the pass through the current cam profile and the PC bit of the currently active
MAPC instruction is set. If the current cam is configured to execute continuously,
the new profile is initiated at the completion of the current pass through the
current cam profile and the IP bit of the currently active MAPC instruction is
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