Rockwell Automation GMLC Reference Manual - Manual (Page 297)

Publication GMLC-5.2 - November 1999
260 Motion Blocks
When a good registration event occurs on the registering axis, the
PCAM_good_registration_count axis variable is incremented and the
previous registration position is subtracted from the appropriate
registration position to determine the distance between this registration
event and the last one. The specified nominal length is then subtracted
from this registration distance to determine the registration error. This
registration error is then unwound to ±
1 /
2
the specified nominal length,
accumulated, and used to phase shift the slave axis via a dedicated auto-
correction indexer to correct for error trends in the registration distance.
See Phase Shift Moves in the Move Axis section of this chapter for more
information on phase shift moves.
The maximum magnitude of the auto-correction move for each cycle is
limited to ±
1 /
2
the specified nominal length by adding or subtracting the
nominal length value to/from the registration error if it exceeds ± 1 /
2
the
specified nominal length. This unwinding of the registration error means
that the slave axis always phase shifts to the closest synchronization point
within the current product cycle.
In addition, unlike absolute auto-registration, if the relative auto-
correction move does not complete before the next good registration
event occurs, the new registration error is added to the remaining distance
to go of the auto-correction indexer. By accumulating the registration
error in this manner, the registration events can occur much more
frequently than with absolute auto-correction, where the full registration
error must be corrected within the current product cycle. This causes
relative auto-correction to correct for trends in the registration error rather
than the full registration error.
When relative auto-correction is enabled:
• PCAM_auto_correction_status = 1
• the current registration error is available in the
PCAM_registration_error variable
• the average registration error over the last ten registrations is
available in the PCAM_average_ registration_error variable