Rockwell Automation 1746-BLM Blow Molding Module Installation Instructions - Manual (Page 18)

18 Blow-molding Module
Publication 1746-IN014B-EN-P - January 2001
Step: 5 Determining an axis setpoint
All position setpoints and process variables are represented in the SLC500 16-bit
signed integer format, where the minimum value of -32768 corresponds to
zero-scale (fully-closed or fully-forward) and the maximum value of +32767
corresponds to full-scale (fully-open or fully-retracted).
The setpoint for a machine axis comes from one of four prioritized sources: an
active profile or one of three hold values. When enabled, the profile setpoint is
highest priority. In absence of an active profile, hold values 0, 1 and 2 are applied
in order of decreasing priority, with value 0 having the highest priority.
The tooling position for hold values is a function of the user setpoint and
calibration data. Profile setpoints may be affected by three other factors:
•
offset adjustment from the axis control structure
•
scale factor from the axis control structure
•
offset resulting from a comparison of the current profiles mean value with
that of a previous profile
The offset and scale adjustments are provided to let you manipulate the weight of a
profile without individually changing each setpoint in the original profile and
re-downloading. The mean value comparison is done as part of an “automatic
weight control” feature.
When the weight control bit in the output file is set, the current profile mean value
is calculated. Subsequent profiles are then offset to achieve this same mean value.
This maintains a constant part weight. Note that all such modifications to profile
setpoints are performed immediately after a profile is downloaded. To modify a
profile iteratively, you must repeatedly set the control bit that downloads the
setpoint profile.