Rockwell Automation 1746-BLM Blow Molding Module Installation Instructions - Manual (Page 12)

12 Blow-molding Module
Publication 1746-IN014B-EN-P - January 2001
Control of Reciprocating Screw Machines
Reciprocating screw machines have multiple heads and a single accumulator.
Control of accumulator position is performed by the SLC processor. The module
may be used to monitor the accumulator (screw) position in either of two ways on
this type of machine:
•
with an analog input to the module: Each module configured in this
manner can control three heads. This method offers optimal performance.
However, hardware utilization may not be as high as the following method
depending on the number of extrusion heads.
•
with a separate high speed analog module: The SLC processor must
read position information from an analog module and update the 1746-BLM.
A selectable timed interrupt (STI) instruction can be used with a 4ms period
and variability << 1ms (tested on a SLC5/04 CPU with no other interrupt
sources). This is adequate for 256- setpoint profiles with drop times > 1
second (~4ms/setpoint). Drop times of less than one second necessitate
monitoring accumulator position with the 1746-BLM. Avoid using other STI
instructions with higher priority.