Rockwell Automation 1771-QDC, D17716.5.86(Passport) PLASTIC MOLDING MODULE - Manual (Page 229)

Tune Your Machine
Chapter 10
10-21
Pressure-limited velocity vs. position differs from both velocity and
pressure injection control. During normal operation, pressure-limited
velocity control acts the same as velocity vs. position control. However,
when ram (screw) pressure exceeds a preset, the QDC module changes
from velocity to pressure control to guard against flashing the mold.
Use pressure-limited velocity vs. position control during:
Set-up – It lets you enter a pressure-limiting preset just below the mold
flash point to guard against flashing the mold.
Normal operation – It lets you run high speed velocity vs. position
profiles while guarding against flashing the mold.
In general, pressure-limited injection velocity works as follows starting
with velocity control:
When the QDC module And And Then the QDC module
Controls ram velocity Ram pressure
exceeds IPC57
Ram position is within
pressureĆlimit zone
defined by IPC58
1) Freezes its outputs at current levels.
2) Starts time delay in IPC59.
Freezes its outputs after
ram pressure exceeds
IPC57 during velocity
control
Time delay IPC59
expires
Ram pressure
exceeds IPC57
1) Switches to PID control of the selected pressure
valve using IPC57 as the PID setpoint..
2) Resets the selected velocity valve (if different
from the selected pressure valve) to its setĆoutput
value from INC09Ć12.
Ram pressure is less
than IPC57
Resumes velocity control.
Controls ram pressure Ram velocity exceeds
a segment setpoint
--- 1) Freezes its out puts as current levels.
2) Starts time delay IPC59.
Freezes its outputs after
ram velocity exceeds a
segment setpoint during
pressure control
Time delay IPC59
expires
Velocity exceeds the
segment setpoint
1) Returns to VelFF control of the selected velocity
valve using current setpoint.
2) Resets the selected pressure valve (if different
from the selected velocity valve) to its setĆoutput
value from INC09Ć12.
Velocity is less than
the segment setpoint
Resumes pressure control
PressureĆlimited
Velocity vs. Position
Injection