Rockwell Automation 1771-QDC, D17716.5.87(Passport) CLAMP AND EJECT MODE - Manual (Page 185)

Tune Your Machine
Chapter 10
10-12
Important: When controlling the clamp and ejectors, we do not
recommend enabling ERC control unless extreme adherence to velocity or
pressure setpoints is absolutely required.
Enable ERC when:
Strict adherence to velocity or pressure (not position) setpoints is
required. One example of when ERC may be of great value is during
closed-loop Low Pressure Close control, when it is absolutely
undesirable to exceed the pressure setpoint.
Disable ERC when:
You cannot achieve repeatable clamp and ejector performance.
Your primary clamp and ejector control objective is repeatable
positioning. Without ERC, the QDC module may not be able to “land”
the clamp or ejector on precisely the position you programmed;
however, it overshoots the programmed position by an absolutely
repeatable amount that is relative to cylinder speed and the QDC
module’s two millisecond scan time.
You have not yet tuned the machine to run accurately under closed-loop
control.
Jerky, abrupt clamp motion is observed after enabling ERC control. This
usually occurs when ERC has been added to a control loop that has not
been properly tuned. The ERC algorithm begins to correct for improper
tuning, and incidentally causes the clamp or ejector to run in a rough
fashion while the QDC module obtains the desired control.
When utilizing excessively slow profile (stroke) acceleration or
deceleration ramp rates in an attempt to “smooth” the clamp or ejector
operation. Ramp rates and ERC do not always function properly
together, and care should be taken whenever utilizing both for
conjunctive control.