Rockwell Automation 1771-QDC, D17716.5.85(Passport) MNL. PLASTIC MOLDING MODULE - Manual (Page 153)

Tune Your Machine for Producing Parts
Chapter 10
10-7
Tune velocity loops with an oscilloscope
Before you begin tuning your velocity loops, confirm that you:
selected the velocity vs. position algorithm
selected closed-loop control
zeroed the feedforward term
did not change the proportional term entered in chapter 7
disabled
ERC
reset ERC values
disabled
ramping
downloaded all setpoint changes to the QDC module
1. Connect the oscilloscope to your selected pressure control valve.
2. Enter the desired operational profile for a production cycle.
3. Run several profile cycles while observing the oscilloscope trace.
Ideally for each step of a multi-stepped profile, the oscilloscope trace
should rise or fall quickly and then flatten without bouncing.
If: Then:
Your scope trace for any given profile step
never levels off (it is either rising or falling for
the entire step)
Increase the proportional term
Your scope trace for any given profile step
rises (or falls) quickly and then bounces" or
chatters" around a voltage/current
Decrease the proportional term
Excessive hammering and vibration is
observed in the cylinder's hydraulic lines
Decrease the proportional term
Important: Each time you change a gain constant, you must download the
change to the QDC module. Refer to the download procedure in chapter 4.
4. Re-run the profile after each change to the proportional term until
oscilloscope traces quickly level off without bounce or chatter.
Important: If you cannot alter the proportional term so that oscilloscope
traces quickly level without bounce, verify that your Unselected Valve Set-
output Values are OK. (See same topic later in this chapter or in chapter 7).
5. If you are satisfied with the Unselected Valve Set-output Values and
still cannot make the oscilloscope trace quickly level off without
bouncing, your control may require a small feedforward gain.
6. If necessary, slowly increase the feedforward term while running
machine cycles until the oscilloscope trace levels off without bounce.
Important: If you must use feedforward gain to adequately tune your
velocity profile, do NOT enable ERC for this profile.