User`s manual

D-6 Motion Mate™ DSM314 for Series 90™-30 PLCs User's Manual – January 2001 GFK-1742A
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2. Connect an oscilloscope to the analog outputs for Motor Velocity feedback and Torque
Command. See Section 4.25 of Chapter 5 for analog output configuration instructions.
3. Set the Velocity Loop Gain to zero. This is a conservative approach. If the application is
known to not have resonant frequencies from zero to approximately 250 Hz, you can start
with a higher value, but do not exceed the value calculated in equation 1 at this point.
4. Generate a velocity command step change. At this point the step change should be relatively
small compared to the full speed of the machine. Ten to 20 % of the rated machine speed is a
good start.
5. Observe the Motor Velocity and Torque Command on the oscilloscope. The objective is to
obtain a critically damped velocity loop response. Pay particular attention to any oscillations
that are occurring in the velocity feedback signal.
6. Increase the
Velocity Loop Gain
in small steps and repeat 4 and 5 until instability in the
Motor Velocity feedback signal is observed. Once this point is reached, decrease the
Velocity
Loop Gain
by at least 15 %. As a general rule, the lower the
Velocity Loop Gain
value that
meets the system requirements the more robust the control. You should carefully observe the
velocity feedback signal. In some applications, running the
Velocity Loop Gain
high enough
to create instability can cause machine damage. If in doubt, adjust the
Velocity Loop Gain
to
be no greater than the value calculated in equation 1. If oscillations are observed in the
Motor Velocity feedback signal prior to this point, decrease the
Velocity Loop Gain
and
continue with step 7 below.
7. The velocity loop is tuned at this point. However, the robustness of the loop must be checked.
To perform this test, introduce velocity command steps in increments of 20% Rated Machine
Speed, 40% Rated Machine Speed, 60% Rated Machine Speed, 80% Machine Rated Speed,
and 100% Rated Machine Speed. Observe the Motor Velocity and Torque Command signals
for any instability. If an instability or resonance is observed, reduce the
Velocity Loop Gain
and repeat the test.
Note
For Digital servos, the %AQ Force Analog Output command can provide
Torque Command or Commanded Motor Velocity. (Velocity = 750 rpm/volt
and %TqCmd = (100/1.111111 Volt)*X Volt or Torque Cmd = 100%
Torque Command = 1.111 Volts, 100%TqCmd = MaxCur Amplifier. For
instance: Beta 0.5 MaxCurAmp = 12 amps => 1.111111Volt = 12 amps.
Sample Velocity Loop Tuning Session
A sample velocity loop tuning session is shown in the plots that follow.