Kollmorgen
Commissioning
SILVER
LINE
®
Product Family
5-13
Command
Gain
Pot
RL + 1/sCL
1
-------
Ls + R
Motor
Current
+
-
PWM
Motor
TP
IFB (.2v = Cont. Current)
RSAMPLE
1/RS
VBus/6
1/RFB
Figure 5-7 Simplified Frequency Domain Model
5.4.2 Non-Linearities
Tuning is based on linear control theory. The most important requirement of a linear controller is that the total
reflected inertia should not change substantially during operation. Load inertia includes all the inertia reflected to the
motor, such as inertia through gearboxes and leadscrews. Inertia can change in ways that are easy to understand, such
as the inertia of a spool of cable decreasing when the cable is unrolled. It can also change in less intuitive ways, such
as chain drives (which have load in one direction but are unloaded in the other) and systems with excessive backlash
(where there is no load when gear teeth are not touching).
When the inertia changes, the system has the following characteristics:
•
System performance is excellent when the motor is in some positions and unacceptable when the motor is in
other positions.
•
Reducing the bandwidth eliminates the problem.
If the system performance is poor because of changing inertia, you can make the following corrections:
•
Correct the system mechanics so that inertia is constant.
•
Detune (that is, reduce the bandwidth of) the system.
5.4.3 Resonance
Resonance is a high frequency (> 500 Hz) where the system mechanics oscillate. Normally, systems with resonance
will be very stable when you tune with lower target bandwidths. As you increase the target bandwidth, you begin to
hear a fairly pure, high pitch. If you want to decrease resonance, use shorter, larger diameter driving shafts.
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