
B-65150E/04 4. SERVO FUNCTION DETAILS
− 117 −
The disturbance torque works on the actual motor. There is a time lag
in the current loop. The POA1 value does not completely coincide with
the actual motor. This is why the motor’s actual velocity differs from
the motor speed estimated by an observer. The observer is
compensated by this difference. The motor model is compensated
proportionally (POK1), and the observer is compensated integrally
(POK2/s).
POK1 and POK2 act as a secondary low–pass filter between the actual
speed and estimated speed. The cutoff frequency and damping are
determined by the POK1 and POK2 values. The difference between
the observer and low-pass filter lies in the existence of a POA1 term.
Using POA1, the observer’s motor model can output an estimated
speed that has a smaller phase delay than the low–pass filter.
When an observer function is validated, the estimated speed in Fig.
4.5.2 (b) is used as velocity feedback to the velocity control loop. A
high–frequency component (100 Hz or more) contained in the actual
motor speed due to the disturbance torque’s influence may be further
amplified by the velocity loop, and make the entire system vibrate at
high frequency. The high frequency contained in the motor’s actual
speed is eliminated by using the velocity feedback that the observer
outputs. High–frequency vibration can be suppressed by feeding back
a low frequency with the phase delay suppressed.
In some systems, the use of the observer function can suppress
vibration during movement but makes the machine unstable while it is
in the stop state. In such cases, use the function for disabling the
observer in the stop state, as explained in Art. (6) of this section.
(3) Setting parameters
#7 #6 #5 #4 #3 #2 #1 #0
1808 8X03 OBEN
2003 1003
OBEN (#2) 1: To enable the observer function
1859 8X47 Observer coefficient (POA1)
2047 1047
Usually, use the standard setting.
1862 8X50 Observer coefficient (POK1)
2050 1050
Usually, use the standard setting.
1863 8X51 Observer coefficient (POK2)
2051 1051
Usually, use the standard setting.