
4. SERVO FUNCTION DETAILS B-65150E/04
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4.5.2 Observer Function
(1) Overview
The observer is used to eliminate the high-frequency component and to
stabilize a velocity loop when a mechanical system resonates at high
frequency of several hundred Hertz.
The observer is a status observer that estimates the controlled status
variables using the software.
In a digital servo system, the speed and disturbance torque in the
control system are defined as status variables. They are also estimated
in the observer. An estimated speed consisting of two estimated values
is used as feedback. The observer interrupts the high-frequency
component of the actual speed when it estimates the speed. High-
frequency vibration can thus be eliminated.
(2) Explanation
Fig. 4.5.2 (a) shows a block diagram of the velocity loop including an
observer.
Fig. 4.5.2 (a) Configuration of velocity loop including observer
Fig. 4.5.2 (b) shows a block diagram of the observer.
Fig. 4.5.2 (b) Block diagram of the observer
POA1, POK1, and POK2 in Fig. 4.5.2 (b) correspond to digital servo
parameters. The observer has an integrator as a motor model. POA1 is
a coefficient that converts the torque command into motor acceleration
and is the characteristic value of the motor. The motor model is
accelerated by this value. The actual motor is also accelerated by the
torque and disturbance torque that it generates.
PK1V/s + PK2V
TCMD
−
Velocity feedback
Estimated speed
+
Kt/(Jm • s)
Observer
VCMD
1/(Jm • s)
TCMD
+
−
Kt
Disturbance
POK1POK2/s
1/s
POA1
+
Velocity feedback
Motor
++
+
+
Motor model
Estimated
speed