
5.FUNCTION DESCRIPTIONS FANUC AC SPINDLE MOTOR αi series B-65280EN/05
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5.10.3 Block Diagram
The following shows a block diagram of dual position feedback:
+
Velocity
control
Move
command
Σ
Velocity feedback
Kp
mplifier
Conversion
coefficient
Σ
Primary delay time
constant
Position feedback (from motor sensor)
Position feedback (from motor sensor)
ER1
Spindle motor
Position gain
+
-
+
+
+
-
Spindle
sensor
ER
ER2
+
-
-
Spindle
Motor
sensor
Position feedback (from the spindle sensor)
As shown in the above diagram, error counter ER1 in the semi-closed
loop and error counter ER2 in the closed loop are prepared. The
primary delay time constant is expressed as follows:
Primary delay time constant = (1 + τ s)
-1
Here, consider actual error ER by time constant.
(1) When time constant τ = 0: (1 + τ s)
-1
= 1
ER = ER1 + (ER2 - ER1) = ER2 (error counter in the closed
loop)
(2) When time constant τ = ∞: (1 + τ s)
-1
= 0
ER = ER1 (error counter in the semi-closed loop)
From the primary delay time constant, control can be provided in the
semi-closed loop when a transition state is present, and control can be
provided in the closed loop when positioning is performed. According
to this principle, vibration during movement can be suppressed to a
level equivalent to the level obtained in the semi-closed loop.