
B-65150E/04 4. SERVO FUNCTION DETAILS
− 123 −
(2) Control method
The following block diagram shows the general method of dual
position feedback control:
Fig. 4.5.4 Block diagram of dual position feedback control
As shown in Fig. 4.5.4, error counter ER1 in the semi-closed loop
system and error counter ER2 in the closed loop system are used. The
primary delay time constant is calculated as follows:
Primary delay time constant = (1 + τs)
−1
The actual error, ER, depends on the time constant, as described below:
(1) When time constant τ is 0 ⋅⋅⋅⋅⋅⋅ (1 + τs)
−1
= 1
ER = ER1 + (ER2 − ER1) = ER2 (error counter of the full-closed
loop system)
(2) When time constant τ is ∞ ⋅⋅⋅⋅⋅⋅ (1 + τs)
−1
= 0
ER = ER1 (error counter of the semi-closed loop system)
This shows that control can be changed according to the primary delay
time constant. The semi-closed loop system applies control at the
transitional stage and the full-closed loop system applies control in
positioning.
This method allows vibrations during traveling to be controlled as in
the semi-closed loop system.
Velocity
control
MCMD
Σ
Velocity feedback
Kp
Amplifier
Conversion
coefficient
Σ
Primary delay
time constant
Position feedback (from motor)
Position feedback (from separate detector)
ER1 Motor
Position gain
+
−
+
+
+
−
Separate
detector
ER
ER2
+
−
+
−