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4. Servo Adjustment
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4-4-3 Dual feedback control (Optional function)
If the motor and machine coupling or machine system's rigidity is low (ex. large machine, etc.) when
using a closed loop system, the response during acceleration/deceleration will vibrate and cause
overshooting. This can cause the position loop gain from increasing. The dual feedback function is
effective in this case.
To validate the dual feedback function, use position feedback with a motor end detector in ranges with
high acceleration to enable stable control. In ranges with low acceleration, use position feedback with
the tool end detector (scale). This will make it possible to increase the position loop gain.
Dual feedback control
The state will approach the semi-closed loop system as the primary delay filter's time constant
increases, so the position loop gain limit will increase. Note that the limit of the position loop gain
increased with the dual feedback function is the same as the position loop gain limit for a semi-closed
system that does not use a tool end detector(scale, etc.). In addition, the positioning time will increase
as the primary delay filter time constant increases.
POINT
1. Dual feedback control is a function that compensates symptoms resulting
from insufficient machine rigidity. If there are items that can be improved on
the machine (improvement of scale installation position, etc.) improve those
first.
2. The position loop gain limit will not increase compared to the semi-closed
loop system even when using dual feedback control.
3. Dual feedback control is an optional function. If the option is not set in the
NC, alarm 37 (at power ON), or warning E4 and error parameter No. 103
(2303 for M60S/E60 Series NC) will be output.
Position control
Primary
delay filter
High frequency
FB element
Low frequency
FB element
dead band
SV052
SV051
Position
command
+
-
Position droop
Servo-
motor
ENC
Linear scale
Table
Speed
command
Tool end
p
osition FB
Motor end position FB
+
-
+
-