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1-3
Configuration Example of Servo System
Command pulses
(Position command)
Deviation counter
Position gain
Speed gain
Current gain
Motor
Current feedback
Speed feedback
Speed detection
Feedback pulse (position feedback)
Encoder
or resolver
Position Control Unit with analog output
Position Control Unit with
pulse-train output
Servo Driver with analog input
Servo Driver with pulse-train input
Servomotor
1-1-2 Gain
The gain is another word for magnification.
The difference between the command and response values in a feedback loop is multiplied by the gain
and the result is output from the feedback loop. The difference between the target position and present
position in the position loop, for example, is obtained as a position deviation or deviation counter value.
The value multiplied by the position loop proportional gain is output as a speed command.
In the actual Servo System, the target position is expressed by command pulses and the present posi-
tion is expressed by feedback pulses, both from which the position deviation per time unit is calculated.
The deviation counter totals all the per-time-unit position deviations to obtain the position deviation of
the Servo System.
Target
position
(Position
command)
Position deviation
x Position loop proportional gain
(Position gain: Kp)
Present position
Speed
command
to speed
loop
The higher the gain of any feedback loop is, the higher the output of the feedback loop is. In other words,
if the gain increases, the output power to fix the deviation will increase. The Servo System with high
gains is ideal because the gains ensure a high response speed and reduce errors. If the gains are too
high, however, the Servo System will cause machine vibration according to the size and rigidity of the
machine system. The Servo System, therefore, requires gain adjustment according to the machine sys-
tem.
Note
Rigidity indicates the engagement strength of the machine system. The backlash or spring por-
tion of a machine system reduces the rigidity of the machine system.
Gain Adjustment
Chapter 1
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