User`s manual
5-27
5
Functions
5. Functions
5.9 Adjusting the control gain
This section describes the method for adjusting the control gain required when adjusting
the servo system.
Adjusting the control gain is not required when setting the parameters by following the
description in 6.3.3, "Reference graph for setting the acceleration and position control
cut-off frequency".
If a higher motion response is needed, set the parameters according to the methods for
adjusting the control gain explained below.
Main parameter constants you need to adjust are as follows.
• Mover mass (Fd-00)
• Speed control cut-off frequency (Fd-01)
• Position control cut-off frequency (Fd-09)
The block diagram for the servo system is shown below.
++
+
Detector
Robot
Position
control
Speed
control
Current feedback loop
Speed feedback loop
Position feedback loop
Position
command
Setting
Mover
mass
(Fd-00)
Position control
cut-off frequency
(Fd-09)
Speed control
cut-off frequency
(
Fd-01
)
Current
control
Power
converter
5.9.1 Basic rules of gain adjustment
(1) The servo system is made of 3 loops consisting of a position control loop, a speed
control loop, and a current control loop. The internal loop process and the response
(cut-off frequency) must be set to a high level. You need to adjust the position control
loop gain and the speed control loop gain. The current control gain has sufficient
response so no adjustment is needed.
(2) The position control loop and the speed control loop require making a setting that
yields a balanced response. Basically, set the loop gain in a range that holds the
relation: "Position control cut-off frequency" (Fd-09) is lower than "Speed control
cut-off frequency" (Fd-01).
As a general guide when making this setting, the "Position control cut-off frequency"
(Fd-09) should be less than 1/6th of the "Speed control cut-off frequency" (Fd-01).
(3) The mechanical system might sometimes oscillate if the response of the position
control loop is set to a high value. The gain cannot be set any higher than this so use
caution. Usually, the response of the position control loop cannot be set higher than
the characteristic oscillation frequency of the mechanical system. Set a loop gain that
matches the rigidity and strength of the mechanical system. Setting the response and
the rigidity of the mechanical system is described next.