SERVO ADJUSTMENT
A.3.2 Manual Adjustment
— A-10 —
Speed Loop Integration Time Constant (Cn-05)
The speed loop has an integration element to allow response to micro-inputs.
This integration element can produce a delay in the servo system, and the positioning
setting time increases and response becomes slower as the time constant increases.
However, the integration time constant must be increased to prevent machine vibration if
the load moment of inertia is large or the mechanical system includes a vibration ele-
ments.
The following formula calculates a guideline value.
Ti: Integration Time Constant (s)
Kv: Speed Loop Gain (Hz)
Ti
≥
2.3
×
1
2
π
×
Kv
Torque Reference Filter Time Constant (Cn-17)
When a ball screw is used, torsional resonance may occur which increases the pitch of
the vibration noise.
These vibrations can sometimes be overcome by increasing the torque reference filter
time constant.
This filter will, however, produce a delay in the servo system, just like the integration time
constant (Cn-05), and its value should not be increased more than necessary.
Position Loop Gain
The position loop gain parameter sets the servo system response.
The higher the position loop gain is set, the better the response and shorter the position-
ing times.
To enable a high setting of the position loop gain, increase the machine rigidity and raise
the machine characteristic frequency.
Increasing the position loop gain only to improve the response can result in oscillating
response of the overall servo system, that is, the speed references output from the posi-
tion loop oscillate. Therefore, also increase the speed loop gain while observing the re-
sponse.
Adjustment Procedure
1) Set the position loop gain to a low value and increase the speed loop gain (Cn-04) within
the range so that no abnormal noise or oscillation occurs.
2) Slightly reduce the speed loop gain from the value at step 1, and increase the position
loop gain in the range that no overshooting or oscillation occurs.
3) Determine the speed loop integration time constant (Cn-05), by observing the positioning
set time and vibrations in the mechanical system.
The positioning set time may become excessive if the speed loop integration time
constant is too large.
A
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