Chapter 4 Running
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3. Position loop gain Kp
The position loop gain directly determines the reaction speed of the position loop. Under
the premise that the mechanical system does not produce vibration or noise, the position loop
gain value is increased to accelerate the reaction speed, reduce the position tracking error, and
shorten the positioning time. However, too large a setting will cause mechanical system jitter or
positioning overshoot. Position loop bandwidth shall not be higher than speed loop bandwidth,
generally:
4
Hz)(bandwidth loop Speed
)(bandwidth loopPosition Hz
If the load moment of inertia ratio G is set correctly (G=J
L
/J
M
), then the position loop gain
Kp is calculated as follows:
4
)(
2)/1(
HzK
sK
v
p
4.5.2
Gain adjustment steps
The bandwidth selections of the position and the speed loop depend on the machinery
rigidity and the application situation. A leather belt conveyer has low rigidity and may set low
bandwidth. Machinery with reducer and ball bearing screw has medium rigidity and may set
medium bandwidth. Machinery with ball bearing screw or linear motor has higher rigidity and
may set high bandwidth. If mechanical characteristics are unknown, may gradually increase the
bandwidth until resonating, and then decreases the gain
In the servo system, if changes a parameter, then other parameters also need to readjust.
Therefore, do not change a parameter far from its original value. About the steps for changing
the servo parameter, please observe the following principle generally:
Increase response Decrease response，restrain vibration and overshoot
1.Increase gain of speed loop K
v
2.Decrease integral time constant of
speed loop T
i
3.Increase gain of position loop K
p
1.Decrease gain of position loop K
p
2.Increase integral time constant of speed loop T
i
3.Decrease gain of speed loop K
v
Gain adjustment procedure for speed control loop:
1. Set the moment of inertia ratio of the load.
2. Set the speed loop integral time constant for larger values..
3. The gain of the speed loop is increased within the range of no vibration and abnormal
sound, and slightly reduced if vibration occurs.
4. The integral time constant of the speed loop is smaller in the range of no vibration, and if
the vibration is slightly increased..
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