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Our purpose is to get the highest system stiffness but lowest motor noise. However,
sometimes we need to trade off between them because high loop gain leads to big
overshoot even vibration. In this example, we start with small loop gain and then
back off, at the time when the motor noise begins. The Kaff (application
feed-forward gain) will be increased to further reduce the position following error if
necessary. The tuning procedure is shown as follows:
①Small Vp/Kp/Kaff ②Vp↑ , Vp↓
Step 1: Set Vp = 90, Vi = 0, Kp = 300, Kaff = 0, Kd = 500, Encoder line = 4000.
Please hit the "Enter" key in the keyboard and click Option->SaveToDrive after
changing the parameter. The initial value for the tuning is depending on supply
voltage, motor and reflected load inertia. The above settings may not suitable for
your system. Please adjust them according to different symptom as follows:
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Decrease Vp/Kp if the motor generates big noise.
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Increase Vp/Kp if the drive's red LED blinks (Protection mode).
Tip: Giving an external torque by rotating the motor shaft (or moving the load)
manually is good way to check whether the Vp and Vd are suitable or not. If it
is hard to rotate/move and the motor generates big noise, you should lower
down Vp/Kp. If it is easy to rotate/move and even the drive goes into
protection mode (the red LED blinks), you should increase Vp/Kp.
Figure 6-27: Observe the motor noise/vibration when increasing loop gain
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③Kp↑ , Kp↓ ④Kaff↑
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Step 2: Increase Vp until motor noise/vibration begins. Then back off. To activate
the noise/vibration, sometimes you need to give a disturbance to the load by either
clicking the Start button or trying to push/pull the load. In this example, we give Vp
120, 150, 200, 250 and find that the noise/vibration at Vp=250 can be accepted. So
we stop increasing Vp. Figure 6-28 shows the velocity (The green curve) and
position following error (The blue curve). And we can see the current position
following error is 1074 at the top of the digital scope.
Tip: The digital scope displays actual velocity (the green curve) and position
following error (The blue curve) as shown in figure 6-28. It is the result of the
trapezoidal velocity test by clicking Start button. Click the button once again to
hold on the curves (The button caption is "Start"). Otherwise the scope will be
always updated (The button is "Stop"). The user can put the mouse (cursor) on
the curve to check the curve point value at the top status bar.
Actual Current
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Actual Velocity
Time
Following Error
Kp = 300
Position following error = 1074
Figure 6-28: Digital scope for position/velocity loop tuning
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Green Curve:
Actual Velocity
Blue Curve:
Position Following Error
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