CNC Setup Utility Manual
P/N 70000490C - Tuning the Current, Velocity, and Position Controller
All rights reserved. Subject to change without notice.
5-5
10-December-04
If the frequency is between 600 and 700 Hz., only the FIR is used with a
gain of 1.
If the frequency is between 700 and 833 Hz., the FIR filter is used with a
gain of 2.
Velocity Controller Auto-tuning Test
The system provides an auto-tuning feature for the velocity controller.
The position loop must be open for this test.
To auto-tune the velocity controller
1. The Software Options menu, select
Motion Setup/Testing
(option 3) and press
ENTER
.
2. Press
TuneMod
(
F6
). Select
Automatic
and press
ENTER
.
3. On the MST screen, select an axis [
X
,
Y
,
Z
,
U
, or
S
(spindle)]. This
activates the axis.
4. Press
Tuning
(
F7
) to display a pop-up menu with the tuning mode
tests. Select
Velocity Tune
, and press
ENTER
.
No initial parameter is needed. The test always starts from low gain
values to avoid motor resonance.
The first phase of the test is proportional gain tuning. The gain is
increased by 200 per test iteration. A step of 600 mm/min is sent to
the velocity controller. After 128 samples (step response), an inverted
step is sent again to return the motor to its original position. The
frequency spectrum of the step response is calculated through a Fast
Fourier Transform (FFT).
Then the power spectral density (PSD) is calculated from the FFT.
The total signal energy is calculated from the PSD, and also the
energy content in the frequency band from 180 Hz. to 540 Hz.
The energy percentage of this band with respect to the total energy is
calculated. If the percentage is more than 50% (system near point of
oscillation), this phase is stopped and half of the proportional gain is
chosen as the optimal. At all moments during this phase, the velocity
proportional gain and the energy percentage are shown in the test
window. After an energy percentage of 20%, there is a check for
increasing motor oscillations (motor becomes unstable). If this
happens, the test is stopped and an error message is issued.
