ElmoMC SimplIQ Digital Servo Drives-Bell Getting Started - Manual (Page 72)

The SimplIQ for Steppers Getting Started & Tuning and Commissioning Guide
MAN-BELGS (Ver. 1.1)
72
Theoretical Tip: We suggest to start the manual tuning with KI/KP= 6
π
,
assuming you can achieve a bandwidth greater than 3 Hz. Then find the
maximum KP where KI/KP=3. Above the bandwidth of 3 Hz, the value of KP
will be responsible for stability rather than KI. The next step is to decrease KP by
about 30% to leave space for increasing KI and leave it fixed while increasing KI.
This procedure converges, except for rare systems for which the bandwidth of 3
Hz cannot be achieved
10 .
A.8.2 Manual Tuning of a PI Controller and a Low Pass
Filter
A low-pass filter enables decreasing and smoothing the current injected to the motor
due to the sensor’s noise and/or due to plant resonance appearing at very high
frequencies. Moreover, it can avoid unexpected mechanical phenomena, as detailed
in section
A.5.3. Most likely, using a PI controller with a low-pass filter decreases the
closed loop agility performance compared to a PI controller. However if agility can
be sacrificed it is highly recommended to use a low-pass filter. The following
procedure for incorporating a low-pass filter is recommended:
1. Start with designing a PI controller without a low-pass filter as described above.
Denote the PI parameters by KI
0
and KP
0
.
2. Add a low-pass filter at the frequency of 0.2/[Speed Sampling Time] with a
damping factor of 0.6.
Design a PI controller as described below. First find the largest KP where
KI/KP=
6
π
. Figure 63 describes two tests, the value KP=50 is too high, KP=40 is
satisfactory. Then choose KP=40/1.3=30 and increase KI until a satisfactory
response is achieved. Figure 66 shows tests with several KI values, KI=5000 is the
recommended value because larger values exhibit undershoot and lower values
exhibit overshoot less than 10%. Repeat this step while decreasing the corner
frequency of the low-pass filter 20% at a time until a satisfactory result is
achieved (see Guideline 4), or follow the instructions in the next step.
10 We don’t recommend implementing closed loop responses slower then 1 Hz, as the numerical
controller of the Drive is not optimized for such low frequencies.