ElmoMC SimplIQ Digital Servo Drives-Bell Getting Started - Manual (Page 67)

The SimplIQ for Steppers Getting Started & Tuning and Commissioning Guide
MAN-BELGS (Ver. 1.1)
67
A.8 Fixed Gain Manual Tuning for a Speed Loop
This section deals with choosing the KI and KP parameters of the PI controller
and the parameters of the High order filter. We first describe how to select the KI
and KP parameters. Then we explain how to add a low-pass filter. Finally we
explain how to decide if a notch filter is needed and how to add it.
A.8.1 Manual Tuning of a PI Controller
We present an iterative process of choosing KI and KP and testing the closed loop
step response. We evaluate the step response in order to iterate the KI and KP
parameters for improved closed loop performance.
The steps are:
1. Start with the very low gains of the PI controller: KI=3 and KP=1 for example,
then set the following step reference command parameters:
(a) Set a long recorder time, as with low gains the response is going to be slow.
Here the Max. Record Time is 0.48 seconds.
(b) Velocity: 12000 counts/second (fits 180 RPM for encoder of 4000 counts per
revolution). This may be too slow a velocity for optimal tuning. We will increase
the reference speed later, when we are more confident of the motor's response.
(c) Displacement: Displacement of at least Max. Record Time multiplied by
Velocity (about 5000 in this example), unless it violates the mechanical limits.
The test data is summarized in the following table.
KP KI Velocity +Displ. -Displ. Rec. T. Rec. Res Profile
1 3 12000 5000 -5000 0.48 sec 400 musec off
Let us observe two plots, the measured speed and the motor current. With the
low gains the motor's response is very sluggish, as in Figure 59.
0 0.1 0.2 0.3 0.4 0.5
-3
-2.1
-1.2
-0.3
0.6
1.5
x 10
4
Tim e (sec.)
C
o
u
n
ts
/s
e
c
.
S peed
Reference
0 0.1 0.2 0.3 0.4 0.5
-0.15
-0.12
-0.09
-0.06
-0.03
0
Am
p
e
re
Tim e (sec.)
Figure 59: First test with low KI and KP