ElmoMC SimplIQ Digital Servo Drives-Bell Getting Started - Manual (Page 61)

The SimplIQ for Steppers Getting Started & Tuning and Commissioning Guide
MAN-BELGS (Ver. 1.1)
61
Treat unbalanced 1 systems with extreme care.
A.3 Make it Simple
This Appendix gives some simple guidelines for manual controller tuning. In
order to simplify the tuning process we divide it into a series of steps.
The rules of simplification are:
Never tune your controller to perform better than you need. A controller of
lower bandwidth decreases stresses and is more robust to changes and ageing.
In this Appendix you will learn how the High order filter may decrease control
stresses.
Tuning a speed controller is simpler than tuning a position controller. If you
need to tune a position controller, try to tune first its embedded speed
controller. The Conductor program lets you tune a speed controller without the
risk that the motor will drift away from its starting shaft position.
If your mechanics are simple and good enough to avoid the High order filter,
adhere to the simple PI speed controller. The High order filter requires more
skill to use. The High order filter always introduces a filtering delay, which
usually limits the achievable bandwidth compared to a simple PI.
Use the High order filter when encountering oscillations and high frequency
noise. The small extra effort of tuning the High order filter can be very
beneficial.
If your encoder has good enough resolution and the friction is low enough, use
a fixed controller.
Use controller scheduling (dynamic adaptation of the controller parameters to
the situation) if you have a low-resolution encoder or high friction. The extra
effort of tuning the High order filter can be very beneficial.
Work linearly. With high controller gains the current command saturates for
very small tracking errors. The saturation makes the evaluation of control
quality very difficult. Keep the motions small enough and verify by the current
waveforms that the current command does not saturate2. Verify how the
controller works with large signals only after it is satisfactory with small
signals.
Work with steps. When you test a controller with limited acceleration or even
smoothed reference waveforms, don't excite high frequencies. The results will
not reveal oscillations and high frequency problems that may exist.
Do not fear overshoots. Overshoots are necessary if the controller is to track
without a time delay. Reducing the height of the overshoots lengthens their
duration. Evaluate the overshoot that you can tolerate by experimenting with
acceleration limited test waveforms, without exceeding the acceleration you
actually use.
1
Systems that do not stay in place when the motor is shut down.
2 Note that the rate of change of the current command is also limited. This is because
L
V
dt
dI
max B
=
where I is the motor current,
B
V is the supply voltage and L is the motor
inductance.