ElmoMC SimplIQ Digital Servo Drives-Bell Getting Started - Manual (Page 63)

The SimplIQ for Steppers Getting Started & Tuning and Commissioning Guide
MAN-BELGS (Ver. 1.1)
63
Manual gain scheduling: The controller parameters may adapt due to a user
program or an external command. For example, the controller gains of a winder
may be increased as it rolls and gains weight.
For convenience, when you program a fixed controller you don't overwrite the
schedulable parameters, and vice versa.
The Auto-tuner always programs an automatically gain-scheduled controller.
A.5.2 Resonance and Notch Filters
Resonance is a very common mechanical phenomenon, in which a flexible system
vibrates in its natural frequencies. In many applications, the natural frequencies
are too high for the motion controller to control. The best policy for the motion
controller is then to avoid exciting the oscillations. You chain a band-stop (notch)
filter to the controller to prevent the controller from driving the oscillatory
frequency.
If you don't use a notch filter where necessary, either:
Severely limit the possible controller bandwidth.
Risk instability and extreme stresses to the controlled system.
Tips:
Normally there is more than one resonance frequency. It may be necessary to
set more than a single notch.
In some systems the resonance frequency changes significantly due to load or
posture changes. Verify that your designed notch covers the entire operational
envelope.
A.5.3 High Frequency Noise and Low-pass Filters
High frequency noise means vibration, acoustically unacceptable noise, and
much greater power consumption than is necessary just to drive the motor to its
desired shaft position. The main reasons for high frequency noises are:
Sensor inaccuracy.
Plays or backlash in the mechanics.
High frequency, unidentified resonance, possibly due to aliasing
6 .
The best policy for the motion controller is to avoid exciting the motor at a high
frequency because the system vibrates there or because the feedback is not
reliable. For this purpose chain a low-pass filter to the controller.
The price of a low-pass filter is an equivalent delay. For a double pole filter with
a damping factor of 0.7, the insertion delay is about 0.23/f, where f is the corner
frequency.
6
We deal with a sampled system. High frequency signals may appear to sampled systems in changed,
low frequencies. For example, if the Drive samples at 300 usec (TS=75), then an oscillation with a
period of 300 usec (3333 Hz) appears to the Drive as a constant value (frequency=0).