Filtering
Overview
Attention: Since Firmware 5.0, only 1st order Position and Velocity Feedback filters are supported.
A digital filter removes unwanted components from the signal which passes through it.
This feature can be used for example as:
-
Position Feedback filter - Reduce encoder noise. A 1st order low-pass filter is supported.
-
Velocity feedback filter - Reduce noise and effects of encoder nonlinearity in the velocity signal. A 1st order low-pass filter is supported.
-
Loop shaping filter - Suppress excitation of resonance frequencies in the output of the motion control loop or in the input of the torque control loop. A 2nd order notch filter is supported.
Any signal can be decomposed into a sum of sine waves with different frequencies. Some of them might negatively affect the control loops. It is possible to attenuate these unwanted frequencies by properly configuring a corresponding filter.
Configurable filters are implemented for the signals that are considered the most important for motion control.
General View
Detail View
The position feedback filter can also be used with a simple PID loop:
Methods
Definitions
-
s - Laplace-domain frequency parameter
-
fc - Cutoff frequency of the low-pass filter or central frequency of the Notch filter, defined in Radians/s *
-
fw - Full width of the rejection band of the Notch filter
defined in Radians/s * -
- Damping ratio
* Radians are used for internal calculation, user input is in [Hz]
Low-pass filter
Torque loop input shaping filter
The following equation was used to design the torque loop input shaping filter:
Application Guide
Position and Velocity Feedback Low-pass filters
Torque loop input shaping filter
Parameters
| Object ID | Name | Description |
|---|---|---|
| 0x2021 | Velocity feedback filter | Cut-off frequency of velocity feedback filter |
| 0x2022 | Position feedback filter | Cut-off frequency of position feedback filter |
| 0x2023 | Notch filter | Center frequency and bandwidth of notch filter |