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 ViewDetail ViewGeneral View
../../../../../_images/control_filters2.png
Detail View
../../../../../_images/control_filters_objects2.png

The position feedback filter can also be used with a simple PID loop:

General ViewDetail ViewGeneral View
../../../../../_images/control_filters_simple2.png
Detail View
../../../../../_images/control_filters_simple_objects2.png

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 1

  • fw - Full width of the rejection band of the Notch filter [fc - fw /2 ,fc + fw/2], defined in Radians/s 1

  • {\zeta} - damping ratio

1(1,2)

Radians are used for internal calculation, user input is in [Hz]

Low-pass filter

Torque loop input shaping filter

../../../../../_images/notch_filter_diagram2.png

The following equation was used to design the torque loop input shaping filter:

BS2(s) =  \frac {s^2 +f_c^2} {s + f_w s + f_c^2}