LinuxCNC Documentation

SYNOPSIS

loadrt lowpass [count=N|names=name1[,name2…​]]

FUNCTIONS

lowpass.N

PINS

lowpass.N.in real in
lowpass.N.out real out

out += (in - out) * gain

lowpass.N.load bool in

When TRUE, copy in to out instead of applying the filter equation.

PARAMETERS

lowpass.N.gain real rw

NOTES

gain pin setting

The digital filter implemented is equivalent to a unity-gain continuous-time single-pole low-pass filter that is preceded by a zero-order-hold and sampled at a fixed period. For a pole at -a (radians/seconds) the corresponding continuous-time lowpass filter LaPlace transfer function is:

H(s) = a/(s + a)

For a sampling period T (seconds), the gain for this HAL lowpass component is:

gain = 1 - e^(-a * T)

e = 2.71828 https://en.wikipedia.org/wiki/E_(mathematical_constant)

Examples: T = 0.001 seconds (typical servo thread period) a = (2 * pi * 100) (100Hz bandwidth single pole) gain = 0.466

   T = 0.001 seconds (typical servo thread period)
   a = (2 * pi * 10)     ( *10Hz* bandwidth single pole)
gain = *0.0609*
   T = 0.001 seconds (typical servo thread period)
   a = (2 * pi * 1)      ( *1Hz* bandwidth single pole)
gain = *0.0063*

AUTHOR

Jeff Epler

LICENSE

GPL