How I can get a cutoff frequency. Also, I wonder how LPF can be applied.

Hi.

I got experimental data from real robot arms.

The attached file is the angular acceleration of each joint.

I would like to apply the cutoff frequency and LPF of this data.

As far as I know, it is done through FFT, but I don't understand well even though I studied. I need your help.

Thank you.

Answer 1

[Mathieu NOE]

hello

see below some LPF examples suing butterworth and sliding averaging techniques

[num,txt,raw] = xlsread('joint_angular_acceleration_data_1s.xlsx') ;
 
 q1 = num(:,1);
 q2 = num(:,2);
 q3 = num(:,3);
 time = num(:,4);       % !! some values are non unique du to rounding effect
 samples = length(time);
 dt = (time(end)-time(1))/(samples-1);
 t = (0:dt:(samples-1)*dt); % new time vector (unique values)
 Fs = 1/dt;
 
 
 % smooth data
  % LP butterworth
 n = 2;
 fc = 0.1*Fs;
 [b,a] = butter(n,2*fc/Fs);
 
q1_smoothed = filter(b,a,q1);

figure(1),plot(t,q1,'b',t,q1_smoothed,'r');grid

% moving averaging 
n = 11;     % must be odd number
q1_smoothed = slidingavg(q1, n)

figure(2),plot(t,q1,'b',t,q1_smoothed,'r');grid