Determine Orientation Using Accelerometer-Gyroscope Fusion

Hi,

If an accelemoter is immobile we can estimate its orientation using gravitational component.

Also, using sensor fusion we can obtain its orientation.

I applied this idea on measurement data that is already available in Matlab. (https://www.mathworks.com/help/fusion/gs/determine-orientation-through-sensor-fusion.html) Measurement device oscillating in pitch (around y-axis), then yaw (around z-axis), and then roll (around x-axis).

When I used imufilter function, I obtain orientation value.

But orientation obtained by imufilter is very different from one that is obtained from only accelerometer data.

For example; the orientation values (Euler angles) at sample 1131 are -11.1, 5.9, 27.5 degrees by imufilter. The tilt is low. The figure below shos the tilt.

But accelerometer values are -0.98, -9.48, 3.09. Y axis value is about -g and z axis value is low. Then the tilt should be high. This gives about 73 degree for z axis.

What's wrong? Thanks

ld = load('rpy_9axis.mat');

acc = ld.sensorData.Acceleration;

gyro = ld.sensorData.AngularVelocity;

mag = ld.sensorData.MagneticField;

viewer = HelperOrientationViewer;

ifilt = imufilter('SampleRate', ld.Fs);

for ii=1:1131

qimu = ifilt(acc(ii,:), gyro(ii,:));

angle = eulerd(qimu,'ZYX','frame');

viewer(qimu);

pause(0.01);

str = sprintf("Euler angles :%.1f %.1f %.1f",angle);

title(str)

end

plot(acc)