I am calculating an Offset using a mean Filter of the last 500 values so that the drive of the IMU is shifted around Zero.
And now, if a movement is detected I just take the last (10,20,100) RAW values minus this offset value. Therefore I see the real difference in the acceleration.
For example, the RAW values are from 100 to 200. I meanfilter these over a long period and shift them so that I see values around -100 to 100. Now if an acceleration occurrs I see like 10 values that are around -100 to 100 and inbetween those like 2 or 3 values in the size of 600 to 900. Those i sum up and integrate.