[Stefan, Kiwamu]

 As a part of the commissioning wrap up porjects we characterized the IMC ASC control.

Adjustment of UGF:

• UGF of the all 6 loops was adjusted to be about 0.08 Hz, measured with an impulse response method
  • we had a difficulty in exciting the suspension with swept sine signals and ended up with the impulse response technique where we inject a step function at the error point and see the behavior of the error signal.
  • Later Stefan managed to measre the open loop with swep sine. See tha attachement.

Change in servo shapes:

• Looking at the spectrum of the WFS error signals we noticed there was a sharp peak at 1 Hz which is a pitch resonance of the triple suspension.
  • The height was about 10 times higher that the floor around this frequency
• We impleted a notch filter at 1 Hz with Q of 2 and heiht of 30 dB.
• Instead of enabling FM6(0.06, 0.1) we decided to go with this simple notch filter.

Adjustment of Output matrix for DOF3:

• We put non-zero numbers in the cross-coupling elements in the outmatrix for DOF3.
  • We have been using only PZT for feedabck, but this made the response of the control slow because DOF1 and 2 needed to wait and follow the movement of DOF3.
  • Instead of doing this cascaded loop we tried a simpler scheme by feeding the signal back also on the suspensions.
  • This worked well.

Some other changes :

• we increased the whitening gain of IM4 TRANS from 15 to 45 dB.
• we enabled the top two whitening stages for each WFS