[Stefan, Kiwamu]
As a part of the commissioning wrap up porjects we characterized the IMC ASC control.
Adjustment of UGF:
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UGF of the all 6 loops was adjusted to be about 0.08 Hz, measured with an impulse response method
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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.
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Later Stefan managed to measre the open loop with swep sine. See tha attachement.
Change in servo shapes:
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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.
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The height was about 10 times higher that the floor around this frequency
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We impleted a notch filter at 1 Hz with Q of 2 and heiht of 30 dB.
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Instead of enabling FM6(0.06, 0.1) we decided to go with this simple notch filter.
Adjustment of Output matrix for DOF3:
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We put non-zero numbers in the cross-coupling elements in the outmatrix for DOF3.
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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.
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Instead of doing this cascaded loop we tried a simpler scheme by feeding the signal back also on the suspensions.
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This worked well.
Some other changes :
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we increased the whitening gain of IM4 TRANS from 15 to 45 dB.
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we enabled the top two whitening stages for each WFS