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Entry  Wed Sep 26 17:09:15 2012, Den, Update, SUS, TT 
    Reply  Thu Sep 27 15:21:04 2012, Steve, Update, SUS, TT height adaptor & PTICH damping 09271201.PDFIMG_1656.JPGIMG_1654.JPG
       Reply  Fri Oct 12 10:39:45 2012, Steve, Update, SUS, TT PITCH damping IMG_1709.JPG
          Reply  Fri Oct 12 14:01:33 2012, Koji, Update, SUS, TT PITCH damping 
             Reply  Fri Oct 12 16:59:26 2012, steve, Update, SUS, TT PITCH damping 
       Reply  Wed Oct 17 08:30:49 2012, Steve, Update, SUS, PTICH damping needed 
          Reply  Wed Oct 17 11:15:05 2012, Den, Update, SUS, PITCH damping needed pitch_damping.png
             Reply  Thu Oct 18 02:42:38 2012, Den, Update, SUS, PITCH damping needed 7x
                Reply  Fri Oct 19 18:30:07 2012, Den, Update, SUS, PITCH damping needed damp.pngpitch.png
                   Reply  Sat Oct 20 01:23:56 2012, Den, Update, SUS, PITCH damping needed P1010059.jpgP1010058.jpgP1010060.jpg
                      Reply  Sat Oct 20 20:37:55 2012, Den, Update, SUS, PITCH damping needed DSC_4778.JPGpitch.JPGyaw.JPGDSC_4776.JPG
                      Reply  Mon Oct 22 11:26:12 2012, rana, Update, SUS, PITCH damping needed 
                         Reply  Tue Oct 23 01:46:53 2012, Den, Update, SUS, PITCH damping needed Mirror_Holder_ECD_NEW_DRAWING.PDFTT_DAMPING_DRAWING.PDF
                            Reply  Tue Oct 23 17:12:30 2012, Den, Update, SUS, PITCH damping needed simple_drawing.PDF
                               Reply  Wed Oct 24 01:02:10 2012, Koji, Update, SUS, PITCH damping needed 
                                  Reply  Mon Oct 29 18:14:55 2012, Den, Update, SUS, PITCH damping needed DSC_4787.JPGDSC_4791.JPG
                            Reply  Tue Oct 23 18:18:29 2012, Jenne, Update, SUS, PITCH damping needed 
Message ID: 7571     Entry time: Thu Oct 18 02:42:38 2012     In reply to: 7568     Reply to this: 7583
Author: Den 
Type: Update 
Category: SUS 
Subject: PITCH damping needed 

Quote:

 

I think we can put ø2mm × 10mm long magnetic material inside 4 holes with actuation magnets. Then magnetic field on the other side of the mirror will be close to one produced by actuation magnet. Magnetic cylinder center of inertia will be in the vertical plane where mirror's center of inertia is. So this should not change alignment significantly. Eddy current dumping will be applied to the end of the magnetic cylinder opposite to the magnet using aluminium disks, we have them in the clean room.

 I've tested this approach. As we do not have required cylinders with high magnetic permittivity, I replaced them with magnets simular to actuator magnets ø2mm × 3mm long. Using them and aluminium disks from other TT I've made a "pitch dumping" construction.

DSC_4759.JPG

Pitch Q reduced but not that much as I could expect. I did a ringdown test. 

Plots:

yaw ringdown using original construction     |  yaw ringdown with added pitch damping

------------------------------------------------------------------------------------------------------------------------

pitch ringdown using original construction   |  pitch ringdown with added pitch damping

    yaw_nodamp_20.JPG   yaw_damped_13.JPG

pitch_nodamp_30.JPG     pitch_damped_10.JPG

 

 From this data I've estimated Q factor for yaw (135 vs 88) and pitch (192 vs 77) (original vs added pitch damping). Thess results diverges with the ones obtained by designes. They measured Q~40-50 for original construction. Pitch and yaw have 2 close resonances so this time domain method can not be very precise. I've measured the same with SR785.

yaw.pngpitch.png

In these comparison plots excitation was not the same as coils are not plugged in yet, but resonance Q factors can be compared.

 

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