Hirata, Yano, Akutsu + remote Miyo; cont'd 17562
Abstract
A nightmare; the suspended table height is about 10 mm lower than the nominal (380 mm); this will affect the entire things on the suspended table. And I found the past post (3198) surely saying that the height has been actually 390 mm here.
Preparation
When I opened some covers on the chambers, I noticed GreeX had been lost in the TMSX PD, while knowing the TMSX Green GigE camera had not worked. As the GigE camera recovered (17593), fortunately we could see a faint spot of GreenX with the camera (while the TMSX PD did not... this would show usability of the GigE camera than the PD in the initial alignment phase). Anyway, Miyo-kun swept PR3 and got (maximized?) the transmission beam (TMSX PD: K1:AOS-TMSX_GR_PDA1_OUT16) and POP GrRFPD DC (K1:ALS-X_ARM_REFL_OUT16); among the two, GrRFPD DC should be the more stringent refrence for the proper alignment of PR3.
As was the same in the previous setup, during our work basically ETMX was in the aligned state, while ITMX was anyway mis-aligned due to the fixed BF for the Takahashi-san's work.
Response of the suspended table
First we attached the last one of the new screw legs (see 17562 for the backgroud). Then let the table sit on the chamber with the full set (four) of the new screw legs to see what would happen for the GreenX. Unfortunately (but we have already known this as reported in 17562), GreenX was lost; no signals in the PDs nor the GigE camera. Fortunately when we released the table again, the signals and the spot image came back. Nice!
Then we put tentatively a pair of the PR2 mid-size baffles at rough locations (HR and AR) referring to the nominal drawings on the table when it sit on the chamber (Figs. 1 and 2). Releasing the table, we lost GreenX; no signals in the PDs nor the GigE camera. Miyo-kun swept PR3 and find a new tentative combination of good oplev numbers, and did ETMX sweeping as well to maximize GrRFPD DC. At this point, we did not know what was the most effective (mechanical) parameter that caused this displacement; according to Miyo-kun (he may report the numbers inn detail later...), the PR3 yaw needed to be adjusted ~ 50urad in total, while pitch was not so much. As the PR2 suspended table does not have vertical springs (good or bad?), it would be natural that the pitch was not so displaced. After several trials, i.e., iterating "do something and release the table", we became to believe that the masses of the baffles themselves cause the change of the suspended table balance in yaw. But note that we need to be careful that the neck of the wires for the suspended table is kind of thin, so too much torqueing the clamps will not be good.
Trial of "precise" adjustment of the baffle
When the table sit on the chamber, we set some positioners and guides, and tried to move the HR baffle gently so that GreenX beam passed through the center of the baffle aparture, and also saw what would happen for the balance of the table when it was released. The move with positioners was smoothly done while the table was sitting. During the pushing, the baffle started to rotate, but we compensated the unwanted rotation by using another positioners additionally set at the opossite side; the lesson we learned is that we need to care about the ordering of pushing. We moved the baffle so that its aperture came centered with respect to GreenX beam in the horizontal direction with these positoners, while we found there was about 10 mm displacement in the vertical direction between the aperture and the beam.
To check this discrepancy, we measured height of the some relevant stuffs, and found that the suspended table's top surface from the GreenX beam, which was (we thought) well in the PR2 center, was 390 mm while the nominal value should be 380 mm. And also we saw the GreenX spot on the POP-POM steering mirror displaced about 10 mm up from the central height... This would be a severe problem not only the mid-size baffles rather for the POP-POM! This point will be investigated further later.
After our works...
We took off the HR baffle out of the chamber to do some investigations later. The "suspended" table is now sitting on the chamber. With this situation, GreenX won't reach Xend.
Note
- The suspended table (while suspended or sitting) seemed balanced in pitch when checked with a bubble level (Fig. 3), well, hard to identfy it in this photo.
- Maybe fortunately, with the baffles, the green beam hit the center of PR2 (Fig. 4); that was slightly displaced the other day in +Y direction.
- The invac POP-POS steering mirror should be also the stuff to be affected with this wrong height of the suspended table. In O3GK we were in trouble by the clipped strange beam profile coming out of this port, and we still do not know the main cause of this; it would be better to resolve such possibile clipping as much as possible now. According to another post (3761),
- The designer (me...) assumed that: to assemble the invac POP-POS, an additional 3-mm thick plate should be inserted between the mirror holder and the obelique; only the mirror holder + the obelisque, the height should be only 377 mm.
- This is a repeat of the descriptions in 3761, there should be 1/300 tilt and the distance from PR2 to the invac POP-POM would be ~70 cm, so there should be additional 2.3-mm rising of the light spot(s) on the invac POP-POM. (this post says "5-6 mm", which seems to indicate a summation of the "380-377=3mm" + this 2 mm).
