D. Chen, Akutsu (w/ help Ushiba); follow up of 19546.
Abstract
Replaced two steering mirrors on the POS in-air table with the ones having PZT (piezo) and picomotor actuators. GreenY is not lost.
Basic knowlege
This is basically the POS version of the work reported in 17825, although there are small diffrences; the logic for the POS case is summarized in JGW-T2213720. As discussed in this document, GrM2 and GrM3 (the naming follows this document, or those in JGW-E1909613) needed to be replaced with new ones having piezo and picomotor actuators. The piezo mirrors have been already assembled (18163), and their PZT efficiencies have been roughly measured as well (18174); note that Uehara-san assigned "3" and "4" to identify each mirror and its piezo actuation efficiency. The mirror holders having picomotors are of two Newport 8821 from Picomotor Controller Kit 8742-4-8821-RL, which should include 8821 and 8821-L (but when I found the mirror holders in the stock, there were only two 8821, and I could not find 8821-L. Maybe on the POP in-air table, there are two 8821-L???).
Setting the references
As in 17825, we started with setting an iris diaphragms in front of the lens GrL2 (in-between GrM3 and HBS... but due to typo, in the document or the drawing above, it is shown as GrL1) as in Figs. 1 nd 2, and also put a cover on the viewport window and marked the point on which GreenY went through; the latter is the same treatment to memorize the optical axis as we did 19546. Note that we left an iris diaphragm in front of the upper mirror on the periscope yesterday (19546).
Replacing one mirror
Firstly, we worked for GrM3. The method is the same as explained in 17825. The difference is as follows. On the in-air POP table, the mirrors to be replaced fold the optical axis in shallow angles, while here on the in-air POS table the angles of incident of the light beam is about 45 deg. So, instead of pushing the base plate of GrM3 by 9 mm in one direction, we pushed the base plate in 9/sqrt(2) = 6.4 mm each in two diagonal directions (Fig. 3). Then we assembled the piezo mirror with the picomotorized mirror holder, and the assembled pizeo-pico mirror was set in place of the old mirror. Referring the beam spots on the prepared targets like iris diagphrams and the mark on the viewport cover, mainly the GrM3's pico adjusters were tweaked, and sometimes GrM2's adjusters were touched (we may need to do so because we need to campensate small lateral errorious shifts of the GrM3 place). When I felt it was enough aligned, we detached the viewport cover, and found the GreenY beam spot in the GigE camera image at the Yend. Then Ushiba-kun slightly swept SR3 to find "nicer" alignment of SR3 for making better the GreenY transmission in the Y end.
Replacing another mirror
Next we worked for GrM2 in the same manner (Fig. 4). We got back the viewport cover and marked the beam spot on it again for making the reference. There were several issues like that it was hard to rotate some screws on the positioners with wrenches due to limited area, but we somehow overcame it; don't think, feel! or, my hand was gradually learning the wrench inserting angle. Then the piezo mirrror was assembled with the picomotor mirror holder, and the whole assembled mirror was put in place of the old one (Fig. 5; the foreground one is GrM2, and the one beyond the shutter is GrM3). After adjusting GrM2 pico and slightly GrM3 (as explained above), we detached the viewport cover, and found the GreenY beam spot immediately. Finally Ushiba-kun swept SR3 to find better new alignment of SR3.
Notes
- We omitted to check centering on SR2 and SR3 with the targets. Anyway, we need to revisit the GreenY alignment after aliging BS, and so let's check such things in that timing.
- We have not yet connected cables for picomotors and piezo actuators (the same at the POP table), and they are just left on the table(s); need to be done soon!
- Again, as in 17825, the mark on the viewport cover is a better reference point than the iris in front of the periscope. Well, today I would touch this iris at my elbow, so that would be one of the reasons. Anyway, better to have proper number of references.
- Of course, we preset the picomotor range at about the mid.
Assigned # in 18174 | Mirror name on the in-air POS table |
3 | GrM2 |
4 | GrM3 |