Scraps of text for incorporation in the VIS Meeting Minutes

KAGRA/Subgroups/VIS/MeetingNAOJ

• Activity report for week of 12/12
  • Mark, Fabian and Enzo continued BS Test Hang work:
    • We shipped BS mirror box parts to Shoda-san and components for a new LVDT cable to Hirata-san.
    • We posed for pictures of the BS by a team from National Geographic.
    • We installed the BF fishing rod stepper motor adaptor cable.
    • We tried to install the BF LVDT cable but first we encountered trouble routing it, and then several wires broke at the D-Sub end.
    • We laid 6 in-air cables from the tank to the PR2 rank for BF and SF picos, steppers and LVDTs.
    • We lifted the BF/IRM/IM/RM/BS section to weigh it and check its balance.
      • It was 195.6 kg, which is 18 kg(!) less than the capacity of the SF.
      • There was a major imbalance in roll: with all four built-in trim masses moved up the +Y end, it still needed 270 g of extra trim mass to be level. This can probably be made up easily by designing the 18 kg of extra mass appropriately.
    • Unfortunately when we put the payload, the IM was slightly yawed and ended up on the horizontal EQ stop screws. This let the IM-BF maraging rod go slack, which disturbed the leveling of the IM (because every time it is picked up the maraging rod settles in a different place, giving a different suspension point).
    • We removed the end panels of the IRM to get access to the IM and rearranged the trim mass on the the IM to get it balance to bubble-level precision. (We still need to do fine pitch adjustment with the OL so that the BS is at the right angle, secure the trim mass properly and replace the IRM panels and OSEMs.)
  • Miyakawa-san and Yamamoto-san redid the cabling from the computer room to the PR2 rack and expected to finish by lunchtime on Friday.
  • Hirata-san
    • Did parts and fastener lists for the SR payload.
    • Did a 3D model with the SR suspension on the BS assembly frame (to help Mark make adjustments to the frame design).
    • Did 2D drawings of Fabian's concept for BS EQ stop parts.
    • Did a 3D model of a wire clamp with replaceable jaw parts (to avoid having to reuse parts with scars from pressure).
    • Did 2D drawings of a new wire clamps for on top of the BS and SR RMs.
• BF issue
  • The BF has four issues that may or may not be related:
    • The keystone is sitting at an angle, so the bottom of the keystone just barely clears the magnet yoke without rubbing.
    • The suspension point for the IM rod is offset. Thus:
      • The BF does not hang level when the IM is suspended from it, even with all built-in trim masses moved to their limits (an additional 270 g stacked on the +Y side of the cap is required).
      • The offset of the rod also causes an offset of the IRM and IM, which uses up all the adjustment range of the IRM OSEMs and means the EQ stops screws between the IRM and IM cannot be inserted without rubbing.
    • The load capacity is slightly less than measured by Hirata-san during tuning at the ATC.
    • The frequency is rather higher than measured by Hirata-san.
  • Also, the BF/IRM/IM/RM/BS system is 18.1 kg light (195.6 kg) compared to the load capacity of the SF (213.7 kg).
  • Diagnosis:
    • The direction of the tilt lines up exactly with one of the blades (the one in the +X,+Y direction on the assembly frame).
    • The blade bases are adjusted symmetrically relative to the outer edge of the BF.
    • Therefore the +X,+Y blade is probably either stronger or weaker than the other two.
    • However even if this was true at the ATC, something has changed during transit.
    • Designing asymmetric trim mass would fix the imbalance problem but not the offset problem (IRM and IM would still be displaced; EQ stop screws could still not be used).
  • Quick summary: this is a major nuisance and is repeatedly costing us time, but we could probably make it work if we absolutely had to.
  • Options:
    • Muddle through.
      • Slow, risky.
    • Bring the BF back to ATC for a tuneup before proceeding with the test hang.
      • Could almost certainly fix the frequency problem.

      • Might be able to fix the offset and/or tilt problems by swapping in the spare blade.

      • Might be able to fix the offset problem by adjusting the blade bases to different distances from the edge.

      • If successful, makes some subsequent steps simpler and/or safer (less asymmetrical trim mass; IRM/IM stops can be used).
      • Reduces the chance of discovering a show-stopping problem with the BF later.
      • Might delay design of 18 kg of trim mass (unless it's very adjustable).
      • Delays finding any problems in other areas (SF, PI etc).
      • Would distract Hirata-san from SRx procurement at a crucial time.
    • Allot time for a tuneup between the test hang and the real hang.
      • Same chance of success at fixing the immediate problem as above.
      • Possible worse delay design of 18 kg of trim mass (unless it's very adjustable).
      • Test hang work is harder and slower.
      • Greater chance of running into a show-stopping problem related to the BF and having to back up in the test hang.
      • Advances finding any problems in other areas (SF, PI etc).
      • Could allow more spare blades to be ordered - better chance of getting a well-matched set.
      • Probably better for Hirata-san.
    • ???