1. ACTR #480 - Blanco Mirror Lift Upgrade
ACTR 9 April 2015

2. Danger! Danger! Safety factors are unacceptable by today’s standards:
FOS is ~1.1 for mirror changes
Moreover, we do unusual things with our system:
The center of the telescope is ~1m south of the center of the platform, which induces a tilt under load from the mirror+cell. It is not clear how this transmits to the lift mechanism.
Preloading the cell onto the telescope is done by jogging the cart jacks with no force feedback.
Politically, we are going to have to improve matters before the next realuminization.

3. Duff-Norton Ball Screws
1978

4. Mayall upgrade
From: single motor, direct-drive of all three 25 ton drive screws + disk brakes
To: three motors, one per 50 ton drive screw, plus safety catchers

5. Mayall upgrade
Mayall upgrade complicated by manufacturing errors and motor control
“Whale song” resulted from component interference, resolved through abrasion?
Drive plate requires very sensitive tilt metering – caused drive to hunt before resolved by motor control algorithm.
FOS improved to ~2.5 for mirror operations
Note: lead time for drive screw delivery is long.

6. AAT
AAT upgraded to 50T ball screws from GROB but used a single-motor drive
Downside: slower
Upside: simpler
Also, they have pneumatic drive for preloading the cell onto the telescope, and a load cell for feedback.

7. Next steps
Meeting with Jay Elias (et al.?) to discuss the Mayall experience and resolution.
Visit AAT?
Needs ME (PS) ~1 month initially to develop a design whether copied from Mayall or AAT.