WP 7372 FRS 9743

As reported in LHO aLog 40171 and 40201, the Corner 4 vertical actuator on HEPI appeared to be very close to the plus-side mechanical stop and exhibited some clipping are larger strokes.  To fix this, the following was done:

With HEPI Isolating, corners 4 and 2 were mechanically locked. Managed this pretty well not tripping until well locked.

Partially installed the Actuator locking screws and positioned the 0.1" shims between the Tripod Base and the Top Foundation

Pressured support jack to hold Actuator just enough to prevent it from dropping.

Loosened the horizontal 1/2-20 SHCS holding the Actuator to the Actuator Brackets.

With those bolts loose, tightened the Actuator locking screws raising the actuator until the shims were clamped.  As I was able to start and turn the locking screws, I had confidence the Tripod assembly was not horizontally out of position and so did not need to loosen the vertical Actuator Bracket bolts.  Had that not been the case, this chore would have taken considerable more time as instead of just 6 bolts to loosen and then tighten, it would have been 18 with a couple iterations of tightening one group then the other and loosening the first to relieve strain.

Now with the Actuator effectively back in 'Installation' setup I was ready to zero the IPS.  Looking at the actuator/stop gap however suggested that the ~3000ct reading was appropriate and IPS was not zero'd.  The Actuator Locking Screws were removed (almost forgot one!) and the platform was unlocked.

At this point before and after positions were viewed on trends to determine new Isolation targets for the vertical dofs: the computed Z, RX, & RY positions changed with the change of V4.  The shifts of these were applied to the target locations to arrive at new target locations.

After re-isolating with these new computed values, it was clear the actuators were pulling down to isolate the platform at the new Z location.  So, I 'raised' the target position from -122k to -92k.  This served to put the actuator drives somewhat around zero rather than all negative; this in turn puts the free hanging platform much closer to the isolated position.  It also put IPSs in better balanced readout.  I can't imagine that 30um in vertical position will impact any beam centering but of course this can easily be recovered.  The RX & RY newly computed targets were very close to the free hanging tilts.  I can not explain why the Z was off enough to warrant further action.

WP closed; FRS Pending