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The XRT had several disabled axes and nearly broken chassis that were causing all kinds of hackery and finagling for ops as a result of rushed commissioning. To make things better we decided to go through each chassis 1 by 1 and fix outstanding issues, enabling all axes, including bending. This post goes over what was fixed and changed, and why. Also you will find the 

 Objectives

• Enable all axes
  • Fix all chassis
  • Fix all cables
  • Verify motion
• Verify all drive settings and capture on google drive
• Improve gantry tuning and control
• Misc improvements

A dead piezo!

While recommissioning all the XRT HOMS we encountered a piezo failure on M2H. For no apparent reason the piezo died, and we had to scramble to replace it. Actually Corey and Daniele replaced it, while Teddy and I completed verification of all other axes. We don't understand why it failed.

Improve gantry tuning and control

Problem

When moving the axes in gantry a gantry difference would accumulate over time. This would ultimately lead to a parasitic pitch. Each axis would move in-sync pretty well, but it might give up moving before it actually reached a final target, and each drive would give up on its own. This lead to a gantry error that would vary between +/- 100um. Not very good for pointing to 30nrad!

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Solution

Each gantry axis had a large settling window, and extremely short settling time. By adjusting in the direction of perfection the axes were able to settle a bit more, leading to a more accurate final position. Additionally, by setting the holding current to something other than zero (0.5 A) the axes would also compensate for any other drift and maintain a sharp encoder position. Now the only concern is any heat making its way into the rest of the system. We'll see how that turns out!

Results

After some testing we found that the gantry error was being maintained over several moves to <1um. A significant improvement.

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Oops, looks like there is some weird drift there... Turns out when we added some guards for position lag monitoring they tripped the axes off due to some rough handling of the mirror enclosure. Resetting the axis did the trick:

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But this means we need to implement the EPICS interface for resetting such faults easily, and diagnosing the problems.

Miscellaneous Improvements

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