Just to inform here.

The mechanical design of the BSC HEPI hardware does not provide for locking the platform 'down.'  It only holds the platform up and locks it horizontally.  Additionally, many of the horizontal locks are very difficult to access; so, we tend to pinch tangentially but only push in radially on each corner for a platform lock down.  As a result, when we unload a HEPI, such as when a Quad is removed for TM rework, the HEPI is at risk to lift while under-weighted.

The removal of the ITMX for optic replacement presented just such a situation to study.  The attached 80 day trends of the ITMX cartesian IPS positions show what happened in this case.  Alog entries sync clearly with shifts seen on the IPS and naturally with the largest seen on the Z dof.  With only 25um of vertical shift seen on the IPS, it may be that there is actually no shift or slippage in the locks but only distortion in the system...Although I'm trying to visualize what is happening and... hmm, not sure I see it.

Regardless, slip or distortion, you can see the platform has basically returned right back to where we locked it once the ITMX was returned although it took weeks to do so maybe suggesting a slip stick process.