• Tilt adjustment range >+- 1 deg
  • incremental step <=30"

Requirement analysis

The remaining tilt to be compensated with the Adaptive Secondary should be:

< 1'

2. Tilt error budget

  • The tilt adjustment is done with the interface between T-Gusset and CalUnit holder.
  • Maximal range and minimal resolution has to be considered.
  • A tilt is dominated by
    • the accuracy of the mount positioning,
    • the beam alignment at the connection to the T-Gusset and
    • the torsion within the T-Gusset
# Error source Relevant parameter Introduced tilt per error Accepted up to Error Budget Comments
1. Mount positioning Mount distance: ~ 2171mm 4.61xE-4 rad ~ 0.027 deg per mm 5.0mm 0.135 deg Dominated by precision of mount points at LBT.

Beam alignment Center distance beams: ~250mm 4.00xE-3 rad ~ 0.231 deg per mm 3.0mm 0.691 deg Dominated by planarity of beam flanges.
Originally better. With 0.05 planarity
1.74mm equal to 0.4 deg.
3. Torsion within T-Gusset Length of Holder interface: ~170mm 5.88xE-4 rad ~ 0.339 deg per mm 0.5mm 0.170 deg  
          0.996 deg  


Available dial gauge have:

0.02mm resolution 2mm max. range

with a distance of about 124mm this results in:

33.46" resolution 0.465 deg max. range

This does only reflect what can be measured not what can be adjusted!!
Topic revision: r2 - 06 Aug 2018, AndrewColson
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