LIGO
T050098-00
LIGO Advanced Laboratory / LIGO Scientific Collaboration
LIGO-T050098-00-D
Advanced LIGO
11 June 2005
Optics Table Hole Size and Spacing based on Suspension Attachment Frequencies (Advanced LIGO)
Dennis Coyne Distribution of this document: SEI, SUS subsystem group This is an internal working note of the LIGO Project. California Institute of Technology LIGO Project MS 18-34 1200 E. California Blvd. Pasadena, CA 91125 Phone [phone] Fax [phone] E-mail: [e-mail] LIGO Hanford Observatory P.O. Box 1970 Mail Stop S9-02 Richland WA 99352 Phone [phone] Fax [phone] Massachusetts Institute of Technology LIGO Project NW17-161 175 Albany St Cambridge, MA 02139 Phone [phone] Fax [phone] E-mail: [e-mail] LIGO Livingston Observatory P.O. Box 940 Livingston, LA 70754 Phone [phone] Fax [phone]
http://www.ligo.caltech.edu/
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Advanced LIGO Change Record:
Revision 00: initial release.
T050098-00
The following are some notes justifying the choice of 3/8-16 UNC-2B threaded holes on 1 inch centers for the BSC optics table. I've modeled the clamp stiffness in the attached spreadsheet using the joint stiffness analysis in A. Slocum's "Precision Machine Design" (see Appendix A for an excerpt on bolted joints from Slocum's text). I've also modeled the clamp with the geometric parameters for D050150-02 using Algor. The closed form analysis gives a clamp stiffness of 2.0e4 lbf/in whereas the Algor analysis gives 1.7e4 (20% lower). An "optimal" clamp design has bending and shear stiffness of the clamp equal to the bolt extension stiffness. Using the model, I've varied the optics table hole pitch and the bolt diameter, optimizing the clamp stiffness, to determine the number of clamps required as show in the plot below. I conclude that we need a 1 inch hole spacing and 3/8 inch diameter bolts at least. Figure 1: Number of Clamps Required to Achieve a Quad Suspension Structure, Vertical Bounce Mode Frequency of 150 Hz
Quad Clamps
35
30 1" hole pitch 2" hole pitch Number of Clamps for freq > 150 Hz 25
20
15
10
5
0 0.25
0.3
0.35 Bolt Diameter model: (in)
0.4
0.45
0.5
Algor Pinned nodes at the far edge of the clamp at it's interface with the optics table, pinned nodes at the end of the effective length of the bolt (using Slocum's definition of effective length) and the force (weight) from the suspension represented as a point load 2
Advanced LIGO
T050098-00
centered on the flat surface of the clamp which interfaces to the suspension structure. Note that this is for the worse case extension of the clamp (i.e. placement of the bolt). Figure 2: Algor Deflection Analysis 0.074 in peak deflection for 1000 lbf load centered in the flat area which interfaces to the suspension frame.
In the analysis I kept the same width to depth ratio. I optimized the stiffness of the clamp so that it is comparable to the extensional stiffness of the bolt. So the 3/8-16 SHCS version of D050150 would have a width of 1.27 in, a section thickness of 0.95 in and a "dog" leg height (at the optics table end) of 0.05 in. This stiffer design takes advantage of the stiffer 3/8" dia. bolt.
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Advanced LIGO
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Figure 3: Clamp Suspension Structure Dog Clamp Dimensions/Variables
LIGO I style clamp which was ~ 5" long and around the bolting section it was .47" thick with a 2.5" long slot. Reference LIGO-...