LIGO Laboratory / LIGO Scientific Collaboration

LIGO- T030104 -01 ADVANCED LIGO 30th May 30, 2003

Mode Cleaner Controls Prototype Blade Measurements: Length, thickness and mode frequencies.

Calum I. Torrie, Helena Armadula, Michael A. Gerfen

Distribution of this document:

LIGO Science Collaboration

This is an internal working note

of the LIGO Project.

California Institute of Technology
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1.1  Introduction

This paper should be read in conjunction with the technical note, T020???, by Mike Plissi of the University of Glasgow. The drawings used for the cantilever blades that were used to create the results below can be found on the LIGO DCC and have the following numbers: - D020201-02 and D020205-01.

In May 2002 two companies in the Southern California area were asked to supply cantilever blades for the advanced LIGO project mode cleaner controls prototype suspension. The order asked for 8 off, upper blades, D020205-01 and 16 off, lower blades, D020201-02. The companies used were Lobart Construction, L and Superior Jig, S.

1.2  Summary of experiment

2 upper and 2 lower cantilever blades from the 2 different manufacturers were compared. The length, B and height, A was measured, as shown in figure 1 below. The length was measured by clamping one end of the blade and (compressed with vice and steel plate) loading the other end with the desired mass measured each blade. All of the measurements were carried out on a Granite Table. A micrometer was used to measure both A and B.

Figure: 1 Sketch showing the length, B and the height, A.

1.3  Results

MEASURED / SPECIFICATION / Distance wire breaks
Blade # / A / B / Overall Length / B / Overall Length / off the end of the blade / Clamping Distance
(inches) / (inches) / (inches) / (mm) / (mm) / (mm) / (inches)
MODE CLEANER UPPER BLADES, D020201-01
4S / 1.807 / 10.599 / 10.58 / 269.21 / 268.73 / 3.0 / 0.79
5L / 1.749 / 10.569 / 10.58 / 268.45 / 268.73 / 3.0 / 0.79
8S / 1.823 / 10.595 / 10.58 / 269.11 / 268.73 / 3.0 / 0.79
1L / 1.72 / 10.562 / 10.58 / 268.27 / 268.73 / 3.0 / 0.79
MODE CLEANER LOWER BLADES, D020205-02
6L / 0.543 / 5.087 / 5.10 / 129.21 / 129.54 / 1.5 / 0.39
5S / 0.556 / 5.097 / 5.10 / 129.46 / 129.54 / 1.5 / 0.39
15S / 0.589 / 5.098 / 5.10 / 129.49 / 129.54 / 1.5 / 0.39
16L / 0.558 / 5.088 / 5.10 / 129.24 / 129.54 / 1.5 / 0.39
KEY: - LOBART: - L and SUPERIOR JIG: - S

1.4  Conclusions

It can be seen in the results section that the two sets of Superior Jig cantilever blades are very well matched.

Appendix A

Measurements were made of the uncoupled mode frequency of the blade and the first internal mode of the blade. These were carried out with the blades under load with m /n mass. Where m is the mass suspended in the stage below and n is the number of blades in the stage e.g. The upper mass in the mode cleaner suspension weighs ~ 3.1kg and is supported by 2 cantilever blades. Therefore the mass supported is 1.55kg.

i)  MC upper blade, D020205-01

Mass, m = 1.55 kg

Frequency, f = 2.28 Hz (cf. 2.2 Hz, theory)

Internal Freq, fint = 86 Hz * (cf. 90 Hz, theory **)

ii)  MC Lower blade, D020201-02

Mass, m = 0.7175 kg

Frequency, f = 3.31 Hz (cf. 3.3 Hz, theory)

Internal Freq, fint = 226 Hz * (cf. 261 Hz, theory **)

* It should be noted that the accelerometer that is placed on the blade will reduce the actual internal mode of the blade.

** Also the wire clamp on the tip of the blade is not modeled into this estimation.

Appendix B

All of the cantilever blades were measured at several positions along the length in order to characterize how tight the thickness tolerance spelled out on the drawings were adhered to.