Pre-isolator Update18th MDI Meeting

F. Ramos, A. Gaddi, H. Gerwig, N. Siegrist

December 17, 2010

“State of the art” update

Mechanical vibrations requirements: Velocity less than 500 nm/s (x,y,z), below 16 Hz and less than 100 nm/s above the 16 Hz band.

Description:• Separated tool platform vibro-acoustically decoupled from building and operator platform;• Massive concrete pedestal (> 65 tons), suppressing frequencies above 25 Hz;• Tool platform with passive mechanical damping, suppressing frequencies above 3 Hz;• Active mechanical damping down to 0.5 Hz;• Operator platform decoupled from tool platform.

IBM/ETH Nanotechnology Center – ZurichDue to be completed by the spring of 2011

Yet another great example of a pre-isolator

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Quick look at the numerical simulations of the pre-isolator’s performance

(LCD Note 2010-011)

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FE Model Layout

Things missing in the model:• Pre-alignment mechanics• Final doublet’s geometries (using, for now, lumped masses with estimated inertias)• Final doublet’s supporting structures (girders, etc.)• Pre-isolator’s supports (using , for now, 1-D springs with appropriate stiffnesses)

Lumical Beamcal QD0 SD0 MULT QF1 SF1

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Harmonic excitation in the vertical direction

Vertical steady-state response at QD0

1 Hz

51.2 Hz

Good performance above the first resonance peak

Main eigenfrequency(design)

Inner support tube(tunned)

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Harmonic excitation in the horizontal directions

Vertical steady-state response at QD0

0.05

0.32

There is a good decoupling between

the different directions

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Test set-up @ Point 5(ongoing work)

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Goals of the test

Validate the results from the finite element model

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Assess the influence of external perturbations in a noisy environment (workshop floor)

Check for energy loss mechanisms (friction, plastic deformation,...)

Evaluate the performance of a real systemwith the pre-isolator’s characteristics (heavy mass and low natural frequency)

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40 ton dead-load

4 tapered steel beams

4 flexure hinges

Support beams

Static Deformation

203 to 205 mm

205 mm

The measured static deformation matches (within 1%) the results from the finite element model.

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Vertical direction – Center dead-load/support beam

1.1Hz 6Hz

12Hz

A. Slaathaug – EN/MME

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• First resonance peak at 1.1 Hz (very close to the pre-isolator’s design goal of 1 Hz);

• Good behavior up to 5 Hz;

• Amplitude decreasing with ~1/ω^2 between 1.5 Hz and 5 Hz indicates very low damping of the set-up (below 1%);

• Above 5 Hz, higher order resonance peaks appear and degrade the performance of the set-up;

WHY?

Dynamic Performance

New simulations

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using a detailed model of the set-up

Eigenfrequencies and Eigenmodes1.1Hz 6.7Hz

17.8Hz 57.2Hz

*Main vibration modes 13

Harmonic response in the vertical direction

• Vibrations in the longitudinal direction induce significant movement in the vertical direction (not the case for the actual design of the pre-isolator);• Must combine the two effects to get an accurate representation of the set-up. 14

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Vertical direction – Center of dead-load/ground (excitation in the vertical direction)

Vertical direction – Center of dead-load/ground (excitation in the longitudinal direction)

Vertical direction – Center of dead-load

Combined harmonic response in the vertical direction

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A. Slaathaug – EN/MME

• Good match at frequencies up to 50Hz 15

Combine

Simulated

Measured

Harmonic response in the longitudinal direction

A. Slaathaug – EN/MME

• Good match at frequencies up to 40Hz.16

Longitudinal direction – Support beam/ground (excitation in the longitudinal direction)

Simulated

Measured

Harmonic response in the vertical direction

• The model doesn’t match the measure data above 40Hz.

A. Slaathaug – EN/MME

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Vertical direction – Support beam/ground (excitation in the vertical direction)

Simulated

Measured

Summary of things to address

dead-load not “rigid” Flexure

hinges added

Support structure not “rigid”

±50 mm

A. Slaathaug – EN/MME

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Not valid if the dead-load isn’t “rigid”

Additional higher order eigenfrequencies

Insufficient stiffness in the longitudinal direction

Uncertainty in the position of the sensors

Proposed changes

• Replace the steel supports by concrete blocks ;• Add 4 sets of horizontal stiffeners to improve the longitudinal stiffness of the set-up;• Change the distribution of the steel blocks that make up the dead-load to improve its internal natural frequency. 19

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Expected improvements

1.1Hz

1.3Hz

6.7Hz17.8Hz

57.2Hz

8.7Hz

31.5Hz

72.7Hz

20Isolation

Initial design

New design

Summary (1)• When compared with the initial simulations, the first set of measurements made on the pre-isolator test set-up showed unexpected results in the mid to high frequency range;

• A refined F.E. model was created and the results match much better the measured data in low to mid range frequencies;

• High frequency data calculated using the average between sensors might not be usable due to the relatively low internal eigenfrequencies of the dead-load;

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Summary (2)• New measurements will be performed with a sensor placed at the center of the “dead load”, concrete blocks as a support to the set-up and horizontal stiffeners in the longitudinal direction;

• The good performance of the set-up at low frequencies is promising. Nevertheless, it should be acknowledged that this design, with its several high frequency modes, is not representative of the future final design of the pre-isolator.

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News• Following Holland@CERN exhibition, contacts were established with TNO Science & Industry;• They developed a 6 DOF passive/active vibration isolation table top (Kolibrie); • Includes innovations in sensor technology and placement.

Current performance (transmissibility)

Passive

Passive+active

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