Benoit BOLZON Nanobeam 2005 – Kyoto Active mechanical stabilisation LAViSta Laboratories in Annecy working on Vibration Stabilisation Catherine ADLOFF

Benoit BOLZON Nanobeam 2005 – Kyoto

Active mechanical stabilisation

LAViSta

Laboratories in Annecy working on Vibration Stabilisation

Catherine ADLOFF Andrea JEREMIE Jacques LOTTIN

Benoît BOLZON Yannis KARYOTAKIS Laurent BRUNETTI

Franck CADOUX Claude GIRARD Fabien FORMOSA

Yan BASTIAN Nicolas GEFFROY


Introduction Future linear collider : vertical beam size of 1 nm

Movements of the two final focus quadrupoles : smaller than 0.3 nm

Problem : nanodisplacement due to ground motion

Goal of our study : active mechanical stabilisation of the final focus quadrupoles

Study sensors and actuators to measure nanodisplacements and achieve the required stabilisation

Model different mechanical structures because of the resonances induced by ground motion

Development of a feedback loop to stabilise the whole system


1. Measurements - Sensor characteristics - Ground motion - Structure vibration

2. Modal analysis - Measurements - Simulation

3. Dynamic response - Comparison measurements/simulation - Fixed-free beam - Addition of boundary conditions

Outline

4. Feedback loop - Mock up - Results

5. Future prospects - New structure design - Simulation of the whole system


1. Measurements - Sensor characteristics - Ground motion - Structure vibration


3. Dynamic response - Comparison measurements/simulation - Fixed-free beam - Addition of boundary conditions



1. Measurements


Goal : Sensor study and ground motion study

Signal analysis :

Coherence : Coherence between two sensors versus frequency

Resolution : Sensor accuracy versus frequency

Signal/Noise ratio

PSD : Normalized signal power versus frequency

RMS displacement : Displacement versus a range of frequency

1. MeasurementsIntroduction Sensors characteristics Stabilisation of the ground Beam vibration study


Seismic sensors : Measurement of the ground velocity

Accelerometers : Measurement of the ground acceleration

2 types of sensors :

1. Measurements

Non magnetic

Introduction

Sensors characteristics Stabilisation of the ground Beam vibration study


1. MeasurementsIntroduction


- Conclusion : Velocity sensors can be used to measure low frequency ground motion whereas accelerometers measure ground motion only above 7Hz

Very low amplitude of ground acceleration below 7Hz : Rate Signal/Noise low Only noise is being measuredHigh amplitude of ground velocity below 7Hz : Rate Signal/Noise high Signal is being measured

0.2Hz 7Hz 100Hz

Good coherence between velocity sensors

Good coherence between accelerometers


1. Measurements

Resolution

Introduction


4Hz

0.2nm

0.6nm


Isolators : contain all the necessary electronics, vibration detection and correction devices, along with passive Isolators.

Honeycomb support

structure

User Interface Controller : to provide communications with and diagnostics of the STACIS 2000 system

Stabilisation of the ground motion with the STACIS 2000 Stable Active Control Isolation System

Isolator

1. MeasurementsIntroduction Sensors characteristics

Stabilisation of the ground Beam vibration study


Guralp sensor

Accelerometers

Velocity PSD

1. Measurements

Passive table

Active table Passive table

Active table

Introduction Sensors characteristics



1. Measurements

RMS

Active bandwidth

Good reduction

Active table Passive table10nm

1nm

0.5Hz 4Hz 50Hz

Introduction Sensors characteristics



1. Measurements

Resonances induced by the excitation of the beam :

Need to use a feedback loop to damp eigenfrequencies

Usefulness of modal analysis

Excitation of the beam measured

Introduction Sensors characteristics Stabilisation of the ground

Beam vibration study


1. Measurements - Sensors characteristics - Ground motion - Structure vibration


3. Dynamic response - Comparison measurements/simulation - Fixed-free beam - Addition of boundary condition



2. Modal analysis


Excitation spectrum

Structural resonances

Develop a know-how concerning

modal analysis

Ground motionCooling system

Air flows

Power supply system…

( Amplified motions)

2. Modal analysisWhy? Experimental Numerical Experimental/Simulation


2. Modal analysisWhy?

Experimental Numerical Experimental/Simulation

Accelerometers

beam

Hammer Acquisition system


• ME' scope• PULSEFourier transform Mode shape

2. Modal analysisWhy?

Experimental Numerical Experimental/Simulation

280.5Hz

Torsion


• Identify eigen frequencies• Display mode shapes

Mode 2: 101 Hz

Mode 2: 101 HzMode 1: 16 Hz

Modal tests on the free-fixed beam

2. Modal analysis

- SAMCEF -

Why? Experimental

Numerical Experimental/Simulation


Good relative accuracy !

2. Modal analysisWhy? Experimental Numerical

Experimental/Simulation

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16 72 97 269 281 428

Experimental eigenfrequencies (Hz)

Dif

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3. Dynamic response


External perturbation

Structure

Dynamic Response

Ground motion

Accelerations Displacements Stresses …

Equations of motion

3. Dynamic responsePrinciple Free-fixed beam Fixed-simple supported-free beam


Check the accuracy of the numerical prediction

Data used for the comparisonwith simulation

Data used as input for the simulation

3. Dynamic response

Mock-up

Principle Free-fixed beam Fixed-simple supported-free beam


Simulation parameters

Structure modeled with “shell” elements

Clamping system

1000 mm

100

20 mm

Model used :

Young modulus = 74000 MPa = 0.34 (Poisson’s ratio)Volumic mass = 2825 kg/m3

Damping : ε = 0.1 %

Beam parameters :

M = 830 g

Lumped mass :

M

3. Dynamic responsePrinciple Free-fixed beam Fixed-simple supported-free beam


3. Dynamic response

Comparison Simulation/Measurements

Principle Free-fixed beam Fixed-simple supported-free beam


3. Dynamic response

Goal of the study : change boundary conditions to change eigenfrequencies

Results shown : block Z-displacements of the structure to damp Z-flexion modes

Principle Free-fixed beam

Fixed-simple supported-free beam

Mock-up


3. Dynamic responsePrinciple Free-fixed beam


34Hz

34Hz18Hz

We expect amplitude of first eigenfrequency to decrease when the simple support moves away from the clamping

The value of the first eigenfrequency goes up when the simple support moves away from the clamping

18Hz

20cm 50cm

34Hz


3. Dynamic response

Pick of excitationExcitation

Big resonanceResonance

Conclusion :

In a general way, the best option is to prevent modes to be much excited, by shifting them. Obviously, the excitation spectrum must be well known…

Principle Free-fixed beam


18 Hz: Eigenfrequency when support is located at 20cm

22.5 Hz: Eigenfrequency when support is located at 30cm







4. Feedback loop


« a steel beam »

2 loudspeakers2 opposite PZT

Experiments

Mock up Principle of rejection Results

4. Feedback loop

Accelerometer


4. Feedback loopMock up Principle of rejection Results

Algorithm of feedback loop developed to allow the simultaneous elimination of several resonance peaks


Rejection of 6 resonances : (without and with rejection)

Resonances of : -beam-support

Mock up Principle of rejection

Results4. Feedback loop







5. Future prospects


Conical shape - 2.5 meter long

Computer Aided Design – 1st version

Φ=14cmΦ=8cm

5. Future prospectsFF quad. Prediction New test bench Whole system simulation


Prototype close to FF quadrupole design : fixed-free structure

2.5 m

• Representative prototype : eigen frequencies• Easy Boundary Conditions : square section• Adaptability to get closer and closer to the FF quadrupole: Hollow core

5. Future prospects

Goal : Simulate modal analysis of the future FF quadrupole

Propose new design (inner supports …)

Propose new materials (composite materials …)

FF quad. Prediction New test bench Whole system simulation


5. Future prospects

Improve efficiency of feedback loop • Type of sensors / actuators• Location of sensors / actuators along the structure• Reliability of the feedback algorithm• …

Simulation could be Simulation could be a great help !...a great help !...

FF quad. Prediction New test bench

Whole system simulation


Conclusion

Velocity sensors can measure ground motion down to 0.1Hz

We are able to predict the response of a structure

New adaptative prototype close to the future FF quadrupole design

Propose new design and new materials of the future FF quadrupole

Feedback loop allows the simultaneous elimination of several resonance peaks on a reduced-size mock-up

Goal : elimination of all vibration frequencies

Simulation of the whole system Mock up of the whole system

Next generation of SP500 non-magnetic sensor soon available : smaller, better sensitivity (20000V/m/s!!)

May be the sensor used for our prototype

Documents

Benoit BOLZON Nanobeam 2005 – Kyoto Active mechanical stabilisation LAViSta Laboratories in Annecy working on Vibration Stabilisation Catherine ADLOFF