1 Nanopositioning of the main linac quadrupole as means of laboratory pre-alignment David Tshilumba, Kurt Artoos, Stef Janssens D. Tshilumba, CERN, 03

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Nanopositioning of the main linac quadrupole as means of laboratory pre-alignment

David Tshilumba, Kurt Artoos, Stef Janssens

D. Tshilumba, CERN, 03 February 2015

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OBJECTIVES

• Investigate ways to combine alignment and nanopositioning into one actuation system

•Upgrade of Type 1 nanopositioning prototype

• Treatment of parasitic resonance modes

• Reduction of translation – roll motion coupling


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CURRENT SYSTEM OVERVIEW

• Coarse stage (cams)• Resolution : 0.35µm• Stiffness: 50kN/µm• Stroke: 3mm

• Fine stage (piezo stacks)• Resolution: 0.25nm • Stiffness : 460N/um (piezo)• Stroke: 5µm

• Limitations: • precision of coarse stage (~10µm)• insufficient stroke of fine stage for

thermal load in tunnel ( >100µm)


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GOALS

Goals:

increase the range of fine stage Perform nanopositioning

Parameters ValueResolution <0.25nmPrecision 0.25nm

step displacement 0.25nm up to 50nmSpeed 10μm/s

Rise time 1msSettling time 5ms


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DISTURBANCE SOURCES

• Ground motion• External forces (Water cooling, ventilation,…)


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STIFFNESS REQUIREMENTS

• External forces (Water cooling, ventilation,…)

• High stiffness • lateral stability requirement met passively (0.55kN/µm)• Active control still needed for vertical direction (1kN/µm)


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CONTROL FORCE REQUIREMENTS

• Assuming P controller• Control force for ground motion compensation (~10N integrated RMS)• Nanopositioning force (~50N integrated RMS)


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FUNCTIONAL AND PERFORMANCE REQUIREMENTS

Parameters ValueResolution <0.25nmPrecision 0.25nm

Stroke ± 3mm step displacement 0.25 up to 50nm

Speed 10μm/sRise time 1ms

Settling time 5msControl bandwidth 300Hz

Stiffness (vertical/lateral)

1/0.55 kN/μm

Vertical force (dynamic)

50N

Horizontal force (dynamic)

30N


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One single stage: Flexure lever mechanism

• Possible monolithic design• No friction• No backlash• No wear

• Avoid plastic deformation!• Effect on the dynamics of the system

n<1 => benefic effect on the dynamics of the system

• Parameters to consider• Coupling stiffness• Pivot stiffness• Intrinsic flexure stiffness

• Effect on the effective attenuation factor•

•

•

in

out

x

x

a

bn

out

in

F

Fn

out

in

k

kn 2

OPTIONS TO FULFIL THE REQUIREMENTS


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One single stage: active feedback

• Features:• Bandwidth increase• Higher robustness to disturbance at low frequency• Removal of steady state error



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• Coarse – fine resolution approach

• Improvement of Coarse stage (Juha Kemppinen)• Improvement in the WPS measurement speed• Improvement in precision via feedback loop

• Improvement of fine stage• Higher stiffness• Larger stroke (>200μm)

Compensation of thermal loads in tunnel Beam time > 50 days


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ACTUATORS

Lorentz actuators

• Based on Lorentz force

• Linear: • Zero stiffness• Resolution dependent on amplifier• Stroke: up to 75mm• Heat dissipation• Compatibility with collider environment?

iF


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ACTUATORS

Hydraulic actuators

• Based on hydraulic pressure

• • High stiffness achievable:

• Resolution dependent of control valves • Stroke: >>1mm• Friction between cylinder and piston• Susceptible to leakage

h

S

h

Fk

rodcapp APAPF 21


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ACTUATORS

Piezoelectric actuators• Based on inverse piezo effect

• Piezo stacks • High stiffness (480N/μm)• Limited stroke: up to 0.2%

• Piezo stepper• Lower stiffness (150N/μm)• Higher stroke (20mm)

• No Heat dissipation• Compatible with collider environment


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ACTUATORS COMPARISON

Resolution Stiffness Stroke Remarks

Lorentz +++ + +++ Compatibility to external magnetic field

hydraulic + +++ +++ Reliability

Piezo stack +++ +++ + Lack in stroke

Piezo stepper

+++ ++ +++Lack in stiffness

Piezo stepper: good candidate for mechanical attenuation


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INTERMEDIATE CONCLUSION

• Overview of the current system

• Requirements for Nano-positioning summarized

• Alternatives to increase the range• single stage

• Passive mechanical solution• Active solution

• coarse-fine stage

• Comparison of classical actuators• Piezo stepper + mechanical attenuation


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UPGRADE TYPE 1

Parasitic resonance modes

• Unexpected eigen modes detected by EMA between 30Hz and 50Hz

• Suspect root cause: connection stiffness between components

• Bolting: up to 40% drop in eigen frequency• Gluing: up to 8.5% drop in eigen frequency

Courtesy of M. Guinchard


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UPGRADE TYPE 1


• Problematic region: base plate

• Improvement after gluing instead of bolting: lowest eigen mode at 50Hz

Courtesy of M. GuinchardD. Tshilumba, CERN, 03 February 2015

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UPGRADE TYPE 1


Further improvement:

• Monolithic base plate design

•Additional stiffeners


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UPGRADE TYPE 1

Roll motion reduction: parallel kinematics • Permissible roll displacement: 100μrad

• Aluminum eccentric shear pins • 5.15μrad/μm coupling

• Alternative: rotational symmetry hinges• 0.47μrad/μm coupling

• Features:• Less components• Tunable translational stiffness

•Design optimization required (Space availability)


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UPGRADE TYPE 1

Roll motion reduction: parallel kinematics

• Permissible roll displacement: 100μrad

• Rotational symmetry hinges • 0.47μrad/μm coupling• Lost motion: 5% (vertical)

• High resonance frequencies


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UPGRADE TYPE 1

Roll motion reduction: serial kinematics

• Permissible roll displacement: 100urad

• Further coupling reduction• 0.094urad/um coupling • Lost motion: 0.02% (vertical)

• Design optimization required• More compact• Avoid flexible deformation modes


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CONCLUSION

• Actuator requirements defined

• Existing actuation technologies Vs performance requirements

• Introduction of concepts for further study to increase the range

• Type 1 upgrade proposals under study


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FUTURE WORK

• Optimize the presented alternative concepts for the kinematic decoupling in type 1 stage • Design a 1dof extended nanopositioning stage with attenuation mechanism + Experimental validation

• Secondment at TUDelft and TNO almost finished


Documents

1 Nanopositioning of the main linac quadrupole as means of laboratory pre-alignment David Tshilumba, Kurt Artoos, Stef Janssens D. Tshilumba, CERN, 03