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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
D. Tshilumba, CERN, 03 February 2015
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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)
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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DISTURBANCE SOURCES
• Ground motion• External forces (Water cooling, ventilation,…)
D. Tshilumba, CERN, 03 February 2015
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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)
D. Tshilumba, CERN, 03 February 2015
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CONTROL FORCE REQUIREMENTS
• Assuming P controller• Control force for ground motion compensation (~10N integrated RMS)• Nanopositioning force (~50N integrated RMS)
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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One single stage: active feedback
• Features:• Bandwidth increase• Higher robustness to disturbance at low frequency• Removal of steady state error
OPTIONS TO FULFIL THE REQUIREMENTS
D. Tshilumba, CERN, 03 February 2015
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OPTIONS TO FULFIL THE REQUIREMENTS
• 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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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UPGRADE TYPE 1
Parasitic resonance modes
• 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
Parasitic resonance modes
Further improvement:
• Monolithic base plate design
•Additional stiffeners
D. Tshilumba, CERN, 03 February 2015
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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)
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015
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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
D. Tshilumba, CERN, 03 February 2015