Monochromator Vibration: Two case studies · 2017-03-30 · Case Study 1: Oasis on the horizon?...
Transcript of Monochromator Vibration: Two case studies · 2017-03-30 · Case Study 1: Oasis on the horizon?...
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Monochromator Vibration: Two case studies
Curt Preissner, Barry Lai, Alan Kastengren, and Mark Erdmann
Mechanical Engineering and Design Group
Advanced Photon Source
Argonne National Laboratory
MEDSI 2014, Melbourne
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Outline
Background: what, why, and how
Case study 1: S07 BM Double Multilayer Monochromator (DMM)
Case study 2: S02 ID DMM
Summary of our method
Conclusions
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Vibration diagnosis can be a bit like wandering the Australian
outback…
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Background: A little (motion) goes a long way
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10 m
20E-6m D = 100E-9 m
40E-9 m
2E-6 rad
Image of beam from S02 ID Double Multilayer Monochromator
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Background: Bearings are most compliant part
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0 50 100 150 200 250 300 350 400 4500
0.5
1
1.5
2
2.5x 10
9
Force (N)
Sti
ffn
es
s (
N/m
)
Stiffness Curves for Different Types of Rolling Element Contact
sphere on spheresphere on cylinder (external)sphere on flatsphere on cylinder (internal, ID=1.1 D sphere)cylinder on flat
P
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Background: Tell me what’s wrong but don’t open it up
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1st check ambient levels
Measure supports/outside tank
Characterize beam motion
Subsequently open instrument to make measurements
S02 DMM
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Case Study 1: Sector 7 BM Double Multilayer Mono
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1st stage stack
1
1
Y1
X1
X-ray beam
2nd stage stack
2
2
Y2
X2
Z2
Z
Y
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Case Study 1: Wandering in the outback
Initial beam characterization was misleading – Camera frame rate was insufficient
– Operational conditions were be different than conditions when imaging beam vibration were different than when measuring vibration
– A roughing pump was connected to an evacuated flight path in the next hutch
A number of “mirages” – Missing fasteners
– Broken/incorrect baseplate mounting
– Damaged vertical stage, fretting
Cycle times between measurements were long
Access to internals was limited
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Case Study 1: Mirages
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Case Study 1: Oasis on the horizon?
Lack of good beam=>mechanics correlation caused lots of time to be spent
Real problems were identified
However, they were not problems that contributed greatly to beam motion
Subsequent beam measurements, vibration measurements, and modal analysis located problems
– 20 Hz peak associated with tank support (also close to 1st crystal stack resonance dominated by Y stage)
– 37 Hz peak associated with 2nd crystal stack Y stage
Fix: Eventually replace 2nd crystal Y stage (only enough money for one)
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Case Study 2: Sector 2 ID Double Multilayer Mono
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First stage stack
1
1
Y1
X1
X-ray beam
Second stage stack
2
2
Y2
X2
Z2
Water cooled 1st crystal
Z
Y
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Case Study 2: Transverse direction ambient vibration
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Case Study 2: Vertical direction ambient vibration
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Case Study 2: Beam motion measurements
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X-ray beam
Slit blade used to mask 1/2 of beam
PIN diode used to measure intensity fluctuations due to
beam motion
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Case Study 2: Beam motion measurements
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Case Study 2: Modal analysis
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Impact frequency response functions (FRFs) at each component of each stage stack provide:
– Direct estimation of stiffness
– Information to identify mode shapes and natural frequencies
Each stack has a mode shape that is primarily in the Z direction (rotation about X), which is the worst for beam motion.
60 Hz mode for the second crystal stack is shown to the right
Points 3-6 are moving portion of Y stage and above
Y stage is “weak link”
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Case Study 2: Dynamic stiffness measurements
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Case Study 2: Static stiffness measurement
Static stiffness measurement: ~37000 N*m/rad
Dynamic stiffness measurement: ~18000 to 20000 N*m/rad
This is very compliant as an APS-designed stage has stiffness of ~313000 N*m/rad
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TK XX
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Case Study 2: Temporary mitigation
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Current status
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A new vertical stage was specified and procured
– Cross-roller bearing
– Torsional stiffness of at least 325000 N*m/rad
Four stages were ordered
Custom item from vendor to fit existing volume and mounting holes
Vendor was told we will check specification upon delivery
– Stages as delivered do not meet specification
– Conversation with vendor reveals different interpretation of cross-roller bearing guided stage
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Conclusions
Diagnosis
– Check ambient environment
– Measure beam motion with sufficient bandwidth
– At some point, you need to open the tank
– Modal analysis or impact measurements
– Correlate beam motion and mechanical motions
Good design practices
– Reduce motion degrees of freedom
– Select stiff bearings (both type and preload)
– Use sufficient bearing separation
– Hard points for cooling lines
– Avoid cantilevered loads
– Trust but verify if application is demanding MEDSI 2014, October 20th to 24th, Melbourne
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Cheers mates! With my collaborators: Mark Erdmann, Alan Kastengren, and Barry Lai
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Background
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Image of beam from S02 ID Double Multilayer Monochromator
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Background: Crystal perturbations and beam motion
Small translations at mono = small beam motion at endstation
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Small rotations at mono = large(r) beam motion at endstation
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Background: Why might an instrument be susceptible?
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0 2 4 6 8 10 12 14 16 180
50
100
150
200
250
300
350
400
450
Deflection (um)
Fo
rce
(N
)
Deflection Curves for Different Types of Rolling Element Contact
sphere on spheresphere on cylinder (external)sphere on flatsphere on cylinder (internal, ID=1.1 D sphere)cylinder on flat
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Background: Tools of the trade
Data Acquisition – Data Physics Abacus
Accelerometers
– PCB 393B31, single axis, 635 grams, 1 nm/√Hz @ 7Hz
– PCB 393B05, single axis, 50 grams, 10 nm/√Hz @ 7Hz
– PCB 356B18, triaxial, 25 grams
Impact hammers
– PCB 086E80, 4.8 grams
– B&K 8202, 402 grams
– PCB 086D50, 5.5 kilograms
Polytec OFV-534 Laser Doppler Vibrometer
Modal analysis can be used to estimate stiffness, and mode shapes (as opposed to operating shapes)
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Case Study 1: Timeline
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October 2008 – Installation
May 2009 – first signs of vibration
issues, user contact
August 2010 – initial
investigation
October 2010 – internal
measurements, broken parts
September 2011 –additional
measurements
November 2012 – beam motion
January 2013 – more internal
measurements
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Case Study 2: Timeline
January 2013 – Installation
July 2013 – Initial measurements
August 2013 – Beam motion
September 2013 – Modal analysis
March 2014 – Beam motion measurements
(after temporary fix)
May 2014 – Order replacement stages
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Temporary mitigation: Before and after
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Before stage removal With aluminum block
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Temporary mitigation: Before and after
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Summary of our method
1. Measure the ambient ground and beam motion
2. Try perturbing stages and measure beam motion
3. Measure beam motion Frequency Response Function (FRF)
4. Measure ambient motion of crystal holders
5. Measure impact-excited FRFs of crystal holders
6. Identify mode shapes and natural frequencies of crystal motion system
7. Correlate beam motion and crystal resonances
8. Correlate dynamic and static stiffness measurements
9. Remove, alter, or replace suspect components
10. Recheck beam motion
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