Transcript MSC - ego

Virgo suspension control
progress
E. Majorana
INFN
Mirror Suspension Control workgroup
ILIAS
Geneva 29 March 2007
The usual “standard-super-attenuator” suspension …
Soft isolator concept:
1. very efficient passive
attenuation
2. active controls for
normal mode damping
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The mission of Mirror Suspension Control workgroup:
commissioning-oriented activity
Virgo sensitivity (at LF !)
Virgo duty-cycle
In fall 2006 the majority of main ITF control issues had been addressed:
- lock acquisition strategy
- automatic alignment (~)
-suspensions and local controls allowed all above
To start noise hunting, stable operation was needed:
=> MSC performance started to be integrated in ITF issues
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Our plan was clear thanks to the previous efforts of MSC
Workgroup, during the first part of the commissioning,
and to some ideas matured meanwhile.
Unavoidable acknowledgments to my friends and colleagues
Giovanni Losurdo and Paolo Ruggi
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Interface with ITF
Noise budget
Angular control strategies
(Local/automatic)
Suspension control chain
Beam centering
(read-out,numerical,digital,actuator)
NOW
Disturbance rejection
Sensor blending optimization
Global Inverted Pendulum Control
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All-the-possible-handles
(completion needed!)
Lock force re-allocation (BS)
SA-chain damping from ground
Vertical damping
Safe-and-soft operation interfaces
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Focus on:
- improvement of disturbance rejection
- reduction of control noise through the suspension
- reduction of ITF coupling with the control noise
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> disturbance rejection: vertical damping needed (1/9)
V-damp
ON/OFF
vs alignment
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> disturbance rejection: vertical damping needed (2/9)
One-By-One
O-B-O
OFF
ALL
OFF
ALL
ON
O-B-O
OFF
ALL
OFF
ALL
ON
No crucial
Improvement
during OBO
OFF Test.
Clear
Improvement
All OFF/ON
Relationship
with
Angular
fluctuations
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> disturbance rejection: vertical damping needed (3/9)
One-By-One (detailed)
TOP stage
Last stage
ITF
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> disturbance rejection: top stage sensor blending (4/9)
Winter issues: STD scheme and blending used until Dec 2006
ACC
HP
+
cross
IP
LP
LVDT
fcrossover = 50 mHz
Trade-off between:
30 mHz (wind disturbance through ACC)
and
70 mHz (mseism disturbance through LVDT)
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cavities locked independently
unexpected !
wind-noise
30 mHz crossover N-arm
70 mHz crossover W-arm
pulling back the
crossover:
benefit expected
mseism (sea) produces angular
excitation of the payload.
wind (reasonably through the tilt)
fake acceleration re-injected.
Key solutions :
- smart experiments to simulate the disturbance ;
- tools to optimize the blending on-the-fly ;
- other smart ideas ….
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Sensor blending:
TWO-SIDE OPTIMIZATION
characterizing Suspension-control_vs_disturbance
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> disturbance rejection: top stage sensors, first attempts (5/9)
old
old
new
new
hybrid filters (on-the-fly tuning)
ACC
HPw
LPw
HPms
+
mix
cross
IP
+
LPms
LVDT
mix =0.5 :
“medium” attenuation of mseism noise
mix =0 (wind):
not worse than old filters against mseism + tilt
noise attenuation below 50 mHz
mix =1 (mseism) :
“strong” attenuation of mseism noise with slightly
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worsened
tilt noise attenuation.
OUR TARGET
How much is it enough ?
The answer is worked out
through a deeper analysis
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> disturbance rejection: top stage sensors (6/9)
hybrid filters in use: noise percolation paths
Pitch excitation
(payload mode)
yaw bump (due
to large zM
correction)
mix=1
Ineffective
@ 0.45 Hz,
(IP notch)
Large zM due to tilt
disturbance through
accelerometers
Calm period
3 mechanisms (at least): F0_z
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zCorr, F0_z
qx, F0_z
qy
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> disturbance rejection: top stage sensors (7/9)
WSR7, heuristic threshold for mix adjustment in-line
wind (mix 0)
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hic sunt leones
sea (mix 1)
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> disturbance rejection: top stage sensors (8/9)
LP/HP optimization, given the standard actual corrector (cross)
LP/HP ratio versus CL TF
mix=0.70
mix=0.90
mix=0.95
mix=1
CL TF
ACC
HPLP
mix
cross
IP
seism
LVDT
Hz
V/sqrt(Hz)
LVDT noise projection into zCorr (NE@step 1)
Two regions can be distinguished:
A) LP/HP ratio plays a role
attenuating LVDT sensor
disturbance (mseism)
B) No effect of LP/HP attenuation
Hz
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WSR7 => WSR8 (optimization example)
patches added to LP to reduce
mirror tilt excitation due to SA
mseismic noise disturbance
HP: anti-wind
(tilt)
previous
WSR7
Hz
Hz
WSR8
LP: accel. comparison
mms-2
Hz
Hz
note: cleaner (LP+HP=1) blending allows to re-tune HP to reduce tilt re-injection
(=> heavier computation…)
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WSR7 => WSR8 optimization
LP: anti-mseism
previous
WSR7
Hz
Hz
WSR8
accel. comparison
mms-2
Hz
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Hz
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WSR7 => WSR8 overall tuning (mix 0-1)
LP/HP
mix 1 => 0
sea => wind
mix 0 => 1
wind => sea
A) assessing how much it is enough to enhance LP/HP to beat tilt re-injection
is not easy. B) more data needed in windy-only conditions… C) optimization
not significantly efficient around the crossing frequency.
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> disturbance rejection and noise budget: 4-marionette (9/9)
Marionette locking force can be distributed to both input and End mirrors
Since WSR8 the lock correction is applied to four marionettes
(NI,NE,WI,WE) instead of two (NE,WE): A) reduction of direct locking
force budget and B) non-linear torque negligible in case of wind
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(=> reduction of large zM by a factor 2 lightens gain request to AA).
Novel strategy (…one smart idea):
GLOBAL OPTIMIZATION
anti-mseism plus coherent wind compensation
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GIPC (Global Inverted Pendulum Control)
benefits: wind disturbance rejection, lock acquisition, duty-cycle.
Once the ITF is locked, the mirror position, provided by the Global
Control, can be used instead of LVDTs, referred to the ground.
GC (reconstructed z)
Features:
- automatic engagement (soft!)
- anti-wind blending in NE-WE-BS-PR
- anti-mseism in NI-WI
Splitted anti-mseism /anti-mseism
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LVDT
LVDT
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Example1: NE_GIPC,WE_GIPC only
step9
NE “follows” NI
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WE “follows” WI
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Example 2: NE_GIPC, WE_GIPC only
step9
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Example 3: NE_GIPC, WE_GIPC, BS_GIPC, PR_GIPC
step9
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Example3: NE_GIPC,WE_GIPC only
step9
Thanks to
GIPC
GIPC
benefit to
Automatic
Alignment
Short
suspension
(i.e.beam)
improvement
necessary ?
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A curiosity: in November GIPC had already been tested but we
Nextour
improvements
andtostudies
needed to improve
knowledge and
optimize the blending
A major effort
necessary at LF
during stormy
weather!
EM-MSC-041206
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Example 4:environmental (central Bld. shock absorption)
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> noise budget: actuation noise & reallocation
-Suitable resistors are used to
reduce coil-drivers noise
(ln=lownoise/HP=highPowe
to accomplish
sensitivity/locking)
-a trade-off with DAC noise
using Emphasis/deemphasis
was found.
Still some work:
Too large correction
directly on the mirror
Low frequency component that can
be moved upwards (marionette)
BS requires marionette
reallocation.
 WE,NE have a mseism
peak that should be reduced
by further force reallocation
to the marionette.
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> synthesis: net improvement of recent activity
In this example:
- red data (now)
show up much larger
mseism
Much more mseism and similar peak at 130 mHz
In spite of this:
=> the force
reallocated
to the marionette
is smaller
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> conclusions
It was mandatory to accomplish this task by considering the suspension
system as a single component of the interferometer
The development was a bit delayed by the requirement of checking
the performance under actual environmental disturbance. Tools to
emulate crucial situation have been developed.
A large effort was spent on sensing optimization and on “soft operation”
Now it is possible to reduce by a factor 3 the rms disturbance due to the
wind, while mseism (sea) does not seem to be the main source of problems.
To be done before (possibly before the MegaRun):
-further technical noise reduction
-improvement of short suspension performance (InjB,MC,OutB)
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