ilias – wg1 hierarchical suspension control g.losurdo infn firenze
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ILIAS – WG1Hierarchical suspension control
G.Losurdo
INFN Firenze
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Virgo Superattenuator
• PASSIVE isolator
• Designed with 3 points of actuation:– Inverted pendulum– Marionette– Recoil mass
• Local controls– Inertial damping of internal modes (IP)– Pre-alignment/damping of the payload
modes (optical levers on marionette/mirror)
• Global control: locking correction distributed hierarchically over the three actuation points
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Digital Controls
• DSP 1: sends correction for inertial damping and tide control to IP actuators
• DSP 2: sends correction for local controls/AA/locking to marionette/RM actuators
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Control electronics
• Digital electronics (16 bit ADC – DSP – 20 bit DAC)
• DSP characteristics:
– Clock frequency 60 MHz
– 2 poles/2 zeroes filter in 330 nsec
– 3x3 matrix-vector product in 1 sec
– Max. sampling freq. 160 kHz (used at 10 kHz)
– Frequency accuracy at 10 kHz: f=2.5 Hz
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Inverted pendulum
• Gravity as antispring: low resonant frequency
• Pre-isolation effect
• Low control forces:
– f0=40 mHz, m=1 ton, l=6 m, x =1 cm
F = 0.6 N !!
• Ideal as control platform: soft actuation
lg
mk
f 21
0
xmF 20
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Sensors/Actuators
• Inertial sensors:– DC-100 Hz bandwidth– Equivalent displacement
sensitivity: better than 10-11
m/rt(Hz)
• Displacement sensors:– Used for DC-0.1 Hz control– Sensitivity: 10-8 m/rt(Hz)– Linear range: few cm
• Coil magnet actuators:– Linear range: few cm
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Control strategy
• From a MIMO to 3 SISO systems:diagonalization with respect to IP modes
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Inertial Damping performance
Fringe signal
Inverted pendulum motion24 hrs
Rms over long periods 1 m
d/dt(L2- L1) ~ 0.25 m/s
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
• Low frequency position control is needed because:– Inertial sensors do not provide DC error signal– Inertial sensors response at f<40 mHz can be spoiled by tilt
• Problem: blend the sensors – dominating the tilt effect – minimizing the seismic noise re-injection– Simplyfing the control strategy
Blending the sensorsx
xAccel.
LVDT0x x
dt xHighpass
Lowpass
+x
Highpass + Lowpass = 1
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
• The seismic noise filtering depends on L(s)
• The loop design is independent on the L(s) cutoff
02
aH l L x L x
s
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Local control setup
• Optical levers read both the mirror and the marionette
• Marionette control allows larger bandwidth
CCD
CCD-MIRROR dist ance =1250 mmCCD focal L. = 25 mmApert ure = 18 mm
incidence 35o
(z) beam axisopt ical port s
dif fusive markers
halogenilluminat or
opt ical port s
XY
Err(xy)
Err(xy)
PSD device on t he focal plane
XY
PSD deviceon t he image plane
Err(z)
14 mW red laserdiode - SM f iber
XY
Err(xy)PSD deviceon t he focal plane
1.4 mW red laserdiode - SM fiber
incidence 30o
f =200 mm
f =200 mm
act uat or
act uat or
t o SA’s f ilt er 7 (F7)
(F7)
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
• Marionette error signal allows a bandwidth of 2-3 Hz
• Uncontrolled resonance (1.2 Hz) exists: needs blending with mirror error signal
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Hierarchical control
• Required locking accuracy: L 10-12 m
• Tidal strain over 3 km: L 10-4 m
The required dynamic range can be covered by two stages. The third one helps for
bandwidth/noise issues…
Tide/drifts compensation
Control of the resonances
Widening the bandwidth…
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
SA local sensing
Mirror PSDMarionette PSD
F7 LVDTs
IP LVDTs/ACC
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
SA sensing
• IP and F7 diagonalized with respect to VRS (P.Ruggi, S.Braccini, F.Frasconi)
P.Ruggi
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
RM actuation
• RM actuators can compensate up to 100 m (in high power/high noise configuration)
• Tidal strain can be larger
• Locking is lost
Power in the cavity IP position Correction to mirror
mic
rons
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Tide Control
• Re-allocation of the low frequency (<10 mHz) correction to the IP
Cavity transmission Correction to the mirror Suspension point position
24 h
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
C4 run
• Tide control: data vs prediction
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
16 mHz – the problem
• Main rotational mode of the SA
• Long decay time, large elongation.
• Hard to be controlled from the marionette
1
2
3
4
7
1
2
3
4
7
1
Braccini, Vicerè
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
16 mHz – solution
• Damp it off using F7 actuators!
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
F7 control
• Hardware/software for F7 control implemented on the NE tower
• 16 mHz resonance control activated
• Used either with or without LC
• Possibility to control other “dangerous” SA modes to be studied
Open loop gaincorrection
error signal
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Locking from the RM: noise
• Reference mass actuators dynamics: 100 m
• DAC noise: 300 nV/Hz1/2
10-1
100
101
102
103
10-20
10-15
10-10
10-5
Actuators noise: current status
Frequency (Hz)
m/H
z1/2
Reference Mass - Mirror Actuators NoiseFilter #7 - Marionetta Actuators NoiseVIRGO Sentivity
A.Gennai
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Standard design
DAC noise: 300 nV/sqrt(Hz) (17.5 effective bits) Coil Driver noise: 80 nV/sqrt(Hz)
10-1
100
101
102
103
10-20
10-15
10-10
10-5
Actuators noise: current status
Frequency (Hz)
m/H
z1/2
Reference Mass - Mirror Actuators NoiseFilter #7 - Marionetta Actuators NoiseVIRGO Sentivity
LCoil3mH
1
2
RCoil10
Ref. Mass Coil
+
-
OUT
R2
R
R1R
Coil Driver
DAC
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Noise Reduction
LCoil3mH
1
2
RCoil10
Ref. Mass Coil
+
-
OUT
R2
R
R1R
Coil Driver
DACRN
500
To reduce the DAC noise we should insert a resistor in series with coil driver. To get closer to VIRGO specs, the resistor value should be about 500 ohms. Bigger values could be used if force will be enough to keep the cavities locked.
The resistor limits the maximum force we can apply and therefore makes lock acquisition very difficult (impossible?)
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
New Solution
LCoil3mH
1
2
RCoil10
Ref. Mass Coil
+
-
OUT
R2
R
R1R
Coil Driver
DAC 2RN
500
DAC 1Transconductance Amplifier We supply the required
additional force for lock acquisition with a transconductive amplifier.
During lock acquisition phase only DAC 1 is used.
During linear phase DAC 1 output set to zero and DAC 2 is used to keep the lock.
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Basic Equations
• Lock Acquisition: g1 = 1, g2 = 0
• Linear Regime: g1 = 0, g2 = 75
CoilNDAC
CoilN
NDACm ZR
VZR
RVgForce
121
zCorrgV
zCorrgV
ssLRZ
R
g
DAC
DAC
CoilCoilCoil
N
m
2
1
3
2
1
10310
500
2
3.0
753.0 21 ggzCorrForce
Note: coil pole shifted above 20 kHz
LCoil3mH
1
2
RCoil10
Ref. Mass Coil
+
-
OUT
R2
R
R1R
Coil Driver
DAC 2RN
500
DAC 1Transconductance Amplifier
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
High power – low noise switch
0 10 20 30 40 50 60-8
-6
-4
-2
0
2
4
6
8
Time (sec)
Cur
rent
Mon
itor
Coil UpCoil Down
switch
0 10 20 30 40 50 601.94
1.95
1.96
1.97
1.98
1.99
2
2.01
2.02
2.03
2.04x 10
-4
Time (sec)
Tra
nsm
itted
Pow
er
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Noise figures
• DAC noise expected (?) @100 Hz:
3 10-16 m/Hz1/2
• Virgo design sensitivity @100 Hz:
2 10-19 m/Hz1/2
• Required noise reduction @100 Hz:
1500
• Using tide control allows to reduce the required correction by a factor 100
• Re-allocating locking to the marionette in the SA resonance region should provide the residual attenuation
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Correction to the mirror in C4
• Marionette control with 3 Hz bandwidth allows to reduce the correction by 50 (Vp= 2 mV)
• Coil driver gain could be reduced by a factor 5000
50
To be re-allocated to marionette
Vp=0.1 V
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Mechanics of the last stages
• Complicated dynamics, important couplings…
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Use of SA simulation
• SA simulation has been important to design the marionette control strategy:– Tuning of SIESTA to reproduce the measured TF – Use of tuned simulation to estimate and subtract the couplings
due to the sensing
– Calculation of a filter to compensate for x marionette motion induced by longitudinal forces
SA mode tuning: I.Fiori, A.Vicerè
LC tuning: S.Avino, E.Calloni, I.Fiori
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Marionette TF matrix
Fz FTx FTy
z
Tx
Ty
I.Fiori
Strongly coupled sy
stem!
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
• Using 4 coils to move the marionette along z: reduce the z-x coupling
• Good data-simulation agreement
I.Fiori, A.Gennai
I.Fiori, S.Avino
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Mechanics
• The two mechanical TF are different– For the structure around 1 Hz – For the asymptotical slope
1/f2
1/f4
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
“Modified” marionette
• Adding two zeroes makes the marionette TF “very similar” to the RM one
1/f2
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
1st scheme: composed lock ACQ
• Advantage: simpler, no need of transition
• Drawback: marionette control bandwidth limited by higher ITF noise (no SSFS)
PHD Lockingcompensator
L(s)(s+s0)2
H(s)
In the GC
In the DSP
zCorr
cavity power RM correction marionette correction
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
2nd scheme: re-allocation
• Advantage: allows wider marionette bandwidth
• To be tested with AA and SSFS
PHD
Anti-Ramp
Ramp 10s
Lockingcompensator
L(s)(s+s0)2
H(s)
In the GC
In the DSP
zCorr
cavity power RM correction marionette correction
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Filters
• To blend the two systems use usual strategy
• L(s) = 3rd order low pass filter, H(s) = 1-L(s)
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Hierarchical control
• The north cavity has been locked by distributing the forces over the three SA stages: the controllability of the SA has been demostrated
1997 !
mic
rons
DC-0.01 Hz
0.01-1 Hz
1-50 Hz
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Performance with no AA/SSFS
Mirror displacement correction over the two stages
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
C4 data - extrapolation
• C4 data (noisy stretch) have been filtered with current hierarchical control TFs to predict the correction one expects on the RM when SSFS is ON
• Expected zCorrrms= 3 mV.
L.Holloway
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
• One should consider peak values of zCorr instead of rms. In C4, over 18 hrs:
zCorrpeak ~ 10 zCorrrms
• With hierarchical control in the present configuration one can assume:
zCorrpeak ~ 30 mV
• Therefore, the coil driver gain can already be reduced by ~ 300
We are not far from Virgo sensitivity…
New promising design is being tested in MATLAB (L.Holloway)
Peak correction rms correction
C4 data
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Interaction with angular control
• The alignment/power fluctuations are larger when hierarchical control is ON
• This is a concern: to be tested with AA
• Larger statistics needed, analysis going on
Standard locking
Hierarchical locking
ILIAS-WG1– July 7th, 2004 G.Losurdo – INFN Firenze-Urbino
Next steps
• Test hierarchical locking with linear alignment
• Widen the bandwidth of marionette control
• Switch to low noise coil driver after re-allocation
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