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Inverted Pendulum Control for KAGRA Seismic Attenuation System. D2, Institute for Cosmic Ray Research Takanori Sekiguchi. Contents. Introduction of IP controls IP control model and simulation Current status of IP control experiment Summary. *IP = Inverted Pendulum. - PowerPoint PPT Presentation
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Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 1
Inverted Pendulum Control for KAGRA Seismic Attenuation SystemD2, Institute for Cosmic Ray ResearchTakanori Sekiguchi
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 2
Contents• Introduction of IP controls• IP control model and simulation• Current status of IP control experiment• Summary
*IP = Inverted Pendulum
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 3
Suspension Local ControlsTarget:• Damping of mechanical resonances• Drift control at low frequencies
Purpose:• Reduction of RMS motions for lock acquisition• Quick recovery after large excursion (e.g. EQ)• Stable operation of the interferometer
RMS displacement 0.1 μm
RMS velocity 0.1 μm/sec
RMS yaw and pitch angle 0.1 μrad
Damping time of resonances ~ 1 minute
Rough idea of the requirement from MIF:
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 4
IP Local Control• Top stage X, Y, Yaw motions are controlled.• Drift control of IP & active damping of resonances
(below 1 Hz)
Sensitivity of sensors
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 5
Starting Point• Starting from 1-D suspension model with simplified system• Check controllability with combined sensor (LVDT & geophone)
≡
Simple suspension model Pre-isolator Prototype in Kashiwa
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 6
Control Model
(Calibration of the sensors are included in “suspension” block)
• Geophone senses top stage velocity• LVDT senses relative displacement between top & ground• Geophone for damping (>0.1 Hz), LVDT for drift control (<0.1 Hz)
Sensor Noise
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 7
Filter Design
Chebychev filter for steep cut-off around micro seismic peak
High pass filter to reject glowing-up noise at low frequencies
Gain boost at micro seismic peak
Open-loop transfer function • Crossover frequency: 0.03 Hz• Unity gain frequency: 0.8 Hz
(phase margin: 60 deg.)
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 8
Frequency Response to Seismic Motion
Active Isolation at micro seismic peak
No seismic reinjection above 5 Hz
Resonance is damped
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 9
Noise Budget @Kamioka in Normal day
RMS dis.: 1.5x10-6 2x10-6 m (@0.01 Hz)RMS vel.: 1.5x10-7 2x10-7 m/s
Geophone Noise
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 10
Noise Budget @Kamioka in Stormy day
RMS dis.: 2x10-5 6x10-6 m (@0.01 Hz)RMS vel.: 2x10-6 5x10-7 m/s
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 11
Summary• We investigate IP controls with combined vibration sensors
(LVDTs and geophones).
• Sensor noise (especially, geophone) is dominant with quiet environment in Kamioka mine.
• Low frequency vibration (<10 mHz) should be stabilized by other ways (global control).
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 12
Current Status of Pre-Isolator Prototype in Kashiwa• IP is currently tuned at 80 mHz.• LVDTs and geophones are installed and calibrated.• X, Y, θ motions constructed by LVDTs and geophones
resemble very well.
Measured Y displacement by LVDT & geophoneWith excitation from virtual Y actuator
• Next step: Apply X control with combined sensors
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 13
END
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 14
Appendix
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 15
Why Local Controls Are Necessary?• Multi-suspension system has many mechanical
resonances to be damped.
• Low frequency oscillators are sensitive to disturbance like temperature change, and drift easily.
Local controls are required for lock acquisition and stable operation of the interferometer
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 16
RequirementFor Lock Acquisition:• Small RMS velocity and rotation angle of the mirror:
RMS velocity ~0.1 μm/sec
RMS yaw and pitch angle ~0.1 μrad
Rough idea of the requirement:
• Short damping time of the mechanical resonances (within ~min.)
During Operation:• Actuation forces on the mirrors must be within the actuator range.
(e.g. ~0.1 μm displacement level is allowed for test masses)
• 10 times smaller local control noises than other fundamental noises in the observation band.
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 17
Control TopologyTop Stage• LVDT: Drift control• Geophone: Damping of pendulum
modes
Intermediate Mass• Damping of residual resonances• Alignment control
Optical Lever• Damping angular resonances?• DC alignment signal
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 18
Control TopologyX, Y• Damp: GEO, OSEM• DC: LVDT
Z• Damp: LVDT, OSEM• DC: LVDTs on GAS
Pitch, Yaw• Damp: OSEM• DC: Oplev
Roll• Damp: OSEM
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 19
Resonances of Pendulum modes• Resonances at low frequencies contribute to RMS• Damped by magnetic damper, but not perfectly
Simulated Mechanical TF of Type-A SAS
Pendulum mode @micro seismic peak
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 20
Pole Plot
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 21
Pole Plot [variable gain]• Too small gain unstable by LVDT control (~0.2 Hz)• Too much gain unstable by geophone control (~0.01 Hz)
Pole plot with variable gain of geophone control (gain 0 to 5, Blue: gain = 1)
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 22
Noise Budget @Kamioka in Normal day
Geophone Noise
Takanori SekiguchiItaly-Japan Workshop (19 April, 2013) 23
Noise Budget @Kamioka in Stormy day