Virtual sensor fusion for high precision control

peer reviewedHigh performance control requires high loop gain and large control bandwidth. However, the spurious resonances at the higher frequencies can limit the performance of such type of systems. This drawback can be overcome by using sensor fusion technique. In sensor fusion, two or more sensors are combined in synergy such that good performance is achieved at lower frequencies while ensuring robustness of the system at higher frequen- cies. This paper presents a new technique, termed as ‘‘virtual sensor fusion”, in which only one of the sensors is physically installed on the system while the other sensor is simulated virtually. The virtual sensor is selected based on desired high frequency response. The effectiveness of the proposed technique is demonstrated numerically for a case of active seismic isolation. A robustness analysis of virtual sensor fusion is also carried out in order to study its stability in the presence of spurious resonances. Finally, the technique is exper- imentally verified on active isolation of pendulum system from ground motion. The results obtained demonstrate good isolation performance at lower frequencies and robustness to plant uncertainties (spurious resonances) at higher frequencies. This technique can be effectively used for high precision control of sensitive instruments

Experimental validation for low frequency isolation of six degree of freedom systems using inertial sensors

peer reviewe

Experimental validation for low frequency isolation of six degrees of freedom systems using optical inertial sensors

peer reviewe

Low frequency high resolution optical inertial sensors

Nowadays, sensors’ resolution limits their performance at low frequency which reduces their operating range. Sensors with a good resolution at low frequency are required to improve the performance of gravitational wave detectors in the sub-Hz frequency range. We are currently developing an inertial sensor with a sufficient resolution at low frequency from 10 mHz to 100 Hz. We are focusing on the improvement of different characteristics of the sensor, among others, its compactness and its thermal noise mitigation. The readout consists of a long-range Michelson interferometer fed by a 1550 nm laser and whose signal is measured by InGaS photodetectors. The use of InGaS photodetector in our interferometer will allow better resolution for future sensor projects. The inertial mass is connected to the frame by a fused silica flexure joint to limit internal damping. Then, translational guidance is implemented to allow the use of a flat mirror. The actual sensor developed at the Precision Mechatronics Laboratory has a resolution of 2x10^(-13) m/√Hz at 1 Hz. Our goal is to reach the same resolution with a compact version: 10x10x10 cm^3

High resolution compact vertical inertial sensor for atomic quantum gravimeter hybridization

peer reviewedInertial sensors are devices capable of measuring the absolute motion of the support they are fixed onto. The advance of very high-end scientific instruments such as gravitational wave detectors, always pursuing ever greater sensitivities and performance, puts a large demand on ultra-high-resolution inertial sensors, capable of measuring very low-frequency and small-amplitude motions. Our group has a long experience in the design of low-frequency inertial sensors intended to be used in active isolation systems. The latest horizontal and vertical interferometric inertial sensors that have been designed have performance that competes with industry standards. They were shown to reach a resolution of 2×10−13 m/Hz−−−√ at 1 Hz and are capable of measuring ground motion from 0.1 to 100 Hz. However, they are large and heavy, measuring approximately 20 × 20 × 30 cm3 each, which makes their integration into practical systems tedious. In addition, experimental characterization of these sensors revealed three main limitations to their resolution. They are: (i) thermal noise, (ii) electronic readout noise and (iii) broadband white noise caused by mechanical and optical nonlinearities. The present paper presents a revised version of the vertical sensor, where the size of the device has been made to fit a 10 × 10 × 10 cm3 while simultaneously addressing the aforementioned sources of noise. The mechanics of the compact sensor is made of a leaf-spring supported pendulum, connected to the frame using a flexure hinge. A moving mirror is connected to the mass and guided using a so-called "4-bar" mechanism, providing the moving mirror with linear translation motion (iii). The joints of the mechanics are made of fused silica, allowing to reach a low natural frequency of ≈1 Hz with a compact design, in addition to significantly reducing structural thermal noise (i) due to the low dissipation rate of fused-silica. On the other hand, the readout system used in this sensor is a homemade design of a Michelson interferometer. The optical scheme features numerous polarizing elements that allow the propagation of two laser beams in phase quadrature, and custom hardware is developed for minimizing electronic noise (ii). Lastly, the vertical sensor is operating in closed-loop, using a homemade actuator design, so as to reduce non-linear effects related to either the mechanics or the optical readout (iii). The sensor frequency response is characterized using a test bench that has been specifically developed for testing low-frequency sensor response. The noise floor is extracted using a Huddle Test

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Active seismic isolation using interferometric inertial sensors

The transmission of ground motion to sensitive equipment can affect their performance or their duty cycle. To overcome this limitation, passive and active isolation solutions have been developed. When it is supported by springs, a system is isolated passively in a frequency range above its resonance frequency. On the other hand, active isolation consists in sensing the motion of the payload to isolate and canceling this motion by injecting a force that opposes this motion. To increase the performance, passive and active solutions can be combined.The goal of this research is to isolate a six degree-of-freedom (d.o.f.) platform from ground motion in the low-frequency range, i.e. between 10 mHz and 10 Hz. At low frequency, the performance of the active isolation stage is limited by the sensor resolution. To overcomethis limitation, one can use inertial sensors whose inertial mass’ motion is measured by an interferometric readout.In this thesis, the characterization of a horizontal inertial sensor (HINS) and a vertical inertial sensor (VINS) developed is presented. The Michelson interferometer used to sense the inertial mass is studied with a numerical model; the current resolution is limited by the optics too sensitive to their mounting’s motion and by the signal drift at low frequency. The mechanical system is made of a pendulum. By deriving the equations of motion of the system, the sensor’s dynamics can be studied; Inertial sensors sense a coupled signal between rotation and translation. Because of this coupling, the dynamics include a pair of complex or real zeroes at low frequency, below the resonance frequency of the inertial system.To subtract the spurious tilt motion from the sensor’s signal, a liquid sensor is under development. The inclination is measured by comparison to the horizontal surface of liquid Mercury sealed inside a container. It has been characterized experimentally to study its sensitivity, 306.75 V/rad, and its resolution on the order of 5 10−5 rad/pHz. The current version is too noisy principally because the viscosity of the reflective liquid is not large enough and hence, the reference surface moves too much with ground motion.The effect of the tilt-translation coupling on inertial control is studied on a 2 d.o.f. model; when applying inertial control, the motion of the payload becomes coupled with the ground inclination at low frequency due to the sensor’s dynamics. Solutions to cope with coupling have been investigated: projecting the system in a decoupled frame (centralized projection and singular value decomposition (SVD)), closing a first loop to control the rotation of the payload or sensing the inclination and subtracting it from the inertial sensor signal. The last two methods gave the most promising results.Finally, a 6 d.o.f. platform has been assembled. It consists of a hexagonal table with three pairs of vertical and horizontal inertial sensors. The table lays on three isolators containing voice coil actuators. The effect of inertial control on a multiple input/multiple output (MIMO) system is studied experimentally and the solutions tested numerically on the 2 d.o.f. model are extended to the full isolation stage. The platform could reduce of one order of magnitude the amplitude of the payload’s motion between 0.1 Hz and 10 Hz in the vertical direction and between 0.1 Hz and 1 Hz in the horizontal direction.Doctorat en Sciences de l'ingénieur et technologieinfo:eu-repo/semantics/nonPublishe

Development of a high resolution optical inertial sensor

info:eu-repo/semantics/nonPublishe

Towards Broadband Seismic Isolation Systems: a one d.o.f. isolation stage study

info:eu-repo/semantics/nonPublishe