Tokio Kasai

Measurements of strain distributions with a long gauge FBG sensor using optical frequency domain reflectometry

We developed a strain measurement system based on optical frequency domain reflectometry and applied it to measuring strain distributions of a specimen in tensile tests. In the sensing region on the specimen, five FBG sensors of 6 mm gauge length or one of 100 mm gauge length was bonded and strain measurements were implemented with both configurations. By using the former configuration, we could successfully carry out accurate quasi-distributed strain measurements. The later allowed fully-distributed measurements for 100 mm at the high spatial resolution. Such performance of high resolution sensing can be applied to health monitoring of a structure which may have stress concentration. In this paper, we describe the principle of the measurement system and the results in the tensile tests.

Vibration monitoring of a helicopter blade model using the optical fiber distributed strain sensing technique.

We demonstrate a dynamic distributed monitoring technique using a long-length fiber Bragg grating (FBG) interrogated by optical frequency domain reflectometry (OFDR) that measures strain at a speed of 150 Hz, spatial resolution of 1 mm, and measurement range of 20 m. A 5 m FBG is bonded to a 5.5 m helicopter blade model, and vibration is applied by the step relaxation method. The time domain responses of the strain distributions are measured, and the blade deflections are calculated based on the strain distributions. Frequency response functions are obtained using the time domain responses of the calculated deflection induced by the preload release, and the modal parameters are retrieved. Experimental results demonstrated the dynamic monitoring performances and the applicability to the modal analysis of the OFDR-FBG technique.

Signal processing method based on group delay calculation for distributed Bragg wavelength shift in optical frequency domain reflectometry

A signal processing method based on group delay calculations is introduced for distributed measurements of long-length fiber Bragg gratings (FBGs) based on optical frequency domain reflectometry (OFDR). Bragg wavelength shifts in interfered signals of OFDR are regarded as group delay. By calculating group delay, the distribution of Bragg wavelength shifts is obtained with high computational efficiency. We introduce weighted averaging process for noise reduction. This method required only 3.5% of signal processing time which was necessary for conventional equivalent signal processing based on short-time Fourier transform. The method also showed high sensitivity to experimental signals where non-uniform strain distributions existed in a long-length FBG.

Distributed strain measurement based on long-gauge FBG and delayed transmission/reflection ratiometric reflectometry for dynamic structural deformation monitoring

In this paper, we propose a delayed transmission/reflection ratiometric reflectometry (DTR(3)) scheme using a long-gauge fiber Bragg grating (FBG), which can be used for dynamic structural deformation monitoring of structures of between a few to tens of meters in length, such as airplane wings and helicopter blades. FBG sensors used for multipoint sensing generally employ wavelength division multiplexing techniques utilizing several Bragg central wavelengths; by contrast, the DTR(3) interrogator uses a continuous pulse array based on a pseudorandom number code and a long-gauge FBG utilizing a single Bragg wavelength and composed of simple hardware devices. The DTR(3) scheme can detect distributed strain at a 50 cm spatial resolution using a long-gauge FBG with a 100 Hz sampling rate. We evaluated the strain sensing characteristics of the long-gauge FBG when attached to a 2.5 m aluminum bar and a 5.5 m helicopter blade model, determining these structure natural frequencies in free vibration tests and their distributed strain characteristics in static tests.

Orbital Experiments of Linearly Interpolated Gain Scheduling Attitude Controller Using ETS-VIII Spacecraft

Abstract This paper describes orbital attitude control experiments carried out on the ETS (Engineering Test Satellite)-VIII in June 2009. These experiments aim to develop a technical basis for the orbital control of a class of future large flexible spacecraft. Several novel robust control laws were tested, including a μ-synthesis based control law, a DVDFB (Direct Velocity and Displacement FeedBack) control law and a linearly interpolated gain scheduling law. Among them, this paper focuses on the gain scheduling law. Experimental results of this control law are presented to show its high control performance and lower computational burden compared with other control laws.

Long-gauge FBGs interrogated by DTR3 for dynamic distributed strain measurement of helicopter blade model

In this paper, we describe characteristics of distributed strain sensing based on a Delayed Transmission/Reflection Ratiometric Reflectometry (DTR3) scheme with a long-gauge Fiber Bragg Grating (FBG), which is attractive to dynamic structural deformation monitoring such as a helicopter blade and an airplane wing. The DTR3 interrogator using the longgauge FBG has capability of detecting distributed strain with 50 cm spatial resolution in 100 Hz sampling rate. We evaluated distributed strain sensing characteristics of the long-gauge FBG attached on a 5.5 m helicopter blade model in static tests and free vibration dynamic tests.

Distributed dynamic strain measurement using long-gauge FBG and DTR3 interrogator based on delayed transmission/reflection ratiometric reflectometry

In this paper, we reveal characteristics of static and dynamic distributed strain measurement using a long-gauge fiber Bragg grating (FBG) and a Delayed Transmission/Reflection Ratiometric Reflectometry (DTR3) scheme. The DTR3 scheme has capability of detecting distributed strain using the long-gauge FBG with 50-cm spatial resolution. Additionally, dynamic strain measurement can be achieved using this technique in 100-Hz sampling rate. We evaluated strain sensing characteristics of the long-gauge FBG attached on 2.5-m aluminum bar by a four-point bending equipment. Experimental results showed that the DTR3 using the long-gauge FBG could detect distributed strain in static tests and resonance frequency of structure in free vibration tests. As a result, it is suggested that the DTR3 scheme using the longgauge FBG is attractive to structural health monitoring (SHM) as dynamic deformation detection of a few and tensmeters structure such as the airplane wing and the helicopter blade.

A study on new Ku-band digital transponder

This paper intends to point out some problem of telemetry for wild birds and future technical expectations to prevent Avian Influenza. For medium to large migratory birds, the data collection system aboard the NOAA meteorological satellites (the ARGOS system) has been able to map their migratory routes. However, recommended C/No for Doppler shift ill be 54dBHz, while calculated required C/No for 400 bps data uplink is 36dBHz. The gap between navigation function and data communication will be almost 18 dB. The bird has to pay this overload. We would like to propose the next generation digital transponder that is an advanced DCS with multibeam on Ku-band to perform the onboard processing (DCS and navigation system with Doppler shift). In case of 42dBi antenna of the spacecraft, the ground terminal with 13dBm RF-output and 2.25dBi antenna can transmit upto 50 bps with BPSK. This terminal attached with a leg of a bird will be suitable for a dove or a gull in size, if we could put new digital transponder on Ku-band.

On-Orbit Experiment Results of Robust Symmetric Attitude Controller for ETS-VIII Spacecraft

Abstract This paper reports results of an on-orbit experiment using Engineering Test Satellite VIII (ETS-VIII) spacecraft. The ETS-VIII was launched into geostationary orbit by the Japan Aerospace Exploration Agency in December 18 2006. The main mission is to support next-generation mobile digital communications, and for this purpose it is equipped with two large deployable antenna reflectors and a pair of large solar paddles that rotate around the pitch axis. For the spacecraft, the authors have proposed several control methods by applying advanced control theories for the linear parameter varying multi-input multi-output system. Among them, this paper describes the results using two degrees-of-freedom control system based on symmetric feedback control.

On-orbit experiment plan of robust attitude control of ETS-VIII

This paper reports a preliminary study result on on-orbit experiments of robust attitude control of Engineering Test Satellite VIII (ETS-VIII). The key issue is to design a reduced-order Multi-Input Multi-Output (MIMO) robust controller for linear parameter varying (LPV) spacecraft system. For that purpose, we have prepared three control laws after trade-off studies. Herein, we describe the purpose, some features of the spacecraft model, the experiment system, and the experiment plan. Then outlines of control laws are shown, followed by numerical simulation results.