Modern telecommunication satellites can benefit from the features of fiber optic sensing wrt to mass savings, improved performance and lower costs. Within the course of a technology study, launched by the European Space Agency, a fiber optic sensing system has been designed and is to be tested on representative mockups of satellite sectors and environment.
Modern telecommunication satellites can benefit from the features of fiber optic sensing wrt to mass savings, improved performance and lower costs. Within the course of a technology study, launched by the European Space Agency, a fiber optic sensing system has been designed and is to be tested on representative mockups of satellite sectors and environment.
Availability of reliable flight sensor data and knowledge of the structural behaviour are essential for safe operation of the Ariane launcher. The Ariane launcher is currently monitored by hundreds of electric sensors during test and qualification. Fibre optic sensors are regarded as a potential technique to overcome limitations of recent monitoring systems for the Ariane launcher [1]. These limitations include cumbersome application of sensors and harness as well as a very limited degree of distributed sensing capability. But, in order to exploit the various advantages of fibre optic sensors (high degree of multiplexing, distributed sensing capability, lower mass impact, etc.) dedicated measurement systems have to be developed and investigated. State-of-the-art fibre optic measurement systems often use free beam setups making them bulky and sensitive to vibration impact. Therefore a new measurement system is developed as part of the ESAstudy [2].
Force-torque sensors are key elements in modern force feedback and robotic control applications. For special applications
resistance against electromagnetic interference, high amount of load cycles or chemical resistance are important. For these
applications, fiber-Bragg-grating based force torque sensors have been seen as possible solutions. Yet the implementation
of a force-torque-sensor with six degrees of freedom and well conditioned sensitivities is still lacking demonstration. In
this work, we demonstrate the design of a miniaturized fiber-Bragg-grating based force-torque sensor with six degrees
of freedom using a numerical nonlinear programming technique. We implement the optimized structure and show its
feasibility and sensitivity.
Multi-axial force and torque sensing is of importance for robot control and many force-feedback applications.
Minimal invasive robotic surgery (MIRS) is a possible field of application of force and torque sensors with up
to six degrees of freedom. Although these sensors are not yet employed in current commercial MIRS systems,
extensive work has been carried out on the development of these sensors. Some of their issues are related to
their electric working principle: they are limited in performance by thermal noise, need electric power inside
the patient and are not usable under influence of strong magnet fields (e. g. in MRI machines). One possible
alternative is seen in fiber optic force torque sensors, since the signal demodulation may be located in some
distance to the actual sensor and they also do not have to include any magnetic material.
This article presents a fiber optic force and torque sensor with six degrees of freedom. The general setup
resembles a Stewart Platform, whereas its connecting beams are formed by the fiber itself, and the element
creating stiffness may be of arbitrary form. Only a single fiber is needed to extract all six parameters since they
are measured on six multiplexed fiber Bragg grating sensors. We demonstrate how the sensor is realized and
show results of torque measurements with variable load.
When measuring strain with a FBG sensor fixed to a structure by an adhesive, one will notice, that only axial strain is
monitored. This is due to the low Young's modulus of both standard coating materials and adhesives. Metal coated fibers
with high Young's modulus have become available recently, which may be surface bonded by soldering. Motivated by this,
finite element simulations with different coating materials and adhesives were carried out. Increasing the Young's modulus
of coating and adhesive in the simulation shows a difference in transverse strain of around 20 % for the two cross sectional
fiber axes. On this basis a process to substitute standard fiber coatings with a copper coating is described. Satisfying results
were obtained using a copper electroplating process. Especially its simple experimental access is noticeable. A sensor
modified in the electroplating process is soldered to a cantilever beam and a quasi-static strain measurement is performed.
Soldering the modified fiber sensors changes the spectral response of the FBG. Towards shorter wavelength which is a
result of the strains induced by cooling.
Monitoring machines during operation is an important issue in measurement engineering. The usual approach to
monitoring specific machine components is using strain gauges. Strain gauges, however, may sometimes not be
used if conditions are harsh or installation space is limited. Fiber optic sensors seem to be an alternative here,
but dynamic health monitoring has been dificult so far. The focus of this field study is to measure vibration
characteristics of machine parts during operation using fiber optic sensors with the objective of early damage
detection. If that was possible, downtime and maintenance costs could be minimized.
Therefore a field test for dynamic fiber optic strain measurement on a roller bearing was carried out. The
test setup consisted of the bearing built into a gear test stand and equipped with an array of fiber Bragg
grating sensors. Fifteen fiber sensors were interrogated with a sample rate of 1 kHz and the vibration pattern
was extracted. The radial load distribution was measured with high spatial resolution and a high degree of
compliance with simulation data was found. The findings suggest that fiber optic health monitoring for machine
components is feasible and reasonable. Especially with the help of distributed sensing on various components
extensive health monitoring on complex technical systems is possible.
Numerous fiber optic measurement systems making use of sensors such as Fabry-Perot or fiber Bragg gratings
incorporate superluminescent or other edge emitting light sources. These sources often have a high degree of
polarization. The combination with birefringence in fibers results in measurement errors. A possibility to overcome
these errors is to depolarize the light source. Low coherence lengths make passive means of depolarization
suitable. A common solution is the fiber Lyot depolarizer, which works especially well with very low coherence
lengths. For coherence lengths corresponding to for example the reflection spectrum of narrow band fiber Bragg
grating, long fiber lengths are required. A second way is offered by fiber ring depolarizers, where the coherence
length is of minor concern.
To estimate the performance of the fiber ring depolarizer in a practical measurement system, we employ both
concepts. The measurement system is a CCD based spectrometric interrogation unit, with a superluminescent
diode as light source. The source itself is well polarized. We observe the effect of birefringence in a transversally
loaded fiber Bragg grating array consisting of eight sensors, when the polarization on the path to the sensor is
rotated. The improvement in polarization dependency when using the two depolarization methods is compared.
A retrieval processor based on rapid forward modeling algorithms and an optimal estimation approach has been developed at Forschungszentrum Juelich, Germany. It has been used to derive global distributions of the chlorofluorocarbons CFC-11 and CFC-12 from Envisat MIPAS measurements. We give a detailed description of the retrieval system, show error analyses, and discuss briefly the seasonal behavior of CFC-11 and CFC-12 for January to March and July to September 2003.
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