Abstract: Structural deformations are one of the most significant factor that affects machine tool (MT) positioning accuracy. These induced errors are complex to be represented by a model, nevertheless they need to be evaluated and predicted in order to increase the machining performance. This paper presents a novel approach to calibrate a machine tool in real-time, analyzing the thermo-mechanical errors through FibreBraggGrating (FBG) sensors embedded in the MT frame. The proposed configuration consists of an adaptronic structure of passive materials, Carbon Fibre Reinforced Polymers (CFRP), equipped by FBG sensors that are able to measure in real-time the deformed conditions of the frame. By using a proper thermo-mechanical kinematic model, the displacement of the end effector may be predicted and corrected when it is subjected to external undesired factors. By starting from a set of FE simulations to develop a model able to describe the MT structure stresses, a prototype has been fabricated and tested. The scope was to compare the numerical model with the experimental tests using FBG sensors. The experimental campaign has been performed varying the structure temperature over time and measuring the tool tip point (TTP) positions. The obtained results showed a substantial matching between the real and the predicted position of TTP confirming the effectiveness of the proposed calibration system.
A fibreBragggrating (FBG) is defined as ‘a periodic or aperiodic perturbation of the effective refractive index in the core of an optical fibre’ (Paschotta 2013). These perturbations are formed in the core of the fibre by the means of exposure to intense short wavelength (<300nm) ultraviolet (UV) radiation along the length of the grating, disrupted by an interference pattern (Hill & Meltz 1997). Short wavelength UV radiation produces enough energy to break the highly stable silicon-oxygen bonds within the core material (Doyle 2003). This damages the structure of the fibre and causes a slight increase to its refractive index. These inscriptions in the fibre core form the grating. The distance between these inscriptions is called the index variation. When light travels down the core, the wavelengths corresponding to the index variation are reflected. This is best illustrated by Figure 2.9.
Different approaches have been worked out for all- optical format conversion. One part of this conversion is related to nonlinear signal processing: semiconductor optical amplifier (SOA)/distributed feedback laser (DFB- LD) , SOA-loop-mirror , SOA/fibreBragggrating (FBG) , nonlinear optical loop mirror (NOLM) and four-wave mixing (FWM) . Other part is related to linear optical signal processing: specially designed silicon mirroring resonators (MRR) have been used for modula- tion format conversion [9,10]. The main idea of this ap- proach is use of optimized MRR with appropriate transfer function for shaping of input optical spectrum. Different approach could be based on uniform FBG . In this paper cascadability of uniform fibreBragggrating for 40 Gbit/s RZ-OOK to NRZ-OOK conversion has been shown using OptSim simulation program.
machines. To address this ever-growing demand for new and more reliable designs, electrical machines are increasingly required to be monitored in real-time with the data obtained being used for both model validation and prototype diagnostics. The latter helps to identify potential modes of failure and thus ensures the drive’s reliability, as required by owners of the equipment or the end users. If a conventional approach were to be adopted to achieve such multipoint, multi-parameter measurements, it would involve a drastic increase of component count, thus reducing the overall reliability of the system in question. To do this effectively requires the use of sensors, indeed sensor systems, well suited to the demanding environment of the electrical machines in which they are to be placed. Conventional sensors are problematic in such environments, due to the limitations of space and the need to feed cables out from a rotating machine, as well as difficulties that may occur due to electromagnetic interference and short circuits. Further to this, due to the relatively large size of insulated conventional sensors, the resulting sensor system created from the use of a number of such sensors could potentially occupy a spatial envelope larger than the drive itself. New and better tailored solutions are needed and this work thus aims to address the above challenges by replacing such conventional sensors with an integrated optical fibre-based, quasi-distributed, sensing system in electrical machines for real-time monitoring. Such an approach takes full advantage of the fibre sensors’ reduced spatial envelope and immunity to electromagnetic interference, critically important for this particular application. One of the first efforts made in the direction of introducing an optical fibre sensor development for motor and drive applications was to exploit Rayleigh backscattering in conjunction with a fibre having its outer cladding modified at intervals to create a quasi-distributed temperature measurement system using an optical time domain reflectometry (OTDR) approach . Since then different optical sensing techniques have been applied to monitoring a number of key motor parameters: end-winding vibratory behaviour , stator housing vibration , thermal effects [4- 7] and torque [8,9], for instance. In a previous report, the authors introduced a successful stator wave and rotor speed tracking system based on FibreBraggGrating-based (FBG) sensors .
Schmidt-Hattenberger, Naumann & Borm (2003), specifies there is a growing need in geotechnical engineering, to develop newer sensing technologies that will withstand the ‘hostile’ environments they have to operate in. Optic fibre sensing technology can provide a solution to these problems. FibreBraggGrating (FBG) sensors are resistance to both corrosion and electromagnetic radiation, while being able to provide results that are both accurate and reliable.
FibreBraggGrating (FBG)-based methods have previously been reported for AE detection . Compared to conventional PZT ultrasonic sensors, the FBG sensors are of smaller size, showing potential for simultaneous, multi-node measurement using a single connection (multiplexing them on a single fibre). Their immunity to electromagnetic (EM) interference and resistance to the harsh operational conditions that damages many conventional sensors is an advantage, and being optical and not electrically-based, they are ideally suited to operation underwater (including highly conducting sea water).
This paper presents the results obtained from fibreBragggrating (FBG) sensors integrated into a railway current- collecting pantograph for accurate measurement of contact force and contact location when it is subjected to various temperature conditions. The temperature change of the pantograph is simulated, at the industrial laboratory of Brecknell Willis in the UK, by changing the DC current applied to pantograph from 0 to 1500 A. This test is primarily designed to verify the effectiveness of the temperature compensation mechanism built in the FBG sensor design. For this verification, 3 thermocouples co-located with the FBG sensor packages are used to measure the temperature change seen from 25 ºC to 55 ºC. The tests were repeated several times and the sensor system has shown its temperature- independence, confirming that the intrinsic cross-sensitivity of FBGs to temperature variation for strain measurement has been fully compensated through the use of this innovative sensor design and data processing.
characteristics of such Lamb waves have been analyzed extensively in the literature [6-8]. Thus they are widely used in non-destructive Structural Health Monitoring (SHM) of plate structures as they are scattered and the relf4ected energy captured allows an estimation of the type and size of the damage encountered . Here PZT based transducers are widely used due to low cost, reliability and robustness – but they show key limitations when electromagnetic Interference (EMI) is present and remote monitoring is required [10, 11, 12]. Thus they are not sufficiently versatile for measurements under more adverse circumstances, for example in remote monitoring applications where long cable lengths between the transducer and the receiver are used and EMI effects and ‘signal fade’ are seen over these over long distances. . Fibre optic acoustic emission sensors offer an alternative – the majority of such sensors (hydrophones) are based on fibre optic interferometry, such as using Mach-Zhender , Michelson  or Fabry- Parot techniques [16, 17]. FibreBraggGrating (FBG)-based methods are an excellent alternative for AE sensing applications  and recently, distributed feedback (DFB) fibre lasers have been used, as reported elsewhere .
Optical fibre offers a number of distinguishing and excellent advantages over conventional sensors. FibreBragggrating (FBG) sensor is one of the most important and useful optical fibre sensors. The concept of FBG was discovered three decades ago by Hill and his co-workers (Hill, 1978). However, most o f the recognized pioneering work about FBG and its applications were only published a decade later after it’s discovery by a group o f researchers at United Technology Research Centre (Meltz et al., 1989).
The invention of fibre optic wire or “Optical Waveguide Fibres” by Corning Glass researchers in 1960 has had a tremendous impact on global communication as it revolutionized the telecommunications industry. Fibre optics is a major industry and today it plays a key role in modern day life such as long-distance telephone service, internet and use in health care services. The invention of the fibre-optic gyroscope in 1976 led fibre optic sensor explorations for the next ten years (McLandrich & Rast, 1978). Commercialization of optical fibres provides more components for other uses which have led to the opportunity for their use as sensors in many field applications. Since then various ideas have been suggested and techniques have been developed for many measurands and applications. According to statistics presented at OFS-15 (Optical Fibre Sensors Conference held in Portland, Oregon, USA 2002), strain and temperature are the most highly studied measurands, with fibreBragggrating (FBG) sensors becoming increasingly popular. According to statistics of OFS-22, FBG sensors had the highest number of patent issued among optical fibre sensors (Kersey, 2012). Figure 1.1 illustrates FBG sensor popularity, as derived from an industry survey (Patent Insight Pro, 2011).
Presented in the paper is a method for identifying defects within the brazed joints of metal packaged fibreBragggrating sensors for temperature and strain measurement. Twenty four sensors were fabricated via an induction brazing process. This was the first time a relatively large number of sensors had been fabricated allowing for a statistical sample to be investigated for defects. A defect is most likely to occur at the joint between the capillary and fibre, as a proper bond here is critical for the consistent performance of these sensors. Through optimising the brazing process, a high percentage (92%) of consistently performing sensors were fabricated. Any defective sensors can be identified by the method proposed in this paper. It utilises a preliminary defect screening by subjecting the sensors to an elevated constant temperature for 8 hours. Following this, the repeated temperature cycles of the temperature calibration procedure can determine sensors with inconsistent temperature coefficients from cycle to cycle. This is only possible if a batch of sensors is calibrated together in order to distinguish between experimental variation in the temperature coefficient and inconsistency due to defective brazing joints. By applying the temperature coefficient variation analysis, two temperature sensors were identified as performing inconsistently. This was further confirmed when they were placed at 35°C for eight
Internationally, a significant number of nuclear power plants have now been operating for a period in excess of twenty years and some for more than thirty years. As a result, interest in the management of the ageing of civil engineering structures has received a higher priority than was hitherto the case in order to confirm or extend the operational life of nuclear power plants. The ability to monitor the pre-stress in pre-stressing tendons using Smart Fibre ‘Bragggrating’ technology in a real time environment, would augment the available information that civil engineers require to confirm the continued fitness for purpose of critical structures. It would also allow continuous monitoring of the strains experienced at key points of an instrumented pre-stressing tendon. However, prior to any full-scale installation of an instrumented pre-stressing tendon, it is necessary to conduct a feasibility study and identify a suite of tests to confirm that the fragile fibre optic cable installed along a length of pre-stressing tendon, would survive the installation process and the environmental conditions in service.
Citation: Fabian, M., Jia, Y., Shi, S., McCague, C., Bai, Y., Sun, T. & Grattan, K. T. V. (2016). Optimization of the accelerated curing process of concrete using a fibreBragggrating-based control system and microwave technology. Proceedings of SPIE, 9916, 99160P. doi: 10.1117/12.2236856
Citation: Kerrouche, A., Boyle, W. J. O., Gebremichael, Y., Sun, T., Grattan, K. T. V., Taljsten, B. and Bennitz, A. (2008). Field tests of fibreBragggrating sensors incorporated into CFRP for railway bridge strengthening condition monitoring. Sensors and Actuators A: Physical, 148(1), pp. 68-74. doi: 10.1016/j.sna.2008.07.014
This kind of FBG sensor bonding was frequently mentioned in their paper as ’cantilever type FBG.’ Although the signals obtained by the cantilever type FBG show a low SNR, yet it was able to acquire higher frequency contents than the one that was fully bonded. Another interesting claim which Seo et al. (2009) had in their conclusion was, the longer the FBG grating, the better its sensitivity. Meanwhile, Wild & Hinckley (2007) introduced FBG sensors for AE detection as an intention, to be utilized in a robotic non-destructive evaluation in SHM. The validation of the FBG-AE system was done by dropping the bolts and nuts on the specimen and also the pencil lead breaking test. The results were promising as the detection of the signals were clear and the SNR was high. However, the work did not clearly indicated how accurate the frequency contents detection was by the FBG-AE system, since they were focussing on communication by acoustics transmission.
The FBG-based sensors used as the basis of each sensor element were as follows. Each individual sensor was created using a Type I FBG (of 6 mm length), fabricated using the conventional zero-order nulled diffraction phase mask technique . To do so, 248 nm laser pulses (12 mJ at 300 Hz) from an ATLEX-300-SI Excimer laser were focussed via a 20 mm focal length plano-cylindrical lens through a series of commercially available phase masks (Oe-land, QPS) into the core of a photosensitive fibre (Fibercore PS1250). The sensors were configured into a number of individual channels for convenience and to minimize the number of external optical fibre leads coming from the blade (as can be seen from Figure 2). Thus in each channel seven different FBG wavelengths, set to be between 1525 nm and 1565 nm were chosen, to ensure that there was no spectral overlap from one sensor to the next, even when each sensor responds over its maximum range of vibration-induced strain to avoid any ambiguity in the measurement. These FBG-based channels then formed the Table 2. Characteristics of propeller in this experiment
A. Kerrouche is a PhD student at City University Lon- don within the School of Engineering and Mathematical Sciences. He was awarded the degrees of Master of phi- losophy in Electronics at Pierre & Marie Curie Paris VI University (France) and a Master of Electronics, Electro- technique and Automatics at Marne-La-Vallee University, France. His research interest is strain measurement mon- itoring system based on FBG (ﬁbre Bragggrating) sensors. He completed a training course at ESME-Sudria (private school of engineer) in collaboration with Tenon hospi- tal in Paris to develop new software for segmentation of optical images. He has ﬁnished a work placement at Oxford Brookes University in the Medical Instrumentation Laboratory to develop a computer based system to record, store and analyze respiratory signals during Anesthesia.
Nonlinear effects in Fiber BraggGrating (FBG) are currently under intense investigation by many leading groups of researchers. Bragg gratings in optical fibers are excellent devices for studying nonlinear phenomena particularly based on the Kerr nonlinearity . The stationary properties of one-dimensional Bragg gratings were first analyzed by Winful et.al . Several group of researchers has done many researches and reported the existence of soliton in Fiber Bragg gratings [1-5]. Chen and Mills coined the term gap soliton in their numerical work covering the nonlinear optical super lattices . Mills and Trullinger obtained an analytical solution for stationary gap solitary waves . Sipe and Winful , Christoudolides and Joseph , Aceves and Wabnitz , de Sterke and Sipe  and recently K. Senthilnathan et. al has derive the formation of bright and gap soliton solution for nonlinear coupled mode equation, which governs the pulse propagation in FBG .
Abstract—This paper reports results obtained using FibreBraggGrating (FBG)-based sensors to investigate the displacement mode shapes of a cantilevered steel propeller blade, using FBG arrays for vibration monitoring for the first time. The experimental data obtained are cross-compared with those from a finite element analysis of the same blade, undertaken using proprietary software. In the experimental configuration used, a network of gratings, forming a series of sensor arrays, was mounted on the blade under study to monitor its bending modes, whilst a further set was mounted perpendicular to this array to monitor torsional modes. To obtain the shape of the strain modes generated in the blade at specific frequencies, the dynamic response of the FBG arrays, as a function of time, was captured and then processed using Fourier Transform algorithms to show the natural frequencies of the blade. As a result, the displacement modes shapes for the bending, torsional and coupled modes of the first nine natural frequencies of the plate were obtained. The experimental data show very good agreement with theoretical analysis. This work demonstrates the potential of using the lightweight, minimally invasive sensing technique described for the analysis of propeller blades and thus illustrating an effective method to overcome the deleterious effects of propellers seen in some commercial propeller designs.
Australian Nanotechnology Network • Bestech Australia Pty. Ltd. (Australia) • Boeing Research and Technology Australia • Centre of Excellence in Engineered Fibre Composites, University of Southern Queensland (Australia) • Department of Industry, Innovation, Climate Change, Science, Research and Tertiary Education, Australian Government • Engineers Australia • Lastek Pty. Ltd. (Australia) • Materials Australia • Queensland Government • University of Southern Queensland (Australia)