The strain of structure is an important parameter in the structural health monitoring of spacecraft. FBG (Fiber Bragg Grating) sensors have the advantages of small size, light weight, anti-electromagnetic interference andeasy to network, which is suitable for the strain measurement of spacecraft structure. In order to improve the accuracy and in-orbit reliability of the strain measurement of spacecraft structure, an FBG strain sensor with metal encapsulation is designed, in which the structure of metal elastomer is optimized by finite element analysis. Meanwhile, a calibration method for the FBG strain sensor is presented, in which the clamping displacement sensitivity, strain transfer coefficient and temperature compensation coefficient are calculated. At last, the FBG strain sensor is verified by ground environmental tests, whose relative error of strain measurement is less than 1.6%, and it has been successfully applied to the in-orbit real-time structure strain measurement of the new spacecraft of China.
In order to achieve the high accuracy measurement of strain parameters of spacecraft structure with optical fiber sensors, a demodulation approach based on the composite wavelength reference of Fabry-Perot(F-P) etalon and acetylene(C2H2) gas cell is presented. In the approach, an adaptive threshold method is used to resolve the difficulty of peaks searching of F-P etalon waveform, which is caused by poor flatness of light source. Meanwhile, the strain sensitivity coefficient of optical fiber sensors is accurately obtained by a two-step method, so as to eliminate the influences of the sensor substrate and the bonding layer on the measurement. Finally, the measuring results of strain sensors are compensated with the temperature sensor to improve the measurement precision of strain parameters. The experiments results show that when the temperature variation range is 85°C(-25°C~60°C), the FBG wavelength demodulation deviation of the approach in this paper is within 3pm, while the relative measuring error of strain parameters is within 4%, which can realize the stable and high-precision measurement of the strain parameters of spacecraft structure.
One of the main tasks of the spacecraft is to carry out long-term spaceflights, science research and other activities. For different scientific applications, we need to know about the strain of cabin for evaluating the health condition of spacecraft. Here, two factors mainly work. One is the temperature, and another is refueling operations. For the latter, it is necessary to carry out the unscheduled refueling for life or experiments. The advantages of FBG sensor is suitable for application in aircraft. This paper shows the detection of static and dynamic strain under in flight environment of a certain aircraft by FBG sensors and resistance strain gauge. In the static strain detection, taking the resistance strain gauge as measurement standard, FBG sensors have a large measurement error. For example, for testing position "A", the initial error is around 28.13%. After thermal compensation of bulkhead for FBG sensors, error value reduces to 5.95%. After thermal compensation of bulkhead both for FBG sensors and resistance strain gauge, error value reduces to 0.36%. In the dynamic strain measurement, the impact test of different positions in the same height and different heights on the same position for the bulkhead is carried out. The results show that the two measurement methods are accordant in high frequency and able to identify impact signals effectively. It is very important for structure prediction and health assessment.
The unmanned aerial vehicle (UAV) in flight needs to face the complicated environment, especially to withstand harsh weather conditions, such as the temperature and pressure. Compared with conventional sensors, fiber Bragg grating (FBG) sensor has the advantages of small size, light weight, high reliability, high precision, anti-electromagnetic interference, long lift-span, moistureproof and good resistance to causticity. It’s easy to be embedded in composite structural components of UAVs. In the paper, over 1000 FBG sensors distribute regularly on a wide range of UAVs body, combining wavelength division multiplexing (WDM), time division multiplexing (TDM) and multichannel parallel architecture. WDM has the advantage of high spatial resolution. TDM has the advantage of large capacity and wide range. It is worthful to constitute a sensor network by different technologies. For the signal demodulation of FBG sensor array, WDM works by means of wavelength scanning light sources and F-P etalon. TDM adopts the technology of optical time-domain reflectometry. In order to demodulate efficiently, the most proper sensor multiplex number with some reflectivity is given by the curves fitting. Due to the regular array arrangement of FBG sensors on the UAVs, we can acquire the health state of UAVs in the form of 3D visualization. It is helpful to master the information of health status rapidly and give a real-time health evaluation.
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