In recent years, some important achievements have been made in the field of optical fiber intelligent structure research. For example, distributed fiber grating intelligent structure, optical fiber intelligent interlayer, hollow fiber intelligent structure, etc. The wavelength of the front-end light source of the traditional optical fiber intelligent structure is generally fixed, but in some experimental systems, the optical fiber intelligent structure requires different wavelengths of light to be transmitted under different circumstances.] The action of each light source needs to be analyzed and judged by the monitoring system to control the structure. Ordinary photoelectric detection can no longer meet the requirements. This paper proposes and designs a new type of intelligent structure health monitoring system, which can monitor the various states of the structure in real time, such as load, damage, damage, etc., and perform data analysis and damage location to address various situations of various intelligent structures in a timely manner. Perform different treatments.
Intelligent structure is a brand-new cross-discipline that has emerged internationally in recent years. Generally, the application of optical fiber technology in advanced composite materials, together with corresponding monitoring and control systems, constitutes an optical fiber intelligent structure. The US military first proposed the concept of optical fiber intelligent structure in the mid-1980s. The research object focused on aviation and space vehicles, and then penetrated into many fields such as civil engineering, ships, automobiles, and medicine, and soon became a research hotspot. At present, no matter in the laboratory or in practical applications, there have been some examples of optical fiber intelligent structures.
1 Monitoring system design
1.1 System hardware
The hardware system of the monitoring system is mainly composed of a light source group, an optical system, a photoelectric sensor, a monitoring host and a Pc machine.
The light of different wavelengths emitted by the front-end light source group is coupled to the composite material specimen containing a special optical fiber network through the optical system. The influence of the external environment on the composite material is modulated by the light intensity in the optical fiber. The design of the light source group uses laser diodes of multiple wavelengths. The laser diode has the advantages of small divergence angle, concentrated power, small size, simple modulation method, good linear working area and bandwidth.
The optical signal carrying the health status information of the optical fiber intelligent structure is converted into an electrical signal through the photoelectric sensor group, and then passed into the monitoring host, and then after the signal is filtered, amplified, and analog / digital conversion, the microprocessor performs data collection and processing. Obtain the relative value of the light intensity of each group of light signals and store it; at the same time, the monitoring host will also judge and analyze each data, send out various control signals, and perform different processing on the light source group; in addition, the monitoring host will also receive the monitoring computer The order of the data transfer with the monitoring computer, so that the computer can analyze the various states of the structure in time and create monitoring records.
1.2 Software design of monitoring system
Since the work of hardware is divided into two parts: monitoring host and monitoring computer, the software of the system is also composed of two parts: monitoring host software and monitoring computer software. The cooperative work of the software is completed through the serial port protocol.
In addition to completing signal acquisition, A / D conversion, data processing and control, the program of the monitoring host is also responsible for communicating with the PC. Therefore, two interrupt methods are used in the lower computer program to handle these two aspects of work: timer interrupt and serial port interrupt. Figure 2 is a flow chart of the monitoring host program (data collection, processing, communication part).
The program of the monitoring computer is written in a mixture of visual programming language VB6.0 and Matlab language. The most powerful aspect of VB6.0 is the rapid creation of user interfaces, and the use of the complex and perfect Windows operating system in a high-level language that is easy to learn and function. Therefore, it has become one of the preferred development tools for interface programming. In terms of data analysis and calculation processing, Matlab is Fig 2 Flow chart of monitoring host program
The internationally recognized (IEEE) optimized technology application software, its powerful scientific computing function, open and extensible environment, and multiple toolbox (Toolbox) support for different fields, make Matlab a computer in many subject areas Basic tools and preferred platforms for design and analysis, algorithm research, and application development. Therefore, the optical fiber intelligent structure computer monitoring software calls the Matlab function when writing code with VB6.0. By establishing the automatic connection of VB6.0 and Matlab AcTIveX, the computer interface and the speed of data analysis and processing can be combined as well as possible. .
2 Test and analysis
2.1 Test device
The test uses a new type of special optical fiber intelligent structure (optical fiber orthogonal grid embedding method) to determine the damage location. The schematic diagram of fiber embedding is shown in Figure 3.
Figure 3 Schematic diagram of intelligent structure fiber embedding method
Fig 3 SchemaTIc diagram of buried method ofopTIcal fiber
in specim en
2.2 Test data and analysis
In the E51 composite material board commonly used in aerospace vehicles, special optical fibers with a mesh cross (the interval between the optical fibers is 3 cm) are embedded, and the composite material board is tested for loading, unloading, damage and destruction. When there is no deformation or damage to the composite material board, the output signal curve of the 8-channel optical fiber is shown in Fig. 4 (a). The 8-channel fiber output signal curve is shown in Figure 4 (b). Comparing Figure 4 (a) and Figure 5 (b), after loading, the output of the second and seventh optical fibers is significantly smaller than the output of the optical fiber without any deformation and damage, while the other 6 channels have a small change. Therefore, referring to FIG. 3, it can be seen intuitively that the load is applied at the intersection of the second fiber and the seventh fiber. Similarly, Fig. 5 (b) shows the output signal curve of the 8-channel optical fiber when the composite material plate is subjected to a certain applied load at the intersection of the fourth optical fiber and the fifth optical fiber. The curve can be found that the output intensity of the fourth fiber and the fifth fiber is significantly reduced, which shows that the load is located at the intersection of the fourth fiber and the fifth fiber. The results of the system data analysis and the actual experiment The conditions are consistent, and the test results show that the data processing and analysis of the monitoring system are correct and can accurately and reliably determine the location of the load and damage of the intelligent structure test piece.
This paper proposes and designs a new type of health monitoring system based on optical fiber intelligent structure, analyzes the composition of the system, expounds the design and working principle of the system, and conducts a health monitoring test on the optical fiber intelligent structure specimen: commonly used in aviation In the composite material board, special sensing optical fibers are embedded in a mesh-crossed manner to form an optical fiber intelligent structure test piece, and the health monitoring and control test study of the test piece is performed, and data analysis and damage location judgment are made. The test results show that the system has coordinated software and hardware work, correct data processing and analysis, can accurately and reliably determine the location of the load and damage of the smart structure test piece, and perform corresponding light source control actions to open up the further application of special optical fiber smart structures A new way.
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