Research On Practical Techniques Of White-light Interferometer Signal Demodulation And Processing

As a high-precision absolute measurement method, the white-light interferometry which is nearly 30 years since was first proposed is widely used for displacement, temperature, strain, pressure and other physical quantities. With the development of the theory and technology, the basic theory and testing methods of white-light interferometry have been relatively mature. But problems about its signal demodulation accuracy, real-time and stability are a key constraint technology that restricts the technology is mature and end to the application bottleneck. However, a number of practical problems about the signal demodulation accuracy, real-time and stability of this technology restrict the application of mature technology. Through the study of white-light interferometry of fiber, this paper makes a detailed discussion and analysis on high-precision optical path scan, the design and implementation of small-scale demodulation system, systematic methods of temperature compensation. Finally, white-light interferometer strain measurement system has been put into practice, which laid the foundation on the application of white-light interferometry.Firstly, the optical path scan structure is the core of the demodulation system, which determines the signal measurement accuracy, measurement range, the number of multiplexed sensors, measurement stability, suitable environment, outside dimensions and other technical indicators of this system. In order to achieve high-precision optical path scan, in this paper, we select the electric displacement rail station which is formed by a precision guide as the scanning structure, uses high-precision grating position to achieve real-time location platform displacement feedback. At last, sub-micron scanning resolution response about optical path has been achieved.Secondly, for hardware requirements of signal demodulation of white-light interferometer, we design a white-light interferometer measurement system hardware development platform. This paper discusses the various parts of the system function modules of the design and implementation methods in detail, successful achieves the integration of the whole system. The hardware platform is not only realize the White-light Interferometer signal acquisition and demodulation and processing, but also integrates the Ethernet control circuit of the strain gauge network control and communication. Finally, having made analysis and research on the influence of the temperature demodulation system, we use passive temperature compensation scheme. The method is to make temperature shielding and isolation for testing optical scan and the optical path scanning structure, to use multi-channel temperature sensor to make temperature compensation on light road, matching optical fiber, chassis, and other structures to eliminate the impact of temperature on the demodulation system.To sum up, with high-precision optical scanning structure and the integrated signal acquisition and processing hardware platform, the system achieves the resolution of 0.2μm, scan range of 0～100mm, test speed 5 Hz signal demodulation performance. After temperature compensation, the temperature effect on the system is less than 40μm.