Stress-strain detection of scattering materials, such as metal surfaces, is an unavoidable issue during bolt assembly monitoring; conventional strategies of laser morphology will be limited by scattering illumination. Contact and marked measurement have been considered as acceptable solutions for long time. Herein, we implement the multimodal characterization for bolted joint surface. A reflection digital holographic microscope (RDHM) has been combined with laser triangulation measurement for achieving quantitative micro-deformation description of the connecting region between bolts and metal plate. The calibrated laser triangulation instrument is installed on the electronically controlled translation platform for two-dimensional scanning. A structure extraction algorithm is proposed to realize fast 3D reconstruction of the scanned area. The profiles obtained by triangulation are used, as ground truth, to calibrate the measured reflective holographic morphology. Affected by the strong scattering from the metal surface, it is difficult to completely characterize the metal surface by the single shot holographic measurement results. But considering that the spatial resolution requirement of strain measurement is low during bolt installation, holographic measurement will be an excellent compromise with high temporal resolution. In this case, the triangulation will complement digital holography well. Therefore, the strategy of mixing the two methods will become a preferred solution in near future.
The Sagnac loop mirror of high birefringence fiber is developing greater more than other fiber because it has the advantages of high precision, wide spectrum and simple structure in applications. In this paper, general theory of Sagnac loop mirror of high birefringence fiber is presented. Since Sagnac loop mirror of high birefringence fiber is more sensitive to its environmental temperature, an intelligent temperature measurement system based on Sagnac loop mirror of high birefringence fiber is designed. A 1550nm-laser is used as source light going through the high birefringence fiber Sagnac loop mirror. The amplitude of output beam is converted into electrical signals with Photo-Diode (PD), and the signal is collected by the MCU(Microcontroller Unit) to complete the analog-digital conversion. After calibration, the temperature is calculated, and then shown on LCD displayer. Various parts of the electronic measurement system are introduced in details, containing MCU C8051F020 with microcontroller, its internal AD-convert, calibration program and measurement program of temperature.The fiber optic temperature measurement system is compact, solid with good portability, as well as independent real-time analysis of data processing capability. It’s provides a good preliminary basis for implementation the new fiber-optic temperature measurement system. And this system has broad application prospects of a good practice. The arrangement of temperature measurement is from 30°C to 50°C with accuracy ±0.2°C in recent research experiment.
In this paper, general theory of Fourier-transform spectrometer and polarization interferometer is presented. A new
design is proposed for Fourier-transform spectrometer based on polarization interferometer with Wollaston prisms and
linear CCD. Firstly, measured light is changed into linear polarization light by polarization plate. And then the light can
be split into ordinary and extraordinary lights by going through one Wollaston prism. At last, after going through another
Wollaston prism and analyzer, interfering fringes can be formed on linear CCD behind the analyzer. The linear CCD is
driven by CPLD to output amplitude of interfering fringes and synchronous signals of frames and pixels respectively.
DSP is used to collect interference pattern signals from CCD and the digital data of interfering fringes are processed by
using 2048-point-FFT. Finally, optical spectrum of measured light can be display on LCD connected to DSP with RS232.
The spectrometer will possess the features of firmness, portability and the ability of real-time analyzing. The work will
provide a convenient and significant foundation for application of more high accuracy of Fourier-transform spectrometer.
A wave-meter based on Michelson interferometer consists of a reference and a measurement channel. The voice-coiled
motor using PID means can realize to move in stable motion. The wavelength of a measurement laser can be obtained by
counting interference fringes of reference and measurement laser. Reference laser with frequency stabilization creates a
cosine interferogram signal whose frequency is proportional to velocity of the moving motor. The interferogram of the
reference laser is converted to pulse signal, and it is subdivided into 16 times. In order to get optical spectrum, the analog
signal of measurement channel should be collected. The
Analog-to-Digital Converter (ADC) for measurement channel is
triggered by the 16-times pulse signal of reference laser. So the sampling rate is constant only depending on frequency of
reference laser and irrelative to the motor velocity. This means the sampling rate of measurement channel signals is on a
uniform time-scale. The optical spectrum of measurement channel can be processed with Fast Fourier Transform (FFT)
method by DSP and displayed on LCD.
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