Based on the relationship model between the interference fringe shape and the interference angle, a method that applies the four-quadrant detector to recognize the interference fringe shape is presented. The theoretical formula about the shape parameters of interference fringes with the phase difference of signal obtained by the detector has been deduced using the algorithm of area integration for the intensity of interference fringes, and the relationship between the phase difference and the interference angle is given. The dynamic modulation of the interference fringes is realized by using PZT to drive the reference mirror uniformly, and the recognition accuracy of signal phase difference has been improved. The phase difference from 0 to π is achieved with high precision through the ellipse fitting technology, and the identification of the phase difference in the range (-π, π) can been achieved combined with a specific sinusoid and cosine integral calculation, so the measurement of deflection angles can be realized. Comparing with the traditional recognition method that uses the shape of CCD stripe, this method expands the measurement range of the angle, and is more suitable for dynamic measurement. Comparing with high-precision autocollimator, experiment results demonstrate that the precision is 3 arcsec for the range from -300arcsec to 300arcsec, and the measurement owns high precision.
The grating projection measurement method has broad applications in surface 3D topography measuring due to its measurement speed and accuracy. Along with the grating, the phase-shift method is usually adopted for calculating the field phase. This is achieved by projection scanning in order to obtain more grating fringe images. The higher the projection fringe density is, the higher resolution can be achieved. However, because the results of the projected grey value periodically change, once the fringe period is over the single-period, the absolute-phase will become wrapped-phase. Always obtain the absolute phase by means of an unwrapping algorithm because the traditional projection unwrapping algorithm, which is based on phase continuity and changing conditions, it is not suitable for step-height measuring. Aiming to solve this problem, an unusual sub-step projection scanning method for variable widths of grating periods is proposed. According to the principle of minimum error, using the step-by-step phase estimation and connection method, we can directly determine the high-density fringe projection absolute-phase.
Online analytical instruments have been increasingly widely applied to various kinds of industrial facilities. And the Raman spectrum analyzer is one of the typical representatives, which has been widely used in chemical,environment, biological, medical, court and identification science, geology, material, oil and other fields of study. With the rapid development of Chinese economy and sharp increase in demand of fossil fuels, it’s crucial to figure out how to measure the intensity of Raman spectra in high precision and how to use the Raman spectra to acquire the high precision result of each component in natural gas. Therefore, how to process the natural gas Raman spectra’s base has become one of a vital and indispensable steps. So this paper proposes a new method to acquire the base which based on the designed Raman spectrometer structure system. The designed laser Raman gas analysis system shown as the following figure 1. The method of real-time difference which has been used to eliminate the background noise of basement can be fulfilled by adjusting the black baffle position up or down. By this way, intensity of gas signal spectra can be obtained. Compared to the method of using argon basal calibration, the hardware operation to preprocess the basement is more simple, and what just need to do is to adjust the electromagnetic valve to control the upper and lower position of the panel. It has important practical application value for saving cost and implementing easily.
A circuit processing method is present to restrain DC drift after analyzing the traditional signal processing method of interferometry for micro vibration measurement. At first, the circuit diagram is designed and its mathematical model is built, then the theoretical equations of the output signal are derived with the practical parameters. By using SIMULINK simulation, the process for restraining DC drift is present on the conditions of the variations of background intensity. The validity of feedback circuit was verified through analyzing the real experiment data. Theoretical predictions match simulation results, showing that this method effectively restrains DC drift for interferometry of micro vibration measurement and it greatly improves the system’s stability.
Single wavelength microscopic interferometry, driven by the Piezoelectric Transducer (PZT), is a common surface topography measurement method. Its measurement accuracy is directly determined by the original phase acquisition precision of every pixels in area array CCD. Traditional phase identification methods adopt 3 points or 4 points algorithm to obtain the phase. However, they require the displacement step, actuated by the PZT, to strictly keep the same to satisfy the 90° phase condition. Therefore, these methods are only suitable for the strict anti-vibration experimental environment or conditions with high precise closed-loop PZT actuator and strict calibration of interferometric wavelength. An auto-acquisition driving step method for the single wavelength microscopic interferometry is presented in this paper. Firstly, interference sequence diagrams, containing the surface topography information, are gathered by the CCD under open-loop PZT actuating. Next, two pixels whose phase difference is approximate 90° are selected as the calculating center to obtain smoothed gray values with regional gray average algorithm, which can reduce the influence of random noise. Finally, an optimal fitting algorithm for the ellipse, formed by the average gray values, is proposed to obtain the amplitudes and offsets of the two gray values array. According these fitting parameters and gray values, the drive step can be calculated by elliptic equations. Experiments have shown that this method can reduce the requirement conditions of measurement conditions and improve the measurement accuracy.
A high-accuracy signal processing algorithm was designed for the absolute distance measurement system performed with frequency scanned interferometry. The system uses frequency-modulated laser as light source and consists of two interferometers: the reference interferometer is used to compensate the errors and the measurement interferometer is used to measure the displacement. The reference interferometer and the measurement interferometer are used to measure synchronously. The principle of the measuring system and the current modulation circuit were presented. The smoothing convolution was used for processing the signals. The optical path difference of the reference interferometer has been calibrated, so the absolute distance can be measured by acquiring the phase information extracted from interference signals produced while scanning the laser frequency. Finally, measurement results of absolute distances ranging from 0.1m to 0.5m were presented. The experimental results demonstrated that the proposed algorithm had major computing advantages.
A novel two-dimensional small angle probe is introduced, which is based on principle of auto-collimation and utilizes
quadrant Si-photoelectric detector (QPD) as detection device. AC modulation, AC magnification and absolute value
demodulation are incorporated to restrain the DC excursion caused by background light and noise etc and to improve the
sensitivity and stability of angle detection. To ensure that while the laser is shining, the current signal (converted into
voltage signal) of QPD also is linear to the AC modulation voltage, this paper adopted AC modulation signal (5400Hz)
with a DC offset. AC magnification circuit with reasonable parameters is designed to inhibit DC drift and the impact of
industrial frequency noise and to ensure good amplification to signal frequency at the same time. A piezoelectric-driven
micro-angle generator is designed to demarcate the angle. The calibration data are input to single chip, and the
measurement of angles can be shown in SMC1602A.
A new five-degree-of-freedom measuring system was developed as a linear guide. According to the principle of
autocollimation, the system consisted of two semiconductor lasers, two right angle prisms, two lenses, two polarization
spectroscopes and four quadrant Si-photoelectric detectors(QPD). Two axial displacements and three angular rotation
degrees are measured by comparing the position of the spot center on the QPD. Repetitive simulations show that the
accuracy of the system is 3" for measurement of angle, which proves the feasibility of this system. The advantages of the
system include simple structure, easy operation, high accuracy, low cost and real-time work.
The standard of technology without an interesting name (TWAIN) was introduced and a displacement measurement
method was presented. Based on the theories of image capture and image measurement, a displacement measurement
system was developed and subpixel and centroid technique were used to improve the measurement precision. The
Experiment results show that the proposed method has low cost and high precision.
KEYWORDS: Sensors, Optoelectronics, Photodiodes, 3D metrology, Signal detection, Mirrors, Applied research, Signal to noise ratio, Reflection, Reflectance spectroscopy
A spatial arrangement of four-quadrant optoelectronic detector is presented to detect interference fringes in 3D surface topography measurement. By putting the '⊞-shaped symmetry four-quadrant optoelectronic detector into the interference fringes region inclined at a certain angle, the difference signal with a higher SNR can be obtained even the shape or width of fringes may vary in a certain range. The relationship between interference fringe width d, photodiode arrays rotary angle β, and amplitude, phase difference of the difference signal is analyzed by integral analysis in ideal conditions. Appropriate value of fringe width d and associated rotary angle β that meets orthogonality relation are given. The results of the experiment and analysis indicate that the two difference signals satisfy the requirement of counter and subdivision and thus can reach the accuracy of nanometric scale measurement by the spatial arrangement of the photodiodes.
This paper presents a new method of high-precision calibration with grating grooves for precision vision measurement
system of micro-size part. After an image of high precision grating grooves are grabbed by CCD, a black-and-white
striped picture may be gotten. A group of data being similar to sinusoid is gotten by calculating the sum of gray-value of
pixels in each column. These calculated data are elaborately showed a Lissajous figure in one plane by translation for pixel. The size mapping coefficient between the grating groove and their image pixels of the optical measurement system
is calculated by analyzing and processing the Lissajous figure. It is not necessary to calculate the interior and exterior
parameters of the camera for the calibration of measurement system when this method is adopted. Finally, this paper
gives the result of calibration and its error analysis for one optical system.
Automatic high-precision chip mounter have been applied frequently in high-precision and complex craft situations. The key to the equipment is the vision alignment system. The leveling adjustment is the important part and preconditin of the alignment. On the basis of a correlative leveling adjustment technlogy, a novel optical alignment system for leveling adjustment is presented. Its optical system is designed and its flow of image processing is discussed. To avoid the influence of interference, the polarization of the light is used skillfully in the optical system. The result of simulated experiments of the reticle-mark collected by a charge couple device (CCD) indicates that the system can meet the precision needs of an automatic chip mounter vision alignment system and it is reasonable.
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