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- Front Matter: Volume 11439
- Optoelectronic Measurement Technology and System
Front Matter: Volume 11439
Front Matter: Volume 11439
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This PDF file contains the front matter associated with SPIE Proceedings Volume 11439, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.
Optoelectronic Measurement Technology and System
Design and research of phase-locked loop for infrared laser ranging system
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Phase-locked loop (PLL) is a circuit that can synchronize the output signal with the input signal in frequency and phase. Generally, it consists of three parts: Phase Detector (PD), Loop Filter (LF) and Voltage Controlled Oscillator (VCO). In modern technology, it is widely used in various fields, such as modulation and demodulation, frequency synthesis, power system, laser ranging, image processing and so on. According to the number of zero and pole in open loop transfer function, PLL can be divided into two types: TYPE I and TYPE II (Charge Pump). In TYPE I PLL, there is only one zero and pole produced by VCO. Therefore, when the loop is locked, there is always a phase error between input and output. However, in TYPE II phase-locked loop, not only does it contain a zero and a pole generated by VCO, but it also introduces a charge pump into the phase-locked loop and provides another pole for the whole loop together with a phase detector, thus making the phase error zero when the loop is locked. Charge Pump Phase-Locked Loop (CPPLL) has a large phase-locked range. Charge pump phase-locked loop (CPPLL) is widely used because of its large capture range and relatively simple structure. In this paper, the principle of charge pump phase locked loop (CPPLL) in phase laser ranging is analyzed, the linear model is built, and the performance of speed conversion is studied. The frequency-locked, phase-locked precision and conversion speed of the loop are analyzed, and the charge pump phase-locked loop circuit is designed. Experiments show that the circuit effectively prevents the charge sharing effect and improves the accuracy and speed of the system.
Surface profile measurement based on continuous wavelet transform in line-scan dispersive interferometry
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This paper presents a signal processing method based on continuous wavelet transform in our line-scan dispersive interferometric system. Our method enables us to extract phase information from the spectrum by applying continuous wavelet transform, which is more effective and reliable in analyzing non-stationary signal compared with FT transform. Experimental results obtained by measuring a step standard with a height of 1.806μm reveal that this method has high accuracy and a good performance over noise resistance, which makes it suitable for complicated in-line measurement condition.
Defective samples simulation through neural style transfer for automatic surface defect segment
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Owing to the lack of defect samples in industrial product quality inspection, trained segmentation model tends to overfit when applied online. To address this problem, we propose a defect sample simulation algorithm based on neural style transfer. The simulation algorithm requires only a small number of defect samples for training, and can efficiently generate simulation samples for next-step segmentation task. In our work, we introduce a masked histogram matching module to maintain color consistency of the generated area and the true defect. To preserve the texture consistency with the surrounding pixels, we take the fast style transfer algorithm to blend the generated area into the background. At the same time, we also use the histogram loss to further improve the quality of the generated image. Besides, we propose a novel structure of segment net to make it more suitable for defect segmentation task. We train the segment net with the real defect samples and the generated simulation samples separately on the button datasets. The results show that the F1 score of the model trained with only the generated simulation samples reaches 0.80, which is better than the real sample result.
Micro-vibration calibration system based on laser Doppler
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In modern society, the measurement of low-frequency micro-vibration has received more and more attention. Highprecision piezoelectric acceleration sensors are often used to measure small vibrations of objects. Therefore, the calibration of such high precision piezoelectric accelerometers is particularly important. The high-precison piezoelectric sensor, however, cannot be calibrated by a general calibration system since it has its own high measurement accuracy and the attenuation frequency is low frequency. This paper implements a low-frequency micro-vibration acceleration sensor calibration system based on non-contact laser measurement, which can calibrate high-precision piezoelectric sensors and accurately measure the sensor under low-frequency conditions. First, the high sensitivity of the heterodyne laser interferometer in the case of small amplitude can be used to calibrate the high-precision sensor in the case of 10-7 g . Secondly, for the calibration of low-frequency sensors, the cantilever structure can effectively calibrate the acceleration sensor at an attenuation frequency of about 0.5 Hz, which improves the calibration range and calibration sensitivity of the calibration system.
3D extrinsic joint calibration of 3D-Flash-LiDAR and camera system
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Recent years, people pay great attention to the fusion of different kinds of sensors include camera, radar, LiDAR and so on. Since each sensor has its own advantage and disadvantage in automatic drive and obstacle detection, the fusion of sensors is more robust and reliable. In this paper, we present a novel target calibration of LiDAR-camera system. We use a 3D Flash LiDAR which has a resolution of 320×240, much cheaper and more reliable than Scanning LiDAR, and we use the camera which has a resolution of 1280×1024. We propose a novel target calibration method. The 3D target can provide both geometric features and visual features. This method is fast, easy to estimate all the six parameters of the extrinsic calibration. Our experiments validate our method and show that it achieves good accuracy.
Sub-pixel wavelength calibration of spectrometer
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Fiber spectrometers have important applications in many areas. In order to obtain accurate measurement results, the wavelength of the spectrometer needs to be calibrated. A fussy but more accurate calibration method is proposed, which uses more than 100 spectral lines from 6 element gas discharge lamps to perform peak coarse positioning, interpolation and peak seeking processing to derive a wavelength correction formula. Compared with the original data, the calibrated wavelength has higher accuracy. After calibrated, the errors are within 0.008 nm if we measure the certain corrected spectral lines. In addition, the error of any wavelength, which is not included in 6-element gas discharge lamp, is less than 0.025nm in the full spectrum range (200nm-1080nm). The results show that the calibration of a large number of standard lines allows the spectrometer to achieve sub-pixel wavelength accuracy. But the overall accuracy improvement is limited.
Design of chip character recognition system based on neural network
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At present, the sample comparison of intelligent electric meters in power grid companies mainly relies on manual inspection. With the development of semiconductor technology and the increasing demand of intelligent electric meters, the disadvantages of this method, such as low detection efficiency, high misjudgment rate, are becoming more prominent. In this paper, a method for automatically detecting and identifying the intelligent electric meter circuit board chip is proposed, and a chip character recognition system based on convolutional neural network (CNN) is designed. The system is mainly divided into two parts: chip positioning and character recognition. The chip is positioned based on the method of layout analysis and edge detection. According to the difference between the characteristics of the chip and the characteristics of the PCB background, preprocess the images, detect the chip identification and obtain multiple candidate regions. Finally, candidate regions are screened based on chip characteristics. The gray-level projection method is used to segment characters. A single character image is obtained by row segmentation and column segmentation. At the same time, the optimization algorithm for character adhesion and fracture problem is proposed to improve the segmentation accuracy. For the character recognition module, build a convolutional neural network to extract character features, and the normalized character is input into the trained neural network for recognition. The recognition accuracy of test sets is high, and the time for recognizing a single character is about 0.35 seconds. Compared with the traditional detection methods, the proposed method has higher detection efficiency and recognition accuracy.
Indoor point cloud recognition with deep convolutional networks
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With the development of laser radar technology, more and more fields have begun to use laser radar to acquire 3D point cloud information. The crux and premise of 3D object recognition and 3D model semantic segmentation is the depth feature of 3d point cloud. Therefore, it is significant for indoor intelligent robots to recognize 3D objects by using laser radar. However, unlike the regular arrangement of pixels in 2D images, the 3D point cloud data is irregular and disordered, which means it is difficult to acquire local related information between the 3D point cloud with direct convolution operation. At present, the research focus of 3D object recognition is the method based on deep learning. At this stage, the deep convolutional neural network constructed by PointConv can achieve a high level in the semantic segmentation of 3D point cloud. First, this paper introduces a model named PointConv. To balance the performance and complexity of the model, this paper simplifies the PointConv which called Mini-PointConv to reduce the occupation of network computing resources while ensuring the accuracy of the model segmentation results. Furthermore, the method of ScanNet is adopted to test the Mini-PointConv, which shows that the improved network has achieved a good experimental result in 3D scene semantic segmentation tasks and gained a better performance as balance as well. Finally, the Mini-PointConv is tested in a variety of indoor environments using laser radar and obtain a good indoor 3D point cloud recognition result.
An on-site calibration method for on-line detection system of wheelset geometric parameters
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Wheelset is one of the most important parts of the train, and the malfunction of the wheelset will directly affect the driving safety. Accurate and efficient wheelset geometric parameters detection is of great significance to the development of railway systems. Online measurement system using structured light is the current research hotspot, which has the advantages of non-contact, fast speed, etc. This paper proposes an in-field calibration method that is with simple operation, high efficiency and high precision for the on-line detection system. Position of the feature points was obtained with the accuracy of sub-pixel level. Considering two kinds of (radial and tangential distortion) distortions at the same time, the LM (Levenberg-Marquardt) optimization algorithm was used to obtain the nonlinear equations with the smallest comprehensive error. Then the internal and external parameters of the camera are obtained. In addition, the method has been applied to the site. High-precision result of wheel diameter which is obtained from on-line diameter inspection equipment can be used to correct the situation when the structure light deviates from the center of the circle. The field measurements show that the error of the wheel pair parameters using this algorithm is within 0.3 mm and has good repeatability.
Study on non-phase-shifting phase retrieval methods for interferogram with large phase gradient
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As a non-contact, high-precision optical component testing method, interferometry performs the measurement by solving the interferogram containing the phase information of the object to be measured. The non-mechanical-phase-shifting phase retrieval method based on single or two interferograms has the advantages of good vibration resistance, fast speed and simple system, which can meet the increasingly urgent online and on-site detection requirements. Aiming at the large gradient phase detection requirements in processing, this paper compares the accuracy of typical non-mechanical-phaseshifting interferometric phase retrieval methods, including carrier Fourier method, digital moiré interferometry (DMI), and two DMI-based methods, namely two-step carrier stitching method and DMI combined with Newton iterative algorithm proposed by the authors. In this paper, the influences of the magnitude of the phase gradient and the noise of the interferogram on the phase retrieval accuracy of the above methods are analyzed. The simulation results in this paper will provide a theoretical basis for the selection of algorithms for in situ interferometry.
High-bandwidth angular jitter measurement for acquisition, tracking and pointing system
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In order to achieve precise pointing and high-resolution imaging, acquisition, tracking and pointing (ATP) system is usually required to stabilize the line-of-sight (LOS) within arc-second or even higher level. In case of ATP system mounted on moving platform, broadband angular disturbance is the most serious factor to prevent the LOS being stabilized. Due to the limited sampling frequency of detectors, the angular disturbance is usually mitigated by incorporating inertial stabilized platform (ISP) and fast steering mirror (FSM) into ATP system. The need for small, inexpensive inertial angular rate sensors(ARSs), which may be employed in these devices to measure angular jitter at sufficiently wide bandwidth, is urgent. However, there is no single angular rate sensor (ARS) currently available that could measure angular jitter from DC to hundreds of hertz while maintaining comparable accuracy. Multi-sensor fusion is a practical solution to broadband angular jitter measurement for the purpose of jitter control. In this paper, the measurements from Magnetohydrodynamics (MHD) ARS and MEMS gyro are blended together using closed-loop fusion (CLF) method. The approach does not rely on accurate models or transfer functions of sensors, and meanwhile, can be easily implemented in real-time system. Experimental results indicate that the measuring bandwidth of CLF method is within overall frequency range covered by MHD ARS and MEMS gyro.
Compact high-stability and low-nonlinearity heterodyne grating interferometer
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A heterodyne grating interferometer (HGI) with high stability and low nonlinearity is presented. An optical arrangement with Littrow configuration combined with Wollaston prism is proposed for the HGI. The compact and symmetrical design make it insensitive to environmental disturbances. The optimal separate angle of the Wollaston prism is investigated with rigorous coupled-wave analysis (RCWA), and the value of 44° corresponding to the grating pitch of 845 nm is selected. The approximately equal diffraction efficiencies of 76.54% and 76.64% for TE and TM polarizations are respectively obtained, which is beneficial to the signal-to-noise ratio (SNR) of HGI. Additionally, the nonlinear errors including polarization mixing, frequency mixing and polarization-frequency mixing are analyzed. The polarization mixing error is dramatically decreased owing to the high extinction ratio of Wollaston prism. It reveals that the developed HGI has the potential for nanometric displacement measurement.
A new pose measurement method based on microlens arrays
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In pose measurement where infrared marking point is adopted as feature identification, only point coordinate information can be provided. In order to improve the accuracy of pose measurement, it is necessary to increase the number of feature points involved in pose solving, which limits the application of pose measurement method. A new pose measurement method based on two-dimensional optical coding marking orientation is designed. In the process of measurement, not only the coordinate information of the marking point can be used, but also the orientation information of the visual sensor to shoot the marker can be obtained, which improves the accuracy of pose measurement. The optical marker in this method includes a microlens array, a back two-dimensional code pattern and a background light source. When the visual sensor shoots the optical marker from different angles, different two-dimensional coding patterns can be obtained, which provides orientation information for pose measurement. Firstly, the images captured from different viewpoints are preprocessed, including segmenting the optical marker with the surrounding environment and transforming the images into undistorted frontal views. Then, on the basis of the pixel information of the microlens array’s surface pattern, every single microlens for different viewpoints is encoded to obtain a set of code strings varying with the viewpoint. Finally, the code string information of different viewpoints is processed and the orientation model of two-dimensional optical coding marker is established. In addition, the factors that may impact the pose measurement accuracy are evaluated.
A novel image points matching method by intersecting into space for close-range photogrammetry
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Image points matching between multiple uncalibrated images has always been an important task in Close-range photogrammetry and difficulties are often experienced. Epipolar geometry constraint method is considered to be an effective way to solve this problem and it has been studied in detail. However, large amount of applications have shown that epipolar geometry is hard to be recovered accurately due to image distortion and positioning error, which leads to numerous mismatches when image points are distributed intensively. In order to solve this problem, an alternative image points matching technique to the epipolar geometry constraint method is investigated, which matches the image points combining with a bundle adjustment process and using their corresponding spatial collinear lines intersected on 3D space instead of finding on 2D epipolar line. In this paper, the matching principle and process of this method are described in detail. Experiment results and comparison with epipolar geometry constraint method are displayed, which verifies the flexibility and effectiveness of this method.
Fast deflectometric measurement of freeform surfaces for ultra-precision optical manufacturing
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The measurement of freeform optical surfaces is a challenging task in precision manufacturing. Those widely used instruments such as the point-scanning profiler and sub-aperture stitching interferometer are costly expensive and time consuming. The phase measuring deflectometry is a powerful measuring technique for complex optical surfaces. To image the measuring efficiency and reduce the number of the captured images, the modulating information can be reutilized in the second direction in the bi-directional phase shifting, so that totally only 6 images are needed. The tracing deviations caused by the form errors behave differently with those caused by the position errors. Then precise localization of the measured surface can be realized by error separation, so that detecting of feature points can be avoided. Experimental results demonstrate that the measurement error is below 150 nm.
Thermostatic chamber for Doppler broadening temperature measurement
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With the redefinition of the Boltzmann constant and the basic international temperature unit of Kelvin, the international agreement on temperature scale is gradually transferred to the thermodynamic temperature scale. Based on the Doppler broadening of the cesium atom’ absorption spectrum the thermodynamic temperature of cesium atom cell can be measured. The accuracy of temperature measurement and the verification of experimental principle depend on the surrounding temperature stability of the absorption cell. In this paper, a thermostatic chamber with precise temperature control system was designed and realized. The thermostatic chamber consists of an aluminum cavity, a support layer, a shielding layer, a heat insulation layer and a copper column. The influence of size and material parameters on temperature control effect was analyzed by finite element method. Based on theoretical analysis, the structure of the chamber was optimized. In the experiment, circulating water cooling was used to provide the base temperature for the cavity. A negative feedback control program was developed to regulate the heating power of the electric heating film to achieve rapid temperature regulation and stabilization. The maximum temperature difference of the copper column inside the constant temperature chamber with a length of 380 mm and a diameter of 210 mm was less than 8 mK. The temperature fluctuation within 12 hours were less than 1 mK and the temperature stability was less than 0.16 mK, and the standard uncertainty of the camber temperature was 11.02 mK. This study will improve the development of the calibration-free, chip-scale thermodynamic temperature sensors.
Performance analysis of software-based methods to expand the dynamic range of Shack-Hartmann wavefront sensor
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The traditional Shack-Hartmann wavefront sensor requires that the focal spot of each microlens must remain in its corresponding sub-aperture range to avoid mistakes in spot-subaperture matching. We present a software-based recognition algorithm that can obtain a much larger dynamic range while maintaining high precision: Iterative extrapolation method. In order to find the corresponding spots of all the subapertures, the method first select a 3x3 spot-array and establishes a polynomial function about the spot position to predict and find the adjacent spots, and then carry on this procedure in successive steps of the iterative algorithm. The performance of the iterative extrapolation method to expand the dynamic range of various wavefront are studied and compared with the sorting method by simulation. Finally, experiments were carried out to further verify the performance of the method. Both simulation and experimental results show that this algorithm can effectively expand the dynamic range of SHWS and the deviation of reconstructed wavefront from ideal one is below 0.08λ（PV）.
Vertex radius of curvature fabrication error measurement of aspheric surface based on aberration analysis in partial compensation interferometry
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Vertex radius of curvature (VROC) is one of the most important shape parameters to determine the properties of an optical conicoid surface. Precisely measuring the VROC error is critical for manufacturing and aligning optical conicoid. In general, the VROC error is measured directly by curvature fitting from profile measurement data from contact or noncontact testing. And to our knowledge there is no effective way to measure VROC error with non-null interferometry. In this paper, partial compensation interferometry (PCI) with aberration analysis is presented for determining the VROC error. PCI is a kind of non-null interferometry proposed by the authors aiming at testing conicoid or generally aspherical surface figure error (SFE). SFE is defined as the irregular difference between the measured and nominal surface. It mainly comes from local manufacture error and can be calculated from interferograms with digital moiré phase-shifting (DMPSI) method. Here we suppose SFE has already been measured with PCI. Then we measure the VROC error with aberration analysis of the residual wavefront at the exit pupil of the interferometer. Simulations are done to verify the method, and the results show that the relative measuring accuracy is less than 0.003%.
Laser displacement sensor optimization for space structure vacuum thermal test
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The large spacecraft structure would generate thermal-induced vibration in orbit under specific condition, which will affect the performance of the payload. In order to predict the occurrence of thermal-induced vibration of the spacecraft structure in orbit, it is necessary to carry out tests in the ground simulated vacuum and low temperature environment. The vibration displacement of structure should be measured by laser displacement meter during the test. Due to the special environment such as vacuum, low temperature environment, it is necessary to improve the laser displacement meter. The effect of internal and external pressure difference during pumping is eliminated by design the venting holes. Ensures the temperature uniformity and operating temperature range of the laser displacement meter by thermal control design, to reduce the measurement error caused by the thermal deformation of the sensor. The adaptive design ensures that the laser displacement meter can work normally under vacuum and low temperature environment, and the measurement accuracy is better than 5μm.
Non-orthogonal shafting laser sensor for trans-scale three-dimensional measurement
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For the trans-scale three-dimensional (3D) measurement in regular-size space and industrial applications, there are many deficiencies and application limitations for traditional measurement methods. Reference to the three axes architecture of traditional instruments, a novel non-orthogonal shafting laser sensor is proposed. The novel sensor is mainly composed of two non-orthogonal shafting laser sensing modules, and each module is made up of two one-dimensional rotary tables and one collimated laser. In the novel laser sensing module, the three axes represent a non-orthogonal shafting architecture, with no orthogonal and intersecting requirements. The manufacturing and application costs are greatly reduced. A high-accuracy calibration method based on coordinate measuring machine and image processing is introduced. An improved perspective projection transform model and attitude kinetic model described by quaternion are adopted to calculate the 3D coordinates of spatial points. The simulation and experimental results showed that a maximum error less than 0.1 mm was detected from 100 mm to 500 mm. It is proved that trans-scale 3D measurement is feasible with the proposed non-orthogonal shafting laser sensor.
The calculating method of minimal-distance between aero-engine pipelines by using optoelectronic measurement system
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The minimal-distance between aero-engine pipelines is a very important parameter that can ensure the normal operation of the aero-engine. The traditional measurement method by using the feeler gauge is inefficient. This paper introduces the calculating method by using optoelectronic measurement system. In this way we can get the point cloud data of all the pipelines. Firstly, the points belonged to the same pipeline is picked up and saved in a group. Secondly, a set of equal-interval grid is built along a coordinate direction in which the pipeline stretched longest. Thirdly, on each trend-line point, a projection plane is built vertically to a straight line connecting the point and its adjacent point. Fourthly, the projected points on each projection plane are fitted into a circle using least square fitting method. Finally, traversing method is used to calculate minimal-distance between two groups of center-line points. And minimal-distance of two pipeline surfaces is calculated by subtracting radii of two pipelines from the minimal-distance of center-line points. Four groups of pipelines are examined to verify the proposed strategy. The results show that the deviations of minimal-distance of two pipeline surfaces are within -0.35mm~0.46mm. And the deviations of pipeline radius are within-0.1mm~0.29mm. The proposed method is more robust than mostly used method for calculating center-line data of pipeline.
Accuracy assessment of tissue polarimetric properties based on Mueller matrix images decomposition
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Mueller matrix images(MMI) contain complete polarization information of the media. Mueller matrix decomposition technique, where Mueller matrix polar decomposition(MMPD) and differential decomposition(MMDD) are widely used to decompose MMI, is the key to extract intrinsic polarimetry characteristics of biological tissues. For the decomposition of biological tissue MMI, Satish et al. expressed that MMDD was more suitable for Mueller matrix polarimetric analysis of tissues, while Alali et al. pointed out that MMDD did not offer a great advantage over MMPD. To deal with this problem, we explore how to choose the appropriate decomposition method to accurately extract the polarization information in biological tissues. The experimental results indicate that the linear retardance and optical rotation images obtained from two decomposition methods are different if tissues exhibit significant linear retardance and optical rotation effects simultaneously. According to the physical model of MMDD that the occurrence of polarization effects is orderindependent, MMDD should be applied to MMI of tissues to obtain accurate polarization characteristics in this situation. The biological tissue has low optical rotation in most cases in which the polarimetric images extracted from two decomposition methods are nearly identical, so MMPD and MMDD both can accurately acquire the polarimetric properties of tissues. Meanwhile, comparing the runtime of two decomposition methods to process MMI, we find the processing speed of MMDD is much faster than MMPD. Thus, we summarize that MMDD method is more suitable for the decomposition of the biological tissue MMI, with the advantages of both fast and accurate, which is significant in diagnosis of clinical.
Face 3D measurement by phase matching with infrared grating projection
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In the current face 3D measurement technology, binocular stereo vision has been widely used. For the passive binocular 3D measurement system that does not need to project auxiliary light, it has the characteristics of simple system structure, but the result is not accurate enough and the algorithm is complex. Therefore, this paper proposes a fast measurement method for binocular stereo vision combined with infrared grating structure light. Because Digital-Light-Processing (DLP) projector has slow projection speed, dynamic images acquisition cannot be performed well, and when applied to the face 3D measurement, the eyes of the measured person will be stimulated by strong light, so a Micro-Electro-Mechanical System (MEMS) infrared projector is used in this paper. It has the advantages of high projection speed, high precision and no stimulation to the human eyes, so the MEMS projector can be well applied to 3D measurement of human face. The sinusoidal fringes are projected onto the face by the MEMS projector, and the phase is wrapped and unwrapped by phase measurement profilometry. In this paper, the four-step phase-shift method is used to calculate the wrapped phase, and the phase order is obtained according to the multi-frequency heterodyne principle. Fast matching of corresponding points of two image planes by combining epipolar and phase order constrained algorithms. The experiment verified that the highspeed, stable and low-cost face 3D measurement system was realized.
A fast and cost-efficient technique for estimating feedback strength parameter C in laser self-mixing interferometry
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The parameter C, named optical feedback strength coefficient, has always exhibited significance in the field of laser self-mixing interferometry (SMI), and it can be utilized to assess the feedback regime or reconstruct an external target's motion. Plenty of researchers have concerned about the technique of acquiring C from SMI signals. Instead of empirical conclusions and according to clear mathematical deduction, this manuscript proposes a fast and cost-efficient method to evaluate C, eliminating large calculation consumption as in the reported optimization methods. Regardless of laser types and the line-width enhancement factor α, it is possible to achieve a relative precision within 5% for C ranging from 0.1 to 5, which is helpful for SMI theoretical studies and SMI sensors.
Study on infrared collimation heating technology in thermal vacuum tests
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The large-scale space structures may undergo unstable Thermally Induced Vibration (TIV), called thermal-flutter, on orbit due to the special incidence angle of solar heat flux. Compared with TIV, thermal flutter can cause more serious damage to the large-scale space structures. In this paper, the primary objective of the research is to develop a method for obtaining collimating heat flux so that thermal-flutter phenomenon can be observed in the laboratory experiment. Based on the non-imaging optics theory, a parabolic reflector for infrared lamp was designed and machined. The results show that the infrared lamp array with parabolic reflector can provide collimating heat flux and the method is feasible and effective.
Location of circular retro-reflective target based on micro-vision
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In close range photogrammetry, a scale bar which has fixed targets on it is often used to scale a photogrammetric measurement by giving known distance(s) between the targets. It’s important to make sure that the scale bar can provide precise distances so the measurement can be scaled correctly. An effective way to calibrate a scale bar was realized by getting the microscopic images of the retro-reflective targets (RRT) at two ends of the scale bar and locating their centers, and the distance between two targets was measured by the laser interferometer, then the length of the scale bar could be calculated from geometric relations. In this calibration method, the problem of accurate location of RRT is a key to calibrate the photogrammetric scale bar. So in this paper, we focus on this problem and propose a RRT location scheme based on microscopic vision and image processing. The composition and principle of the target location system are introduced. According to the retro-reflective features of the RRTs and their image characteristics under the microscope, the image processing methods of preprocessing, feature extraction and centering are analyzed. The factors such as image magnification, illumination and offsets in the field of view, which may the significant sources of location error, have been tested and analyzed. The results help to standardize the RRT imaging conditions so the measurement repeatability can be improved. The repeated positioning accuracy is less than 0.3μm.
Research on the application of indoor GPS in aircraft assembly
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With the increase in demand for advanced military and civilian aircraft , aircraft assembly cycle time is getting shorter and shorter while the quality requirement is becoming higher and higher, meanwhile the costs of aircraft assembly are getting lower and lower. It is supposed that intelligent assembly is one of important approaches to solve the issue above. Aircraft assembly state perception and process control are the most essential factors for achieving assembly intelligence. This essay illustrates indoor GPS to build large-scale measurement field respectively on whole plane testing station, docking stations of full aircraft and materials transportation routes, which achieved the goal that whole plane level testing is characterized with high efficiency and accuracy. Dynamic posture-adjustment guidance of intelligent logistic AGV is realized. While quantitative monitoring the quality and process of aircraft assembly, the number of employees in the assembly logistics are reduced, the efficiency and quality of aircraft assembly are greatly improved.
An absolute displacement measurement method of simple graphic decimal shift encoding
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Aiming at the problem that the coding difficulty of the traditional absolute encoder increases with the increase of the resolution, a novel method of simple graphic decimal shift encoding is proposed. This method uses the coarse code plus precision code to realize high accuracy measurement. The coarse code is obtained by encoding the simple graphic, which is captured by the image sensor. The encoding sequence is received according to the light intensity, and then uses a simple mathematical formula to complete the decoding. And the precision code is defined by time-grating measurement. The optical signal of the sinusoidal light transmitting surface is firstly received by the photocell and then transformed by the circuit to the voltage signal. The precision code is finally obtained by comparing reference signal with the electrical traveling wave signal, which is transformed from the voltage signal. According to the proposed principle, a prototype with a grating pitch of 0.6mm and a range of 530mm was set up. Experimental result shows that the absolute measurement accuracy of ±0.30μm is realized. It also proved that the resolution can be improved to 1nm in the experiment
Femtosecond pulse laser distance and angle interferometer
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This paper describes a method of measuring distance and angle by dispersive interferometer using a femtosecond pulse laser. The measurement system is set up based on the modified Michelson interferometer, which combines the advantages of using retroreflector and plane-mirror reflector. The two parallel measured beams and one reference beam can undergo a mutual interference in frequency domain. The three shutters are set to two measure arms and reference arm, respectively. the shutters can be used to change the work mode of interference system. The optical path difference of distance and angle can be acquired by the modulated frequency of interference signal. Angle measurement has been compared to a calibrated rotation stage in the range of 1800 arcsec, the obtained mutual agreement is better than 3 arcsec in ordinary laboratory conditions. The results show the method has the potential for further research of absolute multiple degree-of-freedom measurements.
Design and test of a multi-line structured light projector
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This paper aims to design a multi-line structured light projector with equal spacing, small volume and long-term use. The application background of the projector is the rubber coating detection in the automobile industry, which needs to have the characteristics of high brightness, good monochromaticity, and clear visible projection on the black plastic material. Because the glue is slightly heated, the glue will affect the detection effect. Therefore, it is necessary to ensure sufficient light intensity, and the light is not too strong. Too strong light will cause the glue to be baked and lose the meaning of detection. The projector designed in this paper utilizes a plurality of semi-transparent mirror splitting and wire-cutting processing means to ensure the positional relationship of the light strips. It has the following advantages: simple structure, convenient calibration, small size and low price.
Absolute distance measurement by dispersive interferometry using an electro-optic comb
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We experimentally demonstrated a method for distance measurement using an electro-optic comb based on dispersive interferometry. An electro-optic comb with the repetition frequency of 10 GHz generated by cascaded phase modulators was adopted as the laser source, and a spectrometer with a sampling interval of 0.02 nm was employed to acquire spectral interference signals. Thus, the non-ambiguity range of about 1.5 cm was obtained in this ranging scheme. Subsequently, a low-cost laser range finder with the accuracy of about 1 mm was employed to work as a rough measurement, and the dispersion interference device worked as fine measurement to conduct an absolute distance measurement. Actual tests proved an agreement within 20 μm over 20 m distance.
Design and performance characterization of a quartz crystal micro-retarder array
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Recently, micro-retarder arrays consisting of patterned liquid crystal polymer or sub-wavelength grating arrays with four different orientations are widely used in division of focal plane（DOFP）Stokes polarimeters. However, due to thermal sensitivity of liquid crystal, real-time calibration of the instruments is required to achieve high-precision detection under non-isothermal conditions. Sub-wavelength grating arrays require sophisticated process, and the study of the influence of grating structure errors on measurement accuracy has been rarely reported. To overcome these limitations, we design a quartz crystal micro-retarder array for DOFP full-Stokes polarimeter, which is composed of identical units with different retardances at four neighboring pixels. The retardance errors introduced by the errors of the substrate thickness (t) and etching depth (d) of the micro-retarder array are analyzed. Furthermore, the relationship among the measurement error, the instrument matrix error of Stokes polarimeter, and polarization state of incident light is established. Hereby, the influence of retardance error on the measurement error corresponding to incident light of different polarization state is analyzed. To reduce the measurement error of Stokes parameters to less than 0.02, the tolerances of t and d should be less than 0.11 μm and 0.09 μm, respectively. The micro-retarder array on quartz crystal is fabricated according to our design and tolerances analysis. Finally, the retardance characteristics of the micro-retarder arrays are characterized by the high accuracy (0.1%) Mueller polarimeter developed in house.
Global calibration method for non-overlapping cameras based on mobilephone screens in defocus scene
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The global calibration of multi-camera vision systems with non-overlapping views has been widely studied. However, traditional global calibration methods that using planar targets with invariant relative positions are easily limited by the high cost of manufacturing high-precision large planar targets, and the difficulty of rigid connection between them. This paper proposes a low-cost and convenient global calibration method for non-overlapping multiple cameras using double mobile phone screens in defocus scene. During calibration, phase-shifting circular grating (PCG) arrays are displayed on the high-resolution mobile phone screens, and by phase-shifting methods, the PCG centers as feature points can be extracted accurately even if the phone is located at the defocus part of camera. Then the global calibration can be carried out based on the invariance of the relative positions between the two mobile phones. Experiment results show that this method is effective and has high accuracy.
A method of MRTD parameter measurement based on CNN neural network
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MRTD (Minimum Resolvable Temperature Difference) is an important parameter for comprehensive evaluation of temperature resolution and spatial resolution of infrared imaging systems. It has become one of the necessary detection parameters for manufacturers of thermal imaging cameras. The traditional subjective MRTD parameter test method is gradually replaced by objective test methods due to its long test time and high labor cost. At present, the objective test method has developed the video MTF method and the photometric camera method, but both methods have their corresponding limitations. This paper proposes a new objective MRTD parameter test method based on CNN neural network. Firstly, the four-bar target image used to test the MRTD parameters is analyzed. It is concluded that the process of testing the MRTD parameters is essentially an image classification, which lays a foundation for the learning of CNN neural networks. Then the network model of CNN neural network interpretation of four-bar target image is expounded, and the accuracy of MRTD test results under different network models is analyzed. It was found that the network structure should not be complicated in the classification process of the four-bar target image. Based on the classic CNN neural network LeNet model, this paper proposes a CNN neural network suitable for four-bar target image classification problem by optimizing the convolution layer size, changing the activation function and adjusting the network structure. The experimental results show that the optimized CNN neural network improves the accuracy and repeatability of the MRTD parameter test.
Statistical characteristics analysis of global specific humidity vertical profile
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Studies on the spatial and temporal distribution characteristics of global atmospheric profiles are currently limited. In this study, we analyzed the statistical characteristics of the mean and standard deviation of global specific humidity vertical profiles during 1979 to 2016, using ERA-Interim monthly means of daily means reanalysis data published by the European Centre for Medium-Range Weather Forecasts (ECMWF). The results are as follows. (1) The mean and standard deviation of the specific humidity profiles exponentially decrease with height. (2) There are latitudinal and seasonal differences in both the Northern and Southern Hemispheres. The specific humidity is higher in low latitudes than in high latitudes, and the summer is the wettest and the winter is the driest. (3) The mean and standard deviation of specific humidity are larger over the ocean than over land in the lower atmosphere. This study provides support for evaluating the application performance, radiation transmission algorithm and atmospheric inversion method of new satellite instruments. It can also be used to update and complete current standard atmospheric profiles, and for their comparative analysis.
Influence of nonlinear error on measuring accuracy for a dual-frequency heterodyne interferometer using a polarization maintaining fiber
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Dual-frequency heterodyne interferometer has been widely applied in many fields. It is also an important part for measuring position error in the system that laser simultaneously measure six degree of freedom geometric motion errors of a linear guide. To segregate the heat source, simplify the optical path and obtain a convenient delivery, a polarization maintain fiber (PMF) is used in the system for linking the laser source and the measurement section. However, the nonlinear error caused by PMF will reduce the measurement accuracy, and cannot be ignored in ultra-precision measurement. In this paper, a measurement model for analyzing the nonlinear error caused by the axis misalignment between the laser source and PMF was established with the Jones Matrix. Experiments were performed for verifying and calculating. The results show that the measuring error caused by nonlinear error is less than 2 nm with the axis misalignment being up to 10 degrees.
Off-axis catadioptric partial compensator design for interferometric measurement of optical freeform surface
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Optical freeform surfaces have been widely used in optical systems owing to their design degrees of freedom, which can simplify the structure and improve the performance of optical systems. High accuracy testing for freeform surface is needed due to the improvement of machining accuracy. However, it is still a challenge to achieve high measuring accuracy because freeform surfaces lack rotational symmetry. In this paper, an off-axis catadioptric partial compensator (OACPC) design for non-null interferometric method is proposed to measure freeform surface. The design of OACPC consists of two parts: constructing initial structure and optimizing. The initial structure is obtained by the vector aberration theory and PW method. Based on the initial structure, the OACPC is generated by modelling and optimizing in the optical design software. In order to verify the feasibility, universality and effectiveness, a design example is given. Theoretical analysis and simulation results demonstrate that the design can realize the measurement of freeform surfaces.
A new automatic hand-held laser rangefinder verification system
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At present, the verification method of hand-held laser range finder has characteristics of high labor intensity, low working efficiency and low measuring accuracy. To solve these problems, an automatic hand-held laser range finder verification system is built in this paper. This system contains a 50m marble calibration platform, a measuring trolley with visual measuring module, and a multi-degree of freedom holder of range finder. It can automatically identify the observed readings of rangefinder through optical character recognition (OCR) technology, compare with the standard ranging value obtained by the trolley, and then evaluate error of indication. Thus achieving the purpose of calibrating the rangefinder. All of the communication between PC and trolley is realized by WiFi. Experiments show this device has comprehensive functions, high level of automation, practical application value and broad market prospects.
Research on calibration technology of comprehensive performance parameters of mid-far infrared space load
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Infrared imaging technology has great applications in various fields of social life, especially in the field of remote sensing. Monitoring the ground through infrared loads on satellites can explore natural resources and improve human production. However, due to limitations of equipment, space and other factors, the cost of performance calibration of space load in space is relatively high. To solve the calibration problem of spectral parameters and imaging parameters of space load in the mid-range infrared range, the parameter calibration technique is studied. The mid-far infrared space load comprehensive performance parameter calibration test system is designed by simulating the space vacuum environment on the ground, and the mid-far infrared space load can be tested in an all-round way before going into the space. The test system consists of a vacuum chamber, an infrared collimation system, a medium-far infrared monochromatic source, a standard surface source differential black body, and a series of standard targets. It can realize comprehensive calibration of spectral parameters and imaging parameters on the same device. The load to be tested is placed in a vacuum chamber to simulate a space vacuum environment. The radiation source is radiated into the vacuum chamber through an optical window to simulate ground radiation, which can achieve relative spectral responsivity, MRTD, NETD, MTF, field of view, and magnification, distortion and other parameters of the test, and achieved good experimental results. The results show that the test system can realize the calibration of the spectral parameters and imaging parameters of the mid-far infrared spatial load.
Design and research of automatic cylinder calibration system based on digital image processing technology
Ying Fan,
Zhang Tao,
Wen Wang,
et al.
Show abstract
The measuring cylinder calibration is entirely relied on manually reading data, which lead to high workload and poor repeatability. This research is to design an Automatic Measuring Cylinder Calibration System (AMCCS) based on digital image processing technology to finish the whole calibration process include titration of the measuring cylinder and generating calibration record. The Application of Blob analysis, template matching and optical character recognition (OCR) technology can acquire the image information of the scale and liquid level of the measuring cylinder in real time, feedback to the system, and complete the synchronous output of the record. The methodology used in this research is quantitative method where data obtained through 20 experienced engineers and AMCCS, the result shows that this system is promoted in speed, measurement repeatability, which is 35% and 33%.
Design and simulation on compact type of LED light source radar system for aerosol detection
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Based on the rich selection of wavelengths and small detection blind zone of LED light source radar, the atmospheric remote sensing lidar system with LED light source can achieve the observation of aerosols at near range and special wavelengths. To reduce the volume of radar system and realize portable observation of atmospheric condition, a compact and easy-to-use atmospheric lidar is designed, which receives echo signals from Fresnel lens. The geometric overlap factor is calculated and analyzed according to coaxial radar transmission and reception principles, and the detection blind zone less than 2 m can be confirmed. The system model is constructed by ZEMAX simulation, and the light intensity distribution and light energy utilization rate of the radar transmission system are obtained. At the same time, by calculating the signal-to-noise ratio, the aerosol detection capability is evaluated and the maximum detection distance is obtained. The simulation results show that three types of LED light source radars which single-pulse energies are 96 nJ, 30 nJ and 105 nJ, wavelengths are 475 nm, 530 nm and 625 nm respectively, can reach the detection distance of 480 m, 200 m and 280 m. It verifies that the compact and easy-to-use LED light source radar system has the ability to detect near-ground atmospheric aerosols.
A multi-dimensional evaluation method of the angle measurement performance for the transmitter
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This paper presents a multi-dimensional evaluation method of the angle measurement performance for the transmitter of the photoelectric scanning measurement network. As a distributed measurement system based on the multi-angle intersection, the accuracy of the angle measurement of the transmitter directly determines the measurement accuracy of the entire system. At present, there are few methods of evaluating the angle measurement performance for the transmitter. Multiple receivers are placed around the transmitter in a certain order and kept at the same level as much as possible. Based on circumferential closure and statistical knowledge, this method can evaluate the angle repeatability of different angle positions and the rotational speed volatility of the angular separations between adjacent receivers. The rotational speed volatility of the transmitter is important for the optimization of the angle measurement performance of the transmitter. Through experiments, we find that the method can reflect more information about the shafting, which can provide a good reference for the subsequent system upgrade.
A new methodology for evaluating profile and position errors of blade based on parameter priority
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As one of the core components of a turbine, the quality of the blade manufacturing has a strong impact on the energy conversion efficiency of the turbine, where the key technology of quality evaluation of blades is point cloud registration. However, with the application of structured light three-dimensional measurement technology in full profile measurement, the typical point cloud registration methods only focus on the minimization of surface profile error, ignoring the position error relative to reference datum, which can easily lead to the misjudgment of qualified blades. In this paper, a new blade error evaluation method is presented to register the point cloud data scanned from a physical blade to its theoretical CAD model, which fits the two surfaces based on parameter priority. Firstly, qualified blades are quickly selected after global fine registration using the best-fit algorithm. Subsequently, based on the priority of position error parameters, the coordinate descent algorithm combined with the minimum zone criterion is adopted for local fine registration, which guarantees accurate evaluation results. Finally, the shape and position error of the actual blade is obtained accurately by calculating transformation parameters of registration and the deviation between the registered point cloud and its CAD model of the blade. Experimental results show that compared with state-of-the-art registration methods, the presented method gives higher priority to the parameters which are difficult to finish or repair by machining, and the position errors are controlled in the tolerance area, which effectively reduces the misjudgment. In addition, evaluation results of blade errors with the method are mainly reflected in profile, which is valuable for guiding the blade finishing or trimming in practice.
Research on calibration method of hybrid Body-in-White online measurement system
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In the online measurement of automotive body-in-white, the fixed visual online measuring equipment and flexible visual online measuring equipment are often used in the field to meet different measurement requirements. Therefore, it is necessary to calibrate the two systems separately before measurement. The hybrid measurement equipment’s calibration is involuted and inefficient. So, in this paper, an integral-fast calibration method for flexible and fixed on-line detection equipment is proposed to solve these problems. In this paper, the calibration theory and the on-site calibration technique are described in detail. The following is a summary of the calibration process. First, measuring the same target simultaneously with the fixed vision sensor and the flexible vision sensor. Then, according to the robot's own coordinate equipment relationship in the flexible measurement, the control points are multipath measured and the hand-eye relationship of the robot is calculated. Then, the relationship between the vehicle body coordinate equipment and the robot base coordinate equipment is calculated by using the laser tracker according to the vehicle body positioning reference and the target control point. At last, and the coordinate equipment conversion relationship of the fixed measurement equipment is simultaneously calibrated according to the result of the flexible measurement equipment. Eliminating the section for separate measurement of the fixed measurement equipment by the laser tracker and saving calibration time. Ensuring the overall measurement consistency of the hybrid measurement equipment. We designed a verification test and the test results show that the standard deviation of the calibration method can reach 0.15mm, and the calibration method has high efficiency and simple method, which can meet the calibration requirements of the body-in-white measuring equipment in the field environment.
A noncontact full-field flatness measuring system based on fringe projection
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Flatness is one of the most important properties for quality control of manufacturing mechanical parts. The most widely applied coordinate measuring machine techniques of measuring flatness error are ineffective to collect abundant sample points, and the probes must contact the tested surface. Existing noncontact optical techniques are not full-field measurement and their devices are complex. This paper presents a simple but noncontact full-field flatness measuring system based on fringe projection profilometry technique. The designed device projects fringe patterns onto the tested surface, and by calculating the phase of modulated fringe images and calibrating the phase-height mapping relationship, the full-field surface sample points are acquired. Polarizers are applied to eliminate intense highlight of the measured surfaces. Optimization algorithm is introduced to determine the reference ideal plane and flatness error is then calculated. Several experiments are conducted to demonstrate that the proposed flatness measuring system can be applied to general mechanical parts, and it has high precision and high repeatability.
Theoretical model on underwater sound detection based on laser heterodyne method
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Laser-acoustic joint detection technology is an emerging technology in the field of space-underwater communication, underwater target detection and ocean monitoring in the marine environment. It plays an important role in many new high-end marine equipment manufacturing, deep-sea exploration and security fields. However, accurate detection of multiple sound sources in the case of spectrum aliasing of detection signals has been a technical bottleneck. The purpose of this paper is to extract the underwater sound field information from the sound waves on the water surface, and demodulate the sound frequency of the sound sources close to the underwater frequency. According to the modulation theory of incident laser on the surface of water, this paper introduces the basic principle of laser interferometry to detect sound waves on water surface. This paper proposes a method for detecting the frequency of underwater acoustic signals using optical heterodyne. The expression of the photodetector output current is derived under a plurality of underwater sound source signals. The time domain and frequency domain characteristics of the detected surface wave interference signals are analyzed by simulation. And the feasibility of the method was verified. The results show that the method can detect the frequency and amplitude of the ideal surface wave. In order to obtain a more accurate audible frequency of underwater sound source, this paper proposes a frequency demodulation method based on Hilbert transform. And specific mathematical expressions are derived. This solves the frequency demodulation problem of spectral aliasing of the coherent detection signal. It provides a new method for the detection and processing of underwater acoustic signals.
The research of optical fiber sensor calibration based on acoustic sensor calibration system
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In recent years, optical fiber sensing technology has been greatly developed and widely used in temperature, strain, harmonic vibration testing, especially acoustic detection based on optical fiber sensor, widely used in hydrophones, optical fiber microphones and other real-time detection and early warning systems. However, there is no good solution to the traceability problem of sensors based on optical fiber principle. In this paper, the traceability principle and process of traditional acoustic sensors are introduced in detail. Based on this opportunity, a traceability system which can be applied to optical fiber acoustic sensors is proposed. The system consists of a complete anechoic laboratory, an acoustic analyzer, an acoustic calibrator, a power amplifier, a piston generator, a sound source and microphone. The system has been successfully used to calibrate and trace the acoustic sensitivity and other parameters of the fiber acoustic sensor. The experimental results show that the scheme is effective. This paper has a certain significance for the development of optical fiber technology.
The temperature field measurement method by using schlieren method for aircraft engine
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Aircraft engine is the core power unit in the aircraft, and monitoring the operational status of aircraft engine can improve the safety and economy of the aircraft. The temperature field of aircraft engine tail spray contains effective information such as the degree of fuel combustion inside the combustion chamber, and monitoring its temperature field can be used to evaluate the state of engine operating. The traditional measurement methods for the temperature field of tail spray generally adopts the measurement method of single point thermometer, Laser Induced Fluorescence (LIF), Tunable Diode Laser Absorption Spectroscopy (TDLAS), etc. However, these methods have limitations such as discrete measurement data, complicated application of equipment, and high price. Therefore, in view of the problems existing in the traditional measurement methods, a schlieren method is proposed in this paper. Firstly, the schlieren system images the temperature field to obtain the correct schlieren image. Then the refractive index distribution of the cross section is obtained according to the schlieren image. Finally, the temperature field distribution is calculated according to the refractive index distribution to measure the temperature field. The schlieren measurement method, a non-contact, highprecision measurement method, which does not require a special laser transceiver device, can be effectively applied to the measurement of the temperature field of the aircraft engine tail spray, providing support for the state monitoring of the aircraft engine.
Machine vision based recognition and integrity inspection of printing characters on food package
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Food packaging bags are fast-moving consumer products with large output and fast production speed. Instant noodle bags need to be printed on the production date and number before packaging the food. For the possible date or code printing error, character sticking, incompleteness, etc., the correctness of the characters cannot be judged in real time by the human eye. A set of automatic recognition characters and detection systems are used to binarize, filter and tilt the picture, and use image morphology and horizontal and vertical projection to segment a single character. BP neural network is used to identify the character and compare it to the template to obtain the degree of defect and compare it with the threshold to determine whether the character is qualified. The detection speed of the system can reach 3 images per second, which can realize real-time recognition and detection of characters, so as to eliminate non-conforming products in time.
A spectrally tunable monochromatic integrating sphere photon source for spectral photon radiance responsivity calibration
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A spectrally tunable monochromatic integrating sphere photon source (ISPS) was built based on a laser driven plasma light source, a monochromator, an optical attenuator, and an integrating sphere. The wavelength of ISPS output photons can be tuned from 300 nm to 800 nm with a spectral bandwidth of 1 nm ~ 5 nm; the spectral optical radiant power into the integrating sphere can be adjusted over three decades through the optical attenuator; the diameters of the inner wall and the exit port of the integrating sphere are 100 mm and 50 mm, respectively. The spectral photon radiance of the ISPS can be measured by a photomultiplier-tube (PMT) based photon counter and two precision apertures. An integrating sphere was utilized in front of the PMT-based photon counter and the non-uniformity of the spectral optical radiant power responsivity was reduced to be ~0.5% over a 5-mm-diameter effective detection area. Two precision apertures were adopted to define the effective detection area and the solid angle extended for the field-of-view. The ISPS can be directly applied to calibrate the spectral photon radiance responsivity of a few-photon imaging system, which was demonstrated on a digital color camera and a focusing lens. The spectral photon radiance responsivity of a given imaging system can be effectively validated based on this ISPS apparatus.
Automatic segment assembly in shield method using multiple imaging sensors
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The shield method is one of subsurface excavation method in underground construction. It’s a fully mechanized construction method using shield machine. However, the process of segment assembly now mainly relies on manual work, controlling the assembly robots by experience. This work aims to aid the automation of precise movement control of the assembly robot, especially the movements of sliding, rotating, and deflecting directions. It proposes a new method using multiple imaging sensors to collect image information needed for automatic assembly of segments, and uses information extraction, size measurement and other real-time image processing to determine the spatial attitude of the three directions of the segments to be assembled. By Importing the data into an automation solution, the segments could move along the correct path. Experiments are conducted to test the performance and reliability of the proposed method in an actual underground working environment. The results are validated by successful bolting process in the actual subway construction, showing several different types of segments can move to the correct assembly position and the process is reproducible. Some disadvantages of the method are discussed, and suggestions for improvements are suggested. The proposed method has the potential to be adopted to enable the automation of segment assembly in shield method and may be applied to actual construction.
Robust 6DOF measurement for non-overlapping multi-camera systems based on uncertainty-weighted space resection
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This paper introduces an improved 6DOF measurement method for the non-overlapping multi-camera systems. In contrast to the existing equal-weighted bundle adjustment methods, the proposed method assigns an uncertainty based weight to each of the non-overlapping cameras. The measurement uncertainty evaluation framework is established based on the implicit function theorem. The weight assignment criterion enables the camera in a better observation condition to provide stronger constraints. The 6DOF parameters are obtained by optimizing the uncertainty-weighted space resection model with the nonlinear squares solver. The experiment results demonstrate the robustness of the proposed method to cope with poor observation conditions.
Research on the effects of charge transfer efficiency on X-ray energy spectra taken with CCDs
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The incident low-energy X-ray photon which interacts with CCD detector can produce photoelectric effect and generate photoelectrons[1]. Under the ideal condition, the number of electrons is proportional to the energy of incident X-ray photon. Besides the electrons generated by X-ray absorbed in CCD is converted to readout voltage linearly . Therefore, the voltage is positively correlated with X-ray photon’s energy , and we can measure X-ray energy spectra directly. But in reality, because of the charge cloud diffusion, surface charge loss and charge transfer loss in the detection process based on CCD ， the spectral resolution （FWMH）is broadened. And in the mean time, the spectral peak becomes non-Gaussian with a shoulder and a flat shelf on the low energy side. In this paper , we develop the model and simulation of CCD’s spectral redistribution , including photoelectric conversion process, charge collection process, charge transfer process, and charge readout process. Among other things , we mainly analyze the influence of charge transfer efficiency on X-ray energy spectra.
Coordinate evaluation using three-dimensional reference standard
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To ensure the traceability of coordinate measurements made by large-scale measurement instrument, the direct evaluation based on three dimensional coordinates has been a new trend instead of the traditional verification by the measurement of lengths. This paper proposes a general large-scale coordinate evaluation manner and studies some key technical problems in detail. Firstly, a three dimensional reference standard is established and multilateration is applied to ensure direct traceability of the reference values to a length standard. Secondly, the coordinate reference values and their uncertainties after transformation are calculated. Thirdly, the Measuring Capacity Index ( Cm ) is calculated and some strategies for increasing Cm are recommended. Finally, the evaluation process is demonstrated with several experiments.
Temperature measurements by infrared thermal imaging system in thermal vacuum test
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Infrared thermal imaging technology receives infrared radiation from the measured object, and the temperature distribution will be changed into a visual image by signal processing system. In order to verify the accurate measurement, the temperature measurement experiment under vacuum environment was carried out by constructing the low temperature standard blackbody radiation source, which temperature range was from -80°C to +100°C and temperature control stability was better than ±0.05°C/30min. The general formula of the theoretic temperature of measured object surface is deduced under ultra-high vacuum and cryogenic environment, which was based on the principle of thermal radiation theory. The capability of long-wave infrared thermal imager was verified from -40°C to +60°C. The static characteristics of measurement accuracy, repeatability and linearity were analyzed, and the dynamic measurement characteristics were also tested. The results were compared with the fine thermocouple measurement data.
Based on EMCCD imaging system
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Electronic Multiplying Charge Coupled Device (EMCCD) is the focus of research and development in the field of low-light illumination. It not only has the characteristics of traditional CCD, but also has the advantages of sensitivity nest, high quantum efficiency and low noise, but The commonly used EMCCD camera is designed for only one EMCCD chip, which has low applicability and high cost. Therefore, based on the EMCCD camera's strict requirements on the phase, frequency and amplitude of the drive signal and the characteristics of the output signal, based on the in-depth analysis of the characteristics of the EMCCD camera circuit, a low-noise, real-time, stable and suitable imaging of different EMCCD chips is designed. system. Through the cameralink bus, the host computer receives and displays the EMCCD system image in real time, and can control the EMCCD drive signal amplitude, frequency, phase, matching different EMCCD chip drivers and analog-to-digital conversion requirements. In the case of different micro-illuminance, the system automatically calculates the average brightness of the current frame image. Through the "exposure function", the known current average brightness value can be used to know the relationship between the multiplication gain of the next frame image and the current gain, and calculate the gain. Adjust the value so that the next frame of image reaches the desired brightness value.
A research on extraction of meter line of steel tape image based on Gabor transformation
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In order to raise the robustly of the automatic verification system of steel measuring tapes, a method on extracting the meter lines on steel measuring tapes image based on Gabor transformation is proposed in this paper. This method makes full use of the frequency and direction sensitivity of Gabor filters. Through the Gabor filtering, the particular direction and frequency line structures are filtered out. Based on these line structures, positions of the meter lines in the images can be located and an ROI with the lines in it can be created automatically. Furthermore, through the RANSAC calculation to fit the double edges in the ROI, this method is able to distinguish the broken and stain lines to improve the line detect accuracy and the robustness of the image processing system. Down sampling is used to improve the efficiency of the method. An experiment has been designed to test and verify the method. By standard steel measuring tapes and dual-frequency laser interferometer, the equivalence between pixel and the physical length can be calculated. The moving distance can be calculated with the equivalence and line marker center by the method proposed in the paper. Comparing the calculated value of moving distance with reference value of moving distance measured by dual-frequency laser interferometer, the method proposed in this paper has been proof with accuracy. With the capability of solving stain, complex background, uneven illumination problems, this method can raise the degree of automation of steel measuring tapes verification system.
Research on measurement optical axis eccentricity and fitting method of aspheric mirror
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A method to measurement of optical axis eccentricity and fitting about the aspheric mirror with the high-precision three-coordinate measuring machine(CMM) is presented. By establishing 2d/3d measurement coordinate system, The axis of fitting of the cylinder is selected according to the machining and assembly reference of aspheric mirror, Generating a number of concentric circles automatic measurement strategies, And make the points on each equal circumference, The probe head of the CMM is sampled on the surface of the measured aspheric mirror according to the measured strategy path to obtain the point coordinates of the distance of the reference axis, the measured surface is fitted to obtain the eccentricity of the aspheric mirror optical axis. Hyperboloid concave mirror to make use of the proposed method in the practical testing, the results show the actual processing of eccentricity is 0.0190mm, the standard deviation of 3.6×10-4mm, to meet the requirements of the design of eccentricity is less than or equal to 0.02mm.And testing the high precision centering lathe cutting machine frame fixed axis aspheric reflector components, the data indicators meet the requirements of assembly process. The accuracy of this method is high, and the traditional measuring method is easy to be affected by the precision of the tooling and easy to scratch the mirror. With large work surface, large caliber, back light weight loss (special-shaped structure) of aspheric mirrors optical axis eccentricity detection, not only suitable for different aperture aspheric mirrors the processing quality of qualified determination, but also in the machining, high precision of aspheric mirrors system with adjustable guiding role and effectively promote R-C spherical reflector optical system assembly accuracy and efficiency.
A fiber-based photodetector linearity measurement system from classic to single photon level
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It is important to measure the spectral transmission characteristics of materials when the spatial density of classical optical power (that is, the laser or attenuated light is a small spot, but the optical power hits a fixed position) is different from the spatial density of weak optical power. The most important scientific problem (research or experimental objective) is to distinguish the difference between the probability of photons passing through a sample with a specific absorption rate collectively and the probability of approaching a single photon passing through the same sample. We design an optical fiber system that can measure weak optical power. We use many methods to expand the linear measurement range so that it can measure its linearity in the power range of 1 fA-1 mA. In addition, the system can also verify the linearity of photon counter, starting from 0.1 pA block - essentially, when the detector is adjusted to 0.1 pA, the verification and evaluation of photon counting at the photomultiplier tube level is started. From the power measurement level of cryogenic radiometer to the photon counting level, the optical fiber measurement system covers 12 orders of magnitude, which also shows that the spectral transmittance and reflection ratio can cover a wide range, that is, it can be used to measure the characteristic materials with high transmittance.
A technology of absolute distance measurement based on multi-wavelength self-mixing interferometry of a three-wavelength optical fiber laser
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A technology of absolute distance measurement based on the multi-wavelength self-mixing interferometry of a threewavelength optical fiber laser is presented and experimented. The optical fiber laser which can emit three wavelengths simultaneously is composed of a single fiber ring and three fiber branches. Each fiber branch includes a length of erbium-doped fiber and a fiber Bragg grating (FBG). The erbium-doped fiber is used as the gain medium while the FBG is used as a laser cavity reflective mirror and wavelength selector. Three independent laser cavities have been constructed in the single laser. As there is no laser mode competition, three wavelengths with stable power can be emitted simultaneously and the frequency stability of each wavelength can reach 10-6 . Absolute distance measurement can be performed using multiple self-mixing interferometry of the three wavelengths. Based on the idea that the calculated decimal phase of the self-mixing interferometric signal of each wavelength should equal the measured decimal phase of the self-mixing interferometric signal of the same wavelength, absolute distance measurement can be realized. The nominal length of a gauge block has been used to prove the correctness of the measurement results by experiments. The standard deviation of ten times repeated measurements for a distance of 7 mm is 4.4 nm.
Volume measurement system of large vertical energy storage tank based on optoelectronic measurement technology
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A large vertical energy storage tank volume measurement system is established based on total station scanning technology, which is the photoelectric measurement technology. The horizontal cross-section area is calculated by point cloud data, and then the volume values corresponding to different liquid level heights are automatically calculated by integrating along the vertical height direction. The system is used to measure a large vertical storage tank with capacity of 100,000 m3. The results show that the system has good repeatability and reproducibility. Compared with the traditional measurement results, the relative deviation of the calculated volume is less than 0.1%. The system meets the measurement requirements of JJG168-2018.The feasibility and validity of the system applied to capacity measurement of large vertical storage tanks are discussed.
Accurate piston error detection unaffected by tip-tilt error
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Astronomical observation wants more distant and fainter object with a better resolution, larger primary mirror telescopes are needed to improve the diffraction limit and increase the collected light energy, but limited by monolithic primary mirror manufacture, testing, transportation and launch. And segmented telescopes can address these. However, segmented telescopes also introduce co-phasing errors. In this paper, we put forward a new method to measure piston error based on analyzing the intensity distribution and Fourier optics principle. This method can detect the piston error with a high accuracy in a larger capture when the residual tip-tilt error still exists. A point source is taken as the object of the segmented telescope, the pattern focused on the CCD is recorded as the point spread function (PSF). Fourier transform is performed for the PSF. And we can obtain the optical transfer function (OTF) which is composed of the modulation and phase transfer functions (MTF and PTF). Then we derive the relationships between the piston error and the MTF′s side-lobe peaks and we found that tip-tilt error influences the accurate detection of piston error in term of the relationship. Thus, we take the MTF′s side-lobe peaks obtained when only tip-tilt error exists as the normalized factor, then the influences of tip-tilt error is removed. Simulation has been done to validate the feasibility of the method. The results state that this method's capture range is the operating light′s coherence length, the accuracy is 10.0nm RMS, preliminary experimental results also proved the assumption.
MTF non-redundant distribution for multi-piston errors detection of segmented telescopes
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We propose a MTF non-redundant distribution method, with which the multi-piston errors of segmented telescope can be detected simultaneously. A mask with a sparse multi-subaperture configuration is set in the exit pupil of the segmented telescope. One subaperture matches to one segment and samples the wave-front reflected by this segment. Coherent diffraction patterns, produced by each pair of the wave-fronts, are recorded as point spread function (PSF). A Fourier transform is performed for the PSF to obtain the optical transfer function (OTF). Then, relationship between the piston error and the amplitudes of the MTF sidelobes is derived. The piston error can be retrieved accurately by this relationship, and the capture range is the coherent length of the operating light. The key to realize a multi-piston errors simultaneous detection using this relationship is to avoid overlap of the MTF sidelobes which formed by each pair of subwaves. We research and derive the MTF model of a mask with a sparse multi-subaperture configuration. According to Fourier optics principle, the MTF distribution of this model is analyzed, and rules for the MTF sidelobes non-redundant distribution are obtained. Simulations have been done to validate the rules. Taking an 18-segment mirror as an example, a mask with a sparse 18 sub-apertures configuration is designed to realize the MTF sidelobes non-redundant distribution. Thus, just need to set a mask with a sparse multi-subaperture configuration in the conjugate plane of the segmented mirror, the piston errors of the full aperture can be retrieved simultaneously.