Proceedings Volume 10023

Optical Metrology and Inspection for Industrial Applications IV

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Proceedings Volume 10023

Optical Metrology and Inspection for Industrial Applications IV

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Volume Details

Date Published: 19 January 2017
Contents: 10 Sessions, 58 Papers, 0 Presentations
Conference: SPIE/COS Photonics Asia 2016
Volume Number: 10023

Table of Contents

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Table of Contents

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  • Front Matter: Volume 10023
  • Optical Metrology Methods I
  • Optical Metrology Methods II
  • Optical Metrology Methods III
  • Optical Metrology Methods IV
  • Optical Metrology Methods V
  • Optical Metrology Methods VI
  • Optical Metrology Applications I
  • Optical Metrology Applications II
  • Poster Session
Front Matter: Volume 10023
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Front Matter: Volume 10023
This PDF file contains the front matter associated with SPIE Proceedings Volume 10023, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.
Optical Metrology Methods I
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Software system design for the non-null digital Moiré interferometer
Meng Chen, Qun Hao, Yao Hu, et al.
Aspheric optical components are an indispensable part of modern optics systems. With the development of aspheric optical elements fabrication technique, high-precision figure error test method of aspheric surfaces is a quite urgent issue now. We proposed a digital Moiré interferometer technique (DMIT) based on partial compensation principle for aspheric and freeform surface measurement. Different from traditional interferometer, DMIT consists of a real and a virtual interferometer. The virtual interferometer is simulated with Zemax software to perform phase-shifting and alignment. We can get the results by a series of calculation with the real interferogram and virtual interferograms generated by computer. DMIT requires a specific, reliable software system to ensure its normal work. Image acquisition and data processing are two important parts in this system. And it is also a challenge to realize the connection between the real and virtual interferometer. In this paper, we present a software system design for DMIT with friendly user interface and robust data processing features, enabling us to acquire the figure error of the measured asphere. We choose Visual C++ as the software development platform and control the ideal interferometer by using hybrid programming with Zemax. After image acquisition and data transmission, the system calls image processing algorithms written with Matlab to calculate the figure error of the measured asphere. We test the software system experimentally. In the experiment, we realize the measurement of an aspheric surface and prove the feasibility of the software system.
FPGA-based real-time phase measuring profilometry algorithm design and implementation
Guomin Zhan, Hongwei Tang, Kai Zhong, et al.
Phase measuring profilometry (PMP) has been widely used in many fields, like Computer Aided Verification (CAV), Flexible Manufacturing System (FMS) et al. High frame-rate (HFR) real-time vision-based feedback control will be a common demands in near future. However, the instruction time delay in the computer caused by numerous repetitive operations greatly limit the efficiency of data processing. FPGA has the advantages of pipeline architecture and parallel execution, and it fit for handling PMP algorithm. In this paper, we design a fully pipelined hardware architecture for PMP. The functions of hardware architecture includes rectification, phase calculation, phase shifting, and stereo matching. The experiment verified the performance of this method, and the factors that may influence the computation accuracy was analyzed.
Elongation measurement using 1-dimensional image correlation method
Aim of this paper was to study, setup, and calibrate an elongation measurement by using 1- Dimensional Image Correlation method (1-DIC). To confirm our method and setup correctness, we need calibration with other methods. In this paper, we used a small spring as a sample to find a result in terms of spring constant. With a fundamental of Image Correlation method, images of formed and deformed samples were compared to understand the difference between deformed process. By comparing the location of reference point on both image’s pixel, the spring's elongation were calculated. Then, the results have been compared with the spring constants, which were found from Hooke’s law. The percentage of 5 percent error has been found. This DIC method, then, would be applied to measure the elongation of some different kinds of small fiber samples.
Spindle error motion measurement using concentric circle grating and sinusoidal frequency-modulated semiconductor lasers
Masato Higuchi, Thanh-Tung Vu, Masato Aketagawa
The conventional method of measuring the radial, axial and angular spindle motion is complicated and needs large spaces. Smaller instrument is better in terms of accurate and practical measurement. A method of measuring spindle error motion using a sinusoidal phase modulation and a concentric circle grating was described in the past. In the method, the concentric circle grating with fine pitch is attached to the spindle. Three optical sensors are fixed under grating and observe appropriate position of grating. The each optical sensor consists of a sinusoidal frequency modulated semiconductor laser as the light source, and two interferometers. One interferometer measures an axial spindle motion by detecting the interference fringe between reflected beam from fixed mirror and 0th-order diffracted beam. Another interferometer measures a radial spindle motion by detecting the interference fringe between ±2nd-order diffracted beams. With these optical sensor, 3 axial and 3 radial displacement of grating can be measured. From these measured displacements, axial, radial and angular spindle motion is calculated concurrently. In the previous experiment, concurrent measurement of the one axial and one radial spindle displacement at 4rpm was described. In this paper, the sinusoidal frequency modulation realized by modulating injection current is used instead of the sinusoidal phase modulation, which contributes simplicity of the instrument. Furthermore, concurrent measurement of the 5 axis (1 axial, 2 radial and 2 angular displacements) spindle motion at 4000rpm may be described.
Optical Metrology Methods II
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Concentricity calibration of photogrammetry retro-reflector target
Hengzheng Wei, Weinong Wang, Limei Pei, et al.
Close range digital photogrammetry is being widely used in industrial measurements. The measurements are usually carried out with a mobile retro-reflector target, which is consists of a shaft and reflective target fixed in the center of the shaft. When the center of the target and the axis of the shaft is not consistent, it will introduce measurement error. Therefore, the concentricity of target is an important parameter for the measurement results. To achieve the concentricity of retro-reflector target a multi-sensor coordinate measurement machine with imaging probe and touch probe is used. In this combined measurement system the touch probe measure the axis of the shaft, and imaging probe measure the center of reflective target. An artifact is designed to evaluate the performance of combined system. This artifact is defined as a sharp edged hole in a metal plate. It is suitable to measure with touch probe as well as imaging probe. The touch probe measures 25 points on the hole and then with the imaging probe. With all the points measured by two kinds of probe the evaluation parameters including combination size error, form error and location error are calculated. These parameters are consistent with the ISO standard 10360-9. It indicates that combined measurement uncertainty is 3.2 microns which can meet the calibration requirements of target concentricity.
A field calibration method to eliminate the error caused by relative tilt on roll angle measurement
The roll angle measurement method based on a heterodyne interferometer is an efficient technique for its high precision and environmental noise immunity. The optical layout bases on a polarization-assisted conversion of the roll angle into an optical phase shift, read by a beam passing through the objective plate actuated by the roll rotation. The measurement sensitivity or the gain coefficient G is calibrated before. However, a relative tilt between the laser and objective plate always exist due to the tilt of the laser and the roll of the guide in the field long rail measurement. The relative tilt affect the value of G, thus result in the roll angle measurement error. In this paper, a method for field calibration of G is presented to eliminate the measurement error above. The field calibration layout turns the roll angle into an optical path change (OPC) by a rotary table. Thus, the roll angle can be obtained from the OPC read by a two-frequency interferometer. Together with the phase shift, an accurate G in field measurement can be obtained and the measurement error can be corrected. The optical system of the field calibration method is set up and the experiment results are given. Contrasted with the Renishaw XL-80 for calibration, the proposed field calibration method can obtain the accurate G in the field rail roll angle measurement.
The study of fast measurement hexahedron verticality error by wavefront interferometer
Shijun Peng, Songtao Gao, Dongcheng Wu, et al.
This paper proposes a method to measure hexahedron vertical error based on wavefront interferometer and collimator. The setup of the measurement system and measurement steps is described. Comparing the vertical error of the same hexahedral surface adjacent measured by coordinate measurement machine, the validity of the measurement method is verified. Then not only the verticality error, but also form and shape error data of the two measured surface can be derived. The verticality error of adjacent surface is measured by the combination measurement method. Then surface figure error data for the two surfaces is measured by wavefront interferometer. The form and shape error data of one surface relative to the other can be obtained by added the verticality error to the surface figure error. This is very important in the part's error correction machining process. The effectiveness of the processing method has been verified by experiment. This method can achieve high measurement accuracy of 0.5″ and can be extended to high-precision shape and position errors measurement for other polyhedral parts.
Performance analysis of three-dimensional surface profilometry using a MEMS mirror
Accurate 3-D shape measurement has played an increasingly important role in various diverse industrial applications, such as manufacturing, robot vision etc. To achieve a low cost, compact 3D profiling system, a phase shifting scheme with a single MEMS scanner has been proposed and studied by some international colleagues. In this paper, we establish mathematical model for the 3D profiling system to reconstruct surface contour of the object. A data processing flow chart is designed, and the algorithm is developed correspondingly, in which some means to improve accuracy are also taken into consideration. Then, numerical simulation for the whole work process of the profiling system is performed according to the theoretical model. The simulation results are analyzed in detail to get the optimal parameters. In order to verify the feasibility of the scheme, we build an experimental setup and carry out a series of experiments. The results show that the RMSE is about 6% and the range resolution is about a few millimeters.
Quadrant-division technique for differential sensitivity optical beam measurement
A novel method for optical beam collimation measurement is presented. The collimating lens is utilized in four parts of quadrants with the beam aligned onto the first quadrant and configured to pass the subsequent quadrants. This allows the test beam to pass the collimating lens for four times. Subsequently, the test beam is reversed to achieve a total number of eight passes. Hence, for a defocus introduced, the collimation state of the test beam can be evaluated at the amplification of eight. The evaluation of the test beam is performed based on the approach of collimation testing using lateral shearing interferometer. The proposed technique provides a differential collimation sensitivity for accurate setting of a highly collimated beam.
Optical Metrology Methods III
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Precision requirements and innovative manufacturing for ultrahigh precision laser interferometry of gravitational-wave astronomy
Wei-Tou Ni, Sen Han, Tao Jin
With the LIGO announcement of the first direct detection of gravitational waves (GWs), the GW Astronomy was formally ushered into our age. After one-hundred years of theoretical investigation and fifty years of experimental endeavor, this is a historical landmark not just for physics and astronomy, but also for industry and manufacturing. The challenge and opportunity for industry is precision and innovative manufacturing in large size – production of large and homogeneous optical components, optical diagnosis of large components, high reflectance dielectric coating on large mirrors, manufacturing of components for ultrahigh vacuum of large volume, manufacturing of high attenuating vibration isolation system, production of high-power high-stability single-frequency lasers, production of high-resolution positioning systems etc. In this talk, we address the requirements and methods to satisfy these requirements. Optical diagnosis of large optical components requires large phase-shifting interferometer; the 1.06 μm Phase Shifting Interferometer for testing LIGO optics and the recently built 24” phase-shifting Interferometer in Chengdu, China are examples. High quality mirrors are crucial for laser interferometric GW detection, so as for ring laser gyroscope, high precision laser stabilization via optical cavities, quantum optomechanics, cavity quantum electrodynamics and vacuum birefringence measurement. There are stringent requirements on the substrate materials and coating methods. For cryogenic GW interferometer, appropriate coating on sapphire or silicon are required for good thermal and homogeneity properties. Large ultrahigh vacuum components and high attenuating vibration system together with an efficient metrology system are required and will be addressed. For space interferometry, drag-free technology and weak-light manipulation technology are must. Drag-free technology is well-developed. Weak-light phase locking is demonstrated in the laboratories while weak-light manipulation technology still needs developments.
An automatic large-scale 3D coordinate measurement system based on vision guidance
An automatic large-scale 3D coordinate measurement system based on vision guidance is presented. With a high-accuracy total station accomplishing the basic coordinate measurement, a camera mounted on the total station is used to scan the measuring field. The camera can identify the target in the viewing field and provide its azimuth information for the total station to aim at it automatically. Thus high-accuracy non-contact measurement can be accomplished without additional effort for targeting. The results showed that the measurement system can realize automatic large-scale measurement precisely and efficiently which provides an efficient approach for solving automatic large-scale measurement problems.
Fast in-situ tool inspection based on inverse fringe projection and compact sensor heads
Steffen Matthias, Markus Kästner, Eduard Reithmeier
Inspection of machine elements is an important task in production processes in order to ensure the quality of produced parts and to gather feedback for the continuous improvement process. A new measuring system is presented, which is capable of performing the inspection of critical tool geometries, such as gearing elements, inside the forming machine. To meet the constraints on sensor head size and inspection time imposed by the limited space inside the machine and the cycle time of the process, the measuring device employs a combination of endoscopy techniques with the fringe projection principle. Compact gradient index lenses enable a compact design of the sensor head, which is connected to a CMOS camera and a flexible micro-mirror based projector via flexible fiber bundles. Using common fringe projection patterns, the system achieves measuring times of less than five seconds. To further reduce the time required for inspection, the generation of inverse fringe projection patterns has been implemented for the system. Inverse fringe projection speeds up the inspection process by employing object-adapted patterns, which enable the detection of geometry deviations in a single image. Two different approaches to generate object adapted patterns are presented. The first approach uses a reference measurement of a manufactured tool master to generate the inverse pattern. The second approach is based on a virtual master geometry in the form of a CAD file and a ray-tracing model of the measuring system. Virtual modeling of the measuring device and inspection setup allows for geometric tolerancing for free-form surfaces by the tool designer in the CAD-file. A new approach is presented, which uses virtual tolerance specifications and additional simulation steps to enable fast checking of metric tolerances. Following the description of the pattern generation process, the image processing steps required for inspection are demonstrated on captures of gearing geometries.
Numerical simulation research and applications on scattering imaging of surface defects on optical components
Huiting Chai, Pin Cao, Yongying Yang, et al.
The principle of microscopic scattering dark-field imaging is adopted in surface defects evaluation system (SDES) for large fine optics. However, since defects are of micron or submicron scale, scattering imaging cannot be described simply by geometrical imaging. In this paper, the simulation model of the electromagnetic field in defect scattering imaging is established on the basis of Finite-Difference Time-Domain (FDTD) method to study the scattering imaging properties of rectangular and triangular defects with different sizes by simulation. The criterion board with scribed lines and dots on it is used to carry out experiments scattering imaging and obtain grayscale value distributions of scattering dark-field images of scribed lines. The experiment results are in good agreement with the simulation results. Based on the above analysis, defect width extraction width is preliminary discussed. Findings in this paper could provide theoretical references for defect calibration in optical fabrication and inspection.
Optical Metrology Methods IV
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Spin Hall effect of light applied in optical linear scale
We propose a linear scale of carbon nanotube (CNT) detected by the spin Hall effect of light (SHEL). The SHEL is a phenomena about a correlation between spin angular momentum and orbital angular momentum. When the light reflects on a surface of a dielectric surface, the SHEL gives a slightly position changing of the light about sub-10-nm scale and devides light to two polarized lights. On the other hand, CNT has giant circular dichroism. By re ection on a dielectric surface with the CNT, there is absorption for one of the lights generated by the SHEL and amount of the absorption depends on a position of the CNT. In this paper, we have measured the SHEL via weak measurement by detecting 2D distribution of lights. As a results, distance of two beams generated by the SHEL was about 80nm.
Accurate reconstruction in measurement of microstructures using digital holographic microscopy
Xiaolei Zhang, Xiangchao Zhang, Hong Xiao, et al.
Due to the limitation of traditional interferometry, digital holographic microscopy has attracted intensive attention for its capability of measuring complex shapes. However, speckles are inevitable in the recorded interferometric patterns, thereby polluting the reconstructed surface topographies. In this paper, a phase-shifting interferometer is built to realize the in-axis digital holographic microscopy. The anti-aliasing shift-invariant contourlet transform (ASCT) is used for reconstructing the measured surfaces. By avoiding subsampling in the scale and directional filtering schemes, the problems of frequency aliasing and phase distortion can be effectively solved. Practical experiments show that speckles can be recognized and removed straightforwardly. Therefore the proposed method has excellent performance for reconstructing structured surfaces.
Tip/tilt-compensated through-focus scanning optical microscopy
Jun Ho Lee, Jun Hyung Park, Dohwan Jeong, et al.
Through-Focus Optical Microscopy (TSOM), with nanometer scale lateral and vertical sensitivity matching those of scanning electron microscopy, has been demonstrated to be utilized for 3D inspection and metrology. There have been sensitivity and instability issues in acquiring through-focus images because TSOM 3D information is indirectly extracted by differentiating a target TSOM image from reference TSOM images. This paper first reports on the optical axis instability that occurs during the scanning process of TSOM when implemented in an existing patterned wafer inspection tool by moving the wafer plane; this is followed by quantitative confirmation of the optical/mechanical instability using a new TSOM tool on an optical bench with a Shack-Hartmann wavefront sensor and a tip/tilt sensor. Then, this paper proposes two tip/tilt compensated TSOM optical acquisition methods that can be applied with adaptive optics. The first method simply adopts a tip/tilt mirror with a quad cell in a simple closed loop, while the second method adopts a highorder deformable mirror with a Shack-Hartmann sensor. The second method is able to correct high-order residual aberrations as well as to perform through-focus scanning without z-axis movement, while the first method is easier to implement in pre-existing wafer inspection systems with only minor modification.
The total spectral radiant flux calibration using a spherical spectrometer at National Institute of Metrology China
At present day, in the field of lighting the incandescent lamps are phasing out. The solid state lighting products, i.e. LED, and the related market are developing very fast in China for its promising application, due to the energy-saving and the colorful features. For the quality control and the commercial trade purpose, it is highly necessary to measure the optical parameters of LED light sources with a fast, easy and affordable facility. Therefore, more test labs use the spherical spectrometer to measure LED. The quasi- monochrome of LED and the V(lambda) of silicon photodetector mismatch problem is reduced or avoided, because the total spectral radiant flux (TSRF) is measured, and all the optical parameters are calculate from the TSRF. In such a way, the spherical spectrometer calibration requires TSRF standard lamps instead of the traditional total flux standard lamps. National Institute of Metrology China (NIM) has studied and developed the facilities for TSRF measurement and provides related calibration services. This paper shows the TSRF standard lamp calibration procedure using a spherical spectrometer in every-day calibration and its traceable link to the primary SI unit at NIM. The sphere is of 1.5 m diameter, and installed with a spectrometer and a silicon photodetector. It also shows the detail of data process, such as the spectral absorption correction method and the calculation of the result derived from the spectral readings. The TSRF calibration covers the spectra range of 350 nm to 1050 nm, with a measurement uncertainty of 3.6% ~ 1.8% (k=2).
Optical Metrology Methods V
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Binocular stereo vision system based on phase matching
Huixian Liu, Shujun Huang, Nan Gao, et al.
Binocular stereo vision is an efficient way for three dimensional (3D) profile measurement and has broad applications. Image acquisition, camera calibration, stereo matching, and 3D reconstruction are four main steps. Among them, stereo matching is the most important step that has a significant impact on the final result. In this paper, a new stereo matching technique is proposed to combine the absolute fringe order and the unwrapped phase of every pixel. Different from traditional phase matching method, sinusoidal fringe in two perpendicular directions are projected. It can be realized through the following three steps. Firstly, colored sinusoidal fringe in both horizontal (red fringe) and vertical (blue fringe) are projected on the object to be measured, and captured by two cameras synchronously. The absolute fringe order and the unwrapped phase of each pixel along the two directions are calculated based on the optimum three-fringe numbers selection method. Then, based on the absolute fringe order of the left and right phase maps, stereo matching method is presented. In this process, the same absolute fringe orders in both horizontal and vertical directions are searched to find the corresponding point. Based on this technique, as many as possible pairs of homologous points between two cameras are found to improve the precision of the measurement result. Finally, a 3D measuring system is set up and the 3D reconstruction results are shown. The experimental results show that the proposed method can meet the requirements of high precision for industrial measurements.
Algorithms and applications of aberration correction and American standard-based digital evaluation in surface defects evaluating system
Fan Wu, Pin Cao, Yongying Yang, et al.
The inspection of surface defects is one of significant sections of optical surface quality evaluation. Based on microscopic scattering dark-field imaging, sub-aperture scanning and stitching, the Surface Defects Evaluating System (SDES) can acquire full-aperture image of defects on optical elements surface and then extract geometric size and position information of defects with image processing such as feature recognization. However, optical distortion existing in the SDES badly affects the inspection precision of surface defects. In this paper, a distortion correction algorithm based on standard lattice pattern is proposed. Feature extraction, polynomial fitting and bilinear interpolation techniques in combination with adjacent sub-aperture stitching are employed to correct the optical distortion of the SDES automatically in high accuracy. Subsequently, in order to digitally evaluate surface defects with American standard by using American military standards MIL-PRF-13830B to judge the surface defects information obtained from the SDES, an American standard-based digital evaluation algorithm is proposed, which mainly includes a judgment method of surface defects concentration. The judgment method establishes weight region for each defect and adopts the method of overlap of weight region to calculate defects concentration. This algorithm takes full advantage of convenience of matrix operations and has merits of low complexity and fast in running, which makes itself suitable very well for highefficiency inspection of surface defects. Finally, various experiments are conducted and the correctness of these algorithms are verified. At present, these algorithms have been used in SDES.
Signal processing in white-light scanning interferometry by Fourier transform and its application to surface profile measurements
Songjie Luo, Yongxin Liu, Osami Sasaki, et al.
A general equation of the interference signal of white-light scanning interferometer (WSI) and its Fourier transform are derived. Based on these equations, simulations and experiments are performed to investigate effects of phase random noise and dispersion phase. In the experiments a new method for elimination of a dispersion effect in WSI is proposed. A dispersion phase caused by the two sides of unequal length in a beam-splitter is detected with a spectrally resolved interferometer (SRI). A spectral distribution is obtained by using Fourier transform from an interference signal detected with a WSI. The spectral phase of the SRI is subtracted from the spectral phase of the WSI to get a dispersion-free spectral phase, which provides an improved complex-valued interference signal whose maximum amplitude and zero phase provide two measurement values. These two measurement values are compared to a measurement value obtained from the linear component in the spectral phase.
Calibration of angle-measurement system for direction measurements
Yu. V. Filatov, E. D. Bohkman, P. A. Ivanov, et al.
The report presents the results of experimental research of the angle measurement system intended for measuring angles between normal to some mirrors setting directions in the space. Dynamic mode of system operation is defined by continuous rotation of platform with the autocollimating null-indicator. The angle measurements are provided by the holographic optical encoder. The different ways of calibration of the system is considered in the report. The results of the system calibration with the chosen method are presented.
Optical Metrology Methods VI
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Full-field 3D shape measurement of specular surfaces by direct phase to depth relationship
Zonghua Zhang, Yue Liu, Shujun Huang, et al.
This paper presents a new Phase Measuring Deflectometry (PMD) method to measure specular object having discontinuous surfaces. A mathematical model is established to directly relate absolute phase and depth, instead of phase and gradient. Based on the model, a hardware measuring system has been set up, which consists of a beam splitter to change the optical path, and two LCD screens to display the same sinusoidal fringe patterns. By using model-based and machine vision method, system calibration is accomplished to provide the required parameters and conditions. The verification tests are given to evaluate the effectiveness of the developed system. The 3D shape of an artificial step having multiple specular surfaces and a concave mirror has been measured. Initial experimental results show that the proposed measurement method can obtain 3D shape of specular objects with discontinuous surface effectively.
Three-dimensional surface inspection for semiconductor components with fringe projection profilometry
Fuqin Deng, Yi Ding, Kai Peng, et al.
With the increasing integration level of components in modern electronic devices, three-dimensional automated optical inspection has been widely used in the manufacturing process of electronic and communication industries to improve the product quality. In this paper, we develop a three-dimensional inspection and metrology system for semiconductor components with fringe projection profilometry, which is composed of industry camera, telecentric lens and projection module. This system is used to measure the height, flatness, volume, shape, coplanarity for quality checking. To detect the discontinuous parts in the internal surface of semiconductor components, we employ the fringes with multiple spatial frequencies to avoid the measurement ambiguity. The complete three-dimensional information of semiconductor component is obtained by fusing the absolute phase maps from different views. The practical inspection results show that the depth resolution of our system reaches 10 μm . This system can be further embedded for the online inspection of various electronic and communication products.
Measurement uncertainty evaluation of the three degree of freedom surface encoder
Kai Ni, Huanhuan Wang, Xinghui Li, et al.
A three-DOF surface encoder can be used to measure the three translational degree of freedom (DOF) displacement of a moving table. A measurement uncertainty of the developed three-DOF surface encoder was systematically investigated to confirm its feasibility on the precision positioning of planar motion stage. An expanded uncertainty of 124.4 nm has been calculated in the measurement results of testing three-axis translational motions over a range of 2.5 μm. Among those error sources, cross-talk errors caused by misalignment existing in experimental setup were identified to be the largest error source.
An accurate approach for calibrating rotational angle of camera
In order to obtain the scene information of a larger or 360 degrees field of view, it is necessary to accurately know the rotational angle of a camera around a fixed axis, which directly affects the quality of point cloud registration and integration. This paper presents a novel rotational angle calibration method by using an extra large viewing-angle camera and high precise checkerboard. The large viewing-angle camera is fixed and has the same imaging direction as the calibrated camera. The checkerboard is placed in front of the two cameras to determine their relative positions. The experimental results show that the error between the actual rotational angle and the calibration result is below 0.0959 degrees. The proposed calibration method can accurately and effectively obtain the rotational angle of a camera.
Optical Metrology Applications I
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Embedded 3D shape measurement system based on a novel spatio-temporal coding method
Bin Xu, Jindong Tian, Yong Tian, et al.
Structured light measurement has been wildly used since 1970s in industrial component detection, reverse engineering, 3D molding, robot navigation, medical and many other fields. In order to satisfy the demand for high speed, high precision and high resolution 3-D measurement for embedded system, a new patterns combining binary and gray coding principle in space are designed and projected onto the object surface orderly. Each pixel corresponds to the designed sequence of gray values in time – domain, which is treated as a feature vector. The unique gray vector is then dimensionally reduced to a scalar which could be used as characteristic information for binocular matching. In this method, the number of projected structured light patterns is reduced, and the time-consuming phase unwrapping in traditional phase shift methods is avoided. This algorithm is eventually implemented on DM3730 embedded system for 3-D measuring, which consists of an ARM and a DSP core and has a strong capability of digital signal processing. Experimental results demonstrated the feasibility of the proposed method.
Imaging ellipsometer with large field-of-view
Liyuan Gu, Aijun Zeng, Shiyu Hu, et al.
A polarizer-compensator-sample-analyzer (PCSA) imaging ellipsometer with large field of view is presented. The sample is imaged on a CCD sensor by a telecentric imaging system and its tilt is monitored by an optical autocollimator. The sample, the telecentric imaging system and the CCD sensor satisfy the Scheimpflug condition. In measurement, the light extinction measurement method and the four quadrants average method are used to improve the accuracy. In experiments, a chromium thin film sample is measured by the imaging ellipsometer and a spectroscopic ellipsometer. The measurement results by two ellipsometers are consistent. The usefulness of the imaging ellipsometer is verified.
Hybrid probing technique for coordinate measurement with optically trapped micro sphere
Engineered surfaces have been fabricated to provide enhanced properties such as low friction, anti-adhesive behavior, or low reflection of light. At micro-scales, surface force highly affects the functionality of mechanical parts. In order to reduce surface force such as friction, micro mechanical parts that have engineered surfaces are demanded. In order to investigate the functionality of the textured micro parts, it is necessary to evaluate both the three-dimensional shape and the surface topography along with its geometry. Then we propose novel hybrid probing technique using an optically trapped micro sphere. Tightly focused laser beam makes it possible for a dielectric micro sphere to sustain near the focal point in the air. The dynamic behavior of the micro sphere changes as the result of the interaction of the surface. Therefore, the surface is detected by monitoring the micro sphere. This enables the three-dimensional shape measurement of the substrate. On the other hand, Surface topography is imaged with the lensing effect of the trapped micro sphere. Therefore, this trapped sphere is used as both a probe for coordinate metrology and a micro-lens in optical microscopy in this study. This present investigation deals with the development and fundamental validation of the hybrid probing system with the optically trapped micro sphere. The measurement result with high performance was demonstrated using the tilted diffraction grating.
Research on application of photoelectric rotary encoder in space optical remote sensor
Jun Zheng, Shao-fan Qi, Yuan-yuan Wang, et al.
For space optical remote sensor, especially wide swath detecting sensor, the focusing control system for the focal plane should be well designed to obtain the best image quality. The crucial part of this system is the measuring instrument. For previous implements, the potentiometer, which is essentially a voltage divider, is usually introduced to conduct the position in feedback closed-loop control process system. However, the performances of both electro-mechanical and digital potentiometers is limited in accuracy, temperature coefficients, and scale range. To have a better performance of focal plane moving detection, this article presents a new measuring implement with photoelectric rotary encoder, which consists of the photoelectric conversion system and the signal process system. In this novel focusing control system, the photoelectric conversion system is fixed on main axis, which can transform the angle information into a certain analog signal. Through the signal process system, after analog-to-digital converting and data format processing of the certain analog signal, the focusing control system can receive the digital precision angle position which can be used to deduct the current moving position of the focal plane. For utilization of space optical remote sensor in aerospace areas, the reliability design of photoelectric rotary encoder system should be considered with highest priority. As mentioned above, this photoelectric digital precision angle measurement device is well designed for this real-time control and dynamic measurement system, because its characters of high resolution, high accuracy, long endurance, and easy to maintain.
An accurate and reliable circular coded target detection algorithm for vision measurement
Ran Chen, Kai Zhong, Zhongwei Li, et al.
Distributing coded targets on the measured object is a reliable and common method for achieving optimum target location and accurate matching of corresponding targets among multi-view images. The circular coded targets which based on a central circular target surrounded by a coded band is widely used in vision measurement. However, it is difficult to decode the coded target while the number of pixels in the coded band is small or the projection angle is large. Aiming at solve this problem, a detection algorithm using the gray gradient to get the central angles of each coded section was proposed. In this algorithm, an accurate ellipse detection which can get sub-pixel locations was adopted to extract ellipse centers, and some false ellipses whose error in the fit of best fit is large will be rejected. Then, gray gradients in the coded band are calculated to get the central angle of each coded section, and the coded target will be decoded accurately. The experiment results show that the algorithm can locate and identify coded targets accurately under complex measurement conditions.
Optical Metrology Applications II
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An underwater ranging system based on photoacoustic effect occurring on target surface
Kai Ni, Kai Hu, Xinghui Li, et al.
In this paper, an underwater ranging system based on photoacoustic effect occurring on target surface is proposed. In this proposal, laser pulse generated by blue-green laser is directly incident on target surface, where the photoacoustic effect occurs and a sound source is formed. And then the sound wave which is also called photoacoustic signal is received by the ultrasonic receiver after passing through water. According to the time delay between transmitting laser and receiving photoacoustic signal, and sound velocity in water, the distance between the target and the ultrasonic receiver can be calculated. Differing from underwater range finding by only laser, this approach can avoid backscattering of laser beam, so easier to implement. Experimental system according to this principle has been constructed to verify the feasibility of this technology. The experimental results showed that a ranging accuracy of 1 mm can be effectively achieved when the target is close to the ultrasonic receiver.
Rail profile control using laser triangulation scanners
Аlexandr M. Boronahin, Daniil Yu. Larionov, Liudmila N. Podgornaya, et al.
Rail track geometric parameters measurement requires knowledge of left and right rail head location in each section. First of all displacement in transverse plane of rail head point located at a distance of 14 mm below the running surface, must be controlled [1]. It is carried out by detecting of each rail profile using triangulation laser scanners. Optical image recognition is carried out successfully in the laboratory, approaches used for this purpose are widely known. However, laser scanners operation has several features on railways leading to necessity of traditional approaches adaptation for solving these particular problems. The most significant problem is images noisiness due to the solar flashes and the effect of "Moon path" on the smooth rail surface. Using of optical filters gives inadequate result, because scanner laser diodes radiation frequency varies with temperature changes that forbid the use of narrow-band filters. Consideration of these features requires additional constructive and algorithmic solutions, including involvement of information from other sensors of the system. The specific usage of optical scanners for rail profiles control is the subject of the paper.
Non-uniform sampling knife-edge method for camera modulation transfer function measurement
Traditional slanted knife-edge method experiences large errors in the camera modulation transfer function (MTF) due to tilt angle error in the knife-edge resulting in non-uniform sampling of the edge spread function. In order to resolve this problem, a non –uniform sampling knife-edge method for camera MTF measurement is proposed. By applying a simple direct calculation of the Fourier transform of the derivative for the non-uniform sampling data, the camera super-sampled MTF results are obtained. Theoretical simulations for images with and without noise under different tilt angle errors are run using the proposed method. It is demonstrated that the MTF results are insensitive to tilt angle errors. To verify the accuracy of the proposed method, an experimental setup for camera MTF measurement is established. Measurement results show that the proposed method is superior to traditional methods, and improves the universality of the slanted knife-edge method for camera MTF measurement.
A precise reference position detection method for linear encoders by using a coherence function algorithm
Xinghui Li, Xiang Xiao, Kai Ni, et al.
This paper proposed a new method for reference position detection with high precision for linear encoders by using a home designed scale grating and a coherence function algorithm. Differing from the traditional methods, in which the reference position alignment and calibration of reference position was achieved by detecting the peak of the signal with a negative pulse at the reference position, the method in this paper no longer detects the single peak of the signal, but matching and aligning the integral shape of reference position signal through the algorithm based on the coherence function. The proposed method does not require a complex design and precision manufacturing of reference position. Due to the coherence function algorithm, a multi-pulse reference position signals design is available, which not only reduces the difficulty of reference position design and manufacturing, but also shortens the length of reference position area so that the negative effect on the grating diffraction efficiency is limited. What is more, robustness of the reference detection method introduced here is greatly enhanced. Experimental results show that the accuracy of reference detection can still achieve 2 times of resolution even under the low signal to noise ratio (SNR) of 2dB.
Development of an edge sensor based on polyview optics and laser triangulation principle
Yinan Li, Hagen Bossmeyer, Markus Kästner, et al.
Common 2D laser line triangulation sensors allow a 2D profile measurement in a single line. To scan samples with great curved surfaces like edges, a single laser line triangulation sensor is insufficient. To measure the entire form of such an edge, it normally requires either multiple measurements of one single sensor or a multi sensor system. For this reason, we developed an edge measurement sensor based on an in-house designed polyview optics and the well-known laser triangulation principle. The new developed edge measurement sensor is capable of measuring the object over a 180 field of view (FOV). The configuration, the calibration process and the measurement results of this edge sensor will be discussed in this paper.
Arbitrary optical frequency synthesis traced to an optical frequency comb
An arbitrary optical frequency synthesizer with a broad tuning range and high frequency accuracy is presented. The system includes an external cavity diode laser (ECDL) as the output laser, an Erbium-doped optical frequency comb being a frequency reference, and a control module. The optical frequency from the synthesizer can be continuously tuned by the large-scale trans-tooth switch and the fine intra-tooth adjustment. Robust feedback control by regulating the current and PZT voltage enables the ECDL to phase-lock to the Erbium-doped optical frequency comb, therefore to keep stable frequency output. In the meanwhile, the absolute frequency of the synthesizer is determined by the repetition rate, the offset frequency and the beat frequency. All the phase lock loops in the system are traced back to a Rubidium clock. A powerful and friendly software is developed to make the operation convenient by integrating the functions of frequency setting, tuning, tracing, locking and measuring into a LabVIEW interface. The output frequency tuning span and the uncertainty of the system are evaluated as >6 THz and <3 kHz, respectively. The arbitrary optical frequency synthesizer will be a versatile tool in diverse applications, such as synthetic wavelength based absolute distance measurement and frequency-stabilized Cavity Ring-Down Spectroscopy.
Poster Session
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Dimensional measurement of micro parts with high aspect ratio in HIT-UOI
Micro parts with high aspect ratios have been widely used in different fields including aerospace and defense industries, while the dimensional measurement of these micro parts becomes a challenge in the field of precision measurement and instrument. To deal with this contradiction, several probes for the micro parts precision measurement have been proposed by researchers in Center of Ultra-precision Optoelectronic Instrument (UOI), Harbin Institute of Technology (HIT). In this paper, optical fiber probes with structures of spherical coupling(SC) with double optical fibers, micro focal-length collimation (MFL-collimation) and fiber Bragg grating (FBG) are described in detail. After introducing the sensing principles, both advantages and disadvantages of these probes are analyzed respectively. In order to improve the performances of these probes, several approaches are proposed. A two-dimensional orthogonal path arrangement is propounded to enhance the dimensional measurement ability of MFL-collimation probes, while a high resolution and response speed interrogation method based on differential method is used to improve the accuracy and dynamic characteristics of the FBG probes. The experiments for these special structural fiber probes are given with a focus on the characteristics of these probes, and engineering applications will also be presented to prove the availability of them. In order to improve the accuracy and the instantaneity of the engineering applications, several techniques are used in probe integration. The effectiveness of these fiber probes were therefore verified through both the analysis and experiments.
Simulation of out-of-plane displacement measurement using vortex beam: on the base of liquid crystal spatial light modulator
In ESPI experiment, object beam and reference beam are always planar light. The plane light can be replaced by vortex beam. Vortex beams can be generated by a reflective liquid crystal spatial light modulator (LC-SLM) which added in the optical path. The generated vortex beam can be used as object light or reference light in out-of-plane displacement measurement. The out-of-plane displacement is simulated and analyzed before and after the object deformation. By phase shifting method and unwrapping, the distribution of phase difference is obtained. The simulation results demonstrate the efficacy of the proposed method for the out-of-plane displacement measurements.
Experimental investigation of correlation between surface amplitude parameters of frosted glass diffuser and size of polishing grit
Dong Wei, Tomoya Katagiri, Masato Aketagawa
Frosted glass (FG) diffusers are used for various purposes in optical experiments and are qualitatively classified based on the particle size of the grit used to polish them. Moreover, their surface topographies are known to affect their optical ability. However, a quantitative relationship between the surface topography (especially the surface amplitude parameters) and the polishing grit size is yet to be established. In the present study, a contact-type surface roughness measurement instrument was used to measure the surface amplitude parameters of a variety of commercial FG diffusers. The determined parameters, which are defined in ISO 4287-1997, were then compared with the root mean square of the grit size and the quantitative relationships were investigated. The parameters that were most strongly correlated with the root mean square of the grit size were identified. The established relationships, which statistically reflect the optical properties of an FG diffuser, may be used to optimally select a diffuser for a particular optical experiment or numerical calculation.
A colorful codification method for structured light measurement based on the hue of single image
To measure the shape of object with high-speed and avoid the disturbance of the vibration is remaining challenges faced by structured-light projection method. This paper proposes a high-speed optical metrology by coding three cosine patterns into three channels of RGB model to form the pattern. When the color image is obtained by camera, it will be transformed to HSI color model (hue, saturation and intensity). The hue component is regarded as the phase information to retrieve the 3D shape of object with single image, while the saturation and intensity are applied to avoiding phase errors caused by height steps or spatially isolated surfaces. This method can be used to measure object with non-monochromatic surfaces after the color compensated. Experimental results verify the feasibility of the developed method.
Corner detection and sorting method based on improved Harris algorithm in camera calibration
In traditional Harris corner detection algorithm, the appropriate threshold which is used to eliminate false corners is selected manually. In order to detect corners automatically, an improved algorithm which combines Harris and circular boundary theory of corners is proposed in this paper. After detecting accurate corner coordinates by using Harris algorithm and Forstner algorithm, false corners within chessboard pattern of the calibration plate can be eliminated automatically by using circular boundary theory. Moreover, a corner sorting method based on an improved calibration plate is proposed to eliminate false background corners and sort remaining corners in order. Experiment results show that the proposed algorithms can eliminate all false corners and sort remaining corners correctly and automatically.
3D measurement and camera attitude estimation method based on trifocal tensor
To simultaneously perform 3D measurement and camera attitude estimation, an efficient and robust method based on trifocal tensor is proposed in this paper, which only employs the intrinsic parameters and positions of three cameras. The initial trifocal tensor is obtained by using heteroscedastic errors-in-variables (HEIV) estimator and the initial relative poses of the three cameras is acquired by decomposing the tensor. Further the initial attitude of the cameras is obtained with knowledge of the three cameras’ positions. Then the camera attitude and the interested points’ image positions are optimized according to the constraint of trifocal tensor with the HEIV method. Finally the spatial positions of the points are obtained by using intersection measurement method. Both simulation and real image experiment results suggest that the proposed method achieves the same precision of the Bundle Adjustment (BA) method but be more efficient.
Virtual-stereo fringe reflection technique for specular free-form surface testing
Due to their excellent ability to improve the performance of optical systems, free-form optics have attracted extensive interest in many fields, e.g. optical design of astronomical telescopes, laser beam expanders, spectral imagers, etc. However, compared with traditional simple ones, testing for such kind of optics is usually more complex and difficult which has been being a big barrier for the manufacture and the application of these optics. Fortunately, owing to the rapid development of electronic devices and computer vision technology, fringe reflection technique (FRT) with advantages of simple system structure, high measurement accuracy and large dynamic range is becoming a powerful tool for specular free-form surface testing. In order to obtain absolute surface shape distributions of test objects, two or more cameras are often required in the conventional FRT which makes the system structure more complex and the measurement cost much higher. Furthermore, high precision synchronization between each camera is also a troublesome issue. To overcome the aforementioned drawback, a virtual-stereo FRT for specular free-form surface testing is put forward in this paper. It is able to achieve absolute profiles with the help of only one single biprism and a camera meanwhile avoiding the problems of stereo FRT based on binocular or multi-ocular cameras. Preliminary experimental results demonstrate the feasibility of the proposed technique.
A simple phase-shift ESPI for 3D deformation measurement
Ping Sun, Xinghai Wang, Haibin Sun
A simple setup for 3-D deformation measurement is offered. In the scheme a novel Cube Beam-Splitter, called Non- Cube Beam-Splitter (NCBS), is used for 3-D phase-shift Electronic Speckle Pattern Interferometry (ESPI). By using the NCBS lights from a tested object and lights from a reference surface, the reference and the object light can be combined and then interfere each other on a CCD camera when a laser beam illuminate the test object and the reference surface simultaneously. When three laser beams illuminate the test object at different incident angles respectively before and after deformation, three interference fringe patterns are formed. Then three phase maps corresponding to three lasers can be calculated by using phase-shift, by which three displacement components are completed. The principle of the method is presented and proved by a typical three-point bending experiment. Experimental results are offered.
Evaluation of 3D displacement components by combining DSCM with ESPI
Ping Sun, Kai Shi, Mingyong Sun, et al.
A method for three-dimensional (3-D) deformation measurement is presented by combining Digital Speckle Correlation Method (DSCM) with Electronic Speckle Pattern Interferometry (ESPI). The combination is completed based on a typical ESPI system, in which the reference light is controlled to turn on or shut down. The in-plane displacement components are obtained by using DSCM when the reference light is shut. A phase shifting ESPI is formed when the reference light is used, which can be used for the measurement of the out-plane displacement component. A typical three-point-bending experiment is completed. Experiment results show that the three displacement components can be obtained by the combination effectively.
Numerical calibration of laser line scanning system with multiple sensors for inspecting cross-section profiles
Jingbo Zhou, Yuehua Li, Fengshan Huang, et al.
Line structured light sensors (LSLSs) have gained more and more applications in industry. An interested profile can be easily obtained through the analysis of laser-object intersection stripe. But one sensor is inadequate to get a closed crosssection profile due to the obstacle of the laser light. Thus, multiple LSLSs were integrated as a whole for profile inspection and a numerical calibration method was also proposed. Firstly, the laser planes from all laser projectors were adjusted to coincide with the target plane by adjusting the fixtures of the laser projector. For each sensor, origin of the world coordinate system (WCS) was fixed at the center of a corner calibration dot with its X and Y axis coincide with the row and column direction of target dots. Each sensor camera captured one image of the same target. The relationship between the pixel coordinate system (PCS) and the WCS was established using an interpolation method via the world coordinates of target dot centers and their corresponding pixel coordinates. Then the measurement points from all the sensors were transformed into the global WCS, and a closed cross-section profile can be achieved. This proposed method neither need to establish the intrinsic, the extrinsic and the distortion models of the camera, nor need to solve the complex optimization equations to determine the model coefficients. Finally, a workpeice with stairs and a rectangular block were inspected. The comparison with the measuring results from the coordinate measuring machine further validates the high accuracy of the proposed method.
Uncertainty evaluation of ellipsometer: from instrumentation to material and application in Avogadro's project
Wende Liu, Chi Chen, Qiming Fan, et al.
As directly acquired by ellipsometer, the ellipsometric angles obtain their uncertainties from the instrument. As a metrological tool, one is interest in the derived parameters from the ellipsometric angles, therefore acquiring uncertainties from both instrument and material. As the relative variation of parameters are of interest, ellipsometers are very sensitive and precise. However, for extracting absolute values, calibration by independent method is necessary to elliminate the uncertaintie from the instrument and material. A framework for evaluating the uncertainties from the instrument related parameters, such as the wavelength, bandwidth, the angle of incidence, is given in this work. The framework could facilitate the use of ellipsometer for general measurement of various thin films other than limited type of films like SiO2 or SiNx on Si. For evaluating material related parameters, a typical application in the characterization of surface of silicon sphere is investigated by carefully investigating into the optical constants of sublayers.
Dynamic 3D shape measurement based on digital speckle projection and temporal sequence correlation
Renchao Xu, Fangyan Zhou, Qican Zhang
Based on digital speckle temporal sequence correlation and speckle projection, an experimental platform was developed to measure the dynamic 3D shape measurement in this paper. Speckle patterns generated by computer were projected onto the quartz clock surface by a white-light projector, and the deformed speckle patterns were acquired by a camera. Programming was written to implement the algorithm to reconstruct every motion of the running clock's pointers. Beyond that, a simple Newton's cradle was established, and the collision course between three steel balls was reconstructed. These experimental results show that the method can be used for dynamic 3D shape measurement, which has an effect on the reconstruction of objects with characteristics of steep variation, isolation and small details.
A flexible new method for 3D measurement based on multi-view image sequences
Haihua Cui, Zhimin Zhao, Xiaosheng Cheng, et al.
Three-dimensional measurement is the base part for reverse engineering. The paper developed a new flexible and fast optical measurement method based on multi-view geometry theory. At first, feature points are detected and matched with improved SIFT algorithm. The Hellinger Kernel is used to estimate the histogram distance instead of traditional Euclidean distance, which is immunity to the weak texture image; then a new filter three-principle for filtering the calculation of essential matrix is designed, the essential matrix is calculated using the improved a Contrario Ransac filter method. One view point cloud is constructed accurately with two view images; after this, the overlapped features are used to eliminate the accumulated errors caused by added view images, which improved the camera’s position precision. At last, the method is verified with the application of dental restoration CAD/CAM, experiment results show that the proposed method is fast, accurate and flexible for tooth 3D measurement.
A robust real-time laser measurement method based on noncoding parallel multi-line
Single line scanning is the main method in traditional 3D hand-held laser scanning, however its reconstruction speed is very slow and cumulative error is very large. Therefore, we propose a method to reconstruct the 3D profile by parallel multi-line 3D hand-held laser scanning. Firstly, we process the two images that contain multi-line laser stripes shot by the binocular cameras, and then the laser stripe centers will be extracted accurately. Then we use the approach of stereo vision principle, polar constraint and laser plane constraint to match the laser stripes of the left image and the right image correctly and reconstruct them quickly. Our experimental results prove the feasibility of this method, which improves the scanning speed and increases the scanning area greatly.
Experiments and error analysis of laser ranging based on frequency-sweep polarization modulation
Shuyuan Gao, Rongyi Ji, Yao Li, et al.
Frequency-sweep polarization modulation ranging uses a polarization-modulated laser beam to determine the distance to the target, the modulation frequency is swept and frequency values are measured when transmitted and received signals are in phase, thus the distance can be calculated through these values. This method gets much higher theoretical measuring accuracy than phase difference method because of the prevention of phase measurement. However, actual accuracy of the system is limited since additional phase retardation occurs in the measuring optical path when optical elements are imperfectly processed and installed. In this paper, working principle of frequency sweep polarization modulation ranging method is analyzed, transmission model of polarization state in light path is built based on the theory of Jones Matrix, additional phase retardation of λ/4 wave plate and PBS, their impact on measuring performance is analyzed. Theoretical results show that wave plate’s azimuth error dominates the limitation of ranging accuracy. According to the system design index, element tolerance and error correcting method of system is proposed, ranging system is built and ranging experiment is performed. Experiential results show that with proposed tolerance, the system can satisfy the accuracy requirement. The present work has a guide value for further research about system design and error distribution.
High-speed image acquisition technology in quality detection of workpiece surface
Kaihua Wu, Zexuan Jin, Wenjie Wang, et al.
High-speed image acquisition technology has a great significance to improve the effciency of the workpiece surface quality detection, image quality directly affects the final test results. Aiming at the high-speed image acquisition of workpiece surface quality online detection, a workpiece image high-speed online acquisition method was produced. A high-speed online image acquisition sequence was designed. The quantitative relationship between the positioning accuracy in the high speed online image acquisition, motion blur, exposure time and the speed of workpiece was analyzed. The effect between the vibration between transfer mechanism and workpiece was analyzed. Fast trigger was implemented by photoelectric sensor. The accurate positioning was implemented by using the high accuracy time delay module. The motion blur was controlled by reducing the exposure time. A high-speed image acquisition system was designed based on the high-speed image acquisition method. The positioning accuracy was less than 0.1 mm, and the motion blur was less than one pixel.
The research of weld defect detection based on high precision displacement sensor
Kelin Hu, Chao Gao
Welding is one of the very common process in industrial production. It is a kind of manufacturing process and technology which joint mental or other thermoplastic materials by heating, high temperature or high pressure. Welding quality will directly affect the final quality of workpiece. So during the welding process, each links have strict standard and welding quality evaluation has different indicators. Therefore, how to make a rapid detection to weld defect has become a valuable research. This topic is aimed at weld defect detection of small workpiece. The study contains the selection of sensor, design of detection system, hardware platform, software design, user interface design, etc. In the end, a set of high accuracy detector of weld defect will be designed.
Research of non-contact measurement method for outline dimensions of some special workpiece
Qiaoling Feng, Yongcai Guo
In industrial production, machine vision is widely used in a variety of automated testing industry, because of its non-contact, high precision, fast detection time, etc. This paper introduces a nondestructive detection system for the outline dimensions of a kind of special workpiece. For the purpose of controlling the quality of image,an ultra-high-resolution monochrome CCD image sensor is adopted to capture source image. Then it’s image preprocessing, including image clipping processing, grey scale processing, image denoising, etc. Then it was the progress of edge extraction, using gradient operator to get its contour edge, then a piecewise fitting method to get the dimensions. This method achieves once measuring multiple outline dimensions without moving the workpiece. It has been used in industrial production. The result sees its practical value for meeting the production needs, with the advantages of high accuracy, fast speed high stability of the measurement system through experiments.
GPU-accelerated phase extraction algorithm for interferograms: a real-time application
Xiaoqiang Zhu, Yongqian Wu, Fengwei Liu
Optical testing, having the merits of non-destruction and high sensitivity, provides a vital guideline for optical manufacturing. But the testing process is often computationally intensive and expensive, usually up to a few seconds, which is sufferable for dynamic testing. In this paper, a GPU-accelerated phase extraction algorithm is proposed, which is based on the advanced iterative algorithm. The accelerated algorithm can extract the right phase-distribution from thirteen 1024x1024 fringe patterns with arbitrary phase shifts in 233 milliseconds on average using NVIDIA Quadro 4000 graphic card, which achieved a 12.7x speedup ratio than the same algorithm executed on CPU and 6.6x speedup ratio than that on Matlab using DWANING W5801 workstation. The performance improvement can fulfill the demand of computational accuracy and real-time application.
Study of angle measuring error mechanism caused by rotor run-outs
Dabao Lao, Wenying Zhang, Weihu Zhou
In a rotating angle measuring system, errors of grating sensor, installation and rotor run-outs will affect angle measuring error. The error caused by rotor run-outs is usually the biggest and the hardest to eliminate of them. To improve the accuracy, the table should be fabricated precisely, thus, the table system will be complicated and expensive. This paper provides a method to solve the challenge by using two gratings in the same table, whose gratings respectively grooved on end face and side face. The error mechanism of end face and side face caused by axial and radial rotor run-outs by were deduced. It can be concluded from the analysis that end face grating is sensitive when radial rotor run-outs happens, side face grating is sensitive when axial rotor run-outs happens. Due to the conclusion, combined type gratings with one end face grating and one side face grating can be used to restrain the error caused by Rotor Run-outs of table.
Truncated pyramid artifact for performance evaluation experiments on laser line scanner
Sen Zhou, Jian Xu, Tao Lei, et al.
Non-contact measurement techniques using 3D laser scanning have the power to deliver tremendous benefits to most notably manufacturing, and have the advantage of high speed and high detail output. However, procedures for evaluation and verification of non-contact laser line scanner have not been well-established because of many influencing factors like scan depth, incident angle, probe head orientation and surface properties. A truncated pyramid artifact representation of five- planar with different included angles was designed and used to straightforwardly identify the influence of in-plane and out-of-plane angle, as well as scan depth on dimensional measurement accuracy of the laser scanner. Then, a series of easy, fast and representative experiments, based on this simple artifact, were performed on a commercial laser line scanner, and found that the output of this scanner can be improved for metrology applications after calibration.