Papers by Keyword: Subpixel

Abstract: This paper will develop an automatic and fast optical measurement system for high density optical fiber connector measurement, which base on the optical project method. It will meet the lot of optical fiber connector measurement need. This system includes a high intensity and high collimated LED source, a high accuracy and high stiffness linear stage, 2 multi-degree-of-freedom adjustment mechanisms and a high resolution coaxial telecentric imaging system and image processing software. The system of measurement results and commercial measuring instruments comparing the results of its error is less than 0.6μm. To measure a V groove needs 750ms, this result may satisfy the requirements of automatic inspection.

Abstract: To realize the target of having a precise feature size measurement of multihole sheet metal part, this paper based on HALCON, first calibrates the camera with HALCON's calibration assistant. After acquiring the image of the multihole sheet metal part, the image coordinates of the center of fitting ellipse and the length of the long and short half shaft (pixel unit) can be gotten by proceeding a series of operations like thresholding, subpixel-precise contour extraction, fitting ellipses and so on. At last, the point coordinates in image are transformed into the plane Z=0 of the world coordinate system through translation and rotation, and the value of each feature size of the sheet metal part can be calculated.

Abstract: Subpixel technique of linear CCD is effective to enhance the spatial resolution without increasing the focal length of optics and reducing the pixel size. To compare image quality of two main subpixel imaging modes, quincunx sampling and four-point sampling, a method to quantitatively evaluate image quality of subpixel based on MTF was proposed. The MTF of quincunx and four-point sampling modes were derived. Analytical results shows that theoretical limiting resolution of quincunx sampling and four-point sampling is improved to 1.4 and 1.86 times respectively, and MTF values at Nyquist frequency of two modes are increased by 0.1106 and 0.1679, respectively. MTFA in (0, 0.5) of two subpixel imaging modes were calculated and results illustrates that four-point sampling offers much more improvement with image quality than quincunx sampling, at the cost of double amount of data. A model for simulating subpixel imaging using Matlab was established, and simulation results of spoke target verify the theoretical analysis.

Abstract: The purpose of this paper is to develop a tool image inspection and measuring system by C++ Builder. Firstly, tool images are captured online for geometry analysis via a disassembled inspection mechanism mounted on the Z-axis of a five-axis tool grinding machine. One can use the controller of the machine to set the coordinate location of the mechanism and implement the humanized functions of autofocusing and automatic measurements. The digital images are calculated by the subpixel approach to improve the measurement resolution, and filtered the edge point location by Hough transform to upgrade the precision. The human machine interface (HMI) has a tutoring manner for users to operate the measuring procedures. These proposed functions can measure the geometric dimension such as the diameter, radius, and angle of different end mills or drills after finishing the tool grinding processes. Furthermore, the grinding processes can refer the online measured results to compensate the tool dimension. Therefore, this online image inspection and measuring system can improve the precision of tool grinding, product quality, and reduce the product cost. Finally, experiments are presented to show that the repeatability errors are ± 2 μm and ± 1 μm for the diameter and the radius measurements of end mills, respectively. The percentage error is 0.116％ for measuring the point angle of a drill. Thus, the results demonstrate the effectiveness of the proposed method that can be employed to measure tool geometry of different cutting tools.

Abstract: The accuracy of edge detection determines the accuracy of actual dimension measurement，in order to improve the measuring accuracy, this paper proposes a fast algorithm of detecting the glass bottle dimension based on Zernike moments. Firstly, combines the traditional Zernike moment-based method with Otsu adaptive threshold algorithm and a new fast algorithm for edge detection is proposed. Then uses this fast algorithm to detect the edge of glass bottle with subpixel-level and uses the least square method to fit ellipses formed by the glass bottle mouth and bottom. Calibrated the system with standard gauge block and obtain the actual dimension at last. Experimental results show that the improved algorithm not only can make the edge detection reach the subpixel-level accuracy, but also can avoid the edge misidentification and inefficient causing by repeatedly manual adjustments to select the threshold value when detecting the edge. Making a rapid, accurate, non-contact measuring system becomes a reality.

Abstract: This study breaks through traditional displacement and inclination monitoring methods in excavation engineering, and proposes for the first time that combining excavation engineering with subjects such as Iconology, Signal Processing and Wireless Sensor Network, use Digital Signal Processing, Digital Image Processing, and Micro-Displacement Sensing technology for monitoring and processing various types of displacement. Then collect all monitoring points’ information through Internet of Things technology into database processing platform for processing, in order to achieve automatic real-time monitoring.

Abstract: Aiming at the subpixle edge detection of speckle in autofocus for micro-machine vision, a novel accurate subpixel edge detection algorithm was proposed. The image of the part to be inspected was binaried by simple threshold algorithm. The noise in image was eliminated by blob area threshold algorithm. The pixel level edge detection was done and the single-pixel width connected pixel level contour was acquired by binary mathematical morphological algorithm. The subpixel level edge detection was completed and the subpixel level contour was obtained by 9×9 pixel rectangular lens algorithm based on cubic spline interpolation. The example result indicate that calculation speed of the algorithm proposed herein is fast, anti-noise performance is high, inspection accuracy is high, and subpixel edge location accuracy can reach to μm level.

Abstract: The realization of strain measurement based on digital image processing technique is discussed. Combined with the strain measurement principle and the optical imaging feature, considered the axisymmetrical and non-axisymmetrical distortion, the automatic surface-fitting calibration method based on region growing is adopted. Cubic polynomial is applied to establish the relationship between the object space and pixel coordinate system. The expectations based on wavelet coefficients are used for sub-pixel edge detection, measurement accuracy can reach 0.02 pixels. Accuracy of displacement for strain measurement achieves micrometer-level. The theoretic validity and practical feasibility of the system are proved by the strain measurement of a cantilever steel beam.

Abstract: Image analysis was used to evaluate the curve grinding process. The measurement system organization and its principle of operation were introduced. Some key technologies that influence the system precision were also studied in details. Real-time image of work piece and wheel grinding can be gathered while using CCD camera. For image de-noising, a kind of wavelet threshold function was presented to calculate the new wavelet coefficients. Local threshold algorithm was used to compute different scale threshold, another threshold is suggested when MSE is minimum. Image signals are reconstructed through invert discrete wavelet transformation with the new wavelet coefficients. For the purpose of increasing the measurement precision, a closed mathematical model of sub-pixel edge detection operator was founded according to the gray moment operator’s invariant characteristics and Tabatabai’s first three sample gray moments. An application of system validity and the comparison results of work piece were also given. From experiments it can be said that the proposed method in this paper is effective, and its detection precision and results are reasonable.

Abstract: A CCD on-line image measurement system for curve grinding was schemed out according to the working process. Real-time images of work piece and wheel grinding can be gathered while using synchronal control and outer trigger technology. For the purpose of increasing the measurement precision, we presented a new method for locating edges in digital images to sub-pixel values based on local interpolation and spline fitting. An application of its validity and the comparison results of grinding wheel wear are also given. Experiments show that the proposed method in this paper is effective, and its detection precision and results are reasonable.