Binary pattern defocused projection is a promising method of measuring 3D shapes. However, deep or long-distance defocus prevents high-accuracy 3D measurement. The triangle pattern is preferred because of its slight defocus and ability to overcome the nonlinear gamma. Thus, a novel method combining triangle pattern slight defocus with phase shifting is proposed. The proposed method has two merits: (1) Compared with the sinusoidal pattern, the proposed method can overcome the nonlinear gamma. (2) Compared with the binary pattern, it has the advantage of slightly defocusing to an ideal sinusoidal pattern in a short distance. Thus, the measurement error caused by nonlinear gamma and deep defocus is reduced. The RMS error of the proposed method is <0.03 mm. Theory analysis and experiments demonstrate the feasibility and superiority of the proposed method.
Fringe projection profilometry (FPP) is a rapidly developing technique which is widely used for industrial manufacture, heritage conservation, and medicine etc. because of its high speed, high precision, non-contact operation, full-field acquisition, and easy information processing. Among the various FFP methods, the squared binary defocused projection method (SBM) has been promptly expanding with several advantages: (1) high projection speed because of 1-bit grayscale fringe; (2) eliminating nonlinear gamma of the projector for the defocusing effect. Nevertheless, the method is not trouble-free. When the fringe stripe is wide, it brings down the fringe contrast and is difficult to control the defocused degree, resulting in a low measurement accuracy. In order to further improve high-speed and high-precision three-dimensional shape measurement, this paper presents a new three-dimensional shape measurement method based on double-frequency fringes projection. This new method needs to project two sets of 1-bit grayscale fringe patterns (low-frequency fringe and high-frequency fringe) onto the object surface under slightly defocused projection mode. The method has the following advantages: (1) high projection speed because of 1-bit grayscale fringe; (2) high measurement precision for selectively removing undesired harmonics. Low-frequency fringe is produced by error-diffusion dithering (Dithering) technique and high-frequency fringe is generated by optimal pulse-width modulation (OPWM) technique. The two kinds of fringe patterns have each superiorities and flaws. The low-frequency fringe has a low measurement accuracy, but the continue phase can be easily retrieved. However, the property of high-frequency fringe and low-frequency fringe is the opposite. The general idea of this method proposed is as follows: Because the both fringes test the same object, the height is the same. The low-frequency fringe can be used to assist the high frequency fringe to retrieve continue phase map, then the three-dimensional shape information of the object can be obtained. Theory analyzes the mathematical principle of error-diffusion dithering technique, optimal pulse-width modulation technique and three-dimensional reconstructed algorithm based on double-frequency fringes projection. A second-hand mouse was used to test the proposed method. The experiment results show that the three-dimensional shape measurement method combining OPWM technique and Dithering technique can achieve fast-speed and high-precision three-dimensional shape measurement.
The research of the high accuracy coordinate measuring machine is now playing a more and more considerable role in heightening the technical level of equipment manufacturing industry. With reference to the characteristics of foreign ScanMax coordinate measuring machine, this paper introduces the development of a double parallel-joint coordinate measuring machine with our own dependent intellectual property. This paper details the structural design, the calibration method and the evaluation for the uncertainty measurement of a prototype. The prototype has several advantages when compared with foreign instruments: first, decrease of Abbe error; second, enlargement of the measuring range; third, improvement of the rigidity of the instrument. The measurement test indicates that the measurement uncertainty (when K=2) of special random distance is 10.2 μm. The double parallel-joint coordinate measuring machine studied by this paper is of great academic value and the developed prototype is highly practical and worthy of being popularized.
Blade is the key component of the aero-engine. In generally, it requires precise size and accurate shape, so the three-dimensional shape measurement of the blade is very important. Fringe projection profilometry is generally used to measure the 3D shape of an object, because of the advantages of non-contact operation, full-field acquisition, high resolution, and fast data processing. In this paper, 3D shape measurement method based on surface structured light that combination of gray-code and phase-shift projection is proposed. The wrapped phase of the blade is got by the four-step phase-shift method. In the projection process of the gray-code, due to the ambient light, different surface reflectance and surface physical discontinuous, the edge of gray-code becomes smooth, leading to decode error, so that the gray-code pattern must be binaried before decode. Through the accurate binarization of the blade gray-code pattern, the decoding cycle of the blade is achieved, and the unwrapped phase is achieved by phase unwrapping. Then the unwrapped phase difference between the blade and reference plane is got, the height of the blade can be obtained by the relationship between the phase difference and the height. The experimental and simulation results show that the proposed method can achieve a high precision, high speed and low cost 3D shape measurement of the blade. The measurement accuracy reaches 0.03 mm. The proposed method extends the reliability and practicality of the fringe projection profilometry.
The blade is a key component of the aero-engine. As the blade must have a precise size, accurate shape, the
three-dimensional profiling measurement of the blade is very important. Its complexity and diversity bring considerable
difficulty to the measurement. The optical triangulation method is used in the profiling measurement of the blade in the
paper. The coded technique based on gray-code combined with the phase-shift method is used. The three-dimensional
point cloud of blade is obtained in this method. A high accuracy of three-dimensional profiling measurement of the blade
is achieved, and the measurement accuracy reaches 0.05 mm.
Recently, with the development of the communication and the computer technology and the improvement of the storage
technology and the capability of the digital image equipment, more and more image resources are given to us than ever.
And thus the solution of how to locate the proper image quickly and accurately is wanted.The early method is to set up a
key word for searching in the database, but now the method has become very difficult when we search much more
picture that we need. In order to overcome the limitation of the traditional searching method, content based image
retrieval technology was aroused. Now, it is a hot research subject.Color image retrieval is the important part of it. Color
is the most important feature for color image retrieval. Three key questions on how to make use of the color
characteristic are discussed in the paper: the expression of color, the abstraction of color characteristic and the
measurement of likeness based on color. On the basis, the extraction technology of the color histogram characteristic is
especially discussed. Considering the advantages and disadvantages of the overall histogram and the partition histogram,
a new method based the partition-overall histogram is proposed. The basic thought of it is to divide the image space
according to a certain strategy, and then calculate color histogram of each block as the color feature of this block. Users
choose the blocks that contain important space information, confirming the right value. The system calculates the
distance between the corresponding blocks that users choosed. Other blocks merge into part overall histograms again,
and the distance should be calculated. Then accumulate all the distance as the real distance between two pictures. The
partition-overall histogram comprehensive utilizes advantages of two methods above, by choosing blocks makes the
feature contain more spatial information which can improve performance; the distances between partition-overall
histogram make rotating and translation does not change. The HSV color space is used to show color characteristic of
image, which is suitable to the visual characteristic of human. Taking advance of human's feeling to color, it quantifies
color sector with unequal interval, and get characteristic vector. Finally, it matches the similarity of image with the
algorithm of the histogram intersection and the partition-overall histogram. Users can choose a demonstration image to
show inquired vision require, and also can adjust several right value through the relevance-feedback method to obtain the
best result of search.An image retrieval system based on these approaches is presented. The result of the experiments
shows that the image retrieval based on partition-overall histogram can keep the space distribution information while
abstracting color feature efficiently, and it is superior to the normal color histograms in precision rate while researching.
The query precision rate is more than 95%. In addition, the efficient block expression will lower the complicate degree of
the images to be searched, and thus the searching efficiency will be increased. The image retrieval algorithms based on
the partition-overall histogram proposed in the paper is efficient and effective.
In the industrial detection, the three dimensional of the products are needed measuring usually, so the products can be known eligible or not. The measurement is needed both the high precision and fast speed. In the article, the smooth part of the mouse is taken as the measure object. Grating projected method is used to reconstruct the three dimensional of it. In the experiment, the intersect principle of fourier transform profilometry is used. The electronical grating is projected on the mouse, the deformed grating is collected in the Charge Coupled Device (CCD). And the deformed grating without the mouse is also collected. The fourier transform is used to process the image. In the traditional fourier transform profilometry, the phase is worked out as follows: After fourier transform, the zero frequency spectra is shifted to the origin of frequency, then filter the needed signal. Then the needed signal is shifted to the center of frequency, and then the zero frequency is shifted to both sides. After inverse fourier transform, the imaginary part is getting, so the phase is getting. But it has a difficult in the traditional method, because of three times frequency shift, and the center frequency is difficult to confirm, the frequency shift can't be correct and the filter can't be designed correctly. The error can be transferred, so the result of filter is not well, it has bad effect to the later measurement. The result of measurement is not well certainly. In order to conquer the difficult, after the fourier transform, filtering the needed signal without frequency shifting, then inverse fourier transform. So the phase of mouse relational with the frequency and coordinate is getting. The phase of the reference surface is getting by the same method. Then the difference phase is getting. At last, according to the relation of difference phase and the height in the grating projected method, the three dimensional profilometry of the mouse is reconstructed. The method is more simply and higher precision without three times frequency shift. The three dimensional profilometry reconstruct is realized by two images. It takes 0.3 second to reconstruct the three dimensional profilometry. The precision is 0.5mm. The result indicates that the method suits the smooth object with fast speed and high precision. It is fit for the needed in the practical measurement.
In the industry, the three dimension of the object is often measured. But the method is usually the contact measurement.
And the speed is slowly. The measurement is needed both high precision and fast speed, so the non-contact measurement
is required. The grating projecting is the non-contact measurement with prospects. But there are some difficulties in the
method. Firstly, when the object has the steps shape or there are shadows in the grating stripes, the disconnected phase
can't be correctly unwrapped. Secondly, it is very difficulty to realize the real time digital filter. Now the digital filter is
man-machine conversation, so the speed is slowly. Thirdly, in order to measurement the different object, the adaptive
grating is needed.
In order to resolve the above problems, the grating program is created on the computer. The program has many
functions, including the phase shift, the two-frequency grating and the grating frequency is easy to adjust. So the
adaptive grating is realized. The two-frequency grating is programmed by the computer. And it is projected to the
measured object. The measurement object is placed on the exact rotary platform. The deformed grating is collected in the
Charge Coupled Device (CCD). After getting two images, the two images are mosaiced. Then the clear object image
modulated by the grating is got. The problem of the steps shape or there are shadows in the grating stripe is worked out.
Then the fourier transform is used to process the image. In the traditional fourier transform profilometry, the phase is
worked out as follows: After fourier transform, the zero frequency spectra is shifted to the origin of frequency, then filter
the needed signal. Then the needed signal is shifted to the center of frequency, and then the zero frequency is shifted to
both sides. After inverse fourier transform, the imaginary part is getting, so the phase is getting. But it has a difficult in
the above method, because of three times frequency shift, and the center frequency is difficult to confirm, the frequency
shift can't be correct and the filter can't be designed correctly, and the error can be transferred, so the result of filter is
not well, it has bad effect to the later measurement. The result of measurement is also not well. In order to conquer the
difficult, after the fourier transform, filtering the needed signal without frequency shifting, then inverse fourier
transform. So the phase relational with the frequency and coordinate is getting. The phase of the reference surface is
getting by the same method. Then the difference phase is getting. The real difference phase of low frequency is easy to
got, then the real difference phase of high-frequency is work out based on it. At last, according to the relation of
difference phase and the height, the three dimensional profilometry of the object is reconstructed.
An example of step shape object is done. The three dimensional profilometry is reconstructed successfully. It takes 3
second to reconstruct the three dimensional profilometry. The precision is 0.5mm. The result indicates that the method
has conquered the above problems.
The result indicates that the method is simple, with fast speed and high precision. Three dimension profilometry
measurement of the objected that have the step shape or the shadow in the projecting can be successfully resolved.
In this paper, we introduce a fast Fourier transform algorithm for three-dimension surface analysis in a scanning white-light interferometry system. The interferograms, one for each pixel of the interference image, representing the variation in intensity as a function of scan position, are transformed into the spatial frequency domain and the relative surface height information for each point is extracted from the complex phase as a function of frequency. For optimal speed and efficiency with a minimum of resources, a simple frequency-based discriminator is used in data acquisition to identify the modulation region and a circular buffer technique is adopted for retaining the complete interferogram efficiently. Applying this method to the mapping of the endface topography of fiber connector, we've achieved high measurement repeatability and speed.
A non-contact optical microscopy system is described. It adopts basic Michelson structure to measure the characteristic of end surface of the fiber connector. We take use of the Fourier transform to process interference pattern. Getting the high information of two-dimension section picture. We take use of the First Derivative is extremum and Second Derivative is zero to detect the edge jump points. And we take use of Least Square Method etc. curve fitting method to describe the two-dimension section picture. We analyze the method to measure geometrical parameters of end surface. Then we can measure the characteristic of end surface. For example: the geometric parameters and roughness.