Since standard parts are necessary components in mechanical structure like bogie and connector. These mechanical structures will be shattered or loosen if standard parts are lost. So real-time standard parts inspection systems are essential to guarantee their safety. Researchers would like to take inspection systems based on deep learning because it works well in image with complex backgrounds which is common in standard parts inspection situation. A typical inspection detection system contains two basic components: feature extractors and object classifiers. For the object classifier, Region Proposal Network (RPN) is one of the most essential architectures in most state-of-art object detection systems. However, in the basic RPN architecture, the proposals of Region of Interest (ROI) have fixed sizes (9 anchors for each pixel), they are effective but they waste much computing resources and time. In standard parts detection situations, standard parts have given size, thus we can manually choose sizes of anchors based on the ground-truths through machine learning. The experiments prove that we could use 2 anchors to achieve almost the same accuracy and recall rate. Basically, our standard parts detection system could reach 15fps on NVIDIA GTX1080 (GPU), while achieving detection accuracy 90.01% mAP.
In the trends of intelligent manufacturing, fringe projection profilometry is one of the most widely used techniques for obtaining three dimensional (3D) cloud of parts. However, this measuring technique may introduce interreflections by parts with strong reflection, which leads to phase calculation and 3D point reconstruction mistakes. In this paper we proposed adaptive regional projection method to measure interreflections area of parts with strong reflection. For a parts to be measured, we detect the surfaces of interreflections on it and give their pose in optical measurement system firstly. Then the system measure interreflections areas one surface by one surface. We measure complete cloud of a parts with strong reflection as the experiment, which illustrates our method is feasible.
Machine vision plays an important part in industrial online inspection. Owing to the nonuniform illuminance conditions and variable working distances, the captured image tends to be over-exposed or under-exposed. As a result, when processing the image such as crack inspection, the algorithm complexity and computing time increase. Multiexposure high dynamic range (HDR) image synthesis is used to improve the quality of the captured image, whose dynamic range is limited. Inevitably, camera shake will result in ghost effect, which blurs the synthesis image to some extent. However, existed exposure fusion algorithms assume that the input images are either perfectly aligned or captured in the same scene. These assumptions limit the application. At present, widely used registration based on Scale Invariant Feature Transform (SIFT) is usually time consuming. In order to rapidly obtain a high quality HDR image without ghost effect, we come up with an efficient Low Dynamic Range (LDR) images capturing approach and propose a registration method based on ORiented Brief (ORB) and histogram equalization which can eliminate the illumination differences between the LDR images. The fusion is performed after alignment. The experiment results demonstrate that the proposed method is robust to illumination changes and local geometric distortion. Comparing with other exposure fusion methods, our method is more efficient and can produce HDR images without ghost effect by registering and fusing four multi-exposure images.
Single-pixel imaging (SPI) is a new method to obtain an image using a detector without spatial resolution. Owing to the excellent characteristics of anti-noise and high signal-to-noise ratio, SPI is applied to detect and locate the target region in the week illumination condition. In most previous target detection and location approaches, the original target needs to be imaged. However, the time consumption of image reconstruction for SPI is much larger than conventional imaging method, which indicates a low efficiency for target region location using SPI. In this paper, we propose a target region location method based on Fourier single-pixel imaging to locate the target without retrieving target image. The proposed method adopts the Fourier single-pixel imaging to obtain few Fourier coefficients of the target image, then the target region is located by the central slice theorem and edge detection algorithm. Experiment shows the proposed method has an excellent characteristic of low time consumption and can effectively locate the target region.
Nowadays, 3D measurement and re-construction technologies are widely used not only in industry area, but also in the appreciation and research of ancient architecture and historical relics. Many methods are used for the architecture measurement in large scale, but as for the details of architecture or precision historical relics, these methods meet difficulties. Thus, historical relic objects with specular surface or complex sculptural surface could not be measured by traditional method. Focusing on these problems, this paper proposed 3D measurement technique which contains two levels of measurement. Firstly, when measuring ancient architecture in large scale, laser scanning and photometry methods are used. Then, when measuring details of architecture, a fast and adaptive 3D measurement system is used. Multi-view registration is also used for the measurement of hollowed-out structure of sculptural relics. The experiments indicate that the system can achieve 3D measurement and re-construction of different types of ancient architecture and historical relics.
The fringe projection technology is widely used in 3D measurement fields. However when the technology is applying to translucent objects, the subsurface scattering and absorbing always leads to a decline of the measurement accuracy. The aim of this paper is to propose a dual-direction fringe projection method in order to obtain an more accurate measurement result for the translucent objects as while as change the whole measurement system little and do not reduce the measuring rapidity. The paper mainly includes three parts: (1) The principle of dual-direction fringe projection method and different forms of dual-direction fringe; (2) Analysis of the different effect for the measurement accuracy brought by different factors; (3) Experiments for artificial tooth by various dual-direction fringes and accuracy analysis. The experiment results showed that by this method it is possible to improve the measurement accuracy for the translucent objects.
Large-scale separated surface is very common in modern manufacturing industry. The measurement of the flatness of such surfaces is one of the most important procedures when evaluating the manufacturing quality. Usually, the measurement needs to be accomplished in an in-situ and non-contact way. Although there are many conventional approaches such as autocollimator, capacitance displacement sensor and even CMM, they can not meet the needs from the separated surfaces measurement either because of their contact-nature or inapplicable to separated surfaces. A non-contact large-scale separated surfaces flatness measurement device utilizing laser beam and laser distance sensor (LDS) is proposed. The laser beam is rotated to form an optical reference plane. The LDS is used to measure the distance between the surface and the sensor accurately. A Position Sensitive Detector (PSD) is mounted with the LDS firmly to determine the distance between the LDS and the reference plane and then the distance between the surface and the reference plane can be obtained by subtracting the two distances. The device can be easily mounted on a machine-tool spindle and is moved to measure all the separated surfaces. Then all the data collected are used to evaluate the flatness of these separated surfaces. The accuracy analysis, the corresponding flatness evaluation algorithm, the prototype construction and experiments are also discussed. The proposed approach and device feature as high accuracy, in-situ usage and the higher degree of automatic measurement, and can be used in the areas that call for non-contact and separated surfaces measurement.
In dental restoration, its important to achieve a high-accuracy digital impression. Most of the existing intraoral measurement systems can only measure the tooth from a single view. Therfore，if we are wilng to acquire the whole data of a tooth, the scans of the tooth from multi-direction ad the data stitching based on the features of the surface are needed, which increases the measurement duration and influence the measurement accuracy. In this paper, we introduce a fringe-projection based on multi-view intraoral measurement system. It can acquire 3D data of the occlusal surface, the buccal surface and the lingual surface of a tooth synchronously, by using a senor with three mirrors, which aim at the three surfaces respectively and thus expand the measuring area. The constant relationship of the three mirrors is calibrated before measurement and can help stitch the data clouds acquired through different mirrors accurately. Therefore the system can obtain the 3D data of a tooth without the need to measure it from different directions for many times. Experiments proved the availability and reliability of this miniaturized measurement system.
Measuring the 3D structure of vegetation canopy is of great significance for the validation of remote sensing data and vegetation radiation transfer modeling. When using laser triangulation, because of the limitat ion of the field of view of measuring system, multi-view measurement followed by a registration of the measured point cloud is needed. Most of the existing registration methods cannot be directly applied to our registration task. This paper presents a registration method based on leaf profile matching. Firstly, segment the point cloud into subsets that are correspond to the single leaves. Then the profile of every single leaf is extracted and fitted with splines. Finally, by calculating and matching the parameters of the splines' parameters, the profile of the same leaf in different views are registered, thus the registration of multi-view point cloud is achieved. The experiments on measurement data are presented to show the feasibility of the proposed method.
A three-dimensional shape measurement system based on fiber-optic image bundles was proposed to measure
three-dimensional shape of object in confined space. Fiber-optic image bundles have the advantage of flexibility.
Firstly, based on the principle of phase-shifting and advantages of fiber-optic image bundles, the mathematical
model of the measurement system was established, hardware and software platform of the system was set up. Then,
the problems of calibration and poor quality images brought by fiber-optic image bundles were analyzed, after
which a viable solution was proposed. Finally, experiments for objects in confined space were performed by using
the three-dimensional shape measurement system. As the transmission media of the system, fiber-optic image
bundles could achieve picture’s flexible acquisition and projection. The three-dimensional shape of the object was
reconstructed after data processing of images. Experimental results indicated that the system was miniature and
flexible enough to measure the three-dimensional shape of objects in confined space. It expanded the application
range of structured-light three-dimensional shape measurement technique.
With the development of manufacturing industry, the in-situ 3D measurement for the machining workpieces in CNC machine tools is regarded as the new trend of efficient measurement. We introduce a 3D measurement system based on the stereovision and phase-shifting method combined with CNC machine tools, which can measure 3D profile of the machining workpieces between the key machining processes. The measurement system utilizes the method of high dynamic range fringe acquisition to solve the problem of saturation induced by specular lights reflected from shiny surfaces such as aluminum alloy workpiece or titanium alloy workpiece. We measured two workpieces of aluminum alloy on the CNC machine tools to demonstrate the effectiveness of the developed measurement system.
The antenna which is used in space for satellite control command communication and data transmission is a key unit for
a satellite to work properly and accomplish the task successfully. Accurately measuring the antenna reflector shape and
the reflector distortion shortly after the antenna manufacturing or assembling on the satellite is very important to ensure
that the antenna functions well. Considering the constraints during the measurement, an antenna reflector shape and
distortion measuring system, which is based on the close-range photogrammetry, is proposed. The system configuration,
measuring principles, calibration and measuring procedures, data processing, experiment configuration and results as
well as error analysis are discussed in the paper. The system was constructed and tested in the laboratory environment.
The experiment results show that the system has the ability of accurately measuring the shape of the reflector. The
distortion of the reflector surface can then be gained from the shape data. The average accuracy of measurement about
240 points on a 600mm antenna reflector is less than 0.015 mm (1σ).