Text / Li Lijun • Wuxi Chuangshi New Technology Co., Ltd.
Application fields of machine vision technology
As we all know, "vision" means that the eye can see things, and "consciousness" means that the brain can analyze and treat what is seen. Machine vision technology is to let the machine have visual function, and replace the human eye to make judgments. It is realized through two processes of image acquisition and software processing. The specific application technology is shown in Figure 1.
Figure 1 Application of visual technology
Defect detection Defect detection is widely used in metals, electronics, film, non-woven fabrics, paper and other industries. It is mainly used to check whether the surface of the product has scratches, stains, etc. that do not meet the quality requirements of the product. It is the most widely used field of vision technology. .
Visual measurement Vision measurements are primarily used in the semiconductor industry. In theory, visual measurements are easy to implement. However, in industrial applications, the most important problem at present is how to ensure the accuracy and stability of the measurement.
Visual guidance
Vision guidance is widely used in robots, robots and other industries. It guides the machine position coordinates through the vision system to achieve accurate positioning of the machine. At present, almost all robots need the cooperation of machine vision systems.
Visual recognition Currently, visual recognition is mainly used in face recognition and license plate recognition.
MVC vision measurement system
Modern sheet metal manufacturing tends to be multi-variety and small-volume production. This processing method poses great challenges to the control of production processes. Small batch production of sheet metal parts requires frequent adjustments to the machine tool, such as laser cutting machine programming, mold replacement, etc. Frequent adjustments can cause deviations or errors in the machining. How to ensure the pass rate of each batch of sheet metal parts, which requires the detection of the first piece of each batch. The failure of the first piece will result in the batch scrapping of the product, which will bring waste of materials, labor and so on to the enterprise. In addition, large quantities of sheet metal parts must be processed in conjunction with sampling.
There are two main problems in the traditional sheet metal detection method: one is that the detection time is too long, and some complex sheet metal parts have dozens or even hundreds of holes, and with other sizes, manual measurement often costs a lot. For a long time, this also prolongs the waiting time of equipment downtime, and the more batches, the more serious the machine and labor waste is caused. Second, the accuracy is difficult to guarantee, and the test results are easily affected by human factors, such as “Which point does the measurement start from? "The choice of measurement basis", etc., has led to differences in the test results of different people. If the control is not effective, it will lead to the inferior loss of non-conforming products.
Based on machine vision technology, MVC sheet metal vision detection system integrates optical, electronic and computer image processing technologies, and is specially used for precision measuring instruments for sheet metal detection. It effectively solves the problem of manual measurement deviation and measurement accuracy of one imaging range. The measurement speed is more than 10 times that of traditional measurement instruments, which greatly improves the measurement efficiency and measurement accuracy, eliminates human error, and realizes the intelligence of sheet metal detection.
The MVC sheet metal detection system is very easy to use. Firstly, the measured part is placed on the measuring platform, the part outline is obtained by photographing, and the imported CAD drawing is fitted to realize one-button measurement, and finally the detection result is displayed, and the part is processed. Items such as deviations and missing dimensions can be visualized, and the entire inspection process takes less than a minute.
At the beginning of R&D and design, the MVC sheet metal inspection system is closely integrated with the characteristics of the sheet metal processing industry. Based on the CAD software platform design, the user can directly import the CAD drawings of the tested sheet metal parts and use this as a benchmark for measurement. The drawing specification is based on CAD software. For irregular drawings caused by designers' operating habits, such as multi-point and multi-line, the system will automatically judge and identify. The MVC system is designed with a virtual caliper function that can be used to detect some important dimensions, such as measuring the center-to-center distance between two circles, and simply click on their circumference to get the center-to-center distance data. For oversized parts, that is, sheet metal parts beyond the scope of the inspection platform, the system uses two or more photographs to obtain the image of the part, and selects the reference point for rapid splicing measurement, which solves the problem that the sheet metal piece cannot be detected because it exceeds the measurement range. problem. Reverse measurement enables rapid sample-to-image conversion, providing a basis for product design and more. The detection results of the MVC system can be visually displayed. Different sizes are distinguished by different colors, and the test report can be output and printed, which is convenient for the user to archive and record the test results of each batch of products.
Technical characteristics of the MVC system
Image strobe The focus of vision measurement technology is on optoelectronics and image processing. The light source provides the original information carrier for the machine vision system and is an important part of image acquisition. The illumination effect of the light source directly affects the image processing in the later stage. The LED light source has the advantages of long life, fast response, no flicker, and easy control of shape and color, ensuring the acquisition of high-quality image contours, combined with the image strobe designed by the MVC system. The technology not only saves energy and protects the environment, but also prolongs the service life of the LED light source.
Add material correction function. Considering the use of stainless steel "target=_blank> stainless steel, copper plate, aluminum plate and other materials for sheet metal parts, the sensitivity of different materials is not the same, especially the shadow reflection will have a slight impact on the conversion of the imaging system. In order to ensure the accuracy of the detection results, the MVC system image algorithm adds a coefficient correction function for a variety of materials, which reduces the dimensional deviation of the parts due to different materials.
The use of high-precision standard glass calibration plate calibration plate is a key tool for machine vision, image measurement, photogrammetry, 3D reconstruction, etc. The main function is to correct lens distortion, determine physical size and conversion relationship between pixels, and determine a certain point on the surface of the object. The relationship between the spatial position and its corresponding point in the image. The standard calibration plate with a circular array is photographed by the camera, and the geometric model of the camera can be obtained through the calculation of the calibration algorithm, thereby obtaining high-precision measurement and reconstruction results. The traditional calibration uses the film calibration plate, which has the advantage of being cheap, but not easy to store, and often causes distortion due to factors such as uneven material during use. Although the glass calibration plate is expensive, it is not affected by the material factor. The solid circular array pattern CG-100-D is combined with the image software algorithm to ensure the accuracy of the visual measurement.
Punctuation of the pincushion and barrel distortion by sub-area Due to the large field of view, especially at the edge of the field of view, such as barrel and pincushion distortion, there is a slight influence on the measurement accuracy. In order to correct the lens distortion, ensure the physical size and the conversion relationship between pixels, especially the sub-region distortion calibration method.
The two-arm vertical structure adopts two-arm vertical structure. The imaging system is located above the measuring platform. The arms are tightly combined with the workbench. The whole equipment is not affected by external vibration and other factors. It is very suitable for the workshop and the machine tool.
The sheet metal industry is the basic industry in modern manufacturing. Machine vision technology, as an indispensable technical force for industrial modernization, will usher in greater opportunities. Sheet metal vision inspection system is an application model of machine vision technology. The development of the industry and the entire manufacturing industry has provided strong support.
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