Brief Introduction of Visual Measurement Technology






What is visual measurement technology?

Visual measurement is becoming more and more popular. Sensors are used to collect measurement images, and the precise mapping relationship between image information and geometric information in object space is used to realize measurement. The key of high precision measurement is the "precise mapping" here.



Why should distortion be considered in visual measurement?

The traditional visual imaging model is "small aperture imaging model", which ignores the influence of various errors in the imaging optical path. It is a linear imaging relationship and can be directly used in occasions where the measurement accuracy is not high. Because of the influence of radial distortion, tangential distortion, affine and non-orthogonal distortion, light does not propagate in a straight line, that is, a point on an object in space. We hope that it will hit the image plane directly along a straight line passing through the center of the lens, but the actual situation is that it bends in the lens even if it does. Still passing through the center of the lens, it follows a curve when it hits the image plane. Perhaps this effect can not be felt by our eyes, but even if we deviate 2 pixels, there may be a deviation of 1 mm. So the deviation will be compensated when we measure accurately. At this time, the image we see is distorted. Sometimes the photo ugliness may be due to this reason.


Visual measurement technology uses images as means or carriers of detecting and transmitting information, extracts useful signals from images, and obtains the required parameters by processing the measured images. Visual measurement technology is based on machine vision and integrates optoelectronics, computer technology, laser technology, image processing technology and other modern science and technology into a comprehensive measurement system of optics, mechanics, electricity and computer. It has the characteristics of non-contact, full field of view measurement, high precision and high automation.



Instruments and equipment based on visual measurement technology can realize intellectualization, digitalization, miniaturization, networking and multi-function. They have the ability of on-line detection, dynamic detection, real-time analysis and real-time control. They have the characteristics of high efficiency, high precision and non-destructive detection. They can meet the development needs of modern precision measurement technology. At present, it has been widely used in industry, military, medical and other fields, and has received great attention. We can see many instruments developed by visual measurement technology at home and abroad, such as optical coordinate measuring instrument, AI intelligent one-key measuring instrument, tool presetting measuring instrument based on visual technology and other advanced instruments.



Development Trend of Visual Measurement Technology

Visual measurement technology is a promising automatic detection technology, which can achieve intelligent, flexible, fast and low-cost detection. With the development of computer vision theory, visual inspection will soon be widely used in all walks of life. The development trend of visual measurement technology is mainly reflected in the following points:


1. Realizing on-line real-time detection

Visual inspection system is mostly used in industrial field and production line. For on-line real-time inspection, how to embed the visual measurement system into the corresponding process of production line to make the measurement speed consistent with the production line rhythm is a key step for the practical application of visual measurement. The execution time of visual inspection largely depends on the speed of image processing (image smoothing, filtering, segmentation, etc.).  Therefore, using dedicated hardware to implement environment-independent processing algorithm can greatly improve the speed of image processing.


2. Realizing Intelligent Detection

The vision model and detection information of parts (including position and direction of parts, camera angle of view, etc.) are extracted from the CAD system, the detection items, detection points and detection paths are selected, the intelligent detection planning is established, and the industrial robots are controlled to grab parts and place them in the appropriate position for detection.


3. Achieving High Precision Detection

Compared with visual system, coordinate measuring machine has a great advantage in detection accuracy and measurement space. Therefore, CMM-based visual detection system has become a new trend of visual detection technology. Integrated CMM and visual inspection system can use visual system to quickly identify the shape of parts and their position and state on the measuring platform, complete the transformation between machine coordinate system, part coordinate system and camera coordinate system, and help CMM to realize automatic formation of inspection path and judgment of measurement results. At the same time, the sub-pixel positioning technology is deeply studied and applied to the actual detection system to improve the detection accuracy and reduce the cost of the system.



In short, with the maturity and development of computer vision technology, computer vision measurement technology will be more and more widely used in modern and future manufacturing enterprises.






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