Machine vision system refers to the use of machines instead of human eyes to make various measurements and judgments. A more complex system. Most of the system monitoring objects are moving objects, the matching and coordination of the system and moving objects is particularly important, so it brings strict requirements for the action time and processing speed of each part of the system. In some application areas, such as robots, flying objects, etc., there are strict requirements for the weight, volume and power consumption of the entire system or part of the system.

A complete machine vision system includes: lighting source, optical lens, CCD camera, image acquisition card, image detection software, monitor, communication unit, etc.

Working process of industrial machine vision system

1. The sensor detects that the detected object moves close to the shooting center of the camera, and sends the trigger pulse to the image acquisition card;

2. According to the set program and delay, the image acquisition card sends the start pulse to the camera and the lighting system respectively;

3. The camera is in a waiting state before the start pulse arrives, and starts a frame scan after the start pulse arrives;

4. Open the exposure mechanism before the camera starts a new frame scan, and the exposure time can be set in advance;

5. The other start pulse turns on the light lighting, and the opening time of the light should match the exposure time of the camera;

6. After the camera is exposed, the scanning and output of a frame image are officially started;

7. The image acquisition part receives the analog video signal through A/D to digitize it, or directly receives the digital video data after the camera digitization;

8. The image capture card stores digital images in the computer's memory;

9. The computer processes, analyzes and recognizes the image to obtain the detection result;

10. Processing results Control the action of the assembly line, conduct positioning, correct the error of the movement, etc.

2. Machine vision-related technologies

1, image acquisition technology - the basis of machine vision

The image acquisition part is generally composed of light source, lens, digital camera and image acquisition card. The acquisition process can be simply described as shooting the target object with a digital camera and converting it into an image signal under the condition of illumination provided by the light source, and finally transmitting it to the image processing part through the image acquisition card. In the design of the image acquisition part, we should consider many problems, mainly about the digital camera, image acquisition card and light source.

(1) Light source lighting

Lighting is an important factor affecting the input of machine vision system, which directly affects the quality and application effect of input data. So far, there is no kind of machine vision lighting equipment can be used for a variety of applications, so in practical applications, it is necessary to select the corresponding lighting equipment for the application to meet the specific needs.

Lighting system according to its irradiation method can be divided into: back lighting, forward lighting, structured light and stroboscopic lighting. Among them, backlighting means that the subject is placed between the light source and the camera to improve the contrast of the image. Forward lighting is that the light source and the camera are located on the same side of the object under test, which has the advantage of being easy to install. Structured light illumination is to project a grating or a line light source onto the measured object, and demodulate the three-dimensional information of the measured object according to the distortion generated by it. Strobe lighting is the high frequency light pulse to the object, the camera shooting requirements and the light source.

(2) Optical camera

The task of optical camera is to carry out optical imaging, generally in the field of measurement has a special camera lens for measurement, because it has a key role in the quality of imaging. One thing to watch out for with cameras is distortion. This requires the use of corresponding distortion correction methods, and many automatic distortion automatic correction systems have been developed.

(3) CCD camera and image acquisition card

CCD(Charge Coupled Device) camera and image acquisition card jointly completed the acquisition and digitization of the target image. At present, the application technology of CCD, CMOS and other solid devices, linear matrix sensitive devices, pixel size is decreasing, the number of array pixels is increasing, and the pixel charge transfer rate is also greatly improved. In the PC-based machine vision system, the image acquisition card is an important device that controls the camera to complete the image acquisition and digitization, and coordinates the whole system.

The image acquisition card directly determines the interface of the camera: black and white, color, analog, digital and other forms.

2, image processing and analysis - the core of machine vision

The core of image processing and analysis methods used in machine vision is to solve the problem of target detection and recognition. When the target to be identified is more complex, it needs to be realized through several links from different aspects.

When the object is identified and extracted, the first thing to consider is how to automatically separate the object from the background. The complexity of target extraction generally lies in the fact that the feature difference between target and non-target is not very large. After the target extraction scheme is determined, the target feature needs to be enhanced.

With the development of computer technology, microelectronics technology and large-scale integrated circuit, image information processing is more and more completed by hardware, such as DSP chip, special image signal processing card and so on. The software part is mainly used to complete the immature and complicated part of the algorithm or need to be constantly improved. This improves the real-time performance of the system and reduces the complexity of the system.

Advantages of machine vision technology

1. Higher efficiency: Low efficiency of manual detection. Machine vision inspection is much faster, can detect hundreds or even thousands of components per minute, and can continue to work 24 hours a day.

2. Higher accuracy: The human eye is limited by physical conditions, and will also be affected by factors such as subjectivity and physical energy, which cannot guarantee accuracy. Machines are not subject to subjective control, and as long as there is no difference in parameter Settings, multiple machines with the same configuration can guarantee the same accuracy.

3. Lower overall cost: machines are more effective than manual inspection, and in the long run, the cost of machine vision inspection is lower.

4. Information integration: Machine vision inspection can measure multiple technical parameters at a time through multi-station measurement methods, such as the outline, size, appearance defects and product height of the product to be detected.

5. Digital statistical management: Measure data and generate reports after measurement, without manually adding them one by one.

6. Can be applied to dangerous detection environment: the machine can complete the detection work well in harsh and dangerous environment, as well as in occasions where human vision is difficult to meet the needs.

7. Will not cause contact damage to the product: machine vision in the process of detecting the workpiece, do not need to contact the workpiece, will not cause contact damage to the workpiece. Manual inspection must carry out contact detection on the workpiece, which is easy to produce contact damage.

8. More objective and stable: in the process of manual detection, the test results will be affected by personal standards, emotions, energy and other factors. The machine strictly follows the set standards, and the test results are more objective, reliable and stable.

9. Avoid secondary pollution: Manual operation sometimes brings uncertain sources of pollution, thereby polluting the workpiece.

10. Simple maintenance: low technical requirements for the operator, long service life and other advantages.