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The feature of machine vision technology is automatic, objective, no-contact and precision, compared with the general image processing system, the machine vision emphasizes accuracy and speed, and reliability of the industrial field environments. Previously, this kind of work can only completed by manual inspection, but it increases huge labour costs and management costs, and it cannot guarantee a 100% inspection pass rates(‘zero defect’). Therefore the vision system with its rapid, reliable, repeatable results, combined with highly intelligent human vision and the ability of abstract, entering today industries.
3.3.2 The type of application
Generally speaking, the machine vision system includes lighting system, lens, imaging system, and image processing system. The typical machine vision system can be pided into the image collecting portion, image processing portion and the movement control portion. Overall machine vision system has three main application features are as follows.
1. Positioning function, which can automatically determine the position of the object and product of interesting, and the location information will be output through a certain communication protocol. This function is used for automated assembly and production, such as automatic assembly, automatic welding, automatic packaging, automatic spraying and automatic multi-coordinate actuators (ABB robots, welding torch, nozzles and so on).
2. Measurement function, which is capable of automatically measuring the dimensions of the products, such as external contour, pore size, height and area measurement.
3. Defect inspection function, which is the most using feature of the vision system, it can detect the related information of production surface. For examples, whether the packaging is right, correcting the packaging; whether the printing is correct; whether the surface has particles, scratchers, greasy dirt; whether the plastic pieces has perforations, etc
The main work of a complete machine vision system is as follows:
1. The positioning of the work piece detector detects has moved to close to the center of the field to the camera system, image acquisition part of the transmitted pulse.
2. Image acquisition part according to the preset program and delay, respectively from the start pulse to the camera and lighting system.
3. The cameras stop current scanning, to start a new frame scanning, or the camera before starting pulse comes in a wait state, the start pulse arrival initiates a frame scanning.
4. The camera before starting a new frame scanning mechanism open exposure, exposure time can be set in advance.
5. The other start pulse lights make it lighting, lighting time should matching with exposure time of camera.
6. After exposure, The camera began the first frame of image scanning and output.
7. Image acquisition part receives the analog video signal through the A/D digital or directly receive digital camera digital video data.