Any paper defects that are not included in the paper quality technical requirements can be called paper diseases. Typical paper diseases include black spots, bright spots, folds, holes, rotten edges, etc. If you look at all the paper diseases in terms of gray scale, there are only three types: holes, black spots, and bright spots.
The DZ-WIS paper disease detection system developed by Henan Dazhi Paper Equipment Integration Engineering Co., Ltd. is a paper disease detection system based on machine vision. Its basic principle is: use multiple high-resolution linear array CCD cameras to synchronize The paper web reflected or transmitted by the light source is scanned progressively, and the captured image is converted into electrical signals in real time and transmitted to the computer workstation. Computer workstations use image processing algorithms to process paper web images, analyze images and detailed information of various paper diseases, and output them in multiple forms to meet different needs of users.
It is mainly composed of the following three parts: image acquisition module; computer workstation; paper disease detection software. The above three parts are the core of the paper disease detection system, and their organic combination can meet the requirements of a high-speed paper machine with a working speed of 1500m / min. The detection accuracy can reach 0.1mm2.
Schematic diagram of paper disease detection system
The specific environment of different paper workshops is often different. To meet the requirements of users, the paper disease detection system must improve its own adaptability to different environments. During the installation and commissioning of DZ-WIS, we have experienced many problems caused by vibration, high temperature, high humidity and other environmental problems, but we have also worked hard to find a solution to these problems, and through the solution of the problem, DZ -The WIS system has been improved.
For example, one of the common problems encountered during the operation of the paper disease detection system is the change in ambient light (Note: direct light hitting the detection area cannot be solved). Ideally, the system should operate in a constant light environment , But it's actually hard to do so. In the actual testing process, the paper fault detection system that can operate normally in this workshop is installed in another workshop but there is a problem. After the system runs normally for a period of time, a false alarm occurs. We then modify the parameters to restore the system to normal, but after a period of time The false alarms reappeared, and the problem was not solved completely after repeated times. After eliminating the problem of the procedure, we began to look for other reasons. After comparing the workshop environment, we found that the top and surrounding windows of the paper production workshop are relatively large, resulting in a large difference in the morning and evening light in the workshop. Adjusting the system for a period of time simply does not allow it to maintain normal detection in other periods of time.
For this situation, the solution we adopted is to dynamically ensure the stability of the image grayscale by dynamically adjusting the camera exposure time or gain. This largely eliminates the interference of external ambient light and keeps the system in a stable working state. The process of dynamic adjustment of camera parameters is shown in the figure.
Camera parameter dynamic adjustment process
It should be noted that in practice, we learned that reducing the exposure time can reduce the image blur caused by high-speed paper movement, and increasing the exposure time can also cause interference such as horizontal black lines in the image under certain conditions, and increase the camera. The gain will reduce the signal-to-noise ratio of the image and so on.
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