Application of Machine Vision Lens in Coin Character Detection

Machine vision, as a high - speed, high precision detection system, has been widely used in automotive, pharmaceutical, electronic and electrical, manufacturing, packaging / food / beverage, medicine and other industries. Its characteristics are automation, objective, non - contact and high precision, compared with the general sense image processing system, the machine vision emphasizes the accuracy and speed, and the reliability of industrial site environment.

Firstly, it uses CCD camera and high resolution machine vision lens to convert the captured target into image signal, and then transmits it to a special image processing system, which is transformed into digital signal according to the information of pixel distribution and brightness, color and so on.  The image system performs various operations on these signals to extract the features of the target, such as area, length, number, location, etc.  Finally, according to the preset tolerance and other conditions, such as: size, angle, offset, number, qualified / unqualified, and / without.  The latest printing press of our country is the typical application of visual system in printing industry.  

 The technology requirements of the mint are extremely strict. in order to ensure the reliability of each production process, 100 % of the products in the production must be tested.  In the fifth set of RMB in October 2000, the side processing of one round coin adopts high speed roller hemming machine, which enhances the anti - counterfeiting function.  In view of the strict control requirements of the production process, the engineers selected the visual inspection system installed in the last working procedure of the mint.  

 The final process, the embossing process, is completely online detection.  This paper puts forward higher requirements for image detection system.  The first is high speed, which requires the CCD camera is high speed, and the image recognition system also requires the calculation speed and storage capacity is very strong.  When the coin falls, the speed is similar to free fall.  The average speed is 10 pieces / sec.  Therefore, the time of each measurement must be less than 100 ms, and the moving speed of the object should be considered, so as to adopt the high-speed system as far as possible.  The machine vision lens on industrial camera is monitored by test, its trigger, image acquisition, calculation time and within 40 ms, fully meet the requirements.  

 In addition, the location of the camera is determined.  Because the coins are in high speed operation, to shoot accurately, there must be a synchronous trigger signal.  To this end, we adopt the high - speed reflective optical fiber sensor detection.  On the lens, using high resolution industrial lens, in the lighting, in order to weaken the high reflective effect of the edge of the coin, get better image quality, using two sets of led ring lamp plus strobe controller with image acquisition.