High-speed Wide-width Aluminum Foil Pinhole Online Detection System Based On Photoelectric Method

With the continuous improvement of our people's living standards and the continuous development of manufacturing capabilities,our country has become the largest country in the production and consumption of aluminum foil.Aluminum foil has become an irreplaceable raw material for production in the packaging field due to its good barrier properties,light-shielding properties,printing capabilities,and low cost.However,in the production process of aluminum foil,pinholes will be generated on the surface of the aluminum foil due to the problems of raw materials and technology.The presence of aluminum foil pinholes will seriously affect the sealing and shading properties of aluminum foil packaging,so it has become an important indicator to measure the quality of aluminum foil.At present,the domestic inspection of aluminum foil pinholes mostly uses manual sampling methods,which are inefficient and highly uncertain,so this methods is not conducive to the aluminum foil industry's control of the overall product quality and standards.At present,there are also online aluminum foil inspection equipment on the market.However,most domestic equipment adopts machine vision inspection methods,which have low detection ability and large volume,and cannot adapt to the current high-speed and wide-width development trend.At the same time,foreign equipment mostly uses lasers and PSD position sensors.Compared with domestic equipment,foreign testing equipment has faster detection speed,wider detection width and smaller detection pinhole,but the equipment is expensive.Therefore,in accordance with the current needs of the aluminum foil industry for high-speed and wide-width aluminum foil online testing equipment,this paper proposes a pinhole testing program that can meet the performance indicators of foreign high-end testing equipment.This design uses a silicon photodiode array as the receiving element because the photodiode has the advantages of high sensitivity,fast response speed,and low cost.In addition,in this design,an infrared light-emitting diode array light source with high illumination uniformity is arranged on the back of the aluminum foil.Through the above method,this design realizes 20 um pinhole detection on aluminum foil production equipment with a running speed of 1200m/min and a width of 2m.The realization of the scheme involves multiple disciplines such as optical design,optoelectronic calculation,analog circuit design,digital circuit design,mechanical design and manufacturing.The work done in this paper includes:(1)First,this paper establishes a detection model for pinhole detection on the surface of aluminum foil,and analyzes the model according to the detection conditions of high-speed wide-width micro-pinholes,and then obtains the difficulties of the detection system and specific parameter requirements.(2)In order to ensure the consistency of the pinhole detection results at each position under the wide format,this paper analyzes and studies the array method and illumination uniformity of the infrared light-emitting diode light source.This paper compares the three methods of illuminance uniformity evaluation by Sparrow's rule,standard deviation method,and range method.The above three methods are designed and simulated,and a strip-shaped uniform light with an illuminance uniformity error of 1% within a 2m width is realized.In addition,this paper also carries out other optical design such as convex lens optical path design,shading design and so on.(3)On the basis of the above-mentioned optical design,according to the characteristics of the photodiode,the static and dynamic parameters of the photo-generated electrical signal are calculated.(4)Then based on the calculation result of the photo-generated electrical signal,this article carries out the overall design of the photodiode analog amplifier circuit.The overall circuit is a two-stage operational amplifier circuit with no bias current mode.Then this article selects the amplifier based on the calculation results of the bandwidth and stability of the first-stage operational amplifier circuit.Next,this article calculates the signal-to-noise ratio level of the circuit based on the amplifier selection results.Based on this,the noise reduction design is carried out.Then this article carries on the circuit design of the second stage operational amplifier and the design of other circuit links.(5)Based on the completion of the analog circuit design,this article carries out the digital circuit design.First,calculate the analog-digital sampling circuit and select the analog-digital sampling chip according to the analog circuit parameters,and secondly complete the selection of the FPGA chip and the realization of functional modules.(6)According to the above design,the experiment equipment is made in this article,and the design and manufacture of each circuit board and the mechanical casing with a length of 2m are completed.Next,this article carries on the pinhole detection experiment.Experimental results show that the system can effectively detect pinholes above 20 um.