Research And System Design Of Magneto-optical Imaging Restoration Technology For Damaged Characters

The characters formed by stamping,scribing and dot matrix punching on ferromagnetic materials often cannot be recognized because of wear and tear,so it is necessary to study the method of restoring damaged characters.In this paper,magneto-optical imaging technology is proposed to realize the non-destructive,high-resolution and safe restoration of damaged characters.Based on the atomic pair ordering theory,slip-induced magnetic anisotropy in ferromagnetic materials subjected to plastic deformation is studied in this paper.Taking stamping characters as an example,the effective slip system and magnetic anisotropy energy are analyzed,and it is found that the hard axis(hard magnetizing axis)of the inner edge is coincident with the easy axis(easy magnetizing axis)of the outer edge of character arc outline.This paper also studies the fundamental theory of magneto-optical imaging,designs the magneto-optical imaging optical system to recover damaged characters,deduces the relationship between light intensity and magnetic rotation angle,and analyzes the factors affecting the imaging resolution.According to theoretical research and optical system,a magneto-optical imaging restoration experimental system for damaged characters is designed and built,which is mainly composed of LED area light source,polarizer,splitter,magneto-optical medium,analyzer,CCD camera,electromagnet and stabilized voltage supply.The heteropolar annular electromagnet capable of performing parallel magnetization is designed and different types of damaged character samples are made.The magneto-optical imaging experiments are carried out by three magnetization methods,namely,vertical magnetization of permanent magnet and electromagnet,parallel magnetization of annular electromagnet.The permanent magnet vertical magnetization experiment can clearly restore the damaged characters,but because the magnetic field cannot be adjusted,the imaging resolution is low.The experiments were carried out by using an electromagnet with adjustable magnetic field,which were based on different angle between polarizer and analyzer,basic material,character forming mode and damage depth,respectively.The results show that the damaged characters are clearly restored,and the gray value of the magneto-optical images is analyzed to study the influence of these factors on the imaging resolution.Experimental results show that when the angle between polarizer and analyzer is about 75°,the imaging resolution is the best.The imaging results of Q235 steel and 45 steel samples are the same,but they are completely different from 304 stainless steel samples.The image of stamping characters is better than that of scribing and dot matrix punching.For the characters with a stamping depth of 0.4mm,the maximum damage depth for effective recovery is less than 0.7 mm.In addition,through magneto-optical imaging experiments,it is found that the magnetic induction intensity of the inner edge of the character decreases while the outer edge increases,which verifies the theory of slip-induced magnetic anisotropy of stamping characters.The parallel magnetization of annular electromagnet can be easily excited,as well as can realize the clear restoration of damaged characters.Finally,a magneto-optical imaging recovery device for damaged characters is designed and manufactured.The test results show that the device can clearly restore the position and outline of the damaged characters.