CN104764798B - A kind of visualization leakage magnetic detection device - Google Patents
A kind of visualization leakage magnetic detection device Download PDFInfo
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- CN104764798B CN104764798B CN201510136346.9A CN201510136346A CN104764798B CN 104764798 B CN104764798 B CN 104764798B CN 201510136346 A CN201510136346 A CN 201510136346A CN 104764798 B CN104764798 B CN 104764798B
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Abstract
The invention discloses a kind of visualization leakage magnetic detection devices, the material of reflectance coating is coated with as magnetic sensing element using with magnetic rotation light characteristic and in bottom, that is, measured piece side, and the Visual retrieval that optical image acquisition system realizes leakage field is constituted with light source, CCD camera, two convex lenses, two panels polarizing film.Since detection introduces carrier of the light as information, so leakage field image, that is, flare is very high to the spatial resolution of leakage field.The present invention visualizes the Polaroid area of leakage magnetic detection device and is only limited by the effective area of CCD camera sensor and magnet-sensitive element, and relative to traditional flux-leakage detection method such as GMR, detection efficiency can greatly improve.Simultaneously by controlling the polarizer i.e. polarization direction of the first polarizing film and adjusting the incident angle of incident ray, make incident ray in magneto-optic thin film shows that generation total transmissivity fully enters magneto-optic thin film, to avoid the interference of surface reflection, and then greatly improve detection sensitivity.
Description
Technical field
The invention belongs to technical field of nondestructive testing, more specifically, are related to a kind of visualization leakage magnetic detection device.
Background technology
Non-destructive testing (NDT-Nondestructive Testing) is an important component of detection technique.It is
In the case where not damaging detected object, using caused by material internal structure exception or defect to heat, sound, light, electricity, magnetic
The variation of equal reactions, various engineering material, parts, structural member etc. be internal or surface defect detecting, and to the type of defect,
Property, quantity, shape, position, size, distribution and its variation are judged and are evaluated, to evaluate permissible load, the service life of component
Or the structural imperfection that is generated during manufacture and use of remaining life or detection device and defect situation, to change
Into manufacturing process, product quality is improved, finds failure in time, ensures equipment safety, reliability service.
Currently, there is five big conventional methods in non-destructive testing technology, it is respectively：Ultrasonic method, ray method, magnetic particle method, osmosis
And eddy-current method.In the magnetic material detections such as ferritic steel, widely used Magnetic Flux Leakage Inspecting.However, Magnetic Flux Leakage Inspecting is adopted more at present
Use GMR, hall probe or Hall array as magnetic sensing element, their spatial resolutions and detection efficiency are low, to fine crack
It cannot effectively identify and testing result is not intuitive.Therefore, efficient leakage field Visual retrieval has especially important meaning.
However, in leakage field Visual retrieval, magneto-optic thin film surface (magnetic-optical film) reflected light is not
It carries Leakage flux distribution information and is superimposed upon in flare, interference effect is played to the image information detected, is thereby reduced
Detection sensitivity.To solve this problem, existing method is to apply anti-reflection film on magneto-optic thin film surface, to reduce its surface reflection
By force, but the anti-reflection effect of anti-reflection film can only avoid surface reflection completely in vertical incidence, and anti-reflection effect is also with incidence angle
Increase and reduces.Therefore, in the case where not applying anti-reflection film, effectively avoid the interference of surface reflection that there is important reality meaning
Justice.
Simultaneously.As shown in Figure 1, due to use vertical incidence mode, need with optical splitter carries out light path adjustment and strictly it is right
Together, structure is more complicated, and use is not very convenient.
Invention content
It is an object of the invention to overcome the shortage of prior art, a kind of visualization leakage magnetic detection device is provided, to avoid magnetic
The interference of optically-active film surface reflected light improves detection sensitivity, meanwhile, simplify structure, it is easy to use.
For achieving the above object, the present invention visualizes leakage magnetic detection device, which is characterized in that including：
Magneto-optic thin film (magnetic-optical film) with magnetic rotation light characteristic, bottom surface, that is, iron of the magneto-optic thin film
Magnetic material measured piece side is coated with reflectance coating, using as magnetic sensing element；
Magnetic field generation device, for generating magnetic field and acting on measured piece；
Light source is sent out scattering light and is gathered into directional light by light source, the first convex lens and the first polarizing film, the first convex lens
Line, and as incident ray；Incident ray is incident on after direction adjustment is polarized in the first polarizing film in magneto-optic thin film,
Then reflection light is obtained after the reflection of the reflectance coating of its bottom, after reflection light is pierced by magneto-optic thin film, reaches the second polarization
Piece；
Second polarizing film, the second convex lens and CCD camera, the second polarizing film are adjusted the reflection light of arrival,
The linearly polarized light with leakage field information is obtained, then gathering CCD camera by the second convex lens forms with light and shade region
Flare, the flare reflect the horizontal distribution i.e. defect situation of leakage field indirectly, to reach leakage field (defect)
Visual retrieval；
First polarizing film is as polarizer, using coplanar with the plane of incidence and direction conduct perpendicular to incident ray
Polarizer is polarized direction；
The incidence angle of the incident ray and magneto-optic thin film：
Wherein, n1For the aerial refractive index of light, n2The refractive index for being light in magneto-optic thin film.
The object of the present invention is achieved like this.
The present invention visualizes leakage magnetic detection device and uses with magnetic rotation light characteristic and be coated with instead in bottom, that is, measured piece side
The material of film is penetrated as magnetic sensing element, optical image acquisition is constituted with light source, CCD camera, two convex lenses, two panels polarizing film
System realizes the Visual retrieval of leakage field.Non-destructive testing for ferrimagnet, Leakage flux distribution are with a kind of area image
What mode reflected, so it does not need scale and defect form is intuitive.Since detection introduces carrier of the light as information, so leakage
Magnetic image, that is, flare is very high to the spatial resolution of leakage field.The present invention visualizes the Polaroid area of leakage magnetic detection device
It is only limited by the effective area of CCD camera sensor and magnet-sensitive element, relative to traditional flux-leakage detection method such as GMR, inspection
Surveying efficiency can greatly improve.Simultaneously by controlling the polarizer i.e. polarization direction of the first polarizing film and adjusting entering for incident ray
Firing angle degree makes incident ray in magneto-optic thin film shows that total transmissivity, which occurs, fully enters magneto-optic thin film, to avoid surface anti-
The interference of light is penetrated, and then greatly improves detection sensitivity.
Description of the drawings
Fig. 1 is the theory structure schematic diagram of existing visualization leakage magnetic detection device；
Fig. 2 is the leakage field phenomenon schematic diagram of the lower ferromagnetic material of U-shaped permanent magnet excitation；
Fig. 3 is a kind of present invention visualization specific implementation mode principle schematic of leakage magnetic detection device；
Fig. 4 is laser light incident and reflection schematic diagram, wherein (a) is the transmission schematic diagram of incident ray, is (b) incident light
The reflection schematic diagram of line；
Fig. 5 is the leakage field image on the present invention visualization collected magnetic material of leakage magnetic detection device (measured piece) surface,
Wherein, (a) is simulation rectangular crack；(b) it is the leakage field image of crackle.
Specific implementation mode
The specific implementation mode of the present invention is described below in conjunction with the accompanying drawings, preferably so as to those skilled in the art
Understand the present invention.Requiring particular attention is that in the following description, when known function and the detailed description of design perhaps
When can desalinate the main contents of the present invention, these descriptions will be ignored herein.
1, ferromagnetic material leakage field
Fig. 2 is the leakage field phenomenon schematic diagram of the lower ferromagnetic material of U-shaped permanent magnet excitation.In the present embodiment, as shown in Figure 1,
When, there are when surface or following table planar defect, the path that magnetic resistance can be selected smaller according to magnetic field line passes through in ferromagnetic material measured piece 2
This principle, magnetic field can part slave surface defect (crackle) 3 upper table space of planes in pass through, it is tested to form ferromagnetic material
The surface leakage field of part 2, the magneto optic images acquired in this way (encircled portion in figure) can effectively reflect this non-uniform magnetic field
Distribution, to reach Visual retrieval.In the present embodiment, magnetic field generation device uses U-shaped direct current magnetic core coil or permanent magnet 1
To generate magnetic field.
2, the realization of Visual retrieval
As shown in figure 3, it includes the magneto-optic thin film 4 for having magnetic rotation light characteristic that the present invention, which visualizes leakage magnetic detection device,
(magnetic-optical film), magnetic field generation device (in order to keep schematic diagram succinct, being not drawn into, specific as shown in Figure 1),
Light source 5, the first convex lens 6, the first polarizing film 7, the second polarizing film 8, the second convex lens 9 and CCD camera 10.
The bottom of magneto-optic thin film, that is, 2 side of ferromagnetic material measured piece is coated with reflectance coating, it can serve as magnetic sensing in this way
Element.
Light source 5 is sent out scattering light and is gathered into parallel rays by the first convex lens 6, and as incident ray, the first polarizing film 7
Unidirectional light is only allowed to pass through, so it is linearly polarized light to be incident on the magnetic sensing element i.e. light of magneto-optic thin film 4.
Incident ray is incident in magneto-optic thin film 4, then passes through after direction adjustment is polarized in the first polarizing film 7
Reflection light is obtained after the reflectance coating reflection of its bottom, after reflection light is pierced by magneto-optic thin film 4, reaches the second polarizing film 8.
Second polarizing film 8 is adjusted the reflection light of arrival, obtains the linearly polarized light with leakage field information, then passes through
It crosses the second convex lens 9 and gathers flare of the formation of CCD camera 10 with light and shade region, which reflects indirectly
Horizontal distribution, that is, defect situation of leakage field, to reach the Visual retrieval of leakage field (defect).
Line after leakage field modulation (magnetic field to be incident on the linearly polarized light polarization angle in magneto-optic thin film and changes) is inclined
Shake light, it penetrates the second polarizing film 8, and at this time flare just will appear light and shade region, the difference of light intensity in this same hot spot
The different uneven distribution for just embodying magnetic field.In the present embodiment, 8 physical arrangement of the second polarizing film is identical polarizes with first
Piece 7 is identical, and its polarization direction and reflecting surface are coplanar and perpendicular to reflection light.In this way, being influenced and being occurred by leakage field
The light of certain angle deflection will not pass through, and corresponding part will be dimmed in flare.
3, surface reflection is avoided to interfere：
The bottom surface that the present invention visualizes the magneto-optic thin film with magnetic rotation light characteristic used in leakage magnetic detection device is coated with instead
Film, the collected flare of CCD camera are penetrated, existing magneto-optic thin film surface reflection light also has bottom reflection light.Surface is anti-
It penetrates light not to be uniformly distributed in by the modulation of Leakage flux distribution in flare, it forms leakage field weak image signal folded
Add interference, this greatly reduces the sensitivity of leakage field Visual retrieval.
Conventional method is to apply to increase an antireflective film layer again on magneto-optic thin film surface, increases cost in this way, but simultaneously can not
Reduce surface reflection interference well, because the effect with the increase anti-reflection film of incidence angle can continuously decrease.
The present invention visualizes leakage magnetic detection device adjusting polarizer and is polarized direction perpendicular to incident ray and is total to the plane of incidence
Face simultaneously sets incident angle as θb, it can make incident ray be refracted into magneto-optic thin film completely and surface reflection is avoided to interfere.
A), polarizer is polarized the determination in direction
As shown in Fig. 4 (a), incident ray ErThe s components E in vertical incidence face can be resolved intorsWith the p for being parallel to the plane of incidence
Component Erp, similarly reflection light Ef=Efs+Efp.If the polarization direction parallel component E of initial incident rayrp(i.e. Ers=0),
So component E of the reflection light perpendicular to reflecting surfacefs=0, reflection light E at this timef=Efp, that is, it is equal to point for being parallel to reflecting surface
Measure Efp。
B) incidence angle θbCalculating：
From Fresnel theorems：
Work as θb+θzAt=90 °, there is Efp=0, i.e. reflection light is linearly polarized light, incidence angle θ at this timebReferred to as Brewster
Angle.
From the law of refraction：
n1*sinθb=n2*sinθz (2)
θ againb+θz=90 °, so sin θz=cos θb, thus obtain incidence angle θbFor：
From analyzing above：It is polarized and is oriented parallel to Erp, when incidence angle is θbWhen, reflection light Ef=Efs+Efp=0,
Incident ray (linearly polarized light) at this time can be refracted into magneto-optic thin film completely.By symmetry it is found that incident ray can be through bottom surface
Reflect and again in the complete bounce back air in the upper surface of magneto-optic thin film, as shown in Fig. 4 (b).
The present invention visualizes leakage magnetic detection device and is polarized direction and incident angle by being accurately controlled polarizer, can be complete
The full interference for avoiding surface reflection.
4, experimental verification
Experiment is detected the face crack of the bar shaped silicon steel of 0.33mm thickness, by the laser facula that wavelength is 632.8nm
Transmitter and beam expanding lens constitute light source, diameter about 10mm after hot spot amplification.As shown in figure 5, (a) is the spelling of two blocks of bar shaped silicon steel
It connects, the face crack of magnetic material is simulated with seam crossing；(b) collected anti-for by this visualization leakage magnetic detection device
Penetrate hot spot i.e. leakage field image.
From Fig. 5 (b) it is found that the bar shaped silicon steel rectangular crack that the black stripe region in leakage field image is, the present invention are visual
The Visual retrieval in leakage field region can effectively be realized by changing leakage magnetic detection device.After effectively surface reflection being avoided to interfere, this
Invention visualizes leakage magnetic detection device leakage field that can be detected down to 100Gs.
The present invention is visualized leakage magnetic detection device and is used as using direction coplanar with the plane of incidence and perpendicular to incident ray
Polariscope is polarized direction, using Brewster's angle as incidence angle so that and incident ray can be all refracted into magneto-optic thin film, to
The interference for avoiding surface reflection light substantially increases the sensitivity of Visual retrieval.
The present invention visualizes leakage magnetic detection device innovative point and its value：Improve the spatial resolution of Magnetic Flux Leakage Inspecting；Inspection
Survey visual result；Detection efficiency greatly improves；It proposes control and is polarized angle and incident angle to avoid surface reflection interference
Method, substantially increase detection sensitivity.It is simple and easy to use, real time imagery inspection can be carried out to surface layer and subsurface defect
It surveys；Image does not need scale calibration.
Although the illustrative specific implementation mode of the present invention is described above, in order to the technology of the art
Personnel understand the present invention, it should be apparent that the present invention is not limited to the range of specific implementation mode, to the common skill of the art
For art personnel, if various change the attached claims limit and determine the spirit and scope of the present invention in, these
Variation is it will be apparent that all utilize the innovation and creation of present inventive concept in the row of protection.
Claims (2)
1. a kind of visualization leakage magnetic detection device, which is characterized in that including：
Bottom surface, that is, ferromagnetic material measured piece side of magneto-optic thin film with magnetic rotation light characteristic, the magneto-optic thin film is coated with reflectance coating,
Using as magnetic sensing element；
Magnetic field generation device, for generating magnetic field and acting on measured piece；
Light source is sent out scattering light and is gathered into parallel rays by light source, the first convex lens and the first polarizing film, the first convex lens, and
As incident ray；Incident ray is incident in magneto-optic thin film, then passes through after direction adjustment is polarized in the first polarizing film
Reflection light is obtained after crossing the reflectance coating reflection of its bottom, after reflection light is pierced by magneto-optic thin film, reaches the second polarizing film；
Second polarizing film, the second convex lens and CCD camera, the second polarizing film are adjusted the reflection light of arrival, obtain
Then linearly polarized light with leakage field information passes through the second convex lens and gathers reflection of the CCD camera formation with light and shade region
Hot spot, the flare reflect the horizontal distribution i.e. defect situation of leakage field indirectly, to reach the Visual retrieval of leakage field；
First polarizing film is used as using coplanar with the plane of incidence and direction perpendicular to incident ray and is polarized as polarizer
Mirror is polarized direction；
The incidence angle of the incident ray and magneto-optic thin film：
Wherein, n1For the aerial refractive index of light, n2The refractive index for being light in magneto-optic thin film.
2. detection device according to claim 1, which is characterized in that the second polarizing film physical arrangement and the first polarizing film object
It is identical to manage structure, and its polarization direction and reflecting surface are coplanar and perpendicular to reflection light.
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| CN106093182B (en) * | 2016-05-31 | 2019-02-01 | 电子科技大学 | A kind of visualization Magnetic Flux Leakage Inspecting modeling method based on circular current |
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| CN111307723B (en) * | 2020-03-06 | 2021-06-15 | 山东大学 | Magnetic rotation diaphragm, magneto-optical sensor, and weld joint detection device and method |
| CN113176238B (en) * | 2021-04-22 | 2023-10-31 | 国网安徽省电力有限公司电力科学研究院 | Magnetic imaging device based on diamond film |
| CN113686879A (en) * | 2021-09-09 | 2021-11-23 | 杭州利珀科技有限公司 | Optical film defect visual detection system and method |
Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4625167A (en) * | 1983-07-05 | 1986-11-25 | Sigma Research, Inc. | Flaw imaging in ferrous and nonferrous materials using magneto-optic visualization |
| US4755752A (en) * | 1983-07-05 | 1988-07-05 | Gerald L. Fitzpatrick | Flaw imaging in ferrous and nonferrous materials using magneto-optic visualization |
| US5446378A (en) * | 1993-12-15 | 1995-08-29 | Grumman Aerospace Corporation | Magneto-optic eddy current imaging apparatus and method including dithering the image relative to the sensor |
| CN2720440Y (en) * | 2004-04-29 | 2005-08-24 | 西南科技大学 | Magnetooptical vortex imaging damage free detection apparatus |
| CN103698393A (en) * | 2013-12-03 | 2014-04-02 | 广东工业大学 | Magneto-optical imaging nondestructive detection method of weld defects |
| CN103984126A (en) * | 2014-05-23 | 2014-08-13 | 电子科技大学 | Plane magneto-optical isolator |
-
2015
- 2015-03-26 CN CN201510136346.9A patent/CN104764798B/en not_active Expired - Fee Related
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4625167A (en) * | 1983-07-05 | 1986-11-25 | Sigma Research, Inc. | Flaw imaging in ferrous and nonferrous materials using magneto-optic visualization |
| US4755752A (en) * | 1983-07-05 | 1988-07-05 | Gerald L. Fitzpatrick | Flaw imaging in ferrous and nonferrous materials using magneto-optic visualization |
| US5446378A (en) * | 1993-12-15 | 1995-08-29 | Grumman Aerospace Corporation | Magneto-optic eddy current imaging apparatus and method including dithering the image relative to the sensor |
| CN2720440Y (en) * | 2004-04-29 | 2005-08-24 | 西南科技大学 | Magnetooptical vortex imaging damage free detection apparatus |
| CN103698393A (en) * | 2013-12-03 | 2014-04-02 | 广东工业大学 | Magneto-optical imaging nondestructive detection method of weld defects |
| CN103984126A (en) * | 2014-05-23 | 2014-08-13 | 电子科技大学 | Plane magneto-optical isolator |
Non-Patent Citations (1)
| Title |
|---|
| 铁磁材料表面缺陷的磁光成像检测方法研究;熊新;《万方学位论文数据库》;20140917;正文第3.2节、第4.2节、第4.5节、第4.6节、第5.1节，图3-8、图3-9、图5-2、图5-3 * |
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