JP5629899B2 - Magnetic flaw detection method and apparatus - Google Patents

Description

  The present invention relates to a magnetic flaw detection technique for detecting a surface defect of a cylindrical inspection object made of a magnetic material from disturbance of a leakage magnetic field. More specifically, the inspection object is attracted to a rotating belt by a magnet, and in this state The present invention relates to a magnetic flaw detection method and apparatus in which an inspection object is rotated at a sensor position by moving the rotating belt, and a defect inspection is performed by a magnetic sensor provided in the vicinity of the outer peripheral surface of the inspection object. This technique is useful, for example, for defect inspection of a battery outer case (commonly called “battery can”).

  Conventional flaw detection methods for detecting surface defects in a cylindrical battery outer case made of a magnetic material include a method using a magnetic sensor such as a Hall element or a method using a coil. In the flaw detection method using a magnetic sensor, a defect is detected by bringing the magnetic sensor close to the battery outer case and measuring the leakage magnetic field from the surface of the excited battery outer case (see Patent Document 1). In the method using a coil, a coil through which an alternating current or a pulse current is passed is brought close to the battery outer case, and the defect is determined based on an impedance change or a voltage change due to a defect present in the battery outer case (see Patent Document 2). .

  In these conventional flaw detection methods, the battery outer case is usually rotated around its central axis to inspect the side surface (circumferential surface) for defects. For example, in Patent Document 1, the opening of the battery outer case is fixed and rotated by a holding jig. In Patent Document 2, the bottom portion (closed end portion) of the battery outer case is vacuum-adsorbed and rotated by a holding jig. In any of these rotation mechanisms, in order to hold the battery outer case, the orientation of the battery outer case needs to be aligned in advance, and an alignment mechanism for that purpose must be provided separately. Furthermore, when holding the bottom of the battery outer case, the entire periphery of the side surface can be inspected, but the holding jig is in the way, so the bottom of the battery outer case cannot be inspected as it is.

  Of course, if the defect on the surface of the object to be inspected is large to some extent, it can be inspected with the naked eye or a camera. However, since the battery outer case is molded by pressing, oils and the like are adhered to the surface immediately after molding, and it cannot be inspected with a camera or the like unless it is cleaned to remove dirt. However, for product management, etc., it is desired to develop a method that can detect defects easily and quickly even if it remains dirty without being washed immediately after molding. Therefore, a method using a magnetic sensor is considered useful. Yes.

JP 2006-153856 A JP 2009-252644 A

  The problem to be solved by the present invention is to rotate a cylindrical inspection object around a central axis at a predetermined sensor position without grasping or adsorbing the inspection object with a jig or the like. It is to be able to carry out defect inspection over the surface and at the same time at the edges as required. Another problem to be solved by the present invention is to continuously perform defect inspection by sequentially transferring the inspection object to a sensor position intermittently and rotating the inspection object at the sensor position.

  The present invention relates to a magnetic flaw detection method in which a magnetic field is applied to an inspection object made of a magnetic material, and a disturbance of a leakage magnetic field generated in a defect portion on the surface is detected using a magnetic sensor disposed close to the inspection object. The inspection object has a cylindrical shape, and an outer peripheral surface thereof is in contact with a rotating belt, and a magnetic field is applied to the inspection object by a magnet facing the inspection object via the rotation belt. The test object is attracted to the rotating belt by the magnetic force of the magnet and applied to the rotating belt, and the rotating belt is moved in a state where the magnet is held at the sensor position, so that the cylindrical inspection object is moved to the sensor position. The magnet is rotated around the central axis using the frictional force between the belt and the belt for rotation, and the peripheral surface of the object is inspected by the magnetic sensor. By flaw detection method That. The magnetic sensor may be arranged not only in the vicinity of the outer peripheral surface of the object to be inspected but also in the vicinity of one or both ends, whereby the end surface of the object to be inspected can be inspected at the same time.

  As the magnetic sensor, a magneto-optical element is preferable. This magneto-optical element is installed in the vicinity of the outer periphery of the object to be inspected, light that has passed through the polarizer is irradiated onto the magneto-optical element, and the light reflected by the surface of the magneto-optical element or the magneto-optical element is reflected after transmission. By observing the light through the analyzer, the disturbance of the leakage magnetic field generated in the defect portion on the surface of the object to be inspected is detected as a one-dimensional or two-dimensional light intensity distribution using the magneto-optic effect.

  The magneto-optical element used here preferably has a structure in which a reflective film is provided on one side of the magneto-optical film. In this case, this magneto-optical element is installed in the vicinity of the outer periphery of the inspection object so that the reflection film is on the inspection object side, and the light passing through the polarizer is irradiated from the magneto-optical film side. The reflected light is configured to be observed through the analyzer. The magneto-optical film is preferably a Bi-substituted iron garnet film, and preferably exhibits a characteristic that the magnetic field required for saturation in the direction parallel to the film surface is smaller than that in the direction perpendicular to the film surface.

  A Hall element, a search coil, or the like can be used as the magnetic sensor. As a magnetic flaw detection method, there is known a so-called eddy current flaw detection method in which an alternating magnetic field is applied to the surface of an object to be detected, and a change in a leakage magnetic field is detected by causing an eddy current disturbance at a defect portion. The method can also be applied to this.

  The inspection object is, for example, a cylindrical battery outer case. If the outer diameter in the axial direction is not uniform and changes, the cross-sectional shape of the belt for rotation is changed by changing the outer diameter in the axial direction of the inspection object by providing a step or gap in the width direction of the surface. It may be corrected. The rotating belt is preferably nonmagnetic.

  The magnet may be an electromagnet, but a permanent magnet is easier to handle. By moving the permanent magnet to the sensor position, the inspection object is transferred to the sensor position using the magnetic force of the permanent magnet, and the inspection object to be inspected is transferred from the sensor position by moving the permanent magnet from the sensor position. can do.

  The present invention also provides a magnetic flaw detection apparatus that applies a magnetic field to an inspection object made of a magnetic material and detects a disturbance of a leakage magnetic field generated at a defect portion on the surface using a magnetic sensor disposed close to the inspection object. A rotating belt for placing the cylindrical object to be inspected so that the outer peripheral surface is in contact with the central axis in a horizontal direction, a belt driving mechanism for moving the rotating belt, and the rotating belt. A permanent magnet that faces the object to be inspected, a magnet moving mechanism that intermittently drives the permanent magnet so as to temporarily stay at the sensor position, and a position near the outer peripheral surface of the object to be inspected at the sensor position. And a magnetic field applied to the object to be inspected by the permanent magnet, and the object to be inspected is transferred by using a magnetic force by moving the permanent magnet, and the rotation is performed at the sensor position. For bell A magnetic flaw detection apparatus characterized said using the frictional force to rotate the object to be inspected that to perform the defect inspection by the magnetic sensor by moving the it.

  A pressing roller positioned near the magnetic sensor and holding the distance between the magnetic sensor and the object to be inspected during inspection; and a pressing roller vertical movement mechanism for moving the pressing roller up and down in synchronization with the movement of the permanent magnet It is also effective to provide

  In the magnetic flaw detection method of the present invention, the inspection object made of a cylindrical magnetic material can be rotated around the central axis without being gripped or attracted by a jig or the like, so that only the outer peripheral surface of the inspection object is In addition, the end portion can be inspected at the same time. In addition, since there is no jig for gripping or adsorbing the inspection object as described above, a mechanism for aligning the inspection object in advance is unnecessary in principle.

  In the present invention, when a magneto-optical film is used as a magnetic sensor, a magnetic field distribution over a wide range can be optically detected instantaneously, so that a complicated mechanism for moving the magnetic sensor in parallel to the central axis is not required, and the apparatus is simplified. And can be inspected at high speed. In general, in order to inspect a flat inspection object in two dimensions using a magneto-optical film, a large area is required and expensive. In the present invention, the size of the magneto-optical film required for the sensor portion is as follows. Because it is smaller than that, it can be manufactured inexpensively.

  Further, since the permanent magnet is shared as a magnetic field applying means to the object to be inspected, an auxiliary means for rotating the object to be inspected, and a means for transferring, the entire apparatus has a simple configuration. .

The conceptual diagram of the magnetic flaw detection method which concerns on this invention. Explanatory drawing which shows the other structural example of the magnetic flaw detection method which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows one Example of the magnetic flaw detector which concerns on this invention. Explanatory drawing which shows the principal part of the other Example of the magnetic flaw detector based on this invention.

  A schematic configuration of a magnetic flaw detection method according to the present invention is shown in FIG. Here, A shows a state where the inspection object is rotated at the sensor position, and B shows a state where the inspection object is being transferred from the sensor position. The present invention uses a magnetic sensor in which a magnetic field is externally applied to a cylindrical inspection object made of a magnetic material, and a disturbance of a leakage magnetic field generated in a defect portion on the surface of the inspection object is disposed in proximity to the inspection object. To detect. The inspection object is most typically a battery outer case.

  As shown in FIG. 1, the cylindrical inspection object 10 is placed on the rotation belt 12 in a sideways state (in which the center axis faces the horizontal direction, in FIG. 1, the direction perpendicular to the paper surface). The outer peripheral surface of the inspection object 10 is in contact with the rotating belt 12. A permanent magnet 14 is positioned below the rotating belt 12 so as to face the inspection object 10 with the rotating belt 12 interposed therebetween. At this time, the permanent magnet 14 does not need to be in contact with the rotating belt 12. The permanent magnet 14 is typically a rectangular parallelepiped, and is arranged so as to be parallel to the inspection object 10, and the magnetization direction may be either perpendicular to the longitudinal direction of the inspection object or in the circumferential direction.

  A magnetic sensor 16 is installed above the inspection object 10 at the sensor position with a slight gap with respect to the outer peripheral surface. Here, a magneto-optical element 22 having a reflective film 20 provided on the lower surface (opposite surface to be inspected) side of the magneto-optical film 18 is used as the magnetic sensor 16, and although not shown, the conventional magneto-optical effect is shown. As in the optical system for observing the light, light is irradiated from above the magnetic sensor through the polarizer, and the reflected light is observed with a camera or the like through the analyzer. A change in the leakage magnetic field from the inspection object becomes a disturbance in the magnetization direction of the magneto-optical film, and is detected as a change in light intensity by the magneto-optical effect, so that a defect of the inspection object can be inspected.

  Since a magnetic sensor using a magneto-optical film can detect a magnetic field distribution as a two-dimensional light intensity distribution, for example, if a rectangular magneto-optical film is arranged along an inspection object, the entire peripheral surface of the inspection object is inspected. Compared to a magnetic sensor such as a Hall element or a detection element such as a coil, there is no need to move in a direction parallel to the rotation axis of the object to be inspected, and there is an advantage that the mechanism can be simplified.

  As the magneto-optical film used here, a Bi-substituted iron garnet film having a large magneto-optical effect is preferable, and is generally manufactured by a liquid phase epitaxial (LPE) method. The magnetic characteristics are preferably such that the magnetic field required for saturation in the direction parallel to the film surface is smaller than that in the direction perpendicular to the film surface. The magnetic properties of a Bi-substituted iron garnet film produced by the LPE method are divided into a perpendicular magnetization film that is easily magnetized in the direction perpendicular to the film surface and an in-plane magnetization film that is difficult to magnetize. In general, the perpendicular magnetization film has an easy axis of magnetization in the vertical direction and has a stripe-like domain structure. Since the spatial resolution depends on the size of the domain, it is not so high and the magnetic field required for saturation is small. On the other hand, the in-plane film receives a magnetic field in the direction perpendicular to the film surface, and the magnetization direction rotates smoothly from the in-plane direction. Therefore, the spatial resolution is high and the magnetic field required for saturation is large. In the present invention, a leakage magnetic field is generally generated from the outer peripheral surface of the object to be inspected, and the magneto-optic film is not magnetically saturated when a vertical film is used to detect the disturbance of the leakage magnetic field at the defective portion. Thus, a magnetic field distribution adjustment mechanism using an external bias magnetic field is required, which is complicated. Furthermore, since the leakage magnetic field is particularly large at the edge portion of the object to be inspected, adjustment becomes more difficult. In this respect, it is preferable to use an in-plane film having a large magnetic field detection range in the direction perpendicular to the film surface, and at the same time, the spatial resolution can be increased.

  As shown in A of FIG. 1, a magnetic field is applied to the object to be inspected 10 facing through the rotating belt 12 by the permanent magnet 14 stagnating at the sensor position, and the magnetic force of the permanent magnet 14 is also shown. Thus, the inspection object 10 is attracted to the rotating belt 12. Therefore, the inspection object 10 is pressed against the surface of the rotating belt 12 by its own weight and magnetic force. When the rotating belt 12 is moved in the horizontal direction (horizontal direction orthogonal to the central axis: arrow a direction) in this state (the permanent magnet is stationary), the inspection object 10 and the rotating belt 12 A rotational force is generated in the inspection object 10 due to the frictional force between them, and the inspection object 10 rotates around the central axis while remaining at the sensor position, that is, without changing the position (arrow b). direction). At this time, a leakage magnetic field is generated from the surface of the inspection object 10 to which the magnetic field is applied by the permanent magnet 14 below the rotating belt 12, and the inspection object 10 is 1 by using the magnetic sensor 16 installed above. During the rotation, it becomes possible to inspect the entire outer peripheral surface for defects.

  When the inspection of one inspection object 10 is completed, the permanent magnet 14 is moved in the lateral direction (arrow c direction) from the sensor position as shown in FIG. Then, the inspected object 10 is also attracted by the magnetic force and transferred together with the permanent magnet 14 (arrow d direction). At this time, the rotating belt 12 may be stopped or may continue to move. By utilizing this, a plurality of inspected objects can be intermittently sequentially transferred to the sensor position by arranging a plurality of permanent magnets at intervals and sequentially moving them to the sensor position. When the permanent magnet is moved in the lateral direction, the inspection object is moved to the sensor position, and the rotating belt is moved while the permanent magnet is stopped, the inspection object rotates and inspection can be performed at the inspection portion. When the inspection is completed, the permanent magnet can be moved again to transfer the object to be inspected.

  Although not shown in FIG. 1, if a magnetic sensor is also installed in the vicinity of both ends of a cylindrical inspection object, not only the outer peripheral surface but also the opening at the end and the defect of the closed portion Inspection can be performed at the same time.

  For example, when the object to be inspected is a cylindrical battery outer case, the vicinity of the opening end may have a slightly larger diameter in order to caulk after the battery element is accommodated therein. Thus, when the outer diameter of the cylindrical object is slightly changed in the axial direction, a step in the width direction is provided on the surface of the rotation belt 32 as shown in FIG. It is also possible to correct the change in the outer diameter of the inspection object 30 in the axial direction and correct the inclination of the inspection object 30 in the axial direction. The permanent magnet 34 is positioned below the rotating belt 32 so as to face the inspection object 30, and the magnetic sensor 36 is provided above the inspection object 30 at the sensor position as in the case of FIG. It is.

  If the cross-sectional shape of the rotating belt is made symmetrical in the width direction as shown in the figure, the direction of the inspection object is aligned even when the vicinity of the opening end of the inspection object has a slightly large diameter. Can be transported and inspected Therefore, in FIG. 2, separate magnetic sensors 36a and 36b are provided in the vicinity of both ends of the object to be inspected 30 so that the side of the open end and the closed end (bottom) can be inspected. doing.

  FIG. 3 is an explanatory view showing an embodiment of the magnetic flaw detector according to the present invention. This apparatus is a method of transferring a cylindrical battery outer case 40, which is an object to be inspected, in a horizontal direction (here, a direction in which the central axis is perpendicular to the paper surface). An endless rotating belt 42 supported so as to contact, a belt driving mechanism 43 that moves the rotating belt 42, and a plurality of permanent belts disposed below the battery outer case 40 via the rotating belt 42. A magnet 44; a magnet moving mechanism 45 that intermittently drives the permanent magnet 44 so that the permanent magnet 44 temporarily stays at the sensor position; and a magnetic sensor 46 installed at the sensor position so as to be positioned above the battery outer case 40. ing.

  The rotating belt 42 rotates the battery outer case 40 using frictional force, and the rotating belt 42 is rotated by a belt driving mechanism 43 that rotationally drives rollers located at both ends, as in a normal belt conveyor. In this configuration, 42 can be moved in the direction of arrow a. The magnet moving mechanism 45 is located inside the rotating belt 42, and a plurality of permanent magnets 44 are arranged at intervals and fixed to a connecting belt or the like, and moved separately from the rotating belt 42. It is configured to be able to. The connecting belt is intermittently driven, and the battery outer case 40 is transferred (arrow d direction) using magnetic force by the movement of the permanent magnet 44 (arrow c direction).

  Since the magnetic field is applied to the battery outer case 40 by the corresponding permanent magnet 44, the movement of the permanent magnet 44 is stopped at the sensor position, and only the rotating belt is moved (in the direction of arrow a). Rotates at the sensor position (in the direction of arrow b), and defect inspection is performed. When the inspection for one battery outer case is completed, the permanent magnet is moved again and the next battery outer case is transferred to the sensor position to perform the inspection. In this way, a plurality of battery outer cases can be inspected continuously. Even when oil at the time of pressing is adhered to the surface of the battery outer case, the amount of adhesion is not large, and thus the above-mentioned transfer / rotation operation was possible.

  Here, as the magnetic sensor 46, a Bi-substituted iron garnet film (magneto-optical film) having a thickness of 2 μm is grown on a transparent SGGG single crystal substrate having a thickness of 700 μm by a liquid phase epitaxial method, and a Pt sputtered film having a thickness of 200 nm is formed thereon. A magneto-optical element having a (reflection film) formed thereon was used. The magnetic garnet film is an in-plane film having a magnetic field required for saturation in the direction perpendicular to the film surface of 400 Oe.

  The optical system used for the inspection is as follows. A green LED is used as the light source 50, and the emitted light is linearly polarized using the polarizer 52, the optical path is bent by the beam splitter 54, and the magnetic sensor 56 is irradiated from above. The light that passed through the magneto-optic film and was reflected by the reflecting film passed through the beam splitter 54, passed through the analyzer 56, received by the CCD camera 58, and acquired image data by the personal computer 60. A half mirror may be used instead of the beam splitter.

  Since the magnetization direction in the magneto-optical film is the in-plane direction in a natural state, when linearly polarized light is applied to the magneto-optical film, the polarization plane of the reflected light by the reflection film does not rotate. Therefore, if the transmission axes of the polarizer 52 and the analyzer 56 are orthogonal to each other, the reflected light cannot pass through the analyzer 56 and the image taken by the CCD camera 58 becomes dark (black). When the magnetization direction in the magneto-optical film is perpendicular to the film surface, when the linearly polarized light is applied to the magneto-optical film, the plane of polarization of the reflected light from the reflective film rotates. Therefore, if the transmission axes of the polarizer 52 and the analyzer 56 are orthogonal to each other, the reflected light passes through the analyzer 56 and the image taken by the CCD camera 58 becomes bright (white). In this way, the defect inspection can be performed by detecting the disturbance of the leakage magnetic field generated in the defect portion on the surface of the inspection object as a one-dimensional or two-dimensional light intensity distribution.

  Using the apparatus of this example, a rectangular neodymium magnet was placed in parallel with the cylindrical battery outer case via a rotating belt, and defects on the peripheral surface of the battery outer case were observed. Even linear flaws could be reliably detected.

  Further, as shown in FIG. 4, restraining rollers 48 are provided in the vicinity of the magnetic sensor 46 on both the front and rear sides so as to sandwich the magnetic sensor 46, and the distance between the magnetic sensor 46 and the inspection object 40 is constant during the inspection. If the rotation position is held, the rotational position is determined and stable inspection can be performed. These holding rollers 48 may be free rollers that rotate freely. Further, when a restraining roller vertical movement mechanism 49 is provided that moves the restraining roller 48 up and down in synchronization with the movement of the permanent magnet 44 (indicated by an arrow e), the inspection object is carried into or out of the sensor position. There is no obstacle. The parts shown in FIG. 4 can be applied to FIG. 3 as they are. Therefore, the corresponding parts are denoted by the same reference numerals, and description thereof will be omitted. Here, the magnetic sensor and the pressing roller may be configured to move integrally up and down, or the magnetic sensor may be configured to be fixed and movable only up and down.

DESCRIPTION OF SYMBOLS 10 Test object 12 Belt for rotation 14 Permanent magnet 16 Magnetic sensor

Claims (9)

In a magnetic flaw detection method for applying a magnetic field to an inspection object made of a magnetic material and detecting a disturbance of a leakage magnetic field generated in a defect portion on the surface using a magnetic sensor disposed close to the inspection object.
The inspection object has a cylindrical shape, and an outer peripheral surface thereof is in contact with a rotation belt, and a magnetic field is applied to the inspection object by a magnet facing the inspection object via the rotation belt. In addition, the inspection object is attracted to the rotation belt by the magnetic force of the magnet, and the cylindrical inspection object is moved to the sensor position by moving the rotation belt in a state where the magnet is stopped at the sensor position. Magnetic flaw detection characterized in that the inspection object is rotated around a central axis by utilizing a frictional force between the rotation belt and the peripheral surface of the inspection object while being stopped. Method.   The magnetic flaw detection method according to claim 1, wherein a magnetic sensor is also disposed near one or both ends of the inspection object, and the end surface of the inspection object is also inspected simultaneously.   The magnetic sensor is a magneto-optical element, and the magneto-optical element is placed in the vicinity of the outer periphery of the object to be inspected, and the light passing through the polarizer is irradiated onto the magneto-optical element and reflected by the surface of the magneto-optical element. By observing the light or the light reflected after passing through the magneto-optical element through the analyzer, the disturbance of the leakage magnetic field generated in the defect portion of the surface of the object to be inspected using the magneto-optical effect is one-dimensional or two-dimensional light. 3. The magnetic flaw detection method according to claim 1, wherein the magnetic flaw detection method is detected as an intensity distribution.   The magneto-optical element has a structure in which a reflection film is provided on one surface of a magneto-optical film, and the magneto-optical film is a Bi-substituted iron garnet film in which a magnetic field required for saturation in the direction parallel to the film surface is small compared to the direction perpendicular to the film surface. The magnetic flaw detection method according to claim 3, which is used.   The cross-sectional shape of the rotating belt is a shape having a step or a gap in the width direction of the surface thereof, and the change in the outer diameter in the axial direction of the cylindrical inspection object is corrected by the shape. The magnetic flaw detection method according to any one of 1 to 4.   The magnetic flaw detection method according to claim 5, wherein the inspection object is a cylindrical battery outer case.   The magnet is a permanent magnet. By moving the permanent magnet to the sensor position, the inspection object is transferred to the sensor position by using the magnetic force of the permanent magnet, and the permanent magnet is moved from the sensor position. 7. The magnetic flaw detection method according to claim 1, wherein the inspection object is transferred from the sensor position. In a magnetic flaw detection apparatus that applies a magnetic field to an inspection object made of a magnetic material and detects a disturbance of a leakage magnetic field generated in a defect portion on the surface using a magnetic sensor disposed close to the inspection object.
A rotating belt for placing a cylindrical object to be inspected so that the outer peripheral surface is in contact with the central axis in a horizontal direction, a belt driving mechanism for moving the rotating belt, and the rotating belt through the rotating belt. A permanent magnet that faces the object to be inspected, a magnet moving mechanism that intermittently drives the permanent magnet so as to temporarily stagnate at the sensor position, and a position near the outer peripheral surface of the object to be inspected at the sensor position. A magnetic sensor, and a magnetic field is applied to the object to be inspected by the permanent magnet, and the object to be inspected is transferred using a magnetic force by moving the permanent magnet. A magnetic flaw detector in which a defect is inspected by the magnetic sensor by rotating the inspection object by rotating the inspection object by using a friction force.   There is provided a control roller that is located near the magnetic sensor and maintains a constant distance between the magnetic sensor and the object to be inspected during inspection, and a control roller vertical movement mechanism that moves the control roller up and down in synchronization with the movement of the permanent magnet. The magnetic flaw detector according to claim 8.

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