JP5305706B2 - Electromagnetic ultrasonic probe, ultrasonic flaw detector, and ultrasonic flaw detection method - Google Patents

Description

  The present invention relates to an electromagnetic ultrasonic probe, an ultrasonic flaw detection apparatus, and an ultrasonic flaw detection method, and more particularly, to an electromagnetic ultrasonic probe, an ultrasonic flaw detection apparatus, and an ultrasonic flaw detection method that detect defects and thinning of piping. .

  Generally, there is a method as disclosed in Patent Document 1 as a method for detecting a piping defect or thinning. The method disclosed in Patent Document 1 uses the magnetostriction effect of piping. That is, a coil is wound around a pipe, and a magnetic field is applied to the vicinity of the pipe by a permanent magnet or an electromagnet to generate static magnetostriction. By passing an alternating current through a coil wound around the pipe, an alternating magnetic field is generated in the pipe, and an ultrasonic wave is generated by changing the amount of static magnetostriction. In Patent Document 1, in the case of a pipe having no magnetostrictive effect, a metal band to which magnetostriction is applied in advance is wound around the pipe, and a coil is wound around the metal band. By passing an alternating current through this coil, the amount of magnetostriction of the metal band is changed to vibrate the metal band. By transmitting the vibration of the metal band to the pipe, ultrasonic waves can be generated in the pipe.

  However, the method disclosed in Patent Document 1 is an effective method when the pipe itself has a magnetostrictive effect. However, if the pipe does not have a magnetostrictive effect, it is also disclosed in Patent Document 1. It is necessary to use a metal band (see the publication, page 6, lines 32 to 37). Usually, when this metal band is used to transmit / receive ultrasonic waves to / from a pipe, it is necessary to perform bonding by bonding after positioning. Since general-purpose piping has no magnetostrictive effect unless special treatment is performed, a metal band is joined to the piping. When sending and receiving ultrasonic waves using a metal band joined to piping, it takes time to join, lengthy preparation work, and it is difficult to guarantee joining quality, so depending on the skill of the worker There is a problem that variation occurs in the inspection.

  On the other hand, as shown in Patent Document 2, a method using an electromagnetic ultrasonic probe has been proposed. This is a method of using an electromagnetic ultrasonic probe for receiving ultrasonic waves. In the method disclosed in Patent Document 2, two permanent magnets are arranged so as to have different magnetization directions, and a coil is installed on one surface of the arranged permanent magnets. Since the method shown in Patent Document 2 does not use the magnetostriction effect of the piping, a metal band is unnecessary, and an operation for joining is also unnecessary (see paragraph [0068] of FIG. 4 and FIG. 4).

In the electromagnetic ultrasonic probe shown in Patent Document 2, a pancake coil for receiving ultrasonic waves is installed. As shown in the upper side of FIG. 12, the pancake coil 28 is formed in a rectangular spiral shape from the outer end to which the input terminal to which the alternating current 6 is supplied is connected, and is connected to the output terminal. It has a planar shape that continues to the part. As shown in the lower side of FIG. 12, the two permanent magnets 18 are arranged so that their S poles and N poles have different magnetization directions, and below the arranged permanent magnets 18 (on the ultrasonic receiving side). A pancake coil 28 for receiving ultrasonic waves is arranged. When the alternating current 6 is supplied to the pancake coil 28, the magnetic flux 16 is generated in the direction shown in the lower side of FIG. 12, and the eddy current 7 is generated on the surface of the pipe 3 so that the Lorentz in the direction indicated by the arrow. Force 17 is generated.
Japanese Patent No. 3669706 JP 2006-53134 A

  However, since the pancake coil as shown in Patent Document 2 is manufactured by winding a general-purpose steel wire in a flat shape using a special jig, or by manufacturing a printed circuit board, the manufacturing method becomes complicated. . For this reason, an electromagnetic ultrasonic probe using a solenoid coil that is easy to manufacture has been desired.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide an electromagnetic ultrasonic probe, an ultrasonic flaw detection apparatus, and an ultrasonic flaw detection method using a solenoid coil that can be easily manufactured.

In order to solve the above-described problem, the electromagnetic ultrasonic probe according to the first configuration of the present invention applies a magnetic flux from the permanent magnet to an object by the permanent magnet wound with the coil, and flows through the coil. An electromagnetic ultrasonic probe for generating an ultrasonic wave in the object by generating an eddy current in the object by an electric current, wherein the permanent magnet is magnetized in a radial direction from an outer peripheral surface to an inner peripheral surface. and has a cylindrical shape, the coil is wound to the circumferential direction of the permanent magnet in the axial, characterized and this.

The electromagnetic ultrasonic probe according to the second configuration of the present invention applies a magnetic flux generated by the permanent magnet to an object by a permanent magnet wound with a coil, and vortexes the object by an electric current flowing through the coil. An electromagnetic ultrasonic probe for generating an ultrasonic wave on the object by generating an electric current, wherein the permanent magnet is at least one arc-shaped magnetized in a radial direction from an outer peripheral surface to an inner peripheral surface a permanent magnet, the coil is wound to the circumferential direction of the permanent magnet in the axial, characterized and this.

An electromagnetic ultrasonic probe according to a third configuration of the present invention is the electromagnetic ultrasonic probe according to the second configuration described above, wherein the object has a cylindrical shape, and the permanent magnet is disposed around the object. It is characterized by a plurality of arrangements in the direction.

An electromagnetic ultrasonic probe according to a fourth configuration of the present invention applies a magnetic flux generated by the permanent magnet to a target by a permanent magnet wound with a coil, and vortexes the target by a current flowing through the coil. by generating a current, an electromagnetic ultrasonic probe for generating ultrasonic waves to the object, together with the permanent magnets are arranged along the outer peripheral surface of the object of cylindrical shape, the object At least one cuboid permanent magnet magnetized in the radial direction from the outer circumferential surface to the inner circumferential surface , and the coil is wound around the permanent magnet about a direction perpendicular to the magnetized direction of the permanent magnet. It is attached, and wherein a call.

An electromagnetic ultrasonic probe according to a fifth configuration of the present invention is the electromagnetic ultrasonic probe according to the fourth configuration, wherein a plurality of the permanent magnets are arranged in the circumferential direction of the object. And

In the ultrasonic flaw detection method according to the sixth configuration of the present invention, the magnetic flux density of the electromagnetic ultrasonic probe according to any one of the first to fifth configurations is orthogonal to the surface of the object. arranged, said induced on the surface of the electromagnetic ultrasonic the object by flowing an alternating current to the coil of the probe of the eddy currents, to generate ultrasonic waves by Lorentz force generated in the object, the greater A reflected echo of a sound wave is detected by the electromagnetic ultrasonic probe.

An ultrasonic flaw detection method according to a seventh configuration of the present invention is the electromagnetic ultrasonic probe according to any one of the third and fifth configurations, wherein each of the plurality of permanent magnets is the target object . By arrange | positioning so that an axial direction position may differ, it arrange | positions diagonally with respect to the axial direction of the said target object , It is characterized by the above-mentioned.

  According to the electromagnetic ultrasonic probe, the ultrasonic flaw detector, and the ultrasonic flaw detection method of the present invention, it becomes easy to manufacture a solenoid coil, and it is possible to reliably detect piping defects and thinning at a low cost. Become.

  Hereinafter, embodiments of an electromagnetic ultrasonic probe, an ultrasonic flaw detector, and an ultrasonic flaw detection method according to the present invention will be described with reference to the drawings.

(First embodiment)
First, the first embodiment will be described with reference to FIG. The electromagnetic ultrasonic probe A shown in the first embodiment includes a cylindrical permanent magnet 1 magnetized in a radial direction from an outer peripheral surface to an inner peripheral surface, and the circumferential direction of the permanent magnet 1 as an axis. It is composed of a wound solenoid coil 2. And when using this electromagnetic ultrasonic probe A, as shown in FIG. 1, it installs and uses it so that magnetic flux density may be added with respect to the piping 3 which is a flaw detection object. Further, the electromagnetic ultrasonic probe A is fixed to the pipe 3 by using the fixing jig 4.

  The operation of the electromagnetic ultrasonic probe A configured as described above will be described with reference to FIG. FIG. 2 is an enlarged view of a part of the electromagnetic ultrasonic deep contact A shown in FIG. A magnetic flux density 5 is applied by the cylindrical permanent magnet 1 magnetized in the radial direction so as to be orthogonal to the surface of the pipe to be flaw-detected. Next, when an alternating current 6 is passed through the solenoid coil 2 wound around the permanent magnet 1, an eddy current 7 is induced on the pipe surface in the axial direction of the pipe as shown in FIG.

  Since the magnetic flux density 5 and the eddy current 7 are generated orthogonally, a Lorentz force 8 is generated in the circumferential direction of the pipe 3 according to Fleming's left-hand rule. Since the Lorentz force 8 is generated by the eddy current 7 induced by the alternating current 6, it changes with time. Therefore, this Lorentz force 8 generates an ultrasonic wave having the same frequency as the alternating current 6. In addition, the direction in which the generated Lorentz force 8 is generated is the circumferential direction of the pipe 3 and has no vibration component in the axial direction of the pipe 3, so that pure torsional vibration is generated.

  Here, when the frequency of the ultrasonic wave is high and the wavelength is shorter than the plate thickness of the pipe, it propagates in the radial direction of the pipe as a normal transverse wave. However, when the frequency of the ultrasonic wave is low and the wavelength is longer than the thickness of the pipe, it does not propagate in the radial direction of the pipe but propagates in the axial direction of the pipe. In this case, since the vibration direction is the pipe circumferential direction and the propagation direction is the pipe axis direction, it becomes a torsional wave.

  Although the above description is an operation of generating ultrasonic waves, the operation of receiving ultrasonic waves is a reverse process as shown in FIG. That is, in the electromagnetic ultrasonic probe having the configuration as shown in FIGS. 1 and 2, the torsional wave arrives with the magnetic flux density (B) 5 applied, and vibrates in the circumferential direction of the pipe 3 (V). If there is 9, an electric field (E) is generated on the pipe surface by Fleming's right-hand rule (E = V × B). This electric field (E) generates an eddy current (J = σE, σ is conductivity) 10 on the pipe surface. This current (J) 10 generates linkage flux 11. Since this interlinkage magnetic flux 11 interlinks with the solenoid coil 2, a voltage (Vout) based on Faraday's law is generated by the interlinkage magnetic flux 11 at both ends of the solenoid coil 2, and ultrasonic waves can be detected. Therefore, the electromagnetic ultrasonic probe A shown in FIGS. 1 and 2 can transmit and receive a torsion wave.

  FIG. 4 shows a case where the electromagnetic ultrasonic probe A having the above configuration is used. In FIG. 4, a torsional wave 12 is generated by an electromagnetic ultrasonic probe A. When the pipe 3 has a thinning or a defect 13, the torsional wave 12 is reflected at the location of the thinning or the defect and the reflected echo 14 is detected by the electromagnetic ultrasonic probe A. In this way, it is possible to detect the occurrence of the thinning in the pipe and the occurrence of the defect.

(Second Embodiment)
Next, the electromagnetic ultrasonic probe B according to the second embodiment of the present invention will be described with reference to FIG. In FIG. 5, an electromagnetic ultrasonic probe B includes an arc-shaped permanent magnet 15 magnetized in a radial direction from an outer peripheral surface to an inner peripheral surface, and a solenoid coil 2 wound around the circumferential direction of the permanent magnet 15. Consists of The operation of the electromagnetic ultrasonic probe B having the configuration shown in FIG. 5 is the same as that of the electromagnetic ultrasonic probe A of the first embodiment shown in FIG. 1 and FIG. That is, the magnetic flux density 16 is applied in the radial direction of the pipe by the arc-shaped permanent magnet 15 magnetized in the radial direction as shown in FIG. Next, when an alternating current 6 is passed through the solenoid coil 2 wound around the permanent magnet 15, an eddy current 7 is induced on the pipe surface in the axial direction of the pipe as shown in FIG. Since the magnetic flux density 16 and the eddy current 7 are orthogonal to each other, a Lorentz force 17 is generated in the circumferential direction of the pipe 3 according to Fleming's left-hand rule.

  Since the Lorentz force 17 is generated by the eddy current 7 induced by the alternating current 6, it changes over time. Therefore, this Lorentz force 17 generates an ultrasonic wave having the same frequency as the alternating current 6. In addition, the direction in which the generated Lorentz force 17 is generated is the circumferential direction of the pipe 3 and has no vibration component in the axial direction of the pipe 3, so that pure torsional vibration is generated.

  Here, as described in the first embodiment, when the frequency of the ultrasonic wave is high and the wavelength is shorter than the plate thickness of the pipe, it propagates as a normal transverse wave in the radial direction of the pipe. However, when the frequency of the ultrasonic wave is low and the wavelength is longer than the thickness of the pipe, it does not propagate in the radial direction of the pipe but propagates in the axial direction of the pipe. In this case, since the vibration direction is the pipe circumferential direction and the propagation direction is the pipe axis direction, it becomes a torsional wave.

  The reception of ultrasonic waves is performed by the same operation as in the first embodiment, and is omitted here. The electromagnetic ultrasonic probe of the second embodiment shown in FIG. 5 can transmit and receive ultrasonic waves as in the first embodiment. Further, the occurrence of the thinning in the pipe and the occurrence of the defect are detected in the same manner as in the first embodiment shown in FIG.

(Third embodiment)
Next, an electromagnetic ultrasonic probe according to the third embodiment of the present invention will be described with reference to FIG. In FIG. 6, a plurality of electromagnetic ultrasonic probes B shown in the second embodiment are arranged in the circumferential direction of the pipe 3. The electromagnetic ultrasonic probes B are connected in series or in parallel to transmit / receive torsional waves.

  In this way, even when the transmission intensity is insufficient with the electromagnetic ultrasonic probe B shown in the second embodiment, it is possible to improve the transmission intensity by using a plurality. Further, since the received ultrasonic echoes can be increased by the number of electromagnetic ultrasonic probes B that use them, the reception sensitivity is also improved.

  In the third embodiment, if a sufficient ultrasonic echo level can be obtained with a small number of electromagnetic ultrasonic probes, the cost of the electromagnetic ultrasonic probe can be reduced.

(Fourth embodiment)
Next, an electromagnetic ultrasonic probe C according to the fourth embodiment of the present invention will be described with reference to FIG. In FIG. 7, an electromagnetic ultrasonic probe C is wound around a rectangular parallelepiped permanent magnet 18 that is magnetized in a direction perpendicular to the pipe surface 3 and a direction perpendicular to the magnetized direction of the permanent magnet 18. The solenoid coil 2 is provided. The operation of the electromagnetic ultrasonic probe C shown in FIG. 7 is the same as that of the electromagnetic ultrasonic probe A shown in FIGS. 1 to 4 and the electromagnetic ultrasonic probe B shown in FIGS. I will omit it. In addition, the reception of ultrasonic waves is also performed by the same operation as in the first embodiment, so this is also omitted.

  That is, the direction in which the generated Lorentz force 17 is generated is the circumferential direction of the pipe 3, and since no vibration component is present in the axial direction of the pipe 3, pure torsional vibration is generated. Here, as in the first embodiment, when the frequency of the ultrasonic wave is high and the wavelength is shorter than the plate thickness of the pipe, it propagates as a normal transverse wave in the radial direction of the pipe. However, when the frequency of the ultrasonic wave is low and the wavelength is longer than the thickness of the pipe, it does not propagate in the radial direction of the pipe but propagates in the axial direction of the pipe. In this case, since the vibration direction is the pipe circumferential direction and the propagation direction is the pipe axis direction, it becomes a torsional wave.

  In addition, since reception of ultrasonic waves is performed by the same operation as in the first embodiment, description thereof is omitted here. The electromagnetic ultrasonic probe C shown in FIG. 7 can transmit and receive ultrasonic waves as in the first embodiment. Furthermore, the thinning occurrence location and the defect occurrence location 13 in the pipe are detected in the same manner as in the first embodiment shown in FIG.

(Fifth embodiment)
Next, an electromagnetic ultrasonic probe according to a fifth embodiment of the present invention will be described with reference to FIG. In FIG. 8, a plurality of electromagnetic ultrasonic probes C shown in the fourth embodiment are arranged in the circumferential direction of the pipe. These electromagnetic ultrasonic probes C are connected in series or in parallel to transmit and receive torsional waves. In this way, even when the transmission intensity of the electromagnetic ultrasonic probe shown in the fourth embodiment is insufficient, the transmission intensity can be improved by using a plurality of transmissions. Further, since the received ultrasonic echoes can be increased by the number of electromagnetic ultrasonic probes that use them, the reception sensitivity is also improved.

  In the fifth embodiment, if a sufficient ultrasonic echo level can be obtained with a small number of electromagnetic ultrasonic probes, the cost of the electromagnetic ultrasonic probe can be reduced.

  Also, two electromagnetic ultrasonic probes of the first to fifth embodiments are used, and these electromagnetic ultrasonic probes are installed adjacent to each other, one for ultrasonic transmission and the other for ultrasonic transmission. It may be an ultrasonic flaw detector for receiving sound waves.

(Sixth embodiment)
Next, an ultrasonic inspection apparatus and method according to the sixth embodiment of the present invention will be described with reference to FIG. FIG. 9 shows that two electromagnetic ultrasonic probes according to the first to fifth embodiments are arranged. Moreover, in FIG. 9, it is assumed that the distance between two electromagnetic ultrasonic probes is ¼ of the wavelength of the torsion wave that generates the distance.

  The operation of the electromagnetic ultrasonic probe at this time will be described with reference to FIGS. In FIG. 10 (a), one of the ultrasonic ultrasonic transducers is set as # 1, and the other ultrasonic ultrasonic transducer installed at a quarter wavelength away from the electromagnetic ultrasonic transducer # 1 is # 2. To do. When a sinusoidal alternating current whose current value gradually increases from 0 is passed through the electromagnetic ultrasonic probe # 1, the torsional waves 19a and 19b have amplitudes from 0 as shown in FIG. 10 (b). It gradually increases and propagates symmetrically to the right and left sides of the pipe.

  Next, when a sinusoidal alternating current that flows through the electromagnetic ultrasonic probe # 2 and that has a phase difference of 90 degrees is passed through the electromagnetic ultrasonic probe # 1, the twist is generated. As shown in FIG. 10C, the waves 20a and 20b start from the maximum value and propagate symmetrically to the right and left sides of the pipe. Therefore, these two torsional waves 19a, 19b, 20a, and 20b are added on the pipe 3, so that as shown in FIG. The torsional waves 21a generated by the child # 1 and the electromagnetic ultrasonic probe # 2 are overlapped in the same phase.

  However, on the left side of the piping, the torsional waves 21b generated by the electromagnetic ultrasonic probe # 1 and the electromagnetic ultrasonic probe # 2 are out of phase and cancel each other. Therefore, if the electromagnetic ultrasonic probe # 1 and the electromagnetic ultrasonic probe # 2 are operated with such a configuration and the phase relationship of the alternating current, the torsional wave 21a propagating in one direction can be generated. . If a torsion wave propagating in one direction is used, the intensity of ultrasonic waves is added, so that the level of reflection echo from pipe thinning and defects can be improved.

(Seventh embodiment)
Next, an ultrasonic flaw detection method according to the seventh embodiment of the present invention will be described with reference to FIG. 7th Embodiment is an Example in the case of applying to the elbow piping 22 and the piping 22 with a curvature. In FIG. 11A, the seventh embodiment is the pipe 3 to which the elbow pipe 22 is connected to the electromagnetic ultrasonic probe of the first embodiment to the fifth embodiment and the ultrasonic flaw detector of the sixth embodiment. The torsional wave incidence and reflection from the elbow pipe 22 are schematically shown. The torsional wave 23 generated by the electromagnetic ultrasonic probe has a wavefront 24 perpendicular to the pipe axis direction, propagates without reflecting the pipe 3 on which the electromagnetic ultrasonic probe is installed, and enters the elbow pipe 22.

  Next, since the curvatures of the torsion wave front 25 and the elbow pipe 22 are different at the point (1) where the curvature is greatly changed first, the torsion wave is reflected. Further, the light is also reflected at the end faces of (2) and (3). As described above, in a pipe having a curvature such as an elbow pipe, the torsional wave is reflected where the curvature changes. Therefore, if there is a pipe thinning or a defect at the location in FIG. 11A, it overlaps with the reflected echo from the curvature portion, and the pipe thinning or the defect cannot be identified.

  On the other hand, as shown in FIG. 11B, the electromagnetic ultrasonic probe is installed in the pipe 3 with an inclination of about 45 degrees. In this case, the wavefront 26 of the torsion wave is inclined about 45 degrees in the pipe axis direction. The torsion wave propagates through the straight pipe portion without being reflected and enters the elbow pipe 22. Next, since the inclination angle of the wavefront 27 and the curvature of the elbow pipe 22 are the same even at the location (1) where the curvature changes greatly at first, the reflection does not occur as shown in FIG.

  Further, when the torsional waves reach the end faces (2) and (3), they are reflected by these end faces. Therefore, if the attachment method shown in FIG. 11B is used, the torsional wave is reflected only at the end face of the elbow pipe 22, so that it can be detected even if pipe thinning or a defect exists at the position (1). .

Schematic which shows the structure of 1st Embodiment of this invention. Explanatory drawing of the operation | movement which transmits the torsional wave in 1st Embodiment. Explanatory drawing of the operation | movement which receives the torsional wave in 1st Embodiment. Explanatory drawing of the operation | movement which detects the pipe thinning and defect in 1st Embodiment. Schematic which shows the structure of 2nd Embodiment of this invention. Explanatory drawing which shows 3rd Embodiment which connected two or more electromagnetic ultrasonic probes of 2nd Embodiment in series. Schematic which shows the structure of 4th Embodiment of this invention. Explanatory drawing which shows 5th Embodiment which connected the several electromagnetic ultrasonic probe of 4th Embodiment in series. Schematic which shows the structure of 6th Embodiment of this invention. Explanatory drawing of propagation (a)-(d) of the ultrasonic wave to one direction in 6th Embodiment. The conceptual diagram which shows reflection (a) (b) of the torsion wave in the elbow part in 7th Embodiment. Explanatory drawing which shows the electromagnetic ultrasonic probe using the conventional pancake coil.

Explanation of symbols

A, B, C Electromagnetic ultrasonic probe 1 Permanent magnet 2 Solenoid coil 3 Piping 6 AC current 22 Elbow piping 23 Torsional wave

Claims (7)

An electromagnetic force that generates an ultrasonic wave on the object by applying a magnetic flux generated by the permanent magnet to the object by a permanent magnet wound with a coil and generating an eddy current in the object by a current flowing through the coil. An ultrasound probe,
The permanent magnet has a cylindrical shape which is magnetized in the radial direction of the inner peripheral surface from the outer peripheral surface,
The coil is wound with the circumferential direction of the permanent magnet in the axial,
Electromagnetic ultrasonic probe, wherein a call. An electromagnetic force that generates an ultrasonic wave on the object by applying a magnetic flux generated by the permanent magnet to the object by a permanent magnet wound with a coil and generating an eddy current in the object by a current flowing through the coil. An ultrasound probe,
The permanent magnet is at least one arc-shaped permanent magnet magnetized in the radial direction of the inner peripheral surface from the outer peripheral surface,
The coil is wound with the circumferential direction of the permanent magnet in the axial,
Electromagnetic ultrasonic probe, wherein a call. The electromagnetic ultrasonic probe according to claim 2, wherein the object has a cylindrical shape, and a plurality of the permanent magnets are arranged in a circumferential direction of the object . An electromagnetic force that generates an ultrasonic wave on the object by applying a magnetic flux generated by the permanent magnet to the object by a permanent magnet wound with a coil and generating an eddy current in the object by a current flowing through the coil. An ultrasound probe,
Wherein with permanent magnets are arranged along the outer peripheral surface of the object of cylindrical shape, at least one rectangular parallelepiped permanent magnets magnetized in the radial direction of the inner peripheral surface from the outer peripheral surface of said object,
The coil is wound on the permanent magnet in the axis direction perpendicular magnetized direction of the permanent magnet,
Electromagnetic ultrasonic probe, wherein a call. The electromagnetic ultrasonic probe according to claim 4, wherein a plurality of the permanent magnets are arranged in a circumferential direction of the object . The electromagnetic ultrasonic probe according to any one of claims 1 to 5 is arranged so that a magnetic flux density is orthogonal to a surface of the object ,
Said induced surface eddy current electromagnetic ultrasonic the object by flowing an alternating current to the coil of the probe generates an ultrasonic wave by the Lorentz force generated on the object,
An ultrasonic flaw detection method, wherein the reflected echo of the ultrasonic wave is detected by the electromagnetic ultrasonic probe. The electromagnetic ultrasonic probe according to any one of claims 3 and 5,
The ultrasonic flaw detection method, wherein each of the plurality of permanent magnets is arranged so as to be inclined with respect to the axial direction of the object by arranging the objects so that the positions of the objects in the axial direction are different.

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