JP4902173B2 - Permanent magnet magnetic circuit and permanent magnet device using the same - Google Patents

Description

  The invention of this application relates to a magnetic circuit of a permanent magnet and a permanent magnet device using the same. More specifically, the invention of this application can change the strength of the magnetic field. In particular, in an MRI permanent magnet device or a particle accelerator permanent magnet device that requires a high magnetic field, these permanent magnet devices are assembled. The present invention relates to a magnetic circuit of a permanent magnet and a permanent magnet device using the same, which can solve problems such as danger during disassembly and difficulty in handling.

  Permanent magnets are widely used in motors, actuators, generators, magnetic separators, magnetic material removers, water treatment devices, health equipment for smaller items, and MRI magnet devices and particle accelerator magnet devices for larger items. Has been. Among them, rare earth magnets composed of samarium, neodymium, etc. have a high residual magnetic field strength exceeding 1 Tesla (T). It is necessary to make a special tool / jig that can overcome the repulsive force. In addition, rare earth magnets are vulnerable to impacts and are susceptible to cracking and chipping. Therefore, from this point of view, a special and sturdy tool and jig are required. However, even with tools and jigs, the strength of the magnetic force of rare earth magnets does not change, so precision work is difficult and the work itself is dangerous and often left to the skilled worker.

  Permanent magnets are often carried by aircraft, but in general, magnets are classified as “hazardous properties” in the same way as explosives and radioactive materials. It is said that bringing a magnet close to an electronic control device or bringing it into an aircraft will affect the instrument panel and control panel, possibly leading to a failure or accident. Therefore, in order to reach the standard that can transport magnets by aircraft such as jet aircraft, it is necessary to pack this in a large box, and the leakage magnetic field strength on the surface of the packing box must be shielded to the same extent as the natural magnetic field It's a bad rule. For that purpose, it is necessary to deal with the packing box by separating a large space from the permanent magnet and surrounding the periphery with an iron plate or the like. In addition, it is dangerous to bring a magnet close to a person wearing an electronic medical device such as a pacemaker, which may impair the normal operation of the medical device, and no technical countermeasures have been developed for this purpose.

  As a conventional technique, there is a permanent magnet device that turns a magnet on and off in a classical manner. It is called a magneto chuck. This is to install a rotating magnet in the magnetic circuit, rotate the permanent magnet 90 degrees, create a gap (gap) in the magnetic circuit, and branch the magnetic flux to increase the magnetic resistance and weaken the force as a magnet It is something that can be done. However, the difficulty of this technique is that the application is limited to chucking for fixing a workpiece or the like, and the inventor of this application previously used the saturated iron core effect exceeding the residual magnetic field. When it is applied to a strong magnetic circuit, magnetic flux leaks and its branching effect becomes weak, so that a sufficient effect cannot be exhibited.

  In addition, many of the conventional permanent magnets are used in a state of a constant strength with a fixed magnetic field strength. As a method of changing the magnetic field strength, there is a method in which a direction in which an anisotropic small magnet is changed to form a hollow ring (also called a Harbach type magnet or a REC magnet) is rotated in multiple layers. However, the configuration of the magnet is limited to a hollow ring electromagnet or the like, and it is difficult to produce a general variable magnet.

  Furthermore, the permanent magnet has a problem that the residual magnetic field changes depending on the temperature of the material itself. For example, when the magnetic field strength is desired to be constant at about 1% or less, the influence is large, and the stability of the magnetic field is great. There was a problem in that. In order to solve this problem, conventionally, a method of reducing the overall temperature coefficient by inserting a certain amount of materials having different signs of the temperature coefficient into the parallel circuit has been used.

  Therefore, the invention of this application has been made in view of the actual state of the prior art, and can change the strength of the magnetic field, particularly for MRI permanent magnet devices and accelerators that require a high magnetic field. An object of the present invention is to provide a permanent magnet magnetic circuit and a permanent magnet device using the permanent magnet device that can solve problems such as danger and difficulty at the time of assembly and disassembly of the permanent magnet device. To do.

  In addition, the scope of the invention of this application is not limited to the structure and configuration of the magnet, but the scope of application is wide. Even if it is applied to a very strong magnetic circuit similar to a superconducting magnet, it exhibits its function. An object of the present invention is to provide a permanent magnet magnetic circuit capable of maintaining a stable magnetic field even when the ambient temperature changes, and a permanent magnet device using the same.

In order to solve the above problem, the invention of this application firstly, a pair of rod-shaped permanent magnets whose magnetization is oriented in a specific direction and the pair of rod-shaped permanent magnets are relatively continuous in magnetization direction or A mechanism for rotating and arranging at least one bar-shaped permanent magnet around the axis of the bar-shaped magnet so as to discontinuously change, and the pair of bar-shaped permanent magnets has at least one bar-shaped permanent magnet without a yoke 5T (Tesla) in which the cross-section is directly adjacent to each other in a state of being accommodated in a non-magnetic case having a complementary permanent magnet accommodating space corresponding to the shape of the rod-shaped permanent magnet, and the entire magnetic field strength is variable. The present invention provides a magnetic circuit for permanent magnets for MRI or particle accelerators, which is applicable to a magnetic circuit with a high-intensity magnetic field such as

Second, in the first invention, the pair of rod-like permanent magnets are rod-like permanent magnets having a circular or polygonal cross section, and the magnetic circuit of the MRI or particle accelerator permanent magnet I will provide a.

According to a third aspect of the permanent magnet for MRI or particle accelerator according to the first or second aspect of the invention, the direction of magnetization is in a plane perpendicular to the axial direction of the rod-shaped permanent magnet. Provide a magnetic circuit.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the mechanism that rotates and arranges at least one rod-shaped permanent magnet is configured such that one rod-shaped permanent magnet is continuous with the other rod-shaped permanent magnet. A magnetic circuit for a permanent magnet for MRI or particle accelerator , characterized in that it is a permanent magnet rotation mechanism that continuously changes the direction of one magnetization relative to the direction of the other magnetization by .

Further, in the fifth, in the fourth aspect, the permanent magnet rotating mechanism is an electric motor, MRI, characterized in that rotating the rod-shaped permanent magnet via a gear provided on at least one rod-like permanent magnet Or a magnetic circuit of a permanent magnet for a particle accelerator .

According to a sixth aspect of the present invention, there is provided a magnetic circuit for a permanent magnet for MRI or particle accelerator, wherein the permanent magnet rotating mechanism is an ultrasonic motor in the fourth or fifth invention.

Seventhly, in any one of the fourth to sixth inventions, a magnetic circuit for a permanent magnet for MRI or particle accelerator is provided, wherein the strength of the magnetic field can be varied freely from zero to the maximum value. To do.

Eighthly, in any one of the fourth to seventh inventions, a magnetic field strength detecting means for detecting the magnetic field strength is provided, and the magnetic field strength is controlled based on the detection result of the magnetic field strength detecting means. The magnetic circuit of the permanent magnet for MRI or particle accelerator according to any one of claims 4 to 7.

Ninthly, in any one of the first to eighth inventions, one permanent magnet can be accommodated in the permanent magnet accommodating space with respect to the other permanent magnet so that the magnetization direction is different. A magnetic circuit for a permanent magnet for MRI or particle accelerator is provided.

According to a tenth aspect of the present invention, there is provided a magnetic circuit for a permanent magnet for MRI or particle accelerator , characterized in that in any of the first to ninth inventions, the strength of the magnetic field can be completely turned on and off. To do.

In the eleventh aspect, the magnetic circuit of any one of the first to tenth MRI or particle accelerator permanent magnets is used as one unit, and a plurality of MRI or particle accelerator permanent magnet magnetic circuits are combined. Provided is a permanent magnet device for MRI or particle accelerator characterized by being configured.

Further, in the twelfth aspect, in the eleventh aspect of the present invention, the magnetic field intensity generated by the magnetic circuit of each MRI or particle accelerator permanent magnet is completely set during assembly or disassembly of the MRI or particle accelerator permanent magnet device. There is provided a permanent magnet device for MRI or particle accelerator characterized by being able to be zero or less including a sign or a certain value.

According to the invention of this application, the intensity of the magnetic field generated by the permanent magnet can be varied with a simple configuration, and it can be varied smoothly from zero to the maximum value as well as on / off. According to the invention of this application, in particular, in the MRI permanent magnet device and the particle accelerator permanent magnet device that require a high magnetic field, the danger and difficulty in handling these permanent magnet devices during assembly and disassembly, etc. In addition, the scope of application of the invention of this application is not limited to the structure and configuration of the magnet, but is wide and general.

  Further, even if the invention of this application is applied from a weak permanent magnet magnetic circuit to a very strong permanent magnet magnetic circuit similar to a superconducting magnet such as 5T (Tesla), its function does not change. When the magnetic field is strong in this way, it is impossible to correct the path of the magnetic circuit like a conventional magnet chuck.

  Further, according to the invention of this application, temperature compensation is possible by detecting a residual magnetic field change due to temperature by a magnetic sensor and feeding back this, and the magnetic field can be kept constant with high accuracy for a long time.

Furthermore, according to the invention of this application, it is possible to compensate for deterioration such as residual magnetic field due to radiation exposure by feedback similar to the above.
The conventional method could not cope with any of these problems.

  The invention of this application has the features as described above, and an embodiment thereof will be described below.

  The magnetic circuit of the permanent magnet according to the invention of this application is a pair of two permanent magnets whose magnetization is oriented in a specific direction, and the magnetization direction of these pair of permanent magnets changes continuously or discontinuously. Thus, a mechanism for rotating and arranging at least one permanent magnet is provided to form one unit.

  The pair of permanent magnets may be rod-shaped permanent magnets having a circular or polygonal cross section. When the cross section is a polygon, the number of corners can be arbitrary, and it is preferably a regular polygon so that the direction of magnetization can be changed. In this case, the magnetization direction of the permanent magnet is preferably in a plane perpendicular to the axial direction of the rod-shaped permanent magnet.

  In the invention of this application, the mechanism for rotating and arranging at least one permanent magnet continuously rotates one permanent magnet with respect to the other permanent magnet, thereby changing the direction of one magnetization to the other. Can be a permanent magnet rotating mechanism that continuously changes.

  In the invention of this application, the mechanism for rotating and arranging at least one of the permanent magnets has a permanent magnet housing space having a complementary shape corresponding to the shape of a rod-shaped permanent magnet having a polygonal cross section. The bar-shaped permanent magnet can be accommodated in the space so that the directions of magnetization are different.

  A first structural example of a magnetic circuit of a permanent magnet according to the invention of this application is schematically shown in a sectional view in FIGS. In the figure, (1) is a non-magnetic case, (2) is an anisotropic permanent magnet, and (3) is the direction of magnetization. In these drawings, only the rotating anisotropic permanent magnet (2) is shown for convenience.

  The anisotropic permanent magnet (2) is columnar, and the direction perpendicular to the axis is the direction of magnetization. In FIG. 1, both of the cylindrical anisotropic permanent magnets (2) can be continuously rotated from 0 to 360 degrees. In FIG. 2, one of the cylindrical anisotropic permanent magnets (2) It is fixed and the other is continuously rotatable from 0 to 360 degrees.

  As a permanent magnet rotating mechanism (not shown) for rotating the anisotropic permanent magnet (2), various conventionally known rotating mechanisms can be used. Typically, an electric motor or an ultrasonic motor is used. Can do. When an electric motor is used, a gear is attached to the anisotropic permanent magnet (2) to transmit the rotational driving force. In this case, a gear reduction mechanism may or may not be provided. In addition, when an ultrasonic motor is used, direct drive is possible, and there is an advantage that it does not affect the magnetism, and operation in a strong external magnetic field is possible for the first time. Further, it can be operated with a large-diameter hollow motor.

  The anisotropic permanent magnet (2) has zero magnetic field strength when the magnetization directions are opposite to each other (off state), and the maximum strength (on state) when the directions are the same. Become. And by changing the angle continuously, it can be changed continuously from zero to the maximum value. Of course, it is possible to change it discontinuously.

A second configuration example of the magnetic circuit of the permanent magnet according to the invention of this application is schematically shown in cross-sectional views in FIGS. Oh Ru denoted by the same reference numerals are used for the same elements as FIGS. 1 and 2 in FIGS. Similarly, in these drawings, only the anisotropic permanent magnet (2) that can be rotationally arranged is shown for convenience.

  The anisotropic permanent magnet (2) is columnar, and the direction perpendicular to the axis is the direction of magnetization. In FIG. 3, both of the columnar anisotropic permanent magnets (2) having a polygonal cross section can be discontinuously (intermittently) rotated from 0 to 360 degrees, and in FIG. One of the anisotropic permanent magnets (2) is fixed, and the other is discontinuously (intermittently) rotated from 0 to 360 degrees.

  In order to accommodate the anisotropic permanent magnet (2) in the non-magnetic case (1) so that the magnetization directions are different, the non-magnetic case (1) has a rod-like different cross section. A complementary permanent magnet housing space corresponding to the shape of the isotropic permanent magnet (2) is formed. The anisotropic permanent magnet (2) which can be rotationally arranged can be detachably accommodated in the permanent magnet accommodation space. When changing the direction of magnetization, the anisotropic permanent magnet (2) is taken out, the angle of the anisotropic permanent magnet (2) is rotated by a predetermined angle so that the direction of magnetization changes, and the nonmagnetic case ( It is accommodated in the permanent magnet accommodation space of 1).

  The anisotropic permanent magnet (2) has zero magnetic field strength when the magnetization directions are opposite to each other (off state), and the maximum strength (on state) when the directions are the same. Become. And by changing the angle, it can be changed discontinuously from zero to the maximum value.

  According to the invention of this application, a permanent magnet device for MRI and a permanent magnet device for particle accelerator can be configured by using a plurality of units of the magnetic circuit of the permanent magnet of one unit. In that case, the shape and dimension of the permanent magnet of each unit can be appropriately set according to the application. With such a configuration, the strength of the magnetic field generated by the magnetic circuit of each permanent magnet at the time of assembly or disassembly of the permanent magnet device can be zero or a weak magnetic field of a certain value or less. Problems such as stability and difficulty are solved.

  Further, according to the invention of this application, in the case of the configuration of FIG. 1 or FIG. 2, magnetic field detection means for detecting the strength of the magnetic field generated by the pair of anisotropic permanent magnets (2) is provided, and the detection result Can be fed back to the permanent magnet rotation mechanism to control the strength of the magnetic field. In this way, it is possible to compensate for changes in the residual magnetic field due to temperature, deterioration of the residual magnetic field due to radiation exposure, and the like.

  Further, even if the invention of this application is applied from a weak magnetic circuit to a very strong permanent magnet circuit similar to a superconducting magnet such as 5T (Tesla), its function does not change.

  As mentioned above, although the invention of this application was described in detail based on embodiment, it cannot be overemphasized that the invention of this application is not limited to the said embodiment, and various aspects are possible about a detail.

It is sectional drawing which shows typically the 1st example of the magnetic circuit of the permanent magnet by invention of this application. It is sectional drawing which shows typically the 2nd example of the magnetic circuit of the permanent magnet by invention of this application. It is sectional drawing which shows typically the 3rd example of the magnetic circuit of the permanent magnet by invention of this application. It is sectional drawing which shows typically the 4th example of the magnetic circuit of the permanent magnet by invention of this application.

Explanation of symbols

1 Non-magnetic case 2 Anisotropic permanent magnet 3 Direction of magnetization

Claims (12)

A pair of rod-shaped permanent magnet is magnetized in a specific direction oriented, the pair of rod-shaped permanent magnets, rod-shaped magnet at least one rod-like permanent magnet as relatively magnetization direction changes continuously or discontinuously And a pair of rod-shaped permanent magnets without a yoke, and at least one of the rod-shaped permanent magnets has a complementary permanent magnet accommodating space whose cross section corresponds to the shape of the rod-shaped permanent magnet. It is arranged directly adjacent to each other in a state of being accommodated in a non-magnetic case having a magnetic field, and the entire magnetic field strength is variable, and can be applied to a magnetic circuit having a high strength magnetic field such as 5T (Tesla). Permanent magnet magnetic circuit for MRI or particle accelerator . The magnetic circuit of the permanent magnet for MRI or particle accelerator according to claim 1, wherein the pair of rod-like permanent magnets are rod-like permanent magnets having a circular or polygonal cross section. The magnetic circuit of the permanent magnet for MRI or particle accelerator according to claim 1 or 2, wherein the direction of magnetization is in a plane perpendicular to the axial direction of the rod-shaped permanent magnet. The mechanism for rotating and arranging at least one rod-shaped permanent magnet continuously rotates one rod-shaped permanent magnet with respect to the other rod-shaped permanent magnet, thereby changing one magnetization direction with respect to the other magnetization direction. The magnetic circuit of the permanent magnet for MRI or particle accelerator according to any one of claims 1 to 3, wherein the magnetic circuit is a permanent magnet rotating mechanism that continuously changes. 5. The permanent magnet for MRI or particle accelerator according to claim 4, wherein the permanent magnet rotating mechanism is an electric motor, and the rod-like permanent magnet is rotated via a gear provided on at least one of the rod-like permanent magnets. Magnetic circuit. The magnetic circuit of the permanent magnet for MRI or particle accelerator according to claim 4 or 5, wherein the permanent magnet rotating mechanism is an ultrasonic motor. 7. The magnetic circuit of a permanent magnet for MRI or particle accelerator according to claim 4, wherein the intensity of the magnetic field can be varied freely from zero to a maximum value. 8. The MRI or particle according to any one of claims 4 to 7, further comprising a magnetic field strength detection unit for detecting the strength of the magnetic field, and controlling the strength of the magnetic field based on a detection result of the magnetic field strength detection unit. Magnetic circuit of a permanent magnet for an accelerator . The permanent magnet MRI according to any one of claims 1 to 8, wherein one permanent magnet can be accommodated in the permanent magnet accommodating space so that the direction of magnetization is different from that of the other permanent magnet. Or magnetic circuit for particle accelerator . 10. The magnetic circuit of a permanent magnet for MRI or particle accelerator according to claim 1, wherein the strength of the magnetic field can be turned on and off completely. The magnetic circuit of the MRI or particle accelerator permanent magnet according to any one of claims 1 to 10 is defined as one unit, and a plurality of units of MRI or particle accelerator permanent magnet magnetic circuits are combined. A permanent magnet device for MRI or particle accelerator . The strength of the magnetic field generated by the magnetic circuit of each MRI or particle accelerator permanent magnet at the time of assembling or disassembling the MRI or particle accelerator permanent magnet device can be completely zero or a certain value including the sign. The permanent magnet device for MRI or particle accelerator according to claim 11.