JP4123650B2 - Magnetic field generator and method of assembling the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic field generator and a method for assembling the same, and more particularly to a magnetic field generator for MRI and a method for assembling the same.
[Prior art]
As a method for adjusting the magnetic field in this type of magnetic field generator, there has been proposed a method for adjusting the gap length and the like of the upper and lower magnetic pole plates using bolts as shown in JP-A-2-248008 and JP-A-3-39139. Yes.
[0002]
[Problems to be solved by the invention]
However, according to such a prior art, since it is a structure that is stretched with a bolt, the structure is supported at a point, and the weight of the upper yoke is concentrated on the tip of the bolt. As a result, the bolt tip gets stuck in the columnar yoke due to vibration during transportation, the gap length of the upper and lower magnetic pole plates changes, and the uniformity of the magnetic field strength decreases, resulting in troublesome readjustment after transportation. there were.
Therefore, a main object of the present invention is to provide a magnetic field generator and an assembling method thereof that can be easily readjusted after conveyance.
[0003]
[Means for Solving the Problems]
In order to achieve the above object, a magnetic field generator according to claim 1 is provided with a pair of plate-like yokes that form a gap and are opposed to each other in the vertical direction, on each of the opposed surfaces of the pair of plate-like yokes It arranged the permanent magnet, a pair of plate yokes between the columnar yokes magnetically coupled to, and upper plate yoke and the adjustment member arranged in the connection portion of the columnar yoke, upper plate The shape yoke has a hole opened on the opposite surface side, the columnar yoke is fitted into the hole, and the adjusting member is arranged so as not to be exposed to the outside on the columnar yoke in the hole.
A magnetic field generator according to a second aspect is the magnetic field generator according to the first aspect, wherein the adjustment member is made of a magnetic material.
[0004]
According to a third aspect of the present invention, there is provided a method of assembling a magnetic field generator, wherein a pair of plate yokes that are vertically opposed to each other with a gap formed therebetween, and a permanent plate that is disposed on each opposing surface side of the pair of plate yokes. A magnet, a columnar yoke that magnetically couples between the pair of plate- shaped yokes, and an adjustment member that is arranged at the connection between the upper plate-shaped yoke and the columnar yoke so as to obtain a desired magnetic field strength a method of assembling a magnetic field generator comprising bets, the upper plate yoke has a hole that opens to the opposite side, fitting the columnar yoke in the holes after placing the adjustment member on the columnar yoke The adjusting member is arranged so as not to be exposed to the outside on the columnar yoke in the hole .
The magnetic field generator assembly method according to claim 4 is the magnetic field generator assembly method according to claim 3, wherein the upper plate yoke is lifted to connect the upper plate yoke and the column yoke. An adjustment member is arranged in the part.
[0005]
In the magnetic field generator according to claim 1, since the adjustment member is disposed between the plate-like yoke and the column-like yoke, for example, the plate-like yoke and the column-like yoke can be strongly connected. The change in the uniformity of the magnetic field strength due to vibration during transportation can be suppressed. Therefore, it becomes easy to readjust the magnetic field after conveyance. The same applies to the method for assembling the magnetic field generator according to claim 3.
In the magnetic field generator according to claim 2, since a magnetic material is used as the adjusting member, there is no magnetic gap between the plate yoke and the columnar yoke. Accordingly, the leakage magnetic field is reduced, the magnetic field strength in the imaging space is improved, and the cost of the magnetic circuit can be suppressed.
In the method for assembling the magnetic field generator according to the fourth aspect, the adjustment member can be easily arranged at the connection portion between the plate-shaped yoke and the columnar yoke by lifting the plate-shaped yoke.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows a magnetic field generator 10 for MRI according to an embodiment of the present invention.
The magnetic field generator 10 is configured as a four-pillar type, and includes a pair of plate-like yokes 12a and 12b that are opposed to each other while forming a gap. The plate yokes 12a and 12b are each formed in a substantially rectangular shape, and permanent magnets 14a and 14b are arranged on the respective facing surfaces, and the pole plates 16a and 14b are disposed on the facing surfaces of the permanent magnets 14a and 14b. 16b is fixed. The permanent magnets 14a and 14b are each configured by bonding a plurality of magnet blocks, for example.
[0007]
As shown in FIG. 2, a movable yoke 18 for fine adjustment of the magnetic field is disposed at the center of the plate yoke 12a. The position of the movable yoke 18 is adjusted by the three bolts 20 and the position thereof is regulated by the three stoppers 22. Further, two screws 24 for finely adjusting the magnetic field are screwed into the plate-like yoke 12a in each of four directions, and the magnetic field can be finely adjusted by adjusting the screw 24. The magnetic pole plate 16a is fixed to the main surface of the permanent magnet 14a by four bolts 26 for fixing the magnetic pole plate. The permanent magnet 14 a is covered with a magnet cover 28. The plate yoke 12b is also formed in the same manner. Four screw holes 30 for attaching lifting hooks are formed in the plate yoke 12a.
[0008]
Such plate yokes 12a and 12b are magnetically coupled by four columnar column yokes 32. As shown in FIG. 3, a reduced diameter portion 34 is formed at the upper end of the columnar yoke 32. The reduced diameter portion 34 is fitted into the hole 36 of the plate yoke 12a, and is connected by a fixing bolt 40 to, for example, a disk-shaped cap 38 disposed on the upper surface of the plate yoke 12a. Although not shown, the cap 38 is firmly welded to the plate yoke 12a. Here, in order to adjust the magnetic field, the adjusting member 42 is inserted between the connecting portion of the plate yoke 12a and the columnar yoke 32, for example, between the reduced diameter portion 34 of the columnar yoke 32 and the cap 38. It is. Four holes 44 are formed in the adjusting member 42 (see FIG. 4), and the columnar yoke 32 and the cap 38 are connected by the four fixing bolts 40 with the adjusting member 42 interposed therebetween.
[0009]
As the adjustment member 42, for example, iron having a thickness of 1 to 10 mm, nonmagnetic stainless steel, or the like is used, and is formed in a disk shape, for example. If the magnetic field strength is a little too strong, the magnetic material iron can be used to increase the distance between the magnetic pole plates 16a and 16b while coupling the magnetic circuit, thereby slightly reducing the magnetic field strength. Can do. On the other hand, when the magnetic field strength is too strong, if non-magnetic stainless steel is used, the magnetic coupling between the plate yoke 12a and the columnar yoke 32 is weakened and a magnetic resistance is generated, and a desired magnetic field strength is obtained. Can be adjusted. The same applies to an adjusting member 78 in the magnetic field generator 10a described later.
[0010]
Although not shown, reduced diameter portion is formed in the lower end of the columnar yokes 32, the reduced diameter portion is fitted into a hole formed in the plate yoke 12 b, and columnar yoke 32 and plate yokes 12b Is connected. In addition, leg portions 46 are attached to the four corners of the lower surface of the plate yoke 1 2 b.
Such a magnetic field generator 10 is assembled as follows.
First, the magnetic field generator 10 is assembled once without using the adjustment member 42. Usually, the generated magnetic field is designed to be slightly stronger so that the magnet itself may have some variation. And the magnetic field intensity of the assembled magnetic field generator 10 is measured (not shown) with a measuring instrument. As a result, if the magnetic field strength is strong, the adjustment member 4 2 is inserted for magnetic field adjustment.
[0011]
At this time, as shown in FIG. 4, after attaching a hook (not shown) to the lifting screw hole 30, the chain 48 is attached, and the hook 50 is hooked on the chain 48 and the plate yoke 12a is attached by a crane or the like. Can be lifted. And after the adjustment member 42 is arrange | positioned on the reduced diameter part 34 of the columnar yoke 32, the plate-shaped yoke 12a once lifted is assembled | attached again. Then, the magnetic field strength is measured again. The above adjustment process is repeated until the desired magnetic field strength is obtained, and the magnetic field generator 10 is assembled. Thus, the adjustment member 42 can be easily disposed at the connection portion between the plate yoke 12a and the columnar yoke 32 by lifting the plate yoke 12a.
[0012]
Depending on the state of the magnetic field strength after assembly, the adjusting member 42 is not limited to one, and a plurality of adjusting members 42 may be inserted or ones having different thicknesses may be inserted. If the magnetic field intensity in the imaging space is too high, a magnetic gap is formed between the plate yoke 12a and the columnar yoke 32 by using a non-magnetic plate such as a stainless steel plate for the adjustment member 42. As a result, the magnetic field strength in the imaging space can be reduced.
[0013]
According to such a magnetic field generator 10, unlike the conventional case, the gap between the two is filled by disposing the adjusting member 42 at the connection portion between the plate yoke 12 a and the columnar yoke 32 without using bolts. And the plate yoke 12a and the columnar yoke 32 can be firmly fixed. Therefore, the positional relationship between the plate yoke 12a and the columnar yoke 32 can be stabilized by a simple method, and the assembly accuracy can be increased. In addition, it is possible to suppress changes in the gap lengths or the like of the magnetic pole plates 16a and 16b due to vibration during transportation, and it is possible to suppress changes in the uniformity of the magnetic field strength. Therefore, it is not necessary to adjust the gap dimension between the magnetic pole plates 16a and 16b, and it is only necessary to finely adjust the magnetic field by the movable yoke 18 and the screw 24. Therefore, the readjustment of the magnetic field after conveyance becomes easy. Specifically, the adjustment work that conventionally required one day can be completed in half a day.
[0014]
If a magnetic material is used as the adjustment member 42, there is no magnetic gap between the plate yoke 12a and the column yoke 32, the leakage magnetic field is reduced, and the magnetic field strength in the imaging space is improved. In one example, the magnetic flux density Bg in the imaging space is improved by about 20 Gauss. In this regard, conventionally, since a gap (for example, 5 mm) is formed between the plate yoke and the columnar yoke, more magnets are required to obtain the same magnetic field strength as when there is no gap, The cost was high. However, the magnetic field generator 10 does not cause such a problem and can reduce the cost.
[0015]
FIG. 5 shows an MRI magnetic field generator 10a according to another embodiment of the present invention.
The magnetic field generation device 10a is configured in a two-column type, and includes a pair of plate-like yokes 52a and 52b that are arranged to face each other with a gap. The plate yoke 52a has an octagonal main body 54a and coupling portions 56a and 58a formed at both ends of the main body 54a, respectively. Similarly, the plate yoke 52b has an octagonal main body portion 54b and coupling portions 56b and 58b formed at both ends of the main body portion 54b.
As with the magnetic field generator 10 shown in FIG. 1, permanent magnets 60a and 60b are arranged on the opposing surface sides of the plate yokes 52a and 52b, and on the opposing surface sides of the permanent magnets 60a and 60b, respectively. The magnetic pole plates 62a and 62b are fixed.
[0016]
Similar to the magnetic field generator 10, a movable yoke 64 for fine adjustment of the magnetic field is disposed in the center of the plate yoke 52a. The position of the movable yoke 64 is adjusted in the vertical direction by three bolts 66, and the position is regulated by three stoppers 67. Further, two screws 68 for magnetic field fine adjustment are screwed into the plate yoke 52a in each of four directions, and the magnetic field can be finely adjusted by adjusting the screw 68 to be screwed in. The magnetic pole plate 62a is fixed to the main surface of the permanent magnet 60a by four bolts 70 for fixing the magnetic pole plate. The permanent magnet 60a is covered with a magnet cover (not shown). The plate yoke 52b is also formed in the same manner. Four screw holes 72 for attaching lifting hooks are formed in the plate yoke 52a.
[0017]
The plate yokes 54a and 54b are magnetically coupled by two columnar yokes 74 having a substantially I shape. As shown in FIG. 6, the upper end of the columnar yoke 74 is connected to the coupling portion 56a of the plate-shaped yoke 52a. Here, a notch 76 is formed on the lower surface of the coupling portion 56a, which is a connecting portion between the plate-shaped yoke 54a and the columnar yoke 74, and a strip-shaped adjusting member 78 is provided in the notch 76 to adjust the magnetic field. Is inserted. The adjustment member 78 is formed with a hole 82 for the fixing bolt 80 and two notches 86 for the fixing bolt 80 and the push-up bolt 84. The push-up bolt 84 is used to form a gap in the notch 76 between the plate-like yoke 52a and the column-like yoke 74, and the fixing bolt 80 is used to connect the plate-like yoke 52a and the column-like yoke 74 together. Used for connecting and fixing. The same applies to the coupling portion 58a side of the plate yoke 52a.
Moreover, the leg part 88 is attached to the lower surface of the lower plate-shaped yoke 52b.
[0018]
Such a magnetic field generator 10a is assembled as follows.
First, as in the case of the magnetic field generator 10, after being assembled once, the magnetic field strength of the magnetic field generator 10a is measured with a measuring instrument. As a result, if the magnetic field strength is strong, the adjustment member 78 is inserted for magnetic field adjustment. In the magnetic field generator 10a, since the upper end of the side surface of the columnar yoke 74 is exposed, the plate-shaped yoke 54a is pushed up using the push-up bolt 84. Then, after the adjustment member 78 is inserted in the gap formed in the notch 76 from the lateral direction, the fixing bolt 80 is screwed, and the plate-like yoke 52 a and the columnar yoke 74 are sandwiched between the adjustment member 78. Is connected and fixed. This operation is performed in each of the coupling portions 56a and 58a of the plate yoke 52a. The magnetic field strength is then measured again. The above process is repeated until a desired magnetic field strength is obtained, and the magnetic field generator 10a is completed.
The same effect as the magnetic field generator 10 can be obtained with the magnetic field generator 10a.
[0019]
FIG. 7 shows a magnetic field generator 10b for MRI according to another embodiment of the present invention.
The magnetic field generation device 10b is an open type, and includes a pair of plate-like yokes 90a and 90b that are opposed to each other so as to form a gap. The plate-shaped yoke 90a has a substantially disc-shaped main body portion 92a and two coupling portions 94a and 96a extending from the main body portion 92a. Similarly, the plate yoke 90b has a substantially disc-shaped main body portion 92b and two coupling portions 94b and 96b extending from the main body portion 92b.
Similar to the above-described embodiment, permanent magnets 98a and 98b are disposed on the opposing surface sides of the main body 92a of the plate yoke 90a and the main body 92b of the plate yoke 90b, and the permanent magnet 98a. The magnetic pole plates 100a and 100b are fixed to the opposing surface sides of the magnetic plates 98b and 98b, respectively.
[0020]
A movable yoke 102 for fine adjustment of the magnetic field is disposed at the center of the plate yoke 90a. The position of the movable yoke 102 in the vertical direction is adjusted by the three bolts 104, and the position is regulated by the three stoppers 105. Furthermore, two magnetic field fine adjustment screws 106 are screwed into each of the plate-like yokes 90a in each of four directions, and the magnetic field can be finely adjusted by adjusting the screw insertion of the screws 106. The permanent magnet 98a is covered with a magnet cover (not shown). The plate yoke 90b side is formed in the same manner. About these structures, it is the same as that of the case of the magnetic field generator 10 shown in FIG. A screw hole 108 for attaching a lifting hook is formed in each of the connecting portions 94a and 96a of the plate yoke 90a.
[0021]
The plate yokes 90a and 90b are magnetically coupled by the two columnar column yokes 110. At this time, the columnar yoke 110 is disposed between the coupling portions 94a and 94b and between the coupling portions 96a and 96b.
As shown in FIG. 8, a reduced diameter portion 112 is formed at the upper end of the columnar yoke 110. The reduced diameter portion 112 is fitted into the hole 114 of the plate yoke 90a, and is connected and fixed to the coupling portion 94a of the plate yoke 90a by a fixing bolt 116. Here, in order to adjust the magnetic field, an adjusting member 118 is interposed between the reduced diameter portion 112 of the columnar yoke 110 and the coupling portion 94a. Six holes (not shown) are formed in the adjustment member 118, and the columnar yoke 110 and the plate-shaped yoke 90a are connected by the six fixing bolts 116 with the adjustment member 118 interposed therebetween. In other respects, the adjustment member 118 is formed in the same manner as the adjustment member 42.
[0022]
Although not shown, a reduced diameter portion is also formed at the lower end of the columnar yoke 110, and the reduced diameter portion is inserted into a hole formed in the plate-shaped yoke 90b, so that the columnar yoke 110 and the plate-shaped yoke 90b are connected. Connected and fixed. Moreover, the leg part 120 is attached to the position corresponding to the two columnar yokes 110 in the lower surface front part of the plate-shaped yoke 90b and the lower surface of the plate-shaped yoke 90b.
[0023]
The magnetic field adjustment at the time of assembling the magnetic field generation device 10b is performed by lifting the plate yoke 90a and inserting the adjustment member 118 in the same manner as the magnetic field generation device 10, and thus redundant description thereof is omitted. .
The same effect as that of the magnetic field generator 10 can be obtained in the magnetic field generator 10b.
In each of the above-described embodiments, the adjustment member is not limited to a disk shape, and may be configured in a disk shape by combining a plurality of prismatic members. Furthermore, if the adjustment member is a plate-like member having a uniform thickness, the structure is supported by the surface, so that the mechanical strength is increased and the uniformity of the magnetic field strength is less likely to be lost due to vibration during transportation.
[0024]
【The invention's effect】
According to this invention, since the plate-shaped yoke and the columnar yoke can be strongly fixed by using the adjusting member, it is possible to suppress a change in the uniformity of the magnetic field strength due to vibration during transportation. Therefore, it becomes easy to readjust the magnetic field after conveyance.
[Brief description of the drawings]
FIG. 1 is a perspective view schematically showing an embodiment of the present invention.
2 is an illustrative view showing a magnetic field fine adjustment mechanism in the embodiment of FIG. 1; FIG.
3 is an illustrative view showing a connection portion between a plate-shaped yoke and a columnar yoke in the embodiment of FIG. 1; FIG.
4 is a perspective view showing a state in which an adjustment member is arranged at a connection portion between a plate-like yoke and a column-like yoke in the embodiment of FIG. 1. FIG.
FIG. 5 is a perspective view schematically showing another embodiment of the present invention.
6 is an illustrative view showing a connection portion between a plate-like yoke and a columnar yoke in the embodiment of FIG. 5;
FIG. 7 is a perspective view schematically showing another embodiment of the present invention.
FIG. 8 is an illustrative view showing a connection portion between a plate-like yoke and a columnar yoke in the embodiment of FIG. 7;
[Explanation of symbols]
10, 10a, 10b Magnetic field generators 12a, 12b, 52a, 52b, 90a, 90b Plate yokes 14a, 14b, 60a, 60b, 98a, 98b Permanent magnets 16a, 16b, 62a, 62b, 100a, 100b Magnetic pole plate 32 , 74, 110 Columnar yokes 42, 78, 118 Adjusting member 84 Push-up bolt

Claims (4)

A pair of plate-shaped yokes that are vertically opposed to form a void;
Permanent magnets arranged on the facing surfaces of the pair of plate yokes,
A columnar yoke that magnetically couples between the pair of plate-shaped yokes, and an adjustment member that is arranged at a connection portion between the upper plate-shaped yoke and the columnar yoke ,
The upper plate-shaped yoke has a hole opened on the opposite surface side, the columnar yoke is fitted into the hole, and the adjustment member is not exposed to the outside on the columnar yoke in the hole. A magnetic field generator arranged in   The magnetic field generator according to claim 1, wherein the adjustment member is made of a magnetic material. A pair of plate yokes that are vertically opposed to each other to form a gap, a permanent magnet that is arranged on each of the opposed surfaces of the pair of plate yokes, and a magnet between the pair of plate yokes columnar yokes and method of assembling a magnetic field generator and an adjusting member disposed in the connection portion between the columnar yoke and the upper plate yoke as desired magnetic field intensity can be obtained that bind Because
The upper plate yoke has a hole that opens to the opposite surface side,
A magnetic field generating device , wherein the adjusting member is disposed on the columnar yoke, the columnar yoke is inserted into the hole, and the adjusting member is disposed in the hole so as not to be exposed on the columnar yoke. Assembly method. The magnetic field generator assembly method according to claim 3, wherein the upper plate-shaped yoke is lifted and the adjusting member is disposed at a connection portion between the upper plate-shaped yoke and the columnar yoke.

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