JPH0429304A - Magnetic field generation device - Google Patents

Abstract

PURPOSE:To acquire a uniform magnetic field with high precision by providing a yoke part with an adjusting bolt for a permanent magnet part and a pole piece to finely move integrally in rectangular direction to a central axis direction of the pole piece. CONSTITUTION:In a magnet circuit, a movement body is formed by magnetically connecting a pair of permanent magnet parts 1 opposed each other with a space 7 therebetween and a pair of pole pieces 2 for magnetic field adjustment fixed to the permanent magnet part 1 to a pair of movement yokes 3, and a body formed by magnetically connecting the movement body to a recessed part of a fixing yoke 4 is supported by four pillars 5. A yoke part is provided with an adjustment bolt 6 to finely move the permanent magnet part 1 and the pole piece 2 integrally in a rectangular direction to a central axis direction of the pole piece 2. Thereby, it is possible to realize high precision and to improve uniformity without damaging a permanent magnet and peeling off adhesive.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is directed to a high-strength and This invention relates to a magnetic field generator that generates a highly accurate and uniform static magnetic field.

[Prior art] There are three methods for generating magnetic fields in MHI devices: a permanent magnet method, a normal conducting magnet method, and a superconducting magnet method. Among these, the permanent magnet method does not involve the consumption of electricity or helium. Because it is the most economical. Furthermore, in recent years, with the advent of rare earth magnets with strong magnetic force and improvements in the performance of signal detection devices and imaging technology, permanent magnet MHI devices have begun to be put into practical use. A magnetic field generator for a permanent magnet type MHI device has a structure in which a pair of permanent magnet parts facing each other with a gap formed therein and a pair of pole pieces fixed to the permanent magnet parts are magnetically coupled by a yoke and a support. There is. In an MHI device, the strength and uniformity of the static magnetic field affect the quality of the captured image, so a high-intensity, ppm-order, uniform magnetic field is required near the center of the gap into which the subject is inserted.

In order to satisfy this strict condition in a magnetic field generating device using a permanent magnet, as disclosed in Utility Model Application Laid-open No. 60-166110, a convex protrusion provided at the center of each opposing surface of the pole piece and a convex protrusion provided at the peripheral edge are used. A method of changing the shape of the annular protrusion is mainly used. However, in the actually manufactured magnetic field generator, it is difficult to obtain the uniformity of the magnetic field as analyzed due to variations in the magnetic properties of the magnets, errors in the processing accuracy of each part, and assembly errors. Fine adjustment will be required. In order to solve these problems, a method has been used in which a magnetic field adjustment mechanism is provided in which only the pole piece can be moved in the horizontal direction, as disclosed in Japanese Utility Model Application Laid-Open No. 61-134011.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, since only the pole piece moves, a part of the contact surface on the pole piece side of the permanent magnet part may be chipped, or each rare earth magnet constituting the permanent magnet part may be damaged. There was a problem in that the adhesive for fixing the blocks easily peeled off.

Therefore, an object of the present invention is to provide an adjustment mechanism that makes it possible to obtain a highly accurate and uniform magnetic field without causing such problems.

[Means for Solving the Problems] The magnetic field generating device of the present invention magnetically couples a pair of permanent magnet parts facing each other with a gap formed therebetween and a pair of pole pieces fixed to the permanent magnet parts using a yoke and a support. In a magnetic field generating device that generates a magnetic field in the air gap with this structure, the adjustment bolt is attached to the yoke to allow the permanent magnet part and the pole piece to move minutely in a direction perpendicular to the central axis of the pole piece. It is characterized by being provided in the section.

In addition, in order to obtain a high-strength magnetic field in the air gap, the permanent magnet used in the magnetic field generator of the present invention is an Nd-F magnet with a maximum energy product of 25 mega Gauss Oersted (MGOe) or more.
Rare earth magnets such as e-B series or Pr-Fe-B series are desirable.

Embodiment FIGS. 1(a) and 1(b) are explanatory diagrams showing a magnetic circuit used in a magnetic field generating device in an embodiment of the present invention.

The magnetic circuit forms a moving body by magnetically coupling a pair of permanent magnet parts facing each other with a gap 7 formed therebetween and a pair of magnetic field adjustment pole pieces 2 fixed to the permanent magnet parts with a pair of moving yokes 3. Furthermore, the movable body is magnetically coupled to the concave portion of the fixed yoke 4, and is supported by four pillars 5.

Here, the permanent magnet part l is an aggregate of a plurality of rare earth magnet blocks 12, and as shown in FIG. The rare earth magnet blocks are arranged in the second layer so that the rolling direction of each rare earth magnet block is perpendicular to the rolling direction of the rare earth magnet blocks in the first layer. Moreover, as shown in FIG. 2, the rare earth magnet block 12 has a basic composition of Pr 15 atomic %, Fe 7 atomic %, B 5.5 atomic %, C
An alloy having u1.5 atomic % is melted and cast, the cast ingot 8 is placed in a hot rolling capsule 9, degassed and sealed,
It is manufactured by hot rolling a hot rolling capsule 9 at 950° C. with a rolling roller 10, and the maximum energy product of each rare earth magnet block is 25 MGOe.

In the magnetic field generator having the structure described above,
Four adjusting non-magnetic bolts 6 are arranged at 90'' intervals on each of the upper and lower fixed yokes 4 to enable the movable body to move minutely in the direction of the arrow, that is, in the direction perpendicular to the central axis. The movable body can be moved minutely in the direction of the arrow by the advance/retreat degree of 6.

The effective gap length L of the magnetic circuit is 570 mm, the total weight of the magnet is 1.5 tons, and the pole piece 2 is finely adjusted using the adjustment bolt 6 to make the pole piece 2 approximately 1.7% of the outer diameter of the pole piece 2. When moved horizontally, the magnetic field strength at the center of the gap is 1450G, and 30
A uniform magnetic field of less than 40 ppm was obtained within the ODSV. This fine adjustment of the pole piece 2 by the adjustment bolt 6 has a particularly large effect on the horizontal uniformity, and compared to a magnetic circuit that does not have a fine movement adjustment mechanism for the pole piece 2, the uniformity in the horizontal axis direction is It has improved from 40 ppm to 25 ppm, and the range of uniform magnetic field below 1100 ppm has also been expanded by more than 15%.

[Effects of the Invention] As described above, according to the present invention, the permanent magnet portion is integrated with the pole piece and the moving yoke to form a moving body, and the adjustment bolt provided on the fixed yoke is moved forward and backward. By moving the body horizontally, improved uniformity could be achieved without damaging the permanent magnets and peeling off the adhesive.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are explanatory diagrams showing the basic structure of a magnetic circuit of a magnetic field generating device in an embodiment of the present invention. FIG. 2 is an explanatory diagram showing the hot rolling process of rare earth magnets used in the magnetic circuit of the present invention. FIG. 3 is a partial vertical cross-sectional view of the permanent magnet part of a magnetic circuit in which rare earth magnet blocks are laminated. 1... Permanent magnet part, 2... Pole piece, 3...
Movable yoke, 4... Fixed yoke, 5... Support column, 6.
...Adjustment bolt, 7...Gap, 8...Casting ingot, 9...Capsule for hot rolling, 10...Rolling roller, 11...Rolling direction, 12...Rare earth magnet block , 13...first layer, 14...second layer, 15...
・3rd layer, 16... 4th layer rod/figure ((L)

Claims (1)

[Claims] In a magnetic field generation device that magnetically couples a pair of permanent magnet sections facing each other with a gap formed therebetween and a pair of pole pieces fixed to the permanent magnet sections using a yoke and a support, and generates a magnetic field in the gap using this structure, a permanent A magnetic field generating device characterized in that a yoke part is provided with an adjustment bolt for minutely moving the magnet part and the pole piece together in a direction perpendicular to the central axis direction of the pole piece.