JPH0429305A - Magnetic field generation device - Google Patents

Abstract

PURPOSE:To improve uniformity of central axis direction of a pole piece without changing uniformity in rectangular direction to a central axis of the pole piece by providing a central part of the pole piece with an adjustment bolt which can be moved in the central axis direction of the pole piece. CONSTITUTION:In a magnetic circuit, each pole piece 2 having a hole part whose central part goes through is magnetically connected to one magnetic pole surface of a pair of doughnut-like permanent magnet part 1, the pole pieces 2 are opposed vertically with a space 7 therebetween, the other magnetic pole surface of each permanent magnet part 1 magnetically connects a pair of yokes 3 having a screw hole in a central part and the circuit is supported by four pillars 4. An adjustment bolt 5 which is movable in the central axis direction of the pole piece 2 is provided to a central part of the pole piece 2. Thereby, it is possible to improve uniformity of central axis direction without changing uniformity in rectangular direction to a central axis so much.

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 actually manufactured magnetic field generators, it is difficult to obtain the uniformity of the magnetic field as designed due to variations in the magnetic properties of the magnets, errors in the processing accuracy of each component, and assembly errors. Later fine-tuning is required. In order to solve such problems, conventionally, as disclosed in Japanese Patent Laid-Open No. 62-256416, the distance between the pole pieces is made variable using an adjustment bolt provided at the top of the support, and -1
As disclosed in No. 34011, the uniformity of the magnetic field generated in the air gap was adjusted by moving the pole piece in a direction perpendicular to the central axis.

[Problems to be Solved by the Invention] Generally, the thickness of the annular protrusion at the peripheral edge of the pole piece mainly affects the uniformity in the direction perpendicular to the central axis of the pole piece, and the thickness of the convex protrusion at the center of the pole piece mainly affects the uniformity of the pole piece in the central axis direction.

However, in the method of changing the distance between the pole pieces in the conventional technology described above, the entire pole piece moves simultaneously, so the uniformity of the magnetic field in both the direction of the center axis of the pole piece and the direction perpendicular to the center axis is adjusted simultaneously. It was difficult to do so. Furthermore, in the method of moving the pole piece in a direction perpendicular to the central axis, it is possible to adjust the uniformity in the direction perpendicular to the central axis. It was not possible to adjust the uniformity in the central axis direction.

Therefore, an object of the present invention is to propose a mechanism for adjusting the uniformity in the direction of the central axis of the pole piece without significantly changing the uniformity in the direction perpendicular to the central axis of the pole piece. It is.

[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. The magnetic field generating device that generates a magnetic field in the air gap with this structure is characterized in that an adjustment bolt movable in the direction of the central axis of the pole piece is provided in the center portion of the pole piece.

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 magnetically couples a pole piece 2 having a hole passing through the center to one magnetic pole surface of a pair of donut-shaped permanent magnet parts 1, and connects the pole piece 2 with an air gap 7.
A pair of yokes 3 each having a screw hole in the center are magnetically coupled to the other magnetic pole surface of each permanent magnet part 1, and supported by four pillars 4. ing.

Here, the permanent magnet section 1 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. Further, the rare earth magnet block 12 has a basic composition of Pr1 as shown in FIG.
5 at%, Fe7B at%, B5.5 at%, Cu1.
A cast ingot 8 is obtained by melting and casting an alloy with a concentration of 5 at%.
is placed in a hot rolling capsule 9, deaerated and sealed, and then hot rolled into a hot rolling capsule 9 at 950°C by a rolling roller 10, and the maximum energy product of each rare earth magnet block is is 25MGOe.

In the magnetic field generator having the structure described above,
Insert the adjustment bolt 5 made of a magnetic material into the hole of the pole piece 2 and the permanent magnet part 1 as shown in the figure, and then rotate the hexagonal protrusion 6 of the adjustment bolt 5 to move the screw hole of the yoke 3 forward and backward in the direction of the arrow. As a result, the same effect as changing the surface shape of the pole piece 2 can be obtained. Therefore, the centers of the holes in the pole piece 2 and the permanent magnet part 1 and the centers of the screw holes in the yoke 3 must be aligned. Further, in order to avoid damage to the magnet, the hole diameter of the permanent magnet portion 1 must be designed to be slightly larger than the hole diameter of the pole piece 2.

The effective gap length L of the magnetic circuit was set to 570 mm, the total weight of the magnet was set to 1.5 tons, and the surface shape of the pole piece 2 was finely adjusted by moving the adjusting bolt 5 back and forth. As a result, the magnetic field strength at the center of the air gap was is 1450G and 3
A uniform magnetic field of 35 ppm or less was obtained within 0 ODSV. The fine adjustment of the surface shape of the pole piece 2 by this bolt-shaped shim 5 has a large effect on the uniformity, especially in the central axis direction (vertical axis direction). Compared to a magnetic circuit, the uniformity in the central axis direction has improved from 45 ppm to less than 20 ppm, and 1
The uniform magnetic field range of 100 pp or less has also been expanded by more than 10%.

[Effects of the Invention] As described above, according to the present invention, the center portion of the pole piece is made into a bolt shape and moved back and forth to finely adjust the surface shape of the pole piece. The uniformity in the central axis direction could be significantly improved without significantly changing the uniformity.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are explanatory diagrams showing the basic structure of the magnetic circuit of the magnetic field generator in the embodiment of the present invention. Figure 2 shows the hot rolling process of the rare earth magnet used in the magnetic circuit of the present invention. An explanatory diagram showing. FIG. 3 is a partial vertical 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...
Yoke, 4... Support, 5... Adjustment bolt, 6...
・Hexagonal projection for rotation, 7... Gap, 8... Cast ingot, 9... Capsule for hot rolling, 10... Rolling roller, 11... Rolling direction, 12... Rare earth magnet block , 13...first layer, 14...second layer, 15...
・Third tier, 16...4th tier and higher applicants Kizobe Suzuki, Patent attorney representing Seiko Epson Co., Ltd. 1 person Figure 1

Claims (1)

[Claims] A magnetic field generating device 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 column, and a magnetic field is generated in the gap with this structure. A magnetic field generating device characterized in that an adjustment bolt movable in the direction of the central axis of the pole piece is provided in the center of the pole piece.