Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-08-04
2002-01-08
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S293000, C156S297000, C029S467000, C029S468000, C335S297000, C335S306000, C324S318000
Reexamination Certificate
active
06336989
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a magnetic field generator for an MRI, a method for assembling the same, and a method for assembling a magnet unit for the same. More Specifically, this invention relates to a magnetic field generator for MRI incorporating permanent magnets, a method for assembling the same, and a method for assembling a magnet unit for the same.
2. Description of the Related Art
A magnetic field generator for MRI uses permanent magnets. The magnet used in such an apparatus have to be made up of a plurality of magnet blocks. It is very difficult to place material blocks first and then magnetize each. Thus, in actual manufacturing, the magnetized blocks must be aligned on a plate yoke so that each of the magnet blocks has a same magnetic pole facing upward.
Conventionally, when placing the magnet blocks on the plate yoke, a surface of the plate yoke is first applied with adhesive, and then magnet blocks are bonded to the surface, as disclosed in the Japanese Patent No. 2,699,250 for example.
According to such a bonding method, upper surfaces of respective magnet blocks bonded to the plate yoke surface are not flush with each other, making an uneven surface. A magnetic field generator incorporating the permanent magnets made of such magnet blocks is apt to produce ununiform magnetic field between a pair of piece poles opposed to each other. Further, pole pieces for correcting the ununiformity of the magnetic field may be tilted to produce ununiformity in the magnetic field. Generally, after a step of mounting a pair of permanent magnets to oppose each other, a step of adjustment for uniformly distributing the magnetic field is indispensable. However, if the magnet blocks are mounted according to the above method, the ununiformity of the magnetic field is so large that the adjustment becomes very time consuming with a lot of sub-steps.
Further, according to the above method of bonding the magnet blocks, the magnet blocks each having a very intense magnetism have to be placed from above, onto the upper surface of the plate yoke, making extremely difficult to fit each of the magnet blocks snugly to adjacent magnet blocks. More specifically, when mounting, each magnet block is held with a face of predetermined magnetic pole facing upward. When the magnet block is brought above the other magnet block which is already fixed onto the plate yoke, a pulling force is generated between the two. Further, when the two magnet blocks are brought in adjacency, a repelling force is generated between the two. Since the magnet block to be placed is under such intense forces, the magnet block must be firmly held for safety while being transported. For a conventional holding mechanism, it is very difficult to fit the magnet block snugly to the place of bonding efficiently against these strong forces.
A pair of magnet units thus assembled as above are then opposed to each other so the permanent magnets are faced at a predetermined distance. This process is achieved by first assembling one magnet unit, then connecting a column yoke to the magnet unit, and finally connecting the other magnet unit to the column yoke.
The column yoke is to magnetically connect the pair of magnet units, and therefore must be made of a magnetic material. Thus, when the column yoke is connected to the magnet unit, the column yoke is brought under the pulling force from the magnet unit, making difficult to connect the two at a high accuracy. Likewise, when the second magnetic unit is connected to the column yoke already connected to the first magnet unit, it is also difficult to connect the two at a high accuracy.
SUMMARY OF THE INVENTION
It is therefore a primary object of this invention to provide a magnetic field generator for MRI, a method for assembling the same, and a method for assembling the magnet unit for the same for assembling the magnetic field generator at a high efficiency through easier assembling operation of the magnet unit, easier connecting operation and other assembling operations of the magnet unit and the column yoke.
The method for assembling a magnet unit according to this invention is a method for assembling a magnet unit by bonding magnet blocks to a bonding object provided in a surface of a plate yoke, comprising: an applying step in which adhesive is applied to at least a side surface of the bonding object or a side surface of the magnet block; a transporting step in which the magnet block is transported by sliding on the plate yoke; and a bonding step in which the transported magnet block is bonded to the bonding object.
It should be noted here that the term bonding object as used here in this document refers to an object to which a new magnet block is bonded in the surface of plate yoke. For example, the bonding object may be a projection provided in the surface of plate yoke, or may be a magnet block already fixed in the surface of plate yoke.
According to the above method, the magnet block is transported by sliding to fit the bonding object, i.e. the projection or another magnet block. Then, the magnet block is held press-fitted for a predetermined amount of time to complete the bonding to a predetermined location. Since the magnet blocks are mutually connected side by side, and therefore it is not necessary to apply adhesive to the surface of plate yoke, the upper surface of the resulting permanent magnet is not likely to be uneven. Further, transportation of the magnet block to the predetermined position can be achieved simply by sliding on the plate yoke, making possible to assemble the permanent magnet stably and efficiently. A note should be made here that in order to avoid a short circuit of the magnetic flux the projection should be made of non-magnetic material such as aluminum.
Before the magnet block is transported, a first guiding member is disposed in the surface of plate yoke. Positioning of the magnet block for fixation is achieved by bringing this magnet block into contact with a side surface of the first guiding member. By this operation the magnet block is accurately placed to the predetermined position. The first guiding member may be a pair of rails laid at 90-degree angle from each other.
Preferably, a recess should be formed at a place on a side surface of the first guiding member where two blocks are bonded to each other. The first guiding member must be removed after the permanent magnet has been assembled. The recess provided in the first guiding member effectively prevents, when the magnet blocks are bonded by adhesive, the adhesive squeezed out of the mating surfaces from sticking to the first guiding member, thereby preventing the magnet blocks from being bonded to the first guiding member.
For easy positioning, a new magnet block is fitted to a corner portion formed by side surfaces of a plurality of bonding objects provided on the plate yoke, i.e. a corner portion formed by side surfaces of a pair of adjacent magnet blocks already fixed on the plate yoke, or a corner portion formed by a side surface of the projection and a side surface of the magnet block fixed directly to the projection. Especially, the placement of the magnet blocks can be achieved without misalignment if the new magnet block is transported so that a side surface of the new magnet block is held parallel to one of the side surfaces of the corner portion, i.e. the side surface of the existing magnet block or the side surface of the projection.
Likewise, when the first guiding member is used, a new magnet block is fitted to a corner portion made by the side surface of the first guiding member and the side surface of the bonding object, i.e. a corner portion formed by the side surface of the first guiding member and a side surface of the projection, or a corner portion formed by the side surface of the first guiding member and a side surface of the magnet block fitted directly thereto, for easy positioning. Especially, the placement of the magnet blocks can be achieved without misalignment if the new magnet block is transported so that
Aoki Masaaki
Hashimoto Shigeo
Armstrong, Westerman, Hattori, McLeland & Naughton, LLP.
Ball Michael W.
Sumitomo Special Metals Co. Ltd.
Tolin Michael A.
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