US3781735A

US3781735A - Apparatus for adjusting magnet cores

Info

Publication number: US3781735A
Application number: US00284048A
Authority: US
Inventors: J Haas
Original assignee: Bruker Biospin GmbH
Current assignee: Bruker Biospin GmbH
Priority date: 1971-09-15
Filing date: 1972-08-28
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25
Also published as: DE2146032B2; DE2146032C3; DE2146032A1

Abstract

An improved magnet core mounting is described in which the magnet core is snugly mounted upon two support rings located in a guide tube near its ends. One of these rings is fixed to the guide tube and has a convex spherical surface bearing against the magnet core and the other is radially adjustable in the guide tube. The magnet core has sufficient play in the guide tube to permit the adjustable support ring to correct the position of its pole face; and the convex spherical surface of the fixed support ring cooperates in permitting this adjustment. The radially adjustable support ring is positioned by four screws set 90* apart about the circumference of the ring. Advantageously, two of these screws bear the weight of the magnet core while the other two bias springs against the core.

Description

United States Patent 1191 1111 3,781,735

Haas 1 Dec. 25, 1973 [54] APPARATUS FOR ADJUSTING MAGNET 3,662,304 5/1972 Bringe et a]. 335/297 CORES Primary ExaminerGeorge Harris [75 Inventor. 'g g f ify a Neureut Att0rneyDean S. Edmonds et al.

[73] Assignee: Brulrer-llhysik AG, 57 ABSTRACT Karlsruhe-Forchheim, Germany An 1mproved magnet core mounting 1s described in [22] Filed: Aug. 28, 1972 which the magnet core is snugly mounted upon two support rings located in a guide tube near its ends. [21] Appl' 284048 One of these rings is fixed to the guide tube and has a convex spherical surface bearing against the magnet [30] Foreign Application Priority lData core and the other is radially adjustable in the guide Sept. 15, 1971 Germany P 21 46 032.2 tube- The magnet Core has Sufficient P y in the guide tube to permit the adjustable support ring to correct 52 US. 01. 335/298, 335/297 the Position of its P faee; and the convex spherieal 51 1111. C1. 1101: 3 00 Shrfaee 9f the fixed pp ring eeeperatee in p [58] Field or Search 335/297, 298,296 ting this adjustment The radially adjustable Support ring is positioned by four screws set 90 apart about 5 References Cited the circumference of the ring. Advantageously, two of UNKTED STATES PATENTS these screws bear the weight of the magnet core while 3 417 356 lzllgfig T h 335,298 the other two bias springs against the core.

sc opp 3,611,223 10/1971 Utsumi et al. 335/298 7 Claims, 5 Drawing Figures APPARATUS FOR ADJUSTING MAGNET CORES BACKGROUND OF THE INVENTION Conventional magnets such as those used in spin resonance spectroscopy have a magnet yoke, guide tubes inserted in the magnet yoke, and magnet cores mounted in the guide tubes and separated by an air gap. Frequently, the ends ofthe magnet cores that face each other across the air gap are provided with pole caps. For convenience, such pole caps and, where pole caps are not used, the facing ends of the magnet cores are referred to below as pole faces.

These magnets are used to generate a magnetic field having high field strength and maximum homogeneity in the air gap between the pole faces. To a great degree, the homogeneity of the magnetic field depends upon the uniformity of the spacing (or parallelism) between the pole faces, and deviations of only a few thousandths of a millimeter in the uniformity of the spacing often have a disturbing effect.

Because of manufacturing tolerances and the need to shift the magnet cores longitudinally to adjust the width of the air gap, there is usually some play between the magnet cores and the guide tubes with the result that the axes of the magnet cores frequently are not perfectly parallel to one another. As a result, the pole faces of the magnet cores are also at an angle to one another, i.e. the spacing between the pole faces varies. Consequently, the magnetic field in the air gap is not optimally homogeneous.

To adjust the spacing between the pole faces so as to achieve a uniform spacing and a uniform magnetic field, it has been customary to use leveling screws that adjust the position of the pole caps with respect to the magnet cores. Disadvantages of the use of such leveling screws are that they do not permit sufficiently fine adjustment and that the adjusting process is very awkward. Moreover, the screws do not eliminate play between the magnet core and guide tube. As a result, if the magnet is swiveled around the axis of its guide tubes in order to position it, usually horizontally or vertically, as may be suited for a particular application, the relative positions of the magnet cores in the guide tubes change. Accordingly, the pole caps must be laboriously readjusted every time the position of the magnet is changed.

SUMMARY OF THE INVENTION In accordance with the present invention, an improved magnet core mounting is provided in which the magnet core is snugly mounted upon two support rings located in a guide tube near its ends, one of the rings being fixed to the guide tube and having a convex spherical surface bearing against the magnet core and the other being radially adjustable in the guide tube. As a result of this arrangement, it is no longer necessary to adjust the pole caps relative to the magnet cores, but simply to adjust the magnet core relative to the guide tube. For this purpose, the magnet core has sufficient play in the guide tube to permit it to be moved by the adjustable support ring enough for the adjustment of its pole face.

The convex spherical surface of the fixed support ring cooperates in this adjustment, permitting the magnet core to pivot, without requiring any play between it and the magnet core. At the same time, the convex spherical surface permits the magnet core to be shifted 2 longitudinally in its support rings without jamming. Preferably, this convex surface is formed as a bead on the interior of the tube.

The radially adjustable support ring may be positioned by adjusting screws threaded through the guide tube or through an adjusting ring connected to the guide tube. Preferably, four screws set degrees apart about the circumference of the support ring are used to provide adjustment along two mutually perpendicular radial axes.

It is especially advantageous if one screw in each pair of diametrically opposite adjusting screws bears the weight of the magnet core while the other biases a spring against the core. For this arrangement, a coarse adjustment of the position of the magnet core is made by adjusting both screws in one or both pairs and a fine adjustment is made by adjusting only the screws that support the weight of the magnet core. The springs thus absorb the minor shift in the support ring required for the fine adjustment.

The spring elements are used to eliminate play in the magnet core. To insure that the magnet core is securely held even when the position of the magnet yoke is changed, it is desirable to bias each spring against the core with a force at least several pounds greater than the maximum weight that the spring must bear under any condition. For these purposes, it is desirable to use springs having a very flat characteristic curve. Plate spring packages are particularly suitable, but spiral springs, leaf springs, or rubber elements, for example, can also be employed. In addition to simplifying the adjustment of the magnet core, the use of the spring elements also prevents the magnet core from being jammed between opposite adjusting screws in such a way as to make longitudinal shifting of the magnet core impossible.

Preferably, the weight-bearing adjusting screws and the spring elements bear against pressure plates which contact the adjustable support ring. Such plates insure better distribution of the forces exerted by the adjusting screws and spring elements on the support ring and relieve the support ring of the torsion forces caused by rotation of the adjusting screws. Such plates also permit very fine adjustment of the magnet core position despite the fact that the enormous weight of the magnet core requires adjusting screws with a relatively coarse thread. This may be accomplished by providing each weight-bearing adjusting screw with two threads of the same direction and a slight difference in pitch, one of which engages a female thread in the guide tube or the adjusting ring and the other a female thread in the pressure plate. As a result of this arrangement, one full revolution of the adjusting screw causes a change in the position of the adjustable support ring that is equal to only the difference between the two thread pitches. This permits precise adjustment of the position of the magnet core and therefore the spacing between and parallelism of the pole faces.

Preferably, the adjustable support ring is located in an annular slot in the guide tube or the adjusting ring. As a result, the support ring is secured against axial movement when the magnet core is shifted longitudinally. For insertion into the slot, the support ring may be designed in two sections. Preferably, however, the support ring is broken at one point by a slanting slot that permits the diameter of the support ring to be reduced to the diameter needed to place it into the annular slot.

BRIEF DESCRIPTION OF THE DRAWING These and other objects, features, and elements of the present invention will be more readily apparent from the following drawing, in which:

FIG. I is a partial side view and partial cross section of a magnet using a preferred illustrative embodiment of the adjusting device of the present invention;

FIG. 2 is a top view of the adjusting device of FIG.

FIG. 3 is a cross section along line III-III on the adjusting device of FIG. 2;

FIG. 4 is a partial cross section along line IV-IV on the adjusting device of FIG. 2; and

FIG. is a perspective view of an element shown in FIGS. 2-4.

DETAILED DESCRIPTION OF THE INVENTION The magnet shown in FIG. I has a rectangular magnet yoke 1 in which two guide tubes 2 are fixed opposite one another. A magnet coil 3 surrounds each guide tube 2 and a magnet core 4 is located within each guide tube. 'Pole faces 5 of magnet cores 4 define an air gap 6 in which is generated a magnetic field of high field strength and maximum homogeneity. To permit changes in the length of air gap 6,' both magnet cores 4 may be moved longitudinally in guide tubes 2 by ad'- justing devices 7 attached to the outer ends of each guide tube. In addition, to permit rotation of the magnet around the longitudinal axis of guide tubes 2, the magnet is swivel mounted in a support 8 at the ends of the guide tubes projecting from magnet yoke 1. Because the foregoing features of the magnet are conventional, details of this construction will be apparent to those skilled in the art.

Eachmagnet core 4 is retained in guide tube 2 by only two

support rings

11, 12. As shown in FIG. I, support ring 11 is located near the outer'end of each magnet 'core'4, roughly in the center of the corresponding section of magnet yoke 1. As shown in FIG. 3, support ring 11 isya fixed convex spherical bead on the interior of guide-tube 2. Support ring 12 is located at the other end of the magnet core and is radially adjustable relative to guide tube 2. As shown inFlG. 4, support ring 12 is located in an annular slot 13 of an adjusting ring 14 fixed to the inside end of guide tube 2. Slot l3 prevents any axial shifting of support ring 12. As shown in FIG. 2, support ring 12 is positioned in slot 13 by adjusting

screws

15, 16 that are threaded through adjusting ring 14 to brace

pressure plates

17, 18 against support ring 12. Support ring 12 is provided with a slanting slot 112 (FIGS. 2 and 5) that permits the support ring to be compressed to the diameter needed to place it into the annular slot. I

Two pairs of diametrically opposite adjusting screws l5, 16 located at 90 intervals about adjusting ring 14 permit adjustment of support ring 12 in two mutually perpendicular directions. When magnet yoke 1 is vertical, the axes of both pairs of adjusting screws l5, 16 form an angle of 45 from the vertical plane. In this position, adjusting screws are located below the horizontal plane and thus support the front end of magnet core 4. As shown in FIGS. 2 and 3, each adjusting screw 15 has a threaded pin 19 that extends into a corresponding threaded hole 20 in pressure plate 17 so that there is a rigid connection between adjusting screw 15 and pressure plate 17. In contrast, each adjusting screw 16, which is located above the horizontal plane, is simply braced against pressure plate 18 by a spring 22 on a pin 21. t

With this apparatus. screws 15, 16 are used to adjust pole face 5 of each magnet core 4 so that the two faces are almost parallel. Further adjustments in the position of pole faces 5 to achieve uniform spacing between the faces are then made by using just screws 15 to effect radial movement of support rings 12 in the two guide tubes 2. Advantageously, springs 22 are plate springs (also called Belleville springs) possessing a very flat characteristic curve. The springs are preferably biased against support plate 18 by a force at least several pounds greater than half the weight of the magnet core. This insures that the force exerted on springs 22 is approximately the same for all positions of the magnet yoke, and not too great to prevent shifting the magnet core longitudinally.

To permit extremely fine adjustment of the position of each support ring 12 in its guide tube 2, each adjusting screw 15, as shown in FIGS. 2 and 3, has. two

threads

19, 23 having the same direction and a slightly different pitch. For example, thread 23, which is threaded into adjusting ring 14, may have a pitch slightly greater than that of thread 19 which engages threaded hole 20 in pressure plate 17. Consequently, one full revolution of adjusting screw 15 shifts the position of pressure plate 17 by only a distance equal to the difference in pitch between the two

threads

23 and 19.

. It is therefore possible to achieve shifts of only fractions of a millimeter with one revolution of adjusting screw 15 even though

threads

23, 19 typically have a relatively coarse thread needed for bearing the load of magnet core 4.

Alternatively, the two different-pitch threads on adjusting screw 15 may be arranged coaxially so that a threaded pin connected to the pressure plate engages a female thread coaxial to the male thread that engages the adjusting ring. g

In the apparatus shown in FIG. l,-fixed support ring 11 is located near the outside end of guide tube 2 while adjustable support ring 12 is located near air gap 6. This geometry superimposes on the magnetic field the effects of both the parallelism of the pole faces and the centering of the two magnet cores with respect to one another. If it is not desired that these effects be superimposed, the fixed support ring may be located near the air gap and the adjustable support ring may be located at the outside end of the guide tube.

As will be apparent to those skilled in the art, numerous modifications may be made in the preferred embodiments described and illustrated herein without departing from the scope of the invention as defined in the claims.

1 I claim: 7

1. Apparatus for adjustingthe parallelism between the pole faces of a magnet and capable of maintaining said parallelism substantially independently of changes in the orientation of the magnet, such magnet having a magnet yoke, guide tubes in the magnet yoke, and magnet cores mounted in the guide tubes, at least one such guide tube including first and second support members surrounding a magnet core disposed therein, said first support member comprising a fixed convex bead extending circumferentially about the interior of the guide tube and forming an inner bearing surface of substantially the same diameter as the outer diameter of the magnet core, and said second support member comprising an adjustable support ring mounted on the magnet core and a plurality of threaded members fixedly connected to the guide tube and having adjusting screws mounted therein, at leastone of said screws bearing on the support ring and at least one other of said screws acting on the support ring through a spring.

2. The apparatus of claim 1 wherein the adjusting screws are arranged in pairs diametrically opposed on the circumference of the adjustable support ring, one adjusting screw of each pair supporting the weight of the magnet core and the other biasing a spring against the core.

3. The apparatus of claim 2 wherein pressure plates are interposed between the adjusting screws and the adjustable support ring.

4. The apparatus of claim 3 wherein the adjusting screws that support the weight of the magnet core have two threads of a slightly different pitch, one of which engages a threaded member connected to the pressure plate and the other of which engages the threaded member connected to the guide tube.

5. The apparatus of claim 4 wherein said two threads of a slightly different pitch have the same direction.

6. The apparatus of claim 1 wherein the adjustable support ring is located in an annular slot in an adjustment ring connected to the guide tube.

7. The apparatus of claim 6 wherein a slanting slot is provided in the adjustable support ring to facilitate placement thereof into the annular slot.

Claims

1. Apparatus for adjusting the parallelism between the pole faces of a magnet and capable of maintaining said parallelism substantially independently of changes in the orientation of the magnet, such magnet having a magnet yoke, guide tubes in the magnet yoke, and magnet cores mounted in the guide tubes, at least one such guide tube including first and second support members surrounding a magnet core disposed therein, said first support member comprising a fixed convex bead extending circumferentially about the interior of the guide tube and forming an inner bearing surface of substantially the same diameter as the outer diameter of the magnet core, and said second support member comprising an adjustable support ring mounted on the magnet core and a plurality of threaded members fixedly connected to the guide tube and having adjusting screws mounted therein, at least one of said screws bearing on the support ring and at least one other of said screws acting on the support ring through a spring.