US2873413A - Magnetic-field-producing device - Google Patents

Description

Feb. 10, 1959 M. F. REYNST 2,873,413

MAGNETIC-FIELD-PRODUCING DEVICE Filed Nov. 30. 1955 4 INVENTOR.

M. F. HEYNST AGEQT United States Patent l 2,873,413 MAGNETIC-FIELD-PRODUCING DEVICE Maximilian Felix Reynst, Eindhoven, Netherlands, assignor, by mesne assignments, to North American Philips Company, Inc., New York, N. Y., a corporation of Delaware Application November 30, 1955, Serial No. 550,115

Claims priority, application Netherlands December 4, 1954 directly through a comparatively large range by means of a rotational movement. The device according to the invention is characterized in that an annular soft-iron disc is arranged between the magnets and co-axially therewith, at least one edge of the disc having a particular profile for controlling the magnetic flux, co-operating with a likewise profiled substantially annular and coaxial softiron pole-piece, in such manner that the flux in the gap between the profiles flows substantially between the magnetic rings. The cooperating parts are preferably provided with adjacent toothed portions with the same pitch of teeth.

It may be mentioned that devices for controlling a mag netic flux by means of relatively movable teeth are known per so. However, the control range obtainable therewith is limited, as will be explained hereinafter.

In order that the invention may be readily carried into effect, it will now be described, by way of example, with reference to the accompanying drawing, in which Figs. 1 and 2 show an embodiment, one half in axial section and cross-section, respectively, and the other half in side view and elevation view, respectively.

Fig. 3 shows a slightly modified construction in axial section and Fig. 4 shows a detail of another variant.

Figs. 1, 2 and 3 show a magnetic electron lens which may surround the neck of a cathode-ray tube 1 (not shown further). The lens substantially comprises two flat rings 3 and 5 which are axially magnetized and-consist of permanent magnetic material, preferably ceramic material of the kind described in British Patent No. 798,127. The two rings 3 and 5 are, co-axially arranged side by side with the poles of like polarity-in this case the north polesadjacent one another. Arranged coaxially between the two rings 3 and 5 is a substantially annular disc 7 of soft iron (this is to be understood to include not only soft iron but also all materials having the same magnetic properties as soft iron, such as nickel, ferrites, etc). The assembly 3, 5, 7, is externally covered with two soft-iron discs 9 and 11, constituting flanges on two short soft-iron pieces of tube 13 and 15.

The inner edge of disc 7 is provided with teeth 17 and concentrically embraces a soft-iron disc 19 constituting a flange on a mately the same diameter as that of the tube pieces 13 and 15. The flange 19 externally comprises the same number of teeth (indicated by 23) as the disc 7, which teeth thus have the same pitch as the teeth 17 and in the position shown are in opposition to said teeth (that is to say'in straight opposition). The disc 7 is externally provided with teeth 25, the number and the pitch of which are thus equal to those of the teeth 17 and 23.

short soft-iron piece of tube 21 of approxi-.

The disc 7 and the magnets 3 and 5 are coaxially surrounded by a soft-iron piece of tube 27 comprising teeth 29 and 31 on the two edges and a series of windows 33 provided centrally on its circumference. The series of teeth 29 and 31 are in opposition to series of teeth 35 and 37 formed on the edges of the flanges 9 and 11. The numbers and the pitches of all these teeth and windows are equal to those of the teeth previously described.

Magnetic fields occurs between the piece of tube 21 and the pieces of tube 13, 15, which fields may be used in known manner for concentrating an electron beam passing through the neck of the tube I. Said fields extend wholly symmetrically with respect to the disc 7 and for the sake of convenience only the field at the left of the disc will be considered more fully hereinafter. Part of the fiux-represented by a line of force 41--flows, starting from the magnet 3, directly via the piece of tube 21. A larger portion-represented by two lines of force 43 and 45flows via the teeth 17 and 23 and across their separating air-gap; the extent of this portion is greatly dependent upon whether the teeth 17 and 23 are in opposition or not. At the position shown (see Fig. 2), the teeth 17 and 23 are in straight opposition and it will be evident that at this position the gap is at a minimum and the magnetic reluctance in the circuit of the lines of force 43, 45 is minimum, and maximum at the position at which the parts 7 and 19 have been turned through an angle or equal to the half pitch of the teeth. The magnetic fiux in the neck of the tube 1 is as great and as small as possible at the said two positions, it thus being possible to corn trol the flux (and the field strength) by turning the part 7 or 19 relative to the other.

In know control devices with gearings, it has been found that the control range is greatly limited by the fact that at the position of minimum field strength a considerable stray flux laterally (axially) emerges from and enters the toothed discs. Consequently the minimum field strength is usually only slightly lower than the maximum field strength. According to the invention, said disadvantage is obviated in that (see Fig. 1) the flux which passes from the disc 7 via the teeth 17 and 23 to the disc 19 (lines of force 43 and 45) flows between the magnets 3 and 5, i. e., this variable flux path is located between the magnets 3 and 5. Lateral (axial) emergence of the lines of force from the face areas of the discs is prevented owing to the faces of the magnets 3 and 5which are the sources of the lines of forcebeing positioned in facing relation to the discs, so that at the minimum position (non-opposition of the teeth 17 and 23) the said flux is greatly decreased and hence a large control range (a variation of 1:2 and more) can be achieved.

Another possibility of control-which may also be used separately-is provided by the co-operation of the teeth 25 on the outer edge of disc 7 with the ring 27 provided with the windows 33, since part of the flux of the magnet 3 (see line of force 47 in Fig. 1) may flow along a parallel path via the ring 27 and the flange 9 and thus be largely extracted from the useful flux traversing tube 1. By turn ing one of the elements 7 and 29 with respect to the other, the parallel flux is controlled fundamentally in the same way as the flux 43, 45, but in the opposite sense, sincesee Figs. 1 and 2-the position of non-opposition of the teeth 25 and the bridge pieces 49-which in this case are to be regarded as teethcoincides with the position of opposition of the teeth 17 and 23. In this case also lateral emergence of the lines of force from the disc 7 is prevented or at least substantially suppressed by the mag nets 3 and 5.

The magnetic connection between the flange 9 (or 11) and the ring 27 extends in the case shown via teeth 35 and 29 (and 37, 31) formed on said parts. The magnetic reluctance resulting from said transition is in series with that resulting from the teeth 25 and 49 and is controlled I in the same sense. Theadditional variation thus obtained is not great, since lines of force (for example line of force 51) can laterally enter the flange 9, but it assists in the variation brought about by the teeth and bridge pieces 25 and '49.

As a matter of fact (see Fig. 3), the ring 27 may have inwardly directed teeth 53 to substitute the bridge pieces 49. On the other hand, it is possible for windows 55 cooperating with the teeth 17, similar to the windows 33 in the part 27 (as shown in Fig. 1) and the teeth 25 in the disc 7, to be provided in the piece of tube 2-1. In the embodiment shown in Fig. 3, the edges of the'fianges 9, 11 and those of the ring 27 are not provided with teeth.

' lnorder to facilitate the relative rotation of the various parts required for the control, it is possible (see Fig. 3) tosecure the parts 9, 3, 7, 5, 11 together, to secure the piece'of tube 21 to the tube '1 (or to a separate nonmagnetic supporting pipe surrounding it) and to secure the ring 27 to the chassis'of the apparatus of. which the described device forms part, while the tube pieces '13 and 15 can rotate about the tube 1. The control is'then effected by rotating the assembly 9, 3, 7; 5, 11 while the rings 21 and 27 remain at rest. 7

Fig. 4 shows a profile of amodification of the discs 7 and 21 which may be used, for example instead of the teeth 17 and 23.

What is-claimed is:

1. A magnetic-field-producing. device comprising two, annular, coaxial, closely spaced, permanent magnets each magnetized in its axial direction so that like poles face each other, a first annular soft ferromagnetic member disposed between and coaxially with the two magnets, and a second annular soft ferromagnetic member arranged coaxially relative to' the magnets and adjacent the first soft ferromagnetic member and themagnets, said first and second soft ferromagnetic members having portions facing each other in a radial direction and defining an airgap therebetween and forming, in accordance with their relative positions, reluctance paths of different magnitude, said air-gap being located substantially between said two magnets and lying substantially within an area encompassed by the outer and inner diameters of the annular magnets, said first and second soft ferromagnetic membersbeing relatively movable so as to'vary the reluctance path for the flux produced by said magnets,'whereby magnetic fields with a wide range of intensities are obtainable.

2. A device as set forth in claim 1, wherein thefirst and second soft ferromagnetic members have facingtoothed portions of the same pitch.

3; A'device producing: a'variable permanent magnetic field, comprising a pair of continuous, annular, coaxial, closely spaced, permanent magnets each magnetized in its axial direction producing poles of like polarity on facing surfaces, a first annular soft ferromagnetic member mounted between, abutting and coaxially with the two magnets and a second annular soft ferromagnetic mem- =bert arranged coaxially with the tWO magnets and within and substantially coplanar with'the first member, said first-and second members having radially-extending, facing, toothed portions of the same pitch defining an annular space lying between and adjacent the magnets and substantially within the spacebounded by the magnets, said two members being relatively axially rotatable to thereby vary the reluctance path for flux produced by the magnets and thereby. vary the strength of an internally-produced permanent magnetic field.

4. A device producing a variable permanent magnetic field, comprising a pair of continuous, annular, coaxial, spaced, permanent magnets each magnetized in its axial direction producing poles of like polarity on facing surfaces, said magnets being spaced apart a distance smaller than their radial thickness, a first annular soft ferromagnetic member mounted between, abutting and coaxiallywith the'two magnets, and a second annular soft ferromagnetic member arranged coaxially with the two magnets and substantially coplanar with the first member, said first member having a radially-extending, toothed portion, said second-member having a plurality of circumferentially-arranged apertures aligned with, facing, and of the same p'it'ch as the, teeth on the toothed portion and defining between the two members air-gaps, the airgaps between the facing portions of the first and second members being located substantiallydirectly between the pair of magnets, said two members being relatively axially rotatable to thereby vary the reluctance path for fiux produced by the magnets and thereby vary the strength of an internally-produced permanent magnetic field.

5. A device producing a variable permanent magnetic field, comprising a pair of continuous, annular,'coaxial, spaced,,permanent magnets each magnetized in its axial direction so that like, poles face one another, a first annular soft ferromagnetic member mounted between, abuttingand coaxially with the two magnets, said first member having inner and outer radially-extending toothed portions of thesame given pitch, a second annular soft ferromagnetic member arranged coaxially with, within, abutting and substantially coplanar with the first member, said second member havingv a radially-extending toothed portion'of said given pitch cooperating with the inner toothed portion of said first member to define reluctance paths for the-flux produced by said magnets, and a third annular soft ferromagnetic member arranged coaxially with the first and second members, saidthird member having a toothed portion of said given pitch cooperating with the outer toothed portion of said first member to define reluctance paths for-the flux produced by said magnets, said first member being rotatable relative to said second and third-members to thereby change the reluctance paths for the flux produced by said magnets and thereby vary the strength ofan internally-produced permanent magnetic field.

6. A device asset forth in claim 5 wherein the first, second -and third members are so arranged that the cooperating toothedportions of the first and second members are aligned when the cooperating toothed portions of the first and third members are misaligned.

7. A device as set forth in claim 4 wherein the second member abuts the magnets.

References Cited in the file of this patent UNITED STATES PATENTS 2,333,230 Beechlyn Nov. 2,-1943 2,369,769 Ramb'er'g Feb. 20, 1945 2,608,665 Parker Aug. 26, 1952 2,714,678 Wolff Aug. 2, 1955 2,740,064 Birkbeck Mar. 27, 1956

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