Patent GB-745911-A (GB)
Title: Improvements in or relating to devices of the kind comprising one or more magnetic bodies
IPC: H01F7/02
Filed: 1952-11-25
Abstract: 745,911. Permanent magnet structures. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Nov. 25, 1952 [Nov. 28, 1951], No. 29790/52. Classes 35 and 38 (2). [Also in Group XXXVIII] A device such as a dynamo-electric machine, the erasing head of a magnetic recording machine, or a magnetic coupling, comprises permanent magnetic material with a retentivity B r  in Gauss, not greater than four times the coercivity  B H c  in Oersted, magnetized to form along a pitch line TT (Fig. 2) a number of alternating poles of pitch length s, spaced apart by a distance x and having a length d in the direction of magnetization, the dimensions being such that x is less than 0.7 s and not greater than 2 d, and d is between 0.15 sand s. A suitable material is the composition of non-cubic crystals of polyoxide of iron and at least one of the metals Ba, Sr, Pb and additionally if desired Ca, which forms the subject of Specification 708,127. The material may be magnetized when heated, as described and claimed in Specification 719,004. The poles may be produced in a single sheet, Fig. 4, a ferromagnetic body 5 on one side providing when necessary a magnetic connection. Several sheets may be stacked with the magnetic dipoles in series. These poles may be produced by a magnetizing device comprising two pole shoes 2, 3, Fig. 6, energized by a magnetic field which may be pulsatory, the pole shoes being moved along the sheet and the direction of magnetization reversed after each magnetizing step. Recesses in the pole shoes and the effects of eddy currents induced by the pulsating field in adjacent conducting bodies 7, 8 reduce the stray fields which tend to demagnetize poles previously produced. Several alternate poles may be produced simultaneously from one pair of pole shoes, the intervening spaces for the other poles being screened from the pulsating magnetizing flux by conducting bodies 9, Fig. 7. Several pole shoes carrying oppositely directed fluxes and separated by conducting bodies may be used, Fig. 8 (not shown). To form an erasing head from a body as shown in Fig. 4; the distances x are made to increase in the direction in which the tape passes, the tape then travelling through an alternating flux of reducing amplitude. A highfrequency dynamo-electric machine comprises two cylindrical permanent magnet structures 17, 18 each comprising a large number of poles and backed by ferromagnetic sheets 19, 20 and separated by and relatively movable to windings 21 in cavities in a support 22 of magnetic or non-magnetic material, Fig. 11. A coupling comprises several sheets magnetized as in Fig. 4, interleaved with and slidable relative to similar sheets, Fig. 12 (not shown). Many forms of magnetic coupling for joining two rotating shafts are described. Figs. 13A, 14A show 1-1 couplings between shafts 31, 32, comprising poles arranged around coaxial discs and cylinders 33, 34 respectively. A sheet of conducting foil 40 between opposing faces provides coupling when the speeds of rotation differ. The rods need not be coaxial, they may rotate with a speed ratio differing from unity, and in opposite directions, Fig. 16, or in the same direction, Fig. 17 (not shown). The pitch length d may vary up to about 20 per cent. By avoiding narrow overlap of the poles on opposite discs, and by providing non-magnetized zones c the adverse effects of similar poles overlapping may be reduced. A single disc on one shaft may pass between two discs on the other, Fig. 18 (not shown). To release a cylindrical coupling against the axial force between the poles, this force may be reduced by providing ferromagnetic cylinders 53, 54 which move into position opposite the rings of poles when these separate, Fig. 19. A variable-speed coupling may be formed by replacing member 53 by a pole ring rotating with a different speed. Couplings may have pole faces not arranged parallel to the axis, Fig. 21 (not shown), or may connect shafts at right-angles, Figs. 22, 23 (not shown). For varying the transmission rates, a disc may have two rows of poles, or a spiral arrangement of poles, Fig. 24, and another set of poles on a further disc or a cylinder is movable to or from the axis of the first disc, across the face of this disc. Alternatively a ring of poles on one shaft may co-operate with a cylinder on the other shaft which bears a helical arrangement of poles, of varying pitch, Fig. 26 (not shown). In Fig. 25. (not shown), there are two pairs of coaxial cylinders, one or other pair being selected for engagement by relative axial movement of the shafts. A disc having spirally arranged poles may co-operate with a disc bearing circumferentially disposed poles. Where necessary, magnetic screening plates may prevent cooperation between poles. Specification 745,826 also is referred to.