Patent GB-1493058-A (GB)
Title: Electromagnet
IPC: F16C39/06
Filed: 1975-02-11
Abstract: 1493058 Electromagnets MASCHINENFABRIK AUGSBURG-NURNBERG AG 11 Feb 1975 [11 Feb 1974 12 Feb 1974] 5766/75 Heading HIP An electromagnet (Fig. 1) comprises a magnetizable yoke, and an energizing winding excited from source 3; the yoke having at least two pole shoes 4, 5 and a magnetizable armature 6 (which may be wound) movable by the magnetic force. The yoke may have three pole shoes with separate 3 phase energized windings directed radially inwards to a central armature (Fig. 3, not shown) or may have plural inwardly directed pole shoes (Fig. 4, not shown) and a multiple 3 phase energized winding having a separate coil round the yoke between each pair of adjacent pole shoes. Secondary magnetic fields produced by control coils may act on the armature, e.g. to support it on a magnetic bearing or to introduce energization at other frequencies. To avoid intermodulation between an alternating energization flux and a further alternating flux, e.g. for bearing magnetization, which produces armature vibration; the end faces of one or more of the pole shoes is/are subdivided into two or more discrete partial polar surfaces, 7, 8 interwound with a separate exciting coil 10 generating an auxiliary field opposed to the main field and energized from a source 11 (Figs. 1, 2) whereby intermodulation between the energizations and consequent unbalancing forces are shown to be avoided by field balancing. A double coil can be wound with one part surrounding each partial pole (Fig. 5, not shown) and the pole faces may be chamfered in opposed senses (Fig. 6, not shown). The poles may be subdivided into multiple partial poles each having an energizing coil and so proportioned as to cancel out torques acting on an armature; e.g. by employing three pole surfaces 7, 8, 16 separated by gaps 9, 17 and energized by three coils 14, 15, 18 wound so that the fields of the central pole are opposed to those of the outer poles (Fig. 7). The partial polar surfaces may be annular and separated by an annular gap (Fig. 8, not shown) and the outer pole may be radially gapped. A pole may be subdivided into four partial poles by vertical and horizontal dividing gaps wound with discrete coils, so energized that adjacent poles along one axis are oppositely energized while adjacent poles along the other axis are energized in the same sense. (Fig. 9, not shown). Four coils 14, 15, 18, 19 may be energized simultaneously from a first and a second source 3, 11 functionally separated by connection in a balanced bridge circuit (Fig. 10) so that the fields of coils 14, 19 reinforce while fields of coils 18, 15 oppose. The pole shoe may have only two polar surfaces (Fig. 12, not shown) with a pair of coils wound round one pole surface and another pair wound round another pole surface; so that fluxes reinforce in one pole and oppose in the other as in Fig. 2. A control source may be adapted to energize a measuring device connected to the coils of the control system to measure inductance thereof and thus the distance between pole shoe and armature in known manner; the result being applied to stabilize this distance in a magnetic bearing.