Patent GB-1055650-A (GB)
Title: Improvements relating to magnetic erasing heads
IPC: G11B5/29
Filed: 1963-10-22
Abstract: 1,055,650. Magnetic sensing leads. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. Oct. 22, 1963 [Oct. 22, 1962; May 18, 1963], No. 41627/63. Heading G5R. A multi-track erasing head has a core comprising a first core member extending over the whole width of the tracks and a plurality of other core members individual to the tracks and defining respective air gaps with the first core member, a separate winding being provided on each other core member; and the reluctances of the operative air gaps are so proportioned to the reluctances between the other core members that if all the windings are energized simultaneously a substantially uniform erasing field is formed across the whole width of the tracks, whereas if only one winding is energized the stray flux from the excited core member has a return path through an unexcited other core member so that substantially none of the erasing field appears across the operative air gap or gaps defined by the unexcited other core member or members. The double track erase head shown in Fig. 1 comprises a flat core member 3 extending for the width of the two tracks and two core members 1 and 2 separated by a uniform gap 5 and provided with respective windings 6 and 7. With equal energization of windings 6 and 7 a uniform flux is produced over the whole width of the tape. If winding 6 is energized alone, the stray flux from member 1 does not flow through the air gap between members 2 and 3 but finds a return path through the member 2 and the member 3, the reluctance between members 1 and 3 and between members 2 and 3 being much smaller than that of the air gaps. If the reluctance between members 1 and 2 is the same as that between members 1 and 3 and between members 2 and 3, the stray flux through the unexcited head is the same as the flux in the excited air gap and the power taken from the erasing signal generator is the same as when both windings are energized. Alternatively the reluctance between members 1 and 2 may be made much smaller than that between member 3 and either of members 1 and 2, and when only one winding is excited the other is short-circuited so that the stray flux between members 1 and 2 is attenuated to equal the flux in the operative air gap. This arrangement has the advantage that no switching transients are produced in the tape when switching from single to double track erasing and vice-versa. In a modification, Fig. 2 (not shown), the ends of the U- shaped members 1 and 2 are coplanar and part of the member 3 is ground away to a depth equal to the width of the air gap ; the air gap may be filled with non-magnetic material. In another arrangement shown in side and end views in Fig. 4, members 11 and 12 extend the full width of both tracks and are separated by two members 13 and 14 each provided with a winding and each providing a pair of gaps 15 and 16. The second air gap 16 in the direction of travel of the recording medium is narrower than the first gap 15. A non-magnetic distance piece 17, preferably of ceramic material, is provided between members 13 and 14. In a modification, Fig. 3 (not shown), members 13 and 14 are rectangular and members 11 and 12 are U-shaped.