GB2284921A - A laminated magnetic head core - Google Patents

Abstract

A magnetic transducing head comprises two magnetic half cores each half core including a front toe portion 12 connected by a side limb 14 to a rear heel portion 13. The side limb is of the same width as the front toe portion and the rear heel portion is narrower. An electrical winding 21 extends around the heel portion and is electromagnetically coupled to the core. The narrow heel portion enables the winding to have a relatively small exterior width dimension. Due to the side limb being of the same width as the front toe portion the reluctance of the core is substantially uniform across the width of the toe portion of the core and the head has a substantially uniform sensitivity across the width of the head. The toe and side limbs are wider than the heel portion due to the presence of additional laminations 15, 16. <IMAGE>

Description

MAGNETIC TRANSDUCING HEAD This invention relates to magnetic transducing heads and in particular to magnetic transducing head comprising a magnetic core and an electrical winding electromagnetically coupled to the magnetic core.

Known magnetic transducing heads comprise an electrical winding or coil electromagnetically coupled to a magnetic core and the magnetic core is formed with a non-magnetic gap extending between two opposed poles of the core.

Usually when recording signals onto or reading recorded signals from magnetic medium, the magnetic medium is moved past the magnetic transducing head with the magnetic medium in contact with a face of the core through which the non-magnetic gap extends. During recording, the electrical winding is energised to produce magnetic flux in the core and resultant magnetic flux across the nonmagnetic gap causes magnetisation of the recording medium in the vicinity of the gap so that, as the recording medium moves past the head, signals are recorded in a track of the medium. During reading of recorded signals from a track of the medium, as the medium is moved past the head, magnetisation of the recording medium induces magnetic flux in the magnetic core and this flux electromagnetically couples with the electrical winding to induce electrical signals in the electrical winding. In commonly used magnetic recording systems, the width of the non-magnetic gap, that is to say the dimension of the gap in the direction from one pole to the other pole of the core, is aligned with the direction of movement of the magnetic recording medium relative to the transducing head.

Commonly, the magnetic core comprises two core halves of 'C' shape, the core halves being mounted such that toe and heel end portions thereof are opposed to one another and at least the toe end portions forming front poles of the core are spaced apart by a non-magnetic spacer to form a non-magnetic gap in the core. The electrical winding comprises a coil of conductive wire wound on one core half or coils wound on both core halves. The coils are wound on limbs of the core halves intermediate the toe and heel portions. The magnetic core halves are formed of laminations of magnetic material and the laminations usually are bonded together by a layer of material which serves not only as a bonding agent but also to electrically isolate adjacent laminations to prevent flow of eddy currents in the core. The core halves are usually of uniform width so that the toe portions forming the front poles are of the same width as the intermediate limbs on which the electrical winding is wound. It will be appreciated that the width of winding wound on the intermediate limbs is greater than the width of the front poles and as a result the overall width of the magnetic transducing head is determined by the width of the electrical winding.

In some instances it is required to provide a multi-track head for recording in or reading from two or more closely spaced tracks of the recording medium. If the magnetic cores of the multi-track head are located such that the front poles are aligned at the spacing required for recording on or reading from the closely spaced tracks there is insufficient space between adjacent cores to accommodate the electrical windings of the heads. Also it is sometimes required that the overall width of a single track head is not significantly greater than the width of the front poles of the head.

In one known construction of magnetic transducing head designed such that the width of the winding is substantially the same as or not significantly greater than the width of the front pole faces of the head, the core halves are formed of central stacks of laminations and additional toe and heel laminations are provided ir respect of the toe and heel portions on each side of the core halves. Thus the width of the stack of laminationE together with the additional toe and heel laminations ic chosen to provide the required width of front pole facet while leaving the intermediate limbs of the core halves of lesser width so as to enable windings on the intermediate limbs to be accommodated substantially within the width of the widest portions of the core at the toe and heel. The reluctance of a magnetic flux path through the central stack of laminations and the non-magnetic gap is lower, particularly when the reluctance of the non-magnetic gaE is low, than any flux path which passes through the additional toe laminations. This arises not only because any path for flux which passes through the additional toe laminations is longer than flux paths through the central stack of laminations but also because flux paths passing through the additional toe laminations include nonmagnetic regions in material extending between and bounding together adjacent laminations. Thus any flux path through one of the additional toe or heel laminations includes non-magnetic material bonding that lamination and an) other laminations between that lamination and the central stack of laminations. Accordingly the reluctance of flu) paths increases progressively for laminations further fron the central stack of laminations and is highest for flur paths passing through toe laminations at the outer extremities of the core. As a result the contribution of each toe lamination to transfer of magnetic flux betweer the core and a magnetic medium decreases the further the toe lamination is from the central stack of lamination and the performance of the head decreases towards the edges of the head. The additional heel laminations make substantially no contribution to total magnetic flux ir the core. Where the magnetic transducer head is to be used in reading recordings in tracks of a magnetic mediun and is required to respond to the average magnetisatior across the width of the track decrease in performance towards the edges of the head may not be significant.

However magnetic heads to be used for reading magnetic characters are required to respond to magnetised portions of characters located anywhere across the width of a track in which such characters are recorded and some characters may be distinguished only by portions thereof located towards the extremities of the width of the track.

Therefore such heads are required to have satisfactory sensitivity and performance across the full width of the front pole face of the head.

According to a first aspect of the invention a magnetic transducing head comprises a magnetic core including a front toe portion including a non-magnetic transducing gap, a rear heel portion and two side limbs connecting ends of the toe and heel portions to complete a magnetic flux path extending across the non-magnetic gap and through the rear heel portion; said front toe portion and side limbs being of first width and said rear heel portion being of second width smaller than said first width; and an electrical winding extending around said heel portion of second width and electromagnetically coupled with said flux path.

According to a second aspect of the invention a method of manufacturing a magnetic transducer head includes the steps of forming a plurality of generally 'C' shaped laminations having a front toe portion and a rear heel portion connected by a side limb; forming first and second laminations having a toe portion and a side limb corresponding to the toe and side limb of the 'C' shaped lamination; bonding a stack of laminations comprising 'C' shaped laminations interposed between said first and second laminations to form a core halve having a toe and side limb of first width and a heel of second width less than said first width.

An embodiment of the invention will now be described by way of example with reference to the drawings in which: Figure 1 is an exploded view of one half of a magnetic transducer head assembly, Figure 2 is a cross section of a magnetic transducer head, and Figure 3 is a cross section on line 3 - 3 of Figure 2.

Referring first to Figure 1, a half magnetic core 10 for a transducer head comprises a stack of 'C' shaped laminations 11 having toe portions 12, heel portions 13 and side limbs 14. Additional laminations 15, 16 are provided on each end of the stack of laminations 11. The additional laminations 15, 16 comprise toe portions 17 and side limbs 18 corresponding in shape to the toe portion and side limbs of the laminations 11 but do not have a heel portion corresponding to the heel portion 13 of the laminations 11. The half core 10 is mounted in a recess 19 in a support element 20. An electrical winding 21 is wound on a coil former 22, the coil former having a central wall 23 of rectangular tubular form and end cheeks 24 to support the winding 21. The coil former 22 has a rectangular aperture 25 extending through the coil former from one cheek to the other cheek to enable the coil former to located on the heel portions 13 of the core with the heel portions 13 extending slightly over half way through the aperture. The support element 20 is moulded and has connection pins 26, 27 located therein and projecting from a rear face 28 of the element. Ends 29, 30 of the winding are electrically connected to the pins 26, 27 respectively.

A second similar magnetic core half 31 (Figure 2 and 3) is mounted in a second support element 32, however the second support element is not provided with connection pins. An electrically conductive spacer element 33 is located in the recess of the support element prior to mounting the magnetic core half 31 therein. The spacer element 33 is formed with an earth tag 34 which extends through a slot 35 in the support element 32.

The core halves 10 and 31, mounted in the support elements 20, 32 respectively are assembled with front pole faces 36 on the toe portions and rear pole faces 37 on the heel portions opposed to one another, the front pole faces being spaced apart by a non-magnetic spacer 38 and the heel portions each extending into contact with one another within the aperture 25 of the coil former 22. The assembly of core halves, winding and coil former and support elements is located in a screening can 39 having a front aperture 40 in a front wall 41 through which the toe portions adjacent the pole faces project. The assembly is secured in the screening can by potting in resin. The front of the assembled magnetic transducer head and the front wall of the screening can is ground down, for example by a lapping process, to a required profile indicated by broken line 42.

It will be appreciated that the additional laminations 15, 16 provide a front face adjacent the non-magnetic gap of the head which is wider than the heel portions on which the winding on the coil former is located. As a result the overall width of the head, which is determined by the dimension of the winding on the coil former, for a given width of the pole pieces formed by the toe portions is smaller as compared with a head construction in which the magnetic core is of uniform width. However by making the width of the core uniform as regards the toe portions forming the front pole pieces and the side limbs and making the heel portions of lesser width to accommodate the electrical winding the reluctance of flux paths passing through the outer parts of the core formed by the additional laminations is substantially similar to that of flux paths through the stack of laminations 11.

Consequently the sensitivity of the transducer head when reading recorded data from a track does not decrease significantly from the centre of the width of the pole pieces towards the outer edges.

The central laminations 11 for the core halves preferably are produced by etching sheets of magnetic material, the etching pattern being such as to remove material from adjacent the edges of the laminations while leaving connecting portions 43 between each lamination and surrounding material of the sheets. In this manner a plurality of identical central laminations are formed in each sheet. Similarly, further sheets of magnetic material are etched to produce the additional laminations 15, 16. A plurality of sheets etched to form the central laminations 11 together with further sheets etched to produce the additional laminations 15, 16 are stacked together. The sheets to form the additional laminations 15, 16 are located respectively at the top and bottom of the stack.

The stack of sheets is then bonded together to form core halves having central laminations 11 and additional laminations 15, 16. The bonded stacks of laminations forming the core halves are separated from the remainder of the bonded sheets by cropping or otherwise cutting the connecting portions 43. It is preferred to bond all the sheets to form core halves in a single operation but, if desired, the core halves may be formed by bonding together a number of bonded stacks of etched sheets, for example three stacks gila, llb, lic as shown in Figure 1 together with a stack of laminations 15 and a stack of laminations 16.

The connecting portions 43 are required to maintain the position of each etched lamination relative to the remainder of the etched sheet so that, in the operation of bonding the stack of sheets, all the laminations to form a core half are located in correct alignment with one another and are maintained in this correct alignment until the bonding operation is completed. Accordingly the connecting portions 43 are located such that each lamination is restrained relative to the remainder of the sheet and as shown in Figure 1, a first connecting portion is provided on the toe of each lamination close to the pole face 36 and a second connecting portion 43 is located at the rear end of the side limbs. The location of the second connecting portions at the rear end of the side limbs, ensures that not only are the central laminations 11 maintained in the required alignment but so also are the additional laminations 15, 16.

Claims (7)

1. A magnetic transducing head comprising a magnetic core including a front toe portion including a non-magnetic transducing gap, a-rear heel portion and two side limbs connecting ends of the toe and heel portions to complete a magnetic flux path extending across the non-magnetic gap and through the rear heel portion; said front toe portion and side limbs being of first width and said rear heel portion being of second width smaller than said first width; and an electrical winding extending around said heel portion of second width and electromagnetically coupled with said flux path.

2. A magnetic transducing head as claimed in claim 1 wherein the magnetic core comprises first and second half cores, each half core including a stack of first laminations of 'C' shape each having a toe part and a heel part connected by a side limb part and second and third laminations each having only a toe part connected to a side limb part, said first laminations being located between said second and third laminations whereby the front toe and side limb of the first and second half cores are of the first width and said heel is of the second width.

3. A magnetic transducer head as claimed in claim 2 wherein the electrical winding is wound on a coil former having an aperture extending therethrough and the heels of the first and second half cores extend in the aperture from opposite ends thereof and abut therein.

4. A method of manufacturing a magnetic transducer head including the steps of forming a plurality of generally 'C' shaped laminations having a front toe portion and a rear heel portion connected by a side limb; forming first and second laminations having a toe portion and a side limb corresponding to the toe and side limb of the 'C' shaped lamination; bonding a stack of laminations comprising 'C' shaped laminations interposed between said first and second laminations to form a core halve having a toe and side limb of first width and a heel of second width less than said first width.

5. A method of manufacturing a magnetic transducer head as claimed in claim 4 including the steps of etching the 'C' shaped laminations in first sheets of magnetic material; said 'C' shaped laminations being located relative to remaining portions of the first sheets by connecting pieces connecting the toe portion and a rear end of the side limb respectively to the remaining portion; etching the first and second laminations in second and third sheets of magnetic material; said first and second laminations respectively being located relative to remaining portions of said second and third sheets by second connecting pieces connecting the toe portion and a rear end of the side limb respectively to the remaining portion such that when the first , second and third sheets are stacked, the toe portions and side limbs of all the laminations are aligned and the connecting portions of each sheet are aligned.

6. A magnetic transducer head constructed and arranged to operate substantially as hereinbefore described with reference to the drawings.

7. A method of manufacturing a magnetic transducer head substantially as hereinbefore described with reference to the drawings.