GB2284701A

GB2284701A - A laminated magnetic head with inclined pole faces

Info

Publication number: GB2284701A
Application number: GB9324312A
Authority: GB
Inventors: Rodney Uphill
Original assignee: DATA RECORDING HEADS Ltd
Current assignee: DATA RECORDING HEADS Ltd
Priority date: 1993-11-26
Filing date: 1993-11-26
Publication date: 1995-06-14
Anticipated expiration: 2013-11-26
Also published as: GB9324312D0; GB2284701B

Abstract

A magnetic transducing head includes a magnetic core formed of a stack of planar laminations 32, 33, 34, 35, 36 and has an air gap inclined to the planes of the laminations. Two core halves (Fig. 1, 26, 27) of generally "C" shaped form are each formed of a stack of laminations in which each lamination has a pole defining edge and wherein the pole defining edge of each lamination of the stack is displaced relative to an adjacent lamination of the stack such as to form a pole face inclined relative to the planar laminations. The laminations have substantially the same magnetic reluctance. <IMAGE>

Description

MAGNETIC TRANSDUCING HEAD AND METHOD OF MANUFACTURE THEREOF This invention relates to magnetic transducing heads for recording signals onto and reading recorded signals from a magnetic recording medium.

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.

Magnetic recording is used to record data on a stripe of magnetic recording medium on personal identification cards widely used as credit cards and for operation of remote teller machines. It is necessary with such identification cards to ensure that adequate security is provided to prevent, as far as is practical, fraudulent use of such cards and to prevent copying of such cards for fraudulent purposes. Accordingly coded signals are recorded on the magnetic stripe of such cards which may be read by a suitable reading device for verification, if desired in combination with a personal identification number keyed into the reading device by a user, by a central computer with which the reading device is in communication. In order to provide additional security in use of such identification cards it has been proposed that signals be recorded in an additional track of the magnetic medium and that, instead of magnetising the recording medium in alignment with the length of the stripe in the direction of movement of the medium relative to the head, the recording medium is magnetised in a direction inclined to the length of the stripe and the direction of movement of the recording medium relative to the head.

According to one aspect of the invention a magnetic transducing head comprises a magnetic transducing head includes first and second magnetic core elements each formed of a stack of a series of planar laminations and each having a pole face, the pole faces of the two core elements being spaced apart by a non-magnetic gap, each lamination having a pole defining edge and wherein the pole defining edge of each lamination of the series is displaced relative to a preceding lamination of the series such as to form a pole face inclined relative to the planar laminations.

According to a second aspect of the invention a method of manufacturing a magnetic transducing head includes the steps of bonding a series of planar laminations in a stack, the laminations each having a pole defining edge and the pole defining edge of each lamination of the series being offset relative to the pole defining edge of a next preceding lamination of the series to produce an initial face of stepped form having a pitch line inclined to the planes of the laminations and removing material from the pole defining edges in the initial face to form a planar pole face inclined to the planes of the laminations.

In a third aspect the invention encompasses a method of manufacturing a magnetic core element for a magnetic transducing head.

An embodiment of the invention will now be described with reference by way of example to the drawings in which: Figure 1 is an exploded view illustrating the construction of a composite magnetic transducing head assembly, Figure 2 is an exploded view of a stack of laminations to form a magnetic half core of a magnetic transducing head, Figure 3 is a side elevation of the stack of laminations forming the magnetic half core, and Figure 4 is plan view of the half core of Figure 3.

Referring first to Figure 1, a composite magnetic transducing head assembly comprises a first transducing head 10 and a second transducing head 11. A screen 12 extends between the first head 10 and second head 11. The assembly of the first and second heads and screen 12 is mounted in a screening can 13, a front face 14 of the can 13 having apertures 15, 16 through which pole pieces of the heads extend. The first magnetic transducer head 10 comprises magnetic core halves 17, 18 mounted in support members 19, 20 respectively. The core halves are formed of a stack of so-called 'C' shaped laminations. An electrical winding 25 is wound on the core half 17. The core halves 17, 18 have front pole faces 21, 22 respectively which extend in planes substantially perpendicular to the planes of laminations forming the core halves. The front pole faces 21, 22 are spaced apart by means of a non-magnetic shim (not shown) to form a nonmagnetic gap therebetween of width determined by the thickness of the shim. In use of the transducer head for reading or recording, a strip of magnetic recording medium indicated by dotted line 23 is moved in a direction indicated by arrow 24 relative to the composite head assembly. When mounted in the screening can the first magnetic transducer head 10 is located such that the width of the non-magnetic gap between the pole faces is aligned parallel to the arrow 24. It will be appreciated the alignment of the non-magnetic gap of the first transducer head is as used in conventional magnetic recording systems. The construction of the first transducing head is not pertinent to the present invention and accordingly it is believed to be unnecessary to describe the construction thereof in more detail herein.

The second magnetic transducing head is so constructed that the width of the non-magnetic gap between pole pieces of the second magnetic head is aligned in a direction inclined to the direction arrow 24. The second magnetic transducing head is of similar construction to the first transducing head and comprises two core halves 26, 27 supported in support members 28, 29 respectively and having pole faces 30, 31. The core halves are each formed of a stack of so-called 'C' shaped laminations. However, instead of the pole faces 30, 31 thereof extending perpendicular to the planes of the laminations of the core halves, the pole faces are inclined to the planes of the laminations and the manner of constructing the core halves will be described hereinafter with reference to Figures 2, 3 and 4.

Referring now to Figures 2, 3 and 4, the core half 27 comprises a stack of a series of laminations 32, 33, 34, 35, 36 of magnetic material. The laminations are of generally 'C' shaped form having a toes 32a...36a and heels 32b...36b interconnected by side limbs 37. On the top and bottom of the stack of magnetic laminations are conductive laminations 38, 39. The conductive laminations 38, 39 comprise only toes and heels 38a, 38b and 39a, 39b respectively and have no side limbs. The height 'h' of all the laminations is the same but, as may be seen from Figures 2, 3 and 4, the laminations 32 ... 36 of the series have progressively longer toes and heels such that the toe and heel of each lamination is displaced relative to and projects beyond the next preceding higher lamination in the series of laminations forming the stack.

Thus the ends of the toes and heels have a stepped form.

Additionally inner edges 40 of the laminations extending from the side limbs 37 toward ends of toes of the laminations 32 ....36 are inclined progressively at a larger angle so that toes of the laminations in the series are progressively broader and the extent of the ends of the toes beyond the inner edge is approximately equal for each of the magnetic laminations. By progressively inclining the inner edges and thereby broadening the toes, the magnetic reluctance of the laminations from the side limbs to the ends of the toes is maintained substantially equal despite the differences in length of the toes. It will be understood that if the magnetic reluctance of the laminations is not substantially the same, the outer laminations of the two core halves would have a higher reluctance than the central lamination and as a result the performance of the head adjacent its side edges would be inferior to its performance at the centre of its width.

Accordingly by maintaining the reluctance of each lamination substantially equal, the performance of the head is maintained more uniform across the width of the head.

The two core halves 26, 27 are similar but in the core half 26, one conductive lamination 41 (Figure 1) is of 'C' shape with a side limb connecting the toe and heel and is formed with an earth tag 42. An electrical winding 43 (Figure 1) is wound on the side limbs of core half 27 whereas the core half 26 is not provided with a winding.

After mounting of the core halves 26, 27 in their respective supports 28, 29, the exposed stepped ends of the toes and heels are ground to a plane indicated by dotted line 44 in Figure 4, for example in a lapping process, to produce front and rear pole faces lying in a plane inclined at an angle e to the planes of the laminations of the core halves. Typically the pole faces may be inclined at an angle of 450 to the planes of the laminations. The core halves 26, 27 mounted in their supports 28, 29, after lapping of the pole faces, are secured together with the pole faces opposed and spaced apart by a non-magnetic spacer 45, for example of mica.

The first and second transducer heads are mounted in side by side relationship in the screening can 13 and it will be appreciated that, whereas the width of the non-magnetic gap of the first head 10 extends parallel to the direction 24, the width of the non-magnetic gap of the second head extends with an inclination to the direction 24 and hence also is inclined relative to the non-magnetic gap of the first head. The term "width" in relation to non-magnetic gaps is used herein to means the dimension by which the pole faces of the two core halves are spaced apart.

Preferably the laminations for the core halves 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 46 between each lamination and surrounding material of the sheets. In this manner a plurality of laminations may be formed in each sheet and the core halves are formed by bonding a number of sheets such that a plurality of stacks of laminations are produced. The bonded stacks of laminations are separated from the remainder of the sheet by cropping or otherwise cutting the connecting portions 46. When producing laminations for the core halves of the first head 10, each sheet is etched with the same pattern. However when producing the laminations for the core halves of the second head 11, a series of sheets are etched1 the etched sheets of series corresponding to the series of desired differently shaped laminations.

The composite magnetic transducing head described hereinbefore may be utilised to record data in two tracks on a magnetic recording medium and to read such data from these two tracks. The data recorded by head 10 in one track will be recorded by magnetisation of the recording medium in a direction aligned with the direction of movement of the medium relative to the head and hence aligned with the length of the recorded track whereas data recorded by the second head 11 in the other track will be recorded by magnetisation of the recording medium in a direction inclined to the direction of movement of the recording medium and hence in a direction inclined to the length of the track. While the angle of inclination may be 450, the inclination may be at a different angle if desired.

The core elements are described hereinbefore and shown in the drawings as having five magnetic laminations. However it should be appreciated that the core elements may be constructed of other numbers of magnetic laminations.

Claims

1. A magnetic transducing head including first and second magnetic core elements each formed of a stack of a series of planar laminations and each having a pole face, the pole faces of the two core elements being spaced apart by a non-magnetic gap, each lamination having a pole defining edge and wherein the pole defining edge of each lamination of the series is displaced relative to a preceding lamination of the series such as to form a pole face inclined relative to the planar laminations.

2. A magnetic transducing head as claimed in claim 1 wherein each lamination is formed such as to have substantially the same magnetic reluctance.

3. A magnetic transducing head as claimed in claim 2 wherein the core element laminations are of 'C' shape including a front toe portion and a side limb, and wherein the front toe portion of each lamination of the series is of increased breadth relative to a preceding lamination in the series such as to maintain the magnetic reluctance of the laminations of the series substantially equal.

4. A magnetic transducing head as claimed in any preceding claim wherein the pole face of the core element extends at an inclination of approximately 450 to the planar laminations.

5. A method of manufacturing a magnetic transducing head including the steps of bonding a series of planar laminations in a stack, the laminations each having a pole defining edge and the pole defining edge of each lamination of the series being offset relative to the pole defining edge of a next preceding lamination of the series to produce an initial face of stepped form having a pitch line inclined to the planes of the laminations and removing material from the pole defining edges in the initial face to form a planar pole face inclined to the planes of the laminations.

6. A method of manufacturing a magnetic core element for a magnetic transducing head including the steps of bonding a series of planar laminations in a stack, the laminations each having a pole defining edge and the pole defining edge of each lamination of the series being offset relative to the pole defining edge of a next preceding lamination of the series to produce an initial face of stepped form having a pitch line inclined to the planes of the laminations and removing material from the pole defining edges in the initial face to form a planar pole face inclined to the planes of the laminations.

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

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

9. A method of manufacturing core element for a magnetic head substantially as hereinbefore described with reference to Figures 2, 3 and 4 of the drawings.