GB2149186A

GB2149186A - A magnetic transducer head

Info

Publication number: GB2149186A
Application number: GB08418238A
Authority: GB
Inventors: Nan-Hsiung Yeh
Original assignee: Control Data Corp
Current assignee: Control Data Corp
Priority date: 1983-11-04
Filing date: 1984-07-18
Publication date: 1985-06-05
Also published as: GB8418238D0; FR2554624A1; JPS60103509A; DE3424651A1; AU3119784A

Abstract

A magnetic transducer head comprises a back flux path (19), a pair of outer pole arms (11, 14) forming a continuous magnetic circuit with the flux path (19) and having pole tips (15, 17) spaced apart to form a flux gap of a predetermined length (L), and a centre pole arm (9) forming a continuous magnetic circuit with the flux path (19) and having a pole tip (16) interposed between the pole tips (15, 17) of the outer pole arms (11, 14) to form a flux gap between itself and each pole tip of the outer pole arm. The pole tip of the centre pole arm is substantially shorter in length than the pole tip of the outer pole arms. Write/read operations are detailed. During writing, centre pole arm (9) saturates, allowing writing at the trailing edge of the trailing outer pole arm; during reading, the shorter pole tip increases the resolution. <IMAGE>

Description

SPECIFICATION A magnetic transducer head This invention relates to magnetic transducer heads.

Magnetic data recording as practised today usually employs a magnetic transducer head for writing data onto, and reading data from a magnetic recording medium. A magnetic transducer head includes a small magnetic flux bar comprising a core typically formed of ferrite or a deposited magnetic material and having a gap interposed in it, and a small winding through which an electrical signal current is passed during a writing operation, and from which a signal current is received during a reading operation. The portions of the core adjacent the gap are often referred to as poles or pole tips and the portions adjacent the pole tips are referred to as pole arms. The write operation requires a substantial amount of current to generate flux sufficient to impress a magnetic data pattern on a magnetic recording medium.Typically, the flux path or core of the magnetic transducer head will be driven very nearly to magnetic saturation during the writing operation. However, saturation of the core is not desirable because the data pattern written is distorted thereby.

A new type of magnetic recording technique employs vertical orientation of the magnetic data patterns created on the magnetic recording medium rather than the older horizontal magnetic data patterns now almost universal. The magnetic recording medium used in one type of vertical recording technique has an outer layer in which the actual data is recorded and an inner layer which provides a flux path to complete the magnetic circuit between the poles of the head. To avoid saturation of the core, it is necessary that the poles tips are relatively long (by convention, the length of a flux gap is the dimension specifying the spacing between the pole tips. To maintain consistency, the length of the pole tips will be measured in the same direction that the length of the flux gap is measured).

It is now known that a magnetic transducer head with a relatively long pole tip can be used to write exceedingly dense vertically recorded data so long as the pole tips do not saturate and the trailing corner of the trailing pole tip is not very sharply defined. However, long pole tips are not satisfactory for read back in that resolution of densely packed data is difficult. A very helpful explanation of these considerations is presented in the IBM Technical Disclosure Bulletin, Vol. 23, No. 5, October, 1980, pp. 2148-2149, "Design of Separately Optimised Thin Film Read/Write Magnetic Recording Heads". The solution proposed in this reference is to place read and write heads side by side on a substrate, each being optimised for its particular function, and then simply radially shift the composition transducer depending upon whether reading or writing is desired.Other relevant references are IBM Technical Disclosure Bulletin, Vol.

14, No. 4 September, 1971, pp.

1 283-1 284, "Composite Read/Write Recording Head" and U.S. Patent Specifications Nos. 3,399,393, 3,881,191 and 4,277,809.

Although the present invention is primarily directed to any novel integer or step, or combination of integers or steps, herein disclosed and/or as shown in the accompanying drawings, nevertheless, according to one particular aspect of the present invention to which, however, the invention is in no way restricted, there is provided a magnetic transducer head comprising, a back flux path, a pair of outer pole arms forming a continuous magnetic circuit with the flux path and having pole tips spaced apart to form a flux gap of predetermined length, and a centre pole arm forming a continuous magnetic circuit with the flux path and having a pole tip interposed between the pole tips of the outer pole arms to form a flux gap between itself and each pole tip of the outer pole arms, said pole tip of the centre pole arm being substantially shorter in length than the pole tips of the outer pole arms.

Preferably the magnetic transducer head includes a pair of windings, each encircling the flux path comprising the centre pole arm and a different one of the outer pole arms, the windings being connected.

The connection between the windings may be such as to create opposite handedness in the orientation of the windings.

The pole tips of the outer pole arms may be of equal length.

The pole tip of at least one of the outer pole arms may have a length in the range of 1 to 10,us.

Preferably the pole tip of the centre pole arm has a length in the range of 0.05 to 1 jtm.

Preferably the ratio of lengths of the shorter of the pole tips of the outer pole arms to the pole tip of the centre pole arm is at least substantially 5.

During writing, the relatively great amount of flux generated by the high write current in the windings may cause the centre pole arm to saturate quickly and essentially become transparent to the magnetic flux. Therefore, writing occurs only at the trailing corner of the pole tip of the trailing outer pole arm. Reading occurs between the pole tips of the centre pole arm and the pole tips of the outer pole arms allowing very high resolution of the magnetic data pattern embedded in the surface of a magnetic recording medium. Using the common connection between the windings as neutral, the free ends of the windings can be simultaneously connected to the same terminal of a bipolar current source to generate magnetic flux in the core during a writing operation.

Accordingly, the present invention seeks to provide a magnetic transducer head having a core which does not saturate during a writing operation, which has a relatively high resolution during a reading operation, which employs a bipolar write signal and which has different read and write pole arms, all forming a portion of the same core and flux path.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which Figure 1 is a schematic view, in crosssection, and on an enlarged scale, of a magnetic transducer head according to the present invention; Figures 2a and 2b are respectively a crosssectional side view of a first embodiment of a magnetic transducer head according to the present invention and a projection view of a transducing face thereof; and Figures 3a and 3b are respectively a crosssectional side view of another embodiment of a magnetic transducer head according to the present invention, and a projection view of a transducing face thereof.

Turning first to Fig. 1, a magnetic transducer head accordng to the present invention has a core 10 comprising a back flux path 19 at each end of which are located outer pole arms 11,14. The pole arms 11,14 form a continuous magnetic circuit with a flux path 19. At their ends, the pole arms 11 , 14 have respective pole tips 15,17. The pole tips 1 5,1 7 are spaced apart from each other to form a flux gap of a length L. Integral with the flux path 19 is a centre pole arm 9 having a pole tip 16 interposed between, and whose surface is essentially co-planar with the pole tips 15,17. The length of the pole tip 16 (length being measured for the pole tips in the same direction as is the length of the flux gap) is substantially shorter than that of the pole tips 15,17. This is an important and critical aspect of the present invention.It is convenient that the pole tips 1 5,1 7 have equal length. A pair of windings 1 2,1 3 encircling the flux path 19, are shown respectively as comprising turn segments 1 2b, 1 3a, 1 3c directed, as indicated by the "x" symbols, into the plane of Fig. 1, and turn segments 12a,13b,12c directed, as indicated by"." symbols out of the plane of Fig. 1. The segments 1 2a,1 2b,1 2c together comprise the winding 12, and the segments 13a,13b,13c comprise the winding 13. A conductor path 18 connects the windings 12,13 with opposite handedness, so that they provide a bipolar signal during a writing operation.Therefore, the turn segments 1 2c,1 3c form free ends of the windings 1 2,1 3 respectively to be connected externally.

To use the magnetic transducer head of Fig.

1 for a writing operation, it is preferred to use the windings 1 2,1 3 as a single centre tapped winding. The conductor 18 is connected to one terminal of a current source and the connection of the other terminal to the current source is electronically switched between free ends of the turn segments 1 2c, 1 3c. This causes reversal of flux through a path comprising the pole arm 11, the flux path 19, the pole arm 14 and the gap between the pole tips 15,17. Since the smallest cross-sectional area of the pole arms 11 ,1 4 is much larger than that of the pole arms 9, nearly all the flux flows through the pole arms 11,14 and writing occurs in the conventional manner at the outside trailing edge of the core 10.The relatively large area of the pole arms 111 , 1 4 prevents magnetic saturation of the core by the current flow in the windings 1 2,1 3 During the reading operation, signal current flow is generated in the windings by moving an already recorded magnetic recording medium past the pole tips 15. 16. 17. inducing a signal in the windings 12,13. Because of the extremely short length of the pole tip 16, resolution during the reading operation is substantially improved with the use of the relatively short pole tip 16 at the end of the pole arm 9. The central location of the pole arm 9 and the fact that flux flows out of the pole arm 9 and divides to flow into the pole arms 11,1 4 and vice versa, results in generation of the signal in the windings 12,13 during the reading operation.Since signal flux flow in the pole arm 9 divides nearly equally through the flux path 19, the opposite handedness of the windings 1 2,1 3 results in a signal across the ends of the segments 1 2c, 1 3c during the reading operation which is approximately the sum of the signal in each of the windings 12,13.

Turning next to Figs. 2a and 2b, a first embodiment of a magnetic transducer head according to the present invention is shown as being formed on a magnetic ferrite substrate 20 which forms one pole arm (corresponding to the pole arm 11 of Fig. 1) having a pole tip 27. A centre pole arm 22 forms the continuous magnetic circuit with the substrate 20 in the vicinity of a back flux path 40. Similarly, an outer pole arm 24 having a pole tip 31 forms a continuous magnetic circuit with the pole arm 22 which has a pole tip 29 and also with the substrate 20 and includes the flux path 40. The pole# arms 22,24 and the substrate 20 may be of any convenient shape.

Referring to the projection of a transducing face in Fig. 2b, a flux gap 28 between the substrate 20 and the pole arm 22 is formed by an insulating Layer 21. The insulating layer 21 serves also to insulate from each other and from the pole arm 22, turn segments 25a,25b,25c, of a first winding 25. The winding 25 is interposed between the sub strate 20 and the pole arm 22 and encircles the flux path which includes the pole arm 22, the flux gap 40 and the substrate 20, and substantially in the plane of the flux gap 40.

The insulating layer 21 is shown in Fig. 2a as discontinuous and in fact may be so, but it is more likely to be continuous through areas not shown in Fig. 2b. Similarly, an insulating layer 23 forms the second flux gap 30 between the pole arms 22,24 and also serves to insulate turn segments 26a,26b,26c of a second winding 26 from each other and from the pole arms 22,24. The insulating layer 23 is also shown as discontinuous, and may well be so but is morely likely to be continuous both with itself through areas not shown in Fig. 2b, and with the insulating layer 21. Each of the insulating layers 21,23 are typically created by at least two separate deposition or coating steps. The winding 26 encircles the flux path which includes the pole arm 22, the flux gap 40, and the pole arm 24.A conductor 32 electrically connects the interior end from each of the turn segments 25b,26b so as to create opposite handedness between the windings 25,26. One must also understand that electrical access to the conductor 32 is necessary as well, and can be easily provided during fabrication. Electrical connections are thus to the conductor 32, and the end tap of the windings 25,26 formed by the ends of the turn segments 25c,26c respectively.

Turning to the lower projective view in Fig.

2b, therein are shown dimensions L1, L2, L3, L4, L5 of the transducing face. Dimensions L2, L4 are the lengths of the flux gaps 28,30 and can have any convenient values. The dimensions which are critical in the implementation of the present invention are the relative values of the dimensions L1, L3, L5. The length L3 of the pole tip 29 of the pole arm 22 must be substantially smaller than the dimension L5 which is the thickness of the substrate 20 ("length" of the pole tip 27) which comprises one of the pole arms, and the dimension L, which is the length of the pole tip 31 of the other pole arm 24. As explained in conjunction with Fig. 1, this arrangement avoids saturation of the core during the writing operation and allows greater resolution during the reading operation available with a short pole tip.

Figs. 3a and 3b show another embodiment of a magnetic transducer head according to the present invention and very similar to that shown in Figs. 2a and 2b. However, a substrate 34 is non-magnetic, necessitating a magnetic layer 35 to be formed initially on the substrate 34, and which comprises a first outer pole arm, having a pole tip 37, which also has a dimension L5. Advantages in a more balanced read signal occur when L, = L5, as shown. In every other way, the structure is identical to that of Figs. 2a and 2b and the comments made for Figs. 2a and 2b are appropriate here as well.

Operation of the magnetic transducer heads of Figs. 2a and 3a are identical to that described for the magnetic transducer head of Fig. 1. During the writing operation, the relatively large write current saturates the pole arm 22, and allows writing to occur at the trailing edge of the pole arm 24. During the reading operation, the much shorter pole tip 29 increases the resolution of the data read.

In a typical head of the type shown in Figs.

2a, 2b, 3a, and 3b, and constructed according to these techniques, L, is 6,um, L3 is 0.1 ym, and L5 is 6,us. At the present time it is preferred that the range of lengths of the pole tips 27,31 or 37,31 is 1 to 10 #m, and the range of lengths of the pole tip 29 is 0.05 to 1 jum. The ratio Lt/L3 should in all cases be at least substantially 5 to gain the desired improvements of avoiding pole tip saturation during the writing operation and improving resolution during the reading operation. The actual values of L2 and L4 are not important, but typically are very much smaller than L3, to permit high resolution during the reading operation.

Claims

1. A magnetic transducer head comprising: a back flux path; a pair of outer pole arms forming a continuous magnetic circuit with the flux path and having pole tips spaced apart to form a flux gap of predetermined length; and a centre pole arm forming a continuous magnetic circuit with the flux path and having a pole tip interposed between the pole tips of the outer pole arms to form a flux gap between itself and each pole tip of the outer pole arms, said pole tip of the centre pole arm being substantially shorter in length than the pole tips of the outer pole arms.

2. A head as claimed in claim 1 including a pair of windings, each encircling the flux path comprising the centre pole arm and a different one of the outer pole arms, the windings being connected.

3. A head as claimed in claim 2 in which the connection between the windings creates opposite handedness in the orientation of the windings.

4. A head as claimed in any preceding claim in which the pole tips of the outer pole arms are of equal length.

5. A head as claimed in any preceding claim in which the pole tip of at least one outer pole arm has a length in the range of 1 to 10 cm.

6. A head as claimed in any preceding claim in which the pole tip of the centre pole arm has a length in the range of 0.05 to 1 ym.

7. A head as claimed in any preceding claim in which the ratio of lengths of the shorter of the pole tips of the outer pole arms to the pole tip of the centre pole arm is at least substantially 5.

8. A magnetic transducer head substantially as herein described with reference to and as shown in the accompanying drawings.

9. Any novel integer or step or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.