CA1279726C - Method and apparatus for magnetic transducing - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A magnetic core defining a physical gap and a thin magnetic body of high permability and low coercivity are arranged in close proximity, with the keeper bridging the gap. A magnetic flux directed by the gap saturates the keeper in an area briding the gap, thereby forming a virtual gap forming a transducing zone in the keeper. The core may be moved or scanned with respect to a stationary keeper, thereby moving or scanning the virtual gap in the keeper relative to a magnetic storage medium in proximity to the keeper.

Description

~7~6 METHOD AND APPARATUS FOR MAGNETIC TRANSDUCING

Inventors Beverley R. Gooch Rex Niedermeyer Roger W. Wood This invention relates in general to magnetic recording and reproducing and, more particularly, to the provision of a body of magnetic material to provide a transducing zone for the transference of magnetically defined information between a signal utilization device and a magnetic storage medium. It more specifically relates to the control of the location of a transducing zone in such an additional body of magnetic material.
(By "transducing zone" as, used herein, is meant a zone responsible for coupling magnetic flux to or from the body having ~he zone~. The preferred embodiments of the invention described here relate to the use of the physical transducing gap of an electromagnetic transducer to establish a transducing zone in a magnetically saturable body proximate the physical path of a magnetic storage medium~ In certain of the preferred embodiments, the location in the body of the transducing zone is variedO
There are many instances in which it is desirable to transfer magnetically defined information between a magnetic storage medium and a signal utilization device using an electromagnetic transducer which converts the magnetic state definition of the information into an electrical definition of the same.
An electromagnetic transducer typically has a body of high permeability magnetic material ~hat i5 provided with a physical gap (generally referred to as a transducing gap) between two magnetic poles. This gap interrupts the flux path within the transducer to permit coupling of flux from and to the flux path.
Flux is coupled from the flux path within the -2- ~ 7~7~6 AV - ~2bl Cl transducer to, for example, a magnetic storage mectium by fringing from the body of magnetic material at the gap. The gap also enables the head to "pick-up~
(detect~ magnetic flux which fringes from a properly positioned magnetic storage medium. Signal means are provided to sense the picked-up flux flowing in the flux path and ~xansmit the information defined by the magnetic flux to a desired signal utilization device The signal means typically is an electrical coil positioned to detect changes in the flux threading the flux path and convert the magnetically defined information to a corresponding electrical signal. (It will be appreciated that although this detection is transfer of information in one direction, i.e., from a magnetlc medium to a magnetic txansducer or head, transfer in the other direction, i.e., from a magnetic head to a corresponding magnetic storage medium, is, broadly speaking, quite similar. The information is converted from an electrical signal manifestation to a magnetic state manifestation by passing an electrical signal defining the same through the coil which induces corresponding magnetic flux on the flux path within the head.) This technology is used in disc recorders that have rigid magnetic disc storage media. The electromagnetic transducer of such an arrangement is made to "fly" (be out-of-media contact~ during a record/playback operation. The resulting space between the head and magnetic storage medium gives rise to the well-known wavelength dependent spacing losses.
Moreover, the resulting space also adversely affects the efficiency of flux transfer therebetween.
In other data recorders, such as magnetic tape or flexible (or floppy~ disc recorders, using the technology, the magnetic head is in contact with the medium during signal transfer operations. While spacing loss is not such a major problem in these recorders, head and medium wear can be significant in view of relative movement between the medium and ~3- AV-3~1 Cl contacting head. For example, in wideband magnetic signal recording/reproducing devicas, a high relative transducer-tostorage medium speed is necessary for rec~rding/reproducing high frequency signals with good guality resolution. In such devices, the heads and storage medium frequently wear out and must be replaced. In this connection, wear at the face of a head can be particularly deleterious.
Rotary scan magnetic tape recordexs represent a significant development in increasing the relative head-to-tape speed. Here, the transducer rotates at high speed in contact with a relatively slowly advancing magnetic tape. There are two basic types of rotary scan recorder in common use, generally referred to as transverse and helical scan recorders, distinguished by the angle at which the transducer sweeps the tape. There are many problems associated with obtaining a desired accuracy and reproducibility of a signal recorded by rotary scan recorders. For instance, it is necessary to maintain very small mechanical tolerances between and at tne rotating transducer-carrying drum, the transducer structure and the location of the transducer on the drum. At the same time, it is necessary to accurately maintain the rotational speed of the transducer, hence, drum with respect to the speed at which the tape is transported past the rotating transducer.
In magnetic recorders utilizing magnetically controlled scanning transducers, the disadvantages associated with mechanically rotating the transducer can be eliminated. Such transducers can be held stationary, while high scanning speed is obtained by magnetically scanning the transducing zone across the width of th~ transducer and thereby across the recording medium. An example of one magnetically controlled scanning magnetic transducer relies upon selective magnetic saturation of a region of the body of magnetic material forming the transducer so that a 1~7~7~ AV-3261 Cl selected portion of the body is capable of transferring signals to and from the recordin~ medium. The location of such selected location is controlled by control currents applied to control windings operatively associated with the body of magnetic materi~l.
As will become more apparent from the following, the invention is applicable to a wide variety of arrangements for transferring information definable by magnetic flux in a magnetic head and in a magnetic storage medium. Utilization of the same can provide reduction of transducer and medium wear, reduction of wavelength dependent spacing losses and/or enhancement of transducer efficiency. Moreover, the present invention can be advantageously implemented in magnetically or mechanically controlled scanning transducer arrangements while the advantages of scanning are retained.
The present invention grew out of several discoveries. For one, it was discovered that a transducing zone can be created within a body of magnetic material without the requirement of a physical gap. It further was found that if this body of magnetic material was located to be magnetically proximate a magnetic storage medium such transducing zone can be made responsible for the coupling of flux between the body and a magnetic storage medium.
Moreover, if it was found that the body can be used to couple magnetic flu~ on a flux path therewithin to another magnetic body, such as the core of an electromagnetic transducer. It further was discovered that the physical gap in a conventional magnetic head can be used, as will be described, to establish the transducing zone in the body. (As used herein, the phrase "magnetically proximate" means that the body of magnetic material is positioned relative to the proximate object or field so that flux coupling between the two occurs, assuming that saturation or some similar magnetic affect does not prevent coupling.) 1~ ~97~6 AV~3261 C1 Bodies of soft magnetic material are commonly placed over the ends of a permanent magnet to capture ~nd provide a path for flux between the magnetic poles of the magnet. Such bodies are referred to as "keepers", and serve to protect permanent magnets against being demagnetized. The magnetic material typically used to make a core for a transducer has characteristics similar to those of a keeper. The body of magnetic material utilized in connection with the instant invention basically has the sams characteristics as a keeper. In some embodiments of the present invention the body performs a keeper function as well as provides a transducing zone. It is preferred the material of this body have high absolute permeability, low coercivity and low magnetic saturation density. Such a material is commonly designated a soft magnetic material and is to be contrasted with "hard" magnetic materials, i.e., materials having a high coercivity and magnetic saturation density such as those that magnetically store information.
It should be noted that the existence of the transducing zone can be transitory. That is, it is only important that there be a transducing zone at the time which it is necessary for the coupling of flux between the storage medium and the keeper. For example, if the transducing zone is provided by flux induced by an A.C. current, the flux density discontinuity responsible for the formation of the transducing zone will be cvclic in nature. If the transfer is from a magnetic storage medium, it is only necessary from a practical matter that the transducing zone be in existence when the recorded magnetic states to be detected are in coupling relation to the transducing zone. When changes in magnetic state which are closely spaced in time relative to one another are to be detected and the transducing zone is provided by flux induced by an A.C. current, it is desirable that ~l~'7~7~6 the fllLY responsib1e for ~he transducing zone be induced by a current providingvery fast transitions, such as can be obtained with a square wave form as opposed to a sinewave form. Moreover, in ce~ain situations it may be desirable to control the coupling of flux b-tween a transducer and a storage medium by controlling the existence in the keeper of the transducing zone. This can be achieved by switching off and on the flux that provides the transducing zone.
The transducing zone is formed in the keeper by creating in the same one or more significant magnetic discontinuities, i.e., areas of substantially different magnetic permeability, such as typically are provided in electromagnetic transducers by the inclusion of a physical transducing gap. A permeability gradient provides such discontinuity and it is most desirable that there be a steep permeability gradient between the region of the body prs)viding the transducing zone and adjacent regions. The nature of such gradient and a preferred manner of achieving the same will be described in more detail hereinafter. Such discontinuity is most simply provided in the body by having adjacent magnetically satura~ed and unsaturated regions. Moreover, a transducing zone can be easily generated and defined in the keeper through the cooperation of a physical gap in a conventional electromagnetic transducer and a source of magnetic bias flux.This source of bias flux can be associated solely with the transducer or solely associated with the keeper and, in some instances, associated with both of the same. Moreover the source of bias flux simply can be provided by the record signal flux passing through the keeper.
Thickness of the keeper is isnportant in determining the performance of the keeper. The selection of the thickness of the keeper depends on its purpose and its location. For reproduce operations, for example, a well defined transducing zone is preferred, and for short wavelength signals, one having a short length. Relatively thin keepers are best for such operations. In other rn/
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7~7~i applica~ionsl such as where head and medium wear avoidance is important, it is preferably thicker. Moreover, the transduce-keeper-magnetic storage medium arrangement also can influence the keeper thickness. In any case, the thickness of the keeper is selected relative to potential flux therein to create the transducing zone at the location desired. For example, in arrangements in which the keeper engages the face of a magnetic core having a gap so as to physically bridge such gap and a predominant amount of the bias flux 1OWS in the head as well as in the keeper, the keeper is selected to be thin with respect to the core adjacent the gap, and the keeper-core crosssectional area perpendicular to the bias flux path adjacent the gap is selected to be large, so the portion of the keeper which bridges the physical gap will have a high flux density, preferably one which saturates the region having the same. The permeability of the saturated regions is low, i.e., similar to nonmagnetic materials, while the perrneability of the surrounding regions remains high. These regions cooperate tn define a virtua] transducing zone within the body.
In several preferred embodiments described here, the bias flux which defines the transducing zone in the keeper is provided by a direct current source coupled to a signal winding associated with the magnetic head of the transducer.The magnitude of the direct current is selected to effect magnetic saturation of a selected area of the keeper bridging the ~ace of ~he magnetic head that includesthe physical gap while leaving adjacent areas unsaturated. Ihese areas define a zone in the keeper in the nature of a "virtual" gap. This electromagnetically formed virtual gap is utilized to fonrl a transducing zone for signal recording and playbaclc. The transducing zone extends in a direction through the keeper defined by a line extending between the magnetic head and the rn/
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~797~

magnetic stora~e medium. Moreover, the transducing zone may ~e positioned, moved or scanned within the keeper by corre5pondingly moving the virtual gap in the keeper by mechanical means, such as by mechanically moving the head relative to the keeper~ or by magnetic control means, that is, by changing magnetic flux densities within the keeper. Moreover, the shape or size of the transducing zone in the keeper can be controlled by appropriately controlling the shape and size of the boundary within the keeper between regions of significantly different permeabilities, e.g., between unsaturated and saturated portions of the keeper. For example, in one of the preferred embodiments described and claimed herein, the working dimensions of the transducing zone established in the ~eeper is controlled by controlling saturation wit~in the keeper.
It will be further appreciated that the method and apparatus of the present invention can have the unique feature of not only providing a magnetically formed transducing zone, but also shunting undesirable flux fringing from the physical gap in a transducer head or storage medium, which may otherwise deleteriously affect desired magnetic state storage or flux transfer.
It is known to provide magnetic media for perpendicular magnetic recording and storage having a layer of a soft magnetic material in addition to a layer of hard magnetic material for storage. In the past, however, the main purpose of providing such layers of soft magnetic material is to include means to provide an undefined, highly permeable flux path for signal recording and reproduction flux. These layers have not provided a defined transducing zone, nor have means been provided to create the conditions in layers necessary for the formation of such a zone. Moreover, these layers typically have been intentionally designed _y~ 20i Cl ~2~

to be unsaturable hy being made thick relative to the expected flux density.
The method and apparatus of the present invention are particularly applicable to utilization of magnetic scannin~ of transducing zone locations since, among other reasons, with the instant invention the transducing zone is not part of a physical gap. In several preferred embodiments described here, the location of the transducing zone in the keeper is moved at a relatively high speed by electromagnetic control means, that is, without the use of any mechanically moving control devices. A relatively slowly advancing magnetic storage medium, for example tape, is transported past the keeper body on a path which is in magnetic proximity thereto. However, other embodiments are described wherein the transducing zone is moved within the keeper by mechanically moving a magnetic head relative to the keeper.
In the following detailed description, the method and apparatus of the present invention will be described with reference to specific embodiments thereof. However, it will be appreciated that the keeper body may be utilized in combination with signal utilization devices and magnetic storage media in general, and therefore the invention is not limited to the described embodiments.
With reference to the accompanying drawings:
FIGs. lA, lB, lC, lD and lE illustrate the principles of the invention;
FIG. 2 is a schematic perspective view of a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of a control circuit utilized to drive the transducer of the embodiment of FIG. 2;
FIG. 4 is a control voltage versus control current characteristic obtained by the circuit of FIG.

3;

~ 261 Cl 3L~'7~37~6 FIG. S is an example of a flux density versus permea~ility characteristic of a well known magnetic material;
FIG. 6 shows a front elevation view of two confronting front cores of the transducer of FIG. 2 rotated by 90 degrees;
FIG. 7 shows two superposed flux density versus permeability characteristics of FIG. 5, each corresponding to one front core shown in FIG. 6;
FIGs. 8A to 8C respectively shown various forms of recording which can be obtained when utilizing the apparatus of the present invention;
FIGs. 9 and 10 are exploded schematic perspective views of the embodiment of FIG. 2 depicting different orientations of control current;
FIGs. llA to llD show respective track profile characteristics obtained by measuring;
FIG. 12 is a schematic perspective view of another embodiment of the invention;
FIG. 13 is a schematic representation of control currents and resulting flux path.s in the keeper of the apparatus of FIG. 12;
FIG. 14 is a partially exploded schematic view of a still further embodiment of the invention;
FIG. 15 is a schPmatic perspective view of an alternative embodiment to that of FIG. 12;
FIG. 16 is a schematic diagram of an apparatus utilizing an embodiment of the invention for recording/reproducing on parallel tracks of a storage medium; and FIGs. 17, 18A and 18B are schematic perspective views of embodiments of the invention where the transducer core is providing a reciprocating movement with respect to a stationary keeper;
FIG. 19 is a schematic perspective view of another embodiment of the invention where the transducer core is rotating with respect to a stationary keeper;

~ 9 ~ 3~ AV-3261 Cl FIG, 20 is a schematic perspective view of an apparatus utilizing the transducer-keeper combination of the inven~ion for recording/reproducing on transverse tracks of a medium7 and FIG. 21 is a schematic perspective view of an apparatus utilizing the transducer-keeper combination of the invention for recording/reproducing on helical or longitudinal tracks of a medium.
In the following description and drawings, like elements will be designated by like reference numerals to facilitate comparison between ~arious embodiments. The description of similar elements and circuit portions illustrated in more than one figure of the drawings may not be repeated with reference to each of the figures.
Principles of the invention can best be understood with reference to FIGs. lA-lE. FIGs. lA and lB are basically the same, except for the showing of the physical location of a keeper body of material relative to a core of an electromagnetic transducer and magnetic storage medium. With reference to such figures, an electromagnetic transducer is generally referred to by the reference numeral 1. Such transducer includes a body 2 of magnetic material, commonly referred to as a core, defining a pair of magnetic poles 3 that form therebetween in accordance with conventional practice, a physical gap 4 of the type used to cause magnetic signal transfer.
Transducer core 2 is positioned to interact with a magnetic storage medium represented at 5 to transfer information therebetween. (Such storage medium can be, for example, a thin layer of hard magnetic material forming a magnetic tape or disc. It should be understood that the storage medium commonly is combined with a non-magnetic substrate and in many instances other materials.) Storage medium 5 is a magnetic layer which is deposited on a substrate 252.

-12- AV-3261 Cl 7~97~6 The combination of the magnetic layer 5 with the substrate ~52 forms a record medium 253.
In accordance with conventional practice, transduc2r 1 includes a signal winding 6 that delivers to and/or receives from the magnetic core 2, informa~ion in the form of an electrical signal ~hat is converted to or from a magnetically definable characteristic. The information is definable by magnetic flux on a flux path 259 defined by core 2, and the signal winding 6 is positioned relative to the core to detect magnetic flux on a portion of such path. If the transducer is reproducing information from the storage medium 5, magnetic flux emanating from the storage medium and coupled to the path 259 can induce an electrical signal or signal component in the winding 6. On the other hand~ if transducer 1 is being used to record information, an electrical signal QX signal component in the winding and defining the information, can induce corresponding flux along the path 259 within ~he core 2.
The circuitry included in outline block 7 provides a schematic representation of the means by which an electrical signal is communicated between the transducer and a utilization deviceO That is, winding 6 is connected ~etween ground represented at 211 and a D.C. blocking filter represented by a capacitor 2.12.
The other side of capacitor 212 is connected via a switch 213, which for reproducing information recorded on the storage medium 5, couples the capacitor to the input of a reproduce amplifier 214, the output of which is connected to a signal utilization device as represented at 216. Thus, if a signal is induced in winding 6 by flux on the path 259, a corresponding signal representing the information will be fed to the utilization device. If the transducer-keeper combination is used to record information, switch 213 is positioned to connect the capacitor 212 to a record amplifier 217 to receive electrical current from a source 218 defining the 13- AV-~261 Cl 7~6 information to be recorded. Such signals typically are A.C. signals which are passed by the capacitance filter 212 to coil 6~ A~Co current flow in such coil will result in a corresponding change in the flux on the flux path 259 within the core 2.
In a conventional arrangement~ the magnetic coupling between the magn~tic storage medium 5 and the transducer 1 is provided by the physical gap 4 defined between the opposing poles 3 of the transducer 1. For example, in a playback arrangement of a saturated recording arrangement, regions within a magnetic storage medium having oppositely directed magnetism defining inormation indicia are passed along a path in magnetic proximity to the gap 4. Oppositely directed flux fringe from these storage regions and are coupled by the gap 4 into the core 2 of the transducer. This flux changes the magnetic flux which interacts with the winding 6 and thus induces current flow therewithin.
In keeping with the invention, a body of magnetic material having characteristics of a keeper is provided as an intermediary between the magnetic storage medium 5 and the txansducer core 2. Such body of material is schematically illustrated in FIGs. lA to lE and is designated b~ the reference numeral 8. It is positioned magnetically proximate both the magnetic core and the locati.on for the magnetic storage medium 5. In this connection, it will be noted that in FIG.
lB, the intermediary body 8 is not physically located between the core 2 and magnetic storage medium 5. The physical location of the intermediary body can depènd on many factors. If its purpose is to prevent head wear because of relative movement between the storage medium 5 and the magnetic head 1, it most desirably is positioned between the head and the medium, as in FIG.
lA. Moreover, it simply can be a coating provided by vacuum deposition or the like on either the transducer face across the gap or on the storage medium, That is, insofar as the principles of the invention are .
'-~ ' '' :

-14- AV-3261 Cl 7~7~6 concerned it need not be separated physically from the head or the medium. In fact~ to reduce spacing losses in many instances it is desirable that it be physically close to the storage medium 5, and most preferably, physically in contact with the storage medium 5 of the record medium 253. Intimate contact resulting from a deposition process provides the b~st results when reduction of spacing loss is of concern.
It has been found that a transducing zone 9 can be formed in the body 8 to effect coupling of magnetic flux into such body. Thus, when the body is positioned as aforesaid magnetically proximate both the core 2 of the magnetic transducer and the location of a magnetic storage medium 5, it acts in effect as an interm~ediary which conveys information defined by flux in the storage medium to the core, or vice versa.
The transducing zone 9 preferably is formed by providing different regions of the body with significant differences in permeability. It is desirable to have a steep permeability gradient between such regions. This significant permeability difference is most simply achieved by magnetically saturating a region of the keeper body 8. This is implemented in the embodiments of FIGS. lA to lE by magnetically saturating a region of the k~eper corresponding to the physical transducer gap 4. Such saturation can be provided by separate bias magnetic flux or, in a recording operation, by the use of the actual recording signal flux.
Most desirablyl means are included to provide a bias magnetic flux in the body to create the desired transducing zone. While such a flux bias can be achieved in various ways, e.g., with the use of permanent magnetism as will be described, it further has been found that such a flux bias simply can be created by applying a D.C. or A.C. voltage to the winding 6. The winding 6 and the circuitry otherwise associated with the transducer 1 therefore is used for ~15- AV-3261 Cl ~`7g ~ ~
this purpose. In the embodiment of FIG. lA, a D.C.
voltage source represented at 221 is connected to the winding 6. A variable resistance 219 is illustrated connected between the winding and the source 221 to allow the current provided by th~ D.C. source to be adjusted.
It is adjusted to assure there is sufficient flux emanating from the head 1 at the gap 4 to saturate the transducing zone 9 within the keeper 8. The primary purpose of the filter 212 is to isolate the bias current provided by the D.C. source 221 from the signal record and reproduce circuitry, and thereby prevent undesirable interference with the record and/or reproduce signal information. If an A.C~ bias is used, appropriate filters, such as frequen~y filters, are most d~sirably included in the bias and signal circuit paths to keep such circuits isolated from one another.
The reluctance provided by the keeper 8 to the passage of magnetic flux along a path that shunts the transducer 1 is selected relative to the reluctance for such flux along a path extending through the transducer to assure a desired transmission of information. The relative reluctances are achieved through the selection of appropriate combinations of various charactPristics, such as materials, thickness of materials, size of area of transducer pole faces 222, size of area of saturated keeper region 9 in a plane perpendicular to the face 222 of the transducer 1, thickness of the keeper 8, distance (if any) separating the transducer 1 and the keeper 8 of the record medium 253, and the length, width and depth, of air gap 4.
FIG. lA illustrates an arrangement in which the keeper 8 is physically located between the transducer 1 and the storage medium 5. The path of bias flux created by D.C. current coupled to the winding 6, is represented by solid line 223. This flux path extends through the face 222 of the transducer 1 into the keeper 8. Because of the aforementioned ~16- AVo3~61 Cl various characteristics, the keeper magnetically saturates first proximate the location of the physical gap 4 before other places in the maynetic circuit defined by the transducer 1, keeper 8 ~nd storage medium 5, with the result that he saturated transducing zone 9 will be created. (It should be no~ed that the material of the storage medium 5 is selected to have a significantly higher coercivity and magnetic saturation density than the keeper or transducer core so as to avoid saturation of the same at the bias flux intensities.) The path for signal flux induced within the magnetic core 2 by the winding 6 is magnetically proximate to the winding as is necessary to have signal flux g~enerated within the head 1 during recording or to induce a voltage in the winding 6 during reproduction.
In this connection, it will be apparent that i~ this embodiment in which the coil 6 is us~d both to generate the bias flux and to generate or pick-up the signal flux, the paths for the two fluxes within the interior of the head will be the same, at least along that portion which threads through the winding 6. Thus, although for ease and description separate flux paths 223 for the control flux and 224 for the signal flux, as well as a common path 259 i~ illustrated in FIG. lA, the paths essentially will be the same.
Because of the transducing ~one 9I during recording signal flux from the head is diverted to the storage medium as represented by path 224. During reproduction, flux from the storage medium 5 is diverted by reason of the exi~tence of the transducing zone 9 onto the path 224 within the head for signal flux.
It will be noted that the keeper 8 is in direct contact with the magnetic storage medium 5 of the record medium 253 in the embodiments of FIGs. lA, lB, lC and lE. This assures that the transducing zone is as close as practical to the storage medium to reduce spacing ;' ,.~

I 7 1~'~9~ 6 AV-3261 Cl lo~seq. In thls oonnectlon, it should be noted that ~paolng losses ar~ due to ~paaa betwe~n ~ magnetic 3tora~e medlum and a ~ran~ducing ~one where aoupllng bet~een tlle medium and the transd~oing ~o~e occurSI
through the action of a fringln~ flux, either ~r~m a physical gap 4 in a tr~n~ducer during reoording operations, or from recorded m~gnetic 3tates3 in the ma~neti~ s~o~aye medium during repxoduclng operation~.
In accordance with the prehent invan~ion, placing t:~e highly perme~ble keeper 8 in contact with the storage ~dium 5 provlde~ a low reluctance path ~or flux ~hat ~ould o~herwise fringe ~rom elthe~ the magnetically proxlmate ~o~es 2 of the ~ransduaer 1 or magnetic storage m~dium 5, and dlrectq such ~l~x alo~g a path betw~en ~he transducer and medlum th~t i~ not wa~elength dependent, ~nd there~y ~n~ble elimination of the undesir~ble ~pa~i~g 10R8 effect o Any non-ma~netic separatlon betwee~ ~he tran~ducer and the medlum. ~h~
an advan a~e of ~he inventlon ls that it ~nable~ the spacing ~e~ponsible ~or spaQing 108SeS essenti~lly to ba ~liminated even ~ough ~ere might ~e a neces~ity o ~ome ~pa~e betwee~ a ~rans~ucer ~ore and a re~ord medium ~e~au~ of relatlve motion be~ween the two.
This is p~r~i~ularly i~portant ~n playback operation~, wher~ the effects o~ ~pacing lo~s cannot ~e ea~ily ovexcome as in recordlng operation~ ~y increa~ing ~he recording power~ Furthermore, if playb~ck ~pacin~
Losses Ar~ not a problem, the keeper could be 3eparated ~rom the medlum. Reg~rdle~ o~ whether or not the keepe~ 8 i~ in contact with the storage medium 5, the flux path generally wlll be the ~amc. Thi~ is ~rue even 1~ the keeper a i8 not tn ph~sical ~ntzc~ with either the s~orage medl~ 5 or core 2, or i~ in physlcal contact with only the ~ore of the tran~ducer.
Locating the keepar 8 ~et~een the m~gnetic storage medium 5 and the core 2 18 preferred in tho~e in~tanc~
i~ which it i8 de~lred to physically separa*e the medium and core, such as when it i~ de31red to prevent 18~ 7'g7~ AV-32b 1 C1 head and/or m~dium w~ar due to relative motion between the two.
I~ e~bodiments of the pre~e~t i nvent.ion con~tructed in aecordance with FIG. lA, a k~eper body or layer 8 o~ permalloy ha~ing a thicknes~ in the range of a~out 300 to 1000 Ang~t~om~ wa deposited on a cobalt-pho~phoru~ electroles~ plated magnetia s~orage m~dium 5 having ~ thickne3s in the ~anqe of ~bout 700 to 1500 An~R~roms. The ~hu~ly depo~it~d keeper la~er 8 had a m~gneti~ ~u~r~ivity or 1~8 than one, wher~a0 the magnetic ~torage ~edium 5 had a coercivity of ~b~ut 1000. The magnetic permeabillty of the keeper layer was ln ~he ran~e of 1000 ~o 2000 in the un~aturated region~. In th~ satura~e~ region of the transdu~lng zone 9, the perme~ y was in the range f~om that ~pproa~hi~g 1 to about 100. ~or optimum eff~ n~y, th~ p~rmeabili~y di~er~nce betwaen the ~djacen~
~aturated and uns~turated regi~ns o~ th~ ~ransduaing ~one ~ ~hould be ~ lar~e a3 pr~aticable. ~owever~ a 10:1 ratlo of un~a~u~ed-to-saturated permeabili~y will enable transfers ~f ig~al in~ormation between the transducqx 1 ~nd the magne~ic s~or~e l~r 13~
~ IG. lB lllustrate~ an embodimen~ in which the keeper is phy~ic~lly separated from the transducer head 2 by the magnetlc stor~ge m~dium 5. Such an arrangement i3 partiaularly desirable when it is important to reduce playback spacing losses althou~h p~ysical apace is required ~etween the tran~ducer core, ~uch as core ~, ~nd th~ magnetic stora~e medium~ The bia~ flux follows the path represented b~ the ~olid line 223 thro~gh the keeper. The ~lgnal flux is represented by the dot~ed line 224. ~he phy~ical location of ~he keeper relative to the magnetlc medium illustrated in ~IG. 1~ is ~imilar to ~IG. lA in thAt ~he tran~duoing zone 9 i~ in contact wi~h the storage medium S. The above di~su3sed reduotlon ln ~pacing lo~e~ is achieved ln thi~ embodiment ~ecause the kaeper 8 attract~ and dir~cts ~lux from the magnetic ~ l R . 1~ 7~t~ ;, AV~ 3 2 61 C 1 s~oraga medium ~ to the ~r~nsducer cor~ 2 in the 5ame m~nner a~ previously dl ~cussed.
In the embodiment of FIG. ls, the keeper ~
illu~trated a~ a l~yer separating the ma~ne'cic ~torage medlum 5 from a backing or subatxate ~5 ? for the medium. From the b~oad standpoint, however, the keeper 8 al~o ~ould be a ~eparate piece placed on the side of the ~ub~trate 252 opposite the transducer 1. However, the s~paration o~ the Xeeper ~ and the magnetic ~torage m~dium 5 that re~ults from su~h plac~ment i~ at tke ~acrifi~e of spacing 10~B.
FI~s. lC ~nd lD illustrate th~ use of a permane~t magnet as xepresented at ~4 to form the de~ired trar~sducirlg zoTIe 9 in the k~ep~r R, While the embodiment of FIG~ lc ls ~uite ~milar to that of ~IG.
lA, it sh~llld be rloted that the c~.rcuitry provided ln FIG. lA to ~urnish thP D,C. bias cu~rent in th~ windir.g 6 and thus create th~ ~rans~ucin~ zone i5 elimihated, in ~vor o~ the p~rm~nent magnet 264. Th~ magnetia st~ength, the shApe o~ the magnet ~4 rslative to the -19 AV-3261 Cl L~9~

shape of the keeper 8 and of the magnetic core 2 proximate such magnet, and the spacing betwe~n the magnet 264 and the core 2, should be such that flux produced by the same in the keeper 8 will saturate a region to form the transducing zone 9. The criteria for selecting material for the keeper when a permanent magnet is utilized are the same as discussed above.
FIG. lD is a schematic, partially sectioned view illustrating that the magnet 264 is spaced from the poles 3 of the transducer core 2 to assure that such core will not cause a magnetic short in the magnet.
The purpose of including FIGs. lC and lD is simply to make clear that the invention is not limited to arrangements in which the permeability difference such as provided by a magnetically saturated region in the keeper 8 is formed by an electrically induced magnetic field.
The invention is also not limited to arrangements in which the path of the bias control flux extends through the magnetic head 1. FIG. lE
illustrates an arrangement in which the bias control flux has only a minimal path in the core 2. In an arrangement in which the transducing zone 9 in the keeper is caused by the physical gap 4 in a magnetic core 2, the flux defining such a zone only has to flow in the core adjacent the physical gap to the extent needed to provide saturation in the keeper. Such flux follows a path represented at 223 in FIG. lE, whereas the signal flux will follow the path represented at 224 between the winding and the magnetic storage medium.
It will be recognized from the above that the transducing zone 9 can be formed in the keeper 8 via bias control flux without significant path in the magnetic head 1. The path of bias control flux may be in the head as described in connection with the earlier embodiments, may be within the keeper, or divided between the head and the keeper. Moreover, sufficient magnetic discontinuity may be formed in the keeper to form a tr~n~uclng ~one there~n ~xom other .ype8 of ~nergy fiource~ such aY ~ th ~mal one.
The pElnciples o the inY~ntion will be better under~tood and appreciated by r~ferenc~ to the ~pec~fic lmplementation of the ~ame ~n the embodlment~
of the lnvention de~cr~bed below.
Referring now to FI~ 2, transducer 10 has two confrontlng core3 11~ 12 madQ o~ a magnetic material, for example ferrite. The coxe~ ll and 12 defin a magnetic head and each ha~ a front core 14, 15 and a back core 16 t 17 abutting re~pectively at confronting surfac~s 22 and 24~ The front core~ 14, 15 are made in the form of oppositely oriented wedge sections~ confronting at a gap plane 13. The ~h e con ~r~n~n~
oppositely oriented wedge 6ections o~ ~ c~ ~ J
core 11, 1~2 have cross sectional areas gradually increasing in opposite directions across th~ width, W, of the trans~u~er 10.
The confronting front cores 14, 15 are preferably smoothly lappPd and polished at the gap plane 13 to obtain face~ to provide confronting magnetic pole faces 18~ 19. A winding window 26 is provided in a well known manner in one or both front cores 14, 15 across the width, W, of transducer 10 to accomodate a transducing signal winding 21. Winding 21 is shown as a single turn winding as an example in the form of a conducti~e rod. However~ a conventional mult~turn winding may be ultilized insteadD To keep signal flux losses at a minLmum, it is preferable to provide the signal winding 21 closer to the keeper 28 than to the lateral surfaces 22, 24 opposite the keeper n A suitable nonmagnetic material is placed between the pole faces 18, 19 to obtain a gap 20, utilizing conventional transducing gap forming .
techniques. For example, a layer of silicon dioxide or glass may be deposited on the confronting ~urfaces 18, 19, which surfaces then may be bonded together in a `` ' ~L~'7~37~
well known manner. Further references to gap 20 will be as a "physical" gap to better distinguish it from an electromagnetically formed nvirtual" gap of the keeper 28 of this embodiment as will be described below in detail. The length, 1, of the physical gap 20 as shown is greatly exaggerated.
In the embodiment shown in FIG. 2, respective grooves 82 are pxovided in the back cores 16, 17 inwardly of the lateral surfaces 22, 24. Groves 82 serve to accommodate the bias control windings 38, 39 of each back core 16, 17, respectively, of which control winding 39 is shown in ~IGs. 9 and 10. By placing the control windings 38, 39 in recesses provided by grooves 82, the confronting lateral surfaces of the front and back cores at 22 and 24 are in intimate contact with each other. Air gaps between the front and back cores are thereby substantially eliminated while a desired tight, low reluctance magnetic coupling between these cores is obtained.
A keeper 28 of magnetic material is arranged over front surfaces 57 of the front cores 14, 15 in direct contact therewith and bridging the physical gap 20. As described hereinbefore, the keeper ~8 is preferably made of a magnetic material having a substantially square hysteresis loop, that is, low coercivity and high permeability values with a magnetic saturation density substantially less than that of the magnetlc storage medium t~ith which it is to be used, such as permalloy~ Sendust, ferrite or amorphous metal.
Such keeper 28 is desirably formed by being deposited by vacuum sputtering or plating directly on the surface 57 of front cores 14, 15 utilizing well known material deposition techniques. While the front surface 43 in the medium interface area is shown in FIG. 2 as being generally flat, it may be contoured, if desired, utilizing well known contouring techniques.
It is understood that both the transducer 10 and keeper 28 will assume the ~ontoured shape.

1~'i'9'7~i The keeper 28 pre~erably has a very small thickness t in the direction of the depth of gap 20 so as to have a small cross-sectional area at such gap for saturation by bias flux as will be described~ When constructed for use with common record media, this thickness is preferably between 0.00025 and 0.002 inch.
The thickness of the keeper 28 also influences the length, 1, of the transducing zone 56. Moreover, keepers of greater thickness require more bias flux to establish the desired transducing zon~. For recording operations, a well defined transducing zone of small dimension, 1, is not as critical as for playback operations, because recording in the magnetic storage medium is primarily determined by the magnetic state occurrences at the trailing edge of the transducing zone 56, i.e., the edge of the transducing zone last able to influence the recording on the medium during relative motion between the transducer and the medium.
For playback operations, however, a well defined transducing zone 56 with a small dlmension, 1, is preferred. In any event, to achieve the advantages of reduced spacing loss, the thickness of the keeper 28 and the strength of the magnetic field bias for establishing the transducing zone 56 should be selected so that the length, 1, of the transducing zone 56 is not so large as to permit objectionable fringing flux wavelength dependent coupling from the physical gap 20 of the transducer 10 to th~ magnetic storage medium.
Such objectionable coupling will occur at least when the length, 1, of the transducing zone 56 becomes so large that it appears to the transducer 10 and magnetic storage medium equlvalent to an air space that exists in arrangements without a keeper 28. The thickness and bias flux needed to achieve the desired reduction in playback loss can be determined empirically.
In the embodiment of FIG. 2, the overall size of the planar surface of the keeper 28 matches that of the underlying surface 57 of the front cores.

`~ 79~6 AV-3261 Cl Al~ernatively, the keeper may differ in size, while it bridges the physical transduring gap 20 provided between thP confronting magnetic pole faces 18, 19 of the ~ront cores 14, 15. For better clarity of representation in FIG. 2, the shape of the faces of ront cores 14, 15 underlying the keeper 28 is shown by interrupted lines. The back cores 16, 17 are also formed as oppositely oriented wedge sections similar to the front cores 14, 15. However, the back cores may be of a rectangular or any other convenient shape suitable to provide a bias control flux for selectively saturating the front cores 14, 15.
Each of the control windings 38, 39 is wound around each back core 16, 17 at an angle, preferably at right angles to the direction in which the transducing signal winding 21 passes through the front cores. By the foresoing arrangement of the signal and control ~indings, respective information signal ~transducing) flux 40 and bias control flux on paths 41, 42 are induced in the transducer cores. The bias control flux on paths 41, 42 extend transverse (which is substantially perpendicular in the particular embodiment illustrated in FIG. 2) to the signal flux 40 and flow substantially parallel to the width W of gap 20. This reduces the influence of the bias control flux on the signal flux.
The magnetic material of the front and back cores and of the keeper are selected to be the same.
Moreover, the combined cross sectional areas of each front coxe 14, 15 and keeper 28 in a plane perpendicular to the bias control flux paths 41, 42 are selected smaller with respect to corresponding cross sectional areas of the back cores 16, 17 to assure that the back cores will not be saturated by the bias control flux. The material of the back cores could be selected to have a greater saturation density than the material of the front cores and keeper, to avoid saturation of the back cores.

.

~2~ tt~7~ 6 ~V~3261 Cl With further reference to FIG. 2 respective bias control currents Il, I2 are applied to the control winding 38, 39. As is well known from the theory of electromagnetism, a magnetic flux is thereby induced in each back core 16l 17 in a direction perpendicular to the direction of the control current flow. The bias control flux from the back cores 16, 17 is coupled into the closely spaced front cores 14, 15, respectively, and into the keeper 28 superposed therewith. The bias control currents Il, I2 are applied, for example, from respective D.C. control voltage sources 30, 31 via variable resistors 32, 33 to flow through the respective control windings 38, 39. The magnitude of the bias control current Il is selected such that a resulting control flux 41 induced from the back core 16 into the front core 14 saturates a portion 44 thereof and of the ~verlying keeper layer 28, having a width Wl. The magnitude of bias control cuxrent I2 is selected to induce a cor.trol flux 42 from back core 17 into front core 15 and the overlying keeper layer 28 to also saturate a portion 45 having a width W2. The respective saturated portions are designated by cross~hatched areas. In this particular transducer-keeper combination-embodiment, the uppermost and lowermost portions of the front cores will not become saturated in areas where the front and back cores are in intimate contact with each other. Only areas within a reduced width W' will be saturated.
The entire portion of the keeper 28 which bridges the physical gap 20 is saturated along the width W by the control fluxes 41, 42, as shown by cros~-hatched area 29, because of its vary small cross sectional area as discussed previously in the direction perpendicular to the flux paths 41, g2. The saturated area 29 represents a virtual gap formed in the keeper 28 by the directed bias control flux. The saturated core portions 4g, 45 define respective adjacent permeable unsaturated portions or regions which overlap ~'7~7~1~

across the virtual gap 29, The overlapping perme~ble portions separated by the virtual gap 29 define a permeable transducing zone 56 of width W3. More specifically, an upper edge of the transducing zone 56 is defined by the saturated zone 44 and its lower edge by the saturated zone 45. It is seen from FIG. 2 that the total gap width W'~Wl+W2~W3 is a constant, while a portion thereof having a width W3 becomes effective as a transducing zone 56 when control currents Il, I2 are applied.
When current values Il, I2 are maintained const~nt, for example by setting the variable resistors 32, 33 at a constant value, the transducing zone will assume a fix~d position. This application may be useful~to obtain recording along longitudinal tracks such as shown at 37 in FIG. 8C. By increasing the magnitude of one control current, for example Il, while proportionately decreasing the magnitude of the other control current I2, the respective widths Wl, W2, change proportionally and the transducing zone 56 will be s~lectively moved along the width W' of the gap 20.
For example, when it is desired to periodically scan the transducing zone 56 at a high speed along the width W', a control circuit can be utilized which periodically changes inversely linearly the magnitudes of both currents I1, I2, thereby inversely changing the widths Wl, W2 of the saturated portions 44, 45. To maintain a constant width W3 of the transducing zone 56 during scanning, it is necessary to maintain a constant sum of the changing control currents, that is Il+I2 = a constant.
During recording/reproduction on longitudinal or helical tracks, the position of the transducing zone may be stepped from track to track. In other applications to be described further hereinafter, recorded helical tracks 34, as shown in FIG. 8B, may be recorded and reproduced by fixedly mounting the transducer 10 of the transducer-keeper combination to a , .

:L~797~ ~V ~

rotatinq or other transducer translating member, such as a disc or drum, while the keeper ~8 is detached from the transducer lO and placed stationary in proximity to the transducer 10 and record medium. In such arrangements, the position of the transducing zone 56 within the keeper 28 is moved across the record track width for optimum playback performance as a result of the translation of the transducer 10 relative to the keeper 28.
FIG. 3 is a diagrammatic showing of a schematic control circuit 54 which can be used in place of D.C. sources 30, 31 and resistors 32, 33 of FIG. 2, to drive the control windings 38, 39 of transducer 10 of FIG. 2 for controlling the position of a transducing zone 56 along the width W' of the saturated virtual gap 29 in the keeper 28. In the presently described preferred embodiment, the transducing zone 56 is periodically scanned along transverse tracks 35 of magnetic tape 36, as shown in FIG. 8A. Control circuit 54, however, may be adapted to obtain different operating modes of the transducer 10 when utilized in other recording/reproducing applications as previously mentioned.
The circuit 54 of FIG. 3 utilizes an A.C.
control voltage source 61 generating a periodically changing control voltage, Vc, to effect electronic scanning of the transducing zone 56 across the width W' of the keeper 28 and, hence, across the tape 36.
Voltage, Vc, is converted by the circuit of FIG. 3 into differentially changing control currents Il, I2 as followsO The voltage, Vc, is applied via a reslstor 62 to an inverting input of a first operational amplifier 63, which has a feedback resistor 64, and represents a voltage follower. The output of amplifier 63 is connected via a further resistor 65 to an inverting input of a second operational amplifier 66 which has a feedback resistor 67. Amplifier 66 inverts the output signal of amplifier 63. The output of first amplifier ~ v'--~ i C l 31 ~'7~37~
63 is also connected via a resistor 63 to an inverting input of a third opPrational amplifier 69 having a feedback resistor 70. The output of second amplifier 66 is connected via a resistor 71 to an inverting input of a fourth amplifier 72 having a feedback resistor 73.
An adjustable potentiometer 74 is connected between a source of negative D.C. voltage and ground to obtain a control current offset, Io. The output of potentiometer 74 is connected via a resistor 75 to the inverting input of third amplifier 69 and via a resistor 76 to the inverting input of fourth amplifier 72, respectively. The output of the third amplifier 69 is connected to the previously described first control winding 38 of transducer 10, which in turn is connected via feedback resistor 70 to the inverting input of amplifier 69. Similarly, the output of the fourth amplifier 72 is connected to the previously described second control winding 39, whose second terminal is connected via feedback resistor 73, to the inverting input of amplifier 72. The connection between coil 38 and resistor 70 is grounded via a resistor 77.
Similarly, the connection between coil 39 and resistor 73 is grounded via a resistor 78. As described previously, the respective noninverting inputs of all four operational amplifiers 63, 66, 69 and 72 are grounded. The amplifiers 69, 72 and respective resistors 70, 77 and 73, 73 represent a first and second current source, respectively.
In operation, the voltage, Vc, from source 61 is applied via voltage follower 63, 64 to a first current source 69, 70, 77 which applies to the first control winding 38 a control current Il, which is directly proportional to input voltage, Vc. The voltage obtained at the output of amplifier 63 and inverted by the inverter 66, 67 is further applied to the second current source 72, 73, 78 which applies to the second control winding 39 a control current I2 inversely proportional to the i~put voltage, Vc. The 7~:6 ~ o l C l potentiometer 74 cQnnected to a negative DC voltage sets a desired control current offset, Io, which in the presently described embodiment is half way between the minimum and maximum control current values (that is Io=(ImaxImin~/2) for reasons that will be described below in more detail with reference to FIG. 40 It follows from the foreqoing description that when voltage Vc has a periodically changing amplitude between Vcmin and Vcmax as shown in the diagram of FIG. 4I circuit 54 converts the thusly changing control voltage into substantially linearly changing control currents Il, I2 obtained at the respective outputs of the first and second current source, respectively. The control currents Il, I2, thus change differentially, that is in an opposite sense with respect to each other while changing substantially in linear proportion to the input voltage Vc as depicted in FIG. 4 and defined by the following equations.
Il = KVc. + To (1) I2 = -KVc + Io (2) where K and Io are constants dependent on the parameters of the circuit of FIG. 3 and can be derived therefrom.
As described previously, the respective control fluxes 41, 42 most desirably extend in substantially perpendicular paths to the direction of the signal flux 40, resulting in reduction of interference between these fluxes. However, this is not a necessary condition for proper transducing in accordance with the transducer-keeper combination of the present invention. To obtain high quality performance with the method and apparatus of the invention, a well defined boundary between adjacent regions within the keeper body responsible for the transducing zone should be achieved. In the preferred embodiment being described, the boundaries of interest are the boundaries between the saturated and ~9~ 4~ AV-32~1 Cl unsaturated areas, i.e., the boundaries between the virtual gap 29 in the keeper 28 and khe unsaturated areas adjacent thereto and the boundaries between the regions of the saturated portions 44 and 45 in the keeper. The well defined boundaries are obtained in this preferred embodiment hy selecting the shape of the confronting front cores such that a maximum rate of change in permeability between adjacent cross-sectional areas of each core is obtained across the transducer width W. The foregoing assures that while a selected area of each front core is saturated by a control current so that no appreciable flux passes therethrough, an immediately adjacent contiguous area remains sufficiently permeable as is necessary for transferring information signals between the magnetic storage medium and the transducer 10. In other words, the performance of the transducer-keeper combination depends on the steepness of a permeahility versus flux density gradient between each adjacent saturated and unsaturated region within each front core and the keeper body.
As an example, FIG. 5 shows a well known permeability m versus flux density B characteristic of a suitable magnetic core material, for example ferrite PS52B made by Ampex Corporation. As it is seen from that characteristic, a relatively high permeability m, greater than 400, is obtained at a flux density B below Bl=4000 Gauss, which high permeability is sufficient for desired flux coupling operation. The saturation flux density of that material is approximately B2=6000 Gauss, corresponding to a permeability below 100.
Consequently, for obtaining a sharp transition between a highly permeable region and an adjacent saturated region within the transducer front core, the permeability must change rapidly from below 100 to over 400 in either direction, as it is seen from FIG. 5.
FIG. 7 shows an example of two superposed flux density versus permeability characteristics 53, ~ ~97;~6 S3a, each corresponding to the characteristic of ~IG.
S, and each pertaining to one oppositely oriented wedge shaped front core 14, 15. FIG. 6 is a schematic front view representation of confronting front cores 14, 15 of FIG. 2 rotated by 90 degrees, having a reduced width W', and without showing the keeper 28 superposed on these cores. It is understood that when the keeper 28 is superposed on the front cores 14, 15 as shown in FIG. 2, the herein described control operation remains substantially unchanged and the portions of the keeper in contact with the front cores will have the same saturated/unsaturated characteristics as the underlying front cores. The cross-hatched area 44, ~5 represent the saturated core portions having a permeability less than 1~00. The other core portions in FIG. 6 represent unsaturated highly premeable areas 46, 47 having a premeability over 400. The zone which extends across the transducing gap 20 is formed by the overlapping unsaturated highly permeable regions 46, 47. It is understood that this zone in the core portions causes the transducing zone in the keeper 28 when it is superposed with the core. The transducing zone 56 corresponds to overlapping portions of superposed characteristics 53, 53a, which portions indicate permeability between 100 and 400. From FIGs. 6 and 7 it is seen that it is desirable for having a wel~
defined transducing zone 56, that the overall permeability versus flux density gradient be as sharp as possible. This can be obtained by selecting a material for the transducer core and keeper having a steep characteristic curve, and by designing the wedge section such that large flux density changes take place between adjacent cross-sectional areas over the transducer width W' corresponding to the scanning direction. To further increase the permeability gradient, a transducer core material is preferably used having a magnetic anisotropy, and the core is oriented with an easy axis of magnetization perpendicular to the physical gap plane.

v`--j~ O l ~ ~
97`~
To furth2r maximize the permeability gradient between two adjacent cross-sectional areas for obtaining desired permeability versus flux density characteristics, it is possible to approximate the shape of the wedge sections to that of the curve of FIG. 5, for example, to obtain cross-sectional areas of the wedge shaped front cores 14, 15 that exponentially increase in the direction of the transducer width W.
The foregoing can be obtained by providing exponentially increasing side surfaces 48, 49 of front cores 14, 15, as is shown in phantom in FIG. 6.
To simplify control of the portions of the front cores which are saturated, a predominant portion of the bias control flux generated on each path 41 or 42 by a respective one of the back cores 16 or 17 should not be coupled into the other back core. The signal flux also should not be coupled to the back cores. Therefore, it is preferable to provide between back cores 16, 17 a gap 50 of a substantially greater length L then the length 1 of the gap 20 provided between the front cores 14, 15. Preferably, the ratio L:1 is selected to be 10:1 or more. Both dimensions 1 and L are shown in the FIGs. as exaggerated for illustration purposes.
It is seen from the foregoing disclosure that the transducer of FIG. 2 is relatively simple to manufacture, while various desired core shapes may be obtained to maximize the permeability gradient in the keeper across the potential transducer width. It is preferable to hold the resulting transducer structure in a nonmagnetic holder (not shown) and to bond the respective transducer core elements together, for example by epoxy, utili2ing well known bonding techniques. However, such bonding material is deleted from the FIGs. to facilitate illustration of the embodiment of the invention.
FIGsO 9 and 10 are exploded schematic views of the transducer-keeper embodiments like that of FIG.

3~- AV-32~1 Cl ~2'~3t~
2, which illustrate the operation, particularly with respect to the bias control flux paths in the ~eeper 28. In the embodiment of FIG. 9, the oontrol currents I1, I2 in the respective control windings 38, 39 have the same direction, resulting in bias control flux paths 41, 42 extending through the front cores 14~ 15 and keeper 28 in the same directional sense. The magnetic poles at adjacent ends of both front cores 14, 15 arealike and designated as north poles N at the upper end of gap 20 and as south poles S at the lower end. By selectively saturating areas 44, 45 of the respective front cores 14, 15 and overlying portions of keeper 28, the area 29 of the keeper bridging the physical gap 20 becomes saturated as previously described, and it froms a virtual gap 29. The control flux lines 41, 42 extend through the saturated portion 29 of the keeper 28 in substantially straight lines between the opposite poles N, S. The saturated areaS
44, 45 and 29 are shown in FIG. 9 as crosshatched areas. The areas of the front cores 14, 15 and keeper 28 adjacent to the saturated areas remain permeable and they form a transducing zone 56 across the virtual gap 29, as has been described above with reference to FIG.
2. The width W3 and location of the transducing zone 56 can be positioned, moved or scanned along the width W of the transducer-keeper combination by controlling the magnitudes of the control currents Il, I2 as previously described.
In the embodiment of FIG. 10, the control currents Il, I2 flow in opposite directions with respect to each other through the control windings 38, 39. Consequently, in the front cores 14, 15 oppositelv oriented magnetic poles N, S are formed at adjacent ends of the oppositely oriented wedge sections across the physical gap 20. In this instance, the areas 44, 45 of the front cores and the portions 29 and 29" of the keeper are saturated by the bias control flux on paths 41, 42 flowing in opposite directions. Flux on -33- AV-3261 Cl ~l2'7~7~6 these oppositely oriented paths is repelled and diverted. Because of the diversion of the flux pathsr there is an area 60 formed between respective 5aturated regions 29a and 29b which has a flux density far below the saturation density of the keeper 28, thus it is relatively flux free and does not saturate, i.e., it is highly permeable. Because this region or zone 60 is formed by the bucking effect of the opposite fluxes, it will be further referred herein as the "bucking region"
or "bucking z~ne".
Portions 29a and 29b of the saturated regions 29 and 29", respectively which separate unsaturated, highly permeable areas of the core pieces 14, 15 and superposed keeper 28, form virtual gaps 29a and 29b.
Consequently, highly permeable transducing zones 56a, 56b for coupling magnetic flux are definedO Those portions of saturated keeper regions 29 and 2g"
adjacent to saturated regions 44, 45 do not form transducing zones. Consequently, in the embodiment of FIG. 10, each transducing zone 56a, 56b is defined on one side by a saturated area 44, 45, respectively, and on its other side by the bucking zone 60. Each zone 56a, 56b may be used to record or play back a signal on or from a magnetic medium.
When comparing the embodiment of FIG. 10 to that of FIG. 9, it is seen that instead of one transducing zone 56 as in the embodiment of FIG. 9, two such zones 56a, 56b separated by the bucking zone 60 are provided. As will be further described with reference to FIGs. llA to llD, 'che thusly obtained zones 56a, 56b, 60 can be positioned, moved or scanned along the width W of the keeper 28 by controlling the magnitude of the control currents Il, I2, as previously explained with reference to FIGs. 3 and 4. Such figures show respective track profile characteristics obtained by measuring a playback signal output of a transducer-keeper combination in accordance with the abovedescribed embodiment of FIG. 10. As an example, a -3~- ~V-3261 Cl 79~
track 0.006 inches wide, shown at 133, is prerecorded longitudinally on a magnetic tape 134 and the tape placed in contact with the ~urface 43 of the keeper 2B.
The length of track 133 is perpendicular to the width W
of the physical gap 20. By selectively saturating the transducer front cores 14, 15 and the keeper 28, respective transducing zones 56a, 56b are obtained, separated from each other by a bucking zone 60, as previously described with reference to FIG. 10.
Characteristic line 135 on the graph included as FIG. llD is obtained by moving the tape 134 in the direction of arrow 137, while measuring an output signal from the transducing winding ~1 for each changed position. As the tape moves, the output signal will be proportional to the flux which s detected by the transducer-keeper combination as the track 133 passes by the same. (This is assuming, of course, that the position of the transducing zones 56a, 56b and the bucking region 60 are held stationary). In this example, the graph line represents track displacements of 0.005 inches. It is seen from FIG. llD that the characteristic 135 has two peaks, each corresponding to one transducing zone 56a, 56b, shown in ~IG. llB. It is also seen from the shape of the characteristic 135 that the transition between high and low playback signal output corresponding to the transitions corresponding to the transitions between the bucking zone 60 and the transducing zones 56a and 56b are substantially s-teeper than the transitions on the other sides of the zones 56a and 56b between unsaturated and saturated regions. The foregoing illustrates improved track-edge definition by providing a bucking zone adjacent to the transducing zones. The improved track-edge definition is primarily due to the effect of the opposing fluxes in the bucking zone 60 virtually eliminating flux from the zone. Without the opposing fluxes, such as at the boundaries of zones 44, 45 (FIG.
10) proximate the transducing zones 56a, 56b, there is -35~ 7~j AV-326l Cl a small, but ~inite transition region between the saturatPd and unsaturated regions~
A second characteristic is shown in ~IG. llD
by interrupted line 136. It is obtained by changing the values of the control currents Il, I2 and thereby shifting the transducing zones 56a, 56b and the bucking zone 60 of FIG. llB in the direction of arrow 138 to a new position, as shown in FIG. llC at 56a'~ 56b' and 60'. (As seen from FIG. llC, the respective widths of these zones in the direction W have not changed substantially.) The measurement described with reference to characteristic 135 is repeated for the shifted zones, and the measured values are plotted to obtain the resulting characteristic line 136.
Characteristic lines 135, 136 are similar, each having respective high o-ttput peak portions designated N, R;
P, S for characteristic line 135; and N', R'; pl, S' for characteristic 136, which portions correspond to transducing zones 56a, 56b; and 56a', 56b';
respectively. In addition, each characteristic line represents a low output or valley portion R,P for characteristic 135 and R', P' for characteristic 136, corresponding to the bucking zones 60; 60'.
FIG. 12 shows another transducer-keeper combination embodiment in accordance with the present invention. The transducer 90 of FIG. 12 is made up of two confronting cores 91 t 92 which are similar to the cores 11, 12 of the embodiment of FIG. 2 in that each core has front core portion 94, 95 and a back core 96, 97 portion abutting at confronting planar surfaces 98 and 100. However, the cores 91, 92 are rectangular, rather than wedge shaped. Moreover, each back core 96, 97 has three legs which form two grooves utilized as control winding windows 102 to 105 to accommodate respective control windings 106 to 109. These windows and windings are best shown in FIG. 13. In this embodiment the keeper 28 is made of a thin, soft -36~ AV-3261 Cl ~'~7~
magnetic material having the characteristics previously described with respect to FI~. 2. In the embodiment illustrated ~y FIG. ~2, each control winding 106 to 109 is connected to a separate control voltage source 110 to 113, respectively, via a variable resistor 114 to 117. The variable resistors permit adjustment of the magnitudes of the control currents in the control windings. Al~exnatively9 two control windings diagonally arranged on opposite sides may be interconnected, as illustrated in FIG. 13.
The operations of the transducer-keeper combinations of FIGs. 12 and 13 basically are the same.
Their operations will be described hereinafter with reference to FIG. 13~ FIGo 13 is a schematic representa-tion of a front elevation view of the keeper 28, taken in the direction of arrow 123 of FIG. 12. To ~acilitate showing of the control flux paths 124 to 127 extending between the rear cores 96, 97 and keeper 28 via front cores 94, 95, the rear cores are shown as being rotated by 90 degrees to have their lateral surfaces 128, 129 extending in the plane of the keeper 2~. The control windings 106 to 109 are connected to respective control voltage sources such that the outer legs of each back core form magnetic poles of the same polarity while the inner leg has a different polarity. As a result of such opposite orientation there are obtained oppositely oriented flux lines 124 to 127 extending in the virtual gap area 29 of the keeper 28.
Because of the oppositely oriented magnetic poles, the respective control flux paths originating in the back cores 96, 97 saturate only portions 29a, 29b and 29c of the keeper 28 bridging the physical gap 20, as shown in FIG. 13. In places where the flux on the oppositely oriented control paths approaches that on the other path, such flux is repelled and diverted. A
predominant portion of the flux returns to the same rear core where it originated. As a result of the above described flux diversionp respecti~e bucking regions 130, 131 are ~ormed which separate the adjacent saturated regions 29a to 29c. These bucking regions are similar to the previously described buckinq region 60 in the embodiment of FIGo 10~ As has been described previously with reference to FIG. 10, the flux density in the bucking regions 130, 131 is far below the satur~tion density of the keeper. Consequently, the region 29 of the keeper 28 bridging the gap 20 does not saturate in the bucking region.
It follows from the foregoing description that the transducer-keeper embodiments of FIGs. 12 and 13 have three saturated regions 29a to 29c provided in the keeper 28, separated from each other by relatively flux free regions or bucking zones 130, 131. Because the rest of the keeper area 28 surrounding the saturated regions, as well as of the underlying front cores 94, 95, remain unsaturated and highly permeable~
the saturated areas 29a to 29c provide respective transducing zones in the keeper similar to those previously described with reference to FIGs. 2, 9 and 10.
When desired~ the outer transducing zone 56a and 56c may be eliminated by spacing the front cores 94, 95 (FIG. 12) at a distance from the keeper 28, at both ends of the keeper width W. The cores 94, 95 will still provide a necessary flux path between the back cores 96, 97 and keeper 28, but there will be an increased reluctance in the flux path to prevent saturation of the areas 29a and 29c. Alternatively, a record medium, for example magnetic tape (not shown), of a reduced width may be utilized which spans only a portion of the keeper width between lines 151, 152, thereby excluding transducing zones 56a and 56c from coupling a signal with respect to the mediumO
It is seen from FIGs. 12 and 13 that the control windings which are diagonally located from each other on opposite cores 96, 97 are connected to -3~ '9~Z~; AV-3261 Cl respective D.C. sources of the same polarity.
Consequently, to move the transducing zone 29b in one direction along the keeper width, the control currents o~ one polarity, for example, Il', I2" are increased while the control currents Il", 12' of opposite polarity are decreased, in a similar way as previously described with reference to FIG. 2.
~ IG. 14 shows a partially exploded view of a further embodiment of the electromagnetically controlled scanning transducer-keeper combination of the invention which is similar to the above-described embodiments of FIGs. 12 and 130 However, the ~ransducer 140 of the FIG. 14 embodiment has its back cores 96, 97 joined to the front cores 94, 95 by surfacès 98, 100 of the back cores abutting opposite lateral surfaces 141, 142 of the front cores. These joined surfaces 98, 141 and lO0, 142 extend at an angle "c" with respect to the front surface 43 of the keeper 28 to avoid contact with a record medium, for example tape 146. The foregoing structural change does not substantially alter the previously described control flux paths shown in FIG. 13. The control windings 106 to 109 are connected to respective control voltage sources as has been des~ribed with reference to FIGs.
12 and 13.
The above-described way of joining the back cores to the front cores allows an additional magnetic back core 144 to be attached to the front cores 94, 9S, to accomodate a transducing signal windir.g 145. This embodiment is particularly useful for applications where a sufficiently small dimension D of the transducing zone 29b in the direction of the keeper width W is required. In that case the other, orthogonally oriented dimension thereof becomes a track width TW~ Both dimensions D and TW are illustrated in FIG. 14. The abovedescribed back core 144 and transducing winding 145 serve to provide a transducing flu~ path 148 which fringes across the virtual gap 29b provided in the keeper 28, substantially in parallel with the length D thereof~ This embodiment is ~specially suitable for transducing long transverse tracks of a recording medium as, for example, shown at 118 in FIG. 14. (The front surface of the front cores 94, 95 and the keeper 28 are shown slightly curved or contoured to obtain a better keeper-to~medium contact.) In the transducer-keeper configurations shown in FIGs. 12 to 14, when the control currents in the oppositely oriented control windings have equal values and thus the bias fluxes in the oppositely oriented control flux paths are equal, cancellation of these fluxes may occur to such extent that a desired saturation in the keeper 28 may not take place. To overcome the foregoing, the current values Il, I2, are preferably offset by a constant bias value, for the entire range of control current values. When one of the currents then is increased while the other is decreased to control the location of the transducing zone, a constant bias offset for forming the transducing zone will be maintained throughout the operating range. Alternatively, cancellation of the control fluxes within the operating range of the transducer may be prevented by providing control flux paths having gradually increasing reluctances in opposite directions along the transducer width on opposite sides of the physical gap. For example, to obtain the foregoing a space of variable depth (not shown) may be provided between the front and back cores of the transducer. Such a wedge-like spacing would vary in the direction of the gap depth along the transducer width.
A further example of obtaining control flux paths having gradually increasing reluctances along the transducer width is shown in FIG. 15. The transducer-keeper combination of FIG. 15 is an alternative embodiment to the above described embodiments of FIG. 12-14. The transducer 90a of FIG.

~40~ AV-3261 C1 15 differs from the transducer 90 of FIGs. 12-14 in having oppositely oriented wedge~shaped back and front cores 91a, 92a, 94a, 95a instead of the rectangular cores of the embodiment of FIGs. 12-14. Because of the similarities between these embodiments, corresponding elements in these figures are designated by like reference numberals, while a suffix "a" has been added to the wedge shaped cores and resulting control flux paths of the embodiment of FIG. 15. These wedge shaped cores 91a, 92a, 94a, 95a have cross-sectional areas gradually increasing in opposite directions on either side of the gap 20 along the width of the transducer.
Consequently, the resulting oppositely oriented control fluxes 1~4a, 126a correspondin~ to those fluxes 124-127 illustrated in ~IG. 13 are inherently offset due to varying flux density along the transducer width W.
Undesirable control flux cancellation is thereby prevented.
FIG. 16 is an example of a recording/reproducing apparatus utilizing the above-described stationary electromagnetically controlled scanning transducer-keepex combination of FIG. 14. In such recording/reproducing apparatus, there is shown a record signal processor 166 for processing a signal prior to recording on tape 146, and a playback signal processor 168 for processing a signal played back from the tape. The apparatus of FIG. 16 is especially suited for high density recording and playback of television signals or other high frequency, wideband signals along transverse tracks 118 of tape 146 moving longitudinally in the direction 147. For example, it may be used for segment~d recording and playback of video signals, that is television signals having information pertaining to one field of the television signal recorded along a number of discrete tracks on tape.
A switch 174 is shown for selecting a recording or a playback operation mode. A record V-3~61 Cl ~'~ 7 ~ 7~ ~
currentr Is, is applied ~rom the xecorder ampl~fier 170 to the transducing winding 145 via switch 174 and line 176. Alternatively, the line 176 and switch 174 couple a playback voltage, Vs, from the transduciny winding 145 to the playback amplifier 172. Because recording and playback signal processors, such as shown at 166, 16B, and amplifi~rs 170, 172 are well known in the art, a detailed description thereof is not included herein.
A drive control circuit 54 corresponding, for example, to the previously described circuit of FIG~ 3 t is utilized to drive the control windings 106 to 109 in accordance with the foregoing disclosure. A servo system 180 is utilized for coordination of the scanning of the transducing zone 29b effected by the drive circui~t 54 and the longitudinal tape movement effected by capstan 193 and motor 194. During recording operations, the servo system 180 functions to coordinate the scanning rate of the transducing zone 29~ and speed of transport of the tape 146 so that the recorded tracks 118 are uniformally distributed along the tape transversely at a precise angle relative to the tape's longitudinal dixection. In addition a trac~
184 of control signal is recorded in the longitudinal direction 147 on tape 146 by a stationary transducer 182 to facilitate during reproduction coordination of the scanning of the transducing zone 29b and transport of the tape 146. During reproduction the transducer 182 is utilized to reproduce the recorded control signal from track 184 in a manner well known in the art and is employed to synchronize the transport of the tape 146 with the scanning of the transducing zone 29b.
A multiple pole switch 186 connects the winding 183 of transducer 182 and a servo circuit 191 with an input line 187 when in the position indicated during a recording operation mode. When in the other position indicated, the switch 186 connects the winding 183 with the servo circuit 191 and disconnects the input line 187, hence, the control signal from the servo circuit and -4~- AV-3261 Cl transducer 182. In place of the control ~ignal~ 6wi~ch 186 couples a reproduce or pl~y reference signal received on line 196 to the sexvo circuit 191 for use in a manner that will be described further herein~fter.
During recordingt a control signal, typically, at a rate of one-half the vertical television field rate, is received on line 187. The signal on line 187 is applied via the switch 186 and line 188 to the winding 183 of transducer 182.
Consequently, the transducer 182 records that signal along track 184 on tape 146 simultaneously as information signals are recorded along the transversely extending tracks 118. The control signal on line 187 is applied at that time via ~witch 186 1~o.
the servo circuit l91, which in turn controls the operation of the drive control circuit 54 to be synchronous with the signal on line 187. The synchronous condition is obtained by comparing the control signal to a signal received from the drive control circuit 54 via line 190 that is indicative of the scanning rate and position of the transducing zone 29b. The servo circuit l91 responsively generates a correction signal that corrects deviations of the actual location of transducing zone 29b from the desired location indicated by the control signal on line 187.
During playback, the servo circuit l91 receives information related to the scanning rate and position of the transducing zone 29b received from the drive control circuit 54 via line 190. The servo circuit 191 compares the information received via line l90 to the control signal information reproduced b~
transducer 182 and received over line 189. In response to this comparison, correction signals are generated on lines 192 and 199. The line 192 couples the received signal to the drive control circuit 54 to cause acceleration or deceleration of scanning of the transducing zone 29b along the width W of the keeper .. ,~'' .

2B. The line 199 coup.les the rec~ived cor~ection signal to the motor 194, which control~ ~he capstan 193 to ~djust correspondingly the transport of the tape 146. This control of the capstan 193 and dri~e ~ontrol circuit 54 results in maintaining xegistration of the scanning transducing zone 29b over the tracks 118 extending transversely along the tape 146. Such transducer-to-track registration cont~ol can be enhanced ~y use of a high resolution tachometer operatively linked to the capstan 193 that provides a high rate signal indicative of the speed of transport of the tape 143. This tachometer signal is coupled to the servo circuit 191 for comparison with the play reference signal provided over line 196. A resulting correction signal is generated which is provided over line 199 to the motor 194 for corresponding contxol of the capstan 193.
It follows from the foregoing description that the apparatus of FIG. 16 is suitable for recording and playback of signals along transverse txacks of a longitudinally moving medium which is in contact with an outer surface of a keeper, utilizing the transducer-keeper combination of the present invention.
The medium is out of contact with the physical gap and therefore the gap responsible for the formation of the keeper transducing zone is not exposed to wear or erosion. The wear of the transducer-keeper combination is reduced to that due to a relatively slowly advancing medium in contact with an outer surface of a stationary gap-less keeper. At the same time the keeper shunts any portion of the control flux which may fringe from the physical gap, thereby substantially reducing signal erasure of the medium. Moreover, spacing losses are avoided in view of the contact of the keeper and magnetic storage medium of the record medi~.

~ 7~ ~ ~V ~

Embo~iments ln ~ccordance w~th the present invention will be de~cribed now that have mechanically moving transducer core relative t~ ~
stationary keeper, which doe~ not have a phy~ical gap provided in the tran~ducing areaO In thi~ connection, the tran~ducing zone within the keeper follows the movement of the transducer core~ if the physical yap defined by the core is responsible for the ormation of the transducing zone. With further reference to FIG.
17 there is shown schematically a magnetic transducer 510 having a oore 520, made of a suitable magnetic material, for example ferrite, defining confronting poles 522, 524. A nonmagnetic material, for example glass or silicon dioxide is provided between the poles 522, 524 to obtain a physical gap 526 of the type typically used and referred to as a transducing gap.
The transducer core 520, poles 522, 524 and gap 526 may be constructed by well known magnetic head fabrication methods, and therefore a detailed description thereof is not provided.
An elongated keeper 528 of a thin, soft magnetic material, for example permalloy, having characteristics as described hereinbefore, is arranged adjacent to the poles 522, 524 to bridge gap 526. In this embodiment, the transducer core 520 and keeper 528 are maintained in a closely spaced relationship, with no physical contact between these two elements, as illustrated by a spacing 529. As will be appreciated from the following description, the spacing prevents objectionable wear of the transducer 510 as it is moved relative to the keeper 528. In the presently described embodiment, the width dimension of the gap 526, which corresponds ~o the width dimension W of the tracks 564 recorded along the magnetic storage medium 556, extends at a right angle to the longitudinal direction 562 of the keeper 528.
As in the other embodiments previously described herein, the keeper 528 is constructed as a ~ ~,79 7r~ 6 AV-3261 Cl sol~d~ continuou~ piece or layer o~ mag~etlc materl~l with no physical gap in the transducing are~. In the embodiment of FIG. 17, the width of the keeper i8 equal ~o the width W of the gap 526, but the keeper may be made wider, ~uch as the embodiment illustrated in FIGs.
18. The keeper 528 preferably has a very ~mall thickness t in the direction of the gap depth, for example between 0.00025 and 0.002 inch. It may be made in the form of a thin foil or deposited by sputtering in ~acuum or plating on a thin substrate ~uch as Mylar or ~epton, manufactured by Dupont Corporation. For example, the substrate may have a thickness between 0~0001 and 0.0005 inch.
In the embodiment of ~IG. 17~ a transducing signal core 530 is disposed in magnetic coupling relation with the keeper 528. The core 530 may be made, for example, of maynetic materials commonly used for the fabrication of magnetic transducer cores~ The signal core 530 abuts a latexal surface of the keeper 528 at opposite ends 532, 534 thereof to form a closed signal flux path 53fi therewith~
A transducing sianal winding 538 is wound around the signal core 530. Winding 538 is utilized for converting electrical ~ignals applied to it from an external signal source, schematically shown at 540, into magnetic signals for recording by the transducer-keeper combination on a record medium, such as magnetic tape 556. In addition, windin~ 538 is utilized for converting signals recorded on the magnetic tape 556 and picked up by the transducer-keeper combination into electrical signals, as will be described further in more detail hereinafter. To better distinguish between the signal core 530 and transducer core 520, core 520 will be hereinafter referred to as the rear core, and core 530 as the front core. The front core 530 is preferably arranged at an angle, m/ sloping away from a front surface 541 of the keeper 528, which faces the record '~ 79'~ ~
medi~m 55S, to avoid contact with ~he mediumO A ~ias ~ontrol winding 542 i~ wound around t~e rear core 520 ~nd a ~ontrol eurrent Ic is applied thereto by a variable current ~urce, including variable re i~tor 544 and a D.C. control voltage source 546~
Alternatively, an adjustable A.C~ control cuxrent source may be utilized in this embodiment in place of the D.C. source.
When there is no control current applied to the bias control winding 542, the keeper 528 magnetically shunts the gap 526 and no signal transfers with the record medium 556 take place. However, when a control current Ic is applied from source 546 to the control winding 542, that current induces a ~ontrol flux 548 in the rear core 520. The control flux 548 fringes from the gap 526 into the closely spaced thin keeper 528 magnetically bridging the gap 526. The keeper th~s serves as a return path to the rear core 520 for the fringing bias control flux 548.
Because of the very small cross sectional area of the keeper 528 in a direction perpendicular to the control flux path 548 bridging gap 526, the fringing flux from the gap 526 locally saturates the keeper 528 in a region 550 which bridges the gap 526, as is shown by a hatched area, resulting in the establishment of a low permeability in the saturated region 550 corresponding to that of a non-magnetic material, such as air. The flux density in other areas of the keeper 528 surrounding the saturated region 550 and extending in close proximity over the magnetic core 520 is much lower than in region 550 and therefore these areas do not saturate and remain highly permeable. Consequently, the saturated region 550 is localized between two confronting highly permeable areas 552, 554 of the keeper 528 to provide a n gap-less n transducing zone.
When the region 550 of the keeper 528 is saturated as previously described, a recording signal _~7O ~-3261 ~1 ~ 7 ~v~
flux 536 extend~ng through the signal c~re S30 and permeable portion~ 5~ 554 of keeper 528 i~ coupled by the keeper ~o intercept the magnetic storage med~um or ~ape 556, when in close proximity of the keeper. ~or example, in the embodiment o FIG. 17, a tape 556 slowly advancing in a longitudinal direction 557 past the keeper 528 and in direct contact therewith. When a recording current Is from signal ~ource 540 is appli~d to signal winding 538f a recording flux is induced in flux path 536, which extends through the transducing signal core 530 and keeper 528. Because of the saturated gap region 550, the flux is directed thereby along the wavelength independent, low reluctance flux path exte~ding from the magnetically unsaturated ~reas 552 ~nd~554 of the keeper 528 to the tape 556.
Alternatively, when the transducer-keeper combination of FIG. 17 is utilized in playback operations, a signal flux from the tape 556 intercepts the keeper 528 at the transducing zone 550 and it follows the flux path 536 in the keepex 52B and signal core 530 and intercepts the signal winding 538 to produce an output voltage Vs on output lines 559.
The length l and the width W of the saturated region 550 correspond to equi~alent dimensions of the physical gap 526 of back core 520. As in the othe~
embodiments described hereinbefore, the magnetic characteristics of the keeper are selected such that the bias control flux which is necessary to saturate the region 550 bridging the transducing gap 526 is far below the level that could result in objectionable levels of control flux fringing from the keeper to effect the magnetic state of the medium. The level of bias control flux is primaril.y a function of ~he magnetic material of the keeper 528 and of its cross sectional area in the direction perpendicular to thP
bias control flux path 548. That cross sectional area, on the other hand, is defined by the width W and thickness t of the keeper. For a selected width W, a ~ 7 ~ AV-~2bl ~1 thlcker keeper requlre~ more fl~x for the 6atur~tion of region 550~ It i~ de~irable ~o have the thicknes~ t o~
the keeper 528 ~mall for the many reason~ di~cu6~ed previously. However~ an important rea~on for keeping dimension t small in the embodiment of FI~ 17 i~ that the effective transducing zone depth in the disection of t is small, which maintains the reluctance throu~h the ~aturated tran5ducing 20ne 55D high, hence, the shunt losses through the transducing zone 550 low.
However, in wideband, high density recording and playback devices where the keeper 528 is in contact with the record medium 556, it is also desirable to avoid or minimize life-shortening wear of the keeper.
Consequently, selection of the thickness t of the keeper 528 usually involves a compromise be~ween minimizing shunt losses and maximizing the life of the keeper.
The previously mentioned mechanical movement of the rear transducer core 520 with respect to the s.ationary keeper 528 is obtained in the embodiment of FIG. 17 as follows. The rear core 520 is rigidly attached to one end of a shaft 558, whose other end is attached to a device 560 for providing a reciprocating translational movement in the direction of arrow 562.
For example, device 560 may be implemented as an electromagnetic actuator or 3ther well known reciprocating device. It is important to obtain a linear velocity of movement of the gap 526 relative to the keeper 528 to avoid time-varying or non-linear signal transfers during recording and playback operations. In operation, a control current Ic is applied by voltage source 546 to the control winding 542 of a sufficient magnitude to saturate region 550 of the keeper 528. The tape 556 is advanced in the direction of arrow 557 in contact with the keeper 528, as previously described. The rear core 520 is moved by the reciprocating device 560 in the direction of arrow 562, thereby mechanically advancing the physical ~Lf~J7~37~i tr~nsduc~ng ~ap 526 along th~ keeper 528. A~ de~cx~bed pre~iously, t~e location of the ~aturated region 550 along the keep~r 528 in the direction ~62 follows the movemen~ of the physical gap 52~ along the keeper.
During recording operati~ns, a recording signal current I~ applied to the signal winding ~38 causes a corresponding ~ignal flux 536 to flow through path 53~, which is coupled by the transducing zone 550 to effect recording along transverse tra~ks 563, 564 on the tape 556. One set of parallel tracks, -~uch as 563, is recorded during a movement of the front core 520 in one direction, while a second ~et of parallel tracks, such as 564, is recorded during movement of the front core in the opposite direction. Either set of tracks 563 or 564 may be eliminated by turning off either the recording current Is or the bias control current Ic during movement of the core 520 in one of the directions.
The reproduction of sign~ls recorded along parallel transverse tracks of the tape record medium 556 is obtained by the transducer-keeper combination of the embodiment of FIG. 17 in a manner analogous to the recording of signalsl that is, by reciprocating the front core 520 in the direction 562, while the saturated transducing zone 550 is moved over recorded tracks on the medium 556. However, instead of applying a recording current to the slgnal winding 538, the transducer~keeper combination functions to detect a playback signal flux emanating from the medium 556, which enters the keeper 528 via the unsaturated regions 552, 554, adjacent to the saturated region 550. The playback signal 1ux 536 intercepts the signal winding 538 which, in turn, provides to output line 559 a playback voltage Vs for further processing in a conventional manner.
~ rom the foregoing description, it is seen that the transducer-keeper combination of the embodiment of FIG. 17 may provide a recorded track 5~ l Cl ~ ~ ~ 9 ~2 ~
p~ttern in ~ ~irect~on txanQver8e to ~ rel~tiYely ~lowly adv~ncing tape 556 by rapidly scanning the tran~ducer re~r core 52D along the stationary keeper ~2~. The tape 556 is in direct ~ontact with the stationary ~eeper 528, which does not have a phy#ical gap therein. As described hereinbefore, this contact result în the establishment of a flux path ~etween the tape 556 and ~ignal windin~ 538 that is not wavelength dependent, which reduces the effects of spacing losses.
Furthermore 3 in this embodiment of the invention the need for a rotatable member for carrying the transducer, such as is common in video recorders, is obviated while a relatively high transducer-to-medium scanning speed is obtainedO Moxeover, no rotary transfo~mers or slip rings are needed to transfer the signal between the transducer and record medium.
As in the previously described embodiments, the control current source 546 can be eliminated for record operations in the embodiment of FIG. 17, if sufficient record signal current Is is provided by source 540 to saturate the region 550 of keeper 528.
However, for playback operations, saturation of region 550 requires a bias flux, obtained in the embodiment of FIG. 17 by applying current I~ to th control winding ~42.
FIG. 18A illustrates an embodiment of the invention similar to that of FIG. 17, but differing in that the embodiment of FIG. 18A has no front core. In this embodiment, the signal and control windings 538, 542 are combined into a single winding 539 arranged around the rear core 520. The single winding 539 is connected to the previously described bias control current source 546 via resistor 544 to receive the previously described control current Ic. In addition, the single winding 539 i5 also connected to a record or playback ~mplifier (not shown) via lines 564. A series capacitor 566 is connected in line 564 to isolate the control current source 546 and signal ~7~37;~6 amp~i~iers coupled to llnes 564. Consequently, ~oth the recording ~iqnal fl~x 536 and the control ~lux 548 extend in parallel through the core 520 and keeper ~28.
In recording operations, where a recording current I~
ls applied via line 564 of ~ufficient magnitude to saturate the transducing zone 550 o the keeper 528, the control current ~ource 546 and resistor 544 may be omitted, as ~represented by interrupted li~es coupling the current source and resi~tor to winding 539.
However, in playback applications, ~aturation of the transducing zone 550 requires a bias flux, such as obtained by applying a control current Ic frQm source 546 to the single winding 539. In the embodiment of FIG. 18A, an AC control signal source may be utilized instead~of the DC source 5~6~ In that event, it is necessary to connect a filter (not shown~ in line 564, instead of capaci~or 566, for isolating the AC control signal from the information signal being recorded on or played back from the magnetic storage medium.
With respect to the foregoing description, it will be understood that FIGs~ 17 and 18A are schematic representations of structures in accordance with the present invention. There are numerous ways in which that basic structure may be implemented. For example, the keeper 528 may have a width greater than the width W of the rear core 520, as shown in FIG. 18A. By extending the width of the keeper ~28 beyond one or both sides of the rear core 520, the length 1 and width W of the saturation region 550 are substantially unchanged and correspond to that of gap 526, as previously described. As a further example, the shaft 558 may be held in a rigid ~upporting bracket and the rear core 520 moveably mounted thereto by various known suspension systems (not shown). The keeper 528 and transducing signal core 530 may be fixedly supported by such bracket as well. The control winding 542 may be wound around the rear core 520 and move therewith, as in the embodiments of FIGs 17 and 18A. Alternatively, ~7~7~6 AV-3261 Cl ~he control winding 542 may be made stationary, ~nd attached ~o the bracket, while the rear core 520 is mounted for vertical movement along that winding out of contact therewith. A separate signal winding may also be arranged in this mannerO If desired, a plurality of rear cores 520 may be mounted on a co~mon shaft and driven by a common translating device 560. In such arrangement, each core 520 may be associated with a separate stationary keeper and signal winding, while a common stationary control winding may thread all the cores. The thusly obtained transducers may be utilized for synchronous, either sequential or simultaneous, recording and/or playback relative to a plurality of parallel tracks along a record medium.
FIG. 18B illustrates a further embodiment of the transducer-keeper combination of the present invention. In this embodiment, instead of the rear core 520 forming a closed magnetic circuit through the physical ~ap 526 as in the embodiments of FIGs. 17 and 18A, the gap 526 is formed between two discrete magnetic core members 520a, 520b fabricated from highly permeable magnetic material of low coercivity, such as commonly used to fabricate conventional magnetic heads.
As will become more apparent from the following description, each of the cores 520a, 520b has a length about equal to the length of the stationary keeper 528 in the direction of the reciprocating movement of the cores indicated by arrow 562. The members 520a, 520b are held together by a non-magnetic member 513, for example of aluminum, serving as a bracket. The bracket 513 is attached to the rod 558, which in turn is driven by the previously described translating device 560.
The device 560 drives the cores 520a, 520b in a reciprocating movement in the direction of arrows 562, in a similar manner as previously described with reference to the embodiment of FIG. 17. A combined control and signal winding 539 is wound around the front core 530. Consequently, the bias control si~nal 7;~;

path 5~8 extends through the front core 530, permeable portions 552, 55~ or keeper 528 and magnetic back cores 520a, 520b. The signal flux path 536 is substantially the same as previously described with reference to the embodiment o~ FIG. 17, but instead of extending through the length of the keeper 5~8, it extends with the bias flux through the back coxes 520a, 520b, as illustrated in FIG. 18B. In operation, the region 550 is saturated by the control flux 548 established by a control current Ic from either a DC or AC control source, as previously described with reference to the embodiments of FIGs. 17 and 18A. Because of the length of each of the back cores 520a, 520b, the bias flux established by the control current remains in the cores regardless of the location of the physical gap 526 along the length of the keeper 528, except at the location of the physical gap. In this manner, the desired saturated transducing zone 550 is established in the keeper ~28 opposite the physical gap 526 and follows such gap as the back cores are reciprocated by the translating device 560~
Further embodiments of the present invention will now be described with reference to FIGs. 19 to 21.
In these embodiments, rear core is rotated in close proximity to a stationary keeper. One or more such rear cores are arranged about the periphery of a rotating head wheel, with their portions defining the physical gaps projecting therefrom. The keeper is formed as a thin cylindrical segment, and is disposed in nested relation with the periphery of the rotating wheel. The keeper is maintained stationary and in closely spaced relationship with respect to the rotating cores to bridge the rotating gaps defined by the rear cores, whereby the rotating gaps sweep across the keeper in sequence. The tape is transported in a longitudinal direction past the statior.ary keeper and preferably in contact therewith. In the embodiments of FIGs. 19 and 20 the physical gap formed in each rear 1~ 79 ~ AV~3261 Cl core scans the tape in a ~ransverse direction, while in the embodiment of FIG. 21 the tape is transported in a helical path, as it is scanned by a moviny transducing zone established by a transducer rotated relative to the stationary keeper, as will be described hereinafter.
With further reference to FIG. 19, there is shown a base 570 of a nonmagnetic material, for example, aluminum, on which a rotating transducer-stationary keeper assembl,v 572 is mounted.
A head wheel 574 holds one or more rear cores 520, which are similar to those previously described with reference to and shown in FIG. 17. A control winding 542 is wound around each rear core 520. If more than one core 520 is used, they are preferably spaced equally about the circumference of the wheel. The wheel 574 is made of a nonmagnetlc m~terial, for example, al~min~m, and is fixedly mounted to a motor ~haft 575. The ~haft 575 and wheel 574 are driven by a mot~r 576. The motor 576 is held on the base 570 by means of a nonmagnetic bracket 577, for ex~mple of aluminum. A keeper 578 of a thin, ~oft magnetic material, for example permalloy or another one of the previously described keeper materials, i5 fixedly attached to the base 570 by means of a nonmagnetic bracket 579, for example of aluminum. The thickness of the keeper 578 is preferably within the range previously described with refer~nce to FIG. 17.
In the embodiment of ~IG. 19, the keeper 578 is a cylindrical segment supported concentrically relative to and spaced from the periphery of the rotatably mounted head wheel 574, to obtain a uniform spacing between the rotating physical gaps 526 and the keeper 578. A tape 580 is transported in lonsitudinal direction indicated by arrow 582 past the keeper 578 and in physical contact with an outer surface 585 thereof. A front core 586 having a signal winding 587 arranged thereon is rigidly mounted to the keeper 578 in a manner similar to that of the embodiment of FI~.
17. The front core 586 preferably has a U-shape with both open ends thereof in physical contact with a lateral surface of the keeper 578 to form a substantially closed magnetic circuit therewith in the manner previously described with reference to the embodiment of FIG. 17.
A slip ring assembly 588 and a brush or wiper assembly 589 are also provided in the embodiment of FI~. 19. The slip ring assembly comprises a rod 593 of insulating material, such as plastic, and a plurality of slip rings 590 disposed along the rod, the assembly firmly attached to the motor shaft 575 to rotate therewith. Each slip ring 590 is connected by means of an electrical conductor 591 to a particular control winding 542 arranged on a particular rear core 520.

~5~- ~V~32~1 Cl For ex~mple, ~he slip ring~ 590 may be gold plated onto the surface of the insult~ng rod 593.
The brush or wiper assembly comprises a plurality of individual brushes 5~5 commonly coupled to an adjustable D~CD control volt~ge source 546.
Individual adjustable series resistors 544 are coupled to each brush 595 to permit adjustment of the control current pro~ided to the individual control windings 542. The assembly 589 is rigidly mounted to ~ase 570 by means of an insulating bracket 594, for example of aluminum. Well known and commercially available brush and slip ring assemblies 589, 590 may be utilized to connect the control currents provided by the source 546 to the respective rotating control windings 542~ ~or example, brush block, part number 3751 001, and slip ring assembly, part number 3857-01, both manufactured by Poly-Scientific, Litton Systems Inc., are suitable for use as the brush and slip ring assemblies 589 and 590, respectively. The signal winding 587 is coupled to a recording signal circuit or alternatively to a playback signal circuit in the manner previously described with reference to the embodiments of FlGs. 17 and 18.
The operation of the transducing assembly 572 of FIG. 19 will be now described. The principles of the recording and playback operations utilizing the rotating rear cores and the stationary keeper of FIG.
19 are the same as previously described with reference to the embodiment of FIG. 17. However, instead of the previously described reciprocal movement, the rear cores are rotated in a circular path in one direction relative to the keeper and tape. A more uniform and linear scanning of the record medium is thereby obtained. Synchronization of the rotational speed with respect to the longitudinal tape movement is also facilitated by such movement of the rear cores.
When the above-described rotating transducer-stationary keeper assembly is utilized for .

~ignal recordlng ~long a longitudinally mov~ng tape 580, a recording current is applied to the transducing winding 587 from a conventional recording circuit ~no~
~hown). Simultaneously, the control current Ic is applied via the brush and slip ring assemblies 588~ 589 to the rotating control windings. As each physical gap 526 sequentially rotates past the keeper 578, the flux emanating therefrom saturates a region of the keeper bridging the gap. That saturated region in effect is an extension of the gap 526~ as has been described previously with respect to the various transducer-keeper combination embodiments. The flux from the permeable portions of the keeper 578 which surround the s~turated region pass into an adjacent medium.~ Thus, when tape 580 passes the keeper 578 in contact with its outer surface 585, the signal flux from the keeper records a signal along parallel tracks 597 on the tape.
It will be appreciated that in the embodiment of FIG. 19 the mechanically rotating physical gap 526 is out of contact with both the keeper 578 and medium 580. Gap wear and erosion due to transducer-to-medium contact are eliminated. In addition, the wear of the keeper is minimal, because only a relatively slow moving medium in contact with a smooth gap-less surface of a stationary keeper. Tape shedding, characteristic of recorders having a high relative transducer-to-tape speed, is also reduced because of the much lower keeper-~o-tape speed.
Signal transfers occur with each track during one pass of one transducer core 520 by the keeper 578 Preferably, the rear cores 520 are spaced around the wheel 574 such that a continuous information signal, i.e., a signal having no interruptions in time, may be transferred between the tape 580 and transducing winding 587 by adjacent rear cores consecutively rotating past the stationary keeper 578. However, signal transfers can be arranged to occur selectively, 1 ~,7 ~7~ ~ AV~3~61 C1 such A~ in time ~paced bur~t~, by ~witching the bias control cuxrent on and off ~for re~ord operation~ the record ~ignal current can be 60 controll~d for thi~
purpose) as the keep~r i~ scanned by the plurality of rotating adjacent rear cores.
With reference to the foregoing description of the embodiment of FIG. 18B, it will be understood that it may be utilized in the apparatus of FI~. 19 by attaching the rear cores 520a, 520b of the embodiment of FIG. 18B to the rotating wheel 574.
FIG. 20 illustrates a schematic diagram of a wideband, high density recording and reproducing apparatus utilizing a rotating transducer-stationary keeper assembly 607, similar to the assembly 572 of the embodiment of FIG. 19. ~ere, the keeper 578 is attached to a no~magnetic supporting bracket 579, for example by epoxy. A slot 581 is provided in the ~racket 579 to allow the head wheel 574 to rotate in close proximity to the keeper 578. The transducer-keeper combinations in this embodiment differ from those of FIG~ 19 in that a single winding 539 is wound around the rear core 520 and i~ coupled to receive both the signal current and bias control current. Thus, the rear core 520 serves to provide control and signal flux paths, as has been described previously with respect to the embodiment of FIG. 18A, and a front core is not needed in the embodiment of FIG. 20. In the apparatus of FIG. 20, the control current Ic as well as the recording current IS or playback voltage Vs are coupled to the windings 539 of the rotating rear cores 520 by means of rotating coupling elements, such as the slip ring and brush assemblies 58B, 589 previously described with reference to the embodiment of FIG. 19. The recording signal current or playback voltage are coupled to the windings 539 via a rotary transformer assembly, having a primary portion 610 and a secondary portion 612. The primary portion 610 is rigidly attached together with the head 3t~
wheel 514 to the rotating m~tor 6haft 575 ~nd rotates therewith. There ~s one .rotatlng primary tr~n~former portion 610 for each rear core 52~. Each primary transformer portion 610 has a primary winding 614 attached to one winding 539O A capacitor 566 is coupled between the winding 539 and primary winding 614 to isolate the signal processing circuits from the D.C.
bias control circuits.
The apparatus of FIG. 20 includes a record signal processor 616 and a playback signal processor 618, for processing a signal prior to transfers between them and the tape 580. The apparatus o FIG. 20 may be utilized for high density recording and playback of television signals or other high frequency, wideband signals along tracks 597 extendin~ transversely across a longitudinally moving tape. A switch 624 is shown for selecting a recording or playback operation mode.
During a record mode of operation, the record current s is coupled from the xecord amplifier 620 to a secondary winding 628 of the transformer via switch 624 and line 626. During a playback mode of operation, the line 626 and switch 624 connect a playback voltage Vs from the secondary winding 628 to the playback amplifier 622. Record and playback signal processors 616, 618 and amplifiers 620, 622 employed in the art of recording and reproducing widebank signals, such as television signals may be employed in the apparatus of FIG. 20. Therefore, a detailed description thereof will not be given.

- -:

~7~37~
Moreover, or the apparatus of ~IG. 20, tape transport mechanisms (not shown) of the kind employed in known rotary head transverse scan ~ape record and reproduce apparatus for television signal applications can be utilized to transport the tape 680 in a longitu-dinal direction 582 in contact with an outer surface 585 of the keeper 578. Furthermore, less complex tape transport mechanisms utilized in known audio tape record and rPproduce apparatus may be employed as well.
A servo system 630 is provided for coordinating the rotation of the head wheel drive motor 576 with the longitudinal transport of the tape 580. Other than as described in the following, the servo system 630 is arranged and functions in the manner as the servo system 180 described in connection with the embodiment of FIG. 16. Therefore, other than the differences between the servo system 630 of the embodiment of FIG.
20 and the servo system 180, neither the servo system 630 itself or its operation will be described with reference to FIG. 20. An understanding of the components of the embodiments of FIGs. 16 and 20, as well as their function, identified by like reference numbers can be obtained from the description of the embodiment of FIG.
16.
Regarding the differences in the servo system 630 of the embodiment of FIG. 20, a servo circuit 691 is arranged to coordinate the rotation of the rear cores 520 by the head wheel 574 in response to a tachometer signal indicative of the rotational phase and velocity of the head wheel. This tachometer signal is generated by a tachometer mechanism operatively coupled to the head wheel motor 576 to be responsive to the rate and direction of rotation of the head wheel, as well as the rotational position of the rear cores 520 carried by the head wheel. A line 640 couples the tachometer signal to an input of the servo circuit 691.
In response to the tachometer signal, the servo circuit 691 generates a head wheel control signal over line S92 gr7~ 6 that extends to the head wheel motor 576 to maintain the head wheel 57~ at a desired phase and velocity of rotation determined by a referenc~ ~ignal. In the record operation modP, a signal synchronous with the control signal provided over line 187 ~s compared with the tachometer ~ignal to generate the head wheel control signal. During the playback operation mode, a signal ~ynchronous with the playbac~ reference provided over line 187 is employed to determine the phase and velocity of rotation of the head wheel 574, hence, rear cores 520.
From the foregoing description, it will be appreciated that the apparatus FIG. 20 is suitable for recording and playing back signals along tracks extending transversely along a longitudinally moving medium that is in contact with an outer surface of a keeper. The rotating physical gaps that effect the formation and movement of a gap-less transducing zone are out of contact with both the keeper and the medium and, therefore, such gaps are not exposed to wear or erosion. Wear of the transducer-keeper combination is reduced to that caused by a relatively slowly advancing medium in contact with an outer surface of a stationary, gap-less, smooth keeper~
FIG. 21 illustrates another wideband, high density signal record and reproduce apparatus embodiment of the present invention. While the head wheel of the embodiment FIG~ 20 rotates in a plane substantially perpendicular to the longitudinal direction of tape movement, in the embodiment of FIG. 21, the head wheel rotates in a plane substantially parallel to the direction of tape movement. This arrangement may be particularly useful when it is desired to record substantially longer tracks on tape, such as produced by rotary helical scan and longitudinal tape record and reproduce apparatus. In conventional rotary helical scan apparatus, the tape is introduced to a helical path about a cylindrical tape guide drum from one side of the drum guide for scanning by a rotating 6 ~ 79~ AV-~26l Cl transducer~ and is wrapped around the drum so that it exists fxom another location about the circumference of the drum at a different position axially di~placed along the drum surface relative to the entry position.
Information signals are recorded in discrete parallel tracks that diagonally extend along the tape at an angle relative to the longitudinal direction of the tape, whereby a track length greatly in excess of the width of the tape can be achieved. For a given helical scan apparatus construction, the angular orientation of the recorded tracks is a function of both the velocity of transport of the tape about the tape guide drum, as well as the speed of rotation of the xotating transducer. The resultant angle, therefore, varies depending upon the relative velocities of both the rotating transducer and the transport of the tape. In most helical scan apparatus, the transducer is carried by the tape guide drum, which in tuxn is formed by two axially displaced cylindrical sections, one of which ~usually the upper most) rotates while the other section remains stationary.
However, the apparatus of FIG. 21 significantly differs from a conventional rotary helical scan apparatus in that the physical gap provided in the transducer core does not contact the tape. Instead, the tape is in contact with a stationary keeper, which in this embodiment is arranged circumferentially around and spaced from a portion of the rotating head wheel to be out of contact with the rotating physical gaps of the transducer cores mounted in the wheel.
With further reference to FIG. 21, a rotating head wheel 662 is arranged coaxially with a stationary upper drum 660, both made of aluminum or other suitable nonmagnetic material. The head wheel 662 has one or more rear cores 520 rigidly attached thereto, and is mounted to a shaft that is rotated by a drive motor 699. A portion of that shaft is shown at 661 in FIG.

~62- AV-3261 Cl 9~7'~
21, In the apparatus of FIG. 21, the cores 520 are attached to a lower surface of the head wheel 662, for example by epoxy. However, they may be mounted thereto in any other suitable manner, for example inserted in slots provided in the head wheel and held therein by screws or other fasteners. A stationary lower drum 664 of nonmagnetic material, such as aluminum, is arranged coaxially with the upper drum 660, and has the same diameter as the upper drum. The two drums are axially displaced from each other to define a space or slot 666 between the drums for the rotating rear cores 520. A
keeper 667 of a magnetic material, for example permalloy, Sendust or amorphous metal, is arranged circumferentially around a portion of the periphery of drums 660, 664 and is firmly attached thereto, for example by screws. The thickness of the keeper is preferably selected within the range specified previously for the embodiment of FIG. 17. The keeper 667 is spaced from the rotating cores 520 in such a way that these cores rotate in close proximity to the keeper, but out of contact therewith. The core 520 shown in FIG. 21 has a common transducing signal and control winding 668, similar to ~he previously described winding 539 of FIG. 20.
A magnetic tape 676 is transported in a longitudinal direction 677 along a helical path extending around the stationary drums 660, 664, and in physical contact with the keeper 667. To assure a close contact with the keeper, the tape is guided under tension around the drums by rotating tape guides 690, 691.
A rotary transformer is arranged coaxially with the drum assembly and has a rotating upper portion 669 attached to the motor shaft 661 and a stationary lower portion 670. The winding 668 of each rotating rear core 520 is attached to the primary winding tnot shown) provided on the rotating portion 669 of the rotary transformer. A capacitor 566 is coupled to isolate the signal processing circuits from the D.C.
bias control circuits, as described with reference to ~63~ ; AV-32~1 Cl the embodiments of FIGs. 18A and 20. During playback operation modes, the signal ind~ced from the rotating primary windings into the stationary secondary windings (not shown~ provided in the stationary portion 670 of the transformer is applied via line 626, switch 624 and amplifier 622 to the playback signal processor 618. In record operation modes, the signal to be recorded is applied from the record signal processor 616, via amplifier 620, switch 624 and lines 626 to the winding 668. The slip ring and brush assemblies 588 and 589 are similar to those previously described with reference to FIG. 20 and, therefore, their respective descriptions will not be repeated with reference to FIG. 21. The slip ring assembly 588 is joined to rotate with the motor shaft 661 by a shaft extension 674.
It will be understood from the previous description of the embodiment of FIG. 18B that when the apparatus of FIG. 20 or 21 is placed in a record operation mode, a separate flux bias-creating control current Ic may be omitted, provided sufficient recording current is coupled to the signal winding to saturate the virtual gap or the transducing zone within the keeper 667.
While the apparatus of FIG. 21 is similar to the embodiment previously described with reference to FIG. 20, there is a difference in the way the tape 676 is transported in the direction 677 past the rotating head wheel 662. In the embodiment of FIG. 20, the gap 526 defined by the rotating rear core 520 scans the tape at an angle which is substantially perpendicular to the longitudinal dimension and direction of transport of the tape 580. However, in the embodiment of PIG.
21, the gap 526 scans the tape 676 at a selected angle, as shown at n, with respect to the longitudinal dimension and direction 677 of transport of the tape 676, which angle is selected in accordance with the desired length for the recorded tracks 675. As can be 7~t~

seen from FIGo 2~ ~ the embodiment of the present invention illustrated therein produces long tracks 675 of recorded information extending substantially longitudinal to the length of thP tapQ 676 at a very small angle to the length.
To coordinate the rotation of the head wheel drive motor 699 with the longitudinal transport of the tape 676, a servo system 630 is provided of the kind described herein before with reference to FIG. 20.
This servo system 630 is arranged and functions in the manner as described in connection with the embodiment of FIG. 20. Therefore, neither the servo system 630 itself or its operation will be described with reference to FIG. 21.
~ From the foregoing description, it will be appreciated that, like the apparatus FIG. 20, the embodiment of FIG. 21 is suitable for recording and playback of signals along tracks extending substantially along the length of a moving tape that is in contact with an outer surface of a keeper, which does not have a physical gap therein. As described hereinbefore, this contact results in the establishment of a flux path between the tape 676 and winding 668 for signal information that is not wavelength dependent, which reduces the effects of spacing losses. Also, the rotating physical gaps that effect the formation and movement of a gap-less transducing zone are out of contact with both the keeper and the medium and, therefore, such gaps are not exposed to wear or erosion. Wear of the transducer-keeper combination is reduced to that caused by a relatively slowly advancing medium in contact with an outer surface of a stationary, gap-less, smooth keeper.
While the invention has been shown and described with particular reference to various embodiments thereof, it will be understood that variations and modifications in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (33)

1. Apparatus for coupling information defined by magnetic flux between a first body of magnetic material and a second body of magnetic material defining a magnetic flux path having a non-magnetic gap which causes flux flowing along said path to fringe or flow from said path; characterized in a third body of magnetic material having a transducing zone, being included and disposed to be magnetically proximate said first magnetic material to couple flux to or from the same and to have a portion thereof disposed to be magnetically proximate said gap in said magnetic flux path within said second magnetic material to provide a uniform magnetic reluctance across said gap for coupling flux to or from said flux path.

2. The apparatus of claim 1 wherein flux which fringes from said flux path in said second body of magnetic material forms said transducing zone in said third body.

3. The apparatus of claim 1 in which said third body of material includes adjacent regions of substantially different magnetic permeability to provide said transducing zone.

4. The apparatus of claim 3 wherein one of said adjacent regions is magnetically saturated whereas the other thereof is an unsaturated region.

5. The apparatus of claim 3 wherein said adjacent regions of substantially different permeability have a steep magnetic permeability gradient therebetween.

-66- AV-3261 Cl

6. The apparatus of claim 1 further characterized in that bias control means are included for generating magnetic flux in said third body of material to provide said transducing zone.

7. The apparatus of claim 1 in which said first and second bodies of magnetic material are simultaneously magnetically proximate said third body and during such time there is relative movement between said first and second bodies, further characterized in that said third body is positioned to be between said first and second bodies during said movement.

8. The apparatus of claim 1 further characterized in that means are provided for varying the location of said transducing zone within said third body of material.

9. The apparatus of claim 8 further characterized in that said means for varying the location of said transducing zone within said third body of material periodically scans the location of said transducing zone along a defined path within said body.

10. The apparatus of claim 1 further characterized in that said third body is in contact with at least one of said first and second bodies during the coupling of flux between said one body and said third body.

11. The apparatus of claim 4 wherein said unsaturated region generally is free of magnetic flux.

-67- AV-3261 Cl

12. A method of transferring information definable by magnetic flux between two bodies of magnetic material characterized by the steps of:
providing a magnetic flux path in one of said two bodies, said flux path having a non-magnetic interruption which causes flux to fringe or flow from said path;
forming a transducing zone in a third magnetic body for coupling magnetic flux to or from the other of said two bodies, said zone being formed at a location within said third body at which there is no physical gap and magnetically proximate said interruption in said one body to present a uniform magnetic reluctance thereacross; and positioning said third body of material with said transducing zone at a location to be magnetically proximate said other of said two bodies to provide for coupling of flux between said other body and said third body.

13. The method of claim 12 in which said other body of magnetic material is a magnetic storage medium having higher coercivity than said third body of magnetic material.

14. The method of claim 12 wherein said one body of magnetic material is a magnetic core of a transducer, which core has a magnetic permeability generally equal to or greater than the magnetic permeability of said third body of magnetic material.

15. The method of claim 12 further characterized in said step of forming a transducing zone in said third body of material including providing -68- AV-3261 Cl adjacent regions of said third body with substantially different magnetic permeabilities.

16. The method of claim 15 further characterized in said step of forming a transducing zone in said third body including magnetically saturating one region thereof while at least one adjacent region thereof is unsaturated.

17. The method of claim 15 further characterized in said adjacent regions of substantially different magnetic permeabilities having a steep magnetic permeability gradient therebetween.

18. The method of claim 12 further characterized by including the step of varying the location of said transducing zone along a defined path within said third body of material.

19. The method of claim 15 wherein said step of forming a transducing zone is characterized by coupling a control flux between said third body and said path in said one body, said control flux having a density gradient in a direction substantially orthogonal to the direction of flux flowing in said flux path.

20. A magnetic transducer comprising:
a magnetic core having two magnetic poles defining a magnetic flux path and having a physical gap therebetween which causes flux to fringe or flow from said path;

a body of magnetic material positioned adjacent said magnetic core bridging said physical gap;
bias control means providing a magnetic control flux in said core that has a relatively high flux density in a first region of said body bridging said physical gap and a relatively low flux density in a second region of said body adjacent said gap, to thereby form a transducing zone in said body through which information-defining flux is coupled between said body and a record medium;
a signal transducing device electromagnetically coupled with said flux path defined by said magnetic core for detecting and/or generating the information-defining flux which is coupled between said body and said record medium; and means for varying the location of said transducing zone along a width dimension of said gap.

-69a- AV-3261 Cl

21. The magnetic transducer of claim 20 wherein said magnetic core comprises a corresponding pair of core portions extending on opposite sides of said physical gap, and wherein said control means comprises a respective control winding associated with each of said core portions.

22. The magnetic transducer of claim 21 wherein said corresponding core portions provide control flux paths having gradually increasing reluctances in opposite directions along the width of said physical gap.

23, The magnetic transducer of claim 20 wherein said second region in said body is a highly permeable region that is generally free of magnetic control flux.

24. The magnetic transducer of claim 23 wherein said first region is magnetically saturated by said control flux.

25. The magnetic transducer of claim 20 wherein said magnetic core is movable in the direction -70- AV-3261 Cl of the length of said physical gap to vary the location of said transducing zone within said body.

26. The magnetic transducer of claim 25 further including means for moving said magnetic core with the physical gap defined thereby relative to said body of magnetic material to correspondingly move the location within said body of said transducing zone.

27. A magnetic transducer, comprising:
a magnetic core with poles defining a transducing gap therebetween;
a stationary keeper of magnetic material extending in close proximity to said magnetic core and bridging said transducing gap;
means associated with said magnetic core for providing a magnetic flux which flows in said keeper with different flux densities in different portions of said keeper to thereby define a region in said keeper which establishes an area through which magnetic flux is transferred to or from said keeper;
and means for moving said magnetic core relative to said keeper to thereby vary the location of said transducing region along said keeper.

28. The magnetic transducer of claim 27 wherein said magnetic flux fringes from said transducing gap in said magnetic core to saturate a portion of said keeper in an area bridging said transducing gap to thereby define said transducing region.

-71- AV-3261 Cl

29. The apparatus of claim 27 further including means for transporting a magnetic medium relative to the magnetic core, and means for synchronizing said means for moving said moveable core with the transportation of said medium.

30. The apparatus of claim 27 wherein said means for moving is coupled to provide a linear reciprocating movement of said moveable core with respect to said stationary keeper.

31. The apparatus of claim 27 further comprising means for advancing a magnetic medium past said stationary keeper and in direct contact therewith.

32. The apparatus of claim 27 wherein said means in operative association with said magnetic core includes a winding magnetically linking said magnetic core for receiving a current productive of said directed magnetic flux.

33. A method for transferring magnetically defined information between a magnetic transducer and a magnetic recording medium, comprising:
positioning a body of thin magnetic material in close proximity to a magnetic core having a transducing gap so as to bridge said gap;
advancing said magnetic recording medium in close proximity to said body of magnetic material;
generating a control flux in said magnetic core which flows in said body with different flux densities in different portions of said body to thereby define a region in said body which establishes -72- AV-3261 Cl an area through which magnetic flux flows between said body and said recording medium; and moving said magnetic core relative to said body to thereby vary the location of said region along said body.