US2229293A - Magnetic recording system - Google Patents

Description

Jan' 21, 1941- w. P. HUNTLEY Erm. 2,229,293

MAGNETIC RECORDING SYSTEM Filed June 14, 1938 2 Sheets-Sheet 1 JI Z/YZ'QJ.

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Jan. 21, 1941. v w P HUNTLEY E|IAL 2,229,293

MAGNETIC RECORDING SYSTEM v Filed June 14, 1938 2 Sheets-Sheet 2 lNvENTORf.

ATTORNEY.

Patented Jan. 21, 1941 MAGNETIC RECORDING SYSTEM Walter P. Huntley, Pasadena, Ray M. Chenoweth,

West Los Anteles. and Emmett M. Irwin, Pasadena, Calif., assignors to C-W-B Development Co., Los Angeles, Calif., a corporation of California Application June 14, 1938, Serial No. 213,638

9Claims.

Our invention relates to the art of recording and reproducing sound or similar vibrations and has particular reference to a novel magnetic recording medium upon which sound or other vibrations maybe recorded and from which the same vibrations may be readily reproduced. In the recording of sound or similar vibrations, as for example i`n the phonographic art adapted for business dictation and transcription, it has hererecording medium of wax or similar material, into the surface of which will be engraved the vibrations to be recorded thereon and to be reproduced therefrom. Such wax records have distinct 5 disadvantages, particularly they are consumable, it being necessary to shave o part of the wax record each time the recording and transcription is made therefrom. Further such wax records are not permanent in that they are seriously af- 20 fected by temperature changes and frequently the material recorded upon such records is destroyed and lost before it can be transcribed.

Magnetic recording on the other hand possesses many distinct advantages, among which are that magnetic records upon which sound or other vibration has been magnetically recorded are substantially permanent and are not consumable, being capable of being used repeatedly without the necessity of destroying any portion of the 30 metal of the recording medium. Moreover, such metal records upon which sound vibrations have been recorded magnetically will not be affected by temperature changes or by substantially any other external influence other than a magnetic 35 influence which would injure, destroy or otherwise harm the material recorded upon such medium.

Attempts have been made to record vibrations magnetically upon a magnetic record medium, 40 such as a steel wire or tape. The employment of a wire or tape as the record medium has necessitated movement of such wire or tape at a relatively high speed past a recording or translating mechanism adapted to alter the molecular ar- 45 rangement in the wire or tape. 'Ihe failure of this character of recording medium and recording system has been due primarily to the inability to control the rapidly moving wire or tape and also to provide simple and adequate means for 50 storing the tape before and after recording there- Further when employing tape or wire as the recording medium it is necessary to rewind the wire or tape each time it is desired to reproduce 55 sound or other vibrations that have been retofore been the common practice to employ acorded thereon, rendering this type of mechanism extremely difficult to handle for ordinary oiiice dictation and transcription purposes, wherein it is essential that during the period of dictation the dictator must be able to go back and listen 5 to any of the previously dictated material without loss of time and without complicated adjustment and rearrangement of the machine.

It is, therefore, an object of our invention to provide a magnetic recording medium upon 10 which a sound track may be magnetically recorded along a spiral or helical or otherconvolute path, in which adjacent coils or convolutions of the path may be disposed in close juxtaposition without interference between the' 15 sounds recorded upon such adjacent convolutions.

Another object of our invention is to provide a magnetic recording medium as set forth in the preceding paragraph adapted to permit the concentration of relatively large quantities of magnetic flux upon a minute area of the medium.

Another object of our invention is to provide a record medium of the magnetic type which substantially corresponds in form and shape to either cylindrical or disc records of the wax type now in common use, to permit the handling of such records in the same manner as conventional wax records are now handled.

Another object of our invention is to provide a record medium adapted for magnetic recording in which a compact, self-supporting but extremely thin recording surface is provided, adapted to be placed in a magnetic circuit of relatively low reluctance, whereby a stylus for passing magnetic ux into and through the thin skin surface may present to the recording surface a relatively small area and yet pass relatively large quantities of magnetic flux through the recording mdium to effect the necessary alteration of the molecular arrangement in the recording medium to permanently record sound or similar vibrations.

Another object of our invention is to provide a recording medium, as set forth in the preceding paragraph, in which recording styli may be employed, one on one side of the skin surface and the other on the opposite side of the skin surface but accurately aligned with the rst stylus to permit opposed styli each to present a minute area to the recording medium, to thus prevent the spreading out of the lines of ux as they 60 pass through the medium.

Another object of our invention is to provide a magnetic recording medium which may be constructed of such rugged character as will permit the ready handling thereof without fear of accidental breakage, in which a relatively thin skin surface of high magnetic retentivity capable of permanently registering and retaining a magnetic pattern of sound vibrations may be mounted upon or formed upon a base structure of relatively low magnetic reluctance and relatively low magnetic retentivity,- which will assist in Vthe completion of a low reluctance magnetic circuit.

Another object ofour invention is to provide a magnetic recording medium as set forth in the preceding paragraph in which the recording occurs upon and is' confined to the relatively thin skin of the medium, while the body of the medium provides a path of such low magnetic retentivity and reluctance that no additional pole-piece is required to complete a low reluctance return path for the flux employedto make the record.

Other objects of our invention will be apparent from a study of the following specification, read in connection withthe accompanying drawings.' wherein is disclosed an embodiment of our invention particularly adapted for oflice dictation and transcription, although it will be understood by those skilled in this art that our magnetic recording medium and our apparatus for magnetically recording thereon may be successfully and advantageously employed for the recording of sound vibrations or vibrations of a similar character for many other uses.

In the embodiment of our invention specially illustrated and described herein Figure 1 of the drawings represents a vertical sectional view taken through a simple dictating machine employing magnetic recording medium constructed in accordance with our invention.

Figure 2 is a vertical sectional view through the dictating machine and recording medium shown in Figure 1, the section being taken along lines II-lI of Figure l.

Figure 3 is a vertical sectional view taken through a modied form of dictating machine and magnetic record embodying the principles of our invention.

Figure 4 is a vertical sectional view taken through a still further modled form of dictat- -ing machinehand magnetic record constructed in accordance with our invention and illustrating the manner in which our magnetic record may be constructed in the form of a disc.

Figure 5 is a detail fragmentary sectional view of a portion of one form of recording medium which may be employed in the machine shown in Figure 4; and

Figure 8 is a detail fragmentary sectional view of a portion of a modified manner in which the recording medium may be constructed.

Referring to the drawings we have illustrated in Figs. 1 and 2 one typical form of dictating machine which may be adapted for magnetic recording upon a record having the conventional shape of a wax cylinder record, as comprising a frame I0 which may have a relatively broad at base II adapted to rest upon a table, stand or other suitable supporting device to hold the machine at a convenient level. Formed upon or attached to one end of the base I I is a vertically extending upright I2, from the upper end of which projects an elongated beam I3 disposed a considerable distance above and extending substantially parallel to the base II.

The vertical upright I2 constitutes a bearing member on which is rotatably mounted a mandrel spindle I4 preferably having a spool-like shape providing a pair of heads I5 and I6 disposed at either of the ends to constitute suitable supporting members for engaging opposite ends of a cylindrical recording medium or record I1.

The mandrel may be rotatably mounted upon the upright I2 by means of a shaft I8, formed integrally with or attached to the mandrel Il and extending through a suitable bore I3 in the upright I2. The inner head I 6 of the mandrel should be held in contacting relation against a hat inner surface 2li of the upright I2 as 'by means of a sprocket or pinion 2I rigidly secured upon the shaft I8 by means of a, set screw 22.

Power for rotating the mandrel Il and the recording medium I1 may be supplied in any suitable manner as by securing a pulley 23 upon the shaft I8 to receive a belt 24 driven by any desired motor or other power means.

The beam I3 constitutes a supporting bar and track-way along which a recording device 25 may move lengthwise of the recording medium I1.

the recording device 25 including a carriage block 26 slidably mounted on the beam I3 as by means of a pair of gibs 21 disposed on opposite sides of the block 26 and having ends 23 thereon extending over the upper side of the beam I3. As is illustrated particularly in Figure 2, the beam I3 may be rectangular in cross section to provide a substantially flat lower surface along which the recording device 25 will slide.

Upon the lower surface of the block 26 is mounted an electro-magnetic coil 29, having a core 30 extending therethrough, one end of the core 30 being threaded as indicated at 3I and used as a means -for securing the coil 23 upon the block 26 while the opposite end of the core 30 is preferably formed as an outwardly extending stylus 32. The stylus 32 may be of relative small diameter and may have its outer end sharpened to a relatively sharpV point.

As will be noted from an inspection of Figure 1 the pointed stylus 32 should be disposed immediately above the outer surface of the record cylinder I1, the spacing of the stylus from the surface of the cylinder I1 being preferably just suilicient to prevent actual mechanical contact between these members, although successful operation of our device may be accomplished if 4the pointed end of the stylus actually contacts recording device along the record we provide a feed screw 33 disposed immediately below and extending parallel with the beam i3, the feed screw being mounted for rotation by means of extending one end thereof through a bearing 34 in the upright I2 while the opposite end of the feed screw 33 extends through a bearing bore 35 in a bearing block 36V secured to the outer end of the beam I3.

The feed screw 331s prevented from moving longitudinally relative to beam I3 as by securing upon the right hand end thereof a pinion 31 while a locking collar 38 is secured upon the left hand end of the feed screw by means of a set screw 39. The pinion 31 may bel employed to rotate the feed screw 33 by meshing the pinion with pinion 2| von the mandrel shaft Il, the

pinion 31 being rigidly secured in driving relation upon the feed screw 33 as by means of a 'set screw 40.

The recording device carriage 2C is provided with a feed nut 4I 'formed upon or attached to a lever 42, which in turn is pivoted as by means of a pivot pin or screw 43 upon the carriage block 26. The inner end of the lever 42 is provided; with a spring 44 normally urging the nut 4I into engagement with the threads of the feed screw 33, while the projecting outer end of the lever 42 constitutes a handle by means of which the feed nut 4I may be disengaged from the feed screw 33 to permit the recording device to be manually shifted along the record I1 to any desired point. I

It is well known that in magnetic recording the sound or other vibrations are recorded by creating within the recording medium areas of magnetic poles of varying strength, corresponding to variations in the current which is supplied to the coil of the magnetic recording device. To permit the employment of relatively low rate of motion between the recording medium and the recording device it is essential that the.

area occupied by each of the poles created musi:` be maintained as minute as possible. For this reason the thickness of the recording medium .which will be permanently aected by the flux from the recording device must be maintained suillciently small to prevent the splaying out of the ux lines as they pass into and through the recording medium. Thu's by employing a stylus with a relatively sharp point, the area thereof which is presented to the recording medium I1 may be maintained extremely small and will produce sharply defined poles upon the recording medium. If, however, the recording medium is relatively thick there may be a tendency for flux lines to diverge as they pass further into the recording medium, the condition which is accented by any reluctance in the return magnetic circuit to the stylus.

It is important, therefore, that atleast that part of the recording medimn which is permaently affected by the recording flux must be maintained as thin as it is possible to make it and yet have it sufficiently strong to be selfsupporting and to hold its shape. Further, it is necessary to provide a return magnetic circuit exterorly of the thin recording part of the medium of sulciently low reluctance to permit the concentration of large quantities of ux in a minute recording area.

One form of magnetic recording medium which will satisfy all of the foregoing conditions and yet be sumciently strong to withstand rough handling and which may be made of a size and shape corresponding to the size and shape of conventional wax records is illustrated in Figures l and 2 as comprising the recording medium I1 having a cylindrical shape which may correspond in all'respects to the size and shape of conventional cylinder wax records. The recording medium I 1 includes a relatively thin shell or skin portion 45 formed of -any suitable material having the characteristics of relatively high magnetic retentivity and thus be adapted to have created therein magnetic poles of varying strength and to retain such poles until the recorded material is to be erased. This skin surr` low inagnetic reluctance and relatively low magnetic retentivity.

By making the skin surface extremely thin and by making the body portion of low reluctance the body portion may be employed as a part of the return magnetic circuit, insuring the transmission of lines of magnetic force through the thin skin surface 4l without appreciable divergence of such lines and thus permitting the creation of poles therein\over an extremely minute area.

By referring particularly to Figure 1 it will be noted that the magnetic circuit .for the flux emanating from the stylus 32 will include the skin or shell 45, the body 4l of the cylinder I1, the mandrel I4, the vertical upright I2, the horlzontal beam I3, and the carriage block 23. By constructing the mandrel I4, the vertical upright I2, the beam I3 and the carriage block 23 of material of low magnetic reluctance it is apparent that relatively large quantities of magnetic flux may emanate from the stylus 32 to permanently effect a change in the skin surface 45 of the record cylinder I1, while the remainder of the magnetic path is not permanently affected.

To insure that the entire magnetic path will be of low reluctance we prefer to form the internal diameter of the record cylinder I1 to closely conform with the diameter of the head I5 on the mandrel I4 and to provide an accurately machined .shoulder 41 on the head Ii, thus insuring adeqaute mechanical contact vbetween the cylinder I1 and the mandrel I4. To hold the cylinder I1 tightly upon the mandrel I4 we provide a movable end plate 48 adapted to be secured to the mandrel I4'as by means of a thumb screw 49 or other suitable device which will prevent displacement of the end plate from the mandrel, the outer portion of the end plate bearing against the outer end of the cylinder I1 to force the same snugly against an abutment shoulder 50 on the mandrel head I6.

The transfer of the magnetic flux between the rotating mandrel I4 andthe stationary upright I2 may be adequately providedgfor by maintaining a relatively large surface area of the head Il in snug metallic contact with the vertical upright I2, which may be readily accomplished by inserting a spring washer 5I between the pinion 2I and the outer surface of the upright I2.

Employing machines and records as illustrated and described in Figs. 1 and 2, it will be apparent that our system is adaptedvfor ordinary oillce dictation and transcription, merely substituting magnetic recording devices for the wax recordengraving devices now employed and substituting magnetic recording cylinders in place of the wax record cylinders now in common use.

In employing our magnetic record the-coil 2! will be connected to a suitable microphone or other electrical pickup circuit whereby sounds such as dictation will be transformed into electrical impulses and supplied as variations of electric current to the coil 29.

To start dictation the operator of the machine may elevate the out-er end of the feed nut lever 42 and slide the recording device 25 toward the lef"l to dispose stylus `32 immediately over the left hand end of the cylinder I1. By starting the motor or other power device employed to drive the belt 24 the cylinder I1 will be started into rotation while at the same time the rotation of the feed screw 33 will start the recording device travelling along the length of the record. '111e dictator may then employ the same dictating to listen tothe previously dictated material. The

same recording device 25 may be used both for the Ipurpose of recording and for reproducing previously recorded material from the record by merely shifting the coil connections from the microphone or transmitter circuits to receiving circuits in the manner disclosed in our co-pending application Serial No. 53,396, filed December 7, 1935.

Wlien the dictator desires to resume dictation he may again lift the lever 42 and slide the recording device 25 toward the right to theV point along the record l1 at which he left off dictating thus releasing the lever 42 and shifting the coil circuit back to connection with the microphone and the machine is again conditioned for further dictation.

The magnetic recording medium l1 may be constructed in a number of different ways. For example, one simple and convenient manner of constructing the same is to employ a relatively thick walled tube of iron or soft steel having suitable low magnetic reluctance and low magnetic retentivity and to apply upon the outer surface of such tube a shell jacket or coating of hard steel or any other magnetic material having the characteristics of being highly magnetic retentive.

Such coating or jacket maybe applied by any method adapted to the particular characteristics of the material from which it is made. Thus, certain materials such as hard steel may be machined into shells of relatively thin walls and shrunk upon the soft iron or steel body portion, or suitable magnetic material may be plated upon or sprayed upon the outer surface of the body portion 46 and then ground, machined or otherwise smoothed to provide a smooth surface for presentation to .the stylus 32.

Another convenient manner in which recording medium may be constructed is to form a suitable length of,tube of soft steel and then to harden the outer surface thereof by any suitable process by which the depth of which said material will be hardened may be controlled.

In all such forms the recording portion of the medium comprises a thin sheet or sheet-like member, the length and breadth (circumference) dimensions of which are of like or comparable order of magnitude as distinguished from those of a wire or tape and which therefore provides a compact uniform surface area over which the stylus may describe a convolute path, ad-` jacent onvolutions of which may be arranged close together.

For example, the speed of rotation of the record I1 and the pitch and speed of the feed screw may be so selected that adjacent coils of the helical path described by the stylus may be arranged extremely close to each other. The only limitation is that the poles created in adjacent coils must not interfere with or affect each other. Adjacent poles in a single line of recording may be made as close together as 0.005 inch and it follows that adjacent coils of the helix to insure correct tracking of the stylus on a transcription machine which may be used to transcribe the material.

In Fig. 3 we have illustrated a modified form of our magnetic recording medium and machine which is easily adapted for sharply defined magtions of recorded material may lie extremely close to each other. In this form of device we have illustrated a machine having a frame 52 including a suitable base 52a and a vertically extending upright post 52h formed thereon. 'Ihe post 52h may constitute a bearing member in which is rotatably mounted a suitable record support 53, constructed substantially in the form of a face plate the hub of which may be secured to or formed integrally with a shaft 54. The shaft 54 may be driven in any suitable manner as by means of a belt 55 extended over a pulley 55 which is rigidly secured upon the shaft 54 while endwise motion of the record support 53 will be preventedby butting the hub of the support 53 upon one side of the upright 52h and employing a pinion 51 secured upon the shaft 54 and abutting the opposite side of the upright 52h.l

A beam 58 corresponding in substantially all re.- spects to the beam I3 may extend from the upper end of the upright 52h to be disposed in spaced parallel relation above the base 52. A suitable feed screw 59 may be mounted immediately below the beam 58 in the same manner as was described for the mounting of the feed screw 33, such feed screw being driven by means of a pinion 60 meshing with the pinion 51.

The recording device in this form of our invention includes a carriage 6l Aslidably mounted upon the beam 58 for movement longitudinally relative to a record 62, the carriage 6l being provided Vwith suitable feed nut and lever mechanism, corresponding to the feed nut 4| and lever 42 described with reference to Figures 1 and 2. Secured to or formed integrally with lthe carriage 6| is a substantially U shaped stylus support 63, one leg of which extends substantially parallel to the base 52a and is disposed above the record 62 while the other leg extends parallel to the first leg but is disposed at a suiiciently lower level to permit its introduction into the interior of the hollow record cylinder 62.

The upper leg 64 mounts a recording stylus 66 having a coil 61 surrounding the same, the stylus and coil being constructed in all respects identical with the coil and stylus described with reference to Figure l. The lower leg 65 may be merely provided with a pole piece aligned immediately below the sharpened or pointed end of the stylus 66 or as is illustrated in Figure 3 such pole piece may take the form of an opposing stylus 68 provided with an energizing coil 69 so that current is supplied from the microphone circuit to both coils 61 and 69 to cause magnetic flux to pass from the stylus 56 through the record 62 and to the stylus 68, or vice versa,

the 'return magnetic circuit being completed* through the legs and base of the U shaped stylus netic recording even though vadjacent convolusupport which should be constructed of material having relatively low magnetic reluctance and low magnetic retentivity.

In the form of the device illustrated in Figure 3 the record 62 is constructed solely as a relatively thinv shell of suitable magnetic material having high magnetic retentivity, thickness of the walls of which is preferably such that little or no divergence of the lines of magnetic force will be permitted during the passage ofthe flux from one of the styli to the other. Depending upon the characteristics of the particular material selected for the record cylinder 62 the walls should be made as thin as possible and yet provide suiiicent strength in the walls to retain their cylindrical shape and be self-support- One end of the record 62 is attached to the record support 63 by any suitable means which will support the cylinder for rotation about its longitudinal axis, one form of attachment being illustrated herein as comprising a plurality of spring ngers 18 distributed about the record support 53 and projecting over the outer surface of the record cylinder 62 to frictionally engage the same so that rotation of the record support 53 will cause rotation of the cylinder 62.

If desired the spring fingers 18 may be bent inwardly as shown in Figure 3 to provide projections extending into an annular groove 1| formed about one end of the cylinder 62, and thus prevent inadvertent longitudinal displacement of the record andthe record support. 'I'he end of the record cylinder bearing the groove 1| may be thickened, if desired, as shown at 12.

If desired, the opposite end of the cylinder may be supported and held in horizontal alignment by means of a bearing block 13 rotatably mounted upon the lower leg 65 in which event leg 65 should be constructed as a round rod or shaft upon which the bearing block 13 is readily rotated and along which it may slide The block 13 may be detachably secured to the end of the cylinder 62 as by providing a plurality of spring ngers 14 thereon projecting inwardly of the cylinder 62 to engage a groove 15 formed internally within the cylinder. 'I'hat portion of the cylinder walls bearing the groove 15 may be thickened as is indicated at 16. To prevent undesired magnetic paths the cylinder support 53 and the bearing block 13 should be constructed of non-magnetic material.

In this form of the device the cylinder 62 may be placed in the machine by irst moving the carriage 6| to its extreme left hand position as viewed in Figure 3 and the cylinder 62 may be then pressed between the spring fingers 18 into abutting relation with the cylinder support 53. Then the carriage 6| is moved toward the right to insert stylus 68 and the arm 65 within the interior of the cylinder. The bearing block 13 may be slid along the arm 65 into engagement with the opposite end of the cylinder 62. 'I'he carriage 6| is then moved toward the left to dispose the styli 66 and 68 upon the left hand end portion of the record 62. The dictator may then start dictating and the relative rotation between the cylinder 62 and the styli 66 and 68 and the longitudinal movement of the carriage 6I will cause the styii 66 and 68 to describe a helical path about the cylinder 62 to record the dictated material thereon in the same manner as was described with reference to Figures 1 and 2.

While the styli 66 and 68 may be disposed in spaced relation to the inner and outer surfaces of the cylinder 62, they may be arranged to bear upon and ride directly upon the surface of the cylinder, in which event it may be desirable to mount both of the styli on suitable springs not shown which will cause them to be urged gently against the cylinder surfaces, such moimting of the styli permitting the ready retraction of the stylus 68 as it is withdrawn from the cylinder 82 and passes over the thickened portion 16 thereof.

During dictation any portion of the previously dictated material to which it is desired to listen may be played back by the dictator by merely lifting the feed nut from the feed screw 58 and moving the carriage 5| toward the left to align styli 66 and 68 with such previously recorded material. The coils 61 and 68 may be connected to suitable receiving apparatus by which the dictator may listen to the previously dictated material, in much the same manner as was described with reference to the form of device shown in Figs. 1 and 2.

In Fig. 4 we have illustrated a still further modified form of magnetic recording medium and machine embodying the principles of our invention and illustrating the manner in which the vrecording medium may be constructed in the shape of a disc corresponding in size and shape to the wax disc records now employed in phonographic recording and reproduction. In Fig. 4 we have illustrated our machine as comprising a suitable frame 88 which includes the base 8| from which arises a vertical standard 82 and a second vertical standard 83. 'I'he standard 83 may constitute the bearing mounting for a disc supporting turntable 8l which may be permanently or detachably connected to a centering head 85 secured to or formed integrally with a shaft 86.

The shaft 86 is adapted to be connected for rotation by any suitable power means as by a transmission system illustrated herein as including a bevel gear 81 fixed to the shaft 86 and meshed with a cooperating bevelled gear 88 secured upon a cross shaft 88 rotatably mounted in the uprights 88 and 82. The outer or right hand end of the shaft 88 as viewed in Fig. 4 may be provided with a bevelled gear 88 which in turn meshes with a bevelled gear 8| xed to one end of a stub shaft 82 which is rotatably mounted in the upright 82 and having on its opposite end a gear 83 meshed with a gear 8l rigidly secured to a power shaft 85. Power may be supplied to the power shaft 85 through a suitable pulley 86 and drive belt 81 in the conventional manner now employed for driving dictation machines.

'I'he upper end of the upright 82 is provided with a longitudinally extending beam 88 corresponding in all respects with the beam I3 illustrated and described in the form of the device shown in Figs. 1 and 2, along which is arranged to slide a carriage 88 bearing the recording stylus or styli.

Again it will be noted that the carriage 88 is provided with nut |88 and an operating lever |8| corresponding in all respects to the feed nut 4| and lever 42 shown in Figs. 1 and 2, by which the carriage may be selectively engaged with a feed screw |82 which extends below beam 88.' 'I'he feed screw may be formed integrally with the power shaft 85.

. 'I'he carriage 88 has secured thereto or formed integrally therewith a U' shaped stylus support |03 which may comprise an upper leg |04, a base |05 and a lower leg |00. As illustrated the upper leg and lower leg |04 and |00 should be so located as to be disposed respectively above and below a record disc |01. The upper leg |04 is provided with a recording stylus |00 having a sharp pointed end such as was described for the recording stylus 32 in Fig. I, while the lower leg |06 bears a corresponding stylus |09 aligned with the stylus |00 in the same manner as previously described for the alignment of styli 6B and 00 with reference to Fig. 3. 'I'he styli support |03 should be constructed of material having relatively low magnetic reluctance to constitute a low reluctance magnetic path for ux which may be produced at any point in the magnetic circuit by providing an electro-magnetic coil H0. illustrated herein as extending about the base portion |05 of the U shaped styli support |03.

One convenient manner of mounting the coil ||0 is illustrated herein as by constructing the base |05 of the styli support |03 separate from one of the legs ill or |06 and detachably connecting the same thereto by means of a screw or bolt Ill.

In this form of the device the magnetic record or recording medium |01 may have the shape of a relatively thin but relatively large diameter circular disc, removably mounted on the turntable 8l, and may be constructed in the manner described for the construction .of the record 12 shown in Fig. 3, that is, as a sheet of material of high magnetic retentivity as thin as it is possible to make it and yet be capable of holding its hat disc shape and to be self-supporting, or the record disc |01 may be constructed as shown in Figs. 5 and 6 with a body portion or supporting portion I2, suiliciently thick as to lend rigidity to the disc but provided upon one or both of its faces with a thin layer ||3 and ||3a of materials having high magnetic retentivity so as to adapt it to receive and hold magnetic patterns produced by flux passing between the styli |00 and |09.

In either event the magnetic ux produced by the coil I |0 will pass directly through the recording portion of' the record |01 to record the magnetic pattern corresponding to the dictation.

If the record disc |01 is constructed as an extremely thin sheet of high retentive material the recording made thereon will correspond to the recording made as by the use of a record like that shown at i2 in Fig. 3. however, the record disc |01 is constructed with a body or supporting portion having a thin shell or coating of high retentive material on one face thereof, the body portion H2 should be made of low reluctance material to assist in providing a low reluctance return magnetic circuit to the stylus |08. With the record constructed in this manner the lower stylus |09 may be made as a relatively large area pole piece or may be omitted as shown in Fig. 5, in which event the lower leg |06 of the stylus support |03 may be moved up into close juxtaposition with the disc |01. If, however, asis shown in Fig. 6, both surfaces of the supporting portion ||2 are provided with a highly retentive material ||3 and Ilia the lower stylus |09 will co-act with the stylus |08 to insure the passing of the lines of magnetic flux in a direct vertical path through both of the highly retentive layers on the disc, even through the through the low reluctance supporting portion of the record.

Aswillbeunderstoodbythoseskiliedinthe art of magnetic recording any of the magnetic records shown in Figs. i through 6 may be initially prepared for receiving recordings thereon` by polarizing the records uniformly or by magnetically saturating the records as by passing them through the influence of a strong magnet. so that during the recording of material upon the record the flux passing from or between the various styli will be permitted. to rearrange the molecules of the metal to create a magnetic pattern corresponding to the sound to be -recorded thereon. It will also be understood thatany ot the machines described herein may be used both for dictation and for transcription of previmrsly dictated material without the necessity of moving the records from one machine to another. and that after the material has been transcribed the recordings may be erased by' pasing the records again through the influence of a strong magnetic neld, one manner of erasing such material being illustrated in our co-pending application hereinbefore referred to.-

From the foregoing description it will be apparent that we have provided a simple and economical means for producing magnetic records or recording media which may have the simple, compact shape now employed in the conventional with the same facility with which such wax records are now handled in conventional machines. Our magnetic records however have the additional advantages that the recordings thereon are permanentuntil erased by a magnetic iield and are not subject to consumption by repeated recordings and erasures.

Another advantage which may be achieved by the use of our magnetic records is that any of the previously dictated material is available to be played back without the necessity of re'- versing the operation of the machine or by performing any other complicated rewinding operations which have. heretofore been necessary in attempts to employ magnetic recording for this purpose. The entire recorded material lies upon the surface of the recording medium and is instantly available for playback merely by the shifting of the Styli along the recordto the position at which it is desired to playback the recorded material.

While we have illustrated and described the preferred embodiment of our invention we do not desire to be limited to any of the detail shown or described herein except as denned in the appended claims.

We claim:

1. A magnetic recording medium having the form of a thin sheet of highly retentive magnetic material supported throughout upon a stiifening body of low reluctance magnetic material. said surface having a convolute groove formed therein to guide a magnetic recording stylus in an accurate convolute path over said surface.

2. A magnetic recording medium including a supporting body portion formed as a disc of lowA reluctance magnetic material and a thin coating on at least one of its faces formed of highly lretentive magnetic material.

3. A magnetic recording medium comprising a body portion constructed of low magnetic reluctance material having low magnetic retentivity and carrying a thin surface portion Vof high magnetic retentivity integral with said body portion.

4. A magnetic .recording medium comprising a body portion constructed of low magnetic re luctance material having low magnetic retentivity and having a thin surface portion of harder material to provide a highly magnetically retentive surface integral with said body portion.

5. A magnetic recording medium comprising a soft iron body portion having low magnetic reluctance and low magnetic retentivity, at least one surface of which is provided with a thin, hard surface layer of high magnetic retentivity integral with said body portion.

6. A magnetic recording medium comprising a low carbon content iron body portion having low magnetic reluctance and low magnetic retentivity, at least one surface of which is provided with a thin surface layer integral with said body portion and having a carbon content substantially greater than the carbon content of said body portion to provide a highly magnetically retentive layer.

7. A magnetic recording medium comprising a soft iron body portion having low magnetic reluctance and low magnetic retentivity, at least one surface of which is case hardened to provide an integral surface layer of highly magnetically retentive material.

8. A magnetic recording medium comprising a body portion of para magnetic material and a surface layer integral therewith, said surface layer and said body portion having dissimilar magnetic properties.

9. A magnetic recording medium comprising a body member constructed of low magnetic reluctance material having low magnetic reten. tivity, at least one surface of which has been processed to provide a thin surface layer having high magnetic retentivity.

WALTER P. HUNTLEY. RAY M.A CHENOWETH. EMMETT M. IRWIN.

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