US2925962A - Magnetic core wrapping apparatus - Google Patents

Description

Feb. 23, 1960 c. B. HEBELER MAGNETIC CORE WRAPPING APPARATUS Filed Dec. 31. 1954 2 Sheets-Sheet 1 NVENTOR.

I CHARLES B.HEBELER ATTORNEY United States Patent MAGNETIC CORE WRAPPING APPARATUS Charles B. Hebeler, Yeadon, Pa., assignor to Burroughs Corporation, Detroit, Mich., a corporation of Michigan Application December 31, 1954, Serial No. 479,130 1 Claims. (Cl. 242-74) This invention relates generally to means for forming coils or wraps of strip material, and, more particularly to an improved method of and apparatus for wrapping strips ofmagnetizable material onto spools or bobbins to form magnetic cores.

One type of storage device that is employed in computers and the like is a magnetic core which takes the form-of a non-magnetic spool or bobbin having a hollow center or bore and provided with one or more wraps of magnetizable material secured about its center. Multiple toroidalwindings of electrically insulated wire may also be disposed on the core in order to'permit its utilization in associated electrical circuitry.

The smaller the magnetic core the less electrical power is required to drive the core and consequently the fewer the electrical windings required. However, as the core size is decreased efficient machine application of the magnetizable wrap to the core becomes a practical impossibility, utilizing presently available apparatus. Hand wrapping of the cores, which is presently practiced to a large extent, is not adaptable tomass production ,due to the small size of the bobbin and the difficulty of engaging the leading or starting end of the wrapping material about-the center of the spool or bobbin. The utilization of glue, pressure sensitive tape, or a slot in the center of the bobbin as a means of attaching the wrap is also impractical due to the extreme difficulty in handling the small size bobbins.

An important object of the present invention therefore is to provide means for Winding magnetic coreswhi'ch overcomes the above-mentioned problems.

Another important object of the invention is to provide electromagnetic means forwinding miniature and subminiature cores.

Another important object ofthe invention is to provide an improved method of and apparatus for forming magnetic cores wherein a magnetic flux is utilized to maintain proper winding tension on the wrapping material during fabrication of the magnetic core.

A still further object of the invention is to provide means whereby a magnetic flux path 'which is induced across an air gap is caused to tightly attract a magnetiz able wrapping material to the hub ofa bobbin or spool supported therein. Q i

Fig. l is a view in side elevation, partially broken away, of one embodiment of the invention showing certain operational features of the device;

Fig. 2 is a fragmentary perspective view of the upper portion of the device of Fig. 1 showing the magnetic means for attracting and aligning the inagnetizable wrap on a bobbin;

Fig. 3 is a fragmentary view in side elevation, partially broken away, of the lower end portion of the device of Fig. 1 showing various. operating subassemblies of the invention; 1

Fig. 4 is an enlarged view of the spot welding unit of Fig. 1 showing the electrode tensioning assembly in more detail;

2,925,962 Patented Feb. 23,

Fig. 5 is a schematic viewof the core winder magnet assembly of the invention showing the magnetic flux path through a bobbin in the course of having a magnetizable strip wrapped therearound;

Fig. 6 is a top plan view, partially in section, of a portion of the device of Fig. 1 drawn to an exaggerated scale to show certain internalfeatures of the bobbin supporting and winding structure;

Fig. 7 is aschematic view illustrating anotherand different embodiment of the invention;

Fig. 8 is a side view, partially in section, of a further embodiment of the invention; and

Fig. 9 is a view in side elevation, partially in section, of a still further embodiment of the invention and showing a demountable magnet bobbin mounting means.

Throughout the respective views likereference characters are used to identify similar features in order to simplify comparison. Accordingly, the magnetic core wrapping apparatus of Figs. 1 through 6, inclusive, are discussed simultaneously. I

The apparatus comprises a number of component parts which are generally identified as a bobbin mounting head or fixture 10, a counting mechanism 12 for counting the number of wraps applied to the bobbin, a supply reel 14 of magnetizable wrapping material, a coating device 16 for applying an electrically insulating coating to the mag netizable material as it is applied to the bobbin, and a spot welding device 18 for final securement of the wrapped strip inplace on each bobbin. v

The component parts of the apparatus are shown mounted on an appropriate supporting structure including a table or base 11 upon which is mounted a vertically extending front plate 13 and a rearwardly extending vertical plate 15 which perpendicularly abuts the center portion of the front plate. This construction provides excellent structural rigidity without necessitating the use of multiple massive supporting members. The supply reel 14 containing a supply of magnetizable' wrapping material in the form of a thin, narrow metallic foil 20 isrotatably mounted on a shaft or hub 22, Fig. 3, disposed in the frame or front plate 13. The reel 14 is detachably secured to the hub or shaft 22 by any suitable means such as the nut 24. A'fiexible tensioning member for maintaining a predetermined tension on the reel hub comprises an elongated spring clip 26 of brass or other similar material. The spring clip 26 is fastened by means of a bolt 28 to the plate 13. The member 26 is bent out of its normally horizontal plane slightly so as to be urged under constant tension inwardly against the intermediate portion of the shaft 22, Fig.3. Adjustment of the spring clip 26' is provided by means of the bolt 33 threaded to the supporting block 32 on the plate 13. Rotation of the bolt causes the spring clip 26 to be flexed thus producing more or less tension against the shaft 22 as desired.

The-magnetic wrapping assembly as shown in Fig. 2 of the drawing comprises a jig or fixture indicated at 101 The jig 10 consists generally of a U-shaped magnet 34' having two parallel leg portions 46 and 48 and a base leg 40. An energizing winding 36 for the magnet 34, which may be electrically connected to a suitable source of potential -over the leads 38, surrounds the base leg 40 of the magnet. A pair of oppositely disposed, inwardly facing'and axially aligned poles 42 and 44 forming an air gap 45 are mounted, one to each one of the parallel legs 46 and 48, respectively, of the magnet 34; The pole 42 is displaceable or movable horizontally in the fixture 10 so that the relative spacing between the two poles, and thus the air gap, may be varied at will. This latter construction permits the air gap to accommodate various size bobbins which may be inserted within it.

In those applications wherein magnetic cores are used as storage or switching elements, the number of wraps of magnetizable material which is placed on the core bobbin is extremely critical. Any variation from a predetermined number of turns or wraps deleteriously effects the magnetic characteristics, i.e., alters the shape or rectangularity of the hysteresis loop of the core. To offset this problem the number of turns must be accurately counted during the bobbin Wrapping operation. A counting mechanism of any suitable type, such as the lever actuated rnicroswitch 50 illustrated in Fig. 2, may be used. The rnicroswitch 50 is secured to the outwardly facing side wall of the plate 13 and is provided with an actuating lever 52 which projects from an aperture 54 in the body of the switch.

The lever 52 is disposed in the path or are of travel of the enlarged end portion 55 of a handle 56. As the handle is rotated by the operator the end 55 will periodically strike the actuating lever 52. The switch contacts (not shown) are thus closed and in this manner the electrical output of the switch can be utilized to actuate a mechanical counting mechanism of any conventional type such as the mechanical counter 12, Fig. 3. A typical counter may comprise a rotary number wheel device which is caused to step once in a clockwise direction for each switch closure. This action causes a successive series of individual digit wheels to be brought into view and to indicate to the operator the exact number of turns or wraps of material which have been placed on a bobbin.

The magnetizable material may comprise a ribbon or foil of molypermalloy or other similar magnetizable material which may vary in thickness from mil to 1 mil and in width from less than /3 inch to /2 inch. This material is subject to deformation and breakage from rough or careless handling. Since the ribbon or foil must first be laid or placed by hand around the hub or center of the bobbin or spool, it is desirable to prevent the Wrap from becoming attracted to other magnetic portions of the wrapping apparatus. It is necessary therefore that the leading end of the foil be immediately placed around the bobbin hub. Also, once the wraps are placed on the bobbin and the excess foil is cut away, the loose end of the foil must not be permitted to fall by its own weight or become entangled in other parts of the apparatus.

In order to support the magnetizable ribbon and prevent its loss during the wrapping operatio'n, a small permanent magnet 58 is mounted on the plate 13. This magnet projects outwardly, laterally directly into the path of the foil wrap as it is unwound from the supply reel 14. The magnet 58 may be secured to the side frame in any suitable manner such as by means of a bolt 60. A fiat portion or surface 62 which faces outwardly toward the wrap provides a relatively large attractive surface for the foil 20.

Each one of the several individual turns or layers of magnetizable material must be insulated from the adjacent layers or turns during the core wrapping operation in order to eliminate deleterious effects due to eddy'currents. An insulating coating material is providedby a prepared mixture of magnesium oxide in oil. The co'at ing device 16 comprises a vat or container 64 which is disposed on the base or table 11 by means of screws 66. In order to maintain a smooth and automatic coating operation an idler pulley 68 is rotatably mounted on a shaft 70 within the vat, a slight distance below the top edge of the vat so that the wrap is obliged to encircle the pulley and thus become immersed in the insulating coating material. In this way a uniform coating of relatively constant thickness can be automatically applied to the wrapping material.

Since each of the completed magnetic co'res must be provided with a predetermined and exact number of wraps of magnetizable material, it is therefore necessary to prevent any accidental dislodgment of wraps due to careless or rough handling of the finished core. Care must also be taken to see to it that only the final two turns of the magnetizable wrap are secured together in order to prevent destruction of the magnetic properties of the core and/or to avoid the danger of short circuiting the core when it is placed in use. Since the wrapping material is metallic a small electrical spot welding unit is or may be utilized for this operation.

The spot welding device 18 comprises an insulating bracket member 72, Figs. 2 and 4, which is secured to a handling member 74 having an extension 75 by means of screws 76. The handling member is pivotally mounted on one end of the base leg 40 of the magnet 34. A pair of electrodes 78 and 80 are disposed in individual bores 81 and 83 drilled in the bracket 72. The electrode 78 is slidably reciprocable in the member 72 to permit proper contact pressure o'f the electrode against the article being welded to be maintained during the welding operation. The member 72 is shown as being of V-shaped configuration to permit ease of fabrication and installation and to provide proper mechanical clearances for visual inspection.

The electrode 78 comprises an elo'ngated conductive member having an integral flange 82 intermediate its ends. The flange 82 is seated upon a ridge 84 internally of the bore 81. One end of the electrode is threaded as at 85 while the opposite end thereof is shaped to a slightly rounded point as at 86. A coilspring 87 surrounds the shank'of the electrode and is compressibly retained be tween one end of .a press fit bushing 88 and the upper portion of the flange 82. The spring 87 urges the elec' trode outwardly from the bore of member 72. Set screws 89 and 90 provide individual locking means for the respective electrodes. It can be seen that the electrode configuration shown in Fig. 4 enables two relatively small spots of weld (black dots), Fig. 4, to be placed on the terminal wrap of the foil 20 disposed on a bobbin without the annoying problem of over weld" into adjacent wraps or layers. The two electrodes may be energized from'a D.C. source (not shown) over the leads 92 and 94 through the contact caps 96 and 98 secured to their respective electrode.

Referring now to Fig. 5 of the drawings, there is shown a schematic diagram illustrating the path of the magnetic lines of flux 104 in the U-shaped magnetic member 34 as a result of the application of an energizing potential to the coil 36. It can be seen that a portion of the fiux is normally driven through the air gap 45. The air gap path, however, is one of high reluctance. If a magnetizable element such as the magnetizable foil wrap 20 is introduced into the air. gap by placing the starting turn of the wrap on a nonmagnetic bobbin or spool 95 which has been secured about or within the air gap, the magnetic flux 104 will try to avoid the air gap path and flow through the wrap, asindicated by the dotted lines at 106, since this is now a lower reluctance pathway. The metallic wrap 20 will in this manner be attracted toward the air gap and thus toward the hub of the bobbin since the magnetic flux tends to effect the path of least reluctance. The wrap of foil' is in this manner effectively held by magnetic attraction to the hub of the bobbin so that now the core winding operation can proceed just as rapidly as the operator-can rotate the operating handle of the core winder; h

The magnetic circuit-elements comprising the magnetic poles 42 and 44 of the core winder are substantially symmetrical about a center line running through the axis of the poles in the vicinity of the bobbin 95. It is at once apparent therefore that the leading end of the magnetizable wrapping material can be placed at any point around the bobbin circumference at the convenience and discretion of the operator and'the attractive force of the magnetic field of the magnet 34 will be of sufiicient strength to effect a tight attraction for the wrap.

The electrical circuits with'which magnetic cores are generally used vary to a considerable degree one from another and as a result various size co'res must be utilized toprovidedifierent types of desired electrical operation. The arrangement set forth in Fig. 6 of the drawings illus trates a preferred embodiment of a core winding apparatus incorporating the present invention which enables an operator to quickly and efliciently change the core bobbin sizeas desired. 7

The-base leg 40 of the magnet 34 may be a solid cylinder or shaft about which the earlier-mentioned welding unit 18 is pivoted at 110 by means of the bolt 112 and washer 114. The two parallel leg portions 46 and 48 extend outwardly from the base leg 40. The right leg 48, as viewed in-Fig. 6, fixedly supports the magnetic pole 44 which is or may be pressed fit thereto by means of the shaft 116 integral therewith. In order to adapt the magnetic core winding apparatus for varying size bobbins the opposite leg 46 is drilled to provide an aperture 118 through which the pole 42 is slidably received.

A hollow sleeve 120 having-a flange 128 is provided with an aperture 122 through which the pole 42 is received. The sleeve is secured to the leg 46 by means of screws 136 through the flange 128. A coiled spring 124 is mounted within the sleeve 120 under tension and is urged against one end of the sleeve and a flange 126 integral with the pole 42. A second flange 138 also integral with the pole 42 and disposed adjacent to the flange 126 is adapted to abut the side of the leg 46 at the rim of the aperture 122. The flange 138 provides a positioning stop member for adjusting the relative air gap width. The handle 56 provided with a rotatable member 130 is secured to the end of the pole 42 by means of a screw 132 and a centering pin 13 4.

It is apparent from the foregoing that the pole 42 is now permitted a limited amount of movement axially of the pole 44 by displacing the handle 56 a slight distance to the left as shown in dotted outline in Fig. 6. Varying width bobbins may now be conveniently received between the two poles and the versatility of the winding apparatus is measurably enhanced thereby.

In order to concentrate the flux created by the energizing winding 36 each one of the two poles 42 and 44 is frusto conical in shape. The extreme end portions of the poles in the vicinity of the air gap are reduced as at 140 and 142 to further concentrate the flux. The reduced end portions have an outside diameter slightly less than the inside diameter of the hub of the bobbin or spool. The bobbin can thus be simply and easily loaded onto and removed therefrom.

Inasmuch as the coil 36 which is used to generate the magnetic flux is placed in a remote area some distance behind or away fro-m the air gap 45 and thus some distance from the bobbin 95, Whatever heat may be generated by the coil will not be transmitted into the bobbin wrapping area and thus will have little or no effect on the magnetizable wrap '20 which is placed around the hub of the bobbin. A further advantage of situat-ing the coil remotely from the bobbin is that the pole tips can be physically shaped, as before-mentioned, in the vicinity of the air gap which greatly increases the flux density at the pole tips up to the saturation point without saturating the remaining circuit elements of the core wrapper.

Since it is not desirable to keep the magnetic circuit elements in a constantly energized condition while changing bobbins, due-to the heat generated by the magnetizing coil, it is necessary to provide some means for either removing the energizing current from the coil as by a switch, or of shunting or bypassing the magnetic flux in a direction so as to avoid constant saturation of the pole tips.

The embodiment set forth in Fig. 7 illustrates one means of providing a shunt path for the magnetic flux. This structure comprises a pair of magnetic members 150 and 152 which are shaped or tapered in the vicinity of the air gap as before. The magnetic circuit for this arrangement comprises the base leg 154, two parallel legs 156 and 158 and a cross arm 160 rotatablypivoted by means of a bolt 164. The normal flux path generated by the energizing winding 155 is completed through the pole tips and 166. When it is desired to shunt the flux away from the air gap the cross arm 160 is rotated 90 degrees to the position shown in dotted outline so that the magnetic force is reduced substantially to zero at the pole tips. The flux path is thereby caused to bypass the air gap and to take the path of least reluctance through the cross arm 160. It is at once apparent that this modification provides a relatively simple means for cutting off the magnetic flux as desired. The shunt technique also avoids the use of external switches and electrical circuitry while at the same time providing convenient and simplified operational means for de-magnetizing the air gap area.

Fig. 8 illustrates a further embodiment of the magnetic core wrapperv of the present invention. In this modification a pair of inverted L-shaped permanent magnets and 172 are disposed on aframe or table 174 with the base portions thereof facing towards each other and slightly separated so as to form an air gap 176 therebetween. The end portion of each of the magnets has secured thereto, by any suitable means, a pole piece 178 and 180 respectively. The pole pieces are shaped or reduced as shown to concentrate the flux in the air gap and to effectively mount a bobbin 95'. Insulating washers or shims 182 and 184 may be employed to permit accommodation of varying bobbin sizes. The shims can be slipped over the reduced ends of the pole pieces to fill up the space between the shoulder of the pole piece and the pole tip.

The foregoing modification provides an efiicient means for avoiding the requirement of an energizing coil to provide the magnetic flux forthe core wrapper. It is thus relatively less expensive than the earlier described electromagnetic apparatus.

In Fig, 9 there is shown another and different embodiment of an electromagnetic type bobbin wrapping apparatus. The apparatus takes the form of an enclosed circular or ovoidal magnetic member comprising two substantially U-shaped elements, which is provided with a hinge 192 and a pair of poles 194 and 196 defining an air gap 198. An energizing winding 200 provides means for producing a magnetic flux path across the air gap 198. A miniature bobbin or spool 95" may be mounted or demounted as before quite readily within the air gap by simply opening the magnet at the hinged portion. This structure provides a relatively inexpensively fabricated unitary assembly which lends itself quite well to magnetic core wrapping techniques.

There has thus been described a novel magnetic core wrapping apparatus which utilizes a magnetic flux to attract and secure the starting winding of a magnetizable wrap upon a small bobbin or spool. The wrapping ap paratus herein described avoids the limitations of earlier winding devices wherein a slotted hub, pressure sensitive tape, or glue was used to attach the initial or starting ing wrap to the bobbin or spool.

What is claimed is:

1. Core winding apparatus for applying thin magnetizable coil wraps to non-magnetic core bobbins or spools comprising, a supporting frame, a magnetic structure mounted on said supporting frame, said magnetic structure including axially aligned confronting pole pieces forming an air gap therebetween, said pole pieces being shaped to mount a core bob-bin thereon for rotation about said air gap and for concentrating magnetic flux through said bobbin, and means for rotating said bobbin in said air gap.

2. Core winding apparatus for applying thin magnetizable coil wraps to non-magnetic core bob-bins or spools comprising, a supporting frame, an electromagnetic structure mounted on said supporting frame defining a. sub

stantially closed magnetic loop, said electromagnetic structure including axially aligned confronting pole pieces forming an air gap therebetween, means for energizing said electromagnetic structure in order to create a magnetic flux across said air gap, said pole pieces being shaped to mount a core bobbin thereon for rotation about said air gap and for concentrating said magnetic flux through said bobbin, means secured to said structure for adjusting the size of said air gap at will, and means operatively engaging one of said pole pieces for rotating said pole piece and said bobbin.

3. Apparatus for wrapping magnetizable material on an annular body having an axial bore comprising, an electromagnetic member defining a substantially closed magnetic loop having oppositely disposed axially aligned pole pieces defining an air gap, said air gap having a dimension less than the axial dimension of the annular body to be wrapped, said pole pieces having a radial dimension such that they may be received within the bore of said annular body and support said body, means disposed on said electromagnetic member capable of producing a uni-directional magneticflux across said air gap and through said body whereby said magnetizable wrapping material may be drawn tightly against said body, and means to rotate said body within said air gap so that said wrapping material may be wound therearound.

4. Core winding apparatus for wrapping a web of magnetizable material on a non-magnetic bobbin or spool comprising a magnet structure having two axially aligned pole pieces disposed in confronting relation and defining a high reluctance air gap therebetween, the pole pieces in the vicinity of said air gap being of reduced diameter to form a mounting for journalling said bobbin for rotation thereon, electrical windings disposed on said magnet structure and adapted to produce a uni-directional flux path across said air gap so that a portion of said magnetizable web when placed adjacent thereto is magnetically attracted to the hub of said bobbin by reason of the lowered reluctance path across said air gap afforded by said web, and means for rotating said bobbin.

5. Core winding apparatus for wrapping a web of magnetizable material on a non-magnetic bobbin or spool comprising a magnet structure including two separated portions having inwardly turned ends, two axially aligned polepieces in confronting relation and defining a high reluctance air gap therebetween, the pole pieces in the immediate vicinity of the air gap being of reduced diameter to form a mounting for journalling said bobbin for rotation thereon and for concentrating magnetic flux through said bobbin, electrical windings disposed on said magnet structure for producing a uni-directional flux path across said air gap and through said bobbin whereby a portion of said magnetizable web when positioned adjacent thereto is magnetically attracted to the hub of said bobbin by the lowered reluctance path acrosssaid air gap afforded by said web, normally inoperative magnetic shunt means mounted between-said separated portions of said magnet structure and movable to a position reducing the magnetism in said flux path substantially to zero, and means for rotating said bobbin.

6. Core winding apparatus for wrapping a web of magnetizable material on a non-magnetic bobbin or spool comprising, a magnet structure including a pair of inverted L-shaped elements, one end of each one of said elements being shaped to provide pole pieces disposed in confronting axial alignment defining a high reluctance air gap therebetween, the pole pieces immediately adjacent the air gap being of a diameter to form a mounting for journalling said bobbin for rotation thereon, said magnet structure being such as to produce a unidirectional magnetic flux path across said air-gap so that a portion of said magnetizable web when placed adjacent thereto is magnetically attracted to the hub of said bobbin by the lowered reluctance flux path across said air gap afforded by said web, and mean for rotatably applying said web to said bobbin.

7. Apparatus for wrapping magnetizable material on an annular body having a bore comprising, an ovoidal magnetic member including two substantially U-shaped elements hinged together at one end and having their other ends forming oppositely disposed axially aligned pole pieces defining an air gap, said air gap having a dimension less than the axial dimension of the annular body, said pole pieces having a radial dimension such that they may enter the bore of said body and support said body during the application of said magnetizable wrapping material thereto, means disposed on said magnetic member capable upon energization thereof of producing a uni-directional magnetic flux across said air gap, and means for rotating said body.

References Cited in the file of this patent UNITED STATES PATENTS

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