US2914621A - Electromagnetic transducer - Google Patents

Description

Nov. 24, 1959 J. L. J. DONCEEL ETAL 2,914,621 ELECTROMAGNETIC TRANSDUCER Filed Aug. 29, 1957 Inventor J-L.J.:Doncee\ H.Vqn Ae r Merck A ttorne'y 2,914,621 ELECTROMAGNETIC TRANSDUCER Jules Louis Joseph Donceel and Henri Cornelius Johannes van der Harck, Antwerp, Belgium, assignors to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware Application August 29, 1957, Serial No. 681,018

Claims priority, application Netherlands September 5, 1956 1 Claim. (Cl. 179-1002) The invention relates to an electromagnetic transducer or magnetic head designed to permit recording on a magnetic member such as tape or drum, and also to permit the reading of information previously recorded on such member.

This invention relates particularly to magnetic heads using a magnetic core made of a single magnetic member shaped as a ribbon (at least in the vicinity of the record medium) and bent in the form of a partially closed loop, the ends of the ribbon defining a non-magnetic gap. One or more coils are mounted on the ribbon, and the whole assembly is mounted in a non-magentic housing.

Such magnetic heads are described in the US. Patent Nos. 2,469,444 and 2,674,031 as well as in Belgium Patent No. 525,092.

A general object of the invention is to provide a magnetic head of the above type which is particularly adapted to being produced in large quantities and within given tolerances.

Another object of the invention is to provide such a magnetic head assembly having an overall thickness approximating the width of the magnetic ribbon.

Another object of the invention is to provide a magnetic head assembly adapted for use as an interchangeable unit for a multiple head assembly composed of several such untis closely stacked together.

Another object of the invention is to provide a magnetic head assembly including a separate sub-assembly for terminal strips to be lodged in the main housing.

In accordance with the invention, an electromagnetic transducer, or magnetic head, comprises a magnetic core such as a thin ribbon bent into a partially closed loop with the flat ends thereof separated by a narrow nonmagnetic gap, a coil, or coils, mounted on said ribbon, a non-magnetic housing for said ribbon(s) and coil(s) adapted to squeeze said ribbon ends together and ground and/or lapped next to said ribbon ends to adjust their separation to the desired value. I

In accordance with an aspect of the invention the housing is in the form of a thin non-magnetic block provided with a recess, adapted to house the whole of said ribbon, and terminating as a slot of a depth equal to the width of the ribbon and adapted to house the ends thereof. The central part of the recess houses the coils mounted around the ribbon and the remaining part of the recess houses an insulated flat terminal strip having a thickness equal to the width of said ribbon. The terminal strip is fixed to the housing and is formed of two layers with inside recesses adapted to sandwich securely the external electrical terminals, on which the ends of the thin coil wires are attached. An insulated core former member is squeezed inside the loop so as to press firmly the ends of the loop on the inside of the slot and the opposite central part of the loop against the inside edge of the terminal strip.

Although U.S. Patent No. 2,469,444 discloses a housgap.

ing in the form of a cup-shaped receptacle for the ribbon, constituting the core of the head, the latter is only fixed in said housing at the proximity of the non-magnetic gap. This applies also to the arrangement disclosed in the Belgian Patent No. 525,092. In the US. Patent No; 2,674,031 the mounting block used also houses the ribbon core member only in the vicinity of the non-magnetic In this latter mentioned patent, means are also disclosed for holding the external electrical terminals, but these are secured with the help of the coil formers. In the same patent, a ceramic core former is secured to the block by means of a ceramic pin. Finally, in US. Patent No. 2,662,120, not previously mentioned, but relating to magnetic heads using laminae, a core former is not used but a spring external to the core configuration is designed to place the latter into position.

In accordance with another feature of the invention, an electromagnetic transducer or magnetic head as described above, is further characterized in that the part of the recess designed to house the coils extends through the block, whereby the openings provided house not only the coils of the head mounted in the block but also, in the case of a plurality of closely stacked heads, the protruding part of the coils of the head mounted in the next block.

The multiple magnetic heads adapted for simultaneous multi-channel operation are in themselves known from US. Patent 2,751,440. In that patent a construction consisting of a plurality of thin stacked single channel units which are complete in themselves is disclosed. The disclosed units carry their own terminals and are interchangeable within a particular multiple head.

The above-mentioned and other features and objects of this invention will become apparent by reference to the following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is an elevation view of the magnetic core and of the coils used in the magnetic head of the invention;

Fig. 2 is an end elevation view of the structure shown in Fig. 1;

Fig. 3 is an exploded view of the terminal strip arrangement for the magnetic head of the invention;

Fig. 4 is a perspective view of the main mounting block designed to house both the structure of Figs. 1, 2, and 3; and

Fig. 5 is an elevation view of the complete magnetic head assembly.

Referring to Figs. 1 and 2, the magnetic circuit comprises a magnetic core 1 which may be in the form of a ribbon having a thickness of the order of 0.2 mm. and a width of the order of 1.2 mm. This ribbon is made of high permeability magnetic material such as Permalloy. As shown, the ribbon 1 is bent in the form of a closed loop, right angle folds being provided at 2 and 2, and oblique folds at 3 and 3, the two ends of the ribbon merging together at 4 to form a tail 5. This tail 5 is useful in mounting the magnetic circuit on the mounting plate shown in Fig. 4 and which will be described later. Although a ribbon with a rectangular cross section is shown, another cross-section, e.g. round, might be used, provided the ends of the magnetic core are flattened in the zone which will define the nonmagnetic gap.

Two coils 6 and 6', including their formers, may he slipped on respective legs of the ribbon 1 as shown.

The assembly of the coils and of the core may be made in various ways. The ribbon may initially be bent at 2 and 2' only, this operation being followed by 'slipping of the formed coils on the respective legs, and then shaping the tail of the ribbon as shown in Fig. 1,

Alternatively, the ribbon 1 in its initial straight shape may be folded on itself at its middle to constitute the tail 5, this operation being followed by the separation of the two legs at 4, by bending at 3 and 3', by slipping the formed coils on the respective legs and by bending at 2 and 2, the length of the ribbon being sufli cient to ensure an overlap of the two ends between 2 and 2'. The overlapping ends may then be squeezed together with the help of a small connecting part enclosing the overlapping ends of the ribbon to secure a low reluctance joint.

Alternatively, one may start with the ribbon in two separate parts, one for mounting each coil, all the bends shown in Fig. 1 except those at 2 and 2 being already made before the formed coils are slipped on the respective legs. This operation is then followed by bending at 2 and 2' and the overlapping ends may be joined as explained before. If desired, one can also use this last method including the additional step of bending at 2 and 2 previous to the mounting of the coils which would then have to be wound on the respective legs, a central joint to unite the ends of the ribbon being made as before. The provision of all the folds previous to the mounting of the coils has of course the advantage of avoiding bending the magnetic ribbon after annealing.

The first sub-assembly of the core and the coils having been explained, the second sub-assembly constituted by the terminal strip as shown in Fig. 3 will now be described. A lower plate 7 with a central hole 8. is provided with two recesses 9 and 9' shaped as shown. An upper plate It} is also provided with a central hole 11 and with recesses 12 and 12' substantially corresponding to those in the lower plate. Both plates are made of insulating material and are designed to enclose the external electrical terminals 13 and 13' which are pieces of wire each bent at one of its ends, these bent ends being flattened at 14 and 14 into a shape adapted to fit into the central part of the recesses 9 and 9. Through the grooves 15 and 15 respectively, the ends 16 and 16' of the coils shown in Fig. 1 are inserted. In this manner, the very thin wire forming the coils and which is quite fragile may be secured to the external terminals. After connecting the ends of the coils to the ends 14 and 14' of the terminals, the latter will be firmly clamped inside the terminal strips by pressing together the lower and upper plates. The plates may be pressed together by a screw 17 extending through holes-11 and 8 designed also to attach the terminal strip sub-assembly to the main base plate.

The base plate is shown at 18 in Fig. 4. Apart from two holes 19 and 19' used in the assembly of several such base plates the central portion is recessed at 20 as shown. The recess 2% is designed to accommodate the terminal strip sub-assembly, the screw 17 engaging a tapped hole 22. Base plate 18 is made of nonmagnetic material such as brass and the narrowing part 23 of the recess, terminating into a slot 24, houses the tail 5 (Fig. l) of the magnetic ribbon. At 25 and 25', the recess extends through the base plate 18 to provide sufiicient space for stacked formed coils where several magnetic head assemblies are combined along a direction parallel to the axis of the hole such as 19. Independently of the use of one or more magnetic head assemblies, the holes such as 19 may always serve to mount the assembly on any suitable support.

Fig. 5 shows the complete assembly of the parts already described with the help of the previous figures. The hole it through which passes the scren 17 is preferahly bored to permit the head of this screw to be flush with the upper face of the base plate 28 so that adjacent units may be pressed-against one another.

T he construction described lends itself to high manufacturin-g precision of the order of 0.005 mm. by using precision jigs.

Mounting of the various elements is preferably made in the following manner. Before mounting the core and coil assembly shown in Fig. 1 on the base plate 18, an insulating core former 26 is properly positioned as shown in Fig. 5. This core former 26 closely bears upon the magnetic ribbon. l and particularly against the central part thereof. In Fig. 5, the ribbon core 1 is shown to have been made out of two parts with the ends between the bends 2 and 2' overlapping onean other and enclosed by a joining member 27. The member 2.7 is in the form of a small piece of ribbon material bent on itself so as to enclose the overlapping parts of the ribbon core. At its opposite end, the core former 26 is shaped at 28 so as to closely contact the parts of the magnetic ribbon ending into the tail 5'. The core former 26 is provided with a thin groove 29 through which the part of the windingwire joining the two coils 6 and 6' may be inserted. The core former 26 is surrounded by a very thin ribbon of insulating material 30 which terminates into a tail 31 projecting somewhat beyond the tail 5 of the ribbon core. This permits a double thickness of thin insulation material to separate the parallel parts of the magnetic tail 5. Thus, provided with its former, the coil and core sub-assembly may be inserted in the recess provided in the base plate 18' with the tail 5 fully inserted into the slot 24. The terminal strip may now be mounted as shown so as to rigidly define the position of the core and coil subassembly.

A multiple head arrangement may be produced by stacking the assemblies in alignment. Due to the openings 2S and 25 the coils 6 and 6' project somewhat above the upper plane of the base plate 18. This is due to the magnetic core ribbon-having a width exactly equal to the depth of the main recess. Thus, the coils extend into the corresponding. openings of the next head unit which is directly on top of the head considered.

A single or a multiple magnetic head unit having thus been obtained, plastic material may be used to fill the spaces on the central-recess 2%, by means of the openings 25 and 25' which will afford through channels in the case of a multiple unit. The single multiple assembly may then have its straight edge 32 transformed into the slightly curved edge 32' by a grinding or lapping process. The width of the gap 33 may thus be adjusted to the required value, the tail 5 being cut ofi in this process.

An improved anchoring of the external terminals 13 and 1-3 may be obtained by applying a coating 34 of hard glue in the Zone surrounding the openings in the terminal strip sub-assembly through which these external terminals project.

While the principles of the invention have been described above in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.

What is claimed is:

An electromagnetic transducer comprising a magnetic core in the form of a ribbon, said ribbon being arranged to define a loop, the ends thereof being fiat, and the flat portions being oppositely disposed and separated to define a predetermined narrow non-magnetic gap, a pair of coils mounted on opposite legs of said loop, a non-magnetic housing for said ribbon and coils adapted to maintain said. ribbon ends in given spatial relationship, characterized in that said housing'is' in the form of a thin block and is provided with a recess having a pair of opposite walls symmetrically inclined toward an edge of said block, the inclined walls terminating at the edge to define a narrow slot, said ribbon ends being snugly mounted in said slot, said coils being mounted in the central part of said recess, an insulated terminal strip having thickness approximately equal to the width of said ribbon, fixed to said housing in the remaining part of said recess, a pair of electrical terminals mounted to said strip, means connecting the ends of the coil wires to said terminals, an insulated core former member mounted snugly into said loop and shaped to press the ends of said loop against said inclined walls and to press the opposite central part of said 100p against the inside edge of said terminal strip, and the peripheral edges of said insulating core former being surrounded by a thin strip of insulating material with the ends thereof extending between said opposing flat ends of said ribbon, thereby determining the separation between said ribbon ends.

References Cited in the file of this patent UNITED STATES PATENTS Buhrendorf Apr. 15, 1952 Bauer Sept. 1, 1953 Holmes Nov. 3, 1953 Munro Feb. 9, 1954 Buhrendorf Apr. 6, 1954 Zenel Feb. 14, 1956

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