US2784690A

US2784690A - Bobbin-canister gripper arrangements for sewing machines

Info

Publication number: US2784690A
Application number: US413693A
Authority: US
Inventors: Brandt Kurt
Original assignee: Individual
Current assignee: Individual
Priority date: 1953-04-09
Filing date: 1954-03-02
Publication date: 1957-03-12
Anticipated expiration: 1974-03-12
Also published as: GB747528A

Description

March 12, 1957 K. BRANDT 2,784,690

BOBBIN-CANISTER GRIPPER ARRANGEMENTS FOR SEWING MACHINES Filed March 2, 1954 4 Sheets-Sheet 1 INVENTOR: KW'T Bra- 0 d1 March 12, 1957 K. BRANDT 2,784,690

BOBBIN-CANISTER GRIPPER ARRANGEMENTS FOR SEWING MACHINES Filed March 2, 1954 4 Sheets-Sheet 2 INVENTOR. Ku k1 Bra. r /f March 12, 1957 BRANDT 2,784,690

BOBBIN-CANISTER GRIPPER ARRANGEMENTS FOR SEWING MACHINES Filed March 2, 1954 4 Sheets-Sheet 3 FIG. /7 I 6. /6

INVEN TOR. KurT Bram/f had i M March 12, 1957 K. BRANDT 2,784,690

BOBBIN-CANISTER GRIPPER ARRANGEMENTS FOR SEWING MACHINES Filed March 2, 1954 4 Sheets-Sheet 4 INVENTOR: Ku PT 8 Ya. zdl

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United States Patent BOBBIN-CANISTER GRIPPER ARRANGEMENTS FOR SEWING MACHINES Kurt Brandt, Augsburg, Germany Application March 2, 1954, Serial No. 413,693

Claims priority, application Germany April 9, 1953 26 Claims. (Cl. 112-188) Most sewing machines operate with stay-grippers. Stay grippers have resilient means between the generally swingable stay and the bobbin casing; these resilient means eifect the pushing of the bobbin casing, which is secured from rotary movement by the stay, into the rotating gripper. This arrangement of resilient elements has not proved to be a desirable and absolutely reliable solution in all cases; in addition, owing to the space occupied, the arrangement in question cannot be regarded as very appropriate in view of the very restricted space conditions.

The invention provides remedies by substituting for forces produced by means of the resilient elements, other forces such as are produced by magnetic members. The stay maythen be dispensed with; however, it may be retained for other reasons. i r

In the simplest embodiment of the invention, the gripper formed of magnetisable material and/or the bobbin casing may, for example, be permanently magnetisedto a greater or smaller extent.

Another embodiment provides the arrangement of magnet elements on, at or in the gripper and/or at or on or in the bobbin casing.

The effect of thesaid embodiments is fundamentally such that the attracting magnetic forces tend to pull the bobbin casing into the gripper.

However, another embodiment utilises the mutually repelling effect of like magnetic poles by arranging at least one magnet element in such a manner at, on or in the stay and at, on or in the bobbin casing that the poles that are adjacent in the operative position are like poles. In that case, we are concerned with magnetic pressure forces which tend to press the bobbin casing away from the stay and into the inside of the gripper.

Fundamentally, an air gap which is sufficient for the passage of the thread is left between the bobbin casing (bobbin canister) and the gripper (gripper casing).

Apart from the saving in space and the absolutely reliable action, unallowable backlash is prevented; the noiselessness is considerably more completely realised than hitherto; the passage of the thread in the known manner is not impaired in any way.

Preferably, permanent magnetic elements according to the invention may be used; however, the employment of magnet elements energised by extraneous currents isin no way excluded; the last-mentioned solution renders it possible to obtain, for example by means of variable resistances, a fine variation of the forces produced, which variation can, of course, be dispensed with in most cases.

The invention is represented inthe drawings in a large number of examples of embodiment, but the possible modifications of the principle according to the invention are inexhaustible. r a

As shown in Figure 1, the known rotating gripper 1 is fixed on the gripper shaft 2 bymeans of, for example, a set screw. Inside the gripper is mounted non-rotatably the bobbin casing 3 which is pressed by the closed stay 5, through the intermediary of the helical spring 4, in the direction of the gripper 1. The stay 5 prevents, by means of an anti-twisting device 6, rotation of the bobbin cas ing 3. The open position 5' of the stay 5 is indicated in dot-and-dash lines.

In a construction such as that-shown in Figure 1, the invention can be realised by,- for example, omitting the spring element 4 and permanently magnetising the gripper 1 in order to produce the force which presses the bobbin casing 3 in the direction of the gripper l; this, naturally, presumes the production of the gripper 1 from a mtaerial which permits of permanent magnetisation. Obviously, the bobbin casing 3 may be magnetised instead of or in addition to the gripper 1. 9

in the construction shown in Figure 1, the stay 5 may be dispensed with on employing the invention; however, it may be kept therein for other reasons, but always with the omission of the spring element 4 or of asimilar element.

In the examples of embodiment shown in the remaining figures, the stay has been dispensed with; however, it is possible to rotate a stay or a similar element if other reasons or other purposes appear to render it desirable; however, in such cases the stay has rather the function of pressing the bobbin casing (bobbin canister) into or to the gripper (gripper casing) by means of a spring.

As shown in Figure 2, the gripper ll may be equipped with one or more annular magnet elements 7 which are preferably in the form of perforated discs or laminae and the diameter of which is preferably equal to or smaller than the greatest diameter of the gripper 1. The division of the magnet member into laminae renders possible a sufficiently variable though stepwise, alteration of the magentic forces which tend to press the bobbin casing 3 into the interior of the gripper 1.

As shown in Figure 3, the gripper 1 may have a plurality of bores 8 distributed at approximately equal distances on an imaginary basic circle, these bores being arranged with their axes parallel to the shaft 2 of the gripper in the wall of the gripper 1, that is perpendicular to the shaft 2 of the gripper. These bores 8 house, directly or by means of an interposed insulating jacket (pressboard; a synthetic plastic or the like), pressed-in cylindrical barmagnet elements 9. A magnetic insulation (not shown) of the cylindrical walls of the elements 9 from the insides of the bores 8 may be useful for reducing the formation of eddy currents, but, with the relatively low field strengths that are produced, it does not generally cause any disturbance even in the absence of insulation. The bobbin casing 3 (not shown in Figure 3) is thus attracted by these bar-magnet elements 9.

A specially compact embodiment is shown in Figure 5; the open inner space of the gripper 1 houses an annular magnetic member 10 which has a U-shaped cross-section that is open towards the open end of the gripper; the ends of the open U-shaped cross-section thus form a north pole and a south pole. This embodiment, to a special degree, prevents a spreading out (straying) of eddy currents, since the magnetic circuit is confined to a great extent. Also, in this case, the magnet will therefore attract the bobbin casing 3 (not shown) to or into the gripper 1. The annular magnetic member 10 is therefore, functionally, a pot magnet.

In the embodiment shown in Figure 6, the gripper shaft 2 has been shortened, so that the bore 11 of the gripper 1 can still receive a relatively short cylindrical bar-magnet element 12 which is inserted or pressed in insulated or uninsulated. Naturally, the bar-magnet element 12 may also be fixed exchangeably by a set screw or in some other way, so that it is possible to vary the resulting forces by inserting bar elements 12,- which are magnetised to different extents or are of different lengths, or by axial displacement of the bar-magnet element 12.

Also, in a concentric arrangement, the bobbin casing 3 may carry in its central bore 13 a bar core 14 which, in certain circumstances, is likewise exchangeable or displaceable and which can also be pressed in or fixed; this bar core 14 may be a soft-iron core; however, it may also be a magnet and the adjacent poles of the elements 12 and 14 are, in this case, unlike, so that a mutual attractive action or force is produced.

Naturally, fundamentally, also in the embodiments shown in Figures 1. t and also in the embodiments hereinafter described, the gripper or the bobbin casing may be provided with magnet elements or soft-iron elements; if magnet elements are selected for the gripper or the'bobbin casing, care should be taken that adjacent magnetic poles of the gripper, on the one hand, and of the bobbin casing, on the other, are unlike.

In the embodiment shown in Figure 7, the gripper 1 is free of magnet elements; in this case, the stay 5, on the one hand, and the bobbin casing 3, on the other, are each provided with, for example, a preferably contrally or coaxially arranged magnet member, i. e., the bobbin casing 3 is thus provided with a bar-magnet element 15, whilst,'coaxially therewith in the operative position, the stay 5 carries a bar-magnet element 16; the adjacent poles of the bar-magnet elements and 16 are, in this case, like poles, so that a repelling force tends to lead the bobbin casing 3 away from the stay 5 and into the interior of the gripper 1.

As already mentioned, the magnet elements may also be temporarily energis'able soft-iron elements; they may have suitable windings which are fed, for example through slip rings by a small source of current, for example a small battery or a small rectifier or, if required, a transformer; the strength of the current and, consequently, the forces produced can then be altered very simply by means of :a regulating resistance. However, the permanent magnet is to be preferred by far because electrical conducting elements and the like mean a complication of the sewing machine; su'ificiently aging-resistant material for permanent magnets are quite available at the present time for industrial purposes. \Vhilst'the examples ofembodiment shown in Figures 1 to 7 are only for bobbin casings which are open in the direction towards the gripper, the invention proposes, While retaining the fundamental idea of subjecting the bobbin casing to the action of magnetic forces which attract it or press it into the inside of the gripper (gripper casing), to use bobbin casings which are closed in the direction towards the gripper, so that both the opening of the gripper and the opening of the bobbin casing point in the-same direction. The advantage as compared with the arrangement shown in Figures 1 to 7 lies in the simple nature of the construction of the means which are used for the production and transmission of the magnetic force; in particular, the end face of the bobbin casing may'beforr'ned or serve as an armature to be pulled out by the magnet or may carry a special, e. g., a laminated, armature outside on its surface. However, the examples of embodiment shown in the following figures can, with suitable adjustment, also be employed on bobbin casings (bobbin canisters) which are open in the direction towards the gripper.

As shown in Figure 8, the gripper 1 is, in the known manner, fixed on the end of the shaft 2 of the gripper, for example by means of a set-screw (notshown). The opening of the gripper is, as shown in Figure'8, :directed towards the left. The bobbin casing 3 is,,'in this case,'also one the opening of which is also directed to the left. It carries, in the known manner, the bobbin '17 which is prevented from falling out by means of a snap lever 20 orthe like. A stop or the like 6 (shown in broken lines) prevents, in the known manner, rotation of the bobbin casing. The magnet member 18, preferably a permanent magnet, is inserted'in the gripper 1, preferably with the interposition of a magnetically insulating sleeve 19 of brass, for example. A small air gap 31 is left and the lines of force of the magnet member 18 pass through or into the end face of the bobbin casing 3, so that an elastic attraction of the bobbin casing 3 into the gripper 1 is produced. Such an air gap 31 may, for example, have a width of from 0.3 to 0.5 mm., thus corresponding to the greatest thickness of thread. In the case of this embodiment, therefore, magnetic or armature elements. on the bobbin casing 3 are superfluous.

Figure 9 shows a modification; on the outer surface of the end face of the bobbin casing 3 an armature element 24 (which, in this case, is annular) of soft iron or of laminated material is fixed by means of, for example screws 25 or in some other suitable manner. The direction of Stratification of the laminated armature element 24 may be difierent from that shown in Figure 9. A magnetically insulating layer, in the form of a disc for example, may also be arranged between the armature element 24 and the end face of the bobbin casing 3. In the gripper 1 which is merely indicated, there is arranged, again With the interposition (which is unnecessary but advantageous) of an insulating sleeve 21, the magnet member 22 which, in this case, has two annular poles 26 and 27 which are concentric, but have different diameters, and surround .an annular gap 23. The armature element 24 has a corresponding diameter, so that, in the position of operation shown in Figure 9, there is produced a thorough avoidance of the occurrence of eddy currents, since the lines of force are closed at a short distance. In most cases, however, owing to the small forces that are necessary, the occurrence of small eddy currents is harmless. The armature element 24 may also be dispensed with.

Figures 10 to 17 show preferred proposed forms of magnet member.

As shown in Figure 10 and in Figure ll, which is a section on the line XlXI of Figure 10, the

pot magnet

28, 29 is tightly fitted or fixed on theindicated gripper 1. The outer element 28 of the pot magnet may be in one piece with the core element 29 of thepot magnet; however, the parts 28 and may also be separate and may be structural parts which are connected together in a suitable manner. In the latter case, it is sufiicient for the core member 29 to be apermanent magnet in the form of a cylindrical bar. A magnetically insulating brass sleeve 30 is advantageously arranged between the

parts

28 and 29. Figure 10 shows that the bobbin canister 3, which has been attracted ,to the magnet and leaves an air gap, leads thelines of force 32 for a short distance; this, on the one hand, ensures a reliable action and, on the other hand, affords-the advantage that pulling the bobbin canister 3 by-hand, for example, removes the latter from-the action of the magnetic forces only after a short distance, so that,,in this way, a simplified removal of the bobbin canister .or bobbin casing is possible.

Figure 12 shows separately the pot. magnet represented in Figures 10 and 11, the surrounding-structural parts being omitted.

Figure 13 shows a pot magnet 33 which is connected to a shortened gripper shaft 2 and which is fixed in a suitable manner, by. means of a set-screw (not shown) or-the like, either to the gripper shaft 2 or to the indicated gripper casing 1. The bobbin casing'3 is attracted, leaving an air gap '31, under the action of lines of force 34.

In principle, the leaving of this air gap 31, in all the embodiments of the invention, is eifected by mounting the bobbin *casing'or bobbin canister in the gripper or gripper casing, known per se, in such a manner that a relative rotation between the bobbin canister 3 and the gripper casing l is possible and that the air gap 31 is left with the bobbin canister 3 mounted in this manner.

Figure '14 again shows a section of a pot magnet ar ranged in'a similar manner to that shown in Figure 13. In'this'case, the pot magnet consists of a soft-iron pot 36, a permanent core element 37 with the interposition of a magnetically insulating sleeve 38 of brass or the like and, also in this case, an outer magnetically insulating sleeve 39 of brass or the like is provided. The whole pot magnet is arranged in front of the shortened gripper shaft 2 and is fixed to the latter or to the casing 1 of the gripper in an appropriate manner. In this case also, an air gap 31 is left between the bobbin canister 3, which is attracted by the action of the lines of force, and the gripper or the pot magnet.

In Figure it is shown that a pot-magnet effect is possible also in the case of a bar magnet with the participation of the gripper. casing. Arranged in front of the shortened gripper shaft 2 is a permanent core element 40 of smaller diameter, around which is mounted the magnetically insulating sleeve 41, the external diameter of which is equal to the external diameter of the gripper shaft 2. In such a case, the lines of. force 42 pass, in part, through the adjacent parts of the gripper casing 1, which must therefore, in this case, consist of magnetically insulating material. In this case also, the air gap 31 is left between the end face of the gripper 1 or the magnet 40 and the bobbin canister 3.

An embodiment similar to that shown in Fig. 15 is shown in Figure 16; in this case, the core element 43 has a shape which is offset in cross-section; a sleeve 45 of magnetically insulating material is provided in this case also, so that, in this case also, the lines of force 44 have a part of their path in the adjacent part of the gripper casing.

The embodiment shown in Figure 17 also corresponds substantially to the examples shown in Figures 15 and 16. In this case, a plate 47 of magnetically insulating material is first put on the shortened gripper shaft 2; it adjoins a cylindrical permanent magnet 46 which has a smaller diameter and is surrounded by an insulating sleeve 48. In this case also, the lines of force 49 pass partly through the adjoining parts of the gripper casing 1,,but, in addition, also through the plate 47. The air gap 31 is left in this case also.

A further improvement of the effect can be obtained according to the invention by a device in which there is provided, in the hollow internal space of such a pot magnet, spaced from the inside of its cylindrical wall, a cylindrical member, especially a cylindrical ring of magnetically conductive material.

The special advantage lies in the fact that, owing to the increased effect, i. e., owing to the greater forces of magnetic attraction which are exerted on the bobbin members or bobbin carriers, the dimensions of the pot magnet may be made smaller than hitherto or that, with the same dimensions, a still more reliable action is obtained owing to the greater magnetic forces.

Figures 18 and 19 represent examples of embodiment which are substantially contained in the figures hereinbefore described.

Figure shows the proposal of a special embodiment of the invention.

As shown in Figure 18, the magnet member 50 consists of a cylindrical ring; this is therefore a stamped-out hollow cylinder of permanently magnetic material having a north pole and a south pole.

This hollow-cylindrical magnet member 50 is, as shown in Figure 19, converted into a pot magnet by bringing a magnetically conductive cylindrical pot51, which may be produced by the deep-drawing process, into association with the magnet member 50; in this case, an air gap 57 is left which surrounds the cylindrical peripheral surface of the magnet member 5% and which, if required, may be filled with magnetically inert material. The lines of force 53 run as indicated in this Figure 19.

In. Figure 20, according to the invention, another magnetically conductive hollow cylinder 52 is arranged in the hollowinternalspace of the magnet member 50 in such a manner that there; is left, between the cylindrical inner surface of the magnet member 50 and the cylindrical outer surface of the hollow cylinder 52, anannular gap 58 which may remain empty or be filled with a magnetically inert material.

As shown in Figure 20, in this case the free lines of force extend along the lines 54 and 55. member or the end face 56 of the bobbin member or the like is brought near the end face of the pot magnet,

leaving a small air gap, there are two fields 54 and 55' of lines of force which themselves form a ring and which exert considerable forces of attraction on the end face 5 Evidence of the increase of the effect in the case of otherwise quite constant conditions and dimensions is given by the following results of tests:

The construction of magnet shown in Figure 18 produces a force of attraction of 70 gms. on the bobbin member or the like.

The embodiment shown in Figure 19 with the pct 51 cavity made inside with a slight shortening of the grippershaft; the bobbin casing may remain unaltered or be made suitable by fitting an armature, which can be effected quite simply. Usual structural parts can therefore be employed. Obviously, it is also possible to arrange a small magnet member on the end face of the bobbin cas ing, i. e. to reverse the arrangement. Such magnet mem-' bers may also be provided in the gripper and in the bobbin canister, regard being had to the correct choice of poles so that an attraction effect is produced.

What I claim is:

1. In a bobbin-canister gripper arrangement for sewing machines, the employment of magnetic forces for bringing the bobbin canister into operative association with the gripper, said arrangement comprising a dtay member for securing the bobbin canister against rotary movement, and mutually repellent magnet elments being associated with said stay member and said bobbin canister.

2. In a bobbin-canister gripper arrangement for sewing machines, the employment of magnetic forces for bringing the bobbin canister into operative association with the gripper, said arrangement comprising a pot magnet and a hollow cylinder of magnetically conductive material arranged in the internal space of said magnet, an annular gap being left between the inside of the wall of said internal space and the outisde of the wall of said hollow cylinder, the lines of force being produced in the form of two concentric annular fields of different diameters.

3. In a bobbin-canister gripper arrangement for sewing machines, the employment of magnetic forces for bringing the bobbin canister into operative association.

with the gripper, said arrangement comprising a pot magnet, a hollow cylinder of magnetically. conductive material arranged in the internal space of said magnet, an annular gap being left between the inside of the wall of said internal space and the outside of the wall of said" hollow cylinder, and magnetically inert material filling said annular gap, the lines of force being produced in the form of two concentric annular fields of different diameters.

4. In a bobbin-canister gripper arrangement for sewing machines, the employment of magnetic forces for bringing the bobbin canister into operative association with the gripper, said arrangement comprising a pot mag-' If the bobbin net. consisting of an end face and a. cylindriealshell, and aholl'ow cylinder of. magnetically conductive material arranged in the internal space of said, magnet, an annular gap being. left between the inside of the wall of. internal space and the outside of the wall of said hollow cylinder, the lines of force being produced in the form of two concentric annular fields of different diameters.

5. In a bobbin-canister gripper arrangement for sewing machines, the employment of magnetic forces for bringing the bobbin canister into operative association with the gripper, said arrangement compris W net consisting; of. an end. face and. a cylindrical shell, said end face being perforated for the passage of the shaft of said gripper, and a hollow cylinder of magnetically conduotive material arranged in the internal space said magnet, anannular gap being left between the ins e of the wall of said internal space and the out'zle of the w it of said hollow cylinder, the lines of force being produced. in the form of .two concentric annuiar fields of different diameters.

- 6. In a sewing machine, a bobbin case holding arrangement comprising, in combination, gripper means formed with a recess partly bounded by an annular inner surface; and a bobbin case means having an outer annular surface having av diameter smaller than the diameter of said annular inner surface of said recess and being located in said recess with said outer and inner annular surfaces opposite each other so that said bobbin case means is movable in axial direction of said annular surfaces out of said recess, at least one of said means including a: magnetic part producing a magnetic flux and at least the other of said means having at least a magnetizable part, said magnetic flux passing through said magnetizable part of the other of said means and urging said bobbin case means into said recess for holding said bobbin case means in said recess of said gripper means during operation of the sewing machine, said bobbin case means being manually removable in said axial direction for insertion of a bobbin case therein.

7. in a sewing machine, a bobbin case holding arrangement comprising, in combination, gripper means formed with a reces partly bounded by an annular inner surface; a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface of said recess and being located in said recess with said outer and inner annular surfaces opposite each other so that said bobbin case means is movable in axial direction of said annular surfaces out of said recess, at least a portion or" said bobbin case means being magnetizable; and a magnetic part producing a magnetic flux passing through the magnetizable portion of said bobbin case means and urging said bobbin case means into said recess for holding said bobbin case means in said recess of said gripper means during operation' of the sewing machine, said bobbin case means being manually removable in said axial direction for insertion of a bobbin case therein.

8. In a sewing machine, a bobbin case holding arrangement comprising, in combination, gripper means formed with a recess partly bounded by an annular inner surface; and a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface of said recess and being located in said recess with said outer and inner annular surfaces opposite each other so that said bobbin case means is movable in. axial direction of said annular surfaces out ofsaid recess, atleast a portion ,of said bobbin casemeans being magnetizable, at least said gripper means including a magnetic partproducing a magnetic flux passing through the magnetizable portion of said bobbin case meansand urging said bobbin case means into said recess for holding said bobbin case means in said recess of'said gripper means. during operation of the sewing machine, said bobbin case ,means being manually removable in said axial direction for insertion of a bobbin case therein.

9'. In a sewing machine, a bobbin case: holding, a;- rangement comprising, in. combination-,. grippernmeans formed with a recess'partly bounded by an: annular inner surface; a bobbin case means having an outer annular,

surface having a diameter smaller than the diameter of said annular inner surface of said recess and being located in said recess with said outer and inner annular surfaces opposite each other so that said bobbin case means is movable in axial direction of said. annular surfaces out of said recess, said bobbin case means including: a magnetic part; and a stay member for securing the bobbin case means against turning movement and including. a magnetic part mutually repellent with said magnetic part of said bobbin case means and located opposite the sameoutside of said recess in said gripper means and urging said bobbin case means. into said recess for holding said bobbin case means in said recessof said gripper means: during operation of the sewing. machine, said bobbin case means being manually removable in said axial direction for insertion of a bobbin case therein.

10. In a sewing machine, a bobbin case holding ar-' rangement comprising, in combination, gripper means formed with a recess partly bounded by an annular inner surface; and a bobbin case-.means having an outer an nular surface having a diameter smaller than the diameter of said annular inner surface of said recess and being. located in said recess with said outer and inner annular surfaces opposite each other so. that said bobbin case means is movable in axial direction of said annular sur' faces out of said recess, each of said means including a magnetic part located opposite the magnetic part in the other of said means; attracting the same and urging said bobbin case means into said recess for holding said bobbin case means in said recess of said gripper means during operation of the sewing machine, said bobbin case means being manually removable in said a xial direction for insertion of a bobbin case therein.

11. In a sewing machine, a bobbin case holding arrangement comprising, in combination, gripper means formed with a recess partly bounded by an annular inner surface; and a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface of said recess and being located in said recess with said outer and inner annular surfaces opposite each other so that said bobbin case means is movable in axial direction of said annular sur-- faces out of said recess, at least a portion of said bobbin case means being magnetizable, said gripper means being formed with a plurality of bores arranged in a circle and opening into said recess and including a plurality of magnetic elements located in said bores of said gripper means and producing a magnetic flux passing through the magnetizable portion of said bobbin case means and urging said bobbin case means into said recess for holding said bobbin case means in said recess of said gripper means during operation of the sewing machine, said bobbin case means being manually removable in said axial direction for insertion of a bobbin case therein.

12. In a sewing machine, a bobbin case holding ar rangement comprising, in combination, a gripper means formed with a first recess having an annular inner surface and a bottom surface; and a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface and being located in said first recess with said outer and inner annular surfaces opposite each other, said bobbin case means including a bottom portion abutting against said bottom surface, at least said bottom portion of said bobbin case means being magnetizable, said gripper means being formed with a second smaller recess opening on said bottom surface opposite said bottom. portion, and including a magnetic element located in said second recess and producing'a magnetic flux passing through said bottom portion and urging said bobbin case meansinto said first recess for holding said bobbin .case means in;

said first recess during operation of the sewing machine, said bobbin case means being manually removable in axial direction of said annular surfaces for insertion of a bobbin case therein.

13. In a sewing machine, a bobbin case holding arrangement comprising, in combination, a gripper means formed with a first recess having an annular inner sur face and a bottom surface; and a bobbin case means having an outer annular surface having'a diameter smaller than the diameter of said annular inner surface and being located in said first recess with said outer and inner annular surfaces opposite each other, said bobbin case means including a bottom portion abutting against said bottom surface, and a magnetizable elementfixedly se cured to said bottom portion, said gripper means being formed with a second smaller recess opening on said bottom surface opposite said magnetizable element, and including a magnetic clement located in said second recess and producing a magnetic flux passing through said mag netizable element and urging said bobbin case means into said first recess for holding said bobbin case means in said first recess during operation of the sewing machine, said bobbin case means being manually removable in axial direction of said annular surfaces for insertion of a bobbin case therein.

14. In a sewing machine, a bobbin case holding arrangement comprising, in combination, a gripper means formed with a first recess having an annular inner surface and a bottom surface; and a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface and being located in said first recess with said outer and inner annular surfaces opposite each other, said bobbin case means including a bottom portion abutting against said bottom surface, and an annular magnetizable element fixedly secured to said bottom portion, said gripper means being formed with a second smaller recess opening on said bottom surface opposite said annular magnetizable element, said gripper means including an annular magnetic element located in said second recess and producing a magnetic flux passing through said annular magnetizable element and urging said bobbin case means.

into said first recess for holding said bobbin case means in said first recess during operation of the sewing machine, said bobbin case means being manually removable in axial direction of said annular surfaces for inser tion of a bobbin case therein.

15. In a sewing machine, a bobbin case holding arrangement comprising, in combination, a gripper means formed with a first recess having an annular inner surface and a bottom surface; and a bobbin case means having an outer annular surface. having a diameter smaller than the diameter of said annular inner surface and being located in said first recess with said outer and inner annular surfaces opposite each other, said bobbin case means including a bottom portion abutting against said bottom surface, and an annular magnetizable element fixedly secured to said bottom portion, said gripper means being formed with a second smaller recess opening on said bottom surface opposite said annular mag netizable element, and including a magnetic element located in said second recess and having an outer annular portion, and an inner annular portion spaced from said outer annular portion, said inner and outer annular portions having end faces located opposite said annular magnetizable element so that a magnetic flux passes through said end faces and said magnetizable annular element for urging said bobbin case means into said first recess for holding said bobbin case means in said first recess during operation of the sewing machine, said bobbin case means being manually removable in axial direction of said annular surfaces for insertion of a bobbin case therein.

16. In a sewing machine, a bobbin case holding arrangernent, comprising, in combination, a gripper means formed with a first recess having an annular inner surfacebottom surface opposite said bottom portion, and including a magnetic element located in said second recess and including an outer annular portion and an inner portion located within said annular portion spaced from the inner surface of the'same, said outer annular portion and said inner portion of said magnetic element having end faces located opposite said bottom portion of said bobbin case means and producing a magnetic flux passing through said end faces and said bottom portion for urging said bobbin case means into said first recess for holding said bobbin case means in said first recess during operation of the sewingmachine, said bobbin case means being manually removable in axial direction of said annular surfaces for insertion of a bobbin case therein.

17. An arrangement as claimed in claim 16 and including an annular member located between said annular portion and said inner portion of said magnetic element and consisting of a non-magnetizable material.

18. An arrangement as claimed in claim 16 wherein said magnetic element includes a bottom portion integral with said outer annular portion and forming a pot-shaped part, and wherein said inner portion has another end face remote from said end face which is located opposite said bottom portion, said other end face abutting against said bottom portion of said magnetic element. i

19. An arrangement as claimed in claim 16 wherein said inner portion of said magnetic element has an outwardly projecting flange, and wherein said outer annular pontion of said magnetic element abuts against said flange.

20. In a sewing machine, a bobbin case holding arrangement, comprising, in combination, a gripper formed with a first recess having an annular inner surface and a bot-tom surface, said gripper being formed with a second smaller recess opening on said bottom surface; a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface and being located in said first recess with said outer and inner annular surfaces opposite each other, said bobbin case means including a bottom portion abutting against said bottom surface; a pot-shaped elemertt located in said second recess and including a bottom wall and an annular wall, said annular wall having an annular end face located opposite said bottom portion of said bobbin case means; and at least one inner element located in said pot-shaped element and having one end face located opposite said bottom portion of said bobbin case means, another end face abutting against said bottom Wall of said pot-shaped element and an annular outer surface spaced from the inner surface of said annular wall of said pot-shaped element, one of said elements being ma netic, and the other of said elements consisting of a inagnetizable material so that a magnetic flux passes through said annular end face, said one end face and said bottom portion of said bobbin case means for urging said bobbin case means into said first recess for holding the same secured to said gripper during operation of the sewing machine, said bobbin case means being manually removable in axial direction of said annular surface of said gripper and of said bobbin case means for insertion of a bobbin case.

21. An arrangement as claimed in claim 20 wherein said pot-shaped element is magnetic, and said inner element consists of a magnetizable material.

22. An arrangement as claimed in claim 20 wherein said inner element is magnetic and annular, and wherein said," onev end; face thereof is annular; and whereinrsaid' pot=shaped element consists of a magnetizable material.

23; In a se-wingrmachine, a bobbin case holding arrangement, comprising, in combination, a gripper formed wit'ha-first recess having an annular inner surface and a bottom surface, said gripper being formed with a second smaller recess opening on said bottom surface; a bobbin case means having an outer annular surface having a diameter smaller than the diameter of said annular inner surface and beinglocated in said first recess with said outer and inner annular surfaces opposite each other, said bobbin case means including a bottom portion abutting. against said bottom surface; a pot-shaped element consisting of'a magnetizable material located in said second recess and including a bottom Wall and an annular wall, saidannular wall having an annular end face located opposite said bottom portion of said bobbin case means; and an inner magnetizable element located in said potshaped element and having one end face located opposite said bottom portion of said bobbin case means, and an annular outer surface spaced from the inner surface of said' annular Wall; and an annular'magnet means located between said inner surface of said annular wall and said outer surface of said inner magnetizable element, said annular magnet means having an annular end face 10-' cated opposite said bottom portion of said bobbin case means and between. said one end face of said inner magnetizable element and said annular end face of said annular wall so that magnetic flux passes through said end faces and, said bottom portion in the form'of two concentric annular fields for urging said bobbin case means into said first recess for holding the same secured to' said gripper during operation of the sewing machine, said bobbin case means being manually removable in axial direction of said annular surfaces of said gripper and of said bobbin case means for insertion of a bobbin case.

24/111 a sewing machine, a bobbin case holding arrangement, comprising, in combination, a gripper formed with a first recess having an annular inner surface and a bottom surface, said gripper being formed with a second smaller recess opening on said bottom surface; a bobbin case means having an outer annular surface having'a diameter smaller than the diameter of said annular inner surface and being located in said first recess with said outer and inner'aunular surfaces opposite each other, said" bobbin case means including a bottom portion abutting against said bottom surface; a pot-shaped elcrnent consisting of a magnetizable material located in said second recess and including a bottom Wall and an annular wall, said annular wall "having an annular end facelocated opposite said bottom portion of said bobbin,

case means; an inner annular magnetizable element loca tedcin said pot-shaped element and having one. annular end face located opposite said bottom portion ofvsa id bobb'in case means, and an annular ou ter surface spaced from. the inner surface of said annular wall; and an annular magnet means located between said inner surface of'said annular wall and said outer surface of said inner annular magnetizable element, said annular magnet means having an annular end face located opposite said bottom portion of said bobbin case means and between said one annular end face of said inner magnetizable element and said annular end face of said annular wall so that magnetic flux passes through said end faces and said bottom portion in the form of two concentric annular fields for i ng said bobbin case means into said first recess for iolding the same secured to said gripper during operar L being manually removable in axial direction of said annular surfaces of said gripper and of said bobbin case means forinsertion of a'bobbin case.

25. An arrangement as claimed in claim 24 and including annular-means consisting of a magnetically inert nonmagnetizable'material arranged between said annular Wall,

of said pot-shaped element, said inner magnetizable element, and said annular magnet means.

26. In a sewing machine, a bobbin case holding arrangement comprising, in combination, gripper means of said surfaces out of said recess, at least one of'said means including a magnetic part producing a magnetic llux and at least the other of said means having at least a magnetizable part, said magnetic flux passing throughsaid magnetizable part of the other of said means and urging said bobbin case means into said recess for holding said bobbin case means in said recess of said gripper means during operation of the sewing machine, said bobbin case mean-s manually removable in said axial direction for insertion of a bobbin case therein.

References Cited in the file of this patent UNlTED STATES PATENTS 2,394,369 Colegrove Feb. 5,

2,601,961 Stephenson July 1, 1952 2,608,945 Hagquist Sept. 2, 1952 2,6l0',806 Lathrop Sept. 16, 1952 2,656,127 Bunch Oct. 20, 1953 [Oil of the sewing machine, said bobbin case means