EP0515717B1 - Device for building up thread chain in/on sewing machines with a plurality of needles - Google Patents

Abstract

In order to obtain a stable thread warp after the passage of the cloth, even in respect of overlap seams with two or more needle threads and at least one covering thread, but, if appropriate, without a folding thread, there is proposed, in addition to a looping foot (3), the use of a retaining device (10, 12, 16, 17) for the stitches of the thread warp, said retaining device ensuring, at the critical moment of stitch formation, a reduction of the thread tension which acts on the particular stitch just formed. <IMAGE>

Description

The invention relates to a device according to the preamble of claim 1, to a conveyor therefor according to the features of the preamble of claim 5 and to a needle plate with the features of the preamble of claim 8.

Devices of the type mentioned are already on the market in various versions. The cover seams that can be produced in this way are designated according to US standards, for example with the numbers 402, 403, 405 to 407 and 601 to 604. The usual procedure is to sew one piece of fabric at a time so that there are no particular problems in a continuous succession. Sometimes, however, it is desirable to sew a stable and uninterrupted row of slip stitches from the sewing threads used, i.e. to get a so-called thread chain. This works relatively well if, in addition to the needle threads and the cover thread on the underside, an upper layer thread is also used, which also creates an overlap on the top of the fabric.

A device for obtaining a thread chain that is stable even in the absence of material is described in document FR-A-2 388 918.

However, this involves increased thread consumption, the seam becomes thicker (which is often not desirable) and the overlap may disturb the desired external impression. If, on the other hand, seams are used without such a laying thread, such as the seams designated by 402 or 406 according to the US standard, the stable thread chain desired per se from the three sewing threads used (possibly also more needle threads) has not hitherto been achieved.

The invention is therefore based on the object of designing a device of the type mentioned at the outset in such a way that a stable Thread chain is achieved under all circumstances, ie even with seams without laying thread according to the numbers 402 and 406 of the US standard.

In a first step, the invention is based on the knowledge of the special conditions during the sewing process, namely that due to the successive formation of stitches or stitches, even a disadvantageous pull is exerted on the stitches just formed by the needles themselves. This finding was not obvious because the stitches always remained stable as long as there was a fabric to be sewn. It only turned out that the reason for this functioning was due to the friction of the threads in the fabric, which prevented the loops from being drawn open, whereas, in the absence of fabric, there was no such effect of reducing the thread tension.

Therefore, the above object is achieved in a second step according to the invention by the characterizing features of claim 1, because now that the threads are held in place during the stitch formation, the effect that can be observed with the existing fabric is achieved even if it is missing.

As such, the holding device can be solved in a wide variety of ways, but the result is a structurally simple embodiment in accordance with the features of claim 2, because if a further tooth row surface is in series with the first, the loops which form themselves on the underside can now be created first can be transported in front of and behind them without tension.

However, this effect is also achieved or supported by an embodiment according to claim 3, since the successive webs thus formed contribute to holding the warp stitches which are being formed together with the warp foot pressing on them or keep these stitches free of tension in critical areas.

If one considers the knowledge on which the invention is based, it will quickly become clear that the tension conditions can change with the stitch length, but also with the sewing or transport speed. Therefore, an embodiment according to claim 4 is particularly advantageous, since these measures can further reduce the tension forces acting on the individual stitches that arise.

A conveyor according to the invention is characterized by the characterizing features of claim 5. It would not be impossible per se - depending on the movement given to the transporter - to arrange the successive tooth row surfaces in different planes, but an embodiment according to claim 6 is preferred.

Likewise, the two successive extensions - depending on the design of the transport plate and the movement given to the transporter - could be skewed towards one another, e.g. be divergent, but it is more favorable for the movement sequence if the transporter is designed within the meaning of claim 7, i.e. if the protruding longitudinal axes of the two extensions are at least approximately parallel to one another.

It also follows from the above that a throat plate with the characterizing features of claim 8 is of particular advantage for achieving the object on which the invention is based.

Fig. 1 und 2

schematisch die das Problem ergebenden Überdecknähte 402 und 406 nach US-Norm;

Fig. 3

eine explodierte Darstellung einer erfindungsgemässen Vorrichtung, aus der auch der erfindungsgemässe Transporteur und die Oberseite einer erfindungsgemässen Stichplatte ersichtlich sind, von welch letzterer die

Fig. 4

ein Längsschnitt nach der Linie IV-IV der Fig. 3 veranschaulicht.

Further details of the invention will become apparent from the following description of an exemplary embodiment shown schematically in the drawing

1 and 2

schematically the problematic cover seams 402 and 406 according to the US standard;

Fig. 3

an exploded view of an inventive Device from which the feed dog according to the invention and the top of a needle plate according to the invention can be seen, of which the latter

Fig. 4

a longitudinal section along the line IV-IV of Fig. 3 illustrates.

1 and 2, two needle threads A and A 'run parallel next to each other, which threads through two (in other embodiments, it may also be more to produce a cover seam), needles not shown here, usually through the one to be sewn Substance can be introduced. On the underside (this expression does not necessarily refer to the position of the needles, which could also lie horizontally), at least one gripper (not shown), known per se, forms the stitches connecting the needle threads A, A 'with the help of a warp thread B. Now missing the material in between, there is generally a risk that the stitch formed in this way will dissolve unless an additional thread is attached to the top. This means that if the thread chain formed in this way is not stable, there is a risk that the seam will dissolve again automatically when tension is applied.

According to FIG. 3, an embodiment according to the invention essentially consists of four parts. A throat plate 1 lies between a feed dog 2 and a chain foot 3, 3 'composed of two sections. The needle plate 1 has a U-shaped slot 4, consisting of two legs 5 and a thread chain slot 6 forming the U-bracket, for passing through needle and cover threads. There are piercing holes 7 for at least two needles guiding the needle threads in the two regions of the closed U-leg ends or optionally at any other point on the legs. The two legs 5 and the thread chain slot 6 of the U-shaped slot 4 form 3 sides of a throat plate tongue pointing in the transport direction 8, which separates the fabric from the cover thread. Since fabrics that are sewn are transported from the piercing holes 7 along the legs 5 against the bracket 6, the cover thread in the area of the bracket 6 connects directly to the fabric.

Adjoining the thread chain slot 6 in the transport direction is an area of the needle plate 1, which is designed as a transverse web 10 due to a passage opening 9 which in turn connects in the transport direction. At least one further passage opening 11 and thus another web 12 are provided in the transport direction after the passage opening 9. The webs 10, 12 and 8 serve as a solid base onto which the fabric is pressed by the chain foot 3, 3 'and is thus held in place while the needles pierce the fabric.

According to a special embodiment, at least one but preferably two further passage openings 13 are provided laterally with respect to the transport direction - in the case of two openings preferably on both sides - of the U-shaped slot 4. If necessary, 4 further passage openings 14 can be provided in the direction of the U-shaped slot opposite to the transport direction. The throat plate 1 has holes 15 which are used to attach it to the sewing machine.

The transporter 2 has at least two sliding surfaces one behind the other in the transport direction in the form of teeth arranged in rows in each row of teeth 16 and 17, which are usually designed with transport teeth pointing in the transport direction. The sliding surfaces must exert sufficient static friction on the fabric pressed against them to transport the fabric and can also have a flat surface structure or ribs, grooves or cams. If appropriate, at least one, but preferably two further] rows 18 of teeth are provided laterally with respect to the direction of transport — in the case of two surfaces, preferably on both sides — of the row of teeth 16. The rows of teeth 16, 17 and 18 are End faces of extensions 16a, 17a of the feed dog 2, the longitudinal axes of which are preferably parallel to one another, and fit into the through openings 9, 11 and 13 of the needle plate 1 in such a way that the pushing movement necessary for the material feed can be carried out. When feeding the fabric, the rows of teeth 16, 17, 18 pass through the passage openings and press the fabric against the chain foot 3, 3 ', so that it is clamped enough to follow the movement of the feed dog 2 in the transport direction. The arrangement of the sliding surfaces according to the invention enables tension-free transport of the just-forming chain stitches. Since further passage openings 14 can be provided in the throat plate 1, 2 further sliding surfaces can be attached to the feed dog, which fit into these openings 14.

The section 3 of the chain foot is mostly behind section 3 'in the direction of transport and has a fastening and guide part 19. The part 19 is penetrated by a mounting hole 20 for a mounting rod for attaching the chain foot to the sewing machine. Another hole 21 in part 19 leads to hole 20 and serves to receive a screw that clamps part 19 to the fastening rod.

On a surface 21 of the part 19, which is vertical to the throat plate 1 when mounted on the fastening rod - preferably on the end face of the part 19 as seen in the transport direction - a guide device 22 is provided to enable movement of a foot part 23 perpendicular to the throat plate 1. According to an embodiment of the invention, the longer leg of an L-shaped profile piece of the foot part 23 lies between the surface 21 of the part 19 and a guide plate attached to the part 19. At least two screws are preferably used to fasten this plate, which are perpendicular to one another relative to the throat plate 1 and for which a guide slot is provided as a passage opening in the longer leg of the L-shaped piece of the foot part 22.

A pressing device, preferably a spring 24, protrudes from a surface of the part 19 directed against the throat plate 1 and parallel to it, which presses the shorter leg of the L-shaped piece of the foot part 23 and thus the entire foot part 23 against the throat plate 1. The preload of the spring 24 can be adjusted by means of a screw lying in a hole 25 of the part 19. A presser foot sole 26 of the foot part 23 exerts the contact pressure in the area of the webs 10 and 12 and the passage openings 9 and 11 and thus the sliding surfaces 16 and 17. The foot part 23, together with the corresponding sliding surfaces, is responsible for the warp-free transport of the finished stitches. If the material thickness changes, the spring-guided foot part 23 can adapt to the respective material thicknesses. However, as has been found, this also ensures that the stitches remain tension-free precisely during their formation, and this means that the thread chain obtained remains stable even without fabric.

The foot part 23 has a connection part 27 with a somewhat narrower and thinner cross section in the end region opposite the transport direction. This connecting part comes to lie in a recess in a presser foot sole 28 of the chain foot section 3 '. In the middle area of the presser foot sole 28 there are two through openings 29 for the needles guiding the needle threads. The presser foot sole 28 is the continuation of the presser foot sole 26 of the chain foot section 3, which is pivotable about an axis 30, which is parallel to the throat plate 1 and perpendicular to the direction of transport. The pivotability is advantageous in the case of changing fabric thicknesses. In its initial area, with respect to the direction of transport, the presser foot sole 28 is angled away from the throat plate 1, so that the supplied material never touches the front of the presser foot sole but is always guided under the latter. If sewing has to be carried out over an increasing number of layers of fabric, the part of the chain foot lying in the area of the needles pivots the presser foot sole 28 in this way that the fabric layers are properly guided under the through openings 29 and pressed together sufficiently. The presser foot sole 26 remains parallel to the throat plate 1 and ensures that the contact pressure and transport are unaffected by the increase in fabric thickness.

The end of the presser foot sole 28 in the transport direction has two side plates 31 which protrude from the needle plate 1 and in which the axis 30 is held. The foot 33 of a fastening device 32 is located between the side plates 31. The presser foot sole 28 is connected to the fastening device 32 only by means of the axis 30, which is mounted in the initial region of the foot 33. The fastening device has a fastening flange which can be screwed onto the lower end of a fastening rod which is guided through the hole 20 in the fastening part 19.

On at least one side of the presser foot sole 28 is attached a foot sole part 34 which can be displaced perpendicularly to its contact surface. In order to enable the displaceability, a guide device is provided, which preferably consists of a guide pin 35 mounted vertically on the foot part 34 and a guide jacket surrounding it in a form-fitting manner. The guide jacket is attached to one of the side plates 31 on the outside. A spring 36 is fastened to the guide pin 35 and to the side plate 31 in such a way that the sole part 34 is pressed away from the plane of the presser foot sole 28 against the needle plate 1. By the sole part 34 partly on a passage opening 13 - or. a sliding surface 18 - and partly presses on the part of the needle plate 1 adjoining this or on the fabric located above these areas, ensures that the fabric is well held both when the needles are pierced and when it is transported in the area of the needles.
In order to further reduce the thread tension leading to the loosening of the stitches when there is no fabric, a fabric end sensor, for example a mechanical sensor, capacitive sensor or the like, but here a light-electrical sensor with a source 37 for electromagnetic radiation (visible or invisible light) and (at least) one light-electrical converter 38 is provided. Such a fabric end sensor can be provided at any point, but near the needle plate 1, in order to report the end edge of the fabric at the right time and to emit a fabric end signal.

This end-of-material signal is fed via a line 39 to a drive device d, known per se and therefore not shown here, for driving the feed dog 2, in order to drive this drive d in the sense of a reduction in speed and / or in the sense of increasing the stitch length Taxes. It has been shown that with a longer stitch length, a more stable thread chain can be obtained even without fabric. It is therefore understood that such a control can also be suitable for solving the task without the holding device according to the invention.

As illustrated in FIG. 4, it is additionally advantageous to provide the throat plate 1 on its surface facing away from the chain foot 3 or facing the feed dog 2 with depressions 40 and projections 41, which may also contribute to braking or collecting undesirable thread tensions.

Claims (9)

1. A device for the production of a cover seam of two needle threads (A,A') running adjacent to each other and of at least one cover thread (B) connecting the needle threads (A,A') with each other on the underside of the seam of a material which is to be sewn, with a transporter (2) engaging through at least one passage opening (9,11,13,14) of a stitch plate (1) and provided with at least one row of teeth (16,17,18) on an extension (16a), opposite which a link foot (3,3') lies on the other side, which has at least two sections (3,3') movable relative to each other in the direction of the stitch plate (1), at least one of which is acted upon by a loading device towards the presser foot base (26,28) and in each case at least one of which has a connection arrangement (20,32) for application on a sewing machine or has a presser foot base (28) having at least two perforations (29) for the needles introducing the needle threads, characterised in that to obtain a stable thread chain, even in the absence of material, a securing device (10,12,16,17) is provided, fixing the stitch which has just been formed in each case during the formation of the next stitch.
2. A device according to Claim 1, characterised in that the securing device on the transporter (2) has at least one further row of teeth (17) placed after the first row of teeth (16) - viewed in the feed direction -, on a separate extension (17a) projecting through the stitch plate (1).
3. A device according to Claim 1 or 2, characterised in that the securing device on the stitch plate (1) has at least one cross-piece (12) placed between the successive rows of teeth (16,17), preferably in addition to a first cross-piece (10) placed in front of the first row of teeth (16), adjoining an approximately U-shaped slit (4) for passing needle (A,A') and cover threads(B) through with U-shanks (5) turned towards the conveying direction.
4. A device according to one of the preceding claims, characterised in that a sensor device is provided to emit a material end signal, and that when the material end signal occurs, the transporter drive is controllable in the sense of an increase in the stitch length and/or a reduction of the conveying speed.
5. A transporter (2) for a device according to one of the preceding claims, with a rising extension (16a) for passage through a stitch plate (1), on the upper side of which a tooth row surface (16) is provided with conveying teeth pointing in the conveying direction, characterised in that it has in the conveying direction after this rising extension (16a) at least one further extension (17a), arranged at a distance and likewise rising, with a further row of teeth (17).
6. A transporter (2) according to Claim 5, characterised in that the successive rows of teeth (16,17) lie in the same plane.
7. A transporter (2) according to Claim 5 or 6, characterised in that the successive extensions (16a, 17a) are aligned at least approximately parallel to each other.
8. A stitch plate (1) for a device according to one of the preceding claims, with at least one passage opening (9) for the passage of an extension of a transporter (2) having a tooth row surface (16) for conveying the material, characterised in that it has at least one further passage opening (11) after this passage opening (9) - viewed in the conveying direction -, in which between these openings (9,11) a cross-piece (12) is produced, separating them from each other, in addition to a further first cross-piece (10) placed in front of this cross-piece (12) in the conveying direction, which is delimited on one side by the first passage opening (9) and on the other side by a U-shaped slit (4) bordering a stitch plate tongue pointing in the conveying direction.
9. A stitch plate according to Claim 8, characterised in that on the side facing away from the link foot (3) it has at least one surface, in particular a corrugated surface, having depressions (40) and projections (41) (Fig. 4).

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