EP3399089B1 - Method and sewing machine for generating a bobbin thread end of a seam with a predetermined protrusion - Google Patents

Description

The present invention takes the priority of the German patent application DE 10 2017 207 626.7 in claim.

The invention relates to a method for producing a seam-end underthread with a predetermined desired seam overhang. Furthermore, the invention relates to a sewing machine for carrying out such a method.

A sewing machine with which a seam-end lower thread can be produced with a predetermined desired seam overhang is known from EP 1 847 641 B1 and from the EP 2 330 241 B1 . the DE 102 15 011 A1 discloses a buttonhole sewing machine and an operating method of a buttonhole sewing machine. the DE 1 104 805 A describes a method for cutting the upper and lower threads on lockstitch sewing machines and a device for carrying out the method. the DE 197 46 653 C1 describes a method for shortening the end of the looper thread on the sewing material side on sewing machines with a thread trimmer.

It is an object of the present invention to further develop a method for producing a seam-end lower thread with a predetermined desired seam overhang in such a way that the seam-end lower thread and thus also the desired seam overhang can be made shorter.

According to the invention, this object is achieved by a production method having the features specified in claim 1 .

According to the invention, it was recognized that the position of a lower feed dog can be shifted after a seam has been formed and before the lower thread is cut off at the seam end in such a way that a lower thread path between the last stitch of the seam and a cutting position can be shortened. The result is a correspondingly shortened seam end lower thread. This shortening can be exactly reproduced due to the clearly definable position of the lower feed dog in the cut-off position, so that depending on the position of the lower feed dog a predetermined target seam overhang results. Simultaneously with the production of a seam-end lower thread with a desired seam overhang, a seam-end upper thread with a comparable desired seam overhang, for example not more than 10 mm, can also be produced. The upper thread can be cut off at the same time as the lower thread in the production process. By switching the lower feed dog from the sewing position to the cutting position, an upper thread path between the last stitch of the seam and the cutting position can then be shortened before the upper thread is cut, which leads to a correspondingly shortened seam end upper thread. The result is a correspondingly definable target seam overhang of the seam end upper thread depending on the position of the bottom feed dog. By changing the lower feed dog to a cutting position, in which a lower thread path and/or an upper thread path is lengthened between the last stitch of the seam and the cutting position, a seam-end lower thread and/or a seam-end upper thread can also be used with a longer target seam overhang , for example significantly more than 10 mm. This can be useful for certain sewing tasks where longer seam end threads are required. The lower feed dog can be a feed dog. The drop feed dog can be used together with stitch formation tools the sewing machine, i.e. a sewing needle and a gripper, work synchronously and/or periodically. The lower feed dog is a component that transports the sewing material through frictional contact from below in the sewing direction. The lower feed dog comes into engagement with the sewn material during a stitch period during a period of time and is disengaged from the sewn material during a further period of time.

Before cutting off, a stitch with a shortened stitch length is sewn when sewing. Such a short stitch before cutting leads to the fact that a seam end lower thread produced with the cutting and a seam end upper thread take a comparably long way from the sewing material to the cutting position and are therefore practically the same length due to the last short stitch.

Depending on the design of the sewing machine, a changeover according to claim 3 can lead to an advantageous shortening of the lower thread path between the last stitch and the cutting position. The "reverse stitch" position can be selected as the cutting position for the lower feed dog.

A conversion according to claim 4 can be integrated into the normal operation of a sewing machine. An additional changeover drive can then be omitted.

A further object of the invention is to specify a sewing machine for carrying out the method according to the invention.

According to the invention, this object is achieved by a sewing machine having the features specified in claim 5 .

The advantages of the sewing machine correspond to those that have already been explained above with reference to the method according to the invention. The drive for shifting the bottom feeder can then represent the actuating means of a feeder gear.

The controller for controlling the displacement drive can be designed to be programmable for specifying a residual lower thread length at the end of the seam. The remaining lower thread length can be preselected using a control element on the sewing machine.

A stitch regulator gear according to claim 6 is particularly suitable as a controllable displacement drive for changing over the bottom feed dog from the sewing position to the cutting position. The stitch regulator gear can in particular be designed as a link gear. Such a suitable stitch regulator gear is known from EP 2 330 241 B1 .

A swivel drive according to claim 7 represents a particularly simple drive for changing over the bottom feed dog from the sewing operating position to the cutting position. The swivel drive can be designed as a stepping motor. Alternatively, the swivel drive can be designed as a lifting magnet or as a pneumatic cylinder. The swivel drive can interact with at least one stop for specifying at least one lower feed dog position. The stop can be adjustable. Several such stops can also be provided.

Fig. 1

eine Vorderansicht einer Doppelsteppstichnähmaschine;

Fig. 2

eine Draufsicht auf einen Ausschnitt der Nähmaschine in vergrößertem Maßstab entsprechend dem Sichtpfeil II in Fig. 1;

Fig. 3

eine innere Details freigebende Stirnansicht auf einen Ausschnitt der Nähmaschine entsprechend dem Sichtpfeil III in Fig. 1 in vergrößertem Maßstab;

Fig. 4

eine perspektivische Darstellung eines Fadenziehmessers;

Fig. 5

einen Schnitt gemäß Linie V-V in Fig. 1 in einer Momentanposition eines Untertransporteurs und eines Fadenziehmessers beim Abschneiden eines Unterfadens an einem Ende einer Naht zur Erzeugung eines Naht-Endunterfadens mit einem Soll-Nahtüberstand nach dem Stand der Technik;

Fig. 6

in einer zur Fig. 5 ähnlichen Darstellung einer Momentanposition des Untertransporteurs und des Fadenziehmessers beim Abschneiden des Unterfadens am Nahtende zum Erzeugen des Naht-Endunterfadens mit Soll-Nahtüberstand von höchstens 10mm; und

Fig. 7

schematisch eine Aufsicht auf eine mit der Nähmaschine genähten Naht zur Veranschaulichung eines erzeugten NahtEndunterfadens mit einem vorgegebenen Soll-Nahtüberstand.

Exemplary embodiments of the invention are explained in more detail below with reference to the drawing. In this show:

1

a front view of a lockstitch sewing machine;

2

a plan view of a section of the sewing machine on an enlarged scale according to the arrow II in 1 ;

3

a front view releasing internal details of a section of the sewing machine according to the arrow III in 1 on an enlarged scale;

4

a perspective view of a thread-pulling knife;

figure 5

a cut according to line VV in 1 in an instantaneous position of a lower feed dog and a thread-pulling knife when cutting a lower thread at one end of a seam to produce a seam-end lower thread with a desired seam overhang according to the prior art;

6

in a to figure 5 Similar representation of a current position of the lower feed dog and the thread-pulling knife when cutting the lower thread at the seam end to produce the seam-end lower thread with a target seam overhang of at most 10mm; and

7

Schematically a top view of a seam sewn with the sewing machine to illustrate a produced end-of-seam lower thread with a predetermined desired seam overhang.

A sewing machine 1 designed in particular as a lockstitch sewing machine has a base plate 2 with a stand 3 extending upwards therefrom and an angled arm 4. The latter ends in a head 5. In the arm 4, an arm shaft 6 is rotatably mounted. This drives a crank mechanism 7 with a thread lever 8 in the head 5 . The crank drive 7 is drivingly connected to a needle bar 9 which is mounted in the head 5 in an axially displaceable manner. This has a needle 10 at its lower end. The needle 10 can be moved up and down on a vertical axis 11 by the crank mechanism 7 . The needle 10 guides in an eye a needle thread 13 fed from a coil 12 via a thread tensioning device and the thread lever 8, which thread is also referred to as the upper thread.

The base plate 2 carries a support plate 14 which is fastened with screws and on which a two-layer fabric part 15 rests. The support plate 14 is formed with a recess 16 for the passage of a feed pusher 17, which is also referred to as the bottom feed dog. The latter has a stitch hole 18 for the passage of the needle 10.

A presser foot 17a is arranged opposite the feeder 17 with respect to the piece of material to be sewn 15 .

A Cartesian xyz coordinate system is used below to clarify positional relationships. The x-direction, which runs along a sewing direction, runs in the 1 perpendicular to the drawing plane into this. The y-direction runs in the 1 to the left. The z-direction, along which the axis 11 runs, runs in the 1 up. The material pusher or lower feed dog 17 transports the sewn material part 15 during a sewing process along the sewing direction in the positive x-direction.

The feed slide 17 is in a known manner in drive connection with a thrust and lifting mechanism arranged below the base plate 2 . Such a gear for the bottom feed dog 17 can be designed as a stitch regulator gear and in particular as a link gear, like in the EP 2 330 241 B1 described. Such a stitch regulator gear represents a feed dog gear, via which in particular a feed length of the bottom feed dog 17 can be set, ie a stitch length when creating the seam. The stitch regulator gear is part of a drive for displacing the bottom feeder 17 along the sewing direction x. The displacement drive is in the 1 shown schematically at 18a. The displacement drive 18a acts like the other driven components of the sewing machine 1 with a in the 1 schematically illustrated central control device 18b together. For this purpose, the control device 18b is directly connected to these components of the sewing machine 1 to be controlled and in particular to the displacement drive 18a in a manner not shown. Part of the displacement drive 18a is a swivel drive for a stitch regulator shaft of the stitch regulator gear. Such a stitch regulator shaft is particularly in connection with the 2 the EP 2 330 241 B1 described, the content of which is hereby referred to. Depending on the swivel angle of the stitch regulator shaft, there is a stitch length and also a relative position of the lower feed dog 17 along the x-direction relative to the components of the sewing machine 1 that are fixed to the base plate. The swivel drive is therefore an adjusting means of the stitch regulator gear for a transport length of the lower feed dog 17.

Below the support plate 14 there is a gripper 19 which has a gripper body 20 with a gripper tip 21 . A pot-shaped bobbin housing 22 for receiving a supply of looper thread is mounted in the looper body 20 . A looper thread is also referred to below as a lower thread.

The gripper 19 can be rotated about a vertical gripper axis 23 . A sewing direction of rotation 24 runs in 2 clockwise about the gripper axis 23 running along the z-direction. The shaft 25 is rotatably mounted in a bearing block 26 screwed to the base plate 2 . In this, a drive shaft 27 is mounted, which is connected to a gear mechanism arranged inside the bearing block 26 . The gear train has a transmission ratio of 1:2, so that when the drive shaft 27 rotates, the gripper body 20 located on the shaft 25 rotates twice. The drive shaft 27 is drivingly connected to the arm shaft 6 via a belt drive 28 .

A thread-pulling knife 29 is used to cut off the looper thread. The thread-pulling knife 29 is positioned between an in 2 illustrated basic position and a thread gripping position about a gripper axis 23 parallel pivot axis 30 pivotable. The thread-pulling knife 29 has a view 2 basic shape reminiscent of a sickle, the free end of which is in the basic position in the view 2 around the bobbin case 22 runs around. In the thread gripping position of the thread-pulling knife 29, a gripping groove 31 is adjacent to the stitch hole 18 (cf. 4 ) of the thread-pulling knife 29 with a cutting edge 32 on the groove bottom side. An extended free end portion 32c of the thread-pulling knife 29 is in accordance with the plan view 2 rounded end.

A stationary counter-knife 33 (cf. 3 ) which cuts the thread when the thread-pulling knife 29 is pivoted from the thread-acquisition position to the basic position and interacts with the cutting edge 32 of the thread-pulling knife 29 .

A counter-cutting edge 34 of the counter-knife 33, which interacts with the cutting edge 32 of the thread-pulling knife 29 when the thread is trimmed, runs vertically along the z-direction.

the figure 5 and 6 each show a current position of components of the sewing machine 1 on the one hand in a position "short forward stitch" ( figure 5 ) and on the other hand in the "reverse stitch" position ( 6 .) . Both instantaneous positions after the figure 5 and 6 show cutting positions, i.e. they are shown at the time immediately before the cutting of the upper thread 13 and the lower thread 35 between the cutting edge 32 of the thread-pulling knife 29 and the counter-knife cutting edge 34 of the counter-knife 33. The course of the upper thread 13 on the one hand and the lower thread 35 on the other hand during the last stitches S ₁ to S ₅ in the sewing material 15. The lower feed dog 17 is also shown broken in the area of the stitch hole 18 in order to enable a view of the sections of the thread-pulling knife 29 and the counter-knife 33 lying behind it. the figure 5 and 6 also show details of a motion control of the bottom feed dog 17 with a bottom feed dog carrier 36, a feed dog shaft 37, via which a transport stroke running along the x-direction is transmitted to the bottom feed dog 17, and a feed dog lifting shaft 38, via which a feed dog stroke shaft 38 acting along the z-direction or exchange stroke is exerted on the lower feed dog 17. The displacement drive 18a, on one in the figure 5 and 6 invisible stitch regulator shaft is in the figure 5 and 6 not shown.

figure 5 shows the instantaneous position during normal operation of the sewing machine 1, with which short seam end threads are produced. Before the fifth stitch S _{5 is formed} , the stitch regulator gear is switched to the “short forward _{stitch” position with the displacement drive 18a, so that this last stitch S 5 is} shorter than the stitches S ₁ to S ₄ previously produced. After knotting the fifth stitch S ₅ , both the upper thread 13 and the lower thread 35 run towards the cutting position between the cutting edge 32 and the counter knife edge 34. The lower thread 35 in particular runs along an approximately U-shaped course around a section delimiting the stitch hole 18 39 of the lower feed dog 17 around.

6 shows the corresponding components of the sewing machine 1 in the stitch regulator gear position "reverse stitch", also after the formation of the stitch S ₅ designed as a short stitch. In this position of the stitch regulator gear, a changeover is made by appropriate activation of the displacement drive 18a.

Due to the "reverse stitch" position, the feed shaft 37 is in the figure 5 in comparison to 6 further pivoted counterclockwise, so that the feeder 17 compared to the current position after figure 5 in the current position 6 is shifted in the positive x-direction, i.e. in the sewing direction. This leads to the fact that the feeder section 39 immediately before cutting off the upper thread 13 and the lower thread 35 relative to the cutting position of these threads 13, 35, which is independent of the stitch regulator gear and is basically fixed to the frame, is between the cutting edge 32 and the counter knife edge 34 in the 6 is also shifted in the positive x-direction. When switching to the "reverse stitch" position, the feed dog section 39 moves relative to the piece of material to be sewn 15. The piece of material to be sewn 15 is held stationary relative to the presser foot 17a. A path between the last stitch S ₅ and the cutting position between the cutters 32, 34 is now for the threads 13, 35 and in particular for the lower thread 35 at the current position 6 not as long as the current position after figure 5 , so that after the threads 13, 35 have been cut off, smaller seam end threads on the sewn material part 15 and, in particular, a shorter seam end lower thread with a target seam overhang of at most 10 mm result.

7 shows a seam 40 that is produced with the sewing machine 1. At the seam 40, the seam end lower thread 41 protrudes from the last stitch S ₅ with a target seam overhang A of at most 10 mm.

The method for producing such a seam-end lower thread with a target seam overhang of at most 10 mm includes sewing the seam with the stitches S _i , before the lower thread 35 is cut off at the end of the seam, the lower feed dog 17 is moved out of the sewing operating position, for example from a position " Short forward stitch" is shifted to a cutting position shifted in relation to this along the sewing direction x, i.e. for example the "backward stitch" position. Then the lower thread 35 and the upper thread 13 are cut off at the end of the seam with the thread-pulling knife 29 through the interaction of the cutting edges 32, 34.

The lower feed dog 17 can compared to the cutting position after figure 5 also be shifted into a further cutting position, which is shifted in the negative x-direction, so that a path of the lower thread 35 on the one hand and the upper thread 13 on the other hand is extended even further towards the cutting position between the cutting edges 32, 34. This position of the lower feed dog 17 can be the "maximum forward stitch length" position. The result is correspondingly longer seam end threads 13, 35.

A stitch shortening, for example in the last stitch S _5, is not mandatory. It is also possible to sew with a normal stitch length up to the last stitch, in which case the stitch regulator gear is immediately switched from the "normal forward stitch" position to the cutting position for the lower feed dog 17, for example to the "reverse stitch" position.

The controller 18b is designed in such a way that, at the end of seam production, it activates the displacement drive 18a in a synchronized manner in such a way that the lower feed dog 17 is displaced from the sewing operating position to the cutting position. The controller 18b is designed to be programmable for specifying a residual lower thread length at the end of the seam.

The displacement drive 18a is designed as a stepping motor. Alternatively, it is possible to design the displacement drive as a lifting magnet or as a pneumatic cylinder. At least one stop can be provided in order to specify a position of the stitch regulator gear when the lifting magnet or pneumatic cylinder is activated. Such a stop can be designed to be adjustable. It can also be more than one such attack be provided.

Claims (7)

1. Method for producing a seam end bottom thread with a target seam protrusion of at most 10 mm, comprising the following steps

   - sewing a seam;

   - prior to cutting off a bottom thread (35) at one end of the seam: repositioning a lower feed plate (17) from a sewing operation position into a cut-off position displaced relative to the sewing operation along a sewing direction (x);

   - cutting off the bottom thread (35) at the end of the seam,

   - wherein prior to cut-off during sewing a stitch with a shortened stitch length is realised,

   - wherein the lower feed plate is a component which transports the sewing material by frictional contact from below in the sewing direction, wherein the lower feed plate engages the sewing material during a stitching period for one time period and is out of engagement with the sewing material during another time period.
2. Method according to claim 1, characterized in that the top thread is cut off simultaneously with the bottom thread.
3. Method according to claim 1 or 2, characterized in that the lower feed plate (17) is displaced into the sewing direction (x) upon repositioning the same.
4. Method according to any one of claims 1 to 3, characterized in that the repositioning of the lower feed plate (17) is realised through controlling an adjusting means (18a) of a feed plate gear for a transport length of the lower feed plate (17).
5. Sewing machine (1) for carrying out a method according to any one of claims 1 to 4,

   - with stitch-forming tools (10, 19) for sewing a seam with a top thread (13) and a bottom thread (35),

   - with a lower feed plate (17) than can be displaced along a sewing direction (x), wherein the lower feed plate is a component which transports the sewing material by frictional contact from below in the sewing direction, wherein the lower feed plate engages the sewing material during a stitching period for one time period and is out of engagement with the sewing material during another time period,

   - with a thread blade (29) for cutting the bottom thread (35) at the seam end,

   - with a drive (18a) for displacing the lower feed plate (17) along the sewing direction (x),

   - with a controller (18b) for controlling the displacement drive (18a), wherein the controller (18b) is designed in such a way that it controls the displacement drive (18a) in a synchronized way at the end of a seam production in such a way that the lower feed plate (17) is displaced from the sewing operating position into the cutting position.
6. Sewing machine according to claim 5, characterized by a stitch setting gear for setting a transport length of the lower feed plate (17).
7. Sewing machine according to claim 6, characterized in that the displacement drive (18b) has a swivel drive for a stitch setting shaft of the stitch setting gear.

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